Advances in Marine Biology: v. 13

Advances in

MARINE BIOLOGY VOLUME 13

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Advances in

MARINE BIOLOGY VOLUME 13 Edited by

SIR FREDERICK S. RUSSELL Plymouth, England

and

SIR MAURICE YONGE Edinburgh, Scotland

Academic Press London New York

San Francisco

4 Subsidiary of Harcourt Brace Jovanovich, Publishers

1975

ACADEMIC PRESS INC. (LONDON) LTD.

24-28

OVAL ROAD

LONDON N W 1 7 D X

U S . Edition published by ACADEMIC PRESS INC.

111

FIFTH AVENUE

NEW YORK, NEW YORK

10003

Copyright 0 1975 by Academic Press Inc. (London) Ltd

All rights reserved

NO PART OR THIS BOOK MAY B E REPRODUCED I N ANY FORM BY PHOTOSTAT, MICROFILM, OR ANY OTHER MEANS, WITHOUT WRITTEN PERMISSION FROM THE PUBLISHERS

Library of Congress Catalog Card Number: 63-14040 ISBN:

0-12-026113-8

PRINTED I N GREAT BRITAIN B Y THE WHITEFRIARS PRESS LTD. LONDON AND TONBRIDGE

CONTRIBUTORS TO VOLUME 13 MUZAMMILAHMED,Institute of Marine Biology, University of Karachi, Pakistan. H. E. EVANS,Department of Anatomy, College of Veterinary Medicine, Cornell University, Ithaca, New York, U.S.A. M. FONTAINE,Physiologie gdndrale et comparde, Muse'um national d' Histoire naturelle, Paris, France. €3. G . KAPOOR, Department of Zoology, University of Jodhpur, Jodhpur,

India.

NORMAN MILLOTT,University Marine Biological Station, Millport, Isle of Cumbrae, Scotland. R. A. PEVZNER, Laboratory of Evolutionary Morphology, Sechenov Institute of Evolutionary Physiology and Biochemistry, U.S.S.R. Academy of Xciences, Leningrad, U.S.S.R. H. SMIT,Zoology Laboratory, University of Leiden, Leiden, Netherlands. I. A. VERIGHINA, Zoological Museum, Moscow State University, Moscow, U.SS.R.

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CONTENTS

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CONTRIBUTORS TO VOLUME13

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v

The Photosensitivity of Echinoids NORMAN MILLOTT

I. Introduction . . .. .. 11. Movements of the Whole Animal

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111. The Pigmentary System and Colour Change

IV. Podia1 Responses .. A. The Covering Reaction

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V. Spine Responses .. .. A. Photoreception . . .. B. Integrative Mechanisms

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Rhythmic Activities . .

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VII. Discussion VIII.

References

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The Gustatory System in Fish

B. G. KAPOOR, H. E. EVANS AND

R. A. PEVZNER

.. Review of Literature . . Structure .. .. A. Light Microscopy . .

I . Introduction 11. 111.

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B. Electron Microscopy vii

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C. Nerve Supply .. D. Vascular Supply . . E . Histochemistry . . F. General Considerations

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Origin, Development and Location of Taste Buds

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V. Innervation, Brain Morphology and Function ;, A. Innervation .. . . .. . . B. Brain Morphology .. .. .. C. Function .. . . .. .. VI. Acknowledgements VII. References

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The Alimentary Canal and Digestion in Teleosts

B. G. KAPOOR, H. SMIT AND

I. A. VERIGHINA I . Alimentary Canal, Food and Feeding Habits 11. Morphology, Histology and Cytology A. Mouth, Buccal Cavity and Pharynx B. Oesophagus .. .. .. C. Stomach .. .. .. .. D. Intestine .. E . Rectum . . .. .. ..

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111. Electron Microscopic Findings Histo- and Cytochemistry

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V. Innervation and Allied Aspects VI.

FoodIntake

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VII. Digestion Rate

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VIII. Digestive Enzymes A.Pepsin . . B. Trypsin . . ..

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C. Carbohydrases . . .. . . .. .. D.Lipase . . .. .. .. .. .. E. Other Enzymes .. F. Digestive Enzymes as Related to the Diet IX. Regulation of Gastric Secretion

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X. Absorption and Conversion of Food XI. Conclusions

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XII. Acknowledgements XIII. References

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Physiological Mechanisms in the Migration of Marine and Amphihaline Fish

M. FONTAINE

I. Introduction

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11. Ionic and Osmotic Regulation

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111. Thermopreferendum and Thermoregulation IV. Some Functions Involved in Migrations .. A. Respiratory Function . . B. Circulation .. .. .. C. Excretion .. .. .. D. Reproduction . . .. .. E. Metabolism .. .. .. V. Integration Mechanisms A. Endocrine Glands B. The Nervous System

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VI. Senseorgans . . .. A. Rheotropism . . B. Thermoreception . . .. C.Vision . . .. .. .. D. Chemical Reception . . .. E. Electro- and Magnetoreceptors VII. Conclusion

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VIII. Acknowledgements IX. References . . *.

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CONTENTS

X

Speciation in Living Oysters

MUZAMMILAHMED

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111. Generic Differencesin Ostrea and Crassostrea A. Bio-ecological Differences . . .. B. Cytological Differences .. ..

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I. Introduction

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11. Genera of Living Oysters

IV. Physiological Races A. Crossostrea virginica B. Ostrea edulis . . V . Subspecies

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in the Southern Part of the Range VI. Speciation .. .. A. Crassostrea virginica . . .. .. B. Ostrea lurida . . ..

VII. Superspecies-Semispecies A. Crassostrea gigas B. Saccostrea cuccullata

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VIII. Hybridization .. .. A. Closely Related Species B. Distantly Related Species IX. Generic Divergence X . Discussion XI. Summary

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XII. Acknowledgements XIII. References

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CUMULATIVE INDEX OF AUTHORS . .

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SUBJECT INDEX

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CUMULATIVE INDEX OF TITLES

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AUTHOR INDEX

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Adv. mar. BioE., Vol. 13, 1975, pp. 1-52

THE PHOTOSENSITIVITY OF ECHlNOlDS NORMAN MILLOTT University Harine Biological Station, Hillport, Isle of Cumbrae, Scotland Introduction .. .. .. .. .. Movements of the Whole Animal .. .. The Pigmentary System and Colour Change Podia1 Responses . . .. .. A. The Covering Reaction . . ., .. V. Spine Responses .. .. .. .. A. Photoreception . . .. .. .. B. Integrative Mechanisms .. .. VI. Rhythmic Activities . .. .. .. VII. Discussion . .. .. .. .. VIII. References .. .. .. . .

I. 11. 111. IV.

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I. INTRODUCTION It has long been known that echinoderms respond to light. All classes have received attention but asteroids and particularly echinoids have attracted most of it. Photosensitivity has largely been inferred from behaviour since echinoderms have proved singularly intractable for electrophysiological studies. Larvae have received little attention, indeed almost all of i t has been directed to adults. Echinoids show their photosensitivity in a variety of responses : morphological and physiological colour change, in the responses of particular effectors such as spines and podia and possibly in reproductive activity. I n life such responses may be integrated into complex activities such as those of covering behaviour or locomotion. In the quest for simplicity and understanding several investigators (and the writer is no exception) have sometimes dismembered such elaborate responses by studying the responses of effectors isolated singly or in small groups. It is as well to emphasize a t the outset a fact which has not always been kept in mind, namely that in so doing mere fragments of behaviour as well as of the animal are being studied. Receptors no less than effectors can interact and the simplicity which may emerge can be misleading, for it is partly the creation of the investigator due to his methods. More will be said of this in relation to von Uexkull’s famous and timehonoured aphorism of the ReJEexrepublikas applied to echinoids. 1

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In recent years these photic responses have been reviewed several times: by Millott (1966a) and in wider context by Millott (1957b), Steven (1963), Yoshida (1966) and Millott (1968). The successive reviews reflect the progress of the work, and since the last, though impetus has for the moment slowed down, there has been further work. This, together with the reflexions on earlier work in echinoids cast by later research on the photosensitivity of molluscs, means that some measure of reappraisal is possible. For the purpose of this account the term " photosensitivity " will be used as implying sensitivity to ultra-violet as well as to visible radiation. 11. MOVEMENTSOF THE WHOLEANIMAL For almost a century echinoderms have been favourite targets for the study of so-called elementary patterns of behaviour. I n general, analysis has been grossly inadequate, partly because it has been so incomplete, partly because it has been based on assumptions which are a legacy from the over-simplificationsprevalent in the early part of the century and partly because in interpreting responses the animals have been relegated to a level of organization which is so lowly as to belie their true nature. The reactions of various echinoids to light have been described in scattered, brief accounts. It is generally agreed that the reactions of whole urchins are profoundly influenced by their physiological state, a complex and intangible factor that involves sensory adaptation (see below). Diebschlag (1938) reported that Psammechinus miliaris (Gmelin) overturns when suddenly illuminated on the oral side. This was categorized as a dorsal light reaction despite the sheer inappropriateness of the term as applied to an animal which has undergone such radical changes in orientation in its development. The accounts of phototaxis are disparate, workers using various species have recorded positive, negative and variable responses with respect to the light source (see Yoshida, 1966). Centrostephanus Zongispinus (Philippi) and Diadema setosum (Leske) are described by von Uexkull (1900a) as avoiding light. This is substantiated for the latter by Thornton (1956) and Magnus (1967) who describe migration a t sunset of urchins which sought the shade of crevices during daylight, but they display a lesser tendency to seek shade after light adaptation. Such migrations recall those of clypeastrids reported by Mortensen (1948). Some of the disparity could be the result of adaptation. Simple experiments on Diadema antillarum Philippi (Millott, 1954)showed that

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the sign of the response depends on the light intensity to which urchins had been subjected before the experiment so that a t first they appear to seek light intensities to which they had become accustomed, but the sign of the response does not persist. I n all, the results suggested the existence of an optimum intensity which changes in correspondence with a photosensory system that undergoes adaptation. It is not clear, however, that this is the only factor involved. One additional complication stems from the colour change (see below); juveniles a t least changed colour during the course of some experiments. This could influence their photosensitivity. This possibility will be considered again (p. 25). However, according to Sharp and Gray (1962) Lytechinus variegatus (Lamarck) shows no such adaptation, remaining positively phototaxic in artificial light for hours a t a time, though it is negatively phototaxic to direct sunlight and to wavelengths shorter than 295 nm. A general negative phototaxis is described in Arbacia punctulata (Lamarck) by Holmes (1912) and confirmed by Sharp and Gray (1962). Holmes claims that the animals quickly adapt and become irresponsive, but their responsiveness returns after chemical or mechanical stimulation. It also requires the oral nerve ring. Yoshida and associates (see Yoshida, 1966) report that Temnopleurus toreumaticus (Leske) ceases to show positive phototaxis after a sojourn in darkness, but that this behaviour is progressively restored on illumination. They also showed that separation of a radial nerve from the nerve ring abolishes positive phototaxis in that sector. I n animals from which most of the aboral hemisphere had been removed, leaving only one or two intact ambulacra, the latter took the lead in locomotion when they were illuminated. I n darkness, however, it was the incomplete ambulacra which took the lead. Yoshida attempts to explain this by a formal scheme which invokes the existence of excitatory and inhibitory influences in each radial nerve of which the latter normally predominates unless the nerve is illuminated when inhibition is suppressed. Excitation then becomes the over-riding influence so that the illuminated ambulacrum takes the lead. Removal of the greater part of each remaining radial nerve means that much of their inhibitory influence is lost, so that in darkness most of the inhibition is on the side of the intact ambulacra and consequently movement is toward the opposite side. Very little is known of the responses of larvae. Fox (1925) noted that plutei migrate downwards in light and upwards in darkness. Yoshida (1966) studied the behaviour of developmental stages of Hemicentrotus pulcherrimus Barnard from the early gastrula onwards, which aggregate a t certain light intensities. He used microdensitometry

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FIG. 1. Comparison of the pattern of distribution of larvae of Hemicentrotus pulcherrimus, in a aquare trough before (filled circles) and after (open circles) illumination. Illumination : A, horizontal parallel beam ; B, horizontal beam diverged by 5 degrees ; C, vertical parallel beam. The trough was divided, on photographic negatives, into three horizontal layers (upper, middle, and bottom) and ten vertical sections ; the latter are shown in the abscissae. The optical density of each section of the photographic negatives, which reflects the degree of aggregation, was determined microdensitometrically and it is shown in the ordinates. In each graph the upper, middle, and bottom groups of curves correspond respectively with each of the three horizontal layers mentioned above. Reproduced with permission from Yoshida (1966).

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and photographic methods to determine the degree of aggregation. Parallel horizontal beams produce no effect but larvae aggregate just outside vertical or diverging horizontal beams, which suggests they are doing so a t a preferred intensity (Fig. 1 ) . Light also affects their swimming speed, high intensities slowing down upward migration. The presence of an air-water interphase was also necessary for inducing aggregation. Yoshida therefore surmises that light eventually achieves the observed effects by a combined action on random movements a t the surface and on the speed of vertical movements.

111. THE PIGMENTARY ~ Y S T E MAND COLOUR CHANGE Much has been learned concerning the pigments of sea urchins and although a great deal of attention has been devoted to biochemistry, on which a review would be misplaced here, the findings in Diadema antilZarum have some relevance to photosensitivity. This striking urchin shows both morphological and physiological colour changes, and both are influenced by light. The former is complex and the intimate mechanism of the latter appears in part a t least to be of an unusual type. Accounts of both have been given by Millott and collaborators (for a summary see Millott, 1964). Several kinds of pigment are involved, hydroxynaphthaquinone (echinochrome), melanin, chromolipoid and an iron-containing pigment of nuclear origin. The pigment pervades the skin and viscera, that of the skin is contained in large intercellular spaces which form a network of channels disposed mainly parallel with the body surface (Fig. 2). I n young urchins the

FIQ.2 . Diadema antillarum. Portion of the intercellular network of the channels containing pigment forming a chromatoglyph, as seen in & tangential section of the skin. Note the compacted residual cytoplasm of a chromatocyte which forms the primary pigment (P.),surrounded by secondary pigment (S.). The pigment is stained selectively for melanin by Lillie’s ferrous iron method. Scale, 8.0 pm. Reproduced with permission from Millott (1964).

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NORMAN MTLLOTT

FIG.3. Diadema antillarum. Portion of the intercellular network of pigment channels as seen in a section of the skin cut tangential to the surface, showing the system of fibrils left behind in the space formerly occupied by a chromatocyte (p. 9). Scale, 12 pm. Reproduced with permission from Millott (1966a).

pigment (primary pigment) is contained largely in cellular chromatophores (chromatocytes) but, as the urchins age, this is supplemented and eventually replaced t o varying degrees by secondary extracellular pigment deposited in the channels. The melanin in the chromatocytes is finely granular (Fig. 4)so that they resemble the melanophores familiar in a wide variety of animals. The melanin deposited later appears in the form of much larger spheroids which accumulate together with echinochrome and the other pigments. This activity is largely due to amoebocytes which wander into the channels and degenerate leaving behind their contained pigment. To this is added that left behind in the channels as the pigment cells degenerate (Fig. 2). This morphological change is our concern insofar as the melanin is formed by a photosensitive process in amoebocytes which contain the requisite phenolases and tyrosine (the presumed substrate) (Jacobson and Millott, 1953 ; Millott and Vevers, 1968). The photosensitive nature of the process is supported by the observation (Kristensen, 1964) that pigmentation increases more rapidly in urchins kept in normal light intensities than in those kept in darkness. This has far-reaching implications for the accompanying process of physiological colour change (see below). I n this context we may note in passing, the suggestion from Kennedy and Vevers (1972) in connexion with their discovery of chlorin e6 and coproporphyrin I in the test of Arbacia lixula (Linn.), that potentially photosensitizing pigments may be sequestered in the test. The phenomenon of physiological colour change has excited more interest than the morphological. It was recorded for Centrostephanus

THE PHOTOSENSITIVITY OF ECHINOIDS

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IOprr

ch.

n.1.

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FIG.4. Chromatocyte of a juvenile Diadema antillarum as seen in a transverse section of the skin. Note the finely granular pigment which should be contrasted with that of a chromatoglyph (Fig. 2). ch. chromatocyte, m. muscle, m.gr. melanin granule, n.c. neuron, n.ep. nucleus of epidermal cell, n.1. superficial nerve layer. Reproduced with permission from Millott and Jacobson (1952). Journal of Investigative Dermutology, 18, 91-95.

and Arbacia by von Uexkiill (1897a), and reinvestigated by Parker (1931), who failed to confirm its existence and again by Kleinholtz (1938) who confirmed von Uexkull's findings. Millott (1952) gave a brief description and analysis of the phenomenon in Diaderna antillarum, which was followed by a fuller analysis in Diadema setosum by Yoshida (1956, 1957a, 1960). More recently Dambach and collaborators (Dambach, 1969; Weber and Dambach, 1972) have redirected attention to Centroatephanus. * Responses of the chromatophores to light were evident in all these cases, but it became clear from the earlier studies that the responses were independent of the radial nerves and could be localized by the use of narrow light beams (Millott, 1952). This was confirmed by Yoshida (1956) who in an eminently elegant fashion, used light spots 3 pm in diameter to induce pigment dispersion in individual chromatophores.

* Defined by the authors as Centrostephanus longispinus Peters.

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NORMAN MILLOTT

He was also able to show that the responses were obtained over a broad spectral band (450-500nm) with a maximum at 470. Millott (1952) also revealed that the chromatophores manifest a diurnal rhythm of pigment concentration and dispersion that is independent of the immediate effects of environmental lighting. Although Yoshida assumed that the chromatophores were cellular entities and comparable with those of other animals, he revealed in them some singular properties which are difficult to interpret on this basis. Thus his minute light spots did not exert an effect on a whole chromatophore, but only on the part that was illuminated so that the illuminated branches remained deeply pigmented for so long as the light was projected on to them, while the rest of the unit changed to the punctate form (Fig. 5A). Again chromatophores could be displaced

FIG.5. Behaviour of the chromatophores of Diadema setosum. A. Effect of projecting a minute light spot in the position indicated by arrow between the chromatophores labelled 1, 2 and 6. Note the localized dispersion of pigment induced. B. A chromatophore is cut across by a glass needle a t the position arrowed, while pigment is dispersed. C. The same chromatophore after 30 min. in darkness. Note the apparent re-union of the two portions. A. reproduced with permission from Yoshida (1956). B. and C. reproduced with permission from Yoshida (1960).

bodily by centrifuging as well as by illuminating the adjacent areas of skin. Most remarkable of all was his demonstration that when the pigment was dispersed they could be cut in two by a fine glass needle (Fig. 5B) whereupon the two halves appeared to re-unite into a functional unit when they assumed the punctate condition (Fig. 5C). These somewhat puzzling findings were complemented and highlighted by Millott (1964, 1966a) in Diadema antillarum. Thus when the channels pervading the living skin are punctured by a micro-manipulator, pigment escapes freely and it is forcefully discharged in minute jets on fixation, forming a sooty deposit over the skin. I n coverslip preparations of living skin, pigment masses are seen to undergo continual movement dividing and re-joining so that under the influence of light and shade, when pigment is dispersed and subsequently concentrated, it may become re-distributed among the interlacing channels. Again the masses could be cut across and the separated portions continued to disperse and concentrate under appropriate lighting. As in the case of Yoshida's work these findings were difficult to explain on

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current concepts of the working of pigmentary effector systems and the precise cause of movement remained unsolved. I n this context it should be noted that the walls of the intercellular channels are pervaded by a well developed system of fibrils that in living prepaxations appear to be elastic. The histology of the system exhibits some other significant features. In juveniles the black pigment is contained in what are clearly cells (chromatocytes, Fig. 4) situated in well defined cavities that form the nodes of the intercellular channels, the walls of which embody spindlelike cells attenuated into fibrils. As the animals age the chromatocytes degenerate and their remains, supplemented by secondary pigment of all varieties (Fig. 2), form aggregations of pigment cast in the mould of their cellular precursors. Millott (1964) distinguished these structures as chromatoglyphs (yh+s). As the accumulation of pigment continues, the reversible colour change becomes less evident, disappearing completely in many individuals, but in some it persists in limited areas, so that when the pigment concentrates, a characteristic pattern of white lines develops in the periproct and interambulacra (Fig. 6). Nevertheless sections of these areas of mobile pigment show that much of it is contained in chromatoglyphs. At this stage a most striking feature of the histology is the elaborate web of fibrils that spans the chromatoglyphs and radiates from a nucleus, presumably the relict of a degenerated chrornatocyte. This is suggested by the deeply pigmented pycnotic condition of many of these nuclei, but others, such as that shown in Fig. 3, appear normal and could therefore be the remains of cells which have suffered rupture and dissolution on fixation and discharged their pigment (p. 8). Their regular occurrence and disposition suggests that, together with the fibrils in the channel walls, they could be concerned with pigment movement. These features could explain a t least some of the peculiar behaviour of the chromatophores of Diadema antillarum and i t is tempting to suggest that they could also account for some of the behaviour reported by Yoshida in the allied species. Lacking knowledge of the histology of the latter no stronger assertion is warranted. Thus the strictly localized effect of minute light spots on chromatophores could be the reflexion of their effect on restricted areas of the channel walls. The apparent reunion of separated portions of bisected chromatophores, the bodily displacement of such structures by centrifuging and the redistribution of pigment under the influence of light (p. 9), are easier to explain in the case of chromatoglyphs than in the case of chromatocytes of the usual type forming a tissue constituent. Dambach and collaborators, as a result of their more recent work on Centrostephanus, offer a different explanation. Curiously, Weber and

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Dambach (1972), although echoing the views of the writer concerning the singular nature of echinoid chromatophores, refer to the earlier, but not to the later, findings in Diadema antillarum, aside from quoting a brief private communication from the writer, cited by Yoshida (1966). This is all the more surprising because the findings in both animals

FIG.6. Adult Diaderna antillarum seen from the side, photographed after a period in total darkness. Note that the colour change, so obvious in juveniles, is no longer manifest due to the accumulation of secondary pigment (see p. B), so that the animal remains black, apart from the pattern of white lines which here forms a " lancet arch " in the interambulacrum overlying the gonads (see p. 42). As exposure to light continues the white pattern, which lies below and between bands of iridophores, is replaced by a blue one and eventually largely disappears. Reproduced with permission from Millott, N. (1953). Bulletin of Marine Science, 2, 497-510.

show some similarity. Thus, having used both light and electronmicroscopy, they describe the chromatophores as contained in intercellular lacunae with walls supported by tonofibrils. Moreover they describe a network of fibrils near the nucleus of the pigment cells and bundles of filaments extending into the cell processes. These fibrils are presumed to be contractile and it is suggested that they play a role in pigment movement by exerting an intracellular pressure which extends

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the cell processes. However, the chromatophores described are entirely cellular and no structures comparable to chromatoglyphs are mentioned. The characterization of the structures as singular rests on their existence as free mobile cells lacking firm contact with the surrounding tissue. Weber and Dainbach find no evidence of synaptic contacts and because of the responsiveness of chromatophores in isolated skin preparations, they surmise that any nervous or humoral control, if it exists, could be only local. Most importantly, as a result of this and earlier work (Dambach, 1969), these authors conceive the chromatophores as varying their form and apply the term " amoeboid " to their movement. Contrary to widely held beliefs concerning the intimate mechanism of pigment movement in other animals, these authors find no evidence of the existence of a constant cell form within which pigment is concentrated or dispersed.* I n this context they recall the synthesis and deposition of melanin in amoebocytes reported by Jacobson and Millott (1953). But such synthesis is in itself of little value as an index of affinity between chromatophores and amoebocytes. Setting aside the question of the extent to which the label " amoeboid " is applicable in this instance, it is clear that if attempts were made to apply the concept to Diadema, it would account for some of the findings. Thus it would explain how chromatophores can be displaced bodily both by centrifuging and projecting light spots on to the adjoining areas of skin, as well as how temporarily they can survive bisection, but it would not explain how the halves can apparently re-integrate, neither could it explain the movement of pigment in chromatoglyphs. Although the precise effector mechanism is still unresolved, something has been learned of the recsptor mechanism, by virtue of the demonstration in the chromatophores of Diademu setosum of sensitivity to a spectral band of 450-500 pm, with a maximum a t 470 (Yoshida, 1957a). The photoreceptive pigment involved is obviously not melanin or chromolipoid but it could be the echinochrome, though this will not be known until the spectral absorption of the pigment has been determined in situ (see p. 29). The colour change manifest in diadematid urchins has implications for taxonomy. A discussion would be out of place here, but as already pointed out in respect of the species Diadema untillarum there are

* Since this was written, Weber and Dambach (1974)have claimed to have isolated living chromatophores of Centrostepkanus which change their form with pigment movement. Nevertheless in situ these cells respond to cytochalasin B like other chromatophores (Dambach and Weber, 1975).

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dangers in using the criteria pattern and colour when both can be materially altered by environmental lighting, t o say nothing of age (Millott, 1953a). In their recent attempts to use these criteria, in distinguishing other species of Diadema, Pearse and Arch (1969) and Pearse (1970) encounter difficulties which merit re-examination in the context of the strictures contained in the above report of which they appeared to be unaware. IV. PODIAL RESPONSES The podia of some regular echinoids are clearly responsive to light, but almost nothing is known of the nature and disposition of the photoreceptors involved, and little about their associated nerve supply and its organization. The most striking responses are those of the tropical species Lytechinus variegatus and Diadema antillarum, but they have been examined only in a preliminary way and most of the available information is purely descriptive. The photic responses have not been analysed to anything like the same extent as those of the spines (see below) and the matter calls for thorough investigation. The podia of Arbacia and Lytechinus respond to ultra-violet radiation by a vigorous and immediate withdrawal (Sharp and Gray, 1962), I n general the responses made to visible radiation or to increases in its intensity are extensions (Millott, 1954 ; Yoshida, 1957b) or withdrawals, but they are often variable (Millott, 1956) and difficult to categorize in simple terms. More uniformity appears in the responses to shading where in Diadema (Millott, 1954) and Psammechinus (Millott and Yoshida, 1956), the podia show a sharp withdrawal. I n Lytechinus (Fig. 10) shading may also elicit extension (Millott, 1956). On the other hand, the podia of resting Evechinus chloroticus (Val.) do not respond to either increases or decreases in intensity (Dix, 1970). Again, in Lytechinus, stimuli of other kinds (contact or mechanical) may modify podia1 responses to light and induce attachment or detachment, so that the responses may be integrated into more complex patterns of behaviour such as locomotion or covering. Little has been done to extend the earlier work of Millott in Lytechinus who showed that the rate of extension increased in proportion to the intensity of lighting, or the work of Millott and Yoshida (1956) who showed in Psammechinus that the latency of withdrawal in response to shadows is an inverse function of the intensity of illumination and the depth of shading. It was also shown that a minimum period of illumination is a prerequisite for a shadow reaction. These features a t once recall the spine responses in Diadema and, together with the occurrence of dark adaptation, indicate dependence in part a t least on photo-

T H E P HOT OSE NSIT IV IT Y OF ECHINOJDS

13

chemical reactions. Spectral sensitivity of the shadow response in Psammechinus was shown to be maximal between 440 and 560 nm, but this range is far too great to provide any hint as to the photoreceptive pigment involved.

A. The covering reaction A curious by-product of podia1 photosensitivity is the habit of seizing any available objects that can be lifted, transporting and then holding them on the aboral hemisphere. This habit, known since ancient times, has been referred to as '' dressing ", " covering '' or " heaping ". It is widely distributed among regular urchins, has been reported many times and has excited more interest and controversy than any of their other activities. Many of the observations are conflicting and the interpretations of them are diverse. This is in part the outcome of the tendency to oversimplify already referred to (p. 1). The habit has been variously interpreted as follows. (1) As a means of increasing weight and resistance to displacement by wave action. (2) As a means of camouflage (see Brehm, 1884; MacBride, 1909; Milligan, 1915; Boone, 1925; Mortensen, 1927). (3) As a protection from light (von Uexkull, 1897a ; Lindahl and Runnstrom, 1929 ; Mortensen, 1943 ; CuBnot, 1948 ; Millott, 1956 ; Lewis, 1958 ; Sharp and Gray, 1962). (4) As a protection against desiccation or temperature extremes (Orton, 1929). (5) As the automatic outcome of " relative walking " (Dambach and Hentschel, 1970). (6) As an accessory feeding mechanism (PBquignat, 1966; Dix, 1970). ( 7 ) As a defence against predation (Dayton et al., 1968). Some of the above interpretations rest entirely on inferences and lack the backing of analysis by experiment. Some, if valid a t all, lack universal application. Thus ( 1 ) and (4) are meaningless in relation to Lytechinw, the urchin most given to covering and which is tropical or sub-tropical. It is rarely exposed or subject to forceful wave action, indeed, so far as the latter is concerned acquisition of covering makes the urchin top-heavy and therefore less stable. So far as (2) is concerned a degree of concealment will be achieved automatically by assimilating the surrounding substratum, but its value cannot be assessed adequately in the absence of knowledge concerning the predators involved and their sensory endowment. One of the suggestions that covering may be related to feeding, is a by-product of studies on skin digestion in a variety of echinoderms in addition to both regular and irregular urchins (see PBquignat, 1966). I n the case of those which cover, such as Psammechinus, the fact that the surfaces of spines, podia and pedicellariae produce mucus with

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NORMAN MILLOTT

digestive properties, supplemented by the activities of amoebocytes reaching the surface by diapedesis, means that objects held by the spines and podia as covering are rendered more liable to attack by the enzymes. Thus it is claimed that hard objects such as shells carrying polyzoans, etc., can be cleared of digestible matter in this process of “ aboral feeding ”. The extent to which these findings are applicable to other urchins that cover remains an open question. The other notion concerning a relationship between covering and feeding stems from observations on Ewechinus by Dix (1970) who suggests drifting algae are seized and held before being utilized as food in the more prosaic oral feeding. As regards defence, Dix also reports an account given by Dayton et a2. (1968) referring to the habit of Sterechinus neumayeri (Meissner) which is stated to cover itself with a mat of hydroids and thereby repulse the attacks of the anemone Urticinopsis. The explanation most frequently advanced is that the reaction is a response to light, but whether it serves as a protection against it is a matter of argument. Nevertheless there is much evidence, both direct and indirect, to indicate the importance of light. Moore et al. (1963) report that Tripneustes esculentus (Leske) begins to cover in the spring as the light intensity increases and the urchin then takes to the shade as the summer advances. Lytechinus studied by Millott (1956) takes up covering in the early morning and sheds much of it a t dusk. Sharp and Gray (1962) who also used Lytechinus, report that covering is picked up in the dark but to a far lesser extent than in light, and is picked up to a much greater extent in sunlight or ultra-violet radiation than in artificial ‘‘ white ” light. In addition Millott reported that the amount of covering assembled is greater and i t is held for longer a t higher intensities. He also reported that urchins kept in aquaria can be sensitized to light by a sojourn in darkness or by injecting photosensitizing dyes into the perivisceral coelom, so that they take up covering more assiduously, but only when illuminated. Though all this indicates that light can influence the response, some caution is necessary in accepting too readily as evidence the effect of photosensitizing dyes the mode of action of which is unknown. When dispersed through the animal they could create artificial photoreceptive systems, for example by becoming incorporated into nerve elements, as shown in Sepia by Arvanitaki and Chalazonitis (1961), or even into the effectors. Nevertheless it is relevant to a degree that of the dyes used, those found to be effective absorb extensively in the visible range between 410 and 565 nm, which is much the same range as that found to be effective in eliciting the photic podia1 responses of Psammechinus.

THE PHOTOSENSITIVITY OF ECHINOIDS

15

The evidence is not wholly supporting, thus Gamble (1965) found no relationship between the extent of covering and the vertical light gradient due to depth in Paracentrotus Zividus (Lamarck). Similarly Dix (1970) reports that Evechinus is often covered in dim light and that even after prolonged dark adaptation, light does not influence the extent and rate of covering. Furthermore, the amount of covering retained showed no diurnal changes. The view that covering gives protection against strong light, originally advanced by von Uexkiill (1897a), has often been reiterated. It is supported by limited indirect evidence. Thus in several species there is a tendency for less densely pigmented individuals to seek shade or to cover. This suggests a more acceptable approach to the question of the significance of the reaction insofar as it might confer a selective advantage on a photosensitive species, by permitting diurnal activity in shallow sunlit water and so increasing the range of its distribution. Again, however, there are dangers inherent in this kind of reasoning especially in the instances where the nature of the skin pigment, its disposition in relation to photoreceptors, its optical density, spectral absorption and stability are all unknown. Furthermore such protection as exists may not be obvious. Thus Raup (1959, 1960a, b, 1962a, b) has shown that it can be a matter of the crystalline structure of the test (for a fuller discussion of this problem see Millott, 1956 and 1966a). As to the process itself, the initial brief analysis reported by Dubois (1914) is expanded in the reports of Millott (1956), Sharp and Gray (1962) and Dambach and Hentschel (1970). Millott’s description of covering in Lytechinus stresses the impressive co-ordination of spines and podia which is shown not to depend on the nerve ring. Podia form the primary effectors. They extend in response to continuous illumination or change in its intensity (p. 12) to seize covering by their suckers (Fig. 7) and then by shortening, pull objects on to the spines (Figs 8 and 9) which lever them into position as they are held by the podia acting like “ guy ropes ”. Covering thus obtained may be passed over the surface of the urchin by the continued coordination of these effectors. During the process spines manifest their responsiveness by adapting their activities according to the mechanical stresses set up during the transport and positioning of cover. I n essence the activity recalls that involved in locomotion, save that here the loose substratum is moved over the animal instead of the animal over the substratum (Millott, 1966b). Dambach and Hentschel make much of this similarity, but to the writer its significance is arguable. Much depends on the extent to which the behaviour of echinoids is construed a8 ‘‘ automatic ” in the sense of von Uexkiill’s Reflexrepublik. The

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NORMAN MILLOTT

analysis of photic spine responses has revealed the inadequacy of such a concept (see Millott, 1966b). There is a disconcerting element of variability in the responses of echinoid podia a t least some of which is no doubt the outcome of inadequate experimentation. On the other hand, some could be the outcome of the incorporation of simple reflexes into complex behaviour patterns of more than one kind. Thus the responses of the podia of Lyfechinus t o shadows, the rapid withdrawal followed by slow extension and waving, could be a compromise representing the best the creature can achieve to meet conflicting exigencies, namely the advantage to be gained by withdrawing delicate organs from a potential source of danger or extending them to reach a potential source of covering. Since light also excites taxic locomotory movements, it is only to be expected that behaviour patterns such as those of locomotion and covering, involving co-ordinated activities of the same effect,ors and FIQS7-9. The covering reaction of Lytechinus vnriegntus (see p. 15). Reproduced with permission from Millott (1957b).

FIG. 7. The extended podia (bearing suckers which appear surroundings.

a8

white tips) search the

T H E PHOTOSENSITIVITY O F ECHINOIDS

17

FIQ.8. Two podia adhere by their suckers t o one valve of E bivalve shell.

FIG.9. The shell (seen on the left), is pulled up so as t o bear against the tips of the spines.

subject to the same stimuli (light, contact and mechanical stress), should appear overtly similar. But this does not imply identity and the two could easily be confused. Both patterns of activity, to say nothing of unspecific podia1 activity, could lead to the acquisition of some covering when there is a loose substratum, moreover in certain situations such activities could reinforce each other. Thus pieces of covering assembled in darkness due to contact stimuli and locomotory activity could be augmented by photically excited covering activity. One distinction between the two patterns of specific activity appears to reside in the

FIG.10. Lytechinua wariegntus. Extension of the podia (with terminal suckers showing white and grouped immediately to the right of the arrow) following a decrease in light intensity. The podia in the light beam (directed along the arrow) were photographed while still extending in response to a brief interruption of the beam. Reproduced with permission from Millott (1957b).

A

FIG.11. Diagram showing the placing of cover over localized, brightly illuminated, areas of the surface (p. 19). Four stones, each shaded by a distinctive convention (lines, dots, circles or solid black), are moved into a narrow band of sunlight (stippled) crossing the aboral surface of a n urchin, approximately over the routes shown by successive outlines and arrows, drawn with the corresponding conventions. The interambulacra are distinguished by cross-line shading. The urchin endeavoured to take up stones from area A, but failed. No material suitable for cover was available in area B. P. periproct. Reproduced with permission from Millott (1956).

THE PHOTOSENSITIVITY O F ECHINOIDS

19

placement of cover over brightly illuminated areas (Fig. 11). This is unlikely to be an attribute of locomotion. These suggestions would also offer an explanation of the instances of photosensitive urchins carrying a few pieces of covering in the dark. However, Dambach and Hentschel regard such placement as the result of arresting the transport of covering by a localized effect of light on the locomotory activity of the podia. Be this as it may, Millott found that in Lytechinus, individuals on the march do not readily accept covering. The most pertinent observations indicating a distinction between locomotory and covering activity are due to Sharp and Gray, who, however, appear not to have realized their significance in this context. Thus in Lytechinus the two types of activity can be separated by using radiation of differing spectral composition. Artificial “white” light leads to locomotion toward the light source and is accompanied by little covering, whereas sunlight and ultra-violet radiation also stimulate active locomotion, but away from the light source and accompanied by intense covering activity. Obviously these experiments should be extended and re-examined in this context. I n conclusion it appears likely that these disparities will persist until the photosensitivity of the podia as well as the nervous organization involved in their responses have received a much greater share of attention. Happily more has been bestowed on the spines. V. SPINERESPONSES The spines of echinoids generally respond to mechanical and chemical stimuli, but those of a few respond also to photic stimuli. Von Uexkiill (1897a) and Hess (1914) report rotatory movements of certain club-like spines of Gentrostephanus excited by decreases in light intensity. Holmes (1912) described the spines of Arbacia as erecting after shading and as moving toward illuminated areas, followed by swaying. Diadema responds both to increases and decreases in intensity by a sharp jerk of the spines followed by rapid oscillation. These striking movements attracted the attention of early workers such as von Uexkiill (1897b, 1900a, b) and Dahlgren (1916). They have been reexamined in detail by Millott and collaborators. Von Uexkiill attempted to explain his findings by a highly original scheme involving crude and remarkable mechanical analogies which are now outmoded. His ideas are reviewed and discussed elsewhere (see Millott, 1966b), but it is only fair t o add, against the background of the neurophysiological advances of over half a century, an advantage that was denied to the original investigator !

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NORMAN MILLOTT

Three cardinal features emerged from these early accounts: the spine responses are reflexes; they are executed in response both to increases and decreases in light intensity; they do not require the presence of the oral nerve ring. Von Uexkull and Holmes drew a sharp, fundamental and morphological distinction between the reflexes stimulated by increases and those by decreases in intensity, maintaining that the former involved only the superficial nerve layer, whereas the latter involved the radial nerves. Millott and Yoshida (1959) invalidated the distinction showing that the radial nerves were also involved in responses to increases. It is pertinent to note that Hess gave a hint of an inhibitory influence of light in reporting that spines slowed their rotation when illuminated but quickened it when shaded. Similarly, when the spine responses were re-examined in Diadema, it was soon discovered that they were more vigorous, constant and prolonged after decreases than after increases in intensity and because of this, attention has been largely devoted to shadow responses. The findings up to 1963 have been reviewed by Yoshida ( 1966).

A. Photoreception Identification of the photoreceptors involved in the spine reflex of Diadema has proved unexpectedly difficult. Structures supposed to be eyes corresponding in distribution with the pattern of white or blue spots already mentioned (p. 9) have been described and endowed with an elaborate structure by Sarssin and Sarasin (1887). Their inference, based on an erroneous interpretation of structure, has been accepted with varying degrees of reservation. It was invalidated by scanning the ekin with small light spots which were obliterated to produce test shadows. Spine responses were produced by shading any part of the skin, though most effectively by shading the bases of the podia and (somewhat ironically) least effectively by shading the " eyes " which proved to be iridophores (Millott, 195313, 1954). Studying the histology of the skin and radial nerves revealed no structures resembling even the simplest of eyes and subsequent examination of the most photosensitive areas of the skin by electron microscopy confirmed this (Millott and Coleman, 1969). A clue to the enigma was forthcoming early in the experiments when it was discovered that obliterating light spots projected on to the radial nerves produced vigorous responses. This was later amply confirmed by Yoshida and Millott (1959) using a more refined method (Pigs 12 and 13) and by Takahashi (1964) who demonstrated the electrophysiological concomittant of the response (Fig. 14). Photosensitive elements therefore exist in the radial nerves, a finding which at once

S-

Fig, 12. Apparatus used to demonstrate photosensitivity of the radial nerve in Diadema antillarum. A. ampullae; C. clamp; L. light beam passing below preparation and casting a shadow of the spines (recorded in Fig. 13); M, microscope for viewing the stimulating light spot ; N. radial nerve ; 0. objective lens of compound microscope ; S. position of stimulating light spot ; T. piece of test ; W.L. water level. Reproduced with permission from Yoshida and Millott (1959).

FIG. 13. Diadema antillarum. Photosensitivity of the radial nerve demonstrated by the technique shown in Fig. 12. Left : A light spot of the relative size shown by the black ring was projected on to the radial nerve (white area) in the position shown. The scale represents 0.5 mm. Right : A shows the vigorous spine response which followed extinguishing the light spot. B shows the absence of a response after the same light spot had been shifted to a position just outside the edge of the nerve (white ring). Time scale (in seconds above tracing). Interruption of the beam producing the spot is shown by the disappearance of the black band below each record. Reproduced with permission from Yoshida and Millott (1969).

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NORMAN MILLOTT

ON

0 OFF 10 sec

1 1 2 8’C FIG.14. n C n d ~ r n usefoszcm. ~luctrophysiological demonstration of photosonaitivity in the isolatrcl radial n w w . A , “ On rwpotise ”. S o t o bricf ditichargc. following illuminatioti at risp of signal marker. H , ‘’ Off responso ”. Note vigoroir6 nnd prc~longcd discharge following ccwatiuii of illumination at tho fall of the signal marker. Rvprotlucotl with permission from Takaha3hi ( 1964).

suggested that the photosensitivity of the surface could be attributed to the felt of fine nerve fibres that pervades the epidermis in Diadema as in other echinoids. Though this has never been proved it is reasonable to speculate that this explanation could have a wider application and prove to be the basis of the so-called “ dermal light sense ” t h a t is wellmarked in echinoderms where so much of nervous system is superficial (for a review and general discussion of the phenomenon see Millott, 1968).

The advent of electron microscopy stimulated a search throughout the animal kingdom for the fine structural correlates of photosensitivity. A degree of success, not always devoid of speculation, has been achieved and photoreceptors were endowed with an ordered lamellate ultrastructure. These findings have extended to the nervous system. Thus in the mollusc Aplysia such ultrastructure has been demonstrated in photosensitive neurons by Chalazonitis et al. (1966). I n echinoids, however, the search has so far met with little success. Kawaguti and Ikemot0 (private communication) have found lamellated structures in certain cells in the thickening of the superficial nerve layer (podial ganglion) which occurs a t the base of the podia, but their significance remains uncertain. I n their examination of the most photosensitive areas of the skin of Diadema, namely the podial organs situated a t the ambulacral margins (Figs 15 and l 6 ) , Millott and Coleman (1969) found little sign of strucFIQS15 and 16. Details of the podial organ, the most photosensitive area of the skin of Diadema antillarum. Reproduced with permission from Millott, N. and Coleman, R . : The Podia1 Pit-a New Structure in the Echinoid Diadema antillarum Philippi. Zeitschrift fur Zellforschung und mikroskopische Anatomie , 95, 187-197 (1969). Berlin-Heidleberg-NewYork : Springer.

FIG.15. The podial organ as seen in portion of a meridional section of the aboral region of a radius. The arrow, directed into the mouth of the podial pit, points aborally. b, base of podium ; pg, podial ganglion in superficial nerve layer. Note the secretion passing into the lumen of the pit.

FIG.16. The podial pit (p) and the associated branch of the radial nerve (rn) as seen in tangential section of the body wall. ip, inner (radial) member of the pair of water vascular canals that extends externally into the podium ; op, outer member. A.M.B.-~~

2

24

NORMAN MILLOTT

tural specialization. Aside from the thickening of the superficial nerve layer (podial ganglion) and its minute, densely packed nerve elements (Figs 17 to 19), the most notable feature was the existence of fine nerve fibres packed into spaces between the cells of the epithelium which lines the associated podial pit. In some cases the cell surface was tucked in to receive them (Fig. 20). The nerve proved more superficial than had been revealed by light microscopy and in this area a t least, much of it must be very accessible to light. But there were no signs of

FIG.17. (For legend see p. 26.)

lamellated or other appropriately specialized membrane structures supposedly indicative of photoreoeptors. The lack of structural specialization in the sensory cells of echinoderms generally is noted by Pentraeth and Cobb (1972). They draw attention to the sensory role of relatively unspecialized epithelial cells, but the situation in the podial pit indicates that so far as the photosensitivity of echinoids is concerned the specialization may well be vested in the particularly superficial location of photosensitive nerve. What is clearly required

THE PHOTOSENSITIVITY O F ECHINOIDS

25

now is an extended study of the fine structure of the skin and radial nerves. At this point the observations of Boltt and Ewer (1963) may be mentioned, indicating the existence of photosensitivity in the lantern muscles (or in nerve elements associated with them) in Parechinus anguZ0osus (Leske). The presence in Diadema of superficial photoreceptors interspersed with light absorbing elements such as chromatophores, capable of

dispersing and concentrating their pigment, makes possible a system whereby the intensity, and to some extent the spectral quality, of the light reaching the receptors could be controlled. Experiments with juveniles (Millott, 1954) showed that when their skin pigment is concentrated they become more photosensitive and vice versa, but it remains an open question to what extent the two events are causally connected. It is clear, however, that the level of photosensitivity cannot be adjusted wholly in this way because Yoshida (1966) has shown that photosensory recovery in darkness occurs much more quickly than

26

NORMAN MILLOTT

pigment concentration and changes in photosensory threshold can be great when those in pigment dispersion are small. Indirect evidence concerning the spectral absorption of the photoreceptive pigments involved has been obtained. Using spine responses

FIG.19 FIGS17-19. Details of the superficial nerve layer in the region of the podia1 pit of Diadema antillarum. bj, bj’, bj” inter-locking junctions b e h e e n axons ; ev, vesicle with internal membranes ; gr, glycogen rosettes ; m, mitochondrion ; mg, densecored vesicle ; nt, neurotubules ; v, vesicles with granular or colloidal contents. Arrow in Fig. 18 points to region where axons are tightly packed. Reproduced with permission from Millott, N. and Coleman, R. : The Podia1 Pit-a New Structure in the Echinoid Diadema rrntillnrum Philippi. Zeitschrift f u r Zellforschung u n d mikroskopische A m t o m i e , 95, 187-197 (1969). Berlin-Heidelberg-New York : Springer.

us an index, the spectral sensitivity of the radial nerve was determined

by two methods (for descriptions of the apparatus used see Millott and Yoshida, 1957, and Yoshida and Millott, 1960). The first depended on determining the relative minimum amounts of energy supplied a t various wavelengths that were necessary to elicit the responses of small groups of spines to a standard shadow. The second, a more elaborate

THE PHOTOSENSITMTY OF ECHINOIDS

27

FIG.20. Details of cell of epithelium lining the podia1 pit of Diadema antillarum showing the neural pits (np), invaginations of the cell surface packed with fine nerve fibres (see p. 24). Note also the microvilli (mv). c, Cisternae. Reproduced with permission from Millott, N. and Coleman, R. : The Podia1 Pit-a New Structure in the Echinoid Diadema antillarum Philippi. Zeitschrift fiir Zellforschung und mikroskopische Anatonhie, 95, 187-197 (1969). Berlin-Heidelberg-New York : Springer.

and accurate method, was based on determining the relative effectiveness of instantaneous changes from white light to that of various colours, as a means of eliciting a shadow response from a single spine. Changes to wavelengths at which the urchin is to varying degrees more sensitive are correspondingly less effective in producing a shadow

28

NORMAN MlLLOTT

response. As will be evident from Fig. 21 the resuIts of the two methods agree reasonably well, the maximum sensitivity occurring between 466 and 460 nm. Figure 22 furnishes two interesting comparisons: the first between the action spectrum of the spine response in Diadema antillarum and that of pigment dispersion in the chromatophores of

I

I

Wovelength (nm)

FIG.21. Comparison of the action spectra of the spine response of Diaderna antillarum (see p. 26), obtained by the minimum energy method (broken line) and the method of determining the relative effectiveness of instantaneous changes from white light t o that of various colours (solid line). Reproduced with permission from Yoshida and Millott (1960).

Diadema setosum; the second between the action spectra of these responses and the spectral absorption in the visible range of the echinochrome extracted from the skin in acid ethanol. The approximation of the maxima is striking and since echinochrome occurs in cells resembling neurons of the photosensitive radial nerve (Millott, 1957a; Millott and Okumura, 1968a) as well as in the

T H E PHOTOSENSITIVITY O F ECHINOIDS

29

Wavelength (tnlt)

FIG.22. Comparison of the action spectra of the spine response of Diadema antillarum (0-o-o), and that of pigment dispersion in the chromatophores of Diadema setosum ( o o o o o o o o ) . The spectral absorption of echinochrome extracted from the skin of Diadema antiZZarum by acid ethanol is also shown (----). Reproduced with permission from Millott and Yoshida (1957).

skin, it is tempting to suggest a photoreceptive function for this pigment. Whatever its function in relation to the chromatophores may be, so far as the nervous system and spine responses t o shading are concerned, there are good reasons for caution in interpreting the approximation. The spectral absorption of echinochrome varies with p H and with the manner of its combination. The extracted pigment is red, whereas that in the cells resembling neurons is purple with an absorption maximum (determined microspectrophotometrically ) between 540 and 560 nm. The echinochrome in these cells is therefore unlikely to be involved in photoreception for the shadow response (Millott and Okumura, 1968a). The nature of the photoreceptive pigment remains obscure.

B. Integrative mechanisms The presence of a widespread system of photoreceptors suggests a need for a well-developed and complementary integrative system. Investigation has indicated its existence. I n the first place there is strong indirect evidence to show that it is owing t o nervous interaction that the shadow response exists. The fact that spines respond t o increases in the intensity of light projected on to the skin shows that light can exert an excitatory effect, though the

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NORMAN MILLOTT

extent of the change in intensity and the area of illumination necessary t o elicit such responses are much greater than in the case of shading. Thus in common with other sensory systems both " on " and " off" responses exist and in the latter, though photic energy is being fed into the system whilst the light is on, no overt response appears until i t is cut off. Light therefore appears to inhibit as well as excite. Clear evidence of its inhibitory effect was produced by Millott and Yoshida (1960b) who showed that the spine waving which follows the obliter-

o*Ell

00.0

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FIG. 23. Graded inhibition of the shadow response of Diademn antillarum caused by re-admitting light of progressively increasing intensity. The effect shown is on the duration of the response and is produced in the radial nerve. Abscissae, duration of shading in seconds. Ordinates, ratio of the duration of the response to that of a control response during which no light was readmitted. The vertical dotted line shows the latency (R.T.). The figures alongside each curve show the relative intensity of readmitted light, expressed in arbitrary logarithmic units. Note that the progressively shorter reaction produced by increasing intensities displaces the curves down the ordinate axis. Reproduced with permission from Millott and Yoshida (1960b).

ation of light spots projected on the radial nerve, could be suppressed by projecting light spots of varying intensity (and size) on to the same or neighbouring regions of the radial nerve, while the shadow reaction was still in progress. The degree of suppression achieved was proportional t o the intensity (or area) of the light re-admitted (Fig. 23). Millott and Okumura (196813) advanced further evidence, but of different character, by showing that when the radial nerve of Diademn was stimulated electrically, two propagated waves (presumably massed potentials) could be recorded, of which one (the faster) was associated with spine movement (Fig. 24) the other (the slower) was associated with inhibition of the shadow response (Fig. 25). Inhibitory potentials in the radial nerve can therefore influence the spine reaction, presum-

FIGS24 and 25. The relation between potentials propagated in the radial nerve of Diadema antillarum, recorded extracellularly, and the spine response. Figures 24A and C reproduced with permission from Millott (1968). Figures 24B and D and Fig. 25 reproduced with permission from Millott and Okumura (1968b).

FIG.24. (a) Fast (small) and slow (large) potentials resulting from a single electrical stimulus indicated by the stimulus artifact immediately preceding the fast response. Time scale : 250 ms. (b), (c) and (d),relation of the potentials (upper record), following a single electrical stimulus, and the behaviour of a single interambulacral spine situated alongside the stimulated nerve (lower record). All were recorded at the same speed; time scale : 1.0 8. (b)shows presence of fast and slow potentials and spine response. I n (c) only the slow potential appears and it is not followed by the spine response. I n (d) the fast potential alone persists (at arrow) and is followed by the spine response.

E \ 1

G

FIQ.25. Inhibition of the shadow response of a spine by the slow electrical potential. The radial nerve was illuminated by a light spot 2.0 mm wide. The light was cut off at the lower arrow. I n B-F, the upper traces show the propagatedpotentials (between the upper arrows), the lower, show the response of a single spine. Time scale : 1.0 s. A, oscillation of a single spine produced by shading. B, complete inhibition of the shadow response produced by repetitive electrical stimulation of the radial nerve. C, partial inhibition produced by a similar stimulus. Note reduction in amplitude, frequency and regularity of the spine movements. D, E, the relationbetween stimulus and duration of inhibition. In D stimulation by five pulses produces a relatively short inhibition, so that a response follows shading at the lower arrow. In E, ten pulses of the same intensity produce longer inhibition. F shows the lack of a clear inhibitory effect following repetitive electrical stimulation that is subthreshold for the slow potential. Note only the fast potential appears between the upper arrows.

33

THE PHOTOSENSITIVITY OB ECHINOIDS

ably by synaptic action. Unfortunately it has not proved possible to obtain a clearer electrical picture of events by recording the responses of individual or small groups of nerve fibres, indeed the minute, denselypacked elements in echinoid nerve (Figs 17 and 18) offer little prospect of success in this direction. Realizing this, Millott and Yoshida (1960a,b) had already attacked the problem in Diadema antillarzrm by using the

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100

OJ (t)

FIQ.26. Comparison of the effects of lighting and shading on the reaction time. Curve T duration of lighting, 0-0, Curve I intensity of lighting, 0 - - - 0, Curve i intensity of shading, 0 -.- 0.Curve t duration of shading, A . . @. Abscissae : (T), in seconds; (I),in arbitrary logarithmic units; (i), percentage decrease in field intensity ; ( t ) , in milliseconds. Reproduced with permission from Millott and Yoshida (196Oa).

.

spine response itself, comparing the effects of varying separately lighting and shading on the latency, duration, amplitude and frequency of the spine oscillations. Happily this proved possible because the responses made to standardized lighting and shading were usually sufficiently constant in these parameters. For reasons of experimental convenience the effects of projecting and obliterating light spots on the radial nerves were determined.

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NORMAN MILLOTT

The intensity and duration of lighting exert parallel effects on a,ll the above parameters. Moreover they affect the whole reaction. Shading is different. Whereas its intensity (i.e. the proportionate decrease in intensity of illumination) affects the whole reaction, its duration does not affect the amplitude of the first contraction and it affects the latency (reaction time) only near the threshold and then but slightly and erratically (Fig. 26). I n a shadow reaction two environmental events must be considered, a period of illumination followed by a change in intensity, but they are not equivalent as has sometimes been supposed. Light supplies energy so that the parallel effects of its intensity and duration are only to be expected. I n the case of shading the fact that varying its duration affects only the later part of a response (see above) suggests that once the reaction has been triggered off the continued absence of light has some special significance. If it be recalled that two effects of lightexcitatory and inhibitory-have been shown (p. 30), it is clear that the two will act in opposition and since it is much more difficult to elicit an overt response by admitting light than by cutting it off, the inhibitory effect must usually be overriding. Moreover the effect persists until the light is cut off when a reaction is released which is in proportion to the preceding illumination. I n other words the system is prepared by illumination so as to be able to react when the light stops. This a t once suggests that what follows the shadow is a rebound from inhibition. If the shading is not total then light will remain to exert its inhibitory effect which reveals itself again as the reaction proceeds and it does so in proportion to its intensity. Such a post-inhibitory rebound would imply synaptic interaction and the mechanism appears similar to that revealed in the nervous layers of the retina by the electrophysiological investigations of Granit and others. It differs from that involved in the neural photosensitivity of molluscs such as Spisula (Kennedy, 1960) and Aplysia (Arvanitaki and Chalazonitis, 1961) where again excitation and inhibition are involved but each is mediated by a different photorecepFIQ.27. Spatial interaction in the skin of Diadema antillarum. The diagrams at the top of each column show the positions a t which two light spots were projected. The f i s t was projected in all cases a t position 0. Following its extinction and whilst a shadow reaction was in train, the second light spot was projected at the distances (in mm) on either side indicated by the numbers in the diagrams and the abscissae, positive values oral, negative, aboral. The circles in the diagrams indicate spine bases, that labelled S,being the one corresponding to the spine whose movements were recorded. The positions on the left are ranged along a meridian, those on the right, extend in a plane parallel to the ambitus. Ordinates : A, latency in seconds (values for position 0 fall outside the scale). B, the number of spine beats recorded in the successive periods shown alongside each curve. C, duration of the reaction in seconds. Shaded areas show the maximum range of variation in control experiments in which only the first light spot was used. Reproduced with permission from Millott and Yoshide (1960b).

30

6

3

I

I

I

6

3

0

-3

0

-3

10

-6

I

I

-6

I c

4

0

2

I

5

9

r

I

I

I

I

10

4

0

2

5

9

10

4

2

0

5

9

30

20

6

3

0

-3

-6

36

NORMAN MILLOTT

tive pigment. Moreover, in the former, inhibition is primary in that light suppresses an on-going discharge in the receptor neurons ; in the latter it is both primary and secondary. The foregoing experiments in Diadema performed on the radial nerves were useful not only in revealing the importance of nervous interaction in their photic responses but also in providing valuable clues concerning the intimate mechanism. However, the internal situation of these nerves makes the significance of the mechanism in normal life an open question. For this reason parallel experiments were performed on the skin and though much less easily executed and less extensive, they were suecient to show the existence of similar interaction in the skin. Light spots projected on to the skin or on to the radial nerves up to some 6 m m apart were shown to interact in their effects (Pig. 27). Intenxtion can thus he spatial as well as temporail. Moreover, transection of the radial nerves showed that interaction could occur between the effects of light spots projected on either side of a clean cut. This could only be achieved by nerve pathways passing through side branches to points of confluence in the skin. Summation as well as antagonistic effects were observed. I n all a bewildering variety of integrative patterns could be produced. Additional aspects of the nervous mechanism of the shadow reaction were revealed independently a t about the same time by Yoshida (1962) and Millott and Takahashi (1963). By using a refined technique with electronically operated shutters, Yoshida was able to project inhibitory light spots of differing intensities on to the radial nerve a t very short intervals after the initial illumination of the nerve had been cut off and a shadow reaction was in progress. I n this way he was able to determine the inhibitory threshold and the extent to which it changed during the latent period of the sh.adow reaction. He found that a t first it remained constant and increased suddenly a t a critical point (Fig. 28). He suggested that the sharp change marks the onset of an additional inhibitory mechanism and in view of the foregoing indications of central and peripheral sites of interaction it is but reasonable to suspect that the initial interaction may occur in the radial nerve and the later one in the superficial nervous system. Yoshida’s revelation of a period during which the inhibitory threshold remains constant has other important implications concerning the intimate mechanism, which support the view that i t differs from the mechanism postulated by Kennedy to explain the responses of the photosensitive neurons of Spisula. I n the latter, where again light both excites and inhibits (see above), it is suggested that opposing excitatory and inhibitory receptor potentials

37

THE PHOTOSENSITIVITY O F ECHINOIDS

E 0

0 0

0

0

0

0

25

0

50

0 ,

0

0

I . 200

,.

400 Duration of total darkness (msec ) 100

1

800

FIG 28. Diaderna setosum. Change in the threshold of photic inhibition during the latent period. Five examples are shown in which the radial nerve was illuminated a t different intensities prior to shading. The five curves show the relationship between the inhibitory threshold and the time of re-illuminating the radial nerve. Abscissae, time of re-admitting the light (in ms) scaled logarithmically. Ordinates, intensity of light re-admitted (in arbitrary logarithmic units). Open circles show the minimum intensities of re-admitted light required to inhibit a response. Filled circles show the maximal sub-threshold intensity (at which the shadow response just appeared). Reproduced with permission from Yoshida (1962).

are produced which differ in their time courses, the former taking longer to decay. As a result, at the cessation of illumination the excitability steadily rises and an “ off” response ensues. As Yoshida points out, if such a mechanism were involved in Diadema the threshold of inhibition necessary to counteract the rise would have to increase pro rata. I n fact it remains constant until the sharp break occurs.

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NORMAN MILLOTT

Millott and Takahashi (1963) investigated the basis of protracted rapid heating of the spines in the shadow response and the directional character of their first movement. The former is characteristic of photic responses and distinguishes them fmm rea&ions to stimuli of other kinds. Concerning direction, two generalizations have been made. First that spines move in the direction from which excitation approaches

FIG.29. The innervation of primary spines in Diudema antillarum. The top of the figure is aboral. Direct nerve tracts to the spine base are shown as thick black lines. The nerve ring around the spine base is shaded; no further elements of the superficial nervous system are shown. A, ambulacral spine; I.A., interambulacrel spine ; p.p., pores for water vascular canals extending externally into podium. Reproduced with permission from Millott and Takahashi (1963).

them and therefore toward the stimulus, and second, that the nervous events determining direction are confined to the superficial nerve layer. But these conclusions were based on direct observation using whole animals, or pieces bearing many spines, by which methods, more or less simultaneous responses are not easily resolved. Moreover, the areas illuminated were large, ill-defined and often unspecified. Nevertheless, these views were widely accepted despite the fact that there was something oddly incongruous about them when applied t o photic

THE PHOTOSENSITIVITY OF ECHINOIDS

39

responses (Millott, 1906b). These responses involve the radial nerves from which efferent nerves pass to the muscles of the primary spines along the paths shown in Fig. 29. This means that excitation will often approach these spines from the same direction wherever the stimulus is placed ! Using a technique of projecting minute light spots and photographic recording of spine movement developed from earlier studies, Millott and Takahashi showed that the two generalizations are far from adequate. When light spots are projected a t various positions around a spine and then extinguished, the first movement occurs consistently toward the position of the light spot only in certain circumstances (see below). I n others the same events evoke responses that are erratic with reference to the light spot but more consistent with respect to the position of an ambulacrum or the oral pole. The direction of the first spine movement is therefore conditioned by three factors, the direction from which excitation from the light spot approaches the spine, the position of an ambulacrum-which implies a radial nerve-and the position of the oral pole. The last two are associated and consequences of the topography of the motor nerves supplying the spine, which not only convey excitation from the direction of the radial nerve, but do so with an oral bias (Fig. 29). When factors are spatially disposed to act in concert, for example when the light spot and radial nerve lie on the same side of the spine, the first movement is consistently in their direction, but when factors lie on opposite sides, the movement is erratic. Central and peripheral influences clearly interact and it is likely that they do so a t the nerve ring around the spine base. The foregoing is the essence of a situation that is in reality more complicated especially as regards

FIQ.30. Recording of the movements of two adjacent ,ambulacral spines of Diadema antillarum showing the similarity of their responses to nhading, the onset of which is shown by the trace of the signal marker above the records. The movements before shading, which were spontaneous, also show some correspondence in rhythm. The lower trace marks the time in seconds. Reproduced with permission from Millott and Takahashi (1963).

40

NORMAN MILLOTT reaction time in seconds

R

1

frequency in beat+

FIG.31. The effect of chilling a radial nerve (sce below) on the latency (reaction timo) and frequency of oscillation in the shadow reaction of Diudemtr czntillarum. Reproduced with permission from Millott and Takahashi (1963).

the behaviour of spines situated immediately above a radial nerve and because of interaction between radial nerves. For a discussion of these aspects the reader is referred to the original account. The characteristic rapid beat of the spines appears to be due to the activity of centres in the radial nerve. This is indicated by the responses of neighbouring spines of the same order, which are so similar in amplitude, frequency and duration as to suggest ‘‘ drive ” from common centres in the radial nerve (Fig. 30). The frequency, however, declines with distance from the radial nerve, presumably due to synaptic action. The existence of such centres was substantiated by subjecting the radial nerves to localized changes in temperature which were shown to affect the latency, frequency and regularity of the spine oscillation (Fig. 31). I n addition there is evidence of spontaneous activity in such centres which is reflected in simultaneous outbursts of waving among groups of spines. I n essence therefore it appears that centres in the radial nerves set and regulate the rhythm that is initially determined by the

FIG.32. Slow recording showing simultaneous outbursts of spontaneous movements in four neighbouring spines of Diadema antillarum (see above). Reproduced with permission from Millott and Takahashi (1963).

THE PHOTOSENSITIVITY O F ECHINOIDS

41

effects of the parameters of lighting and its diminished intensity on the receptors and the complex nervous interplay which follows. We may note in passing that, in their attempt to explain by a formal hypothetical scheme the photosensitive mechanism controlling the lantern muscles of Parechinus, Boltt and Ewer (1963) also invoke synaptic interplay between excitatory and inhibitory nerve elements in motor units associated with the muscles. VI. RHYTHMICACTIVITIES A diurnal rhythm of activity has been described in several echinoids. In Diaderna, in addition to the diurnal rhythm of physiological colour change (p. 8), rhythms of locomotory activity (hiding by day, moving by night) have been reported by several observers, particularly in Diadema setosurn. Such activity is reflected in feeding which occurs a t night (for a summary see Lawrence and Hughes-Games, 1972). Thus there are indications that Echinothrix calamaris (Pallas) and Diadema antillarum behave similarly, but the latter only in deep water. Whether this rhythm is related to light is obscure, but it is worth mentioning that Fuji (1967) has reported the inhibition of feeding by light in Strongylocentrotus intermedius (A. Agassiz). However, Pearse ( 1 972) finds no evidence to show that nocturnal artificial illumination affects the feeding of Centrostephanus coronatus (Verrill) living in aquaria and Paracentrotus lividus feeds actively in daylight but seeks the shelter of boulders a t night. Other rhythms particularly in reproductive activity have been described which, it has been claimed, correspond to lunar rhythms, but there is considerable disparity in the reports and grave doubts have been expressed as to the adequacy of the evidence, whether the rhythm is truly lunar and concerning its relationship to light. For a review of the evidence and a discussion concerning the nature of these rhythms see Pearse (1972) : our concern here is with the possible effects of light. Tennent (1910)reported from Tortugas that the gonads of Lytechinus variegatus were empty immediately after full moon, but contained abundant germ cells a, week later. Fox (1923) reported that in Suez the gonads of Diaderna setosum undergo a cycle of growth and development corresponding with each lunation during the breeding season, attaining their greatest size just before full moon at which time the urchins spawn. He considered a variety of environmental parameters-including light-that might show a cyclic variation correlated with the lunar cycle, but without attaining any tangible conclusion, Fox suggested that the length of time during which the urchin was illuminated each

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NORMAN MILLOTT

day might be significant possibly by affecting the length of time during which it was active, though he could find no evidence for the idea. Subsequently he reaffirmed the idea in part, emphasizing the possible significance of the extended period of illumination and a t the same time rejected the possibility of polarized moonlight being responsible (Fox, 1932).

The problem was re-examined by Yoshida (1952) at Misaki but his findings were not so clear. He confirmed the existence in many females of a peak of sexual activity a t full moon, although males showed no lunar periodicity during the breeding season of one year, but did SO a year later. Kobayashi and Nakamura (1967) suggest that populations of Diadema setosum a t Set0 spawn near both full and new moons. Similar rhythms were reported by Moore et al. (1963) who found an increase in gonad volume in Lytechinus a t new and full moon in Bermuda, but not in Miami. A further instance is reported by Kobayashi (1967) in Mespilia globulus (Linn.) a t Set0 which spawns near both full and new moon. I n Centrostephanus coronatus as in Diadema setosum, although a monthly rhythm has been found, it does not show the same relationship to lunar phases in urchins which live in different localities. I n summing up the situation Pearse (1972) suggests that urchins are not influenced by monthly changes in moonlight and that the rhythms may be more closely related t o tidal factors (see also Moore et al., 1963). Nevertheless i t would be premature to discount an effect of light on the reproductive processes of a t least some diadematids. Thus as already suggested (Millott, 1966a) the five white interambulacral spots, which have excited much comment in the literature, lie in the skin immediately over the gonads and could act as windows. A similar suggestion was made later by Pearse (1970). Moreover in Diadema antillarum a t least, the spots are the persistent remains in the light adapted phase, of a more extensive " window '' in the form of a white lancet arch pattern which outlines the gonadial area in the dark adapted condition (Fig. 6). The suggestion, though worth exploring, is not immediately acceptable, for it is not yet clear how much light, especially moonlight, could penetrate the " window " and only some individuals of this species retain the capacity to develop the white pattern throughout life. The action of photoperiodic influences on Xtrongylocentrotus purpuratus (Stimpson) is indicated by Boolootian and Giese (1 959) who suggest that peaks of spawning may be induced by minimal day length and by Boolootian (1963), who induced gametogenesis by reducing 14 h periods of illumination to 6.

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43

VII. DISCUSSION Although investigation is so far from complete, it is clear that generally speaking the photosensitivity of echinoids is characterized by the simplicity of the receptive apparatus and the relative complexity of the associated nerve supply. Aside from the relatively unspecialized epithelial cells, the importance of which in other sensory modalities has been emphasized by Pentraeth and Cobb (1972))one could scarcely imagine a simpler photoreceptor in a metazoan than the neuronal photoreceptors implicated by the study of Diadema. However, it should be emphasized that in photoreceptive neurons, theoretically, all that is needed for their special function is a photoreceptive pigment appropriately coupled to an electron transport system, so that a high order of physiological specialization is not necessarily to be expected. The distribution of the light sensitive nerve in Diadema is somewhat puzzling. Though its presence in the skin is understandable, the photosensitivity of the radial nerves is anomalous, insofar as very little light can reach them, being shielded on one side by dense skin pigment, and shrouded by deeply pigmented gut and mesenteries on the other. Moreover Raup (1960a, b), has shown that in the test itself the orientations of the calcite crystals and connective tissue are such as to ensure minimal transmission of light. All this has led to the idea that neural photosensitivity is primitive and an evolutionary survival of an ancient sentient surface. Ewer and associates, as a result of their studies of photosensitive muscles in Parechinus and Gucumaria sykion (Lampert) adopt a somewhat different view, suggesting that such photosensitivity reflects a metabolic peculiarity frequent in echinoderm nerve and exploited, notably in the instances of Diadema and Lytechinus. Again, Millott has repeatedly urged circumspection in dismissing dermal, and by implication, neural photosensitivity as a primitive survival. I n some cases it may be so, and the existence in some crustaceans and molluscs of neurons the photosensitivity of which is accessory, or even incidental, to other functions, might be explained on this basis. The same could be said of the photosensitivity in the radial nerves of Diadema, which because of their central nervous character is unlikely to be vested in primary neurons. Nevertheless, study of this urchin has opened up a different prospect. Thus the level of sensitivity displayed is higher than that of some specialized photoreceptors. Again the fact that the associated nervous organization shows considerable sophistication (p. 36) renders such a view less easy to accept because the receptive system and its nerve supply must have evolved together. Moreover, the nervous

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NORMAN MILLOTT

organization is not primitive in the sense defined by Gregory (1967), who suggests that in the course of their evolution visual systems have taken over part of the pattern-touch neural system, because in Diadema the nerve pathways involved in photic responses and those associated with touch are already distinct (see Millott, 1967). The presence of extra-ocular photosensitivity is not, therefore, necessarily a hallmark of a primitive organism and indeed it may co-exist with elaborate eyes, the two brands of photoreception fulfilling complementary functions. The attendant nervous organization also serves to distinguish photic responses from those made to other kinds of stimuli. Thus the nervous control of responses of spines to mechanical and chemical stimuli, like that of pedicellariae (Campbell, 1973), is essentially peripheral and does not involve the substantial contribution from elements in the radial nerves. As regards the receptor pigment the notion that the hydroxynaphthaquinone pigment in adults and larvae behaves in this way dies hard, despite lack of evidence. A degree of correspondence between the spectral sensitivity and spectral absorption of this pigment in the visible range, and the occurrence of the pigment in both skin and photosensitive radial nerves, though highly suggestive, is not enough (see p. 29). We may note further that the pigment is not photosensitive, and although this is not essential on theoretical grounds, photoreceptive pigments in representatives taken from a very wide range of animal organization have proved to be so. Moreover, these photoreceptor pigments have proved to be haplocarotenoid-proteins, the molecules of which, with their linear conjugated structure implying the existence not only of light absorption but also of cis-trans isomerization and instability, would appear more suitable for transducing light energy. The variety of ways in which photosensitivity is manifest in echinoids will now be obvious, what is not so clear is the nature of the intimate mechanisms involved and their significance. Although by no means completely resolved the situation is clearest in the case of the spine response. I n considering significance some generalities deserve reiteration. As indicated long ago by Parker, the presence of photoreceptors does not in itself imply that an animal can see, but the existence of nerve centres in relation with them means that it is informed of certain things about its surroundings. Thus echinoids are informed not only of the presence of light but also of differences in its intensity. Detecting the mere presence of light informs the urchin of day, night, diurnal and seasonal rhythms and of shelter or exposure. Detecting differences in intensity means that shadows can be identified, some receptors being

THE PHOTOSENSITIVITY OF ECHINOIDS

45

stimulated, others not, which means that the animal can determine the direction of light, and in turn this can induce co-ordinated activity of effectors resulting in locomotion so directed as to bring animals into the conditions of illumination best suiting their habits, or to maintain them there. Alternatively in some species the co-ordinated activity induced may result in covering. It has been reported several times that Diadema setosum is attracted to dark areas. This may lead individuals into crevices for protection or toward flocks of their own kind, forming part of the characteristic aggregation behaviour described by Pearse and Arch (1969) and interpreted by them as having a protective social function. This apparent ability to detect and move into dark areas, which has been labelled scototaxis, suggests the occurrence of vision of some kind and its physiological basis in sea urchins merits critical investigation. However, it is in detection of changes in intensity, particularly decreases, that the photic sensitivity of sea urchins attains its clearest and most characteristic manifestation from which most has been learned and it is from the study of Diadema antillarum that most of this knowledge has been derived, though some has been obtained from Diadema setosum. The most striking responses are those of the spines which is understandable because these urchins are bottom dwellers and exposed to varying degrees. The spines, especially the aboral ones, provide protection, being long and poisonous. Anything interposed between the animal and the light source that alters the intensity of light reaching the photosensitive skin signals a potential predator. Diadema reacts by sweeping a phalanx of its poisonous armament first in the direction determined by the factors already outlined (p. 36) and then repeatedly over the highly vulnerable ambulacra. Small wonder, therefore, that the response has been repeatedly assigned a protective function. As a defensive measure the response has achieved considerable success in Diadema antillarum, judging by the elaborate means to counteract it adopted by the helmet conch Cassis tuberosa. This assailant resorts to spraying the photosensitive surface of its victim with a salivary neurotoxin in order to inhibit the shadow response (Cornman, 1963). Nevertheless, if in Diadema setosum there are few known predators, there are several tolerated companions in the form of apogonid fish, a shrimp, a squid and one crab of which the first named regularly shelter among the spines (Magnus, 1967). How this shelter is gained without activating the formidable armament remains a mystery. Associated with these protective measures is the habit of seeking

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NORMAN MILLOTT

the shelter of crevices by day, which, judging from the reports of Thornton, Pearse and Magnus already referred to, is more prevalent in Diadema setosum than in the species antillarum. I n such situations the most formidable aboral spines project from the crevice and since they are not photosensitive, such a disposition restricts the area of the sentient surface directly accessible to light. This prompts the suggestion that here the iridophores, hitherto something of an enigma, may come into play. These organs which form the blue spots or lines in the skin visible in bright light (see p. lo), produce their intense blueness by the unusual method of Rayleigh scattering (Millott and Manly, 1961). This light, to which the animal is most sensitive (p. 26), is diffused by the iridophores as a blue glow over the photosensitive skin especially in the deep recesses between the spine bases. Shading only a limited exposed region of the skin will therefore also cut off the light diffused to other regions leading to increased sensitivity. Evidence concerning the intimate mechanism of the shadow response in Diadema (p. 34)has further implications. A moving shadow cast by a predator lurking in the light path continually changes the pattern of stimulation on the photosensitive skin so that nervous interaction is brought into play. As a result, provided there is sufficient light, both ‘(on ” and off ” responses will be produced and each will signal the nerve centres. This will surely pay dividends in enhancing contrast at the boundaries of light and shade and thereby also increasing the perception of movement. There are other possibilities. Thus in a situation of downward lighting, the flickering shadows cast on the skin by the waving spines themselves might have the effect of sustaining sensitivity to the boundaries of light and shade in a manner analogous to the restoration of stabilized retinal images in complex eyes (see Ditchburn, ((

1963).

The importance of the shadow reaction adds a new dimension to the significance of ‘‘ off ” responses ; for far from being mere refinements of sophisticated photosensory systems, in detecting the presence and movement of predators and in ensuring timely responsiveness, they may have assumed in Diadema a substantially important role in survival. Finally it is not inappropriate to reiterate the views already expressed concerning the need to revise earlier concepts of the organization of the echinoid nervous system. Whatever may be urged concerning the responses to other sensory modalities, the study of spine responses to photic stimuli places severe limitations on the credibility of notions such as that of the “Reflexrepublik” advanced by von Uexkiill and of Jennings’s ideas of the activities of independent parts fitting together in some sort of pre-established harmony. Spine move-

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ment shows little that could be described as haphazard and echinoids do not provide us with the opportunity t o study co-ordination in its simplest form as asserted by Jennings (1909). On the contrary, the pattern emerging from the study of photic responses of effectors such as the spines indicates a much higher degree of complexity and refinement in co-ordination and central nervous integration.

VIII. REFERENCES Arvanitaki, A. and Chalazonitis, N. (1961). Excitatory and inhibitory processes initiated by light and infra-red radiations in single identifiable nerve cells (giant ganglion cells of Aplysia). I n " Nervous Inhibition ". (Florey, E., ed.), pp. 194-231. University Press, Oxford. Boltt, R. E. and Ewer, D. W. (1963). Studies on the myoneural physiology of Echinodermata. IV. The lantern retractor muscle of Parechinus : responses to stimulation by light. Journal of Experimental Biology, 40, 713-726. Boolootian, R. A. (1963). Response of the testis of purple sea urchins to variations in temperature and light. Nature, London, 197, 403. Boolootian, R . A. and Giese, A. C. (1959). The effect of latitude on the reproductive activity of Strongylocentrotus purpuratus. International Oceanographic Congress, American Association for the Advancement of Science, 21 6-21 7. Boone, L. (1925). Echinodermata from tropical East American seas. Bulletin of the Bingharn Oceanographic Collection, 1(4),1. Brehm, A. E. (1884). " Merveilles de la Nature ". Baillihre, Paris. Campbell, A. C. (1973). Observations on the activity of echinoid pedicellariae. I. Stem responses and their significance. Marine Behaviour and Physiology, 2, 33-61. Chalazonitis, N., Chagneux-Costa, H. and Chagneux, R. (1966). Ultra-structure des " grains " pigmenth du cytoplasme des neurones d'dplysia depilans. Cornptes rendus des Sdances de la Socidtd de Biologie. Paris, 160, 10141017. Cornman, 1. (1963). Toxic properties of the saliva of Cassis. Nature, London, 200, 88-89. Cukiiot, L. (1948). " Trait6 de Zoologie. Anatomie, Bthologie et systkmatique des gchinodermes ". (Pierre-€'. Grass&, G., ed.), vol. 11, pp. 3-272. Masson, Paris. Dahlgren, U. (1916). Production of light by animals. Journal qf the Franklin Institwte, 181, 377. Dambach, M. (1969). Die Reaktion der Chromatophoren des Seeigels Centrostephanus longispinus auf Licht . Zeitschrift f u r vergleichende Physiologie, 64, 400-406. Dambach, M. and Hentschel, G. (1970). Die Bedeckungsreaktion von Seeigeln. Neue Versuche und Deutungen. Marine Biology, 6 , 135-141. Dambach, M. and Weber, W. (1975). Comparative Biochemistry and Physiology, 50C, 49-52. Dayton, P. K., Robilliard, G. A. and Paine, R. T. (1968). Benthic faunal zonation as a result of anchor ice a t McMurdo Sound Antarctica. Paper presented to S.C.A.R. Symposium on Antarctic Ecology, Cambridge, England. (Cited from Dix, T. G., 1970.)

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Diebschlag, E . ( 1938). Ganzlieitliches Verlialten L i i i d Lunen bei Echinodermen. Zeitschrift f u r vergleichende Physiologie, 25, 612. Ditchburn, R. W. (1963). 1nformat.ion arid control in t h o visiid systein. Nature, London, 198, 630-632. Dix, T. G. (1970). Covering response of the cchinoid Evechinus chloroticus (Val.). Pacific Science, 24, 187-194. Dubois, R. (1914). Action de la lumiere sur les Echinodermes. Compte rendu International Congrks de Zoologie, 9, 148. Fox, H. M. (1923). Lunar periodicity in reproduction. Proceedin,gs of the Royal Society, B95, 523-550. Fox, H. M. (1925). The effect of light on the vertical movement of aquatic organisms. Biological Reviews, 1, 219-224. Fox, H. M. (1932). Lunar periodicity in reproduction. Nature, London, 130, 23. Fuji, A. (1967). Ecological studies on the growth and food consumption of Japanese common littoral sea urchin Strongylocentrotus intermedius (A, Agassiz). Memoirs of the Faculty of Fisheries, Hokkaido University, 15. 83-160. (Cited from Lawrence, J. M. and Hughes-Games, L., 1972.) Gamble, J. C. (1965). Some observations on the behaviour of two regular echinoids. Proceedings of the Symposium of the Underwater Association for Malta (Lythgoe, J. N. and Woods, J. D., eds.) Malta. (Cited from Dambach, M. and Hentschel, G., 1970.) Gregory, R. L. (1967). Origin of eyes and brains. Nature, London, 213, 369-372. Hess, C. (1914). Untersuchungen iiber der Lichtsinn bei Echinodermen. PJlugers Archiv f u r die gesamte Physiologie des Menschen und der Tiere, 160, 1. Holmes, S. J. (1912). Phototaxis in the sea urchin Arbacia. Journal of Animal Behaviour, 2, 126. Jacobson, F. W. and Millott, N. (1953). Phenolases and melanogenesis in the coelomic fluid of the echinoid Diadema antillarum Philippi. Proceedin,gs of the Royal Society, B141, 231-247. Jennings, H. S. (1909). The work of J. von Uexkull on the physiology of movements and behaviour. Journal of Comparative Neurology and Psychology, 19, 313-336. Kennedy, D. (1960). Neural photoreception in a lamellibranch mollusc. Journal of General Physiology, 44, 271-299. Kennedy, G. Y. and Vevers, H. G. (1972). Tetrapyrrol pigments in the test of the echinoid Arbacia lixula. Journal of Zoology, London, 168, 521-526. Kleinholtz, L. H. (1938). Colour changes in echinoderms. Pubblicazioni della Stazione zoologica d i Napoli, 17, 53-57. Kobayashi, N. (1967). Spawning periodicity of sea urchins a t Seto. I. Mespilia globulus. Publications of the Set0 Marine Biological Laboratory, 14, 403-414, (Cited from Pearse, J. S., 1972.) Kobayashi, N. and Nakamura, K. (1967). Spawning periodicity oisea urchins a t Seto. 11. Diadema setosum. Publications of the Set0 Marine Biological Laboratory, 15, 173-184. (Cited from Pearse, J. S. 1972.) Kristensen, I. (1964). The effect of raising Diadema a t different levels of light intensity on pigmentation and preference for darkness. Caribbean Journal of Science, 4,441.

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Lawrence, J. M. and Hughes-Games, L. (1972). The diurnal rhythm of feeding and passage of food through the gut of Diadema setosum (Echinodermata: Echinoidea). Israel Journal of Zoology, 21, 13-16. Lewis, J. B. (1958). The biology of the tropical sea urchin Tripneustes esculentus Leske in Barbados, British West Indies. Canadian Journal of Zoology, 36, 607-21 Lindahl, P. E . and Runnstrom, J. (1929). Variation und Okologie von Psammechinus miliaris (Gmelin). Acta Zoologica Stockholm, 10, 401-484. MaoBride, E. VV. (1909). Echinodermata. I n ‘‘ Cambridge Natural History ”, vol. 1. Macmillan, London. Magnus, B. E. (1967). Ecological and ethological studies and experiments on the echinoderms of the Red Sea. Studies i n Tropical Oceanography, 5, 635-664. Milligan, H. N. (1915). Observations on the foreign objects carried by the purple sea-urchin. Zoologist, No. 894, 441-453. Millott, N. (1952). Colour change in the echinoid, Diadema antillarum Philippi. Nature, London, 170, 325-326. Millott, N. (1953a). Colour pattern and the definition of the species Diadema antillarum Philippi. Experientia, 9, 98. Millott. N. (1953b). Light emission and light perception in species of Diadema. Nature, London, 171, 973-973. Millott, N. (1954). Sensitivity to light and the reactions to changes in light intensity of the echinoid, Diadema antillarum Philippi. Philosophical Transactions of the Royal Society, B238, 187-220. Millott, N. (1956). The covering reaction of sea-urchins. I. A preliminary account of covering in the tropical echinoid Lytechinus wariegatus (Lamarck), and its relation to light. Journal of Experimental Biology, 33, 508-523. Millott, N. (19574. Naphthaquinone pigment in the tropical sea-urchin, Diadema antillarum Philippi. Proceedings of the Zoological Society of London, 129, 263-272. Millott, N. (195713). Animal photosensitivity, with special reference to eyeless forms. Endeavour, 16, 19-28. Millott, N. (1964). Pigmentary system of Diadema antillarum Philippi. Nature, London, 203, 206-207. Millott, N. (1966a). The enigmatic echinoids. I n “Light as an Ecological Factor ”. (Bainbridge, R., Evans, G. C. and Rackham, O., eds.) Symposium of the British. Ecological Society, No. 6, 265-291. Millott, N. (1966b). Co-ordination of spine movement in echinoids. I n “ Physiology of Echinodermata ”. (Boolootian, R. A., ed.) pp. 465-485. Interscience, New York. Millott, N. (1967). Dermal photosensitivity and the “ H e n and Egg ” problem. Nature, London, 215, 768-769. Millott, N. (1968). The dermal light sense. In. “ Invertebrate Photoreceptors pp. 1-36. (Carthy, J. D. and Newell, G. E., eds.) Symposia of the Zoological Society of London, No. 23. Academic Press, London. Millott, N. arid Coleman, H. (1969). The podia1 p i t a new structure in the echinoid Diadema antillarum Philippi. Zeitschrift f u r Zellforschung und mikroskopisch,e Anatomie, 95, 187-197. Millott, N. and Manly, B. M. (1961). The iridophores of the echinoid Diadema antillarum. Quarterly Journal of Microscopical Science, 102, 181-1 94.

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Millott, N. and Okumura, H. (1968a). Pigmentation in the radial nerve of Diadema antillarum. Nature, London, 217, 92-93. Millott, N. and Okumura, H. (1968b). The electrical activity of the radial nerve in Diadema antillarum Philippi and certain other echinoids. Journal of Experimental Biology, 48, 279-287. Millott, N. and Takahashi, K. (1063). The shadow reaction of Diadema antillarum Philippi. IV. Spine movements and their implications. Philosophical Transactions of the Royal Society, B246, 437-469. Millott, N. and Vevers, H. G. (1968). The morphology and histochemistry of the echinoid axial organ. Philosophical Transactions of the Royal Society, B253, 201-230. Millott, N. and Yoshida, M. (1956). Reactions to shading in the sea urchin, Psammechinus miliaris (Gmelin). Nature, London, 178, 1300. Millott, N. and Yoshida, M. (1957). The spectral sensitivity of the echinoid Diadema antillarum Philippi. Journal of Experimental Biology, 34(3), 394-401. Millott,, N. and Yoshida, M. (1959). The photosensitivity of the sea urchin Diadema antillarum Philippi : responses to increases in light intensity. Proceedings of the Zoological Society of London, 133(1), 67-71. Millott, N. and Yoshida, M. (1960a,). The shadow reaction of Diadema antillarum Philippi. I. The spine response and its relation to the stimulus. Journal of E.xperimenta1 Biology, 37(2),363-375. Millott, N. and Yoshida, M. (196Ob). The shadow reaction of Diadema antillarum Philippi. 11. Inhibition by light. Journal of Experimental Biology, 37, 376-389. Moore, H. B., Jutare, T., Jones, J. A., McPherson, B. F., and Roper, C. F. E. (1963). A contribution to the biology of Tripneustes esculentus. Bulletin of Marine Science, 13, 267. Mortensen, Th. (1927). " Handbook of the Echinoderms of the British Isles ". University Press, Oxford. Mortensen, Th. (1943). " A Monograph of the Echinoidea Vol. 111.2. Camarodonta I. Reitzel, Copenhagen. Mortensen, Th. (1948). " A Monograph of the Echinoidea ". Vol. IV, 2. Clypeastroida. Reitzel, Copenhagen. Orton, J. H. (1929). On the occurrence of Echinue esculentus o n the foreshore in the Brkish Isles. Journal of the Marine Biological Association of the United Kingdom, 16, 289-296. Parker, G. H. (1931). The color changes in the sea urchin Arbacia. Proceedings of the National Academy of Science, Wash,ington, 17, 594-596. Pearse, J. S. ( 1970). Reproductive periodicities of Indo-Pacific invertebrates in the Gulf of Suez. 111. The echinoid Diadema setosum (Leske). Bulletin of Marine Science, 20, 697-720. Pearse, J. S. (1972). A monthly reproductive rhythm in the diadematid sea urchin Centrostephanus coronatus Verrill. Journal of Experimental Marine Biology and Ecology, 8, 167-186. Pearse, J . S. and Arch, S. W. (1969). The aggregation behaviour of Diadema (Echinodermata, Echinoidea). Micronesia, 5, 159-165. Pentraeth, V. W. and Cobb, J. L. S. (1972). Neurobiology of Echinodermata. Biological Reviews, 47, 362-329.

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PBquignat, E. (1966). " Skin digestion " and epidermal absorption in irregular and regular urchins and their probable relation to the outflow of spherulecoelomocytes. Nature, London, 210, 397-399. Raup, D. M. (1959). Crystallography of echinoid calcite. Journal of Geology, 67, 661. Raup, D. M. (1960a). Ontogenetic variation in the crystallography of echinoid calcite. Journal of Paleontology, 34, 1041. Raup, D. M. (1960b). Calcite crystallography in sea urchins. Yearbook of the American Philosophical Society, 267. Raup, D. M. (1962a). The phylogeny of calcito crystallography in echinoids. Journal of Paleontology, 36, 793. Raup, D. M. (196213). Crystallographic data in echinoderm classification. Symposium on Data of Classijcation. Systematic Zoology, 11, 98. Serasin, C. F. and Sarasin, P. B. (1887). Augen und Integument der Diadematiden. Ergebnisse naturwissenschaften Forschung, Ceylon, 1, 1. Sharp, D. T. and Gray, I. E. (1962). Studies on factors affecting the local distribution of two sea urchins, Arbacia punctulata and Lytechinus variegatus. Ecology, 43(2),309-313. Steven, D. M. (1963). The dermal light sense. Biological Reviews, 38, 204-240. Takahashi, K.(1964). Electrical responses to light stimuli in the isolated radial nerve of the sea urchin, Diadema setosum (Leske). Nature, London, 201, 1343-1344. Tennant, D. H. (1910). Variations in echinoid plutei. Journal of Experimental Zoology, 9, 657-714. Thornton, I. W. B. (1956). Diurnal migrations of the echinoid Diadema setosum (Leske). British Journal of Animal Behaviour, 4, 143-146. von Uexkiill, J. (1897a). Der Schatten als Reiz fur Centrostephanus longispinus. Zeitsehrift f u r Biologie, 34, 315-339. von Uexkiill, J. (189713). Ueber Reflexe bei den Seeigeln. Zeitschriftjur Biologie, 34, 298-318. von Uexkiill, J. (1900a). Die Wirkung von Licht und Schatten auf die Seeigel. Zeitschrift f u r Biologie, 40, 447-476. von Uexkiill, J. (1900b). Die Physiologie des Seeigelstachels. Zeitschrift f i i r Biologie, 39, 73-112. Weber, W. and Dambach, M. (1972). Ameboid bewegliche Pigmentzellen in Epithel des Seeigels Centrosteph,anus longispinus. Zeitschrift f u r Zellforschung ,und mikroskopische Anatomie, 133, 87-102. Weber, W. and Dambach, M. (1974). Cell and Tissue Research, 148, 437-440. Yoshida, M. (1952). Some observations on the maturation of the sea urchin Diadema setosum. Annotationes Zoologicae Japonensis, 25, 265-271. Yoshida, M. (1956). On the light response of the chromatophore of the sea urchin Diadema setosum (Leske). Journal of Experimental Biology, 33, 119-123. Yoshida, M.(19574. Spectral sensitivity of chromatophores in Diadema setosum (Leske). Journal of Experimental Biology, 34, 222-225. Yoshida, M. (1957b). Positive phototaxis in Psammechinus microtubereulatus (Blainville). Pubblicazioni della Stazione zoologica d i Napoli, 30, 260-262. Yoshida, M.(1960). Further studies on the chromatophore response in Diadema setosum (Leske). Biological Journal of Okayama University, 6, 169-173. Yoshida, M. (1962). The effect of light on the shadow reaction of the sea urchin, Diadema setosum (Leske). Journal of Ezperirnentnl Biology, 39, 589-602.

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Yoshida, M. (1966). Photosensitivity. I n " Physiology of Echinodermata (Boolootian, R. A., ed.) pp. 435-464. Interscience, New York. Yoshida, M. and Millott, N. (1959). Light sensitive nerve in an echinoid. Experientia, 15, 13-14. Yoshida, M. and Millott, N. (1960). The shadow reaction of Diadema antillarum Philippi. 111. Re-examination of the spectral sensitivity. Joztrnal of Experimental Biology, 37(2), 390-397.

Adv. mnr. Biol.,

1701.

13, 1975, pp. 53-108

THE GUSTATORY SYSTEM IN FISH B. G. KAPOOR Department of Zoology, University of Jodhpur, Jodhpur, India H. E. EVANS Department of Anatomy, College of Veterinary Medicine, Cornell University, Ithaca, New York, U.S.A. AND

R. A. PEVZNER Laboratory of Evolutionary Morphology, Sechenov Institute of Evolutionary Physiology and Biochemistry, U.s'.S. R. Academy of Sciences, Leningrad, U.S.S.R. I. Introduction .. .. .. .. .. 11. Review of Literature . . .. .. .. 111. Structure .. .. .. .. .. A. Light Microscopy .. .. B. Electron Microscopy . . . . .. C. Nerve Supply .. .. .. .. D. Vascular Supply . . . . .. .. E. Histochemistry . . .. .. .. F. General Considerations . . . . .. IV. Origin, Development and Location of Taste Buds V. Innervation, Brain Morphology and Function A. Innervation .. .. .. .. B. Brain Morphology .. .. .. C. Function . . .. .. .. .. VI. Acknowledgements .. .. .. .. V I I . References .. .. .. .. ..

..

.. .. .. .. .. .. .. .. .. ..

.. ..

..

.. ..

..

..

.. ..

.. .. .. .. .. .. .. .. .. .. .. ..

.. .. .. .. ..

.. .. .. .. .. .. .. .. ,. .. ..

.. .. .. .. ..

..

.. .. ..

..

.. .. .. .. .. ..

53 54 56 56 57 70 70 71 71 75 82 82 85 89 92 92

I. INTRODUCTION Animals rely on different systems of sensory receptors which act as peripheral outposts to initiate most of the impulse traffic in the central nervous system. I n spite of their morphological or functional differences, these receptors share the ability of transducing physical or 53

54

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a. KAPOOR.

H. E. EVANS AND R .

A. PEVZNER

chemical events into nerve impulses. Such receptors can signal the existence as well as the intensity of a stimulus and thus enable orientation to a gradient. We are especially concerned here with the gustatory system in fish or that component of the communis system which serves the sense of taste in contrast to those communis neurones which serve less specialized visceral sensations. Taste is primarily a close-range sense and its function is the identification of nutrients and the avoidance of noxious substances. A few fish, namely catfish, are able t o use the sense of taste a t a distance and can orient by means of extended barbels to intensity gradients. Taste receptors in vertebrates monitor material taken into the mouth and verify its palatability. They respond to a wide range of concentrations of a large number of chemical substances in the outside milieu. This ability probably developed early in the course of animal evolution. Some substances no doubt elicit both olfactory and taste impulses which in an aquatic environment are difficult to separate. A wealth of information on the structure and distribution of taste buds in all classes of vertebrates has been accumulating. The anatomy of the taste receptors in fish has been studied more extensively than has the physiology of taste in fish. I n this paper we review both anatomical and physiological aspects of the gustatory system of fish.

11. REVIEWOF LITERATURE Herrick (1903) and Kolmer (1927) reviewed the early literature and pointed out that Weber, E. H. (1827) observed taste buds on the palatal organ of the carp, while Leydig (1851) discovered terminal buds in the skin of fishes. Schulze (1863) described a " becherfiirmigen Organe " in fishes and distinguished sensory cells from supporting cells. I n 1870 Schulze demonstrated that terminal buds differ structurally from neuromasts or organs of the lateral-line system. Neuromasts commonly lie below the surface of the skin in canals, tubes, or pits but in some cases they resemble the terminal buds in external form. This latter feature led Leydig (1851, 1879, 1894) to assume that terminal buds and lateral-line organs were the same. Schulze showed that the neuromasts in all cases can be distinguished from the terminal buds by the fact that their specific sensory cells (pear cells) extend only part way through the sensory epithelium and fail to reach the internal limiting membrane, while in terminal buds both specific sensory cells and supporting cells pass through external t o internal limiting membrane. Afanasjev (1875) described taste buds on the skin, lips, barbels and epithelium which lined the oral cavity in several species of fishes, the barbels appearing

55

THE GUSTATORY SYSTEM IN BISIF

to be extremely rich in taste buds. Two cell types could be distinguished -cylindrical and filiform. The latter made contact with entering nerve fibres. This observation led him to conclude that the filiform cells might have a gustatory function. Merkel(l880)gave an account of the structure and distribution of terminal buds in all classes of vertebrates and agreed with Jobert (1872) that the terminal buds of the outer skin were tactile in function. Merkel denied the gustatory function of terminal buds even within the mouth of non-mammalian vertebrates. These assumptions of Merkel and Jobert were proven erroneous by the experiments of Herrick (1903). Research on the chemical senses of fish was reviewed by Teichmann (1962), Bardach and Todd (1970), Bardach and Atema (1971), Hara (1971), and Bardach (1972). Studies on functional aspects were conducted by Strieck (1924), Bull (1928, 1936, 1952), Trudel (1929), Klenk (1930), Hoagland (1933), Sat6 (1938), Hiatt et al. (1953), Hasler (1957), Aronov (1959, 1961, 1962), Konishi and Zotterman (1961a, b, 1963), Tateda (1961, 1964, 1966), Konishi and Niwa (1964), Bardach and Case (1965), Yamashita (1965), Fujiya and Bardach (1966), Konishi (1966, 1967), Konishi et al. (1966), Maljukina (1966), Maljukina and Chauschesku (1966), Bardach (1967), Bardach et al. (1967), Hidaka and Yokota (1967), Konishi and Hidaka (1967, 1969), Maljukina and Schtefanesku (1967), Katsuki and Hashimoto (1969a, b), Katsuki et al. (1969), Konishi et al. (1969), Airapetjanz and Vasilevskaja (1970), Hidaka (1970a, b, c, 1972), Katsuki et al. (1970), Rizhkov (1970), Sutterlin and Sutterlin (1970), Atema (1971), Hara (1971), Hodgson and Mathewson (1971) and Katsuki et al. (1971). Various morphological and physiological studies have shown that the terminal buds of fish are homologous with the taste buds of higher vertebrates. However, taste buds in the region of the oral cavity, particularly on the barbels, were considered to be sensitive to some additional kind of stimulus other than chemical, and were thus called " Wechselsinnesorgan " by Kolmer (1927). Though considered to be homologous with the terminal buds of fish they have been found to exhibit some structural differences from the taste buds of higher vertebrates. Electron microscopic researches on taste buds of fish were initiated by Trujillo-Cen6z (1961), and were followed by the exhaustive accounts of Cordier (1964), Desgranges (1965, 1966, 1972), Hirata (1966), Uga and Hama (1967), Graziadei (1968, 1969), Welsch and Storch (1969), Storch and Welsch (1970), Reutter (1971), Schulte and Holl (1971) and Whitear (1971). (For the fine structure of the taste buds of mammals see Murray, R. G. (1971).) A.M.B.-13

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E. EVANS

AND R . A. PEVZNER

111. STRUCTURE A. Light microscopy The following account is based chiefly on the observations of Hirata (1966) on the taste buds in the barbels of three freshwater fishes

Cyprinus carpio Linnaeus, Parasilurus asotus Linnaeus, and Cobitis biwae Jordan and Snyder. The terminal buds were usually ovoid in shape and extended through the entire thickness of the epidermis. They measured 45 t o 75 p. in length and 30 to 50 p. in width (Fig. 1).

FIG. 1. Histological longitudinal section of an oral epithelium taste bud of Carassius carussius. H. and E. stain. TP-taste pore, RC-receptor cell, RC-supporting cell, BC-basal cell, NP-nerve plexus. (After Pevzner, R. A.) FIG.2. Histological longitudinal section of taste bud in the carp barbel. (a) Apical portion of a terminal bud, toluidine blue stain. TP-taste pore, EC-epithelial cell, TB-taste bud. Fine structure of the terminal buds on the barbels of some fishes. Archivum histologicurn japonicum, 26, 507-523. With permission of the editor. After Hirata, Y. (1966). (b) A terminal bud from the carp barbel. H. and E. stain. TP-taste pore, TB-taste bud. NP-nerve plexus. After Koshida, Y . , Osaka University, Osaka, Japan.

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The cells comprising a taste bud are cylindrical to spindle shaped, being thickest a t the nuclear region in the basal half of the bud. They taper towards the apex to end as h e , pale processes. The apex of the taste bud may either protrude or be retracted from the surface of the epidermis (Fig. 2a and b). Sometimes, two types of cells-light and dark-can be distinguished in the apical region of the taste bud. In the subapical region all components of the taste bud are pale in appearance. Occasionally, two kinds of nuclei can be distinguished: pale, light nuclei with a rather smooth contour and dark ones with an irregular, indented contour. A cell corresponding to the " basal cell " of the mammal (Hermann, 1884; Heidenhain, 1914), is found in the deepest part of the taste bud. It has a pale nucleus and rather scanty cytoplasm. This cell is situated a t the innermost border of the taste bud and its long axis is perpendicular to the long axis of the other cellular elements. Between this basal cell and the nuclear region of other cellular constituents, there are many fine nerve branches constituting an intragemmal nerve plexus entering the taste bud from the subgemrnal papilla. Apical processes by light microscopic observations have been described as sensory hairs, sensory rodlets, bristles, refractive processes, thread-like processes, sensory bars, cilia, hairlets, and taste hairs by Curry (1939), Sarbahi (1940), Al-Hussaini (1946), Moore (1950), Bhatti, I. H. (1952), Girgis (1952), Al-Hussaini and Kholy (1954), Mohsin (1962), von Lukowicz (P966), and Rajbanshi and Tewari (1968). Iwai (1964) found that these hairs were fragile and often torn off by histological fixatives and mechanical action, particularly in protruding taste buds.

B. Electron microscopy Cordier (1964), Hirata (1966), Uga and Hama (1967), Graziadei (1969), Welsch and Storch (1969), Storch and Welsch (1970), Reutter (1971), Schulte and Holl (1971) and Whitear (1971) distinguished receptor cells and supporting cells, in addition to the basal cells already identified in light microscopy (Figs 3 and 4). However, the function of the cell types and their manner of replacement is still in dispute. I n brief, the receptor cells of fishes have specialized apical projections, electron-dense tubular structures in the apical cytoplasm, and an intimate junctional relationship with the nerve elements. The supporting cells exhibit intracytoplasmic filaments and a well-developed Golgi apparatus but they lack specific junctions with neural elements. Occasionally, transitional or intermediate atypical cells are observed and considered to be either undifferentiated or degenerate elements.

T H E GUSTATORY SYSTEM I N FISH

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1. Receptor cells

These elements are also spoken of as sensory cells, gustatory cells or neuroepithelial cells. They are slender in form with a smooth apical contour and are usually provided with one or two characteristic apical processes. The apical process may be attached by a narrow stalk or may appear as a simple protrusion or prolongation of the cell. They may measure 1-5 to 3 p or more in length and 0.5 p in diameter a t the thickest portion. The process is generally electron-lucid and lacks mitochondria and vesicles (Figs 3 and 5a and b). The electron micrographs of the processes observed by Desgranges (1965), Hirata (1966), Graziadei (1969), Welsch and Storch (1969), Storch and Welsch (1970), Reutter (1971), Schulte and Holl (1971) and Whitear (1971) were significantly different from those of mammalian taste buds described by de Lorenzo (1963), Nemetschek-Gander and Ferner (1964) and others. Desgranges (1965) described five types of sensory cells on the basis of the form of apical processes. Hirata (1966) likewise observed different types of processes but believed that they represented different functional stages of the receptor cells. Graziadei (1969), Schulte and Holl (1971) observed a finger-like protrusion of a receptor cell which measured 1 500-2 000 A in diameter and 0.4p-1.5 p in length with the fine filaments while a supporting cell was provided only with microvilli. Storch and Welsch (1970) in various bony fishes and Reutter (1971) in catfish, Ameiurus nebulosus Le Sueur, described only microvilli on the apical part of a receptor cell. The microvilli measured up to 1.5 mp in length and contained filaments running toward the cytoplasm. SEM studies on barbel taste buds of A . nebulosus have demonstrated some taller and longer processes among numerous microvilli in the sensory area (Breipohl et al., 1974). The processes are considered to belong to receptor cells (Fig. 6a and b). Whitear (1971) studied the taste buds of Phoxinus phoxinus Linnaeus, Gasterosteus aculeatus Linnaeus, Trigla lucerna and Pomato schistus (=GoSius) minutus Pallas. She concluded that there were some differences in the patterns of the apical processes and the apical parts of the receptor cells in each species.

-

FIG.3. General view of a longitudinal section of the barbel taste bud of Corydoros paleatus. MV-microvilli, P-receptor cell process, PC-perigemmal cell, Ax-axon. x 4 200. After Schulte, E. and Holt, A (1971). “ Untersuchungen an den Geschmacksknospen der Barteln von Corydoras puleatus Jenyns. I. Feinstruktur der Geschmacksknospen.” Zeitschrift fiir Zellforschung und Mikroskopische Anatomie, 120,450-462. With the permission of Springer-Verlag, Berliii-Heidelberg-New York.

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B. G. KAPOOR, H. E. EVANS AND R. A. PEVZNER

Just below the characteristic apical processes of the cell, many vesicles of 50 to 100 A in diameter were observed in the peripheral cytoplasm (Fig. 5a). Towards the lower region, in the subapical and supranuclear regions of the receptor cell vesicles were seen that appeared

Fro. 4. General view of a transverse section of the barbel taste bud of Corydoruspaleatus. RC-receptor cell, SC-supporting cell, DC-degenerating cell, PC-perigemmal cell. After Schulte, E. and Holl, A. (1971). Untersuchungen an den Geschmacksknospen Bartein von Corydoras paleatus Jenyns. I. Feinstruktur der Geschmacksknospen. Zeitschrift fiir Zellforschung und mikroskopische Anatomie, 120, 466-462. With the permission of Springer-Verlag, Berlin-Heidelberg-New York.

to fuse and form tubular structures which were the most prominent and abundant intracytoplasmic organelles. These tubules, 40 t o 55 A in diameter, were electron dense, usually straight, sometimes tortuous or spiral in form, and were aligned with the long axis of the receptor cell. Hirata (1966) was the first t o find such structures and he

D

FIG. 5. Apical portions of supporting and gustatory cells. (a) Phorinus phoxin,us. sp-sensory process, go-receptor cell of taste bud, d-desmosome, mv-microvillus, cut-cuticle, v-vesicle. After Whitear, M . (1971). Cell specialization and sensory function in fish epidermis. Journ,ul of Zoology, London, 163, 237-267. With the permission of the Zoological Society of London. (b) Trygon pnstinoca. spAfter Pevzner, sensory process, go-gustatory cell, mv-microvillus, v-vesicle. R. A.

FIG.6. SEM micrographs of the barbel taste buds in Ameiurus nebulosus. Note tall and smallmicrovilli. (a) x 4 600, (b) x 10 000. After Breipohl, W. et al. (1974). Scanning electron microscopy of various sensory receptor cells in different vertebrates. I n '' Proceedings of the Workshop on Advances in Biomedical Applications of the SEM." (0. Johari and J. Gorvin, eds.) 'pp. 557-664. I.T.T. Research Institute, Chicago, Ill.

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considered them to be of particular functional significance in the chemoreceptive activity of the sensory cell. Schulte and Holl (1971) distinguished two types of tubular systems-the first dense and 500 in diameter and the second with light contents and 200 d in diameter.

FIG.7. Schematic representation of taste bud of Amiurus nebulosus. LC-light cell, DC-dark cell, B-basal cell, BM-basal membrane, N-nerve ending, V-blood vessel. After Reuter, K. (1971). Die Geschmacksknospen des Zwergwelses Amiurus nebulosis (Le Sueur). Morphologische und histochemische Untersuchungen. Zeitschrift fur Zellforsehung und mikroskopische Anatomie, 120, 280-308. With the permission of Springer-Verlag, Berlin-Heidelberg-New York.,

I n the supranuclear cytoplasm, the smooth-surfaced endoplasmic reticulum has numerous tubules 2OOd in diameter and elongated mitochondria parallel with the long axis of the receptor cell. The Golgi apparatus, rough-surfaced endoplasmic reticulum, dilated smoothsurfaced endoplasmic reticulum and crowded free ribosomes were

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located in the juxta-nuclear region, particularly where dense tubules were scarce. The ovoid nucleus exhibited shallow and deep indentations (Figs 3 and 4). Abundant vesicles of various sizes (300 to 1 000 a) were found in the infranuclear cytoplasm of the receptor cells. Many of these

FIG.8. The basal half of a terminal bud on the raised papilla of the dermis. Carp barbel. B-basal cell, C-connective tissue cell, pl-intragemmal plexus, n-unmyelinated nerve. x 5 000. After Hirata, Y . (1966). Fine structure of the terminal buds on the barbels of some fishes. Archivum histologicurn japonicum, 26, 507-523.

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vesicles were seen concentrated at particular sites of the plasma membrane to which nerve fibres or terminals were in apposition. Reutter (1971) distinguished two kinds of synaptic vesicles a t the presynaptic membrane according to their diameters-vesicles with 300 a and 700 d in diameter (Fig. 7). The plasma membranes, a t some contact areas, showed a degree of increased electron density, or membrane thickening. In some bony fishes (Clarias batrachus Linnaeus and Kryptopterus bicirrhis (Cuvier and Valenciennes)) synapses have characteristic membrane thickenings on both sides (Storch and Welsch, 1970). TrujilloCen6z (1961) did not observe any specialization of the plasma membranes, but did find an assemblage of mitochondria and vesicular structures where the receptor cell contacted the nerve element. Graziadei (1968) demonstrated two types of synapses-one with vesicles clumped near the taste cell membrane and the other with the vesicles clumped near the nerve membrane. These synapses seemed to have double polarity which suggests afferent and efferent contacts in the fish taste buds. There are two kinds of nerve endings which make contact with a receptor cell : one kind of ending contains densely crowded mitochondria, a few vesicles as well as glycogen; the other one contains numerous clear vesicles (Desgranges, 1966 ; Storch and Welsch, 1970) (Fig. 8). Whitear (1971) also observed synaptic thickenings and small internal projections on the nerve membrane just a t the place of contact between the receptor cell and the nerve ending. However, she did not see an aggregation of the vesicles near the synaptic membrane and doubted whether these vesicles were synaptic. Welsch and Storch (1969), Storch and Welsch (1970) and Reutter (1971) considered both " dark " and " light " cells as receptor cells according to the synaptic contacts with the nerve endings. Reutter (1971) described the synaptic contacts between the basal processes of " dark " cells and basal cells (Fig. 7). 2. Supporting cells

The supporting cells, sustentacular cells, or nutritive cells of Pictet (1909) are slender, or fusiform in shape with a smooth apical contour. The basal portions of the supporting cells are branched and interdigitate with the receptor cells, nerve fibres, and basal cells in the depth of the taste bud (Fig. 8). This characteristic configuration of the basal portion of the supporting cells was observed by light microscopy on isolated cells by Schulze (1863) and on silver impregnated materials by Dogie1 (1897).

The supporting cells, on their free apical surface are provided with few but constant microvilli 100-200 d in diameter and 0.5-1 p in

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length (Fig. 5a and b). Intracytoplasmic structures in the form of numerous fine filaments of about 50 A in diameter appear either evenly distributed or in bundles (Fig. 9). These filaments correspond to “ Stiitzfibrillen ” observed in light microscopy by Kolmer (1927). Leydig (1851) noted the similarity of these fibril containing cells to smooth muscle cells (“ muskuliise Faserzelle ”) and ascribed contractility of the taste buds to these fibrous cells. Hirata (1966) believed that the filaments in supporting cells served as the skeleton of taste buds.

FIG.9. Transverse section of the taste bud of Trygon pastinaca. RC-receptor cell, SC-supporting cell, FB-fibrillar bundle, D-desrnosome. After Pevzner, R. A.

Most of the filaments in the peripheral portion of the supporting cells run perpendicular to the axis of the cells ; and they occasionally connect areas of desmosomal junctions between supporting cells, or between supporting and receptor cells or perigemmal cells (Fig. 9). At a little distance above the desmosomal junctions, areas of tight junctions are generally seen. Near the free surface of some supporting cells, vacuoles of various dimensions and configurations are found which Desgranges (1965) considered as characteristic structures of this region. Hirata (1966) found a well developed Golgi-apparatus in the supraiiuclear cytoplasm. I t s elements were disposed parallel with the plasma

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membrane. Mitochondria, small and large vacuoles, smooth and rough surfaced endoplasmic reticulum and free ribosomes were also observed (Fig. 9). The infranuclear portion of the supporting cell appeared as branched foot processes most of which did not reach the basement membrane underlying the bud. The boundaries between supporting cells and between a supporting cell and a receptor cell were rather smooth. Junctional structures such as desmosomes and intercellular digitations were rarely encountered except for an area just below the free surface of the supporting cell. Supporting elements surrounded or enveloped the receptor cells excepting the luminal surface and areas of nerve apposition. Hirata (1966) believed that supporting cells correspond to the type I cells described in the taste bud of the rat by Farbman (1965). The possible functions of the supporting cells are : (1) to mechanically maintain structural unity ; (2) t o insulate the receptor cells ; and (3) to function as a Schwann cell for intraepithelial nerve fibres. 3. Basal cells The basal cell lies directly on the basement membrane and forms the deepest boundary of the taste bud in conjunction with foot processes of supporting cells which reach the basement membrane. Nerve bundles also enter from below into the taste bud. The basal cell is disc-shaped with a rather smooth contour and a central thickening (Figs 7, 8 and 10). The oval or ellipsoid nucleus, situated approximately in the centre of the cell has shallow indentations. The cytoplasm is rich in mitochondria, vesicles and glycogen granules (Desgranges, 1972). The mitochondria are smaller than those of the receptor and supporting cells, but larger than those in the intragemmal nerve elements; the vesicles range from small (300-600 a) to large (600-900 a). Smaller vesicles may be found aggregated in the region of contact of the plasma membrane with nerve elements. Larger vesicles often contain dense cores 300-500 a in diameter. The basal cell cytoplasm near the region of contact with nerve elements is more electron dense than the surrounding areas. Desmosomal systems are occasionally seen at the site of contact with the foot processes of the supporting cell. Other intracytoplasmic organelles include multivesicular bodies, smooth and rough surfaced endoplasmic reticulum, free ribosomes, and fine filamentous structures. The basal cell appears t o be polarized. Its supranuclear area is rich in numerous dictiosomes and mitochondria while the infranuclear area contains a few elements of a granular endoplasmic reticulum (Desgranges, 1972).

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Hermann (1884) first described a basal cell in the taste buds of some mammals. Conflicting opinions were subsequently expressed about basal cells. Griiberg (1899), and Heidenhain (1914) confirmed their occurrence; von Lenhoss6k (1893) and Retzius (1912) considered them to be obliquely sectioned receptor or supporting cells; and von Ebner (1912) considered them to be subepithelial connective tissue cells. Farbman (1965) in the rat and Pevzner (1970) in the frog considered basal cells to be an intermediate stage in the course of differentiation

FIQ.10. Basal cell of the taste bud of Trygonpaslinaca. BC-basal cell, SC-supporting cell, BM-basal membrane, NE-nerve ending, CT-connective timue. x 10 000. After Pevzner, R. A.

of the peripheral cells into the typical spindle-shaped cells of the taste bud. Fahrmann et al. (1965) and Pevzner (1970) showed electron microscopically that the basal cells in the amphibian taste bud differ considerably in size, shape and cytoplasmic contents from the other cell types. I n fishes, Bhatti (1952) reported 15 to 25 basal cells in the taste bud of Rita rita (Hamilton); Iwai (1964) observed basal cells in the taste buds on the gill rakers of several freshwater and marine fishes ; Cordier (1964) found basal cells in the taste buds of Corydoras hastatus (Eigenmann and Eigenmann) and Macronus; and Uga and Hama (1967)

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described the basal cells in the taste buds of carp (Cyprinus) and demonstrated the specific contacts between the basal cells and the nerve fibres. Reutter (1971) in Anaeiurus nebulosus and Desgranges (1972) in Ictalurus melas (Rafinesque) showed similar arrangements (Fig. 11).

FIG. 11. Basal part of taste bud basal cell of carp barbel. Arrows show the synaptic contact areas. BC-basal cell. After Uga, S. and Hama, K. (1967). Electron microscopic studies on the synaptic region of the taste organ of carps and frogs. Journal of Electron Microscopy, 16, 269-277. With permission of the Japanese Society of' Electron Microscopy, Tokyo.

Hirata (1966) speculated that the basal cell might represent a particular type of receptor cell, or " accessory receptor cell ", which could be activated by a stimulus different in nature from those stimulating the ordinary chief receptor cells. He assumed that the taste bud is a multi-sensory organ (" Wechselsinnesorgan "), as suggested by earlier researchers. Rajbanshi and Tewari (1968), without mentioning Hirata's

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paper, referred to the peculiar basal cells in the taste buds of the maxillary barbels of Saccobranchus fossilis (Bloch). Reutter (1971) believed that there might be an additional way of transmission of excitation from receptor cell $0 CNS khrough basal cells by adrenergic means. Desgranges (1972) considered that the basal cell might be responsible for peripheral control of taste receptor activity by exerting a trophic influence on receptor cells. C. Nerve supply Myelinated and unmyelinated components of the facial nerve (7th cranial) enter the dermal papillae underlying taste buds. Cordier (1964), Hirata (1966), Uga and Hama (1967), and Graziadei (1969) observed nerve elements exclusively in the basal region. There were never any nerves seen in the nuclear or apical regions as were previously reported by light microscopy in silver impregnated materials. Unmyelinated nerves ranging in size from 0.3 to 1.0 p in diameter were seen by Hirata (1966) to enter the dermal papilla accompanied by Schwann, cells. The nerves formed an intricate intragemnial plexus, some making contact with receptor cells and others with basal cells (accessory receptor cells?). The nerve fibres within and immediately below the taste bud possessed neurofilaments, small mitochondria, multivesicular bodies, and cored or non-cored vesicles of different sizes (Fig. 8). These vesicles were not restricted to any particular part of the axolemma. I n mammalian taste buds, the regions of contact between neural elements and receptor cells generally do not show the specializations which are found in the taste buds of fish, i.e. the membraneous thickening and aggregation of vesicles in the receptor cells. Gray and Watkins (1965) observed, in the taste buds of the rat, rows of dense projections spaced along the presynaptic membrane. Such a type of membrane specialization was not observed by Hirata (1966) in the taste buds in fish but Whitear (1971) could see both synaptic thickenings and small internal projections on the nerve membrane a t the point of the synaptic contacts.

D. Vascular supply Jakubowski (1958, 1959, 1960a, b, 1966) described the vascularization of the skin of a number of fishes and made mention of blood vessels supplying taste buds. He and Reutter (1971) found that looplike vessels branched from a subepithelial net and extended into the epidermis together with the basal membrane. They were always

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associated with the taste buds. The greatest number of these loop-like vessels were found in the skin of the head, the region which bears the greatest number of’kaste buds. Hirata (1966) also observed capillary loops in the subgemmal papilla of the dermis below the taste bud.

E. Histochemistry Pevzner (1962, 1964a, b, 1966, 1969), Rajbanshi and Tewari (1969)) Tewari and Rajbanshi (1969, 1971) and Reutter (1971, 1973) have investigated histochemical aspects of the various cells composing the taste buds. The taste buds showed high activity of succinic dehydrogenase, alkaline phosphatase, ATP-ase, 5-nucleotidase, non-specific esterases, monoamineoxidase and low activity of acid phosphatase. The high activity of alkaline phosphatase was demonstrated at the peripheral part of the taste buds where the supporting cells were localized. Receptor cells were richer in these substances than were supporting cells. Both receptor cells and supporting cells were found to be rich in nucleic acids (RNA, DNA) (Fig. 12a), proteins (Fig. l2b) and protein functional groups (SH-SS-COOH). They were very poor in glycogen. The nuclear portion of receptor as well as supporting cells have high activity of alkaline and acid phosphatases. The apical and basal parts of the cells were richest in proteins and enzymes. However, Tewari and Rajbanshi (1971) failed to demonstrate the ATP-ase, 5-nucleotidase but reported a moderate non-specific esterases activity in the apical parts of the receptor cells. Acetylcholinesterase and glycogen were localized in the basal part of the receptor cells (Fig. 12e). RNA was localized near the nucleus and formed a cone directed towards the apical part. Mucopolysaccharides, enzymes and proteins were present in the taste pore. The basal cells showed high activity of monoamine oxidase (Fig. 12c) and positive reaction on serotonin (Fig. 12d). The nuclear part of the basal cell is devoid of phosphatases (alkaline and acid) whereas the cytoplasm showed high activity of the enzymes (Reutter, 1971). F . General considerations The size and shape of the taste buds are closely related to the thickness of the epithelial layer. They are more elongate in older fishes having a thicker skin. When folds or papillae are present the taste buds are usually situated along the crest or a t the apex of the papilla. They may occur singly, in pairs, or as compound clusters sharing a gustatory pore. Taste buds may be bulbiform or elongate and are similar in both freshwater and marine fishes. I n the oro-pharyngeal cavity of elasmobranchs, placoid scales and taste buds are found on all surfaces of the mucous membrane.

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lwai (1964) has described structures on the gill arches and rakers of Trachurus japonicus (Temminck and Schlegel), Hippocampus coronatus (Temminck and Schlegel), and Lophiomus setigerus (Vahl), which though bulbiform in shape, are composed of irregularly arranged cells showing no clear differentiation between sensory and supporting cells. These bulbiform cells may or may not be gustatory in function. Whitear (1952, 1965) reported spindle-shaped or flask-shaped cells in the skin of minnows which were assumed t o be chemosensory. I n their fine structure as well as in their general appearance they resembled the sensory cells of the taste buds. Swarup (1959) reported that a rich nerve supply in the submucosa of the buccal cavity, pharynx, and oesophagus is responsible for carrying gustatory sensations t o the brain in Hilsa ilisha (Hamilton), a fish which is said to be devoid of taste buds. Glaser (1966) found secondary chemoreceptive cells that were capable of the same performance as the primary ones. He ascertained thresholds of taste in Phoxinus, Gasterosteus and Hemigrammus caudovittatus Ahl. There did not seem to be any connection between the structural formula of the taste substance and the capacity of the fish to detect it. Kulshreshtha (1967) reported a new type of sense organ from the buccal cavity and tongue of Notopterus notopterus (Pallas). It consisted of a spherical cell mass with a lumen, situated near the basal epithelial layer and containcd many neuroepithelial cells with whip-like extensions and nerve fibre connections. There were also sustentacular cells without protoplasmic extensions or nerve connections. No mention was made of which nerves supply the organ or what its function might be.

FIG.12. (a)Light microscopy photograph stained for nucleic acids according to Einarson. Taste bud of lip of C . carassius. EC-pithelial cell, TB-taste bud, CT-connective tissue. After Pevzner, R. A. (b) Light microscopy photograph stained for proteins according to Danielli. Taste buds of carp barbel. TB-taste bud, BC-barbel core. After Pevzner, R. A. (c) Light microscopy photograph stained for monoamine oxidase according to Glenner, Burtner and Brown. Taste bud of Amiurua nebulosus. TB-taste bud, BG-basal cell. (d) Fluorescent microscopy photograph stained for serotonin according to Carlsson, Falck and Hillarp. The basal cell of the taste bud of Arniurus nebulosus. (0) and (d) After Reutter, K. (1971). Die Geschmacksknospen des Zwergwelses Amiurus nebulosus (Le Sueur). Morphologische und histochemische Untersuchungen. Zeitachrift f u r Zellforschung und mikroskopische Anatomie, 120, 280-308. With the permission of Springer-Verlag, Berlin-Heidelberg-New York. ( e ) Light microscopy photograph stained for acetylcholinesterase activity according to Koelle and Friedenwald. Barbel taste buds of C y p i n u s carpio. TB-taste bud, NP-nerve plexus, BC-barbel core. After Pevzner, R. A.

FIG.13. Taste buds of different type from the head gut of Xiphophorus helleri. Heckel (a) Taste bud from the tongue, lying within an elevated papilla of the epidermis; x 4 200. (b) and (c) Taste buds within the epithelium of the teeth bearing metabranchial apparatus. Only t5e pores of the non-elevated taste buds are seen (arrows). (b) x 425, (c) x 3 700. After Reutter et al. (1974). Tast,e bud types in fishes. 11. Scanning electron microscopical investigation on Xiphophorus hclleri Heckel (Pocciliidae, Cyprinodontiformes Teleostei), Cell and Tissus Rcsearch, 153 (S), 151-166.

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Reutter (1973) has described three types of the taste buds within the epithelium of the head gut in sword-tails, Xiphophorus helleri Heckel (Fig. 13). Type I taste buds rise distinctly above the epithelium and are distributed in the mouth region, especially on the breathing valves. Type I1 taste buds rise only a little above the epithelium and are found within the oral cavity, the palate and pharynx. Type I11 taste buds are not elevated and lie within metabranchial foregut. Reutter concluded that type I taste buds may also have a mechanoreceptor function whereas type I1 and I11 taste buds mainly act as chemoreceptors.

.IV. ORIGIN, DEVELOPMENT AND LOCATION OF TASTEBUDS Landacre (1907) studied the sites of first appearance and the rate and manner of distribution of the taste buds in a developmental series of the catfish Ameiurus melas. He noted that taste buds appeared simultaneously in the extreme anterior portion of the oral cavity (ectodermal field) and on the first three gill arches (endodermal field). The buds spread caudally from these places of origin by discontinuous groups. Those of the anterior oral cavity spread to the pharynx, and also over the lips and outer surface of the body. The first buds to appear on the outer surface of the body were continuous with those just inside the lips but subsequent cutaneous buds appeared in discontinuous groups in antero-posterior sequence. No taste buds from the pharyngeal group spread to the outer surface of the head. Considerable attention has been directed in the past to the germ layer origin of the taste buds in fishes. The ectodermal genesis of taste buds on the body surface is generally accepted but there has been disagreement over the origin of the taste buds of the mouth and pharynx. Some authors (Jacobshagen, 1911 and Fahrenholz, 1915) have postulated ectodermal invaginations into the pharyngeal cavity which give rise to taste buds while others (Cook and Neal, 1921) denied such inward migrations of ectodermal elements. Johnston (1905, 1910) suggested a reverse migration of endodermal buds over the lips into the ectodermal territory. Edwards (1930) observed developing taste buds in the oro-pharyngeal cavity of larval carp 22 hours after hatching. By 26 hours after hatching the taste buds in the pharyngeal cavity were not only numerous but appeared to be more highly developed than those in the oral cavity. He concluded that the taste buds in the oro-pharyngeal cavity of the carp are endodermal in origin. It thus appears that the taste buds of the oro-pharyngeal cavity are of both endodermal and ectodermal origin. Further considerations of

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these oro-pharyngeal taste buds are available in the papers by AlHussaini (1946))Ishida and Sat6 (1960) and Iwai (1963, 1964). I n elasmobranchs taste buds are lacking in the skin but are present in the mucosal lining of the mouth and pharynx. Cook and Neal (1921) found that taste buds in Squalus acanthias Linnaeus are more numerous and more uniformly distributed on the roof than on the floor of the oral cavity. The taste buds are situated upon small papillae which project slightly above the surrounding multi-layered epithelium. The slender sensory cells form barrel or flask-shaped clusters and terminate in hair-like projections. Daniel (1922) observed that taste buds in the mouth of Heterodontus were often surrounded by a more or less circular group of stomodial denticles. Boeke (1934) stated that papillae in the oral cavity of sharks are most numerous on the mucosal folds just behind the teeth. Additional papillae are distributed uniformly on the tongue, palate, and pharynx. I n teleosts taste buds are commonly found on the fins and body as well as within the oral cavity and pharynx. The number of taste buds may vary greatly from one part of the body t o another but the greatest number are found in regions most closely associated with food contact. Breder and Rasquin (1943) studied Mexican characins and found a notable increase in the number of taste buds on the head and body from the normal-eyed river fish to the blind fish of La Cueva Chica and a further increase in the blind fish of Cueva de 10s Sabinos. I n this series hhe taste mechanism was enhanced while the other senses were reduced. Complete serial sections were made of the three forms and the distribution of taste buds was illustrated. The morphology of the taste buds was different for each region: within the mouth they were raised on little papillae ; those in the thick epidermis of the head were level with the surface ; and those on the body in the thin epidermis were broadened and flattened in a manner suggestive of neuromasts. Taste buds have been recorded from many structures that serve more than one function and occasionally they are found in unlikely places such as the conjunctiva of a minnow, Bxlrarius aestivalis tetranemus (Girard) (Moore, 1950). One would expect and does find taste buds located in adhesive organs, barbels, free fin rays, lips, oral valves, tongue, palatal organs, pharyngeal cushions, epibranchial organs, branchial apparatus, and oesophagus (Figs 12a, e ; 14a, b and 15).

Distribution of the taste buds in the sucker Mozostomu uriornmum. (a) neotion of two papillae on the lower lip. (b) Section of the palat,e. H. and E. stain. X440. After Miller, R. J. and Evans, H. E. (1965).

F I G . 14.

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FIG.15. Distribution of the lip taste buds in the Pyramid lake sucker Chasrnistes cujus. Mallory stain, x 80. After Tibbitts, F. D., University of Nevada, Reno, Nevada.

I n the rostra1 hood of the adhesive organs of Glyptothorax telchitta (Hamilton), Bhatia (1950) described two types of receptors on the basis of shape and staining reaction. She distinguished a flask-shaped tangoreceptor from a spherical chemo-receptor. Saxena (1959) and Saxena and Chandy (1966) also described the adhesive organs in Garra mullya (Sykes) and some other Indian torrential water fishes. Branson (1966) reported on a structure in the sturgeon chub, Hybopsis gelida (Girard), which resembled the adhesive apparatus seen by Saxena, and Saxena and Chandy. It consisted of ventral rugosities caudal to the mouth opening which bore an exceedingly large number of simple and compound taste buds. Branson suggested that this rugose region increased tactile and chemosensory ability in this Great Plains minnow which is adapted for life in seasonally torrential turbid streams where the eyes are almost useless. I n addition to the taste buds some very large, clear cells were seen in the epithelium which may be neurosecretory in nature. Although the barbels of fishes are almost always provided with taste buds, those of the sturgeon, Acipenser ruthenus Linnaeus, have few (Baecker, 1926) and those of Pristiophorous japonicus Gunther have none (Sat6, 1937d). Taste buds are generally more numerous on the distal parts of the barbel. On the barbels of the loach, Misgurnus fossilis Linnaeus, there are 41 to 109 such organs per square millimetre (Jakubowski, 1960b). Herrick (1901) found many taste buds on the barbels of the catfish, Ameiurus, and investigated their gustatory function. Alexander (1965, 1966) and von Lukowicz (1966) have also dencribed the functions of barbels in fish.

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The occurrence of taste buds on fins has been reported by Miyadi (1929) in the loach Misgurnus anguillicaudatus (Cantor); Moore (1950) in several cyprinids ; Weber H . (1963) in anabantid genera : Trichogaster and Colisa; and by Jakubowski and Oliva (1967) in the stone loach

Noemacheilus barbatulus (Linnaeus). Taste buds on free pelvic fin rays were found by Herrick (1907a) in the tom-cod and hake ; on free ventral fin rays in Trichogaster trichopterus Pallas by Scharrer et al. (1947) ; and in the upper caudal filament of Sisor rabdophorus Hamilton by Mahajan (1967). I n several fishes with free fin rays such as gurnards Trigla, and searobins Prionotus, the finger-like free rays of the pectoral fins act as chemo- and tactile-receptors but do not bear recognizable taste buds (Scharrer, 1935 ; SatB, 1942 ; Bardach and Case, 1965). The lips are usually well supplied with taste buds particularly in those fishes with lobate, plicate, papillose or expanded lips (Figs 12a, 14a and 15). I n the suckers, Catostomidae, there may be 41 to 57 taste buds per 1.3 mm2 field (Miller and Evans, 1965). I n Labeo horie (Cuvier) (Girgis, 1952) there were more taste buds in the outer lobes of the lips than in the central region. Many freshwater and marine fishes are equipped with oral valves behind the lips (Mitchell, 1904 ; Gudger, 1946), whose surfaces are provided with taste buds (Kapoor, 1957a). Frequently a " tongue " is present as a ventro-rostra1 extension of the branchial skeleton and its epithelium usually has taste buds. Observations on the structure and function of the " lamellar organ " of the palate in the roof of the buccal cavity are a t variance. Girgis (1952) considered that the lamellar organ increases the sensory surface of buccal mucosa as its epithelium and subepithelium are provided with nerve endings similar to those of adjacent mucosa. This organ in Cirrhina mrigala (Hamilton) (comb-plate region, Majumdar, 1952) and Labeo dero (Hamilton) (Majumdar and Saxena, 1961 ; La1 et al., 1964) possesses few taste buds. The palatal organ found in various cyprinids, catostomids, cobitids and salmonids is well suppliedwith taste buds (Weber, E . H., 1827 ;Wunder, 1927, 1936; Miyadi, 1929 ; Curry, 1939 ; Dorier and Bellon, 1952 ; Evans, H. E., 1952; Girgis, 1952; Majumdar, 1952; Ducros, 1954; Majumdar and Saxena, 1961; Weisel, 1962; Iwai, 1964; Khanna and Pant, 1964; La1 et aZ., 1964; Miller and Evans, 1965, and Sutterlin and Sutterlin, 1970). Whitear (1971) described scattered chemoreceptor cells as well as taste buds in the palatal epithelium. The cytoplasmic structure of these cells was similar to that of the gustatory cells. Striated muscle fibres in the submucosa of the palatal organ suggests a possible manipulative

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or deglutitional function. It may also serve to reinforce the action of the branchial arches (Dorier and Bellon, 1952) and as an adaptation for sorting nutrients from detritus (Evans, H. E., 1952). It has been shown that the chemoreceptors of the palate of Cyprinus, the carp, are sensitive to various organic compounds (Konishi and Hidaka, 1969), t o carbon dioxide (Konishi et al., 1969), to ionized as well as uncharged molecules (Sutterlin and Sutterlin, 1970), and to salts and acids (Hidaka, 1972). As chain length increases in the aliphatic series the compounds become increasingly stimulatory. Hidaka and Yokota (1967) have suggested that there might be a t least two types of sugar receptors ; one for all sweet substances and the other for glycine alone. External chemoreceptors located on the snout of Atlantic salmon parr are sensitive to chloride salts and mineral or organic acids but insensitive t o uncharged molecules (Sutterlin and Sutterlin, 1970). Bertmar et nl. (1969) discussed the location and function of taste buds in certain epibranchial organs-accessory digestive structuresin lower teleostean fishes. I n Mugil cephalus Linnaeus many taste buds are found between the pharyngeal teeth on the caudal part of the pharyngeal cushion (Kawamoto and Higashi, 1965). Gill rakers show marked structural correlation with the feeding mechanism of fishes (Iwai, 1964 ; Kapoor 1965a). Generally, taste buds are widely and densely distributed over the gill rakers and gill arches of freshwater fishes. They are more numerous on each end and on the anterior surface of slender gill rakers whereas they cover the whole surface of short nodular rakers. Twin taste buds, bound side-by-side and sharing the same nerve bundle and papilla are found on the gill arches of Gnathopogon biwae Jordan and Snyder. Except for the sea catfish, Plotosus anguillaris (Lackpkde), taste buds are relatively sparse on the gill rakers and gill arches of marine fishes, as compared with those of freshwater fishes. There is no significant correlation between the number of gill rakers and the development of taste buds (Iwai, 1963, 1964). For additional specific information on the location of taste buds in fish, the reader may refer t o : Sat8 (1937a), Bhatti, H. K. (1938), AlHussaini (1949), Islam (1951), Kapoor (1953, 1957a, b, c, 1958, 1965b, 1966), Raffin-Peyloz (1955), Sat6 and Kapoor (1957), Al-Hussaini and Lutfy (1958), Bodrova (1958, 1960, 1962, 1965), Sarkar (1959), Disler (1960), Chaudhry and Khandelwal (1961), Bath (1962), de Kock (1963), Bodrova and Krajuchin (1965), Marshall (1965), Bishop and Odense (1966), Singh (1966), Davis and Miller (1967), Liem (1967), Kapoor and Bhargava (1967), Singh and Kapoor (1967a, b, 1968), Tandon and

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Goswami (1968), Weisel (1968), Campos (1969), Schmitz and Baker (1969), Western (1969), Khanna and Mehrotra (1970), Parzefall (1970), and Moitra and Sinha (1971). Bardach et al. (1969) counted cutaneous taste buds on three brown bullheads and averaged the number of taste buds seen per square centimetre (Fig. 16). They found that the barbels had the highest density, averaging 1 675/cm2 with the maximum concentration a t the tips where up to 3 400/cm2 were counted. The next highest concentration was on the tail 225/cm2, followed by the back 165/cm2,and flanks 120/cm2. Atema (1971) summarized and illustrated the distribution of taste buds in the yellow bullhead. The counts were based on five adults,

FIG.16. Average number of taste buds per square centimetre of various regions of tha body in the brown bullhead, Ictnlurus nebulosus. After Bardach, J. E., Johnson, G. H. and Todd, J. H. (1969). Orientation by bulk messenger sensors in aquatic vertebrates. Annals of the New Yo& Academy of Science, 163, 227-235. With the permisrion of the New Yorli Academy of Science.

25 cm in length. He found five taste buds per square millimetre over the body with a slightly higher count over the dorsum. Ahead of the dorsal fin, the concentration increases to 7/mm2, on the nasal area and lips 10/mm2 and on the barbels to densities of 10 to more than 25/mm2. It was estimated that the total number of taste buds on the eight barbels was 20 000, on the lips 3 000 and on the rest of the body 155 000. This would total about 175 000 taste buds on the body surface which are transmitting via the 7th cranial nerve t o the facial lobes of the medulla. Within the oral cavity and pharynx, Atema found patches of taste buds t o number from 3 to 5/mm2t o 10,25 or up to 50/mm2 on the gill arches. The estimated total number of these internal taste buds was 20 000. Impulses from the taste buds of the oral cavity and pharynx would be received via the 9th and 10th cranial nerves by the vagal lobes of the medulla.

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V. INNERVATION, BRAINMORPHOLOGY AND FUNCTION A. Innervation Outstanding contributions to the functional anatomy of the nervous system of fishes were made by Charles Judson Herrick (see references). Several of these studies have been reviewed by Kappers et al. (1936) in their two-volume “ Comparative Anatomy of the Nervous System ” which they dedicated to Herrick. This pioneer investigator gave special attention to peripheral and central taste receptors in catfish Ameiurus (1901), codfish Gadus morhua (Linnaeus) (=G. callarias) (1900 and 1907a), and carp Cyprinus (1905).

FIG.17. A projection of the cutaneous branches of the communis foot of the right facial nerve in Ameiurus melas. After Herrick, C. J. (1903). The organ and sense of taste in fishes. U.S. Fish Commission Bulletin, Washington (for 1902). With the permission of the U.S. Department of Commerce, National Oceanic and Atmospheric Administration, National Marine Fisheries Service, Seattle, Washington.

I n his study of the cranial nerves and sense organs of siluroid fishes, Herrick (1901) described the innervation of the cutaneous end-organs. He divided the organ-nerve components into two functional groups : a communis system and an acoustico-lateralis system. This communis system received impulses from taste buds of the skin and oral cavity and thus subserved a gustatory function. The acoustico-lateralis system received afferents from the neuromasts of the internal ear and lateralline canals, and the pit organs of the skin. Herrick found that although the taste buds of all fishes were innervated by cranial nerves VII (facial), I X (glossopharyngeal), and X (vagus) the pathways and shared nerve trunks for the gustatory fibres differed between fish groups. Thus, it is important to know what fish is being considered when discussing nerve pathways. All cutaneous taste buds are supplied by branches of the facial

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nerve whose cell bodies lie in the geniculate ganglion (Fig. 17). Distal to the ganglion the branches of the facial nerve join branches of other cutaneous nerves belonging t o general cutaneous or lateral-line systems. Proximal t o the ganglion, the communis root of the facial nerve passes to the primary gustatory centre in the medulla. I n most fishes this root passes caudally close to the floor of the fourth ventricle to terminate within the visceral sensory column on the same side. However, in catfishes (silurids) and minnows (cyprinids) where numerous taste buds of the outer skin are all innervated by the communis root of the facial nerve, the consequent increase in the size of this receptor nucleus has resulted in a great enlargement of the rostral end of the visceral afferent column so that it appears as a distinct swelling, the facial lobe. This lobe is paired in catfish and single in minnows. Within the deep layers of the facial lobe of the catfish trigeminal root fibres terminate thus providing a correlation centre for touch and taste to the motor centres of the barbels and jaws. I n the codfish (Gadus)there is no discernible facial lobe. The pectoral fins act as exploratory organs and are innervated by the facial nerve for taste and by cutaneous branches of cervical nerves for touch. The incoming visceral sensory fibres end in the lateral facial nucleus and from there appear to connect (Herrick, 1907a) directly with motor centres. Thus, instead of a rostral facial nucleus as in minnows where the trigeminal-facial correlations are important, we have a lateral facial nucleus and a facial-cervical correlation centre. The communis root of the facial nerve of the catfish (Ictalurus) has a large geniculate ganglion a t its base. Arising from the most dorsal and proximal portion of this ganglion is the ramus lateralis accessorius, more commonly known as the recurrent branch of the facial nerve. (Wright (1884) called this the ramus lateralis trigemini.) This nerve is distributed to all of the cutaneous taste buds of the trunk and tail. The recurrent ramus passes caudally within the cranium along the dorsolateral border of the medulla and just before passing out of a foramen in the supraoccipital bone it gives off a twig for taste buds over the supraoccipital region. At the level of the first spinal nerve, a small branch of the recurrent ramus passes ventrally along the lateral face of the occipital bone to join the ventral ramus of the first spinal nerve. Successive spinal nerves receive twigs from the recurrent branch a t regular intervals. Caudal to the 2nd spinal nerve there are communicating rami from the spinal ganglia to the recurrent ramus. These carry general sensory fibres to be distributed along with gustatory nerves. Other gustatory fibres leaving the main communis root supply taste

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buds in the skin of the head and in the barbels. Herrick (1901) traced many of these fibres and identified the following bundles : 1. An otic ramus carries lateralis, general cutaneous and communis fibres to the lateral cranial roof and dorsal part of the operculum. 2. A meningeal ramus courses rostrally over the cerebellum and divides into many twigs before perforating the cranial roof to innervate taste buds in the overlying skin. 3. A dorsal branch passes to the skin of the supraoccipital region. 4. A small bundle 1eaves.the ventral edge of the hyomandibular trunk to supply the skin of the preopercular region. 5 . The hyomandibular trunk courses ventrally and divides into a hyoid ramus and an external mandibular ramus. The former may supply the branchiostegal membrane. The external mandibular ramus has an internal branch for the mandibular lateral-line canal organs and an outer cutaneous branch which carries fibres from lateral-line organs, tactile receptors, and taste buds. 6. The infraorbital trunk is the largest complex leaving the brain. It lies ventral to the optic lobe and has several named branches leaving it. 7. A posterior palatine branch leaves the ventral aspect of the infraorbital trunk through its own foramen to supply the hyoid arch. (This has been called the pretrematic branch of the facialis by Herrick (1898 and 1907a) in Menidia thomasi Meinken and Gadus.) 8. A trigeminal superficial ophthalmic ramus in Ictalurus carries equal proportions of general cutaneous and communis fibres. The gustatory fibres are from the facial nerve and pass to the skin in front of the eye and around the nasal apertures. 9. An accessory maxillary nerve separates from the infraorbital trunk and conducts general cutaneous fibres and communis fibres to the infraorbital region. 10. The main continuation of the infraorbital trunk consists of superolateral and inferomedial bundles which combine to form the maxillary and mandibular nerves. The latter nerves, which supply the upper and lower jaws and their respective barbels, contain equal proportions of general cutaneous and communis fibres in addition to trigeminal motor components. The taste buds of the pharyngeal cavity and palate are innervated by glossopharyngeal (IX) and vagus (X) nerves. When a palatal organ is present, the number of taste buds is greatly augmented and the terminal centres in the visceral sensory column of the medulla are similarly enlarged as vagal lobes. The term vagal lobe as originally

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used by Johnston (1901) designated the nucleus of termination for the visceral sensory fibres of VII, I X and X because it was largest a t the level of entrance of the vagus nerve in the sturgeon which he studied. Neither the glossopharyngeal nor the vagus supply any of the cutaneous taste buds. For descriptions of the nerve supply to the taste buds in species other than the catfish see: Sat6 (1937b) for the goat-fish Upeneoides bensasi (Temminck and Schlegel) ; Sat6 (1937d), and Grzycki (1954) for the carp Cyprinus. Landacre (1907), Olmsted (1920) and May (1925) noted that the presence of a gustatory nerve is the causative factor in the differentiation and transformation of epithelial cells into a taste bud whether in an ectodermal or endodermal field. The subsequent studies of Olivo (1928), Torrey (1934, 1936), Kamrin and Singer (1953, 1955) and Wagner (1953) strengthened this concept by showing that transection of the facial nerve t o the barbel of Ameiurus resulted in destruction of the taste buds and their absence from the barbel until such time as a regrowth of the nerve again stimulated the formation of taste buds. Torrey (1936) found that the neural arborizations of the taste buds began to degenerate within five days after sectioning the nerve. The breakdown of the taste bud was complete by the end of the tenth day. Degeneration of fibres in the central nerve trunk goes on synchronously with that of the distal elements.

B. Brain morphology (Fig. 18a and b) The teleost brain is well suited for correlative studies of sense organs, brain pattern, and behaviour. Feeding is performed in a variety of ways, which in turn finds its expression in the pattern of the brain, particularly the hind-brain. Telencephalon The olfactory bulb lies adjacent to the olfactory capsule and is connected by an olfactory stalk with the forebrain. The length of the stalk varies greatly between species and the relative positions of the olfactory bulb and forebrain may change during ontogeny. There does not appear t o be any consistent correlation between the position of the central olfactory regions and the feeding habits. Electrophysiological studies of olfactory bulb neurons have been made by Hara (1967, 1971). Atema (1974) has shown that the medial and lateral olfactory tracts in Ictalurus nebulosus are distributed ipsilaterally and contralaterally

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li a

b!Y b

FIG.18. Brain of (a) Carassius auratus and (b) Rhhichthys atratulus. oc-Olfactory capsule, ob-olfactory bulb, 0s-olfactory stalk, fb-forebrain, 01-optic lobe, c-cerebellum, fl-facial lobe, vl-vagal lobe. After Evans, H. E.

in the telencephalon. The medial olfactory tract projects into a hypothalamic terminal field as well as into the contralateral olfactory bulb and appears to be most important behaviourly.

Diencephalon The epithalamus consists of a pineal which projects dorsally as a delicate evagination on the midline caudal to the forebrain. Since the pineal functions in melanophore contraction it plays a role in protective colouration and predator-prey interactions. The thalamus is small whereas the hypothalamus is relatively large. Mesencephalon The optic lobes are the most prominent external features of the brain. They are oval in form and separated from each other on the midline by a fissure or groove. They have a common ventricle which is occupied in part by an extension of the cerebellum, the valvula cerebelli.

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Metencephalon The cerebellum is well developed in most fishes and is associated with the maintenance of body position. The relative size of the cerebellum varies among species and often appears to be associated with habitat (Karamian, 1949). A gradual increase in the size of the cerebellum in catastomid fishes appeared to be correlated with life in faster water (Miller and Evans, 1965) as was suggested earlier by Herrick and Herrick (1891) who noted the large size of the valvula cerebelli of Cycleptus. The acoustic tubercles are better developed in some fishes than in others. They are associated with the acoustico-lateralis system and the eighth cranial nerve. Myelencephalon I n regard t o gustatory function, it is the medulla that grossly reflects any increase in the number of taste buds that are present on the body surface or within the oral cavity and pharynx. This is due to the fact that all taste buds are innervated by cranial nerves V I I (facial), IX (glossopharyngeal), or X (vagus) which have their primary receptive nuclei in the medulla. These nuclei form gross enlargements of the visceral sensory column and have been designated as facial and vagal lobes of the brain. The facial lobe receives facial nerve fibres from the lips, barbels, and skin. Many fishes have a median facial lobe while others have a bilobed structure (Prasada Reo, 1967). The vagal lobes receive gustatory fibres from the glossopharyngeal and vagal nerves. The glossopharyngeal nerve supplies taste buds on the hyoid arch and pharynx (also palatal organ) while the vagus nerve innervates the taste buds of the caudal oro-pharynx. Those fishes which select their food by means of oro-pharyngeal taste show a marked enlargement of the corresponding vagal nuclei. The goldfish Carassius, carp Cyprinus, and sucker Catostmus commersoni (LacBpBde), are good examples. I n Carpiodes velifer (Rafinesque), and Ictiobus bubalis (Rafinesque), two catostomids, the vagal lobes are larger than the rest of the brain and reflect the great number of taste buds found on the palatal organs (Miller and Evans, 1965). The vagal lobe may be highly differentiated internally as was shown by Mayser (1882) and Herrick (1905) for the carp. They described four cell layers, one of which could be further subdivided into seven bands. A.M.B.-13

4

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The correlation between feeding habits and the gross structure of the brain has received the attention of Evans, H. M. (1931, 1932, 1940), Bhimachar (1935, 1937), Sat6 (1941), Mookerjee et al. (1950), Evans, H. E. (1952), Uchihashi (1953), Yamaguchi (196l), Schnitzlein (1964), Miller and Evans (1965), Khanna and Singh (1966), and Davis and Miller (1967). On the basis of brain pattern and feeding behaviour, many groupings have been suggested which show functional correlations. Evans (1931,1932, 1940) placed the species of British cyprinids in threegroups : I. Fishes with well-developed vagal and sometimes well-developed facial lobes that fed on the bottom ; 11. Fishes with large optic lobes which fed primarily by sight; and 111. Fishes with well-developed facial lobes and sensory barbels. Bhimachar (1935, 1937) studied Indian cyprinids and cyprinodonts and made two divisions : Taste feeders and Sight feeders. He further subdivided the taste feeders into mouth tasters and barbel tasters. Sat6 (1941) examined the hind-brains of fourteen species and followed the classification of Evans and Bhimachar. Mookerjee et al. (1950) studied the brains of twenty-five species in thirteen families and established three groups: I. Fishes which fed largely by taste and had well-developed facial lobes and poorly developed optic lobes ; 11. Fishes which fed by taste and sight and had welldeveloped facial, or vagal lobes or both, plus prominent optic lobes; 111. Fishes which fed mainly by sight and had well-developed visual structures, and poorly developed vagal and facial lobes. Evans (1952) studied four species of North American cyprinids and placed them in three groups : I. Mouth tasters, 11. Sight feeders, and 111. Skin tasters. Miller and Evans (1965) studied the brains of forty-six species in thirteen genera of Catastomidae and pointed out the well-developed facial lobes of many non-barbeled forms. Khanna and Singh (1966) studied eight species in six families and placed them in three groups : I. Fishes that feed by sight and taste and show prominent optic lobes, facial lobes and relatively large vagal lobes ; 11. Fishes which feed with the aid of barbels, and possess highly developed facial lobes and less prominent vagal lobes ; and 111. Fishes which feed by sight and have better developed visual structures, and suppressed development of facial and vagal lobes. Davis and Miller (1967) studied the brain and gustatory structures in twenty-one species of the genus Hybopsis, and on the basis of their dominant sensory features they assigned them t o three groups : I. Sight feeders, 11. Skin tasters, and 111. Mouth tasters. Fishes inhabiting turbid waters had the greatest number of taste buds, reduced optic lobes, flattened longitudinal tori, and enlarged facial lobes.

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Sensory elaborations for taste or enlarged central nuclei for taste are not evident in sharks or rays. The behavioural responses of elasmobranchs to food or prey depend primarily upon olfaction and electroreception rather than taste. Interconnecting brain tracts and receptive brain nuclei are fewer and more diffuse in sharks than in teleosts.

C. Function Taste is a close-range sense in most fishes and plays the role of food item discriminator after the other senses such as smell, sight, or hearing have recognized its presence or caused its ingestion (Wunder, 1927; Andriashev, 1944a, b, 1955 ; Aronov, 1959, 1961 ; Teichmann, 1962 ; and others). However, recent studies have shown that some fishes, namely catfish, utilize taste as a long-range receptor. Bardach et al. (1967), Atema et al. (1969) and Todd (1971) have demonstrated that it is not olfaction but taste that guides catfish (Ictalurus) to food. Blinded catfish deprived of their olfactory receptors are able to swim directly to a food source in still water. When taste reception was eliminated on one side of the body by surgical procedures, the fish had difficulty in locating a food item and did so only by constantly circling towards the side where taste reception was intact. Thus taste functions as a true distance receptor in this fish. From a behavioural point of view, two fairly distinct chemosensory channels exist in the catfish : taste, which dominates food search and ingestion, and olfaction which governs social behaviour. Atema (1971), in the catfish, studied the interaction of the taste buds of the skin and the barbels with those of the oral cavity and pharynx by removing the entire sensory area of the medulla for each receptor field. When the facial lobes of the medulla were removed the fish was unable to localize food accurately or take it into the mouth. This reflected the sensory deprivation of the skin and barbels. On the other hand when only the vagal lobes of the medulla were removed the fish had no difficulty in finding the food or taking it into the mouth but it could not swallow the food due to the elimination of the swallowing reflex whose afferent arc is via the glossopharyngeal (IX) and vagus (X)nerves to the vagal lobe of the brain. Thus as Atema points out, the two taste inputs (VII us. IX and X) have different functions. One guides body propulsion and triggers the pickup, while the other controls the swallowing reflex. The integrated functioning of gustatory, olfactory, common chemical, tactile and other senses in feeding varies with the species to such an extent that further studies are necessary before generalizations can be

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made. Many sense organ receptors are ambiguous in function. Sensitivity to one modality may be only incidental to normal use of the same receptor in a less obvious sensory function. As Bullock (1973) has noted, each year we witness the discovery of ‘‘ new ” organs or new functions for “ old ” organs and the multiplicity of functions of many sensory organs makes i t unwise to name a new sensory receptor simply because of its response to a given stimulus. Blind fishes and fishes living in caves or turbid waters show a compensatory development of other senses particularly the gustatory and lateral line organs (Breder and Rasquin, 1943 ; Moore, 1950; Humbuch, 1960; Schemmel, 1967 ; Glsser, 1968). The use of olfactory receptors for locating food or prey has been referred t o by Strieck (1924), Wunder (1927, 1957), Sat8 (1937c), Grimm (1960) and Teichmann (1962). Olfaction also plays a role in enabling fish to distinguish between different species (von Frisch, 1941 ; Goz, 1941). Sharks and other elasmobranchs have a keen sense of smell which is of prime importance t o them in locating food. For considerations of elasmobranch feeding behaviour see Sheldon (1909), Parker (1910, 1912, 1914), Springer (1958), and Tester (1963). The exact nature of the common chemical sense (Parker, 1922; Hasler, 1954, 1957; Murray, R. W., 1961) and its receptors is not clear a t present. Such sensations may be medisted by free nerve endings or as yet unknown receptors which may be found all over the body. Maljukina (1966) and Maljukina and Chauschesku (1966) described chemoreception in predator-prey relationships of fishes in response to skin extracts. Maljukina and Schtefanesku (1967) have noted the role of chemoreception in schooling of crucian carp. 0 ther observations on chemoreceptors in teleosts have been made by Katsuki et al. (1971), and Bardach and Atema (1971). Chemosensory orientation of sharks (Neyaprion and Ginglymostoma) showed them to be particularly ssnsitive to amino-acids and amines (Hodgson and Mathewson, 1971).

Zippel and Domagk (1971a,b) have described some experiments which indicate the transfer of chemical sensory (taste ‘1) preference from trained t o untrained goldfish via injected brain extracts. Fish were trained to show a preference for quinine or acetic acid, for which they have an innate aversion, and extracts of their brains were injected intraperitoneally into untrained fish. Recipients of brain extracts taken from trained donors showed a positive reaction to the previously disliked taste quality. Subsequent experiments showed that there was no cross-transfer in taste preference between acetic acid conditioned iiah and quinine conditioned fish. I n recent years the function of the pit organs of fishes has been

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clarified and it is now believed that their primary function is electroreception although they do respond t o salinity changes and chemical stimulation. I n the past, pit organs have been considered as external taste buds (Budker, 1938, 1958), free neuromasts (Tester and Kendall, 1967; Tester and Nelson, 1967), or chemoreceptors (Katsuki et al., 1969). Similar structures in elasmobranchs, particularly on the snout, have long been known as the ampullae of Lorenzini. These ampullae open to the surface via a long canal and were first believed to function as mechanoreceptors, later as thermoreceptors and presently as electroreceptors. Kalmijn (1971) demonstrated that sharks use the ampullae to detect the electric field from " prey " such as a flatfish buried in the sand. He found that nearly all animals emit directcurrent fields into sea water which are well above the detection threshold of sharks. The sensitivity of these ampullae to electric fields is remarkable since the voltage required for detection is only 0.01 pv/cm. Micro-ampullae have been seen in freshwater elasmobranchs, gymnotids, mormyrids, gymnarchids, siluroids, dipnoans, and brachiopterygians. Some of these species are electric fishes. Bennett (1971) notes that all known electroreceptors (pit organs, ampullae, tuberous organs) are modified lateral-line organs of the acoustico-lateral system. Most electroreceptors are of two types, tonic and phasic, characterized by morphological and physiological features. Tonic receptors are almost constantly active and respond to low frequency or DC stimuli. They appear as ampullae under the epidermis with a long canal to the exterior as in the ampullae of Lorenzini of sharks or as unpigmented pits distributed over the body of catfish. Phasic receptors are not responsive to maintained or DC stimuli but are sensitive to high frequencies. They appear as bulbous or tuberous structures beneath the skin with their lumen occluded by a plug of epithelial cells. There are no phasic receptors in non-electric or marine fish. Some fish groups have both tonic and phasic receptors (Gymnotids and Mormyrids) whereas others have only tonic receptors (Elasmobranchs and Siluroids). According to Bennett (1971),phasic receptors are quite insensitive to mechanical, thermal, and other modes of stimulation but tonic receptors may be rather sensitive to temperature and salinity changes, and also have some sensitivity t o mechanical stimulation. The sense of touch is also used for food discrimination. Most commonly the tactile receptors are found on free fin rays or head appendages. Bardach et al. (1959)and Bardach and Loewenthal(l961)reported dermo-neural structures, closely resembling touch corpuscles of higher

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vertebrates, on the lips and dorsal buccal cavity of moray eels, Gymnothorax wicinus (Castelnau) and G. moringa (Cuvier). They found the frequency and distribution of touch corpuscles coincided with those of the taste buds present. Each touch receptor was composed of a lamellated capsule with a core of " tactile cells ". Nerve fibres entered the deepest end of the corpuscle and terminated on or around the tactile cells. Similar structures also occur on the free anterior pectoral fin rays of sea-robins Prionotus (Lagler et al., 1962). General tactile discrimination in fishes has been studied by Herrick (1903, 1907b), Jordan (1917), Hoagland (1933), Hubbs (1938), Mohres (1941), Weber (1963), Bardach and Case (1965) and Bardach et al. (1967).

VI. ACKNOWLEDGEMENTS Dr B. G. Kapoor thanks Professor S. D. Misra (Dept. of Zoology, University of Jodhpur) and Dr M. L. Bhatia, retired Professor of Zoology (University of Delhi) for encouragement. We thank Dr A. M. Sutterlin (Biological Station, St. Andrews, Canada) and Professor Y. Katsuki (Tsurumi University, Yokohama, Japan) for helpful suggestions and Professor F. D. Tibbitts (University of Nevada, Reno) for sending histological sections. Dr W. Breipohl (Ruhr-University, Bochum, and Dr K. Reutter (University of Tiibingen) kindly loaned scanning micrographs.

VII. REFERENCES Afanasjev, M. (1875). On the nerve endings in the tactile organs in fishes. Zapiski Akadernii N a u k , 25, 1-25. (In Russian.) Airapetjanz, E. Sch. and Vasilevskaja N. E. (1970). On the chemical analyzer of fishes. UspekhiJisiologicheskikh nauk, 1, 63-83. (In Russian.) Alexander, R. McN. (1965). Structure and function in the catfish. Journal of Zoology, London, 148, 88-152. Alexander, R.McN. (1966). The functions and mechanisms of the protrusible upper jaws of two species of cyprinid fish. Journal of Zoology, London, 149, 288-296. Al-Hussaini, A.H. (1946). The anatomy and histology of the alimentary tract of the bottom-feeder, Mulloides auriflamrna (Forsk.). Journal of Morphology, 78, 121-153. Al-Hussaini, A. H. (1949). On the functional morphology ofthe alimentary tract of some fish in relation to differences in their feeding habits : anatomy and histology. Quarterly Journal of Microscopical Science, 90, 109-139. Al-Hussaini, A. H. and Kholy, A. A. (1954). On the functional morphology of the alimentary tract of some omnivorous teleost fish. Proceedings of the Egyptian Academy of Sciences, Cairo, 9 (1953), 17-39. Al-Hussaini, A. H. mid Lutfy, R.G. (1958). O n tlre microscopic anatomy of the skin of fishes. 1. The histology of the skin of some silurids of the Nile. Ain Shams Science Bulletin, Cairo, no. 3, 215-263.

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Andriashev, A. P. (1944a). On a way of the feeding in Mullus barbatus. Zhurnal obtschei bioZogii, 5, 193-196. (In Russian.) Andriashev, A. P. (1944b). The role of sense organ8 in feeding in hiirbot. Zhurnal obtschei biologii, 5, 123-127. (In Russian.) Andriashev, A. P. (1955). The role of sense organs in feeding in fishes. Trudy sovetschanija PO metodike isuchenija kormovoi busy i pitanija ryb, 135-142. (In Russian.) Aronov, M. P. (1959). On the outer gustatory apparatus in burbot. Nauchnie doklady vysshei schkoly biologicheskikh N a u k , 4, 38-41. (In Russian.) Aronov, M. P. (1961). The role of sense organs in feeding of Corvina nigra. Yoprosy ikhtiologii, 1, 194-199. (In Russian,) Aronov, M. P. (1962). The role of sense organs in feeding in fishes. Uspekhi Sovremennoi biologii, 54, 115-128. (In Russian.) Atema, J. (1971). Structures and functions of the sense of taste in the catfish (Ictalurus natalis). Brain, Behavior and Evolution, 4, 273-294. Atema, J. (1974). Seminar Section of “ Neurobiology and Behavior ”, Cornell University, Ithaca, New York. Atema, J.,Todd, J. H. and Bardach, J. E. (1969).Olfact’ionand behavioralsophistication in fish. In “ Olfaction and Taste ”, Vol. 111 (C. Pfaffmann, ed.), pp. 241-251. Rockefeller University Press, New York. Baecker, R. (1926). Beitriige zur Histologie der Barteln der Fische. Jahrbuchfiir Morphologie und mikroskopische Anatomie, 6, 489-507. Bardach, J. E. (1967). The chemical senses and food intake in the lower vertebrates. I n “ The Chemical Senses and Nutrition ” (M. R. Kare and 0. Maller, eds.), pp. 19-43. The Johns Hopkins Press, Baltimore, Maryland. Bsrdach, J. E. (1972). The chemical senses of fishes. Final report (1 May, 196331 December, 1971) ORA Project 018990, Ann Arbor, pp. 1-98. Bardach, J. E. and Atema, J. (1971). The sense of taste in fishes. I n “ Handbook of Sensory Physiology ” (H. Autrum et al., eds.), Vol. IV, part 2, pp. 293336. Springer-Verlag, Berlin, Heidelberg and New York. Bardach, J. E. and Case, J. (1965). Sensory capabilities of the modified fins of squirrel hake (Urophycis chuss) and searobins (Prionotus carolinus and P. evolans). Copeia, no. 2, 194-206. Bardach, J. E. and Loewenthal, L. A. (1961). Touch receptors in fishes with special reference to the moray eels (Gymnothorax: vicinus and G . moringa). CopeDeia, no. 1 , 42-46. Bardach, J. E. and Todd, J. H. (1970). Chemical communication in fish. I n I ‘ Advances in Chernoreception” (J. W. Johnson, D. C. Moulton and A. Turk, eds.), Vol. I, pp. 205-240. Appleton-Century-Crofts, New York. Bardach, J. E., Fujiya, M. and Holl, A. (1967). Investigations of external chemoreceptors of fishes. I n “Olfaction and Taste”, I1 (T. Hayashi, ed.), pp. 647-665. Pergamon Press, Oxford and New York. Bardach, J. E., Johnson, G. H. and Todd, J. H. (1969). Orientation by bulk messenger sensors in aquatic vertebrates. Annals of the New York Academy of Sciences, 163, 227-235. Bardach, J. E., Todd, J. H. and Crickmer, R. (1967). Orientation by taste in fish of the genus Ictalurua. Science, N e w Yo&, 155, 127g-1278.

94

B. U . KAPOOR, H. E. EVANS AND R . A. PEVZNER

Bardach, J. E., Winn, H. E . and Menzel, D. W. (1959). The role of the senses in the feeding of the nocturnal reef predators Gymnothorax moringa and c f . vicin.us. Copeia, no. 2, 133-139. Bath, H. (1962). Vergleichende biologisch-anatomische Untersuchungen uber die Leistungsfahigkeit der Sinnesorgane fur den Nahrungserwerb, ihre gegenseitige Abhangigkeit und ihre Beziehungen zum Bau des Gehirns bei verschiedenen Knochenfischarten. Zeitschrift fiir wissenschaftliche Zoologie, 167, 238-290. Bennett, M. V. L. (1971). Electroreception. I n " Fish Physiology " (W. S. Hoar and D. J. Randall, eds.), Vol. V, pp. 493-574, Academic Press, New York and London. Bertmar, G., Kapoor, B. G. and Miller, R . V. (1969). Epibranchial organs in lower teleostean fishes-an example of structural adaptation. I n " International Review of General and Experimental Zoology '' (W. J . L. Felts and R. J. Harrison, eds.), Vol. IV, pp. 1-74. Academic Press, New Pork and London. Bhatia, B. (1950). Adaptive modifications in a hill-stream catfish, Glyptothoraz telchitta (Hamilton). Proceedings of the National Institute of Sciences of I n d i a , 16, 271-285. Bhatti, H. K. (1938). I. The integument and dermal skeleton of Siluroidea. Transactions of the Zoological Society of London, 24, 1-102. Bhatti, I. H. (1952). On the cutaneous sense-organs of a common siluroid fish, R i t a rita (Hamilton). Proceedings of th,e National Institute of Sciences of India, 18, 547-556. Bhimacher, B. S. (1935). A study on the correlation between the feeding habits and the structure of the hind brain in the South Indian cyprinoid fishes. Proceedings of the Royal Society of London, B117, 258-272. Bhimacher, B. S. (1937). A study of the medulla oblongata of cyprinodont fishes with special reference to their feeding habits. Proceedings of the Royal Society of London, B123, 59-68. Bishop, C. and Odense, P. H. (1966). Morphology of the digestive tract of the cod, Gadus morhzta. Journal of the Fisheries Research, Board of Canada, 23, 1607-1615. Bodrova, N. V. (1958). On the morphology of gustatory and olfactory analyzers in some teleost fishes. Tesisy dokladov V I Vsesojusnogo s'esda anatomov, gistologov, embriologov, Kiev. (In Russian.) Bodrova, N. V. (1960). The peripherical nerve apparatus of chemical sense in burbot. T r u d y Instituta biologii vodokhranilitsch ANSSSR, 3, 249-265. (In Russian.) Bodrova, N. V. (1962). The receptors of chemical sense in Abramis Brama (L.). Voprosy ichtiologii, 2, 693-702. (In Russian.) Bodrova, N. V. (1965). The receptors of chemical sense of fishes. T r u d y Institutu biologii vnutrennikh vod ANSSSR, 9, 148-162. (In Russian.) Bodrova, N. V. and Krajuchin B . V. (1965). The main results of the investigations of physiology in fishes. T r u d y Instituta biologii vnutrennikh vod A N S S S R , 9, 39-47. (In Russian.) Boeke, J. (1934). Organe mit Endknospen und Endhugeln nebst eingesenkten Organen. I n " Handbuch der vergleichenden Anatomie der Wirbelt,iere " (L. Bolk et al., eds.), Vol. 11, pp. 949-988. Urban und Schwarzenberg, Berlin und Wien.

THE GUSTATORY SYSTEM IN FISH

95

Branson, B. A. (1966). Histological observations on the sturgeon chub, Hybopsis qelida (Cyprinidae). Copeia, no. 4, 872-876. Breder, C. M. and Rasquin, P. (1943). Chemical sensory reactions in the Mexican blind characins. Zoologica, 28, 169-200. Breipohl, W., Bijvank, G. J. and Pfefferkorn, G. (1974). Scanning electron microscopy of various sensory receptor cells in different vertebrates. I n “ Proceedings of the workshop on advances in biomedical applications of the SEM ” (0.Johari and J . Gorvin, eds.), pp. 557-564. I.T.T. Research Institute, Chicago, Ill. Budker, P. (1938). Les cryptes sensorielles et. les denticules cutan6s des Plagiostomes. Annales de l’lnstitut Ocdanographique, 18, 207-288 (cited by Tester, 1963). Budker, P. (1958). Les organes sensoriels cutan& des s6laciens. I n “ Trait6 de Zoologie”, (P. P. Grass6, ed.), Vol. XIII, pp. 1033-1062. Masson et Cie, Paris. Bull, H. 0. (1928). Studies on conditioned responses in fishes. Part I. Journal of the Marine Biological Association of the United Kingdom, 15, 485-533. Bull, H. 0. (1936). Studies on conditioned responses in fishes. Part V I I . Temperature discrimination in teleosts. Journal of the Marine Biological Association of the United Kingdom, 21, 1-27. Bull, H. 0. (1952). An evaluation of our knowledge of fish behaviour in relation to hydrography. Rapport des Reunions Conseil permanent international pour I’Esploration de la Mer, 131, 8-23. Bullock, T. H. (1973). Seeing the world through a new sense: electroreception in fish. American Scientist, 61, 316-32.5. Campos, H. (1969). Die Geschmacksknospen im Vorderdarm von Sufiwasserfischen, Zahl, Verteilung und Entwiclrlung (Phoxinus phoiinus L., Gasterosteus aculeatus L., Hemigrammus caudovittatus Ahl, Anoptichthys jordani Hubbs et Innes und Salmo gairdneri Rich). Zeitschrqt f u r zcissenschaftliche Zoologie, 179, 253-299. Chaudhry, H. S. and Khandelwal, 0. P. (1961). The anatomy and histology of the alimentary tract of Oreinus plagiostomus (Heckel). Annotationes Zoologicue Japonenses, 34, 139-152. Cook, M. H. and Neal, H. V. (1921). Are the taste-buds of elaamobranchs endodermal in origin? Journal of Comparative Neurology, 33, 45-63. Cordier, R. (1964). Sensory cells. I n “ The Cell ” (J.Brachet and A. E. Mirsky, eds.), Vol. VI, pp. 313-386. Academic Press, New York and London. Curry, E. (1939). The histology of the digestive tube of the carp (Cyprinus carpi0 communis). Journa,l of Morphology, 65, 53-78. Daniel, J. I?. (1922). “ The Elasmobranch Fishes ”, pp. 334. University of California Press, Berkeley. Davis, B. J. and Miller, R. J. (1967). Brain patterns in minnows of the genus Hybopsis in relation to feeding habits and habitat. Copeia, no. 1, 1-39. Desgranges, J.-C. (1965). Sur l’existence de plusieurs types de cellules sensorielles dans les bourgeons du goiit des barbillons du Poisson-chat. Comptes rendus des Sdances de I’Acaddmie des Sciences, Park, 261, 1095-1098. Desgranges, J.-C. (1966). Sur la double innervation des cellules sensorielles des bourgeons du goat des barbillons du Poisson-chat. Comptes rendus desSdames de l’dcaddmie des Sciences, Paris, 263, 1103-1 106.

96

B. G. KAPOOR, H. E. EVANS A N D R. A. PEVZNER

Desgranges, J.C. (1972). Sur les bourgeons du goQt du Poisson-chat Ictalarus melas: ultrastructure des cellules basales. Cornptes rendus des Skances de I’Acaddmie des Sciences, Paris, 274, 181.1-1817. Disler, N. N. (1960). The sense organs of the lateral line system and t,heir significance for behaviour of fishes. I z d . A N S S S R , Moskwa. (In Russian.) Dogiel, A. S. (1897). Uber die Nervenendigungen in den Geschmacksendknospen der Ganoiden. Archiv f i i r rnikroskopische Anatomie, 49, 769-790. Dorier, A. and Bellon, G. (1952). Sur l’organe palatin des Cyprinidks. Travawz du Laboratoire d’Hydrobiologie et de Pisciculture de 1’ Universitk de Grenoble, 43 and 44, 47-60. Ducros, C. (1954). Les barbillons et l’organe palatin de Misgurnus fossilis Linn6 et de Cobitis barbatula LinnB. Travaux du Laboratoire d’Hydrobiologie et de Pisciculture de 1’ Universitd de Grenoble, 45, and 46, 55-70. Ebner, V. von. (1912). Von den Geschmacksknospen. I n ‘‘ Kolliker’s Handbuch der Gewebelehre der Menshen ”, Vol. 111,pp. 17-31 (cited by Hirata, 1966). Edwards, L. F. (1930). Origin of taste buds in the oro-pharyngeal cavity of the carp (Cyprinus carpi0 Linnaeus). Ohio Journal of Science, 30, 385-397. Evans, H. E . (1952). The correlation of brain pattern and feeding habits in four species of cyprinid fishes. Journal of Comparative Neurology, 97, 133-142. Evans, H. M. (1931). A comparative study of the brains in British cyprinids in relation to their habits of feeding with special reference to the anatomy of the medulla oblongata. Proceedings of the Royal Society of London, BlOS, 233257. Evans, H. M. (1932). Further observation on the medulla oblongata of cyprinoids; and a comparative study of the medulla of clupeoids and cyprinoids with special reference to the acoustic tubercles. Proceedings of the Royal Society of London, B111, 247-280. Evans, H. M. (1940). “ Brain and Body of Fish. A study of brain pattern in relation to hunting and feeding in fish.” 164 pp. The Blakiston Co., Philadelphia, Pa. Fahrenholz, C. (1915). Uber die Verbreitung von Zahnbildungen und Sinnesorganen im Vorderdarm der Selachier und ihre phylogenetische Beurteilung. Jenaische Zeitschrift f u r Naturwissenschaft, 53, 389-444. Fahrmann, W., Hoffmann, G. and Schuchardt, E. (1965). Die Zellen der Geschmacksknospe und der Zellersatz. Naturwissenschaften, 14, 438-439. Farbman, A. I. (1965). Fine structure of the taste bud. Journal of Ultrastructure Research, 12, 328-350. Frisch, K. von (1941). Uber einen Schreckstoff der Fischhaut und seine biologische Bedeutung. Zeitschrift f u r vergleichende Physiologie, 29, 4G-145. Fujiya, M. and Bardach, J. E . (1966). A comparison between the external taste sense of marine and fresh-water fishes. Bulletin of the Japanese Society of Scienti$c Fisheries, 32, 45-56. Girgis, S. (1952). On the anatomy and histology of the alimentary tract of an herbivorous bottom-feeding cyprinoid fish, Labeo horie (Cuvier). Journal of Mo~phology,90, 317-362. Glaser, D. (1966). Untersuchungen uber die absoluten Geschmacksschwellen von Fischen. Zeitschrift fur vergleichende Physiologie, 52, 1-25. Glaser, D. (1968). Zum Verhalten blinder Fische. Zeitschrijt fiir Tierpsychologie, 25, 648-658.

THE GUSTATORY SYSTEM IN FISH

97

Goz, H. (1941). Uber den Art- iind Individualgeruch bei Fischen. Zeitschrift fiir vergleichende Physiologie, 29, 1-45 (cited by Glaser, 1966). Graberg, J . (1899). Zur Kenntnis des zellularen Baues des Geschmacksknospen beim Menschen. Anatomische Nefte, 12, 337-368 (cited by Hirata, 1966). Gray, E. G. and Watkins, K. C. (1965). Electron microscopy of the taste buds of rat. Zeitschr4ft f u r Zellforschuna crnd mikroskopische Anatomie, 66, 583-595. Graziadei, P. P. C. (1968). Synaptic organization in vertebrate taste buds. I n “ Proceedings of the XXIV International Congress of Physiological Sciences ”, Vol. VII, p. 167. Graziadei, P. P. C. (1969). The ultrastructure of vertebrate taste buds. I n “ Olfaction and Taste”, I11 (C. Pfaffmann, ed.), pp. 315-330. Rockefeller University Press, New York. Graziadei, P. P. C. (1970). The ultrastructure of taste buds in mammals. I n “ Symposium on Oral Sensation and Perception ” (E. Bosma, ed.), pp. 5-35. Springfield, Ohio. Grimm, R. J. (1960). Feeding behavior and electrical stimulation of the brain of Carassius auratus. Science, New York, 131, 162-163. Grzycki, S. (1954).Badania nad zakohczeniami nerwowymi w nask6rku wasik6w i warg u Cyprinus carpio L. Annales Universitatis Mariae Curie Sklodowska, Lublin, Polonia, Sectio DD, 9, 141-146. Gudger, E. W. (1946). Oral breathing valves in fishes. Journal of Morphology, 79, 263-285.

Ham, T. J. (1967). Electrophysiological studies of the olfactory system of the goldfish, Carassius auratus L. 11. Response patterns of the olfactory bulb neurons to chemical stimulation and their centrifugal control. Comparative Biochemistry and Physioloqy, 22, 199-208. Ham, T. J. (1971). Chemoreception. I n “Fish Physiology ” (W. S. Hoar and D. J. Randall, eds.), Vol. V, pp. 79-120. Academic Press, New York and London. Hasler, A. D. (1954). Odour perception and orientation in fishes. Journal of the Fisheries Research Board of Canada, 11, 107-129. Hasler, A. D. (1957). The sense organs : olfactory and gustatory senses of fishes. 1% “ The Physiology of Fishes ” (M. E. Brown, ed.), Vol. 11, pp. 187-209. Academic Press, New York. Heidenhain, M. (1914). Uber die Sinnesfelder und die Geschmacksknospen der Papilla foliata des Kaninchens. Beitrage zur Teilkorpertheorie 111. Archiv f u r mikroskopische Anatomie, 85, 365-479. Hermann, F. (1884). Beitrag eur Entwicklungsgeschichte des Geschmacksknospens beim Kaninchen. Archiv f u r mikroskopische Anatomie, 24, 216-229. Herrick, C. L. and Herrick, C. J. (1891). Contributions to the morphology of the brain of bony fishes. I. Siluridae. 11. Studies of the brains of some freshwater fishes. Journal of Comparative Neurology, 1, 21 1-248 ; 333-358. Herrick, C. J. (1898). The cranial nerves of bony fishes. Journal of Comparative Neurology, 8, 162-170. Herrick, C. J. (1900). A contribution upon the cranial nerves of the codfish. Journal of Comparative Neurology, 10, 265-316. Herrick, C. J. (1901). The cranial nerves and cutaneous sense organs of the North American siluroid fishes- Journal of Comparative Neurology, 11, 177-249.

98

B. G . KAPOOR, H. E . EVANS A N D R . A. PEVZNER

Herrick, C. J . (1903). The organ and sense of taste in fishes. U.S. F b h Commission Bulletin, Washington, 22 (1902), 237-272. Herrick, C. J.(1905). The central gustatory paths in the brains of bony fishes. Journal of Comparative Neurology and Psyc!ology, 15, 375-465. Herrick, C. J. (1907a). A study of the vagal lobes and funicular nuclei of the brain of the codfish. Journal of Comparative NeuPology and Psychology, 17, 67-87. Herrick, C. J. (1907b). The tactile centers in the spinal cord and brain of the sea robin, Prionotus carolinus L. Journal of the Comparatiz:e Neurology and Psychology, 17, 307-327. Hiatt, R. W., Naughton, J. J. and Matthews, D. C. (1953). Relation of chemical structure to irritant responses in marine fish. Nature, London, 172, 904-905. Hidaka, I. (1970a). Effects of salts and p H on fish chemoreceptor responses. Nature, London, 228, 1102-1103. Hidaka, I. (1970b). The effect of carbon dioxide on the carp palatal chemoreceptors. Bulletin of the Japanese Society of Scienti$c Fisheries, 36, 1034-1039. Hidaka, I. (1970~).The effect of transition metals on the palatal chemoreceptors of the carp. Japanese Journal of Physiology, 20, 599-609. Hidaka, I. (1972). Stimulation of the palatal chemoreceptors of the carp by mixed solutions of acid and salt. Japanese Journal of Physiology, 22, 39-51. Hidaka, I. and Yokota, S. (1967). Taste receptor stimulation by sweet-tasting substances in the carp. Japanese Journal of Physiology, 17, 652-666. Hirata, Y. (1966). Fine structure of the terminal buds on the barbels of some fishes. Archivum histologicum japonicum, 26, 507-523. Hoagland, H. (1933). Specific nerve impulses from gustatory and tactile receptors in catfish. Journal of General Physiology, 16, 685-693. Hodgson, E. S. and Mathewson, R. F. (1971). Chemosensory orientation in sharks. Annals of the N ew York Academy of Sciences, 188, 175-182. Hubbs, C. L. (1938). Fishes from the caves of Yucatan. Carnegie Institute Publications, 491, 261-295. Humbach, I. (1960). Geruch und Geschmack bei den augenlosen Hohlenfischen Anoptichthys jordani, Hubbs und Innes und Anoptichthys hubbsi, Alvarez. Naturwissenschaf ten, 47, 551-559. Islam, A.-ul- (1951).The comparative histology of the alimentary canal of certain fresh water teleost fishes. Proceedings of the I ndian Academy of Sciences, B33, 297-321. Ishida, M. and SatB, M. (1960). The anatomical and histological observations of the alimentary tract of a catfish, Parasilurus asotus (L.). Science Reports of the Hirosaki University, Hirosaki, Ja p a n , 7, 57-63. Iwai, T. (1963). Taste buds on the gill rakers and gill arches of the sea catfish, Plotosus anguillaris (LacBpBde). Copeia, no. 2, 271-274. Iwai, T. (1964). A comparative study of the taste buds in gill rakers and gill arches of teleostean fishes. Bulletin of the Mi sak i Marine Biological Institute, Kyoto University, no. 7, 19-34. ,Jacobshagen, E. (1911). Untersuchungen uber das Darmsystem der Fiache und Dipnoer. I. Beitrage zur charakteristik des Vorder-, Mittel- und Enddarms der Fische und Dipnoer. Jenaische Zeitxhrift f u r Naturuiissenschaft, 47, 529-568 (cited by Edwards, 1930). Jakubowski, M. (1958). The structure and vascularization of the skin of the pondloach (Misgurnzcsfossilis L.). Acta Biologica Cracoviensia. Skrie : Zoologic, 1, 113-127.

'

THE GUSTATORY SYSTEM IN FISH

99

JakubDwski, M. (1959). The structure and vascularization of the skin of the st,oneloach (Noemacheilus barbatulu,sL . ) and burbot (Lota Lota L . ) . Acta Biologica, Cracoviensia, SBrie : Zoologie, 2, 129-149. Jalrubowslri, M. (1960a). The structure and vascularization of the skin of the eel (Anguilla anguilla L.) and the viviparous blenny (Zoarces viviparus L.). Acta Biologica Cracoviensia, SBrie : Zoologie, 3, 1-22. Jakubowski, M. (19GOb). The structure and vascularization of the skin of tlic leathern carp (Cyprinus carpio L. var. nuda) and flounder (Pleuronectes Jesus luscus Pall.). Acta Biologica Cracoviensia. SBrie :Zoologie, 3, 139-162. Jakubowki, M. (1966). Cutaneous sense organs of fishes. 111. The lateral-line organs in some Cobitidae. Acta Biologica Cracoviensia. SBrie : Zoologie, 9, 71-80. Jakubowski, M. and Oliva, 0. (1967). Note on pearl organs of the stone loacli, Noemacheilus barhatulus (Linnaeus, 1758) (Osteichthys, Cobitidae). V'btnik 6zskoslocenskb spolec'nosti Zoologickb, 31, 25-27. Jobert, A. (1872). Etudes d'anatomie cornparhe sur les organes du toucher chez divers Mammiferes, Oiseaux, Poissons et Insectes. Annales des Sciences naturelles, 16, 1-162. Johnston, J. B. (1901). The brain of Acipenser: a contribution to the morphology of the vertebrate brain. Fischer, G., Jena. Johnston, J. B. (1905). The cranial nerve components of Petromyzon. Gegenbaurs Morphologische Jahrbuch, 34, 149-202. Johnston, J. B. (1910). The limit between ectoderm and endoderm in the mouth and the origin of taste buds. American Journal of Anatomy, 10, 41-46. Jordan, H.(1917). Rheotropic responses of Epinephelus striatus Bloch. American. Journal of Physiology, 43, 438-454. Kalmijn, A. I. (1971). The electric sense of sharks and rays. Joiirnal of Experimental Biology, 55, 37 1-383. Kamrin, R. P. and Singer, M. (1953). Influence of sensory neurons isolated frcm central nervous system on maintenance of taste buds and regeneration of barbels in the catfish, Ameiurus nebulosus. American Journal of Physiology, 174, 146--148. Kamrin, R . P. arid Singer, M. (1955). The influence of the nerve on regeneration and maintenance of the barbel of the catfish, Ameiurus nehulosus. Journal of Morphology, 96, 173-188. Kapoor, B. G. (1953). The anatomy and histology of the alimentary canal in relation to its feeding habits of a siluroid fish, Wallago attu (Bl. & Schn.). Journal of the Zoological Society of India, 5, 191-210. Kapoor, B. G. (1957a). Oral valves of teleosts. Japanese Journal of Ichthyology, 5, 127-131. Kapoor, B. G. (195713). The digestive tube of an omnivorous cyprinoid fish, Barbus stigma (Cuv. & Val.). Japanese Journal of Ichthyology, 6 , 48-53. Kapoor, B. G. ( 1 9 5 7 ~ ) . A study on the tongue of fishes. Japanese Jourr;al of Ichthyology, 6 , 82-86. Kapoor, B. G. (1958). The anatomy and histology of the digestive tract of a cyprinoid fish, Catla catla (Hamilton). Annuli del Museo Civico di Storia Naturale di Genova, 70, 100-115. Kapoor, B. G. (1965a). Gill-rakers of a few Indian freshwater fishes. An,nali d d Museo Civico di Storia Naturale di Genova, 75, 126-143.

100

B . G. KAFOOR, H. E. EVANS AND R . A . PEVZNER

Kapoor, B. G. (1965b). Histological observations o n the skin of the head of a siluroid fish, Wallago attu (Bl. & Schn.). Mikroskopie, 20, 123-128. Kapoor, B. G. (1966). Histological notes on the skin of the head of a cyprinoid fish, Catla catla (Hamilton). Zoologischer Anzeiger, Leipzig, 176, 264-270. Kapoor, B.G. and Bhargava, S. C. (1967). A study on the barbels of a marine catfish, A ri u s thalassinus (Riipp.). Japanese Journal of Ichthyology, 14, 201-206.

Kappers, C. U. A., Huber, G. C. and Crosby, E. C. (1936). " The Comparative Anatomy of the Nervous System of Vertebrates, Including Man ", 1845 pp. Macmillan, New York. Karamian, A. I. (1949). Evolution of functional interrelations between cerebellum and cerebral hemispheres. I. Functional interrelation of cerebellum to cerebral hemispheres in bony fishes, Fiziologicheskii Zhurnal, 35, 167-181. (In Russian.) Katsuki, Y. and Hashimoto, T. (1969a). Shark pit organs: enhancement of mechanosensitivity by potassium ions. Science, Ne w York , 166, 1287-1289. Katsuki, Y. and Hashimoto, T. (196910). Chemoreception in the lateral-line system of the bony fish. Proceedings of the J apan Academy, 45, 209-214. Katsuki, Y., Yanagisawa, K., Tester, A. L. and Kendall, J. I. (1969). Shark pit organs : response to chemicals. Science, N e w York , 163, 405-407. Katsuki, Y., Hashimoto, T. and Yanagisawa, K. (1970). The lateral-line organ of shark as a chemoreceptor. Advances in Biophysics, 1, 1-51. Katsuki, Y., Hashimoto, T. and Kendall, J. I. (1971). The chemoreception in tne lateral-line organs of teleosts. Japanese Journal of Physiology, 21, 99-1 18. Kawamoto, N. and Higashi, T. (1965). Studies on the structure and function of the pharyngeal organ in the mullet, Mugils cephalus Linne. Bulletin of College of Agriculture and Veterinary Medicine, Nihon University, Tokyo, no. 21, 1-8. Khanna, S. S. and Mehrotra, B. K. (1970). Histomorphology of the buccopharynx in relation to feeding habits in teleosts. Proceedings of the National Academy of Sciences, I n d i a , B40, 61-80. Khanna, S. S. and Pant, M. C. (1964). On the digestive tract and the feeding habits of some teleostean fishes. Agra University Journal of Research (Science),13, 15-30. Khanna, S. S. and Singh, H. R. (1966). Morphology of the teleostean brain in relation to feeding habits. Proceedings of the National Academy of Sciences, I n d i a , B36, 306-316. Klenk, F. (1930). Untersuchungen uber die Geschmackswirkung von Siiuren bei Fischen mit einem Vergleich am Menschen. Zeitschrijt f u r wergleichende Physiologie, 13, 359-396. Kock, L. L. de (1963). A histological study of the head region of two salmonids with special reference to pressor- and chemo-receptors. Acta Anatomica, 55, 39-50.

Kolmer, W.(1927). Geschmacksorgan. I n " Handbuch der Mikroskopischen Anatomie des Menschen " (W. von Mollendorff, ed.), Vol. 111,pp. 157-191. Springer-Verlag, Berlin. Konishi, J. (1966). Freshwater fish chemoreceptors responsive to dilute solutions of electrolytes. Journal of General Physiology, 49, 1241-1264.

THE QUSTATORY SYSTEM IN FISH

101

Konishi, J. (1967). Studies on the stimulation of chemoreceptors of fresh-water fish by dilute solutions of electrolytes. I n " Olfaction and Taste ", 11, T . Hayashi, ed.), pp. 667-692. Pergamon Press, Oxford and New York. Konishi, J. and Hidaka, I. (1967). Stimulation of the chemoreceptors of the sea catfish by dilute electrolyte solutions. Japanese Journal of Physiology, 17, 726-737. Konishi, J. and Hidaka, I. (1969). On the stimulation of fish chemoreceptors by dilute solutions of polyelectrolytes. Japanese Journal of Physiology, 19, 315-326. Konishi, J. and Niwa, H. (1964). Some properties of taste receptors in freshwater fish : responses to weak solutions. Japanese Journal of Physiology, 14, 328343. Konishi, J. and Zotterman, Y. (1961a). Function of taste fibres in the carp. Nature, London, 191, 286-287. Konishi, J. and Zotterman, Y. (1961b). Taste functions in the carp. An electrophysiological study on gustatory fibres. Acta physiologica scandinacica, 52, 150-1 61. Konishi, J. and Zotterman, Y. (1963). Taste functions in fish. I n " Olfaction and Taste ", I (Y. Zotterman, ed.), pp. 215-233. Pergamon Press, Oxford, London, New York and Paris. Konishi, J., Uchida, M. and Mori, Y. (1966). Gustatory fibers in the sea catfish. Japanese Journal of Physiology, 16, 194-204. Konishi, J . , Hidaka, I., Toyota, M. and Matsuda, H. (1969). High sensitivity of the palatal chemoreceptors of the carp to carbon dioxide. Japanese Journal of Physiology, 19, 327-341. Kulshreshtha, S. D. (1967). A new sense organ in buccal cavity and tongue of the fish Notopterus notopterus. Science and Culture, 33, 541-542. Lagler, K . F., Bardach, J. E . and Miller, R. R. (1962). " Ichthyology ", 545 pp. John Wiley, New York. Lal, M. B., Bhatnagar, A. N. and Oberoi, S. (1964). Bucco-pharyngeal region of Labeo dero (Hamilton). Proceedings of the National Academy of Sciences, India, B34, 419-428. Landacre, F. L. (1907). On the place of origin and method of distribution of taste buds in Ameiurus melas. Journal of Comparative Neurology and Psychology, 17, 1-67. LenhossBk, M. von (1893). Der feinere Bau und die Nervenendigungen der Geschmacksknospen. Anatomischer Anzeiger, 8, 121-127. Leydig, F. (1851). Ueber die iiussere Haut einiger Siil3wasserfische. Zeitschvift fiir wissenschaftliche Zoologie, 3, 1-12 (cited by Herrick, 1903). Leydig, F. (1879). Neue Beitriige zur anatomischen Kenntniss der Hautdecke und Hautsinnesorgane der Fische. Festschrift zum Feier des 100-Jiihrigen Bestehens Naturf. Gessell, Halle, 129-186 (cited by Herrick, 1903). Leydig, F. (1894). Integument uncl Hautsinnesorgane der Knocheniische ; weitere BeitrLge. Zoologische Jahrbiicher (Abt. Anat.), 8, 1-162. Liem, K. F. (1967). Functional Morphology of the integumentary, respiratory, and digestive systems of the synbranchoid fish Monopterus albus. Copeia, no. 2, 375-388. Lorenzo, A. J. de (1960). Electron microscopy of the olfactory and gustatory pathways. Annals of Otology, Rhinology and Laryngology, 69, 410-420.

102

B . G . KAPOOR, H. E . EVANS A N D R . A. PEVZNER

Lorenzo, A. J. de (1963). Studies on the ultrastructure and histophysiology of cell membrane, nerve fibers and synaptic junctions in chcmoreceptors. I n “ Olfaction and Taste ” (Zotterman, I. Y., ed.), pp. 5-17. Pergamon Press, Oxford, London, New York and Paris. Lukowicz, M. von (1966). iiber die Barteln und die Lippenepidermis verschiedener agyptischer SiiBwasserfische mit einigen Versuchen zum Geschmackssinn. Zoologischer Anzeiger, Leipzig, 176, 396-41 3. Mahajan, C. L. (1967). The integument, exoskeleton and cutaneous sense organs of Sisor rabdophorus Hamilton. Proceedings of the National Institute o j Sciences of India, B33, 27-36. Majumdar, N. N. (1952). On the anatomy and histology of the palate of Cirrhina mrigala (Hamilton), with special reference to the papillae present on i t together with comments on their possible respiratory function. Journal of the Zoological Society of India, 3, 255-265. Majumdar, N. N. and Saxena, B. P. (1961). On the palatal organs of Labeo dero (Hamilton). Proceedings of the National Academy of Sciences, India, B31, 109-116. Maljukina, G. A. (1966). The functional peculiarities and the role of the organs of chemical sense in shoal behavior. Tesisy dokladov Vsesojuznogo Sovetschania P O ecologicheskoi Jisiologii ryb, 133-134. (In Russian.) Maljukina, G. A. and Chauschesku, I. (1966). The study of the role of chemoreception in the complex forms of behavior in fishes. Recue Roumaine de Biologie, serie zoologie, 11, 293-299. (In Russian.) Maljukina, G. A. and Schtefanesku, M. (1967). On the role of chemoreception in “ group effect ” in crucians. Voprosy ikhtiologii, 7, 415. (In Russian.) Marshall, N. B. (1965). Smell and taste. I n “ The Life of Fishes ”, pp. 14ti-149. Weidenfeld and Nicolson, London. May, R . M. (1925). The relation of nerves to degenerating and regenerating taste buds. Journal of Experimental Zoology, 42, 371-410. Mayser, P. (1882). Vergleichende anatomische Studien iiber das Gehirn der Knochenfische mit besonderer Beriicksichtigung der Cyprinoiden. Zeitschrift f iir wissenschaftliche Zoologie, 36, 259-367. Merkel, F. (1880). “ Uber die Endigungen der sensiblen Nerven in der Haut der Wirbeltiere.” Stiller, Rostock (cited by Herrick, 1903). Miller, R.J. and Evans, H. E. (1965). External morphology of the brain and lips in catostomid fishes. Copeia, no. 4, 467-487. Mitchell, E. G. (1904). Oral breathing valves of teleost.s, their modifications and relation to the shape of the mouth. American Naturalist, 38, 153-164. Miyadi, D. (1929). Notes on the skin and the cutaneous sense organs of some cobitoid and gasterosteid fishes, with special reference to the rudimentary nature of the lateral canal system. Memoirs of the College of Science, Kyoto Imperial University, B4, 81-96. Mohres, F. P. (1941). Untersuchungen iiber die Frage der Wahrnehmung von Druckunterschieden des Mediums. Zeitschrift f u r vergleichende Physiologie, 28, 1-42. Mohsin, S. M. (1962). Comparative morphology and histology of the alimentary canals in certain groups of Indian teleosts. Acta Zoologica, Stockholm, 43, 79-133.

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Moitra, S. K. and Sinha, G. M. (1971). Studies on the morpho-histology of the alimentary canal of a carp, Chagunius chagunio (Hamilton) with reference to the nature of taste buds and mucous cells. Journal of the Inland Fisheries Society qf India, 3, 44-56. Mookerjee, H. K., Gsngufy, D. N. and Mookherji, P. S. (1950). Study on the structures of the brains of some Indian fishes in relation to their feeding habits. Proceedings of the Zoological Society of Bengal, Calcutta, 3, 119-153. Moore, G. A. (1950). The cutaneous sense organs of barbeled minnows adapted to life in the muddy waters of tho Great Plains region. Transactions of the American iVlicroscopica1 Society, 69, 69-95. Murray, R . W. (1961). The initiation of cutaneous nerve impulses in elasmobranch fishes. Journal of Physiology, 159, 546-570. Murray, R. G. (1971). Ultrastructure of taste receptors. I n “Handbook of Sensory Physiology” (H. Autrum et al., eds.), Vol. IV, part 2, pp. 31-50. Springer-Verlag, Berlin, Heidelberg and New York. Nemetschek-Gansler, H. and Ferner, H. (1964). Uber die ultrastruktur der Geschmacksknospen. Zeitschrift fiir Zellforschung und mikroskopische Anatomie, 63, 155-178. Olivo, 0. M. (1928). Rigenerazione di organi scnsitivi in Amiurus nebatlosus. Bolletino della Societa italiuna di Biologia sperimentale, 3, 1019-1023. Olmsted, J. M. D. (1920). The nerve as a formative influence in the development of taste buds. Joiirnal of Comparative Neurology, 31, 465-468. Parker, 0. H. (1910). Olfactory reactions in fishes. ,lournal of Experimental Zoology, 8, 535-542. Parker, G. H. (1912). The relation of smell, taste and the common chemical sense in vertebrates. Proceedings of the Academy of Natural Sciences oj Philadelphia, 15, 219-234. Parker, G. H. (1914). The directive influence of the sense of smell in t.he dogfish. Bdletin of the U.S. Bureau of Fisheries, Washington, 33, 61-68. Parker, G.H. (1922). “Smell, Taste and Allied Senses in the Vertebrates”, 192 pp. J. B. Lippincot, Philadelphia. Parzefall, J. (1970). Morphologische Untersuchungen a n einer Hohlenform von Mollienesia sphenops (Pisces, Poeciliidae). Zeitschrift f u r Morphologie dei* Tiere, 68, 323-342. Pevzner, R . A. (1962). Cyto-histochemical studies of taste buds in bony fishes (Cyprinus carpio and Carassius carassius). Doklady Akademii Nauk SSSR, 147, 1187-1192. (In Russian.) Pevzner, R . A. (1964a). Distribution of suceinate dehydrogenase activity in the taste buds of some vertebrates. Doklady Akademii Nauk SSSR, 155, 191-196. (In Russian.) Pevzner, R. A. (196413). Distribution of acetylcholinesterase activity in the taste buds of some vertebrates. Doklady Akademii Nauk SSSR, 155, 930-934. (In Russian.) Pevzner, R. A. (1966). The oytochemical organization of taste buds in vertebrates. In. “ Primary Processes in the Receptor Elements of Sense Organs ”, pp. l l P 1 1 5 . Izd. Nauka, Moskwa. Pevzner, R . A. (1969). Structural and cytochemical bases of the mechaniem of taste buds function. Uspekhi sovremennoi biologii, 67, 53-67. (In Russian.) Pevzner, R . A. (1970). Electron microscopical study of the receptor and supportcells of taste buds in frog. Tsitologia, 12, 971-977. (In Russian.)

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Pictet, A. (1909). Contribution $. 1’6tude histologique du tube digestif des Poissons Cyprinoides. Revue suisse de Zoologie, 17, 1-78. Prasada Rao, P. D. (1967). Studies on the structural variations in the brain of teleosts and their significance. Acta Anatomica, 68, 379-399. Raffin-Peyloz, R. (1955). Etude histologique des barbillons de quelyues Poisson d’eau douce. Travauz d u Laboratoire d’Hydrobiologie et de Pisciculture de Z’Universite’ de Grenoble, 42, 73-97. Rajbanshi, V. K . and Tewari, H. B. (1968). Structure of the taste bud ofSaccobranchus fossilis. Zeitschrift fiir Biologie, 116, 22-28. Rajbanshi, V. K . and Tewari, H . B. (1969). Histochemical studies on the distribution of alkaline and acid phosphatases in the barbels of a fresh-water teleost, Saccobranchus fossilis. Acta Biologica Academiae Scientiarum Hungaricae, 20, 1-9. Retzius, G. (1912). Zur Kenntnis des Geschmacksorganes beim Kaninchen. Biologische Untersuchungen, Stockholm, N. F., 17, 72-80. Reutter, K.(1971). Die Geschmacksknospen des Zwergwelses Am iurus nebulosus (Le Sueur). Morphologische und histochemische Untersuchungen. Zeitschrift f u r Zellforschung und mikroskopische Anatomie, 120, 280-308. Reutter, K. (1973). Typisierung der Geschmacksknospen von Fischen. I. Morphologische und neurohistochemische Untersuchungen an Xiphophorus helleri Heckel (Poeciliidae, Cyprinodontiformes, Teleostei). Zeitschrift f u r Zellforschung und mikroskopische Anatomie, 143,409-423. Reutter, K., Breipohl, W-.and Bijvank, G. J. (1974). Taste bud types in fishes. 11. Scanning electron microscopical investigations on Xiphophorus, helleri Heckel (Poeciliidae, Cyprinodontiformes, Teleostei). Cell and Tissue Research, 153, 151-166. Rizhkov, L. P. (1970). The role of some receptors for formation of group effect in bream, Abramis brama (in Russian). Voprosly ikhtiologii, 10, 499-505. Sarbahi, D.S. (1940). The alimentary canal of Labeo rohita (Hamilton). Journal of the Royal Asiatic Society of Rengal, Science, 5 (1939), 87-116. Sarkar, H. L. (1959). Studies on the morpho-histology of the digestive system in relation to the food and feeding habits in a siluroid fish Mystus (Osteobagus)seenghala (Sykes). Proceedings of the Zoological Society of Bengal, Calcutta, 12, 97-109. SatB, M. (1937a). Preliminary report on the barbels of a Japanese goatfish, Upeneoides bensasi (Temminck & Schlegel). Science Reports of the Tdhoku Imperial University, Sendai, Ja p a n (Fourth Series, Biology), 11, 259-264. SatB, M. (193713). Further studies on the barbels of a Japanese goat,fish, Upeneoides bensasi (Temminck & Schlegel). Science Reports of the Tdhoku Imperial University, Sendai, J a p a n (Fourth Series, Biology), 11, 297-302. SatB, M. ( 1 9 3 7 ~ ) .On the barbels of a Japanese sea catfish, Plotosus anguillaris (LachppBde). Science Reports of the TBhoku Imperial University, Sendai, J a p a n (Fourth Series, Biology), 11, 323-332. SatB, M. (1937d). Histological observations on the barbels of fishes. Science Reports of the Tdhoku Imperial University, Sendai, J apan (Fourth Series, Biology), 12, 265-276. SatB, M. (1938). The sensibility of the barbel of Upenes spilurus Bleeker, with some notes on the schooling. Science Reports of the Tdhoku Imperial U n i versity, Sendai, Ja p a n (Fourth Series, Biology), 12, 489-500.

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Sat6, M. (1941). A comparative observation of the hind-brain of fish possessing barbels, with special reference to their feeding habits. Science Reports of the Tbhoku Imperial University, Sendai, Ja p a n (Fourth Series, Biology), 16, 157-164. SatB, M. (1942). Notes on the finger-like pectoral fins in three Japanese fishes. Science Reports of the Tbhoku Imperial University, Sendai, J apan (Fourth Series, Biology), 17, 1-8. Sat6, M. and Kapoor, B. G. (1957). Histological observations on the barbels of Indian fresh-water fishes, Alaska codfish and Podothecus acipenserinus. Annotationes Zoologicae Japonenses, 30, 156-1 61. Saxena, S. C. (1959). Adhesive apparatus of a hill-stream cyprinid fish, Garra mullya (Sykes). Proceedings of the National Institute of Sciences of India, B25, 205-214. Saxena, S. C. and Chandy, M. (1966). Adhesive apparatus in certain Indian hill-stream fishes. Journal of Zoology, London, 148, 315-340. Scharrer, E.(1935). Die Empfindlichkeit der freien Flossenstrahlen des Knurrhahns ( T r i g l a )fur chemische Reize. Zeitschrift f u r vergleichende Physiologie, 22, 145-154. Scharrer, E., Smith, S. W. and Palay, S. L. (1947).Chemical sense and taste in the fishes, Prionotus and Trichogaster. Journal of Comparative Neurology, 86, 183-198. Schemmel, C. ( 1967). Vergleichende Untersuchungen an den Hautsinnesorganen ober- und unterirdisch lebender Astyanax-Formen. Zeitschrift fur Morphologie der Tiere, 61, 255-316. Schmitz, E. H. and Baker, C. D. (1969). Digestive anatomy of the gizzard shad, Dorosoma cepedianum, and the threadfin shad, D . petenense. Transactions of the American Microscopical Society, 88, 525-546. Schnitzlein, H. N. (1964). Correlation of habit and structure in the fish brain. American Zoologist, 4, 21-32. Schulte, E. and Holl, A. (1971). Untersuchungen an den Geschmacksknospen der Barteln von Corydoras paleatus Jenyns. I. Feinstruktur der Geschmacksknospen. Zeitachrift fur Zellforschung und mikroskopische Anatomie, 120, 450-462. Schulze, F. E. (1863). Uber die becherformigen Organe der Fische. Zeitschrift f u r wissenschaftliche Zoologie, 12, 218-222. Schulze, F. E. (1870). Uber die Sinnesorgane der Seitenlinie bei Fischen und Amphibien. Archiv f u r mikroskopische Anatomie, 6, 62-88. Sheldon, R.E. (1909). The reactions of dogfish to chemical stimuli. Journal of Comparative Neurology, 19, 273-31 1. Singh, B. R. (1966). On the gill-structure of a cobitid fish, Lepidocephalichthys guntea (Ham.). Japanese Journal of Ichthyology, 14, 103-106. Singh, C. P. and Kapoor, B. G. (1967a). Histological note on the skin ofthe head of a cyprinid Labeo calbasu (Ham.). Annali del Museo Civic0 d i Storia Naturale d i Genova, 76, 211-216. Singh, C. P. and Kapoor, B. G. (1967b). Histological observations on the barbels of a bagrid catfish, Rita rita (Ham.). Japanese Journal of Ichthyology, 14, 197-200. Singh, C. P.and Kapoor, B. G. (1968). Contribution on the histology of the headskin of a carp, Cirrhina reba (Ham.). v 6 t n i k ceskoslovensk6 spoleEnosti zoologickd, 32, 27 2-274.

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Springer, 8. (1958). Field observations on large sharks. A.I.B.S. Shark Conference, New Orleans. Storch, V. N. and Welsch, U. N. (1970).Electron microscopic observations on the taste-buds of some bony fishes. Archivum histologicum japonicum, 32, 145-153. Strieck, F. (1924). Untersuchungen uber den Geruchs- und Geschmackssinn der Elritze (Phoxinus laevis A.). Zeitschrift fur vergleichende Physiologie, 2, 122-154. Sutterlin, A. M. and Sutterlin, N. (1970). Taste responses in Atlantic salmon (Salmo salar) parr. Journal of the Fisheries Research Board of Canada, 21, 1927-1942. Swarup, K. (1959). The morphology and histology of the alimentary tract of Hilsa ilisha (Hamilton). Proceedings of the National Academy of Sciences, I n d i a , B29, 109-126. Tandon, K. K. and Goswami, S. C. (1968). A comparative study of the digestive system of Channa species. Research Bulletin (N.S.)of the Panjab University, 19, 13-31. Tateda, H. (1961). Response of catfish barbels to taste stimuli. Nature, London, 192, 343-344. Tateda, H.(1964). The taste response of the isolated barbels of the catfish. Comparative Biochemistry and Physiology, 11, 367-378. Tateda, H. (1966). Taste receptors of organic acid and hydrogen ion in catfish and frog. Memoirs of the Faculty of Science, Ky ushu Gniversity, Pukuoka, J a p a n , Series E (Biology), 4, 95-105. Teichmann, H. (1962). Die Chemorezeption der Fische. I n “ Ergebnisso der Biologie (H. Autrum et al., eds.), Vol. XXV, pp. 177-205. Springer-Verlag, Berlin, Gottingen and Heidelberg. Tester, A. L. (1963). Olfaction, gustation and the common chemical sense in sharks. I n “Sharks and Survival” (P. W. Gilbert, ed.), pp. 255-282. D. C. Heath & Co., Boston. Tester, A. L. and Kendall, J. I. (1967). Innervation of free and canal neuromasts in the sharks Carcharhinus menisorrah and Sphyrna lewini. I n “Lateral Line Detectors ” (P.Cahn, ed.),pp. 53-69. Indiana University Press, Bloomington. Tester, A. L. and Nelson, G. J. (1967). Free neuromasts (pit organs) in sharks. I n “ Sharks, Skates and Rays ” (P. v”. Gilbert, R. F. Mathewson and D. P. Rall, eds.), pp. 503-531. The Johns Hopkins Press, Baltimore, Maryland. Tewari, H. B.and Rajbanshi, V. K. (1969). Histochemical studies on the distribution of alkaline phosphatase in the cutaneous gustatory epithelia of fresh-water teleosts. Acta Biologica Academiae Scientiarurn Hungaricae, 20, 269-279. Tewari, H. B. and Rajbanshi, V. K. (1971). Histochemical studies on the distribution of a few hydrolytic enzymes in cutaneous gustatory epit,helia of a freshwater teleost, Saccobranchus fossilis. Annales d’Histochimie, 16, 255264. Todd, J. H. (1971). The chemical language of fishes. Scienti$c American, 224, 98-108. Torrey, T. W. (1934). The relation of taste buds to their nerve fibers. Journal of Comparative Neurology, 59, 203-220. Torrey, T. W. (1936). The relation of nerves to degenerating taste buds. Journal of Comparative Neurology, 64, 325-336.

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Trudel, P. J. ( 1929). Untersuchuiigen iiher Geschinacksreaktioiieii der E’ische anf suoe Stoffe. Zeitschrift f u r vergleichende Physiologie, 10, 367-409. Trujillo-Cen6z, 0. (1961). Electron microscope observations on chemo- and mechano-receptor cells of fishes. Zeitschrift fiir Zellforschzing und mikroskopische Anatornie, 54, 654-676. Uchihashi, K. (1953). Ecological study of Japanese teleosts in relation to the brain morphology (in Japanese). Bulletin of the J a p a n Sea Regional Fisheries Research Laboratory, Niigata, no. 2, 1-166. Uga, S. and Hama, K. (1967). Electron microscopic studies on the synaptic region of the taste organ of carps and frogs. Journal of Electron Microscopy, 16, 269-276. Wagner, C. E. (1953). Dedifferentiation of taste bud cells following transection of their nerve supply. Anatomical Record, 115, 442. Weber, E. H. (1827). Ueber das Geschmacksorgane des Karpfen und den Ursprung seiner Nerven. Archiv f u r Anatomie und Physiologie, 309-315 (cited by Moore, 1950). Weber, H. ( 1963). Die Sinnesfunktion der freieri Bauchflossonstrahlen der Labyrinthfische (Anabantidae) und ihr Zussammenwirken mit den Augen. Zeitschrift f u r vergleichende Physiologie, 47, 77-1 10. Weisel, G. F. (1962). Comparative study of the digestive tract of a sucker, Catostomus catostomus, and a predaceous minnow, Ptych,ocheilus oregonense. American Midland Naturalist, 68, 334-346. Weisel, G. F. (1968). The salmonid adipose fin. Copeia, no. 3, 626-627. Welsch, U. and Storch, V. (1969). Die Feinstruktur der Geschmacksknospen von Welsen [Clarius batrachus (L.) und Kryptopterus bicirrhis (Cuvier et Valenciennes)]. Zeitschrift f u r Zellforschung und mikroskopische Anatomie, 100, 552-559. Western, J. R. H. (1969). Studies on the diet, feeding mechanism and alimentary tract in two closely related teleosts, the freshwater Cottus gobio L. and the marine Parenophrys bubalis Euphrasen. Aeta Zoologica, Stockholm, 50, 185205. Whitear, M. (1952). The innervation of the skin of teleost fishes. Quarterly Journal of Microscopical Science, 93, 289-305. Whitear, M. (1965). Presumed sensory cells in fish epidermis. Nature, London, 208,703-704. Whitear, M. (1971). Cell specialization and sensory function in fish epidermis. Journal of Zoology, London, 163, 237-264. Wright, R. R . (1884). On the skin and cutaneous sense-organs of Amiurus. Proceedings of the Canadian Institute, Toronto (New Scrics), 2, 251-269. Wunder, W. (1927). Sinnesphysiologische Untersuchungen iiber die Nahrungsaufnahme bei verschiedenen Knochenfischarten. Zeitschrift fiir vergleichende Physiologie, 6, 67-98. Wunder, W. (1936). Physiologie der Susswasserfische Mitteleuropas. In “Handbuch der Binnenfischerei Mitteleuropas” (Demo11 and Maier, eds.) E. Schweizerbart’sche Verlagshuchhandlung, Vol. I1 B, pp. 174-198. Stuttgart. Wunder, W. (1957). Die Sinnesorgane der Fische. Allgemeine Fischerei-Zeitung, 82, 3-24.

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Yamaguchi, M. (1961). Taxonomic and ecological studies on the Japanese cyprinoid fishes on the basis of brain morphology. Nagasaki Prefecture Eqdoration Station. 60th Anniversary Reports, 1, 1-1 19. (In Japanese.) Yamashita, E. (1965). Physiological properties of freshwater fish barbels. I n " Symposium on Comparative Neurophysiology ". Tokyo. Zippel, H. P. and Domagk, G. F. ( 1 9 7 1 ~ ) .Transfer of taste preference from trained goldfish (Carassius auratus) into untrained recipients. PflQigers Archiv fur die gesamte Physiologie des Menschen und der Tiere, 323, 258-264. Zippel, H. P. and Domagk, G. F. (1971b). Experiments concerning the transfer specificity of brain extracts in the taste discrimination of goldfish. PJtigers Archiv fur die gesamte Physiologie des Menschen und der Tiere, 323, 265-272.

Adv. mar. B i d , Vol. 13, 1975, pp. 109-239

THE ALIMENTARY CANAL AND DIGESTION IN TELEOSTS B. G. KAPOOR Department of Zoology, University of Jodhpur, Jodhpur, India

H. SMIT Zoology Laboratory, University of Leiden, Leiden, Netherlands AND

I. A. VERIGHINA Zoological Museum, Moscow Xtate University, Moscow, U .X.X. R. .. I. Alimentary Canal, Food and Feeding Habits .. 11. Morphology, Histology and Cytology . . . . A. Mouth, Buccal Cavity and Pharynx . . . . B. Oesophagus .. .. . . .. .. C. Stomach . . .. . . . . . . .. D. Intestine . . . . .. .. .. .. E. Rectum . . .. . . .. .. .. .. .. .. 111. Elect,ron Microscopic Findings .. .. .. .. IV. Histo- and Cytochemistry .. .. .. V. Innervation and Allied Aspects .. .. .. .. .. .. VI. Food Intake .. .. .. .. .. VII. Digestion Rate . . .. .. .. .. .. V I I I . Digestive Enzymes A. Pepsin . . .. .. .. .. .. B. Trypsin . . .. .. .. .. .. C. Carbohydrases . . .. .. .. .. D. Lipase .. . . .. .. .. .. E. Other Enzymes . . .. . . . . .. F. Digestive Enzymes &g Related t o the Diet . . .. .. .. IX . Regulation of Gastric Secretion .. X. Absorption and Conversion of Food . . . . .. . . .. .. .. .. XI. Conclusions , . .. .. .. .. XII. Acknowledgements .. .. .. .. .. .. XIII. References

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I. ALIMENTARY CANAL,FOOD AND FEEDING HABITS Fishes occupy different ecological niches and trophic levels and most efficiently face the challenges of a complex aquatic life. I n a teleost fish, the alimentary canal, though of simpler form than that of higher vertebrates, successfully accomplishes a variety of functions. Besides processing the food, certain parts of the alimentary canal may have 108

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evolved into air-breathing organs and also serve in osmoregulation. I n addition, the canal has become more interesting due to the loss of the stomach and gastric glands in many taxons of teleosts. Since the publication by Barrington (1957) of a chapter dealing with the alimentary canal and digestion in fish, contributions have been published on various fish, but there are many species, chiefly the deep-sea inhabitants and migratory forms, which remain t o be investigated. Interest in this field has intensified owing to the identification of various structurally and functionally distinct cells in the alimentary tract of fish. I n sharp contrast to other vertebrates, fishes consume a great variety of food and there are many modes of feeding. Based on the nature of the food taken, these consist of often overlapping categories, namely (I) herbivores and detritophags, (11)omnivores, consuming small invertebrates, and (111)carnivores, consuming fishes and bigger invertebrates. Often the diet is mixed. According to the diversity of their food, fishes are classified as (I) euryphags, with a mixed diet, (11)stenophags, with a limited assortment of types of food, and (111) monophags, consuming only one sort of food, e.g. crustacea-feeders, mollusca-feeders, etc. According to the feeding conditions some ecological groups are distinguished, for example, pelagic planktonfeeders, benthos-feeders, etc. (see Suyehiro, 1942; Al-Hussaini, 1947a; Gohar and Latif, 1959; nas and Moitra, 1963; Nikolsky, 1963, 1974). Herbivorous, omnivorous and carnivorous fishes can be found in t,he same family, for example the Cyprinidae, although amongst the toothless Cyprinidae, carnivorous species are rare. Some fishes lead a parasitic mode of life (Nikolsky, 1963). Facial structures (Gregory, 1933; Al-Hussaini, 1947b; Mookerjee and Ganguly, 1951), sensorial factors (Nikolsky, 1963; de Groot, 1969; Bardach and Atema, 1971; Hara, 1971) and brain patterns (Aronson, 1963; Davis and Miller, 1967; Prasada Rao, 1967; Hara, 1971) provide an index of the feeding behaviour of the fish. The feeding habits of the adult fish become apparent when a single organ or a few organs are examined or sometimes only when every organ of the digestive system has been examined (see Suyehiro, 1942). Some fishes fast during winter and the spawning season (Suyehiro, 1942). The feeding habits of fishes are different according to locality, season, age or sex (Suyehiro, 1942). Emphasis on the influences of some of these factors has been placed by Pillay (1953) and Moitra (1956). The advantage of adaptability has been discussed by Groenewald (1964) on the basis of a piscivore; Clarins gnriepinus Burchell living in certain Transvaal waters takes aquatic and terrestrial invertebrates as auxiliary or emergency food and

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111

this feature makes it a very successful species capable of populating and surviving in virgin waters devoid of any fishes on which it can prey. Many researches have been conducted on the extent of adaptation of the alimentary tract in fully grown teleosts to a particular kind of natural diet (e.g., Ghazzawi, 1935; Suyehiro, 1942; Al-Hussaini, 1945, 1946, 1947a, b, 1949a; Angelescu and Gneri, 1949; Girgis, 1952b; Kapoor, 1953, 1957c, 1958a, b; Pillay, 1953; Khanna, 1961; Mohsin, 1962; La1 et al., 1964; Sehgal, 1966a; Lal, 1968; Schmitz and Baker, 1969; Sehgal and Salaria, 1970; Sriwastwa, 1970a, b ; Bucke, 1971; Verma et al., 1974b, c). It has been found that different species with the same type of diet may differ in the structure of the alimentary system, but the functional adaptations related to the nature of food and feeding habits remain similar (Angelescu and Gneri, 1949), although the degree of relation between digestive tract and food varies. Angelescu and Gneri (1949)reported multiple specialization of the digestive apparatus in an iliophagous fish, Prochilodus lineatus (Val.). Moreover, Greenwood (1964) found Haplochromis species (Cichlidae) of lake Victoria showing wide adaptive radiation so making the best use of every available food, and grouped them into: I. a generalized insectivorous species ( H . macrops (Blgr)), 11. a " winkle-picking " mollusc-eater ( H . sauwagei (Blgr)), 111. a species feeding on embryos and larvae obtained from the mouth of brooding females ( H . parwidens (Blgr)),and IV. a piscivorous predator ( H . cawifrons (Hild)). Fryer and Iles (1972) also describe such radiation in Cichlidae of the African Great Lakes. Nikolskaya and Verighina (1974) mention some characteristics in the structure of the alimentary canal of some Pleuronectidae living in different ecological niches. Harder (1960) and Bishop and Odense (1966) raised doubt as to the relation between feeding habits and gut structure; the latter also pointed out that the food of the carnivorous cod Gadus morhua L. is not specialized and varies with population, season and size of the individual. It is known that the structure of the digestive apparatus is related to the form of the body. Besides the food and feeding habits, the phylogeny of a species is another important factor in the final construction of the digestive apparatus (Suyehiro, 1942 ; Al-Hussaini, 1949a; Angelescu and Gneri, 1949). Weisel (1962) reported that a macrophagous, toothless cyprinid Ptychocheilus oregonense (Richardson), a predator on small salmon, has inherited the stomachless condition from its suctorial ancestors, the catostomids, but has evolved

112

U . C . KBPOOR, H. SMIT AND I. A. VERIOHINA

mechanisms to compensate for ancestral deficiencies, though a stomach and teeth would better equip the species to a piscivorous life. The feeding behaviour is a species characteristic formed during its evolutionary history (Nikolsky, 1963). Consideration of two components-the relative length of the gut (AI-Hussaini, 1947a, 1949b ; Girgis, 1952b ; Al-Hamed, 1965)) and the surface area of the intestinal mucosa (Al-Hussaini, 1949a ; Unnithan, 1965; Konfal, 1966; Siankowa, 1966) has been made. The length of the gut in Characinoidei is associated with the feeding habits (Table I ) . The longest intestine occurs in microphagous and in herbivorous species, the food of which contains a high proportion of undigestible material. Even in two species of Distichodus ( D . niloticus (L.) and D.rostratus (Gunth.)) with only quantitative differences in feeding habits, the relative gut-length is clearly connected with the different feeding habits, particularly with the quantity of indigestible material (Fig. 1). The length of the gut is exactly connected with the feeding habits in Cyprinidae (Table 11). The greatest length is observed in species that feed on detritus and algae (microphags), the food of which contains a high portion of indigestible ballast (sand, mud, cellulose, etc.), but this length varies in different taxons (Tables I and 11). The carnivorous species have the shortest gut. It has been suggested that in some cases differences in relative gut-length depend on the presence of a " gizzard " or some other structures in the forepart of the alimentary canal (pharyngeal teeth; pharyngeal or oesophageal sacs) which triturate the food (see Verighina and Medani, 1968; Verighina, 1969b, Table IV). Quantitative data about the correlation between the surface area of the gut and the feeding habits are not numerous (Al-Hussaini, 1949a; Unnithan, 1965; Siankowa, 1966). I n some fishes, particularly in microphagous Cyprinidae: Xenocypris (Borutsky, 1950), Labeo (Girgis, 1952b), Hypophthalmichthys (Verighina, 1961), Varicorhinus (Verighina, 1969a), and in Cichlidae: Tilapia mossambica (Peters) (Verighina, 1967), the great length of the gut compensates for poor development of folds which do not hamper the passing of roughage through the intestine. On the other hand complicated branched folds can be found in highly specialized predators, e.g. Ptychocheilus (Weisel, 1962), Elopichthys (Verighina, 1963), Parasilurus and Siturus soldatowi Nik & Soin (Verighina 1965), which have a short intestine (see Verighina, 1963, Fig. 1 Verighina, 1965, Fig. 5 ) . The gut-length depends upon the relation ships between the components in the diet of omnivorous fishes. Con siderable variability of intestinal length occurs in some species. Vicken (1962) and Shuljak (1968) drew attention to the variability of thc

TABLEI. STRUCTURE OF

RELATIVELENGTH OF THE GUT IN DIFFERENT FEEDING HA4BITS

THE STOMACH AND

WITH

Structure of the stomach Species

PyrrhulinaJilamentosa. Cuv. & Val. Alestes macrolepidotus Gunth.

A. kotsehyi Hydrocyon forskalii Cuv. Serrasalmo sp. Ichthyoborus besse Joan Distichodus niloticus (L.) D . rostratus Giinth. Xenocharax spilurus Gunth.

blind sac

musc. stom.

+

+ + + (small)

+ + + + +

Insectivorous -

Authors

+ + + +

Daget, 1960

Mainly carnivorous Carnivorous 0.7-1.05 Pterophag 2.77 Plants and detritus 2.35 Plants and detritus 2.0 Plant and invertebrates 1.8 Plant and invertebrates (well devel.) 4 Microphag (well devel.) 4-5 Microphag 4-75 Microphag (well devel.) (well devel.) 4.5-6.2 Micr0pha.g (well devel.) 6-0-7.5 Microphag 3 Microphag c 3 Microphag 0.75 0.8

-

Feeding habits

CHARACTNOID FISHES

Jacobshagen, 1911,1913,1915 Jacobshagen, 1911,1913,1915 Rowntree, 1903 Rowntree, 1903 Rowntree, 1903 Rowntree, 1903 Daget, 1967 Verighina and Medani, 1968 Verighina and Medani, 1968 Jacobshagen, 1911,1913,1915

1.0 1

I

Xenocharax spilurus Giinth. Citharinus congicus Blgr. C . macrolepis Blgr. C . distichodoides C . gibbosua Blgr. C . cithcsrus (Geoffroy). Prochilodus sp., Curimatus sp. P . lineatus (Val.)

Relative length of the gut

SOME

+

Daget, 1962 Daget, 1962 Daget, 1962 Daget, 1962 Daget, 1962 Rowntree, 1903 Rowntree, 1903

300

200

2-

100

20

40 Length ( c m )

(c) FIQ.1. Digestive tract of (a) Distiehodus niloticus (L.) and (b) D. rostmtus (Giinth.) (c) relative length of the gut &/I) of both Distorhodus species in connection with their feeding habits. 1 : 1,/1 ; 2 : percentage of green plants in food. From Verighina, I. A. and Medani, J. I. (1968). Voproay ikhtiologii, 8, 710-721. (0) has been modified.

THE ALIMENTARY CANAL AND DIGESTION I N TELEOSTS

115

intestine length in Carassius and connected this with the individual character of the diet during ontogenesis. AganoviE and VukoviE (1966) in Aulopige hugelii Heckel and VukoviE (1966) noted in Barbus meridionalis Heckel variabilities of the intestine length in various local groups which live in conditions of different food supply. I n the local groups which had satisfactory food supply intestinal length and variability were less than when feeding conditions were unsatisfactory. Shuljak (1968) described some anomalies in the intestinal structure in low-bodied forms of Carassius auratus gibelio (Bloch) as a result of bad

FIQ.2. Ciliated epithelium in the fore-gut of Ctenopharyngodon idella (Val.). (haem.eos.) (Verighina.)

food supply. The length of the gut is a variable entity which reacts sensitively to changes in feeding condition. However, in fish-stenophags such plasticity will be limited by their narrow specialization, as described by Spanovskaya (1961) in some gudgeons and by Verighina (1963) in Elopichthys bambusa (Rich.). The mutual dependence of the intestine length and feeding habits occurs not only in adult fishes but also during development. Lange (1962) showed in three sub-species of Rutilus an increase of intestinal length with increasing amounts of indigestible matter (shells of Mollusca or periphyton) in the diet (Table 111). It is also interesting that intestinal length varies between the sexes of Rhodeus sericeus amarus (Bloch) (Dumitru and Mihai, 1962). Stroganov and Buzinova (1971) investigated seasonal and ngerelated changes in the liver and intestines of Ctenopharyngodon idella

TABLErr. FEEDING HABITS AND RELATIVE LENGTH OF GUT IN SOME CYPRINIDAE

Species

Labeo horie (Cuv.) L. lineatus Blgr. L. variegatus Pell. L . niloticus (Forsk.) L. horie (Cuv.) Cirrhina mrighala (Ham.) Hypophthalmichthys molitrix (Val.) Varicorhinus heratensis Keys. V . cupoeta sevungi (Fil.) V . tanganicae Blgr Catla catla (Ham.) Garra dembensis (Rupp.)

G. congolensis Pell. Ladislavia taczanowskii Dyb.

Feeding habits

Algae, detritus Algae, detritus Algae, detritus Algae, detritus Algae, detritus Algae, detritus Phytoplankt,on Algae, detritus Algae, detritus Periphyton, plants, insect larvae Periphyton, plants, insect larvae Algae, invertebrates Algae, invertebrates Algae, invertebrates

Relative length of the gut

Authors

15-5 16.1 16.95 16.9 15-21 8 13 6-7.5 6-94 5

Matthes, 1963 Matthes, 1963 Matthes, 1963 Matthes, 1963 Girgis, 1952b Jacobshagen, 1911,1913,1915 Bromlej, 1936 Grib and Krasyukova, 1949 Verighina, 1969a Matthes, 1963

4.68

Kapoor, 1958b

4.5 4.5 2.0-2.5

Matthes, 1963 Matthes, 1963 Spanovskaya, 1961

Oreinus sinuatus (Gunth.) Ctenopharyngodon idella (Val.) Amblypharyngodon mola (Ham.) Barbua sharpeyi Gunth. B . grypus (Heckel) B . tor (Ham.) B . ticto (Giinth.) Labeo calbasu (Ham.) Gobio gobio (L.) Rostrogobio amurensis Tar. Leptocypris modestus Blgr. Compostornabarbus wittei Day Engraulicypris minutus (Blgr.) Chelethiops elongatus (Blgr.) Erythroculter erythropterus (Bas.) Elopichthys bambusa (Rich.) Barilius moorei Blgr. B . chrysti Blgr. CheEa bacaila (Ham.) Ptychochedus oregonense (Rich.)

Plants Plants Plants Plants Plants Invertebrates, plants Invertebrates, plants Plants, weeds, algtte, diatoms Invertebrates 1nvert.ebrates Invertebrates, plants Zooplankton Zooplankton Zooplankton Carnivorous, insects Carnivorous Carnivorous Carnivorous Carnivorous Carnivorous

3.78 2.5 2.8 2.79-3.18 2.00-2'76 1.24 1.58 3.75-10.33

Khanna and Pant, 1964 Hickling, 1966 Khanna, 1961 Al-Hamed, 1965 Al-Hamed, 1965 Khanna and Pant, 1964 Khanna and Pant, 1964 Sehgal, 1966a

0.8-0.81 0'8-1.4 0.85-0.1 0.7-0.85 0.7 0.75 0.77-1.50 0.63 0.65-0.8 0.65-0.8 0.88 0.78

VukoviE, 1966 Spanovskaya, 1961 Matthes, 1963 Matthes, 1963 Matthes, 1963 Matthes, 1963 Verighina, 1963 Verighina, 1963 Matthes, 1963 Matthes, 1963 Khanna, 1961 Weisel. 1963

118

B. G. KAPOOR, H. SMIT AND I. A. VERIGHMA

TABLE111. 1,/1 AT DIFFERENTDEVELOPMENTAL STAGESIN THE ROACH ( R . rutilus), CASPIANROACH ( R .rutilus caspius) AND CUBANIANROACH ( R . rutilus heckeli) (According t o Lange, 1962) Stage

Sit bspecies

Feeding habits ~-

~~

A B

C

Roach Casp. roach Cuban. roach Roach Casp. roach Cuban. roacli Roach Casp. roach Cuban. roach Roach Casp. roach Cuban. roach Roach Casp. roach Cuban. roach Roach Casp. roach Cuban. roacli

1

I } I

1,/1(%I

Yolk

45-49

Mixed diet with yolk a n d exogenous food

42-45

Algae, Rotatoria, small Nauplii

42-45

Cladocera

75-89

Cladocera arid periphyton

90-95

Crustacea and periphyton

90-95

Crustacea, larvae, insects, algae

100-112

I d e m a n d Mollusca

120-130

(Val.) and Hypophthalmichthys molitrix Val. Length and weight of the intestines and weight of the liver with respect to body weight changed at different ages and a t different times of the year. Angelescu and Gneri (1949) reported that the intestinal coefficient varies with age and nutiitional conditions in Prochilodus lineatus. During starvation a reduction of 30% in body height and a diminution of 30-45y0 in intestinal length, as well as a loss of weight of more than 70% takes place. The values were higher during periods of intensive feeding and declined in autumn and winter and with age. 11. MORPHOLOGY, HISTOLOGY AND CYTOLOGY The alimentary canal in a teleost is composed of “Kopfdarm” (mouth, buccal cavity and pharynx) and “ Rumpfdarm ” (remainder of the alimentary canal), the latter is efficiently equipped with sphincters and valves a t various regional junctions. The order of the various layers in different regions of the gut is generally uniform and regular in a teleost, often highly infiltrated by granulocytes and lymphocytes; only strata compactum and granulosum are not uniformly present in the alimentary canal of all fishes (see Mohsin, 1962).

J 19

THE ALIMENTARY CANAL AND DIGESTION I N TELEOSTS

A . Mouth, buccal cavity and phargnz The mouth, buccal cavity and pharynx are associated with the selection, seizure, orientation and predigestive preparation of the food. The form and position of the mouth, dentition on the jaws and in the bucco-pharynx and the gill rakers show a close relation with the mode of feeding and the kind of food (Al-Hussaini, 194713 ; Tortonese, 1952;

FIG.3. Position of the mouth in some Coregonidae. (a) C . sardinelln Val., (b) C. autumnalis (Pallas), (c) C . Zawaretus pidschian (Gmel.). After Nikolsky, G . V. (1971). Tshasnaya ikhtiologia ‘‘ Vysshaya Bhkola ”, Moscow.

Gohar and Latif, 1959; Khanna, 1962; Greenwood, 1964; Kazansky, 1964; Khanna and Pant, 1964; Dalela, 1969 and many others). Descriptions of mouth types are given by Suyehiro (1942);Al-Hussaini (1947b), and Nikolsky (1963) (Fig. 3). Interest in the mechanics of feeding action in teleosts has recently increased due largely to the papers of Alexander (1966, 1967a, b, 1969, 1970), a study by Osse (1969), and a brief account by Gupta (1971), but this work has not been conA.1M.R.-13

5

120

B. G. KAPOOR,

H.

SMIT AND I.

A. VERIGHINA

sidered here. Earlier, the cycle of events in the feeding process was considered by Al-Hussaini (1949a), Girgis (1952a), Greenwood (1953), Matthes (1963), Branch (1966), Field (1966) and Vrba (1968). Greenwood (1964) reported that the paedophagous Haplochromis parvidens has large and expansible jaws and quite poor oral dentition. It engulfs the snout of a mouth-breeding female and consequently forces her to jettison the brood direct into its mouth. Bogachik (1969) detailed the mechanism of breaking and splitting of shells in the labrids Ctenolabrus and Crenilabrus. Common histological features in the wall of the bucco-pharynx and associated structures are a stratified epithelial lining on a basement membrane provided with mucous cells and taste receptors in varying numbers, and the striated muscle in the subepithelial tissue. MUCUS production and gustation are the main functions. Besides, some teleosts possess large club-cells in bucco-pharyngeal epithelia, usually with a central nucleus and without an opening to the exterior (Vanajakshi, 1938; Islam, 1951; Al-Hussaini and Kholy, 1953; Kapoor, 1953; Sarkar, 1959; Ishida and Sat6, 1960; Sehgal, 1960; Khanna, 1964 ;Pasha, 1964a ;Agrawal and Sharma, 1966 ;Khanna and Mehrotra, 1970; Medeiros et al., 1970a). Sac-cells, exactly like the mucous cells in form but different in staining reaction, have been seen in the buccopharyngeal mucosa of Ophicephalus species (Islam, 1951 ; Singh, 1967a, b). The lips, the primary food procuring organs, assume different forms and may be adhesive in some teleosts. Girgis (1952a, b) observed a stratum eorneum and even horny protuberances on the lips of the herbivorous bottom-feeder Labeo horie (Cuv.). Two sharp horny cutting edges in the upper and lower borders of the mouth immediately inside the lips enable the fish to take up food. A horny cutting edge on the lower lip is present in the periphyton-eater Chondrostoma nasus variabile Jak. (Verighina, 1971). Horny plates on the inner face of the lips in Noemacheilus barbatulus L. are used in trituration (Mester, 1971). The granular processes on the very broad queer lips of bottom-feeding Pseudogobio esocinus (T. & Schl.) are important food finders (Suzuki, 1956). Recently, Branson and Hake (1972) noted the rich vascularization of the lips (and bucco-pharyngeal tissues) of Piaractus nigripinnis (Cope), indicating a respiratory function in this fish which inhabits waters poor in oxygen. The buccal valves, found in many teleosts in a variety of forms (Saxena, 1958; Bellisio, 1962), are usually provided with taste buds (Kapoor, 1957a; cf. Nagar and Khan, 1958). Furthermore, the participation of the lower oral valve in mouth brooding of the cichlid

THE ALIMENTARY CANAL AND DIGESTION I N TELEOSTS

121

aeophagus jurpari Heckel (Reid and Atz, 1958) and the apogonid Cheilodipterus a@& Poey (Smith et al., 1971) has been indicated. Only the bucco-pharynx bears a variety of specialized structures for specific purposes. The " lamellar organ " of the palate in Labeo horie presumably represents an expansion of the sensory surface of the buccal mucosa (Girgis, 1952b) ; in Cirrhina mrigala (Ham.) it serves as an accessory respiratory organ (Majumdar, 1952) and in Labeo dero (Hem.) it has a digestive function (La1 et al., 1964b ; cf. Majumdar and Sexena, 1961). The palatine cushions in Gobio gobio (L.) act as food selectors (Al-Hussaini, 1949a). The tongue, not always sharply demarcated and not freely movable, rarely with a movable tip, generally possesses a skeletal support, striated muscles and connective tissue (Kapoor, 1957d ; Maggese, 1967 ; Mikuriya, 1972). A thin keratinization of tongue epithelium has been observed in Gadus morhua (Bishop and Odense, 1966). The tongue is better developed in carnivorous, particularly piscivorous species (Khanna, 1959). Tandon and Goswami (1968) expressed the view that the tongue of Channa species, apart from supplementing the function of the teeth in the retention of prey, may also compensate for the absence of barbels and other integumentary sense organs. The protrusible tongue in the microphagous Dorosoma petenense (Gunth.) is an adaptation for occasional zooplankton predation (Schmitz and Baker, 1969). I n adult Plecoglossus altivelis T. & Schl. a fleshy tongue-lappet, comprising a main median flap and two lateral flaps arising from the posterior part of the main flap and devoid of skeletal structures, extends from the symphysis to the tongue (Iwai, 1962). This, in association with comb-like teeth on the jaws and with a profuse mucus secretion by mucous cells on the tongue-lappet and by palatal glands opposite to it, collects the algal particles scraped off by the comb-like teeth. Recently, Mikuriya (1972) discussed briefly four gross and histologically different structures in Actinopterygii, all considered to be tongues. The palatal glands in P . altivelis, composed of columnar cells with basal nuclei, probably also secrete digestive enzymes (Iwai, 1962). A thick or cushiony papillated palatal organ (pharyngeal pad), is reported in some members of Cyprinidae, Catostomidae, Cobitidae, (see Curry, 1939; Dorier and Bellon, 1952; Girgis, 1952a, b ; Majumdar, 1952; Jara, 1957; Majumdar and Saxena, 1961; Weisel, 1962; La1 et at., 1964b; Khanna and Pant, 1964; Miller and Evans, 1965; Eastman, 1971; Mester, 1971) and Salmonidae (Sutterlin and Sutterlin, 1970). This organ removes excess water from the ingested food (Jara, 1957). Its role in assisting in feeding and its gustatory function are generally

122

B. G. KAPOOR. H. SMIT AND I.

A. VERIGHINA

agreed; its alleged accessory respiratory function (Majumdar, 1952; Majumdar and Saxena, 1961) is still uncertain. Verigin (1957) supposed that the deep longitudinal folds in the palate of Hypophthalmichthys molitrix conduct the water currents towards the centre. Pharyngeal glands have been reported in certain mouth-breeding teleosts. Oppenheimer (1970) listed them and analysed divergent views on the bactericidal properties of mucus, and discussed the function of mucus as a lubricant, in the prevention of coughing, and as a food source for the fry. He suggested that these glands may actually function in feeding as well as in parental care, a t least in herbivorous cichlids (some mouth-breeding cichlids are carnivorous). The pharyngeal valve hanging in the roof of the pharynx in scarid fishe3 probably rejects over-large pieces of coral (Al-Huseaini, 1945) or prevents them from passing anteriorly while being ground up by the pharyngeal teeth (Gohar and Latif, 1959). Large amounts of mucus are dischzrged to lubricate the food while it is being ground up (Gohar nnd Latif, 1961). Attention has recently been paid to epibranchial organs, accsssory to the digestive system, in lower teleosts (Svetovidov and Skvorszowa, 1968; Bertmar et al., 1969; Miller, 1969; Schmitz and Baker, 1969). Bertmar et al. (1969) have reviewed the early litemture, dealing with the epibranchial organs of fish, describing distribution and position, accessory elements, morphology, histology, innervation, ontogeny, food contents, function, and phylogeny. The paired epibranchial organs lie above the posterior branchial arches, on either side of the midline. The lumen of each organ appears as an anteriorly extending diverticulum of the posterior roof of the pharynx. Seven general types of epibranchial organs have been recognized: (I)a primitive expanded sac, (11)a continuous tube. (111)a spiral tube, ( V I ) a derivative sac, ( I V ) a vestigial tube, (V) an entrance canal into a blind sac, and ( V I I ) a tube with leaf-like lobes. Fishes with epibranchial organs feed on a range of organisms, from phytoplankton (by filtration) to small fish (by selection). For details of the epibranchial organs in Hypophthalmichthys molitrix (Fig. 4) see the above-mentioned review and papers by Verigin (1957),Wilamovsky (1972) and Bertmar (1973). A probable mechanism of the organ’s function is discussed by Verighina (1972). Schmitz and Baker (1969) confirmed the views on these organs, held by Bertmar et al. (1969), in their study of cohabiting species, Dorosoma cepedianum (Le Sueur) and D . petenense. Another set of interesting but generally overlooked structures, the pharyngeal organs (pharyngeal cushions, pharyngeal pads, hanging pharyngeal disc-,), structurally and functionally totally different from

THE ALIMENTARY CANAL AND DIGESTION IN TELEOSTS

123

the epibranchial organs though similarly located occur on both sides of the pharynx in various species of Mugil (Ghazzawi, 1935; AlHussaini, 1947b ; Pillay, 1953 ; Mahadevan, 1954; Thomson, 1954; Nagar et al., 1961 ; Kawamoto and Higashi, 1965 ; Agrawal and Bale, 1967 ; Yoshida, 1967). According to Kawamoto and Higashi (1965), each organ in M . cephalus L. is round, flattened anteriorly and sunken interposteriorly, with neither any evidence of contained food nor any direct connection of the organ with the pharyngeal cavity. The organ

FIG.4. External view of the epibranchial organ of Hypophthalmichthya molitril: (Val.). After Verigin, B. V. (1967). Zoo~oqiacheakijZhurnal, 36, 696-602.

has many small pharyngeal teeth over the entire outer surface and many taste buds in the epithelial tissue between the pharyngeal teeth of the posterior side and many strong spines on the outer surface of the ring wall of its anterior part. It is supported by a thin bony skeletal system of cylindrical bones firmly connected by epipharyngeal bones, and hangs freely from the upper side of the pharyngeal cavity. There is a considerable change in size and shape of the pharyngeal lobe in the sea and in fresh water. Al-Hussaini (1947b) reported that the superficial teeth on the pharyngeal organs are absent in Mugil auratus Risso. Thomson (1954) stated that the teeth on t8he pharyngeal organs

124

B. 0. KAPOOR, H. SMIT AND I.

A. VERIQHINA

become more numerous or apparent with age in Australian species of mullet. Fukusho (1972), describing the organogenesis of the digestive system of Lixa haeniotocheila T. & Schl., also dealt with the development of the pharyngeal organs. Functionally, the presence of generally claw-shaped teeth with forked bases and fibrous ligaments, with their tips directed towards the opening of the pharynx, and that of taste buds on the external surface of the organ, indicate an auxiliary digestive role. The teeth, together with the nearby, curved, triangular special gill rakers of the modified fifth branchial arch, act in selecting food from the ingested material and conveying it to the pharynx. The lack of a connection between the pharynx and the cavity of the organ indicates that it cannot be a temporary concentrating site (Kawamoto and Higashi, 1965). Their roles in straining (Pillay, 1953; Nagar et al., 1961; Agrawal and Bala, 1967) and in food selection (Mahadevan, 1954), had been described earlier. Yoshida (1967) stated that the detritus and microbenthos feeder, Mugil cephalus, seems to strain the food contained in bottom muds by the first and second gill rakers, and drain and concentrate it by the action of the third and fourth gill rakers, hanging pharyngeal discs and pharyngeal rakers. Kawamoto and Higashi (1965) thought that a possible role played by the organ is as a centre of osmoregulation in this euryhaline fish, in view of the isotonity of the organ-fluid with serum as well as some structural characteristics. Further, the organhistology indicates that it does not act as a subsidiary respiratory centre nor does it have haematogenic significance. Pads on the roof and the floor of the pharynx, bearing numerous fine bristles, act as an effective filter in some gobiids (Venkateswarlu, 1962). Dentition in fish varies greatly. The teeth vary widely in position, even the lip (Pillay, 1953) and tongue (Thomson, 1954; Khanna, 1959; Mohsin, 1962; Pasha, 1964c; Bucke, 1971) are not excluded. Information on the fixation of teeth is provided by Ishibashi (1956) and Soule (1969a), on t h e importance of teeth in food retention by itfiles and Poole (1967), on the (fine) structure of teeth by Ishibashi (1956), Isokawa et al. (1959, 1964, 1968, 1970), Poole (1967), Soule (1969b) Herold (1970a, b, 1971b) and Herold and Landino, (1970), and on osteodentinogenesis by Herod ( 1971a). The following papers on the various aspects of pharyngeal teeth are recommended :-their origin (Edwards, 1929), taxonomic significance (Chu, 1935 ; Eastman and Underhill, 1973), loss and replacement phenomena (Evans and Duebler, 1955 ; Schwartz and Dutcher, 1962), bones and muscles with their functions (Girgis, 1952a ; Holstvoogd, 1965; Eastman, 1971), and changes in the feeding habits during onto-

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125

genesis (Hickling, 1966 ; Lange, 1966). The pharyngeal masticatory apparatus (pharyngeal teeth and chewing pad), an important acquisition correlated with the feeding regime, is best developed in herbivorous fishes where it is employed in tearing and triturating vegetable material (Hickling, 1966). I n Varicorhinus capoeta sevangi (Fil.), pharyngeal teeth with flat tops together with the chewing pad act as a press to squeeze water out of food (Verighina, 1969a). A relationship between the development of the apparatus and the share of plant food in the diet has been indicated (Al-Hussaini, 1949a; Vasisht, 1959; also refer Khanna and Mehrotra, 1970). The chewing pad (horny, callous or cornified), containing basal columnar cells standing on a basement membrane, polygonal cells with protoplasmic bridges between them, and superficial irregular cells with disintegrating nuclei or without nuclei, is placed on anchoring areolar tissue papillae provided with striated muscle fasciculi (Kapoor, 1957b ; Chaudhry and Khandelwal, 1961 ; Weisel, 1962). The elaboration and perfection of the filter apparatus varies (Verigin, 1957; Matthes, 1963; Kazansky, 1964). The number of gill rakers may not be uniform within the same species, for example in Salvelinus (Reshetnikov, 1961 ; Martin and Sandercock, 1967). The gill raker equipment may vary in fishes with identical modes of feeding (Khanna and Mehrotra, 1970). We have observed a remarkable connection between the number of gill rakers and the feeding habits in Salmonidae. A certain connection between the number of gill rakers and feeding habits also exists in Characinoidei. The gill rakers taste, filter or prevent the escape of food material in different fish (Iwai, 1963, 1964 ; Kapoor, 1965). Western (1969) reported EL corresponding gill raker development in relation with the increase in fish size: food size ratio in Cottus gobio L. and Parenophrys bubalis Euphrasen. When specifically considering the lining and its constituents, certain interesting observations should be mentioned. Varute and Jirge (1971) reported a cyclic folding and unfolding and hypertrophy and hypotrophy of the oral epithelium in the breeding cycle of the mouthbreeding Tilapia mossambica. The lining of the buccal and pharyngeal cavities of some teleosts is richly vascularized to play a supporting role in aerial gas exchange (Johansen, 1970). Mohsin (1961) believed that the development of mucous glands in Glossogobius giuris (Ham.) is correlated with the feeding habits and the nature of the food. Western (1969) observed prominent taste buds in the vicinity of the teeth in carnivorous Cottus gobio and Parenophrys bubalis, presumably to feel the prey in their grip or taste it during laceration. Dixit and Bisht (1972) suggested that the large number of taste buds in the

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anterior pharynx of Schizothorax richardsonii (Gray and Hard) play a role in food selection in this region; the unwanted material being expelled through the gill slits. I n the absence of true taste buds, a rich concentration of nerve cells and fibres just below the mucosal epithelium of the bucco-pharynx of Gudusia chapra (Ham.) (Srivastava, 1958; also of the lip and tongue) and Hilsa ilisha (Ham.) (Swamp, 1959) may act as primitive taste buds. The feeding procedure and not the type of food is probably linked with the number of taste receptors (Al-Hussaini, 1949a; Khanna and Mehrotra, 1970; Moitra and Sinha, 1971). The club-cells and presumably the sac-cells indicate genetic relationships rather than an adaptation to feeding habits (Islam, 1951; refer also to Khanna and Mehrotra, 1970). B. Oesophagus The lining of the alimentary canal behind the pharynx possesses throughout mucous cells in a strip of columnar epithelium (stratified epithelium’ is generally found in the oesophagus) ; this applies also to an “ oesogaster ” (Ghazzawi, 1935 ; Kapoor, 1958a ; Ldpez and De Carlo, 1959). Mucous cells are sometimes so abundant that they leave only a few intercalated epithelial cells. Very few club-cells and even taste buds may be present in the oesophagus (Mehrotra and Khanna, 1969). The layers of thick striated muscle vary in disposition in the oesophageal wall ; sometimes only the circular muscle layer occurs, whilst the longitudinal muscle layer is absent as a distinct coat or muscle occurs as bundles dispersed in the subepithelial tissue. In Salmo salar L., a muscularis mucosa has been found in the oesophageal wall (Kudinsky, 1966). Oesophageal mucosal folds teeming with mucous cells in Chanos chanos (Forsk.) are spirally disposed to aid in rapid movement of food (Chandy, 1956). Ghazzawi (1935) described a perforated cuticular covering, pierced through by necks of mucous cells, protecting against abrasion by hard diatom food on the oesophageal mucosa composed entirely of mucous cells in Mugil cupito (Tobar), and Khalilov et al. (1963) described the keratinization of superficial cells of the stratified epithelium in the oesophagus of Bruchymystax lenok (Pallas). There are reports on the occurrence of oesophageal glands, for example complex racemose glands with inconspicuous ducts leading t o the lumen in Labeo rohita (Ham.) (Sarbahi, 1939); tubular glands with giant cells having a clear hyaline fluid and basal nuclei, situated a t the transitional zone between oesophagus and stomach, with no clear-cut evidence of mucus production

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(though labelled in the figure as tubular mucous glands) or enzyme secretion in Chanos (Chandy and George, 1960); simple mucous glands just below or adjacent to mucous cells in Glossogobius giuris (Mohsin, 1961); an elaborate one in Notopterus notopterus (Pallas) (Mohsin, 1962); secretory glands, probably enzyme producing, composed of cuboidal cells with basal nuclei in Plecoglossus altivelis (Iwai, 1962); mucous and serous cardiac glands in Salmo gairdneri irideus Gibbons (Weinreb and Bilstad, 1955) ; complex tubular glands (Fig. 5), their upper part consisting of large mucous cells full of PAS-positive contents and their lower part containing small cuboidal cells with PAS-positive granules in Distichodus niloticus and D. rostratus (Verighina and Medani, 1968). Simple alveolar glands, in the upper to middle oesophagus, composed of pyramidal cells, each with a spherical nucleus, surrounding small alveoli, and abundant simple or branched tubular glands in the middle and lower oesophagus occur in Dorosoma cepedianum and D. petenense (Schmitz and Baker, 1969). Oesophageal (pharyngeal) sacs with thick striated muscle coats (inner circular, outer longitudinal) have been reported in a few fishes (Isokawa et al., 1965; Khanna and Mehrotra, 1970). Isokawa et al. (1965) distinguished (a) kidney-shaped oesophageal sacs with (I) a wrinkled mucosa in Ocycrius japonicus Doderlein, Psenopsis anomala T. & Schl. and Iticus pellucidus Lutken and (11)with a polypoid mucosa having teeth in Ariomma lurida J. & Sn. and Nomeus albula Meuschen, and (b) elliptical sacs with a polypoid mucosa (I) having teeth in Pampus argenteus Euphrasen and P. echinogaster Basilewsky, and (11) without teeth in Tetragonurus cuvieri Risso and T . atlanticus Lowe. The wrinkled mucosa is lined by a thin bony plate embedded in connective tissue (details not studied by the authors). I n contrast, the supporting tissue of a polypoid process is (I)a porous bone filled with fat cells and loose connective tissue, with either 5-6 radial basal processes in N . albula, P. argenteus and P . echinogaster or a scaly process in A. lurida, and (11)a cartilage with ramifications located in the submucosa in T . cucieri and T . atlanticus. The radial and scaly basal processes of each polypoid process are not only out of contact with each other but radiate and occupy different levels in the submucosa. Each tiny oesophageal tooth, attached to its skeletal support, with its tip penetrating through the mucosal epithelium and exposed in the sac cavity, consists of homogeneous dentin and pulp but it is not clear whether it is covered with an enamel-like substance. The tooth is fixed to an attachment bone (pedic1e)-a projection of the supporting bone with a disc of connective tissue fibres (contact area). The oesophagus, besides acting as a transit tube for the food, has

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FIQ.8. Oesophageal glands of Distichodus : (a) Appearance of the gland in D . niloticua (L.) (haem. eos.); (b) serous cells in D . niloticus; (c) serous cells in D . rostratus (Gunth.) (PAS). From Verighina, I. A. and Medani, J. I. (1968). Voproq ikhtioZogG, 8, 710-721.

been reported as having a variety of functions in different fish. The posterior oesophagus with gastric-type glands (oesogaster), occurring in Mugil capito (Ghazzawi, 1935), Cottus gobio and Parenophrys bubalis (Western, 1969), increases the effective gastric surface area and indicates an early form of accessory digestion. The likelihood of an absorptive role, on the basis of blood vessels in the tunica propria reaching the columnar epithelium, has been indicated in Mugil crenilabis (Forsk.) (Mahadevan, 1954). Intra-epithelial capillaries in the oesophagus of Monopterus albus (Zuiew) make it an accessory respiratory organ (Liem, 1967). I n Gudusia chapra (Srivastava, 1958) and HiEsa ilisha (Swamp, 1959)) both devoid of taste buds, a concentration of nerve cells just underlying the oesophageal m ucosa conducts impulses originating in gustatory stimuli. The oesophageal sacs in fishes are for food storage (Isokawa et al., 1965) or trituration and mucus production (Khanna and Mehrotra, 1970).

C . Stomach The oesophagus leads into the stomach the size of which is related to the duration between the meals and the nature of the food. The

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disappearance or reduction of internal folds depends on the bulk of the stomach contents. The stomach wall consists of a number of layers, characteristic for the whole vertebrate series. A distinct muscularis mucosa can be distinguished (Greene, 1912 ; Al-Hussaini, 1946; Burnstock, 1959a; Khanna, 1964; Bishop and Odense, 1966). A deviation from the normal (unstriated) nature and disposition of muscles is rare. The striated muscles may extend into the stomach, and even a reversed arrangement has been found in which striated muscles occur in the pyloric region instead of the cardiac region (see Al-Hussaini and Kholy, 1953 ; Mohsin, 1962). The mucoid nature of the gastric columnar epithelium has been recognized in many teleosts. Further, specific mucous cells in the gastric epithelium have been observed-a rare feature-in Trichiurus haumela (Forsk.) (Mahadevan, 1950), Glossogobius giuris (Mohsin, 1961) and Anabm testudineus (Bloch) (Mohsin, 1962). The gastric mucosa varies in thickness in different parts of the stomach due to the degree of development of gastric glands. Mohsin ( 1 962) stated that the extent of development, ranging from elaborate and complex to simple gland-types, is an adaptation to the digestion times in fishes with different feeding habits. Any kind of correlation between the appearance of the gastric glands and feeding behaviour or food could not be established. According to Konfal (1966), the presence of gastric glands depends on the taxonomic position, not on the feeding habits. There is often a marked tendency of gastric glands to be confined to the cardiac part of the stomach. A distinction, on the basis of staining reaction, has been made in " neck cells ", generally mucus producing, and " granular, enzyme secreting cells " of the gastric glands ; e.g. in Pleuronectes platessa L. (Dawes, 1929 ;Nikolskaya and Verighina, 1974), Peristedion longispatha (Goode and Bean) (Chan, 194l), Ophicephalus gachua Ham. (Islam, 1951), Morone chysops (Raf.) (Sublette, 1956), Tilapia mossambica and T. zilli Rich. (Verighina, 1967), Trigla gurnardus L. and Scorpaena porcus (L.) (Vegas-Velez, 1972). Weinreb and Bilstad (1955) reported that the cells of short shallow basal glands of the pyloric stomach in Salmo gairdneri irideus are mucus secreting. Verighina (1967) described primitive mucus-secreting pyloric glands in Tilapia mossambica and T . zilli. It is well established that only one type of secretory cell has been histologically identified in the gastric glands of teleosts ; no physiological division of secretory functions exists (Barrington, 1957 ; Smit, 1968; Western and Jennings, 1970; Verma and Tyagi, 1974). The isolated report by Wier and Churchill (1945) on the distinction between chief and parietal cells in the gizzard glands in Dorosoma

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cepedianuna on the basis of form and distribut>ion is unconvincing. The pyloric stomach in several members of Clupeodei, Chanoidei, some Characinoidei (Table 11)and Mugiloidei has a characteristic thick muscularis (often a circular muscle layer only), a reduced submucosa, and a special protective inner covering ; thus modified to act as a gizzard for trituration and mixing (Schmitz and Baker, 1969). Observations are in variance on the composition of the inner coating of the mucosa. It is described as : (I)a thick mucus sheet (Ghazzawi, 1935 ; Al-Hussaini, 1946, 1947b; Mahadevan, 1954; Thomson, 1954; Castro et al., 1961; Nagar et al., 1961); (11) a horny (Ishida, 1935) keratinous layer (Zambriborsch, 1953) ; (111)a layer of non-cellular material (Wier and Churchill, 1945; Swarup, 1959); ( I V ) a cuticle (Kapoor, 195%; L6pez and De Carlo, 1959) ; (V) a stratified epithelium with a layer of noncellular or keratinized tissue possessing scattered groups of isolated cells detached from the underlying epithelium (Chandy and George, 1960). According to Castro et al. (1961),the mucoid plaque in Mugil sp. has a lamellar structure, traversed by sinuous canals which run from glandular apices to the free surface, and are completely filled with cells which desquamate continuously from the glandular epithelium. Schmitz and Baker (1969) reported a squamous layer varying seasonally from a simple (in summer material) to a stratified condition (winter material) in the gizzard, covered by a non-cellular basophilic secretion, probably mucoid in nature. The coating is extended either by epithelial arms (Ghazzawi, 1935) or by glands (Wier and Churchill, 1945 ; Kapoor, 1958a; Castro et al., 1961 ; Schmitz and Baker, 1969). Chandy and George (1960) reported that in fingerlings of Chanos chanos (34-4 in length) the cuticular layer is absent in the gizzard. There is the opinion that the gizzard partly compensates for poor dentition (Pillay, 1953; Mahadevan, 1954). The development of a gizzard has been considered as one of a series of gut specializations (development of epibranchial organs, loss of teeth, proliferation of gill rakers, and lengthening of the intestine) in fishes with microphagous habits (Nelson, 1967 ; Schmitz and Baker, 1969). According t o Schmitz and Baker (1969), the oesophagus passes into the gizzard (divided into cardiac and pyloric regions), which is a secretory as well as a masticatory organ. Fukusho (1972) has studied the organogenesis of the digestive system in Liza haematocheila with special reference to the gizzard. Obviously, two types of glands are differentiated : gastric juice secreting, and mucus-secreting (Weinreb and Bilstad, 1955 ; Verighina, 1967; Schmitz and Baker, 1969; Verighina and Savvaitova, 1974).

The stratum compactum is a protective, supporting and strengthen-

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ing layer, which keeps the distension of the wall within bounds, and is regarded as an adaptive characteristic in many carnivorous fishes (Burnstock, 1959a; Bucke, 1971). It may be concerned with food absorption (in caeca) (Greene, 1912). In fish which lack a stratum compactum in the stomach, a very thick muscularis serves as an alternative adaptation (Burnstock, 1959a). I n Salmo species (Weinreb and Bilstad, 1955; Burnstock, 1959a; Bullock, 1963) and Esox Eucius L. (Bucke, 1971),the stratum is composed of collagen. Burnstock (1959a) observed the perforation of this stratum in S. trutta L. by blood vessels and nerves but not by muscles (cf. Greene, 1912 on king salmon). Weinreb and Bilstad (1955)reported that a distinct stratum compactum is seen only after the fourteenth week in fingerlings of S. gairdneri irideus. Bullock (1963) found that the stratum compactum in the intestine of salmonids was not visible in very young fish but distinct in 7 cm fish. The stratum granulosum is situated between the stratum compactum and the muscularis mucosae and in the meshes of the stratum compactum and is pierced by blood vessels. The granular cells are present by the twelfth week in the fingerling of S. gairdneri irideus (Weinreb and Bilstad, 1955). Burnstock (1959a) suggested that the stratum granulosum in S. trutta is composed of active fibroblasts which form collagen fibrils and during this process fine granules appear in the cytoplasm. There are various explanations of the function of these granular cells. They produce lipase in the king salmon according to Greene (1912). Al-Hussaini (1946) observed granular cells with a propensity to wander in various parts of the stomach of Mulloides aurijiamma (Forsk.) only during active digestion ; he was unable to establish the exact relationship between these cells and the digestive process. Al-Hussaini (1949b) thought that they may perform different functions in different species. Mohsin (1962) conjectured that they help in absorption and transport of digested food. Bishop and Odense (1966) indicated a possibility of another type of secretion of the granular cells in Gadus morhua but did not specify it. Some authors suggest an absorptive function of the stomachal epithelium. The epithelial cells of the stomach in king salmon perform an absorptive function according to Greene (1912). The numerous blood vessels in the tunica propria of the glandless pyloric stomach of Peristedion longispatha (Chan, 1941) and the cardiac stomach of Mugil tade Forsk. (Pillay, 1953) and 1M. crenilabis (Mahadevan, 1954) indicate such a function. The presence or absence of a stomach has been used as a criterion for distinguishing the teleosts into gastric and stomachless types. Both

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may occur in the same families (e.g., Blenniidae, Cobitidae) and even in the same genus (e.g., Gobius). Several hypotheses have been put forward t o explain the loss of the stomach. Karpevitch (1936) thought that the cause of the disappearance of the stomach in some marine fishes is the alkalification of the gastric juice by seawater swallowed with the food. This alkalification inhibits the peptic activity and leads to the loss of gastric digestion. Not all fish lacking a stomach take similar food. Jacobshagen (1937) concluded that the explanation of the lack of a stomach cannot be based on the kind of food taken. From the viewpoint of Hirsch (1950), the presence of a masticatory apparatus makes that superfluity and consequently the disappearance of the stomach. Szarski (1956; see also Szarski et al., 1956) suggested that the absence of a stomach in various groups of fish is probably a result of adaptation to the ingestion of food organisms with calcareous shells. The alkalification tends to neutralize the acid contents of the stomach and confines digestion to an alkaline medium which might eventually lead to reduction of the stomach. Another possibility is an intensification of hydrochloric acid secretion, though this may be exSuch intensification is especceptional (catfishes-Anarrhichadidae). ially difficult for freshwater organisms as the ambient water is poor in chlorine. The development of efficient digestion in an alkaline medium is of high biological value for a freshwater fish and this explains the wide occurrence of Cyprinidae in fresh waters. Barrington (1942, see Table 1, p. 20 for examples of stomachless fishes, 1957)considered several possible causes of the loss of the stomach in different teleosts. I n this connection we can point to another possible cause for loss of the stomach, in Cyprinidae for instance (Verighina, 1969b). The consumption of food containing a high proportion of indigestible ballast (sand, mud, cellulose, etc.) in mud-feeding microphags and herbivorous species involves great quantities of food passing through the gut. The stomach as a reservoir detaining the food is therefore of little significance. Indeed, in mud and plant-feeders the stomach is very small in different taxons, in Cichlidae for instance (Pasha, 1964b ; Verighina, 1967). I n herbivorous Acanthurus the stomach is a narrow tube (Al-Hussaini, 1947b) in which the food is not contained for long. I n microphags of the family Cyprinidae (Labeo, ~ y ~ o ~ h t h u l ~ i c Vuricorhinus, hth~~, Xenocypris), the alimentary canal is highly specialized and adapted for maximal absorption. The absence of a stomach together with the great length of the gut occurs in microphags, in Loricaridae (Siluroidei) and in Theutidae (Percoidei). Therefore, the disappearance of the stomach may be considered in some cases as a consequence of food containing a high proportion of ballast. The adaptation t o carnivorous feeding

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habits may be considered as a secondary specialization in some Cyprinidae. I n the stomachless fish, the fore-gut is enlarged in varying degree and referred to as an intestinal bulb, duodenum, swollen part of the intestine, large arm of the intestine and even erroneously as stomach (see Kapoor, 1958b ; for intestinal swellings see Al-Hussaini, 1947b). The intestinal bulb deserves some attention. It is possible to consider this an analogue of the stomach from the morphological point of view. It is more remarkable in predators: Ptychocheilus (Weisel, 1962), Barilius (Matthes, 1963), and Elopichthys (Verighina, 1963), but it is almost inconspicuous in microphags. Besides the use of intestinal morphology as a diagnostic character in taxonomical studies, the pattern of convolution of the intestine has been used as a criterion of relationships in fishes (Fukusho, 1969).

D. Intestine The intestine, in both gastric and stomachless types of fish, shows a variety of mucosal ingrowths. Villi are never found in fish intestinal mucosae; crypts have been described in Gadidae (Jacobshagen, 1937). Typhlosoles in the ileum (Al-Hussaini, 1945), ileorectal valves (AlHussaini, 1947b; Maggese, 1967 and many others), annulo-spiral septa of unknown function in the rectum (Burnstocli, 1959a; Bullock, 1963; Korovina, 19731, rectal caeca, absorptive in nature (Agrawal and Singh, 1964; Singh, 1966, 1967b), and anal sphincters (Dawes, 1929) have been reported in different teleosts. Intestinal glands have been observed in some Gadidae (Bishop and Odense, 1966) and Macrouridae (Geistdoerfer, 1973). With few exceptions, the intestine has a simple, columnar absorbing epithelium lined with a brush border (striated free border, striated cuticular border, cuticle, top plate ; see Al-Hussaini, 194913 for cytology of the free border). The oeso-intestinal bulb region possesses mixed epithelia (Girgis, 1952b ; Santa and Pollingher, 1955 ; Kapoor, 1957c, 1958b). The “ cilia” obcurring in various places in the intestinal epithelium may according to some authors be the inter-canal substance in an unusually thick border (Al-Hussaini, 1949b), although ciliated epithelia do appear in some parts of the alimentary canal in some fishes (Fig. 2) (see references in Mohsin, 1962). Al-Hussaini (1949b) suggested that the variation in thickness of the free border in different parts of the intestine of the same fish could be related to the absorption of digested food into the cells. Other common constituents are goblet cells and cellular migrants (lymphocytes and various types of granulocytes) (see Al-Hussaini, 1949b). I n fishes possessing a stomach, this is concerned with the production of zymogen granules. I n stomachless

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fishes this role is taken over by the goblet cells of the intestine; the highest concentration occurs in the posterior segment of the intestine (Al-Hussaini, 194913). Yamagishi et al. (1969) reported that some columnar cells of the mid-gut in c a w e d eels were light and some were dark. No morphological differences concerning nuclei and granules could be distinguished. I n the mid-gut of Chondrostoma nasus variabile the epithelial cells situated at the top of the folds are considerably lower than the cells situated a t the base. The cytoplasm of the former cells is distinctly basophilic (Verighina, 1971).

FIG.6. Position of the stratum oompaotum in the gut of Salwelinus ,fontinaZis (Mitchell) From Korovina, V. M. and Vasilieva, N. E. (1971). Voprosy ikhtiologii, 11, 502-508.

Kato (1935) found the principal columnar cells interrupted by a few goblet cells and extremely minute glandular cells (a-cells) in most parts of the intestinal mucosa of Nomeus gronovii (Gmelin). I n another part of the intestinal mucosa he found the normal principal cells to be lacking and replaced by characteristic glandular cells (b-cells) interspersed by goblet cells and " a-cells '' which are comparable, if not identical, to pear-shaped cells (Bullock, 1963). The goblet cells are chiefly mucus producers. It has been suggested that their secretion contains digestive enzymes ; moreover, their high water content may facilitate absorption (Siankowa, 1966). Vickers (1962) reported in the intestinal epithelium of Carassius auratus (L.),in addition to goblet cells,

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similar cells with acidophilic granules which stained feebly with PAS but more strongly with Gomori’s aldehyde-fuchsin. They were presumably enzyme secreting cells comparable perhaps with the Paneth cells of the mammalian intestine. Bishop and Odense (1966) observed intestinal glands composed of rounded cells, alcian blueand PAS-staining goblet cells (found also among the epithelial cells near the openings of the glands) and “ striated ” cells in Gadus morhua. Geistdoerfer (1973) reported intestinal glands in Chalinura mediterranea Giglioli formed by cuboid cells, each with a large spheroid nucleus and

‘‘ Pear-shaped” cells in the gut of Erythroculter erythropterus (Bas.) (haem. 00s.). From Verighina, I. A. (1963). Nauchnye doklady Vysshej shkoly. Biologicheskie nauki, no. I, 38-42.

FIG.7.

granules in the cytoplasm; neither secretion nor division of these gland cells has been observed. An interesting controversy exists on the structure and function of the “ pear-shaped ” cells (Fig. 7 ) in the intestinal epithelium (AlHussaini, 1949b, 1964; Iwai, 1968; Verighina and Medani, 1968; Kimura, 1973). According to Bishop and Odense (1966),the “ striated ” cells are similar to these cells. The striated cells have been reported to show rods (Al-Hussaini, 1949b), nine to twelve beaded strings (Vickers, 1962), rodlets (Bullock, 1963, 1967; curved and basophilic, Hale, 1965), and rows of eosinophilic granules extending from the basal oval nucleus to the cell-apex (Bishop and Odense, 1966, cf. Weisel, 1973). They have

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been considered as a st.age in the life-cycle of a goblet cell (Al-Hussaini, 1949b), or an occasionally appearing phase (Vickers, 1962); unicellular glands (Klust, 1939; Bullock, 1963), and protozoan parasites, though somewhat resembling the specialized leucocytes described by Duthie in 1939 (Hale, 1965; Iwai, 1968; cf. Bullock, 1963). Bishop and Odense (1966) suggested that they could be enzyme-producing. The " pearshaped " cells resemble discharging coarse granulocytes as described by Catton (1948, 1951) (Fig.8). The granules become elongated and clubshaped and form a pattern converging a t the epithelial surface. MGC

DCG

CG

FIG.8. Intestinal epithelium of trout with discharging coarse granulocyte (DCG), migrating coarse granulocyte (MigCG), and mucous goblet cell (MGC). From Catton W. T. (1948). Nature, London, 162, 894.

Some teleostean intestines have a muscularis mucosae of smoothmuscle cells, strata compactum and granulosum (Fig. 6) and even an extension of the striated muscles. I n Salmo, Salvelinus and Stenodus, besides the stratum compactum, there are also supplementary thin collagenous fibres situated parallel with the intestinal surface (Korovina and Vasilieva, 1971).

E . Rectum The rectum has attracted the attention of many investigators. It is distinguished by a thicker muscular coat and by a marked increase in the number of goblet cells and sometimes granulocytes. Liem (1967) suggested that the fluctuations in the number of goblet cells reported by various authors might be due to different feeding conditions in the

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investigated fishes. I n contrast to well-fed Monoptems alhus, the starved fish shows a rapid and marked diminution of goblet cells in the rectum only (Liem, 1967, read also Bucke, 1971). Moitra and Bhowmik (1967) found a greater number of goblet cells in the rectal region of young Catla catla (Ham.) (carnivore) than in tlhe adult (omnivore). Conical cells, suggested as increasing the absorptive surface in the rectum of Labeo rohita (Sarbahi, 1939), have been condemned as artefacts formed by the precipitation of mucus by fixatives (Mohsin, 1962). Various histological constituents of the intestinal make-up have been functionally connected. Dawes (1929) stated that the spaces in the areolar tissue of the intestine in Pleuronectes platessa probably serve as lacteals. The mucosa of the rectum of Cymatogaster aggregatus Gibbons serves as a temporary repository of unesterified xanthophyll, a carotenoid pigment (Young and Fox, 1936). Cloacal and intestinal respiration has been suggested in Plecostomus plecostomus (L.) (Sawaya and De Petrini, 1960; see Angelescu and Gneri, 1949; Johansen, 1970). I n a heavily fed stomachless Gambusia afinis (Baird and Girard), the anterior rectum is the chief site of digestion and absorption of food (Bullock, 1967). I n the rectum of some teleosts a rich blood supply (Pillay, 1953; Western, 1969; Berry and Low, 1970; Gupta, 1971) and lymphatic tissue (Western, 1969; Berry and Low, 1970) have been considered to have physiological significance. I n this connection it is of interest t o mention some studies on changes taking place in the intestine during starvation, and in intestines having respiratory function. Belonozhko (1966, 1967a, b) studied the changes in the gut in summer a t the time of intensive feeding and in winter a t the time of starvation. I n summer Rutilus rutilu6 (L.) (1966) has an increased amount of cytoplasm in the intestinal epithelium; the epithelium of the end-gut is rich in fat and lipids, while small PAS-positive vacuoles appear. DNA-content shows small seasonal changes. I n bream (1967b), the highest number of vacuoles in the epithelium is found in summer and autumn, and in summer there appear oxyphilic vesicles in the epithelium of the end-gut. Fat absorption in bream and pike is most intensive in the period of copious feeding, accompanied by an increase of the RNA-content. Vasilieva and Melnikova (1965) and Vasilieva and Korovina (1968) have reported changes in the intestine of some Salmonidae in the starvation period during migration and spawning : the diameter of the intestine decreases, the mucosal folds become smooth, the quantity of cytoplasm decreases and in accordance with this the nucleocytoplasmic ratio in the epithelial cells increases.

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Simultaneously pseudomultinuclearity in the epithelium as well as increase in the size of the goblet cells and decrease in the quantity of RNA is observed. After spawning the normal structure of the intestine is restored and the quantity of RNA increases. Tamura and Honma (1971) observed a clear-cut narrowed lumen, pronounced degeneration of the mucous layer, and considerable thickening of the submucosa and muscular layers of the intestine of Leucopsarion petersi Hilgendorf caught in its spawning bed. I n 1941 Fontana had described the changes in the histological picture of the gut in Anguilla in estuarine conditions. I n Misgurnus species, the fore-part of the intestine has only a digestive role and exhibits no histological change during the respiratory phase. The remaining part of the intestine seems t o have no respiratory function in the digestive phase but in the respiratory phase, which is marked by a drastic histological deformation (flattening of epithelial cells ; subepithelial capillaries and lymphatics in a highly congested state), although very dubious, a digestive function cannot be ruled out with certainty (Wu and Chmg, 1945; Jeuken, 1957). Intestinal caeca (appendices pyloricae, pyloric caeca) form auxiliary appendages in many teleosts (absent in certain families, see Rahimullah, 1943, 1945). They differ in number, form, disposition and communication with the intestine. They are histologically almost identical with the intestine (Rahimullah, 1943, 1945 ; Saddler and Ashley, 1960; Khanna and Mehrotra, 1971 and many others); in some cases provided with cilia (see Rahimullah, 1945), and even with a sphincter a t the base (Greene, 1912 ; Blake, 1936 ; Burnstock, 1959a). The length and the morphology of the alimentary canal is not correlated with their occurrence (Mohsin, 1962). The presence or absence of the pyloric caeca has no apparent correlation with the nature of the food or with feeding habits (Khanna, 1961 ; Mohsin, 1962). Even the number of caeca is not always constant in a species (Bernard, 1949-50). On the other hand, the number of pyloric caeca has been used in the identification of species of Mugilidae (Hotta and Tung, 1966). Reshetnikov (1961) noted that the number of pyloric caeca increases with increasing length of the fish. Svetovidov (1934) and de Groot (1969) found a correlation between the number of intestinal caeca and the kind of food and even an increase in their size with bulk of food. Martin and Sandercock (1967), however, did not confirm this in a study on the intestinal caeca and the development of gill rakers in Salvelinus namaycush Rich. Various functions have been suggested for the intestinal caeca, e.g. accessory food reservoirs, a digestive function supplementing that of the stomach, absorption of carbohydrates and fats, resorption of

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water and inorganic ions, to augment or compensate or supplement the functions of the alimentary canal, t o increase the intestinal surface, and as a space-saving device. 111. ELECTRON MICROSCOPIC FINDINGS Recent extensions in knowledge of the ultrastructure and function of the various components of the alimentary canal tunics have greatly supplemented the optical microscopic observations. Albright and Skobe (1965) compared the palatal epithelial of Corydorasjulii Steindachner and Helostoma temmincki (Cuv. & Val.). I n Corydorasjulii, with the exception of the most superficial layer of cells in the palatal epithelium which are divergent, the cytoplasm of basal and other cells contains free ribosomes, tonofilaments (average diameter of about 80 A), ovoid mitochondria with transverse cristae, and a small amount of endoplasmic reticulum near the nucleus (Fig 9). The basal cell plasma membrane adjacent to the lamina propria lacks hemi-desmosomes; however, desmosomes between cells and interdigitations of the plasma membrane were noticed (Fig 10). The outermost cells show apparent compacting and dehydration of cellular contents coupled with the disappearance of some cytoplasmic organelles, which suggests a primitive type of keratinization. Remnants of organelles, vacuoles, degenerating mitochondria and small rounded evaginations of the outer free surface of the plasma membrane were seen. The most striking points observed in the oral epithelium of Helostoma temmincki are : an apparent desquamation of outermost cells with some degree of degeneration of nuclear and cytoplasmic components ; indistinct hemi-desmosomes, and randomly oriented collagen fibres in the lamina propria. Highly specialized cells containing large amounts of agranular endoplasmic reticulum oriented into a lattice work of hollow tubes (about 75 mp in diameter), an irregularly shaped nucleus, and well developed mitochondria were occasionally identified. Desmosomes form attachments t o neighbouring cells. Philpott and Copeland (1963) described an agranular endoplasmic reticulum in the chloride cells of gill filaments from three species of Fundulus and suggested a possible osmoregulatory function. The lamina, propria exhibits an orthogonal orientation of collagen fibres. A felt-like basement membrane, several hundred d in thickness, is separated from the plasma membrane of the basal epithelial cells by a relatively clear space. Recently, Whitear (3971) reported so-called chloride cells from the oral epithelium of Gasterceteus aculeatw L. (Fig. 11).

FIG.9. Palatal epithelial cells of Corydoras julii Steindachner. Desmosomes (d), tonofilaments (t), mitochondria (m), ribosomes (r), nucleus (N), plasma membrane (pm). From Albright, J. T. and Skobe, 2. (1965). Archives of Oval Biology, 10, 921-927.

FIG.10. Oral mucosa cell of Corydoraa julii Steindachner. Agranular endoplasmic reticulum (ar),desmosomes (d), mitochondria (m). From Albright, J. T. and Skobe, Z. (1965). Archives of Oral Biology, 10, 921-927.

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FIG. 11. Gasterosteus aculeatus L. Section of oral epithelium from the roof of the mouth, showing a taste bud and other cell types. The mucoid cuticle, which in life covered the surface of the epithelium, is not presont. (1) gustatory cell; (2) chemosensory cell; (3) goblet cell; (4)chloride cell; (5) blood cell; ( 6 ) nerve entering taste bud. From Whitehead, M. (1971). Journal of Zoology, Lonrlon, 163,237-264.

Whitear (1971) reported that the surface layer cells of the oral epithelium of Gasterosteus aculeatus have characteristics linked with the secretion of a mucoid cuticle ; they have a dense outer border, and bear microvillar ridges. The goblet mucous cells in the oral epithelium of G. aculeatus exhibit characteristic dark cytoplasm and parallel membranes of granular endoplasmic reticulum (Whitear, 1971). Linss (19694 found an eccentrically located, often flat nucleus in the oesophageal goblet cells of Esox lucius. The cytoplasm contains a well-developed non-

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granular endoplasmic reticulum and is poor in mitochondria and ribosomes. It forms a narrow band adjacent to the cell membrane if the cell is heavily loaded with secretory granules. The secretion is eccrine. The fine structure of the club-cell in the skin has also been described : the club-cell in the ostariophysous fish, recognizable by the large size and occasionally indented nucleus in the centre has mitochondria, Golgi apparatus, Palade’s granules, a few lysosomes, endoplasmic reticula, fine vesicles and a characteristic fine homogeneous dispersed fibrillar material filling most of the cytoplasm and quite distinct from the filaments of adjacent cells. Complicated interdigitations and desmosomes between club-cells have been observed (Sat6 and Sannohe, 1967 ; Henrikson and Matoltsy, 1968; Pfeiffer et al., 1971). The club-cell in non-ostariophysous Anguilla has a central vacuole displacing the nucleus, characteristic round or oval structures approximately 260 d in diameter having a dense rim and a light centre, and strands about 250A wide that have dense cross striations with a period of about 220 A (Henrikson and Matoltsy, 1968). The club-cells of the ostariophysians are thought to be involved in the fright reaction, whereas in non-ostariophysians (e.g., Anguilla), they probably contribute to the formed elements (threads?) in slime (Henrikson and Mntoltsy, 1968, see references). They display phagocytosis, ingesting wandering cells in Synodontis schall B1. & Schn. (Lutfy, 1964). Mester (1971) discussed their function in pinocytosis or also phagocytosis in Noemacheilus barbatulus. Wilke ( 1972) reported that both mucous and club-cells in Anguilla anguilla (L.)epidermis originate from small basophilic cells by modification and grow by incorporation of other modiEed basophilic cells. The club-cells of ostariophysous Gyrinocheilus aymonieri (Tirant) also appear to grow by incorporation of modified basophilic cells. An examination of fish taste buds on the body surface has revealed the existence of three different cell types : receptor cells, supporting cells and basal cells. Further, the receptor cells have been distinguished into: (I) light cells characterized by clear cytoplasm and generally well-oriented systems of supra-nuclear microtubules and smooth endoplasrnic reticulum, and (11)dark cells with dense cytoplasm, electron dense granules, only a few microtubules, rough endoplasmic reticulum more prominent than the smooth variety and a lot of filaments. Both types of cells bear specialized apical processes at their free surface. Mitochondria, Golgi apparatus and free ribosomes have been recognized. The supporting cells bear microvilli and have numerous fine filaments, well-developed Golgi apparatus, mitochondria, vacuoles, endoplasm ic

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reticulum, and free ribosomes. The boundaries between the supporting cells and between the supporting cell and receptor cell are rather smooth ; desmosomal system and intercellular digitations are very rare except for the site immediately below the free surface where the junctional complex is always present. The basal cells, disc-like in form, contain abundant mitochondria, a lot of vesicles, multi-vesicular bodies, endoplasmic reticulum, free ribosomes and fine filamentous structures. Desmosomes are occasionally observed a t the basal processes of the supporting cell that contact the basal cell. Certain transitional or intermediate forms of cells have also been encountered (Hirata, 1966; Storch and Welsch, 1970; Bardach and Atema, 1971; Hara, 1971; Rentter, 1971; Schulte and Holl, 1971). The structure of these external taste buds is almost similar to that of the taste buds in t,he palatal epithelium (Whitear, 1971). Whitear (1971) also observed scattered chemosensory cells, closely resembling the gustatory cells of the taste buds of some teleosts. Nerve fibres were associated with the bases of these cells, and synaptic specializations were seen. A desmosome exists between the chemosensory cell and an epithelial cell. Linss (1969b) described the indifferent cells of the stratified oesophageal epithelium in Esox Zucius possessing large ovoid nuclei, a well-developed granular endoplasmic reticulum, Golgi apparatus and clusters and fasciculi of tonofibrils joining the desmosomes. The cytoplasm of basal normal epithelial cells, rich in tonofibrils, often contains pinocytotic vesicles. The apically-placed cells contain sometimes lipoid granules. Goblet cells and serous cells also occur. The probable functions are covering or supporting, transport of different substances from epithelium to lamina propria and secretion. Linss and Geyer (1968) have examined the fine structure of some secreting cells, the " Einkornzellen )'in Esox Zucius oesophageal mucosa (Fig. 12). They refer to the paper by Purrmann (1963) who found in such cells tryptophan, histidine, cystine and cysteine. The cell is protein-secreting, rich in granular endoplasmic reticulum, mitochondria and with a well-developed Golgi apparatus. The cell resembles the exocrine pancreatic cell, the salivary gland cell and the Paneth cell of the small intestine. However, it is different from these cells in that it contains one single large granule of pro-secretory material, which is separated from the cytoplasm by a membrane. This membrane is a part of the Golgi apparatus so that the big granule is to be considered as a great Golgi vacuole. Emptying of the cell is eccrinous: the cell membrane and the membrane of the Golgi vacuole fuse and then rupture, so that the content of the vacuole is secreted into the oeso-

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phageal lumen. Probably, the secretion contains digestive enzymes. They supposed that the digestion in Esox lucius begins in the oesophagus.

FIG.12. Secretory oescphageal epithelium cell (" Einkornzelle ") of pike. L, lumen; N, nucleus ; G, Golgi apparatus ; S, secretory complex. From Linss, W. and Geyer, G. (1968). Anntorniseher Anzeiger, 123,423-438.

The fine structure of the gastric mucosa is not yet known. The main locus of interest has been the intestine (intestinal bulb and caeca have been considered simultaneously ). The luminal surface of the columnar epithelial cells is covered with cytoplasmic projections (microvilli), a standard structure in the intestinal epithelium. The

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electron microscopic pictures of microvilli appear to vary in different fishes, e.g. the fibrils attached to the outside of the microvilli and the filaments in the microvilli extending into the apical region of the cell (Odense and Bishop, 1966; Yamagishi et al., 1969) ; several microvilli arising from a single protoplasmic projection (Jansson and Olsson, 1960); antenulas microvillares at the tips of the microvilli (Yamagishi et al., 1969) have been observed. The microvillous membrane is trilamellar (Yamagishi et al., 1969).

FIG.13. Mucosal ridges of the posterior intestine of Carassius aurcctus L. Secretory cells, in which the secretory product is intensely basophilic, are present especially along the lateral surfaces. Supranuclear bodies are prosent, especially in the apical portions of the ridges. From Gauthier, G. F. and Landis, S. C. (1972). Anatomical Record, 172, 675-702.

Invaginations of intermicrovillous plasma membranes into the terminal web and apical cytoplasm have been observed (Ozaki, 1965; Luppa, 1966 ; Yamamoto, 1966 ; Gauthier and Landis, 1972 ; NoaillacDepeyre and Gas, 1973). The apical cytoplasm contains a variety of vesicles, tubules and vacuoles (Ozaki, 1965 ; Yamamoto, 1966 ; Gauthier and Landis, 1972) (Fig. 13). Similar vacuoles have been described by earlier light microscopists. It has been suggested that these vacuoles appear in direct relation tJothe presence of food in the intestinal lumen :

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they represent an early stage in mucus formation or they represent loci occupied by fat globules (see Yamamoto, 1966). An association of invaginations of the apical plasma membrane with vesicles and vacuoles in the apical cytoplasm of columnar epithelium in the posterior intestine of the goldfish has been linked with pinocytosis (Yamamoto, 1966; Gauthier and Landis, 1972). Gauthier and Landis (1972) further stated that protein is absorbed by the distal segment (posterior intestine) whereas lipid is absorbed proximally in Carassius auratus. I n their view, the ability to absorb protein by pinocytosis appears to be related to a lack of extra-cellular proteolytic digestion. A fine filamentous complex (the terminal web), immediately beneath the microvillous border, is generally free of cell organelles except for a few, small smoothed vesicles and tubules (Ozaki, 1965 ; Yamamoto, 1966; Gauthier and Landis, 1972). I n the immediate supranuclear region, Gauthier and Landis (1972) observed supra-nuclear bodies-large membrane bound bodies with a very dense content-regularly aligned in a row across the absorptive epithelium of the posterior intestine in Carassius auratus, having a role in intracellular digestion (protein digestion and absorption). An almost general characteristic of fish intestine is the extensive formation of lamellar structures-an unusual variety or a specialized form of agranular endoplasmic reticulum-orientated parallel with the long axis of the cell and mainly concentrated in the infra-nuclear cytoplasm; a lamellar structure composed of two very regular parallel membranes, separated by a distance or facing a t an interval of about 2 5 0 A to 350A. The cavities of these lamellae contain more or less dense, homogeneous material or dense fine particles. The lamellar structure has a trilamellar unit membrane consisting of two thick membranes and a light one between. The electron density of these membranes is slightly higher than that of endoplasmic reticula. They are never associated with ribosomes and never anastomose (Ozaki, 1965; Yamamoto, 1966; Yamagashi et al., 1969; Bergot and Flhchon, 1970a). Continuity of peripheral lamella with the intercellular space through a short tube is sometimes observed (Ozaki, 1965 ; Yamamoto, 1966). Sometimes, their intimate morphological relationship with mitochondria is seen (Yamamoto, 1966). Yamamoto (1966) reported that lamellar structures have multiple fenestrations and vesicles associated with their margins. The function of these lamelhe is not well established. They are presumably involved (I) in concentrating salts, and (11)in the transport of water or nutrients or both (Ozaki, 1965 ; Yamamoto, 1966). Yamamoto (1966) observed fine filamentous material, mostly

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parallel with the long axis, more or less grouped and some of them converging on the desmosomes in the intestinal columnar cells of Carassius auratus and Salmo irideus L. He also reported numerous, small, cirG,ular membrane bodies containing a fine granular material of low density in the basal part of the epithelial cells of goldfish and trout intestine, and remarked that, though they appear similar to secretion granules, their secretory significance has still t o be established. The lateral plasma membranes rarely show complex, elaborate interdigitations with the adjoining cells (Ozaki, 1965; Yamamoto, 1966; Yamagishi et al., 1969), and generally make smooth contact with them ; interlocking is sometimes seen (Yamamoto, 1966). Desmosomes occur between adjacent cells (Ozaki, 1965; Luppa, 1966; Yamamoto, 1966). I n rainbow trout, Yamamoto (1966) reported a terminal bar type of cell-attachment a t the level of the terminal web and " multidesmosomal attachments '' in locations corresponding to the level of the coarse filament layer just beneath the terminal web in the cytoplasm of the columnar epithelium of the intestine. Odense and Bishop (1966) found regions of thickening (zona occludens, zona adhaerens, macula adhaerens) a t the cell junctions in the rectum of Gadus morhua. Apart from a few differences in quantity and disposition, the cytoplasm of the columnar cell contains mitochondria in supraand infra-nuclear zones, Golgi apparatus, endoplasmic reticula (granular and agranular), R N P granules, lysosomes, and SER containing lipid droplets (Jansson and Olsson, 1960 ; Ozaki, 1965 ; Luppa, 1966 ; Yamamoto, 1966 ; Yamagishi et al., 1969 ; Gauthier and Landis, 1972 ; for mitochondria and Golgi element, see also Al-Hussaini, 1949b). On the basis of morphological differences of endoplasmic reticula, Yamagishi et al. (1969) distinguished three types of cells in the columnar intestinal epithelium of reared eel : (I)light cells (L, cells) containing dense, circular SER and RER, and relatively few free R N P granules ; (11)light cells (L, cells) possessing rough, large and irregular E R containing glycogen particles, and abundant free R N P granules, and (111)dark cells, having E R in circular and irregular forms and many RNP granules. A small number of dark cells bearing microvilli situated between the light cells contain less clear cytoplasm and fewer lamellar structures. The fine structure of the goblet cell in the intestine is similar t o that found in other vertebrates (Ozaki, 1965). The goblet cells in the caecal epithelium of Perea JEuviatilis L. apparently have microvilli in the inactive phase, which finally disappear when the cells become loaded with mucinogen globules (Jansson and Olsson, 1960, cf. Luppa,

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1966). Al-Hussaini (1949b) reported basal mitochondria and Golgi elements in the intestinal goblet cells of fish. yamamoto (1966) observed a thin clear layer interposed between the basement membrane and the intestinal epithelium in Salmo irideus. He found that the basement membrane is not homogeneous but filamentous in nature, with often embedded small particles (possibly fat droplets). Earlier, Jansson and Olsson (1960) stated that the basement membrane appears structureless in micrographs but is frequentlj. provided with small projections towards the epithelial cells in the caeca of Perca Jluviatilis. The attenuation and sometimes fenestration of the blood capillary wall facing the intestinal epithelium (Ozaki, 1965 ; Yamamoto, 1966 ; Bergot and Fldchon, 1970a) might indicate an absorptive function (Yamamoto, 1966). Bergot and Flkchon (1970a) found lymphatic vessels in the basal parts of the fold intersections in Salmo gairdnerii Rich. Suzuki et al. (1963) stated that the blood capillaries from the lamina propria get into tjhe intercellular spaces of the columnar cells of the straight (lower) intestine, which carries out its respiratory function, and swell towards the lumen in Misgurnus anguillicaudatus (Cantor). Their pressure had no deforming effect on the goblet cells but the columnar layer turns into a thin layer and loses its striated border. Ozaki (1965) reported that a granular cell in the intestinal epithelium of Spheroides stictonotus (Schl.) contains large granules bound by a single membrane, a variety of agranular vesicles and tubules, a few mitochondria, a poorly developed granular endoplasmic reticulum, abundant glycogen particles, and has no lamellar structure. He added that since these cells do not exhibit any desmosomes with neighbouring epithelia, and a similar kind of cell is recognized in the lamina propria, they may be of migratory nature. Recent electron-microscopic studies indicate that rodlet cells are protozoan parasites, and not tissue cells (Iwai, 1968; quoted by Weisel, 1973). On account of his electron-microscopical investigations, Kimura (1973) considers the pear-shaped cells to be neither parasitic cells, nor a developmental stage of goblet cells, nor wandering cells. Kilarski and Bigaj (1971) described the ultrastructure of striated muscle fibres of the tunica muscularis of the oesophagus of Tinca tinca L., Carassius auratus, Noemacheilus barbatulus and Gobio Jluviatilis L. Tinca tinca has the muscular tunic of striated fibres over the entire length of the alimentary canal. The muscularis of T . tinca intestine is composed of two layers of striated muscles (outer longitudinal and inner circular) and a layer of smooth muscles (circular). The fibres of the oesophagus differ from each other in diameter, length of sarcomeres,

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glycogen content and, in the case of one species, organization of SR (sarcoplasmic reticulum). The organization of sarcomeres indicates that the fibres are slow-contracting (broad Z line). The SR is organized according to the Z type, except the fibres of the oesophageal muscles of Gobio jluviatilis in which the SR represents the A-I type. Both layers of striated muscles of T . tinca are made up of two types of muscle fibres differing in length of sarcomeres; both types seem devoid of glycogen.

IV. HISTO-AND CYTOCHEMISTRY Many histochemical investigations on certain constituents occurring in the various coats of different parts of the alimentary canal have increased our knowledge after the publication by Arvy (1962). The reader is referred to relevant papers for numerous standard techniques and interpretations of histo- and cytochemical findings. The mucous epithelium of the alimentary tract in various vertebrates has been shown to contain mucous substances of marked chemical diversity presumably of physiological significance in digestive processes and also playing a protective role against mechanical and chemical injuries, including auto-digestion. The entire digestive tract lining of a teleost is mucified and much attention has been paid to the mucussecreting cells. The different mucus-cell types in various parts of the alimentary tract contain either neutral or acidic mucosubstances (for specific types, see Weinreb and Bilstad, 1955; Jansson and Olsson, 1960; Castro et al., 1961; Bsrbetta, 1962; Dumitru and Mihai, 1962; Bullock, 1963, 1967; Bishop and Odense, 1966; Sivadas and Govindan, 1966-69; Wetzig and Bruchmiiller, 1967; Godinho et al., 1970; Jirge, 1970; Konfal, 1970; Bucke, 1971 ; Western, 1971 ; Gauthier and Landis, 1972 ; Vegas-Velez, 1972 ; Suvorova and Treschuk, 1973). Western (1971) believes that the fore-gut of Cottus gobio, Enophrys bubalis, Salmo trutta and Noemacheilus barbatuhs is the chief site of PAS positive mucus production while in the remaining part of the gut an AB positive type predominates. Verighine observed PAS positive granules in the apical part of the epithelial cells in the fore-gut of Ctenopharyngodon idella (Fig. 14), and Belonozhko (1967a) in Rutilus rutilus. The goblet cells in the caeca of Perca $uviatilis often show tiny lipid droplets and their secretion shows the Astra blau reaction after permanganate oxidation for protein (Jansson and Olsson, 1960). The mucus in the goblet cells in the intestine and rectum of Gambusia a&& stains intensely with paraldehyde fuchsin and the Hale-Muller colloidal iron technique, and also metachromatically with various azure stains (Bullock, 1967; see Konfal, 1970, for these regions in A.M.B.-13

6

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Umbra krameri Wa1b.-positive stain for goblet cells with paraldehyde fuchsin, PAS, Masson’s trichrome). Further, the mucoid plaque in the gizzard of Mugil sp. contains neutral mucopolysaccharides (Castro et al., 1961). Also, the free border of the anterior intestine of Gambusia aflnis stains with PAS, paraldehyde fuchsin, alcian blue and the Hale-Muller colloidal iron technique, which indicates a mixture of mucoproteins and acid mucopolysaccharides (Bullock, 1967 ; see also Konfal, 1970). Medeiros et al. (1970b) reported amino groups from the goblet shaped cells of the intestine in Pimelndus maculatus LacBpBde.

FIG.14. Mucopolysaccharides in the epithelium of the gut of Ctenopharyngodon i d e l h (Val.). (PAS) After Verighina, I. A.

In Thymallus arcticus baicalensis Dyb. the goblet cells of the oesophagus show the presence of glycogen, neutral MPS, hyaluronic acid, chondroitin sulphates and sialic acid, and those of the intestine glycogen and acid MPS (glycogen being absent in those of the pyloric appendages) (Suvorova and Treschuk, 1973). Varute and Jirge (1971) stated that the mucosubstances in the oral mucosa of female mouthbreeding Tilapia mossambica contain sulfomucins, sialomucins and neutral mucosubstances. Such mucosubstances show seasonal variations in concentration during the breed-

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ing-non-breeding cycle, probably under hormonal control. I n Pimelodus maculatus, arginine, tyrosine, cysteine and cystine have been identified in the mucous cells from the mouth and oesophagus. The mucous cells in the terminal portion of the oesophagus do not contain free amino groups (Medeiros et al., 1970b). Weinreb and Bilstad (1955) reported neutral MPS from the stratified epithelium of the upper oesophagus, the columnar cells of the intermediate oesophagus, and the striated border of the absorptive cells of intestine and caeca in Salmo gairdneri irideus. Jirge (1970) found acid MPS in the striated border of the epithelial lining of Labeo rohita ; acid MPS and neutral MPS in the serosa, and neutral MPS, glycogen and sialomucins in the submucosa of the stomach or intestinal bulb of some fish. He observed that the gastric glands in Tilapia mossambica show granular basophilia with AB (pH 2.5) and also the presence of neutral mucins. He attempted to correlate the distribution of MPS with the feeding habits of the fish. I n Pimelodus maculatus, the peripheral squamous cells of the stratified epithelium from mouth t o oesophagus contain free amino groups, arginine, tyrosine and cysteine, while those of the terminal portion of the oesophagus also contain cystine. The basal layer cells and polyhedral cdls of the stratified epithelium from mouth t o oesophagus contain free amino groups, arginine, tyrosine, cysteine and cystine. Tryptophan could not be detected in the epithelium of mouth and oesophagus (Medeiros et al., 1970b). Medeiros et al. (1970b) localized the occurrence of free amino groups, arginine, tyrosine, tryptophan, cysteine and cystine from gastric mucus-secreting cells in Pimelodus maculatus. Suvorova and Treschuk (1973) reported neutral MPS and acid MPS in the gastric epithelium and connective tissue (also of oesophagus) of Thymallus arcticus baicalensis. The club-cells in the skin of Carassius and Corydoras are not deeply stained with HIE, PAS or Azure B techniques; those in Anguilla are faintly eosinophilic after Harris’ haematoxylin and eosin but slightly basophilic when this haematoxylin is used to counterstain the PAS reaction (Henrikson and Matoltsy, 1968; see also Sat6 and Sannohe, 1967 ; Mittal and Munshi, 1969). The secretory material of the club-cells in the skin of ostariophysous teleosts does not contain carbohydrates in the form of aldehydes or mucopolysaccharides (Mittal and Munshi, 1969). The presence of glycogen granules (Mittal and Munshi, 1969; Pfeiffer et al., 1971) has been demonstrated. The cells contain proteins (Sat6 and Sannohe, 1967 ; Mittal and Munshi, 1969 ; Pfeiffer et al., 1971) and diastase-resistant polysaccharides have been encountered in the cytoplasm (Pfeiffer et al., 1971). It has been shown that the specific secretion is a protein of low molecular weight (Pfeiffer et al., 1971 ; see also Bremer, 1972).

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I n the club-shaped cells found in the epithelium of the digestive tract of Pimelodus maculatus, Medeiros et al. (1970a) detected (I)only amylase resistant neutral polysaccharides and among the carboxylated chiefly hyaluronic acid, and (11)tyrosine, cysteine and amino groups (see also Medeiros et al., 1970b). On the basis of morphology and .vc-eal
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according to them, there are only zymogenic or chief cells in the gastric glands. There have been few attempts to localize the source of acid production. Al-Hussaini (194913) found no precipitate of Prussian blue in the gut of cyprinid fishes and concluded that free HC1 did not occur. Western and Jennings (1970) used the Prussian blue reaction for the in vivo demonstration of gastric hydrochloric acid in some teleosts. They did not observe intracellular precipitation of Prussian blue, but the presence of precipitate in the innermost portions of the gastric gland tubules indicates that the acid responsible for its formation is produced by the lining cells, which are all histologically identical and contain numerous pepsinogen granules (Fig. 15). Manfredi Romanini (1959) reported lipoid granules in the gastric gland cells of Amiurus catus L., Salmo irideus and Scorpaena scrofa L. and Bishop and Odense (1966) observed eosinophilic granules in the cells of the compound tubular gastric glands in Gadus rnorhua. The granules in the glands of the stomach of Umbra krameri stain with paraldehyde fuchsin and Masson’s trichrome and do not stain with PAS and aniline blue (Konfal, 1970). In the neck-cells of gastric glands in Tilapia mossambica and T . xilli Verighina found neutral and acid mucopolysaccharides. Alkaline phosphatase in the free border microvilli of the intestine and caeca of teleosts has been detected by a number of authors (AlHussaini, 1948, 1949b ; Weinreb and Bilstad, 1955; Reznik, 1958 ; Prakash, 1961 ; Verighina, 1961, 1963; Bullock, 1963, 1967; Khalilov et al., 1963 ; Luppa, 1966 ; Srivastava, 1966 ; Sivadas and Govindan, 1970; Western, 1971; Mester et al., 1972; Goel and Sastry, 1973; for further information on intestinal alkaline phosphatase, see Whitmore and Goldberg, 1972a, b). Alkaline phosphatase activity has been recorded by various workers at a variety of locations, and in different intensities : the stratified epithelium of the bucco-pharyngeal cavity, granulocytes, connective tissue and blood vessels in the intestine of some Cyprinids (Al-Hussaini, 1949b; cf. also Al-Hussaini, 1948); the stratum compactum in Gobio gobio (Al-Hussaini, 1949b); the stratified epithelium of the upper oesophagus, the columnar cells of the intermediate oesophagus in Salmo gairdneri irideus (Weinreb and Bilstad, 1955); epithelium and fold stroma of caeca in Perca JEuviatilis (Jansson and Olson, 1960); the stratified epithelium of the bucco-oesophageal wall, lymphocytes, granule cells and blood capilliaries of the oesophageal region, the gastric wall (lamina propria, granule cells and fibroblasts of the submucosa), the intestinal caeca and rectal region (nuclei of columnar epithelium, fibroblasts, granule-cells, mast cells and lymphocytes, endothelial cells of blood capillaries, reticular connective tissue and lymphatics in the lamina propria) in adult steelhead trout

FIG. 15. (a) Transverse section of tho stomach wall of Enophrys bubalis (Euphrasen). Precipitates of Prussian blue in the openings of the gastric glands indicate the presence of HCl. (b) Sagittal section of the stomach wall of Cottus gobio L. Dark spots in the lumina of the gastric tubules indicate gastric acid. (From J. R. H. Western and J . B. Jennings ( 1970). Comparative Biochemistry and Physiology, 35, 879-884).

FIG.16.

a

and b.

Fro. 16.

c

and d.

FIG.160.

FIG. 16. Horizontal longitudinal sections of the pyloric caeca of Enophrys bubalis (Euphrasen). (a) Acid phosphatase. (b)Alkaline phosphatase. ( 0 ) Leucine aminopeptidese. The activity of these enzymes is restricted to the epithelial cell microvilli. (d) Esterase activity in the cytoplasm of the epithelial cells. (e) Acid phosphatase in the stomach wall of Cottus gobio L. Enzyme activity is restricted to the connective tissue, muscularis and serosa. ( f ) Esterase activity in rectum of Enophrys bubalis. Enzyme activity is present in the epithelium only. (From J. R. H. Western (1971). Journal of F i s h Biology, 3, 225-246.)

162

B. a. KAPOOR, H. SMIT AND

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VERIOHINA

(Prakash, 1961); the lamina propria of the intestine in some salmonids (Bullock, 1963); the outer region of the oesophageal epithelium, the junction of submucosa and muscularis in the posterior intestine of Gambusia afinis (Bullock, 1967); the gastric glands and tunica propria of the corpus, tunica propria of pylorus, nuclei of columnar cells of the intestine and its tunica propria of Tilapia mossambica (Sivadas and Govindan, 1970). Weinreb and Bilstad (1955) reported that alkaline phosphatase activity and neutral MPS occupy the same sites and they believe the oesophagus, intestine and caeca to be areas of active absorption in Salmo gairdneri irideus. Srivastava (1966) mentioned that glycogen follows the distribution of alkaline phosphatase in Heteropneustes fossilis (Bloch),Ophicephalus striatus (Bloch) and Mastacembelus pancalus (Ham.). Acid phosphatase has been demonstrated in the striated border microvilli of fish intestine and caeca (Jansson and Olsson, 1960 ; Jirge, 1970; Western, 1971). The distributian of acid phosphatase in different intensities has also been recorded from the subepithelial connective tissue, muscularis and serosa of the stomach in Cottus gobio and Enophrys bubalis (Western, 1971) (Fig. 16), and in subepithelial connective tissue throughout the intestine of Carassius auratus (Gauthier and Landis, 1972). I n the goldfish, Gauthier and Landis (1972) also found acid phosphatase activity just below the terminal web of the absorptive cells in the intestinal bulb and in the posterior intestine a t sites which coincide in position with regions containing supranuclear bodies. Khawaja and Jafri (1968) stated that the concentrations of acid and alkaline phosphatases vary considerably in different regions of the alimentary canal of Ophicephalus punctatus Bloch. The activities of these enzymes are lowest in the oesophagus and fairly low in the rectum. I n the stomach, a high acid phosphatase activity is accompanied by a low activity of alkaline phosphatase, whereas in the intestine the alkaline phosphatase activity is higher than the acid phosphatase activity. The highest acid phosphatase activity occurs in the stomach and the highest alkaline phosphatase activity in the caeca. Hollands and Smith (1964), during their study of the location of phosphatases within the goldfish intestine, found that (I)ATP, AMP and glycerophosphate are hydrolyzed a t the luminal border of the mucosal cells in the intestinal bulb and the intestine proper, but not in the rectum. UTP was only incubated with sections of the anterior intestine where it is hydrolyzed at the luminal border of the mucosal cells ; (11)ATP and UTP, but not AM? or glycerophosphate, are hydrolyzed by enzymes in the muscle of the goldfish intestine, and (111)ATP-ase is

THE ALIMENTARY CANAL AND DIGESTION I N TELEOSTS

163

found at the base of the mucosa throughout the whole length of the tract and exhibits a high degree of substrate specificity ; AMP gives only a faint reaction, glycerophosphate no reaction, and ATP is not hydrolyzed at this site.

Leucine aminopeptidase has been demonstrated in the intestinal microvilli of Cottus gobio and Enophrys bubaZis (Western, 1971) and Misgurnus fossilis (Mester et al., 1972). Esterase hydrolyzing indoxy: acetate and a-naphthyl acetate has been localized in the cytoplasm of epithelial absorptive cells of the mid- and hind-gut of Cottus gobio and Enophrys bubalis (Western, 1971). Lactate dehydrogenase, malate

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R . G . KAPOOR, H . SMIT AND I.

A. VERIGHINA

DH and isocytrate DH are present along the whole length of the intestinal mucosa, their activity being higher in the posterior (respiratory) part in Misgurnus anguillicaudatus. They fulfil multiple functions of secretory, resorptive and possibly synthetizing characters (MeSter et al., 1972).

Jansson and Olsson (1960) reported an effective peptic digestion on the striated border of the columnar cells of the caeca of Perca Jluviatilis. The methyl greenlpyronine procedure showed low nucleoprotein content of the columnar cells. Medeiros et al. (1970b) demonstrated arginine, tyrosine and tryptophan in the intestinal columnar cells of Pimelodus maculatus.

THE ALIMENTARY CANAL AND DIGESTION I N TELEOSTS

165

Luppa (1966, see Table 1, p. 322) localized the activities in the intestinal caecal cells of PercaJluviatilis of un-specific alkaline phosphomonoesterase, naphthol-AS-D-acetate-esterase, leucineaminopeptidase, succinate-dehydrogenase, cytochromoxidase, DPN-diaphorase, glucose6-phosphate-dehydrogenase,glutamate-dehydrogenase, glycerophosphate-dehydrogenase, malate-dehydrogenase, and monoamineoxidase (Fig. 17).

FIG. 17. (a) Caecal epithelium of PercajZuwiatiZia L. Acid phovphatave in (dark) lining cells. Goblet cells are white. (b) Leucine aminopeptidase activity (dark). (c) Glucose6-phosphate-dehydrogenes3activity (dark). From Luppa, H. ( 1956). Morphologiachea Jahrbuch, 109, 3 15-339.

Verighina (1961) described in the epithelium of the mid-gut o f Hypophthalrnichthys molitrix eosinophilic inclusions of unknownnature (Fig. 18). Gauthier and Landis (1972) stated that the supranuclear bodies of the posterior intestine in Carassius auratus contain protein material, which is slightly acidophilic a t p H 4.1 and slightly basophilic

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B . G . KAPOOR, H. SMIT AND I . A. VERIGHINA

a t pH 5.3; the content of the bodies is also PAS-positive. Certain differences have been observed in the distribution of RNA in the intestinal epithelium. The quantity of RNA in the epithelium, situated a t the bases of the folds, is higher than in their summits (Vasilieva and Korovina, 1968; Khalilov, 1969). Belonozhko (196713) noted an increase of RNA by fat absorption in Abramis brama (L.). F a t absorption is an easily observed process and has been covered by Reznik (1958), Verighina (1963), and Bergot and FlBchon (1970a, b, see references). Positive histochemical demonstration of lipase has

F I ~18. . Eosinophilic inclusions in the epithelium of the mid-gut of Hypophthalmichthys mo2itriz (Val.). (haem. 83s.) After Verighina, I. A. (1961). Sbornik Trudov Zoologicheskogo Museya Moscowskogo Universiteta, 8, 189-196.

been obtained in the intestinal mucosal epithelium of the cyprinids Cyprinus carpio L., Rutilus rutilus and Gobio gobio (Al-Hussaini, 1949b). The columnar caecal cells of P e r m Jluwiutilis are highly sudanophilic. With the Sudan black B technique, the striated border gave a faint reaction; the subcuticular zone gave no reaction and the mitochondria1 zone intense reaction (Jansson and Olsson, 1960). Khalilov (1969) reported great quantities of DNA and RNA in the epithelium of the pyloric caeca of Brachymystux lenok and believed that synthesis of digestive enzymes is possible there. It has been indicated that the most intensive fat absorption takes place in the foreand mid-gut of the tench accompanied by enlargement of the Golgi

THE ALIMENTARY CANAL AND DIQESTION I N TELEOSTS

167

apparatus and an increase of the alkaline phosphatase activity. These phenomena are also observed when starch is introduced into the gut (Khalilov, 1969). Jansson and Olsson (1960) found a low nucleoprotein content of the caecal calumnar cell in Perca Jluviatilis. Sivadas (1965) pointed out that the intestine in Tilapia mossambica absorbs sudanophilic fat, which in its particulate form is transferred from the lumen into the absorptive cells through spindle-shaped canals located in the free border (see also Al-Hussaini, 1949b). Dawes (1929) found a marked increase in the fat content of the gastric epithelium after feeding in Pleuronectes platessa. Bergot and Fl6chon (1970a) reported that the epithelial absorbing cells in Salmo gairdnerii appear to be able to esterify long chain fatty acids in the diet and pass them on in a form similar to chylomicra or very low density lipoproteins, and suggested that these particles may leave the intestine by portal as well as lymphatic pathways (see also Gohar and Latif, 1963). Read and Burnstock (1968) observed scattered enterochromaffin cells with bright yellow fluorescence in the cytoplasm, probably due to their 5-hydroxytryptamine (5-HT) content, in the mucosal epithelium of all regions of the gut, particularly the stomach and the small intestine of Anguilla occidentalis australis Schmidt, and in the mucosa of the oesophagus and stomach (not of the intestine) of Salmo trutta and S. irideus. Therefore, they contradicted the earlier claim of Erspamer (1954) and Fange ( 1962) that typical 5-HT-containing enterochromaffin cells are not found in teleosts and cyclostomes (see review by Dawson (1970) on enterochromaffin cells). The absence of Paneth and argentaffin cells was pointed out earlier by Suzuki et al. (1963), Hale (1965), and Godinho et al. (1970) on the basis of various techniques used by them. Read and Burnstock (1968) also observed in the cytoplasm adjacent to the free margins of the mucosal epithelial cells of the large intestine in Anguilla occidentalis australis and Salmo t r u t h (also S. irideus) respectively, numerous, conspicuous brown, bright golden or greenish yellow eutofluorescent granules (probably of some secretory material) (Fig. 19). These were also found in the gut of Tinca vulgaris Cuv. (Baumgarten, 1967a). Dull cream or orange autofluorescent cells were observed in the lamina propria connective tissue of the large intestine of Anguilla occidentalis australis (Read and Burnstock, 1968) as well as in the connective tissue of the gut of Tinca vulgaris (Baumgarten, 1967a). Different staining properties of the “pear-shaped ” cells have been reported ; more work is required to get a definite picture. These cells give a positive reaction with PAS, aldehyde fuchsin, Gram method and Azan (Vickers, 1962). They do not stain with alcian blue or PAS techniques according to Bishop and Odense (1966); rodlets stain well

168

B . 0. KAPOOR, H. SMIT AND I. A. VERIGHINA

with fast green, aniline blue, PAS and aldehyde fuchsin, while the cell membrane becomes prominent on staining with fast green or orange G. (Bullock, 1967). The granular cells in the different parts of the digestive tract of fish are diverse : basophilic, acidophilic, basophilic changing t o acidophilic, both acidophilic and basophilic (Bolton, 1933 ; Al-Hussaini,

FIG.19. Mucosa of eel large intestine. Brown autofiuorescence (au) and part of an enterochromaffin cell (ec) are visible in the mucosal epithelium (ep). There are scattered cells (g), with autofluorevcent granules, in the lamina propria. From Read, J. B. and Burnstock, G. (1968). Histochemie, 16, 324-332.

194913, Table I, p. 333 ; Weinreb and Bilstad, 1955) ; therefore they pose a complex problem. Even in one species the contents may differ in chemical composition, probably in connection with a variety of functions (Al-Hussaini, 1949b). Weinreb and Bilstad (1955) found that in the granule cells of Salmo gairdneri irideus, the granules vary in

THE ALIMENTARY CANAL AND DIGESTION I N TELEOSTS

169

size and shape with the fixative used (optimal fixation was obtained with Helly’s, 10% buffered formalin, and the mitochondria1 fixatives of Regaud and Champy). The examination by Weinreb and Bilstad (1955) and Bullock (1963) revealed that each granule appears to possess a protein core containing arginine, an outer lipid-phospholipid shell, and a trace of non-acid mucopolysaccharide. Further, according to Weinreb and Bilstad (1955), these cells were not comparable to mast cells, and were not directly involved in haemoglobin breakdown. The phagocytic cells in the digestive organs are granulocytes located in the tunica propria and submucosal layers ; the granule cells of the stratum granulosum are not involved in phagocytosis. We find that PASreaction in granules is from pink up to strong red in Salmonidae. Alkaline phosphatase in the granular cells is observed in 8. trutta, S. gairdneri, S. salar (Bullock, 1963), Rutilus rutilus and Cyprinus carpio (Al-Hussaini, 1949b) and steelhead trout (Prakash, 1961). A negative reaction on alkaline phosphatase takes place in Salvelinus fontinalis (Mitchell) (Bullock, 1963). Bullock (1967) observed that the granular cells in Gambusia afinis distinctly stain dark red against a pale background by the use of trichrome stain after fixation in neutral buffered formalin. They do not stain noticeably with H/E and PAS. Al-Hussaini (1949b) reported the presence of glycogen in granular cells in Rutilus rutilus and Cyprinus carpio. For details on lymphocytic wandering cells (with a typical large nucleus, basophilic cytoplasm, slight PAS reaction) and polymorphonuclear wandering cells (with a lobed nucleus, moderately acidophilic and slightly granular cytoplasm, intense PAS reaction) in the intestine of salmonid fish, read Bullock, 1963. The stratum compactum in the intestine of some salmonid fishes is acidophilic, stains intensely with PAS, stains yellow with Mallory’s phosphotungstic acid haematoxylin and red with the Rinehart and Abul-Haj technique (Bullock, 1963).

V. INNERVATION AND ALLIEDASPECTS The taste buds, confined not only to the oro-pharynx and associated structures but spread over the body surface (in some teleosts), are innervated by branches of the facial, glossopharyngeal and vagus nerves (Aronson, 1963; Bardach and Atema, 1971 ; for details see Hirata, 1966; Uga and Hama, 1967; Storch and Welsch, 1970; Reutter, 1971 ; Whitear, 1971). The tongue of Gnathonemus pertersii (Gunth.) is innervated by a branch of the facialis nerve (Mikuriya, 1972). The accessory digestive organs-epibranchial organs-are innervated by the vagus (Bertmar et al., 1969; Schmitz and Baker, 1969; Campbell, 1970).

170

B.

0. KAPOOR,

H. SMIT AND I.

A. VERIGHINA

Succint accounts of Auerbach’s plexus are available in a number of papers. Burnstock (1959b), in a fine description on the extrinsic and intrinsic innervation of the gut of Salmo trutta, described the paths of the vagus nerves in the stomach, the single anterior splanchnic r

i

cm

sm mm SC

me

FIG.20. Nervous elements in the stomach wall of the trout. me, mucosal epithelium; sc, stratum compactum ; mm. muscularis mucosae ; sm,submucosa ; cm, circular muscle ; lm, longitudinal muscle ; s, serosa ; NI, NIII, two types of nerve-cella. From Burnstock, G . (1959b). Quarterly Journal of M ~ C T O S C OScience, ~ ~ C U ~100, 199-220.

nerve in the stomach and intestine, and two posterior autonomic nerves in the rectum ; he distinguished on the basis of distribution and structure three main types of nerve-cells, and recognized, besides Auerbach’s plexus, a subepithelial plexus, the sub-mucous plexus, but unlike Meissner’s plexus of the mammalian sub-mucous coat no nerve-cells are present ; further, a subserous plexus, and an ‘‘ inter-

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171

stitial cell network ” (Fig. 20). Earlier Sublette (1956) had found Meissner’s plexus in the submucosa of the oesophagus and stomach in Morone chysops. Vickers (1962) stated that groups of nerve-cells (presumably parasympathetic neurones) are present within the outer muscular layers of the intestinal bulb, especially in the vicinity of the sphincters, in Carassius auratus. Recent reviews on the innervation of the gut of teleosts are written by Campbell and Burnstock (1968) and by Campbell (1970) who discussed the general inference that stimulation of the vagi causes contraction of the stomach, but not of the intestine, in those animals having a stomach. I n stomachless fish, vagal stimulation may cause contraction of the whole intestine or just a part of it. Campbell and Burnstock (1968) have suggested that the sympathetic supply to all regions of the gut contains both excitatory and inhibitory nerve fibres. It may be suggested that the excitatory nerve fibres are cholinergic and the inhibitory fibres adrenergic (see Campbell, 1970). Ito and Kuriyama (1971)showed the existence of three different kinds of nerve fibres in the muscular layers of the alimentary canal of the goldfish, i.e. excitatory vagal fibres, inhibitory vagal fibres, and inhibitory sympathetic fibres. Adrenergic nerves generally occurring in the perivascular plexuses in the lamina propria have been demonstrated histochemically in the tench (Baumgarten, 1967b) and eel and trout (Read and Burnstock, 1968). Burnstock (1972) sums up the existing evidence for the occurrence of purinergic inhibitory nerve fibres in Auerbach’s plexus of the teleostean stomach. These nerve fibres make use of ATP as a transmitter substance. Apart from those in the vascular plexes, only a small number of fluorescent nerve fibres have been detected in the lamina propria of fish gut (Baumgarten, 1967a; Read and Burnstock, 1968) and few, if any, are present in the muscularis mucosae of the eel (Read and Burnstock, 1968). Frantsuzova (1971) distinguished two main forms of interoreceptors (bushy and glomerulus) in the digestive tract of Stenodus leucichthys (Gidd.) and added that the receptors of different parts of the digestive tract are morphologically distinct ; differences between receptor terminations may be found even within the same section. Nilsson and Fange (1969) investigated adrenergic and cholinergic vagal effects on the stomach of Gadus morhua. They reported that the contractive effects of adrenaline and noradrenaline, and the relative lack of contraction after isoprenaline indicates the existence of a-adrenergic receptors (Fig. 21). The relaxing effect of isoprenaline as well as the relaxing effect of adrenaline after phenoxybenzamine is probably due to the presence of adrenergic p-receptors. They added

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that contractions produced by electrical stimulation of the vagus nerve, or by adrenergic drugs, are inhibited by atropine, and this may indicate that the effects are mediated via cholinergic neurons. Such neurons could be represented by ganglionic cells of Auerbach’s plexus or similar structures. Earlier (1967), they reported the presence of a-receptors only in the gastric caecum and ,!-receptors only in the oesophagus and intestine of Anguilla anguilla. Ohnesorge and Rauch (1968) conducted pharmacological investigations on the peristaltic movements of the gut of Tinca vulgaris which contains both smooth and striated muscle. They reported that the striated muscle elements do not participate in peristaltic movements. The reflex is enhanced by both acetylcholine and physostigmine, and inhibited by atropine and adrenaline. They suggested that peristaltic movements are caused by a genuine reflex. The intramural

Cholinergic

?<-D:

M U alpha receptor

1

E

VAGUS FIBERS Adrenergic

FIG.21.

Hypothetical interactions between vagal nerves and muacle. Adrenorgic a receptors may be situated in postganglionic cholinergic neurons. From Nilsson, S. and Fange, R. (1969). Comparative Biochemistry und Physiology, 30, 691-694.

ganglionic cells are obviously involved in the reflex pathway. Ohnesorge and Schmitz (1968) indicated that, in vitro,the conOractions of striated and smooth muscle of the gut of Tinca vulgaris may be influenced by the adaptation temperature of the living fish. As regards the neural control of gastric, hepatic, or pancreatic secretion in fish, investigations are too scarce to permit any definite conclusions to be drawn (see Campbell, 1970, and also section IX).

VI. FOOD INTAKE Food consumption in fish and the factors governing food intake and feeding rate are of interest with respect t o fish production, the ecology of fish populations, and the behaviour and physiology of fish. Several methods are available for measuring the quantity of food ingested. Direct methods are based on observation of the quantity of food consumed by a single fish or a group of fish under laboratory conditions, field methods on the estimation of the contents of the stomach and/or intestines. Pearse (1924), who kept small specimens of Micropterus

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salmoides (LacBpBde),Lepomis gibbosus L. Ictalurus nebulosus (LeSueur), and I . natalis (Le Sueur) a t 19"C, found that when given an excess supply of their natural food, the daily consumption amounted to 5-9y0 of the body weight on a fresh weight basis. Moore (1941) studied food intake in Lepomis cyanellus Raf., Helioperca incisor (Cuv. & Val.) and Perca JEavescens (Mitchill) kept in glass aquaria a t roughly constant temperature and fed (chopped liver and scraped beef) once, twice, or three times daily. The daily food intake was variable, but, when considered over a longer period, the consumption rate proved to be constant for a given species and size and was independent of the daily feeding frequency. Hunt (1960), working with Chaenobryttus gulosus (Cuv. & Val.), Micropterus salmoides, and Lepidosteus platyrhincus, also found day-to-day fluctuations in the amount of food eaten, but each species could be characterized by the average quantity consumed. The food intake of predatory fish can be easily measured under experimental conditions. After known numbers of a predatory species and its prey are placed in a pond, the consumption over a certain period of time can be calculated by introducing a known number of tagged prey fish shortly before sampling the pond. From the ratio between tagged and untagged prey specimens in the sample, the number of missing prey fish can be computed. A field method for the estimation of food consumption was devised by Bajkov (1935), based on studies on whitefish collected in their natural habitat. The stomach contents of some of these fish were examined immediately after capture ; the remaining fish were kept in tanks and sampled from time to time. The daily food consumption (D) was calculated by means of the formula D 24A/n, where A = average amount in the stomach, and n = stomach-emptying time in hours. This method, however, does not take into account the chronology of feeding intensity throughout the 24-hour cycle and presupposes that the digestion rate is independent of the amount of food ingested. TO accommodate t o these objections, Darnel1 and Meierotto (1962)collected their fish in a series of catches over a 24-hour period for the determination of the feeding chronology. To estimate digestion rate they made laboratory studies of the time course of digestion of the " standard food item ", i.e. the food item consistently present in fairly high concentrations in the stomachs a t capture. Several modifications of the volumetric method for the analysis of food consumed by fishes have been described (e.g.: Hellawell and Abel, 1971 ; Jearld and Brown, 1971 ; see also VII.2. Digestion Rate). Indirect methods for the estimation of food intake are based on the relation of growth or the assimilation of nutrients t o the amount of

+

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B. G . KAPOOR, H. SMIT AND I. A. VERIGHINA

food consumed. For example, the relationship between food intake and growth rate has been investigated by Baldwin (1956) for Xalvelinus fontinalis, by Brett et al. (1969) for Oncorhynchus nerka Walb., and by Carline and Hall (1973) for Oncorhynchus kisutch (Walb.) Since growth can be defined as the synthesis of new protoplasm, Gerking (1954, 1955, 1962, 1971) used protein synthesis as a measure of growth, which in turn was considered as a measure of the amount of food consumed. Because the protein content of fish is the least variable of the three main body constituents (proteins, fats, carbohydrates), in his study of Lepomis macrochirus (Raf.), Gerking estimated the amount of nitrogen consumed in the natural habitat on the basis of laboratory data on the relationship between nitrogen retention and consumption. Another approach t o the estimation of food intake by fish is the use of a radioisotopic method. Kevern (1 966) determined the average daily food consumption of carp in the natural environment by estimating the turnover of 137Cs by carp living in a lake receiving radioactive wastes. Estimation of the rate of element intake and the mean concentration of the element in the food gave an approximate assessment of the annual mean of daily feeding rates. Kolehmainen ( 1 974) determined the actual daily feeding rates of bluegill (Lepomis macrochirus) living in an empoundment recsiving radioactive effluents, by dividing the daily intake of 137Cs by the concentration of 137Cs in the diet. The daily meal, taken by these bluegills, varied from 0.8% of body weight in February to 3.2% in June with an annual mean of 1.750/,. Fish are able to regulate their food intake, but this intake is influenced by several factors. The food supply often influences food intake. I n case of predatory fish, the predation rates are not simply proportional to the food supply since the diet of the fish is more closely correlated with the behavioural properties rather than the density of the food species (Ware, 1972). The minimum amount of food a fish must eat to provide for L‘ routine metabolism ” while maintaining its body weight, is termed the ‘‘ maintenance requirement ”. Fish are able, however, to adapt to a certain ration. Reduction of the amount of food toward the maintenance level resulted initially in weight loss, followed by a weight gain after the fish had become adapted (Brown, 1946, 1957). This observation weakens the concept of “ maintenance requirement ”. Temperature too is an important factor affecting feeding rate. The influence of temperature on eagerness of food consumption has been demonstrated by Krayukhin (1963) who measured ithe feeding reaction time of Ictalurus nebulosus a t various temperatures (Table

IV).

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TABLEIV Temp.

("C) 17-20 10 5 4 3

Feeding reaction time

(8)

1.4 3 15 25 no reaction

Acclimation to low temperatures resulted in a decrease of the feeding reaction time. Hathaway (1927) found that Lepomis gibbosus, L . macrochirus and Micropterus salmoides consumed about three times as many earthworms per day a t 2OoC as a t 10°C. The daily amount of food consumed by roach (Rutilus r . caspius Jak.) was found by Bokova ( 1 938) t o be strongly temperature dependent (Table V). TABLEV Temp.

("(2

1-5 6-10 10-15 15-20

Food intake

(yoof bodyweight) 0.5 3-5 7.8 12.8

Goldfish decreased their food intake by one-half to one-third in response to a drop in temperature from 25OC t o 15OC (Rozin and Mayer, 1961). Daily consumption of minnows by brook trout (Salvelinus fontinalis) amounted t o 5% of their body weight at 9°C) 7 % at 1 3 O C , and about 1% a t 21°C (Baldwin, 1956). For food consumption rates in piranha, see Foxx and Martin (1970). Since basal metabolism and activity are highly dependent on temperature, the maintenance requirement varies strongly with temperature, and since neither basal metabolism nor activity shows a simple relationship with temperature, the relationship between requirement and temperature will also not be simple, as demonstrated by Brown (1946) for Salmo trutta. At higher temperatures the maintenanoe requirement was more rapid when the temperature

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I. A.

VERIGHINA

rose from 9°C to 12"C, than when it rose from 5OC to 9°C and from 12°C to 20°C. Brown suggested that this rapid increase resulted from increased activity between 9" and 12°C. Brett et al. (1969) determined the maintenance ration in young sockeye salmon a t acclimation temperatures ranging from 1' to 24°C. They assured a greater uniformity of activity by having their fish swim against a constant low velocity was then found to increase water current. The maintenance ration (R) b. semilogarithmically with increasing temperature (T) : log R =aT At 5"C, the excess ration was 11.5 times greater than the maintenance ration, a t 15°C about 4.6 times, and a t 20°C the maximum food intake was about 3 times greater than maintenance level. At 23"C, which is close to the lethal upper temperature limit, the fish lost their appetite. Seasonal fluctuations in food intake may depend on a variety of factors, but even when temperature, food availability, and illumination are kept constant throughout the year, fluctuations in food intake indicate the existence of a physiological cycle. Sehgal (1966b) did not find any difference in feeding habits between young and adult Labeo calbasu (Ham.)except during the breeding season when the feeding rate of the mature fish declined, whereas the juveniles showed no such seasonal fluctuation. I n the striped bass (Roccus saxntilis Walb.) fasting occurs for a bricf period before and during spawning (Trent and Hassler, 1966). After a period of fasting, fish tend t o conslime more food than before the starvation period, as demonstrated for Lepornis cyanellus by Moore (1941): after a 5-week starvation period the higher food intake during the following 2 weeks resulted in a weight gain amounting to almost 17%. Feeding activity and eagerness are above normal after fasting (Pegel, 1950; Krayukhin, 1963; Hotta and Nakctshima, 1969). Schooling mag result in local depletion of food in the area occupied by a school, and therefore may suppress individual food intake (Barber and Minckley, 1971). Swimming requires energy and therefore food consumption increases with the activity level. Hunt (1960) investigated voluntary food consumption in warmouth (Chaenobryttus gulosus), gar (Lepidosteus platyrhincus), and bass (Micropterus salmoides). The daily food consumption of gar amounted t o 0.6 times that of warmouth and 0.4 times that of bass ; these differences corresponded with differences in activity, bass being the most active and gar the most sluggish fish. The activity level is influenced by temperature, but besides its effect on activity, temperature influences the feeding rate via its efYect on standard metabolic rate. Other factors affecting activity are food density, predation, migration, oxygen content of the water, spawning, and strength of the water current. Lowering of the ambient oxygen

+

THE ALIMENTARY CANAL AND DIGESTION I N TELEOSTS

177

concentration has been found to suppress food intake by Oncorhynchus kisutch (Herman et al., 1962) and Micropterus salmoides (Steward, 1962). Food intake must cover the total energy expenditure for growth and metabolism. Increased activity does not mean a concomitant increase in the feeding rate, since the energy costs of locomotion can be deducted from energy channelled into growth (see Beamish and Dickie, 1967). The feeding rate is also affected by the digestibility of the food. Part of the food material may be indigestible, and this is voided as faeces. Fresh weight is not a valid measure of food intake when energy supply rather than bulk is under consideration. Windell (1967) analyzed food for its percentage of organic matter and chitin, and estimated digestible organic matter by subtracting ash weight and chitin from the total dry weight of the food. The nutritional value of the food, and therefore total food intake, depends on the relative proportions of proteins, fats, carbohydrates and minerals. Food intake further depends on the size of the fish ; this does not merely mean that a bigger fish consumes more food than a smaller fish ; as a matter of fact the food consumption rate per unit fish weight is normally lower in big fish. For example : small gars had an average daily food consumption of 4.26% of their body weight, whereas gars weighing three times as much, had one of 2.81$/, (Hunt, 1960). Pearse (1924) reported the following data, from which the inverse relationship between body weight and relative food intake is apparent (Table VI). TABLEVI Species Rock bass Pumpkinseed Largemoutl I Bullhead

Body weight (9) 31 18 4.6 4.4

Food intake

(%) 2.5 4.1 6.2 10.7

For brook trout ranging from 40 t o 180 g, Baldwin (1956) found that the smaller fish ate about 1.4 times as much as the bigger fish, in terms of food consumption per gramme live fish. Pandian (1967) reports the following results (Table VII). The fact that food intake is relatively larger the smaller the body size, is in agreement with the well-known fact that smaller fish have

178

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A. VERIGHINA

relatively higher metabolic and growth rates than larger fish. This generalization is weakened, however, by many other influences on growth rate and food intake, such as the sexual cycle and the condition factor. The recognition of relationships between feeding rate and temperature, season, activity, body size, etc., raises questions concerning the mechanism regulating the food consumption rate. One may speculate that gut capacity, digestion rate, satiety, and metabolic rate will play some role. If a fish with an empty gut is fed, it takes food greedily, and when food remains available feeding activity slows down gradually (Hotta and Nakashima, 1969). When there is only one feeding per day, the amount of food then taken is large. As the frequency of feedings increases, the amount of food consumed per feeding declines with the increase in the daily ration, but the maximum daily ration is Boon reached (Ishiwata, 1969). Trout fry fed only a few times a week TABLEVII Species Megalops cyprinoides Ophicephalus striatus

Body weight (9)

Food intake

1.3 13 149.6 1 *9 13 123-8

9.2 5.8 1.8 7.2 3.1 1.8

(%)

so gorged themselves on each occasion that they bulged visibly (Brown, 1951) ; when fed daily this bulging never occurred. Therefore, although gut capacity might limit the amount of food ingested in the former case, it is not likely to be the limiting factor in the latter case. I n goldfish, too, the initial amount of food consumed after a period of fasting is probably limited by the gut capacity (Rozin and Mayer, 1964). Goldfish deprived of food for variable times and then allowed to eat for 1 h, ate about the same amount in this hour after deprivations ranging from 4 to 47 h. This 1-h food intake increased in amount with increasing deprivation time more than 4 h. Since lengthening of deprivation time more than 4 h did not increase the 1-h food intake, it is probable that intake was maximal. If the levelling of the intake curve after the 4-h point is explained by the limitation

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179

set by the gut capacity, it would have to be assumed that the gut was emptied 4 h after the meal, but this did not appear to be the case. Possibly only the fore-gut is involved in limiting the short-term intake. Bokova (1938) showed in roach (Rutilus r . caspius)that the time lapse between two meals equals the emptying time of the fore-gut, and Pegel (1950) also observed that food intake coincides with a certain degree of emptiness of the fore-gut. When goldfish were allowed t o take food a t will, they seemed t o eat to obtain calories rather than bulk (Rozin and Mayer, 1961): they increased their food intake in response t o dilution of their normal diet with kaolin, and they lowered their food intake as temperature dropped. The effect of food dilution provides evidence that distension of the gut is not the primary mechanism regulating food intake. The depression of food intake accompanying a drop in temperature may have a dual cause, i.e. a lowered metabolic rate and slowing down of intestinal clearance. Beukema (1968) measured the degree of hunger in the three-spined stickleback by investigating the behaviour elements of feeding, and concluded that hunger in the stickleback should be described by a t least two parameters, one of them the stomach contents, the other probably of a metabolic nature, since in fish with completely empty stomachs the initial feeding rate increased with deprivation time. (In this respect there is a difference between the stickleback and the goldfish, possibly due t o the fact that the latter lacks a true stomach.) I n the skipjack tuna, the fullness of the stomach did not closely determine the amount of food taken by the fish during a feeding session in which the fish were fed every 15 min (Magnuson, 1969). After a 12-h deprivation period, they stopped consuming food before the stomach was filled; 15 min later they ate more, but still did not fill the stomach, and about eight such feeding periods were required t o fill the stomachs t o capacity. De Ruiter (1968) has pointed out that hunger is the reverse of satiety; both are mutually related over their quantitative range: a metabolic deficit in the animal gives rise to signals that increase the feeding response, and ingestion evokes signals that decrease the feeding response. However, the absence of a feeding response does not indicate the satiety level, nor does the feeding rate define the degree of hunger, so that neither state can be fully described quantitatively in terms of feeding behaviour. De Ruiter therefore prefers to define hunger in terms of feeding history and metabolic condition. Kuz’mina (1966) found a correlation between eagerness of food consumption and the nutritional state of the fish. The feeding reaction time of carp fed with small pieces of meat was defined as the time interval between contact ofthe meat with the water surface and consumption of the meat.

180

B. G . KAPOOR, €1. SMIT AND I.

A. VERIGHINA

Well-fed fish had a constant feeding reaction time of 2.73 & 0.03 a, whereas that of starved fish was 0.57 & 0-03 s. A glucose injection given prior to feeding lengthened the reaction time in the starved fish by about 50%. Injection of Ringer solution did not change the feeding reaction time. Injection of essential amino acids produced a greater lengthening of the reaction time than administration of unessential amino acids. Apparently, hunger is related to the loading of the blood with nutrient matter. Although the basic factors controlling food intake in fish are not yet known, the studies mentioned suggest that some mechanism regulating the fish's nutritional state is operative ; this mechanism is probably influenced by distension stimuli originating from the gut and by interaction with other behaviour systems, such as flight, aggression, parental care, etc. (see De Ruiter, 1968). VII. DIGESTION RATE Several methods have been used to determine the digestion rate in fish. (1) Rate of digestion has been assessed by measuring the time elapsing between food intake and defecation. This interval has been measured in the Caspian roach (Rutilus r . caspius) by Bokova (1938) and in the pond loach by Scheuring (1928). I n this species when the amount of food consumed is small the faeces are expelled as a single dropping, so that the time of defecation can be established accurately. Rozin and Mayer (1961) fed their goldfish food pellets a t a constant rate during 1 hour per day, substituting pellets containing carmine on a given day, the interval between the intake of coloured food and the appearance of coloured faeces provided a measure for the rate of digestion. At the test temperature (24.5"C), the median time of the first appearance of red faeces was 7 h after ingestion ; the great majority of the red faeces were excreted from 8 t o 24 hours afterwards. (2) Rate of gastric digestion has been established by measuring the stomach contents of fish a t different intervals after feeding, either by autopsy or by pumping out the stomach. The amount of partially digested food recovered from the stomach is measured volumetrically by water displacement, and is expressed as a percentage of the volume of the food consumed. Bajkov (1935) determined stomach contents of whitefish a t different times after capture but, as already mentioned, this is not an accurate method, because the digestion rate can be influenced by the quantity and quality of the food consumed. Other investigators therefore preferred to measure digestion under laboratory

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181

conditions, with a known amount of food of constant quality administered t o the fish. Darnel1 and Meierotto (1962) collected 10 to 20 fish (Ictalurus rnelas (Raf.))from a stream and kept them fasting in the laboratory a t acclimation temperature for 12 h. After this prestarvation period the fish were fed a standard meal of amphipods, and digestion was followed by killing two fish a t hourly intervals for analysis of the stomach contents. The amphipods (Hyalella sp.) were chosen as " standard food item ", because they made up 54% of the stomach contents of the bullheads a t capture. On the basis of the results of the quantitative analyses of stomach contents of fish caught over a 24-h period and the digestion rates measured in the laboratory, an attempt was made to calculate the chronology of feeding intensity and the total food consumption of the natural population, keeping in mind that the results were susceptible to the influence of several inadequately known factors. Hunt (1960) fed his experimental fish (gar, warmouth, and bass) 2.5 g of Gambusia, measured the stomach contents by the water displacement method a t various times, and calculated the percentage of standard meal digested. There appeared to be an almost linear relationship between digestion percentage and time. Although all the fish were kept a t the same temperature, the species showed substantially different rates of digestion, bass digesting 2.5 times faster than gar and warmouth showing an intermediate digestion rate. Hunt saw a relationship between these differences in digestion rate and differences in activity between the three species. Pandian (1967) kept his fish (Megalops cyprinoides (Brouss)) a t a constant temperature (28OC), and starved them for two days before giving them a standard meal consisting of prawns, weighing 2% of the fish's body weight. At various intervals after feeding, fish were killed for estimation of the amount of food digested. An almost linear relationship between digestion percentage and time was observed. A more precise description is given by Windell (1967), who observed the digestion rate as the percentage decrease of digestible organic matter (i.e. fresh weight of meal minus water, ash and chitin) from the stomach. Windell kept his bluegill sunfish a t a constant temperature (20°C), and fed them a standard meal after a 3-day fasting period. After autopsy of a periodically sampled number of fish, the percentage decrease of digestible organic matter from the stomach was measured. This dry weight method has also been applied to rainbow trout (Windell and Norris, 1969a, b). Daan (1973), working with cod (Gadus morhua), maintained a t 12°C and kept on a diet of shrimps, fed his fish known amounts of food (dead sprat) and dissected them after different time intervals. Remains of fish and shrimps in the stomach could easily be separated. Using the wet weight as well

182

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G. KAF’OOR,

H. SMIT AND I. A. VERIGHMA

as the dry weight method, he found a linear relationship between digestion percentage and time. I n experiments with thermally acclimated largemouth bass (Micropterus salrnoides), Beamish ( 1972) found that the stomach contents (dry weight, protein N, lipid and calories) decreased curvilinearly with time after a test meal of shiners. Seaberg and Moyle (1964) force-fed their fish (Esox, Micropterus, Stizostedion) with small perch of known volumes, and removed the stomach contents a t timed intervals by use of a stomach pump. Reduction of the volume of the stomach contents with time was taken as a measure for the digestion rate. Force-feeding experiments were also done by Shrable et al. (1969) in their study of digestion rate in channel catfish (Ictalurus punctatus (Raf.)), the difference between the amount of dry matter consumed by the fish and the amount of dry matter recovered from the digestive tracts a t various intervals being taken as a measure for the rate of digestion. The feed consisted of two pellets of known composition, and recovery of remains was done post rnortem. Swenson and Smith (1973)force-fed their fish (Stizostedion sp.) with minnows and removed food remains by pumping stomachs after various digestion periods. Tyler (1970) acclimated his young cod to a given temperature, after which he applied a 3-day fast prior t o the feeding of a standard meal of shrimp tails. The stomach contents were removed a t various times after the meal and the dry weight measured. Brett and Higgs (1970) sampled the stomach contents of young sockeye salmon (Oncorhynchus nerka) by freezing the anaesthetized fish, after which the hard-frozen contents could be easily removed, Stomach contents were expressed as percentage of organic matter, i.e. mg organic content/100 mg dry body weight. Another method based on recovery of the stomach contents is Mette’s method in which a glass tube is filled with food and put into the alimentary canal, from which it is removed after a given time. Riddle (1909) placed Mette’s tubes, filled with egg-albumen, in the stomach of A m i a calva L. ; after various periods the fish were killed, the tubes recovered, and digestion recorded by measuring the number of millimetres of coagulated albumen that had been dissolved. Pegel (19501,working with Leuciscus 1. biacaZensis Dyb., provided his fish with an intestinal fistula through which Mette’s tubes could be introduced, so that the digestive power of fore-gut and hind-gut could be investigated separately. Mette’s method was also used by Chepik (1964) to measure digestive rates in carp. (3) I n predatory species consuming prey a,ninials, the progress of digestion can be followed radiographically, the decreasing visibility of the bony elements of the prey and the position of these elements in relation t o each other serving as measures for the progress of digestion.

183

THE ALIMENTARY CANAL AND DIGESTION IN TELEOSTS

This method has been used by Blain and Campbell (1942) to study the digestion of prey by snakes and by Molnar and Tolg (1962) for investigating digestion in predatory fish. Bass, pike perch, sheat fish, and perch were force-fed with small fish. The skeleton, swimbladder, and otoliths of the prey fish were easily recognized on the radiographs. Disappearance of the swimbladder, falling apart of the vertebral column, and dispersion of the otoliths indicate different stages of digestion. MolnBr and Tolg (1962) and Edwards (1971) used the X-ray method for investigation of the influence of temperature on gastric digestion. In some transparent fish species, digestion rate can be estimated from visible-light photographs. Rosenthal and Hempel (1970) investigated the rate of digestion in transparent herring larvae in which food items in the gut were visible as a straight chain. Digestion rates were easy to estimate from photographs taken a t 2-h intervals. The time course of digestion does not always give a straight line when digestion percentage is plotted against digestion time (Fig. 22), and it is difficult to compare the results obtained by different authors, because experimental conditions are usually not comparable. Differences in temperature, size of fish, and amount of food may account for the divergent shapes and slopes of the curves in Fig. 22. It may be inferred from comparison of curves 1 and 4, relating to smaller and bigger specimens of the same species, respectively, that it small fish has a higher digestion rate than a large fish. Comparison of curves 2 and 3, based on data obtained from experiments in which identical methods were employed, suggests that Lepomis gibbosus has a more intensive digestion than L. macrochirus, although the difference could be related to differences in body weight. Curves 1, 6 and 7 indicate that over a long period the digestion percentage increases linearly with time. In other experiments, however, the digestion rate was initially slow and ended faster (curve 4), or the reverse (curves 3 and 8). I n mammals, the time course of'gastric digestion is often described as an exponential one, i.e. the logarithm of the values for food-remains in the stomach is linearly related to digestion time, although a t the beginning and end of the digestive period gastric emptying has been found to be faster. I n man, the square root of the values for food-remains is linearly related to time (Hopkins, 1966). Neither the exponential nor the square root hypothesis applies to the results shown in Fig. 22, with the exception of the results obtained by Brett and Higgs (1970) on sockeye salmon (curve 9), which do show an exponential function. Also Elliott (1972) found that gastric evacuation in the brown trout proceeds exponentially, and so does gastric emptying in the plaice (Edwards, 1971). A.Y.B.-13

7

184

B. G. KAPOOR, H. SMIT AND I. A. VERIOHINA

digestion time (hours)

FIG.22. Time course of gastric digestion in some fish species.

Curve

Fish species

Fish size

Temp. (“C)

1

Megalops cyprinoides

5.12 g

28

2

Lepomis gibbosus

20.9 g

19-22

3

Lepomis macrochirus

34-64 g

18-22

4

Megalops cyprinoides

90.6 g

28

5 6

Ocyurus chrysurus & Huemulon plunaieri Ictalurus punctatus

20 cm 19 cm 380 g

23.9

7 8 9

Chaenobryltus gulosus Gadus morhuu Oncorhynchus nerka

72-113 g 229 g 30.7 g

24.5 10 15

120.

24

Food

Author

prawns : 2% of body weight 250 mg damselfly naiads natural food organisms prawns: 2% of body weight

Pandian, 1967

Anchoviella

Pierce, 1936

Kitchell and Windell, 1968 Windell, 1967 Pandian, 1967

Shrable et al , 1969 2.5 g Gambusiu Hunt, 1960 shrimp tails Tyler, 1970 canned salmon Brett and Higgs. and pellets 1970

pellets

Gastric emptying is a complex process, and is very incompletely understood for fish. Gastric digestion and emptying could be dependent on the quantity and quality of the food, the rate of secretion of gastric juice, gastric motility, and the capacity of the intestine t o accept chyme from the stomach. The quantity of food consumed may influence the gastric secretory rate via stimuli by distension of the stomach wall ; since the composition of the gastric juice changes with

THE ALIMENTARY CANAL AND DIGESTION I N TELEOSTS

185

changing rate of secretion (Smit, 1967), the digestive power of the juice depends on the quantity of food ingested. Stomach motility may be stimulated by the elevated intraluminal pressure arising from the presence of food. I n brown trout, peristalsis occurs in the gut in response t o distension; the main sites of initiation of peristalsis are the antrum and anterior duodenum, whose walls have a greater density of nerve cell bodies than neighbouring regions (Burnstock, 1959b; see Campbell and Burnstock, 1968). On the other hand, stomach motility may be inhibited by (nervous or hormonal) influences from the intestine, evoked by the presence of chyme in the duodenum. Via this inhibitory mechanism, the rate of gastric emptying may depend, apart from food intake, on the rate of transport through the lower gut, which in turn is dependent on the rate of intestinal absorption. It should be kept in mind, however, that the existence of such an inhibitory mechanism has not been demonstrated in fish. Related to these considerations is the notion that a larger meal is more intensively digested than a smaller meal, so that digestion time is not proportionately lengthened as meal size is increased. For example, Hunt (1960) found that when meal size is increased by a factor of three, the digestion rate slightly more than doubles. Windell (1967) also found that the amount digested per unit time increases with increasing meal size. Kitchell and Windell (1968) found for sunfish fed a single or double standard meal that the percentage decrease of digestible organic matter taken from the stomach followed the same time course in both cases, which means that in the latter case the digestion rate was twice that in the former. Windell and Norris (1969a) observed in rainbow trout that gastric emptying increased as meal size increased beyond 1.1 1 % of the fish’s body weight ; Tyler (1970) found this value t o be about 1.5% for cod a t 10°C. However, Lipskaya (1959)) working with Mullus barbatus (L.), and Elliott (1972), working with brown trout, found that the duration of digestion is directly correlated with the amount of ingested food, while Rosenthal and Paffenhofer (1972)) working with Belone belone (L.),observed that a threefold increase in meal size (Daphnia) caused only a slight increase of digestion rate. I n predatory fish, which swallow large lumps of food, the superficial layer of prey is digested first ; once this layer has been transported to the duodenum, the next layer is digested, digestion thus gradually proceeding inward. Stomach motility accelerates this process. The radiographs made by Moln&r et al. (1967) showed that bass, which exhibited a more rapid gastric digestion than pike-perch, also had a greater stomach motility. Little work has been done on the influence of specific dietary com-

186

B. G. KAPOOR,

H.

SMIT AND I. A. VERIGHINA

ponents on digestion rate and the digestive capability of the fish under study. Karpevitch and Bokova (1936, 1937)showed that different sorts of food are digested a t different rates, these rates being slowed down by food containing fat. I n his investigation on the digestion rate in sunfish, Windell (1967) found that the time course of digestion of crayfish, darters, and oligochaetes was the same, although it might have been expected that the chitinized crayfish would be digested more slowly than the oligochaetes. I n the pond loach, Scheuring (1928) found no differences in time for the digestion of earthworms or gammarids when meal size was standardized (0.2% of body weight). On the other hand, rainbow trout evacuated 70% of the stomach contents during a 12-h period following a meal of earthworms, whereas only 28% was evacuated when mealworms were fed (Windell and Norris, 1969b). Walleye (Stizostedion) digested crayfish a t a much slower rate than amphipods (Kelso, 1972). Increased fat content of the food slowed down gastric emptying in rainbow trout, as did a high percentage of dry matter (Windell and Norris, 1969a). I n the surmullet, Lipskaya (1959) observed that digestion of polychaetes proceeded a t a slower rate than that of gammarids, but was more rapid than digestion of shrimp. Herring larvae digest copepod nauplii faster than they do Artemia nauplii (Rosenthal and Hempel, 1970). Pegel (1950) points out that the digestion rate is influenced by the amount of roughage in the food. Since the digestion rate may be expected to be influenced by the rate of intestinal absorption, the digestibility of the diet components should have some bearing on digestion rate. Trout digest fats, carbohydrates, and proteins very efficiently, but a large amount of starch in the diet decreases the digestion of proteins (see Phillips, 1969). The digestibility of a mixture of food ingredients is not necessarily the average of that of its separate constituents (Maynard and Loosli, 1962). For the rest, digestibility of food has been studied principally in relation to conversion of food into fish flesh, rather than in relation to digestion rate. A relation between the rate of food digestion and body size has already been hinted a t in Fig. 22, where curves 1 and 4 represent the time course of digestion in small and large specimens, respectively, of the same species under comparable experimental conditions. The bigger fish digests a greater amount of food than the smaller fish per unit time, but when the size effect is under consideration the amounts of food digested per gram of fish should be compared : it then appears that the same amount of food was digested by Pandian’s 5.12-g fish in 6-5h as his 90-6-g fish digested in 20.8 h. Moriarty and Moriarty (1973)found in Tilapia that the quantities ingested (and digested) are

THE ALIMENTARY CANAL AND DIQESTION I N TELEOSTS

187

linearly related to the weight of the fish. However, the size range of their fish was relatively small. For a number of marine fish species Karpevitch and Bokova (1936, 1937) showed that digestive rate is higher in young fishes than in old ones. Brett (1971b), working with sockeye salmon (Oncorhynchus nerka) found that small fish can consume relatively more voluminous meals than big fish; also the maximum daily food intake of small fish is much greater than that of big fish : 16.9% of bodyweight for 4-g fish, and 4.3% for 216-g fish. Apparently the small fish has a higher rate of food processing. I n poikilotherms, the digestive rate is highly dependent on the environmental temperature and the thermal history of the animal (Smit, 1968). A distinction must be made between data obtained a t acclimation temperature and those obtained a t temperatures deviating from that level. I n cold-blooded organisms many physiological functions compensate for the effect of temperature changes. For example, in Precht's type 3 compensation, the intensity of the physiological process gradually decreases until the proper acclimation level has been reached (Precht, 1964). Therefore, experiments involving acute temperature changes may yield quite different results than those obtained under conditions of chronic temperature change (see Fry, 1967, and Fry and Hochachka, 1970, for additional literature). With respect t o digestive functioning, temperature changes can affect the digestion rate via a t least five temperature-dependent processes : ( 1 ) feeding rate; (2) secretory rate of digestive juices; (3) hydrolic activity of digestive enzymes ; (4) gastric and intestinal motility ; and (5) rate of intestinal absorption. Some data taken from the literature are shown in Fig. 23. These data indicate that the digestion rate is increased by a factor of 3 t o 4 when the temperature is raised by 10 degrees. It should be stressed, however, that the fish in these experiments were not always fully acclimated to each of the temperatures, so that the data are not easily comparable. As a generalization it can be said, that if the digestive process had been tested a t acclimation temperatures, the curve of the temperature-digestive rate relationship would probably show flatter slopes than some of those shown in Fig. 23. Nicholls (1933), who measured the digestion rate in the killifish, used temperatures ranging from 5°C to 2 9 6 ° C (Fig. 23, line 1). However, his fish had been acclimated t o temperatures between 15" and 19"C, so that the experiments a t low temperatures were performed below the acclimation level, and the digestion rate will be lower than in acclimated fish, while in experiments performed a t temperatures above the acclimation level, this rate will be higher than when the fish have

188

B.

a . KAPOOR,

H. SMIT AND I . A. VERIGHINA

0.41

I

I

,

I

,

,

tamp. ("C)

FIG.23. Digestion rato in relation to temperature

Curue ?LO.

Fish speeies

Food

Author

Fundulus hetevoclitus Misgurnus fossilzs Mullus barbntus Micropterus sdmoides Sebastes inermis Luciopercu lucaopercu Ictulurus punctntus (Calculated from tune of 5076 depletion of stomach contents) Gadus morhun Oncorhynchus nerkn

clam mantles Oligochaetes and Garninarus Polychaetes Alburnus ulb. 7 % of body weight Alburnus alb. pellets

Nicholls, 1933 Scheuring, 1928 Lipskaya, 1959 Fabibn el nl., 1063 Kariya, 1969 Molnrir and Tolg, 1962 Bhrable et al., 1969

shrimp h i l s canned salmon and pellets

Tyler, 1970 Brett and Higgs, 1970

become acclimated t o each test temperature. The same holds for the experiments done by Scheuring (1928) (Fig. 23, line 2 ) ) who kept his pond loaches a t 12" to 15°C and transferred them t o the test temperature, ranging from 7" t o 2O"C, shortly before the beginning of the experiment. Although not completely acclimated to each test temperature, the pike-perch used by Molnsr and Tolg (1962) were acclimatized

THE ALIMENTARY CANAL AND DIGESTION IN TELEQYTS

189

to the low test temperatures in winter and to the high test temperatures in summer, so that line 6 in Pig. 23 also reflects seasonal changes in the digestion rate. The same holds for the results obtained in bass by P&bi&net al. (1963) (Fig. 23, line 4),according to whom the rate of gastric emptying in pike-perch is about 9 times faster in summer than in winter ; for bass, this figure is about 5. This conclusion may hold for fish living in a body of water without any appreciable short-term temperature fluctuations. Acute temperature changes, however, affect the intensity of physiological processes severely. If the digestion rate in fish is to be described in relation t o environmental temperature conditions, specimens of the fish species under study should be acclimated to temperatures within the physiological temperature range, and the intensity of digestive processes then measured a t each acclimation temperature. At the same time, the influence of temperature deviations from the acclimation level on the rate of digestion should be studied. Such a description of a temperature-dependent process may be applied to field conditions, although it should be realized that a fish is not involuntarily exposed to every change in environmental temperature, in the sense that it can select a preferred temperature, this preference again being dependent on the temperature to which the fish has been acclimatized.

VIII. DIGESTIVEENZYMES Digestive enzymes, which are secreted into the lumen of the alimentary canal, originate from the gastric mucosa, the pyloric caeca, the pancreas, and the intestinal mucosa, which secrete a number of enzymes that hydrolyse proteins, peptides, carbohydrates, and fats. The gastric mucosa produces a protease with an optimal proteolytic activity a t a low pH, resulting from the secretion of HC1 by the same gastric mucosal glands, probably even by the same type of cell (Western and Jennings, 1970). The pyloric caeca, which form an extension of the intestine, secrete essentially the same enzymes as the mid-gut, i.e. variety of protein-carbohydrate-, and fat-digesting enzymes that are active a t a neutral or slightly alkaline pH. The pancreatic juice is especially rich in trypsin, a protease with optimal activity under slightly alkaline reaction, and contains amylase, maltase and lipase. The part played by each of these organs in the total production of digestive enzymes varies considerably in different species. A number of fish lack the stomach and the pyloric caeca, so that the proteolytic active juice is mainly of pancreatic origin. The results of certain studies provide evidence supporting the view that the enzymic composition of digestive juices is adapted to the diet of the given species.

190

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A. Pepsin This gastric protease, with an optimal proteolytic activity in the vicinity of pH 2, is found in all vertebrates except the stomachless fish (Vonk, 1937). Peptic activity has been explicitly demonstrated for the stomachs of the following teleosts: Anguilla japonica (T. & Schl.) (Morishita et al., 1964), Roccus chrysops (Raf.) (Kenyon, 1925), Seriola quinqueradiata (T. & Schl.) (Morishita et al., 1964), Thunnus sp. (Norris and Mathies, 1953), Trachurus tr. L. (Kandyuk, 1967), Tilapia mossambica (Fish, 1960; Nagase, 1964), Pleuronectes platessa (Kandyuk, 1967), Trutta fario (Buchs, 19541, Salmo gairdnel-ii (Kitamikado and Tachino, 1960; Morishita et al., 1964), Oncorhynchus sp. (Norris and Elam, 1940), Esox lucius (Kenyon, 1925; Mennega, 1938; Buchs, 1954), Ictalurus sp. (Nordlie, 1966; Smit, 1967), Micropterus salmoides (Sarbahi, 1951), Lepomis incisor (Cuv. & Val.) (Kenyon, 1925), Pomoxis sparoides (LacBpBde) (Kenyon, 1925), Perca sp. (Kenyon, 1925; Fish, 1960), Zoarces anguillaris (Peck.) (MacKay, 1929). Peptic activity depends strongly on pH, temperature, and kind of substrate, among other things. Vonk (1929) found that the peptic activity of gastric mucosa extracts of pike showed a peak at about pH 2 when fibrin was used as substrate. Bayliss (1935) found that gastric mucosa extract of the plaice digested casein maximally at pH 2. The activity curve for Ictalurus of gastric juice acting on edestin shows a rather broad maximum between pH 3 and 4 (Smit, 1968). Norris and Elam (1940) found a double-peaked curve for crystalline salmon pepsin, a sharp peak occurring a t pH 1.3 and a broader optimum between pH 2.5 and 3.5; they used haemoglobin as substrate. Using this substrate, Norris and Mathies (1953) found two pH optima for tuna pepsin. Such double-peaked curves are also known for mammalian pepsins, which have been investigated more extensively than those of fish (Taylor, 1959). The two peaks appeared to depend on the nature of the substrate ; for example, pig pepsin shows a pH vs activity curve with two optima for edestan as substrate, but for its effect on several protein fractions of horse serum, the curve has only one peak (Geilenkirchen and Elbers, 1951) ; human gastric juice digests plasma proteins and serum albumin with two optima, i.e. at about pH 2.5 and 3.5, whereas digestion of egg albumin results in a single-peaked curve with the optimum below pH 2 (see Taylor, 1968). According to Taylor (1962), the two optima are not based on the activity of two proteolytic enzymes ; instead, the pepsin molecule has two enzymatic active sites attacking the substrates maximally a t different pHs. Electrophoresis has demonstrated the existence of several (possibly up to seven) different pepsin fractions in mammals (Taylor, 1968). How-

THE ALIMENTARY CANAL AND DIGESTION IN TELEOSTS

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ever, these differences may arise from conformational variations of the enzyme protein leaving the structure of the catalytic centres undisturbed. Fish pepsin has not been investigated by chromatography and electrophoresis, but it may also prove t o be composed of a number of pepsins. I n particular, the possible existence of a cathepsin in the piscine stomach, suspected by Bramstedt (1949) and Buchs (1954) and rejected by Taylor (1962))would seem to justify further investigation of fish pepsin. It will be clear that the digestive power of the gastric juice depends on the amount of pepsin and on the pH. At a given enzyme concentration, proteolytic activity of the juice will be maximal at pH values lower than 4. The gastric juice may contain enough HC1 to have a pH value even below 2, e.g. for the stomach contents of Cottus gobio, pH values as low as 2 were measured by Western and Jennings (1970) ; for pure gastric juice of Ictalurus nebulosus, titration values of 280 rnN have been obtained (Smit, 1967). Ingested food usually has a considerable buffering power, which means that in the chyme the pH will be higher than that of pure gastric juice. For acidification of the gastric contents, the amount of acid secreted is more important than the acid concentration of the secretion. Therefore, the more food ingested, the higher the secretory rate must be (see under Regulation of gastric secretion, Section IX). Mennega (1938)found in the pike stomach that only the outer layer of the food (a roach) has a pH favourable for peptic digestion, the core having a much higher pH value. Once this outer layer has been liquified, the following layer is acidified, etc. Tilapia fed on a protein-rich diet was found to have pH values of the gastric contents lying between 3 and 5, while the pH optimum of its pepsin was 2.8 (Nagase, 1964). Kenyon (1925) reports that the stomach contents of sunfish, crappie, pike, perch and white bass always redden blue litmus. For perch, Fish (1960) found a peptic optimum a t pH 2 and a gastric pH between 2-5 and 3.5 four hours after feeding. For Tilapia, Fish obtained gastric pH values between 2 and 3. Moriarty (1973) found in Tilapia nilotica (L.) stomachal pH values as low as 1.4. The cells of the blue-green algae, on which Tilapia feeds, are lysed by the gastric acid. Pepsinogen was detected in the stomach wall, but peptic digestion occurs in the intestine, after lysis of the algal cells. In many cases, and especially during the initial phase of digestion, the pH of the chyme is not as low as might be expected from the optimal pH for peptic action. The occurrence in some fish of a second peak of peptic activity a t pH values up to 4, suggests that the pH of the chyme is not extremely critical, proteolytic digestion proceeding a t a level of considerable intensity through a rather wide pH range, possibly from 1 to 5. It

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should be added that, apart from the effect of the pH of the gastric contents, the proteolytic digestion is also enhanced by a high pepsin concentration, high temperatures, and intense stomach motility.

B. Trypsin An intestinal protease maximally active in an alkaline medium, has been found in all fish species studied so far, and is normally considered to exhibit ‘‘ tryptic ” activity. Reports in the literature do not indicate whether this protease is secreted exclusively by the pancreas or that some part of the intestine also participates ; it is also not clear whether the ‘‘ trypsins ’’ of different species are enzymologically comparable. As long as our knowledge of digestive enzymes in fish remains as fragmentary as it is now, it is better to reserve the term << trypsin ” for the pancreatic proteolytic enzyme that is active in between pH 7 to 11, depending on the substrate. The exact localization of the source of this enzyme is difficult, due to the diffuse form of the pancreas in many teleosts ; pancreatic tissue is partly situated along the portal veins and penetrates the liver, and partly suspended in the mesenteries between the intestine and liver, often hidden in fat tissue. I n fish species possessing pyloric caeca, pancreatic tissue is also situated in between them. This inaccessible anatomical situation hampers the determination of the source of the enzymes concerned. Ishida (1936) found tryptic activity in pancreatic extracts from some stomachless species of fish : Salarias, the wrasses Calotomus and Thalassoma, and the puffer Spheroides. Morishita et al. (1964) found traces of proteolytic activity in extracts of liver in Seriola, eel, rainbow trout and carp. They probably did not incubate the enzyme a t an optimal pH, nor did they exactly localize the source of this proteinase. Bondi and Spandorf (1954) incubated pancreas extract of carp with casein a t pH 7 . The digestive action of the extract was increased markedly when intestinal extract was added, which may be ascribed to the activation of trypsin by enterokinase. Bayliss (1935) found tryptic activity with an optimum a t p H 7.5 to 8.5 in the alimentary canal of the plaice when extracts were incubated with casein. Due t o the diffuse form of the pancreas, no clear evidence as to the source of the enzyme could be obtained. The gall-bladder, which is surrounded by pancreatic tissue, exhibited the highest proteolytic activity between pH 7.5 and 8.5. Since tryptic activity of gall-bladder extract was enhanced by the addition of intestinal extract, enterokinase activity may be assumed. Proteolytic activity a t pH 8 has also been found in pancreatic tissue of perch and Tilapia (Fish, 1960) ; a tryptic enzyme showing an optimum a t pH 8.0 to 8.2 was found by Nagase (1964) in

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intestinal extracts of Tilapia. These results too are inconclusive as to the source of the enzyme. Kitamikado and Tachino (1960) found alkaline protease activity in the pyloric caeca and intestine of rainbow trout, and Strogsnov and Buzinova (1969) found in the grass carp (Ctenopharyngodon idella) that tryptic activity in the intest'ine was even higher than that in the pancreas. Sarbahi (1951) demonstrated tryptic activity a t p H 8.4 in extracts of mixed liver and pancreas and in extracts of goldfish intestine ; in largemouth bass trypsin was found in extracts of pancreas, liver and pyloric caeca. For the pyloric caeca of rosefish (Sebastes), Stern and Lockhart (1953) reported a proteolytic action with a p H optimum a t 8.75. Croston (1960) investigated the endopeptidases in extracts of pyloric caeca of chinook salmon ; it was assumed that these extracts also contained enzymes from pancreatic tissue. The caseinolytic activity of the mixed enzymes showed a maximum a t p H 9. Also the partly purified proteinase from the pyloric caeca of mackerel showed maximal caseinolytic activity a t p H 9 (Ooshiro, 1971). These findings indicate that a trypsin, possibly identical with mammalian trypsin, is an important proteolytic enzyme in the digestive tract of fish, but the precise site of its synthesis and secretion remains obscure. It seems reasonable to consider the pancreas as the main source of trypsin. The tryptic activity sometimes found in intestinal extracts may be caused by pancreatic trypsin previously absorbed by the intestinal mucosa. To clarify the secretory site and kinds of proteolytic enzymes in fish, much work on digestive proteases remains to be done.

C. Carbohydrases The existence of several carbohydrases in the piscine digestive tract has been demonstrated unequivocally. Chesley ( 1934) showed amylase activity in extracts of diffuse pancreatic tissue and pyloric caeca of menhaden (Brevoortia)as well as of pancreas and intestine of mackerel (#comber) and puffer (Spheroides). I n menhaden and puffer the bile also exhibited amylolytic activity, and in the sea robin (Prionotus) the bile was the main site of amylase action, the pancreatic tissue containing only traces of this enzyme. The presence of amylase in the bile is comprehensible, because pancreatic tissue is scattered through the liver and a distinct pancreatic duct may be absent, so that the gall-bladder may receive pancreatic secretions. I n the mackerel, which has a compact pancreas, the bile showed no amylase activity. Bayliss (1935) cannulated the bile duct of the plaice and did not detect any amylolytic activity in bile sampled via the cannule : however, such activity could

194

B. G . KAPOOR, H. SMIT AND I. A. VERIQHINA

be demonstrated when the bile was collected by slitting the gallbladder. Intestine and liver of the plaice showed amylolytic action, possibly originating from pancreatic tissue embedded in the liver and surrounding portal vessels, pyloric caeca, and the gall-bladder. Ishida (1936) found that intestinal extracts of certain stomachless fish (Calotomus, Thalassoma, Spheroides, Salarias) contained several carbohydrases : amylase, maltase, glycogenase and saccharase. He quotes Vonk (1927), who maintained that amylase and maltase found in the intestinal mucosa originate from the pancreas rather than from the intestinal mucosa. Sarbahi (1951) found amylase, maltase and saccharase in extracts of mixed liver and pancreas, oesophagus and intestine of goldfish, but could not detect these enzymes in the digestive tract of largemouth bass. However, McGeachin and Debnam (1960) did find amylase activity in the pyloric caeca, intestine, liver and bile of largemouth bass as well as in these organs of bluegill sunfish. The amylase activity of liver and spleen extracts may have been caused by fragments of pancreatic tissue, since it was impossible to separate the diffuse pancreas from the liver. Amylase activity has also been detected in the digestive tract of rainbow trout (Kitamikado and Tachino, 1960), perch pancreas, intestine and pancreas of Tilapia (Fish, 1960)) pyloric caeca of Oncorhynchus and cod, intestine of carp and flounder (Ushiyama et al., 1965)) intestine and pyloric caeca of yellowtail jack and rainbow trout, intestine, liver and pancreas of eel and carp (Morishita et al., 1964), throughout the digestive tract of Tilapia with the greatest activity in the intestine (Nagase, 1964)) the intestine of mackerel and plaice (Kandyuk, 1967), and in stomach and intestine of Ophicephalus and Mugil (Seshadri, 1967). Phillips (1969) assumes that amylase, saccharase, maltase and lactase occur in the digestive tract of brook trout, since starch, sucrose, maltose and lactose are absorbed by trout. The pancreas is the most likely site of the secretion of carbohydrases ; the intestinal mucosa possibly produces less carbohydrases, or perhaps none at all. The occurrence of amylase and maltase in the intestine might be explained by assuming that the intestinal mucosa adsorbs pancreatic enzymes, but this cannot be inferred with certainty from the papers cited. I n some instances amylase activity was even found in the stomach and oesophagus; this could be the result of regurgitated duodenal contents. D . Lipase Fats are normally ingested by fish together with their natural food, and are known to be utilized. An appropriate amount of fat in the diet of trout has a protein-sparing action (Phillips, 1969), and some

THE ALIMENTARY CANAL AND DIGESTION IN TELEOSTS

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fatty acids have been found to be essential if salmon are to thrive (Nicolaides and Woodall, 1962). The occurrence of a lipase in the digestive tract may be assumed for all fishes and has been demonstrated in a number of species. I n mackerel (Scomber), menhaden (Brewoortia), scup (Stenotomus), and sea robin (Prionotus), lipase activity has been found in extracts of the pancreas, pyloric caeca and upper intestine (Chesley, 1934). Lipolytic activity has been demonstrated in extracts of intestine and liver of the plaice (Bayliss, 1935), but since the liver is penetrated by pancreatic tissue, the lipase may originate from there. This view is supported by the results obtained by Chesley, who found a higher lipolytic activity in the compact pancreas of the mackerel than in the diffuse pancreases of other fish species. Extracts of intestinal mucosa of the killifish (Pundulus) exhibited lipolytic action (Babkin and Bowie, 1928), as did carp intestine (Chepik, 1964). Ishida (1936) detected lipase in the gut of Salarias and of some Labridae. I n goldfish, lipase was found in extracts of mixed liver and pancreas and in intestinal contents by Sarbahi (1951), who also detected the enzyme in the pyloric caeca and the intestinal contents of largemouth bass. Esterase activity was demonstrated by Kitamikado and Tachino (1960) in the liver, spleen, bile, intestine, pyloric caeca and stomach of rainbow trout. Lipase activity in stomach extracts has also been observed by Nagase (1964) for Tilapia and by MacKay (1929) for Zoarces. Brockerhoff (1966), working on cod (Gadus), fed his fish on labelled fats. Two days later, the lipids were recovered from the gut and analysed. The triglycerides had been degraded to diglycerides, monoglycerides and fatty acids by a lipase the action of which corresponded to that of mammalian pancreatic lipase. Although these experiments clearly demdnstrate the action of a lipolytic enzyme, Brockerhoff did not find the enzyme in the pyloric caeca and in the diffuse pancreas of the cod ; he thinks that it is possible that the enzyme is of pancreatic origin, but that the conditions to demonstrate it have not been found. I n any case, Brockerhoff’s work has yielded a more detailed description of the activity and specificity of a digestive enzyme in fish, addi o our fragmentary knowledge of piscine digestive enzymes. I E. Other enzymes The literature contains incidental reports on other enzymes found in the alimentary canal of fish. Their existence can be inferred from the hydrolysis of specific substrates, but nothing is known about their site of formation or about their specificity or kinetics. Exopeptidase activity has been reported for the intestine of plaice

T

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B. G . KAPOOR, H . SMIT AND

I. A.

VERIGHINA

(Bayliss, 1935), carp (Kenyon, 1925 ; Bondi and Spandorf, 1954), Clarias and Ophicephalus (Sastry, 1972), killifish (Babkin and Bowie, 1928), and certain other stomachless fish (Ishida, 1936). Evidence for the existence of an enterokinase has been presented by Ishida (1936) for some stomachless fish species, by Bayliss (1935) for plaice, by Kandyuk (1968) for mackerel, plaice and sprat, and by Bondi and Spandorf (1954) for carp. Oligosaccharidase activity has been detected in some ccbses, e.g. a-glucosidase action was found in the intestine of rainbow trout by Kitamikado and Tachino (1960) andin the pyloric caeca of Oncorhynchus keta(Wa1b.) (Ushiyama et al., 1965);maltase and saccharaseactivityhas been found inmixed liver and pancreas and intestine of goldfish (Sarbahi, 1951); saccharase was also found in stomach extracts of Colisa, Gudusia and Barbus (Agrawal and Verma, 1966). Adult carp showed maltase, sucrase, lactase, melibiase, cellobiase, and methyl-a-D-glucosidase activities in the intestine; even carnivorous fish such as red sea bream (Pagrus major (T. & Schl.)) and marine ayu (Plecoglossus altivelis) had active maltase in their digestive tract (Kawai and Ikeda, 1971). Okutani et al. (1967) claim the existence of a chitinolytic enzyme with optimal activity a t p H 4.5 in the stomach of Salmo irideus. I n Tilapia macrochir Boulenger, Piavaux (1972) showed laminarinase activity in extracts of intestinal mucosa. Part of the proteolytic activity of extracts deriving from the digestive tract may be due t o the action of cathepsins, which can be found in animal tissues in general.

F. Digestive enzymes as related to the diet With regard to the natural diets of fish, a distinction can be made between herbivorous, omnivorous and carnivorous fishes. It may be assumed that the production of digestive enzymes is correlated with the composition of the diet, e.g. carbohydrases would be more copiously secreted in herbivores, whereas proteases would be quantitatively more important in carnivores. There is indeed some evidence that such a relationship does exist, although it is by no means clearly established. The evidence stems mainly from comparison of amylase aetivity, e.g. McGeachin and Debnam (1960) found the amylase levels in mixed liver and pancreas of carp t o be about 100 times as high as that of visceral organs of blyegill sunfish and largemouth bass ; the digestive amylase level in rainbow trout was also lower than that in carp (Kitamikado and Tachino, 1960); Morishita et al. (1964) found a much higher amylolytic activity in the alimentary canal of carp and Plecoglossus than in that of salmon, eel and yellowtail jack ; amylase activity in the

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digegtive tract of Tilapia is much higher than that of perch (Fish, 1960), and in carp much higher than in pike (Vonlr, 1941). However, Chesley (1934) found the amylase level in the alimentary canal to be correlated with general activity rather than with diet. As far as the digestive protease level is concerned, adaptation to the natural diet is much less prominent. Stomachless fish, which lack a pepsin, are herbivores or omnivores, whereas carnivorous fish possess a true stomach in which peptic digestion takes place. In fish having a stomach, no clear-cut correlation has been found between proteolytic activity and diet. Moitra and Das (1967) presented some evidence that in Tilapia mossambica the relative activity of the digestive enzymes may be correlated with the actual diet of the fish. Fish (1960) reports that as far as proteases are concerned, differences between Tilapia and Perca are small; and Morishita et al. (1964) and Chesley (1934) found differences in proteolytic action in the alimentary canals of a number of fish species, that could not be correlated with their diet. Turpayev (1941) compared tryptic and amylolytic activities of some cyprinid fish species with their feeding habits (Table VIII). TABLEV I I I ~

~~

Species Scardinius Blicca Alburnus Aspius Cypsinus

~

~

Feeding habit herbivorous omnivorous omnivorous carnivorous omnivorous

~~~~

~

Amylase activity 1.0 1.1 1.0 0.15 5.8

Trypsin activity 0.4 0.9 0.9 1.2 1.7

Volya ( 1966) investigated the proteolytic, lipolytic and amylolytic activities in the alimentary canal of Trachurus, Scomber, Mullus, Mugil and Pleuronectes. The highest proteolytic and lipolytic activities were found in the predatory species, Trachurus and Scomber. The lowest protease activity but the highest amylolytic activity was found in Mugil. Finally, it should be stated that comparison between fish species with respect to the existing data on secretory levels of digestive enzymes is not entirely justified, since the experimental conditions maintained by the various authors differed and so did the physiological condition of the fish, the latter being influenced, among other things, by nutritional state and season. Berman and Salenitse (1966) com-

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pared the activity of digestive enzymes attached to the free border of the intestinal epithelial cell with that of the enzymes in the lumen. They found for carp that the rate of “ contact digestion ” was nine times higher than the digestion rate in the intestinal lumen. They are of the opinion that their finding may partly explain the different results obtained by different methods.

IX. REGULATION OF GASTRIC SECRETION Our knowledge of gastric secretory regulation in teleosts is very scanty. For purposes of comparison, secretory control in mammals will be considered briefly first. The use of gastric fistulae and the pouch technique have greatly contributed to the understanding of secretory regulation in mammals. Pavlov’s sham feeding experiments showed that secretion in dogs can be evoked by conditioned and unconditioned reflexes, the vagus nerve being part of the reflex arc. This reflective phase is also called the cephalic or first phase. The second regulatory phase of gastric secretion is chemical, and may be subdivided into a gastric and an intestinal phase. I n the gastric phase the hormone gastrin is operative, the pyloric antrum being the site of hormone release. Since the intramural nerve plexus of the stomach wall is involved in the activation of the antral endocrine function, there is a synergism between first and second phase. The cephalic and gastric phases both act via a neuro-hormonal mechanism : cholinergic stimulation releases gastrin and enhances the sensitivity of the parietal cell to gastrin. Besides the mechanisms evoking the secretion of gastric juice, there is also a way to stop secretion. The cephalic phase terminates when adequate stimulation subsides ; the gastrin mechanism is blocked by acidification of the antrum. There is evidence that in fish too, a cephalic phase is operative in the control of gastric juice secretion. Krayukhin (1959) found in the bullhead (Ictalurus nebulosus) that the act of swallowing leads to abundant secretion of juice, probably activated by an unconditioned reflex. Krayukhin (1963) proved that a reflective phase is operative in the regulation of gastric secretion in bullheads, provided with a fistula connected to a rubber collector. Food was shown to them while they were prevented from taking it. Fishes that attempted to seize the food secreted gastric juice whereas control animals did not. Gomazkov and Krayukhin (1963) severed the intestinal branch of the vagus nerve in the burbot (Lota lota L.). Six days after the operation, food was artificially introduced into the stomach. After some time, the fish were killed, the stomach contents removed, and wet and dry weight, pH, and proteolytic activity of the contents were determined. Gastric digestion in

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treated fish lasted twice as long as in intact fishes. The results indicate that the vagus nerve plays some role in secretory regulation. It is known that in mammals gastric secretion is evoked by distension of the stomach wall which activates the neuro-hormonal mechanism. Secretory response to stomachal distension is also known from Rana (Smit, 1968). Distension of the piscine stomach wall also evokes secretion of gastric juice. Krayukhin (1958) observed in fish that gastric digestion of large particles is more intensive than that of smaller ones. In bullheads (Ictalurus sp.) gastric secretion can be evoked by distending the stomach wall by inserting a piece of sponge or foam plastic into the stomach (Quispel, 1940; Smit, 1967) or by injection of a cholinergic drug (urecholine); and secretion can be reduced by atropine injection (Ashir, 1967). These findings offer strong evidence for the existence of nervous regulation of secretion. The effectiveness of the distension stimulus in producing gastric acid has also been demonstrated in the Cottidae (Cottus gobio and Enophrys bubalis) and in the brown trout (Salmo trutta) by Western and Jennings (1970) who evoked gastric acid secretion in fish by introducing inert starch into the stomach. I n the bluegill (Lepomis macrochirus), Norris et al. (1973) stimulated gastric secretion by introducing glass beads into the stomach. The latter concluded from the decline of gastric secretory output 5 or 6 h after ingestion of the glass beads, that large meals cannot be adequately processed by the fish. This conclusion, however, is premature, since acidification of the stomach may inhibit secretory response. After ingestion of a meal, a sharp decrease of the pH will be prevented by the buffering action of the food, so that the results obtained on experiments with glass beads cannot be applied to the digestion of food. Since the presence of inert material (foam plastic, glass beads, sponge, starch) in the stomach stimulates the secretion of gastric juice, it would appear that bulk, distending the stomach wall, is responsible for the adequate stimulus rather than the chemical nature of the material. Whether a hormonal mechanism is also involved cannot be deduced from the results of these experiments. I n the opinion of Ashir (1967), there are a t least some indications of hormonal control : the peak gastric secretion produced by distension or by cholinergic stimuli is reached after a lag period of 2-6 h ; although atropine inhibits pepsin secretion, it does not do so completely. The inconstant body temperature of fish is a special feature as compared with mammals. The substantial influence of temperature on the rate of digestion in fish (see Fig. 23) suggests that gastric secretory rate may also depend on the body temperature of the fish. Gastric mucosa extracts of brook trout (Salvelinusfontinalis),acclimated

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€3. G. KAPOOR, H. SMIT AND I. A. VERIGHINA

to 5"C, showed a 30% higher peptic activity than extracts of trout acclimated to 12°C (Owen and Wiggs, 1971). A marked temperature effect on secretory rate has been found for the bullhead (Ictalurus nebulosus), for both acid secretion and the secretion of pepsin (Smit, 1967). Acid secretory rates measured a t various acclimation temperatures ranging from 10°C to 30"C, showed a peak a t 25"C, the rate at 10°C being only 3% of peak rate ; pepsin secretion a t 10°C amounted to 1yo of that a t 25°C. The acidity of the gastric juice secreted a t 10°C was much lower than that of juice secreted a t 25°C; but the pepsin

u 0.4 v

n

I acclimation temperature ( " C )

FIG. 24. Rates of gastric acid secretion in the brown bullhead (Ictalurus nebulosus Le Sueur) in relationship to temperature. Secretion was evoked by a standardized secretory stimulus. Tests performed at various acclimation temperatures and a t temperatures either 5" above or 5' below acclimation level. Test temperatures are indicated in the columns. Data taken from Smit, H. (1967). Comparative Biochemistry and Physiology, 21, 125-132.

concentration of the juice was higher a t the lower temperature. When the acclimation temperature was raised by 10 degrees, the acid output per unit time in response to the distension stimulus showed a tenfold increase, while the pepsin output was roughly doubled. This must be of great importance for the acidification and digestion of the increased amount of food consumed when the temperature rises. Figure 23 shows that the digestion rate increases by a factor of 3 to 4 with a 10-degree rise in temperature. At least part of this increased digestion rate results from the increased acidifying and peptic power of the gastric juice. When the acclimation temperature exceeds 25"C, there is a sharp decline of the gastric secretory rate in the bullhead :acid secretion

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at 30°C is only 34% of that a t 25°C when a standardized distension stimulus is applied. Temperature deviations from the acclimation level strongly influence the response of the gastric glands t o secretory stimuli (Fig. 24). Gastric juice secretion in the bullhead exhibits the phenomenon of temperature compensation within the acclimation range from 20°C to 30"C, i.e. when secretion is measured a t the intermediate temperature (25"c), the 20°C-acclimated fish show a higher rate than the 30°Cacclimated fish.

X. ABSORPTION AND CONVERSIONOF FOOD Ingested food is useful to the animal only if it can be digested and then absorbed by the intestinal epithelium. When there is an excess foods supply, the rates of food intake and of digestion are mutually adjusted. However, the amount of energy available to the animal depends not only on the amount of food consumed but also on the caloric value of the food and its digestibility. Digestibility (= digest,ion coefficient) can be derived from the equation nutrient intake - nutrient in faeces x 100 nutrient intake in which intake is expressed as calories or as nitrogen. I n the latter case one should make allowance for metabolic nitrogen, so that the equation should read intake N - (faecal N - metabolic N ) x 100 intake N (see Hastings, 1969). If digestibility is low, losses via the faeces are high. This occurs, for instance, when the food contains vegetable material with a high proportion of indigestible cellulose or animal material with a large quantity of indigestible chitin. An example is Tilapia esculenta Graham which feeds on phytoplankton of which only diatoms are digested, whereas the blue-green and green algae pass undigested through the alimentary canal (Fish, 1951). It should be pointed out that chitin may not be completely indigestible, since fish may house chitin-decomposing bacteria in their intestines (Okutani and Kitada, 1968). Digestibility can be assessed when the amount and composition of the food consumed and of the faeces expelled are known. Shcherbina (1964) studied digestibility of food and food absorption in the carp with the aid of Cr,O,. Digestibility (D) was calculated by means of the formula : value of food indicator in faeces D 100 - _caloric __-_____~ __ x 100%. Xindicator in food caloric value of faeces I

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When the feeding rate is high, the digestibility can drop, probably due to inadequate time for digestion or absorption. Dataon fat, carbohydrate and protein digestibility in trout, obtained in the Cortland Hatchery, have been reported by Phillips (1969). Different carbohydrates were digested by brook trout with widely varying efficiency : glucose 99%, lactose 60%, and raw starch only 38%. Fat digestibility was found to be about 85%. Protein digestibility in Megalops cyprinoides and Ophicephalus striatus was measured by Pandian (1967), energy o f digestion

---- -,

f o o d consumed

--------, absorption---. c

i

----- - - - --1

cnergy l o s t Ivia excretion L

conversion (utilization)

Energy absorbed

I

--------- J

I

J

I

f o r growth

energy I

I

I

r---- -----i 1 energy lost I v i a SUA

I

C

e x t e r n a l work (active notabolisn)

FIG.25. -

Bx A

Energy -. balance.

Gross conversion efficiency = gross growth efficiency ~~

100. Net conversion efficiency

tion = C

+ D + c.

(a

+

=

+

A - ( a b) b) equals about 0.2 x A .

x 100. Total heat produc-

who fed his fish on prawns. Absorption efficiency (= digestibility percentage) of protein was estimated by relating total nitrogen absorbed (= total N of food minus N content of faeces) to total nitrogen consumed, and amounted to about 95%. If a correction was made for the indigestible chitinous nitrogen, the efficiency of absorption of protein was about 97%. The total food absorption efficiency was found to be about 91% after correcting for the chitin. Thus, since digestibility of the proteins is 97%, that of the other nutrients (fats and carbohydrates) must be lower. The calorific value of the food can be measured in the bombcalorimeter. Calorimeter values are : 5.65 Cal per g protein, 4.10 Cal

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per g carbohydrate, and 9.45 Cal per g fat (Brody, 1945). The energy that can be spent by the fish on growth and metabolism is, however, less than the bomb-calorimeter value, because of losses through faeces and excretion via kidney and gills (Fig. 25). According to Brody, energy losses through excretion may amount to 23% for protein, so that 77% is useful energy. If 95% of the food protein is absorbed and 77% of the absorbed protein is metabolizable, there remains 0.95 x 0-77 x 5.65 = 4.13 Cal/g protein for metabolism and growth. If fats and carbohydrates are 96% metabolizable when absorbed, and absorption efficiency is 80% and 50% respectively, the physiological energy value for fats is 0.96 x 0.8 x 9.45 = 7.26 Cal/g, and that for carbohydrates is 0.96 x 0.5 x 4.10 = 1.97 Cal/g. However, these values are not generally applicable, because of species differences and because the relative proportions of the nutrients in the food influence the utilization of the various food components. Carbohydrates and fats have a protein-sparing action; protein is used more efficiently in growth than in metabolism ; in periods of rapid growth, much of the protein intake is channelled into body material. These factors affect the fraction of the total energy intake that is physiologically useful. Winberg (1956) estimated for mixed (protein-rich) food, that the quantity of energy available for growth and metabolism is about 80% of the energy content of the food consumed, which may be a reasonable working value. For example, an energy budget of small plaice fed on Arenicola and Mytilus was drafted by Birkett (1970). The total daily intake amounted to 48 cal/g day, which was taken as 100%. Faecal losses amounted to 8yo,so the absorbed energy was 92%, and losses through excretion were 8%, leaving 84% as metabolizable energy. Total heat output amounted to about 65%, and about 16% of the total energy intake was available for growth. Niimi and Beamish (1974) drafted an energy budget for bass. As a coefficient of food utilization the so-called conversion factor is used, which is the ratio of food intake and weight gain, or growth efficiency is used, which is the inverse of the conversion factor. Food intake is expressed in dry weight and fish gain in wet weight, or both are expressed in dry weight, calories or protein-N. The fraction of the energy contained in the food that is utilized for growth, varies considerably and depends, among other things, on standard metabolic rate and activity (see Phillips in Halver, 1972). Temperature is an important factor controlling energy distribution within the energy system. Standard metabolic rate is strongly temperature-dependent ; when temperature rises, the " scope for growth " usually decreases as a result of the increased standard

204

B. G. KAPOOR, H. SBIIT AND I. A. VERIGHIN-4

metabolic rate. (The term " scope for growth " was proposed by Warren and Davis (1967) in parallel with Fry's (1947) concept " scope for activity ".) However, depending on the location of the initial temperature on the physiological temperature scale of the fish, a temperature rise may result in an increase of the fish's activity, leading t o such high rates of feeding, digestion and absorption that the increase of the total metabolism is surpassed by the increased energy absorption, resulting in an increase of the scope for growth. Baldwin (1956) found in brook trout that food consumption and weight gain increased with rising temperature, due to accompanying increase of maintenance requirements. However, when sufficiently wide ranges of temperature and ration are considered, growth efficiency increases with rising temperature within a restricted range and when appropriate rations are given (Brett et al., 1969). A kind of " growth acclimation " is suggested by the experiments of Pessah and Powles (1974) on growth rates of sunfish (lepomis gibbosus) kept a t different constant temperatures. The relative growth rates of sunfish exposed to 15", 20", 25" and 30°C were separable for the first month or so, after which growth declined and became uniform in all thermal groups. Sockeye salmon (Oncorhynchus nerka), when living in thermally stratified lakes, show a diurnal vertical migration pattern, the fish feeding a t night in the warm surface layers and spending the day in cold deep waters (Brett, 1971a). This migration pattern is probably related to the bioenergetics of the fish. Feeding takes place when activity and appetite are high because of the high temperature, whereas digestion occurs a t the low temperature of the deep water layers, when maintenance metabolism is low and food conversion efficiency is high. Brett compares this pattern of behavioural thermoregulation for the purpose of reaching high bioenergetic efficiency with the metabolic oscillation occurring in bats that feed a t dawn and dusk and lower their body temperature during daytime. The amount of energy lost as heat through specific dynamic action (SDA) in relation t o the total amount of metabolizable energy, depends on the fraction of absorbed protein that is deaminated, which in turn depends on the fraction that is converted into fish proteins. Savitz (1971) measured the ratio of consumed nitrogen to excreted nitrogen in 29-g bluegills (Lepomis macrochirus). By subtracting the nitrogen excretion of starved fish from that of fed fish, an estimation was obtained of the N-excretion resulting from SDA. This N-excretion due to SDA was found t o be zero a t a feeding rate of 3 mg N/day, 2.95 mg N/day a t 9 mg N/day, and 5.45 mg N/day a t 15 mg N/day. At low temperatures, when metabolic rate is low, SDA makes up a greater

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percentage of the total energy consumption than a t higher temperatures (Warren and Davis, 1967). Great amounts of heat loss through SDA can account for such a large part of the total metabolism that activity is considerably suppressed. Muir and Niimi (1972) measured extra 0,-consumption due to SDA in Kuhlia sandvicensis (Steindachner)fed on tuna flesh. They estimated the SDA of tuna flesh to be from 16 to 19% of its total caloric content. Such extra consumption of oxygen would suppress swimming activity; on the other hand, low oxygen concentrations or moderately high swimming speeds will suppress food uptake and growth, simply because there is no oxygen available for the SDA. It has already been pointed out that the maximum daily food intake expressed as percentage of body weight is higher in small fish as compared with bigger fish. This phenomenon can be related to the capacity t o grow which decreases with increasing size. Food consumption and growth can also be influenced by the ambient oxygen level. The oxygen concentration a t which growth is impaired depends on the availability of food. Juvenile largemouth bass, fed unrestricted rations, showed reduced food uptake and growth rates a t reduced oxygen concentrations. This growth rate reduction is temperature dependant. Underyearling coho salmon showed a decline of growth rate with any reduction of oxygen from the air-saturation level, although they continued t o grow even a t 2 m g 02/l. (at 19'C) when excess rations were supplied (Doudoroff and Shumway, 1970). Food intake and weight gain dropped sharply a t oxygen concentrations of 4 ppm and less (Hermann et al., 1962). These young coho salmon were also less active a t low ambient oxygen levels, which means that low ambient oxygen has the effect of depressing food intake as well as metabolic rate and growth rate. Hermann et al. (1962) also found a seasonal influence on the growth of coho salmon. Compared with the summer level, food consumption decreased during the fall and the food conversion ratio increased. Because the fish were kept a t a constant temperature, this seasonal variation cannot be attributed to temperature. The relatively low oxygen consumption rate in the fall seems to accord with the high food conversion ratio in that season. Brown trout kept a t constant conditions of temperature, light and feeding also exhibited a seasonal growth rate cycle (Brown, 1946). Net growth efficiency (= the ratio of weight gained to total food intake minus maintenance ration, in terms of calories) in sculpins (Cottus perplexus Gibb and Evermann) has the same value in the fall and winter a t intermediate feeding levels. When the feeding rate increases, the net growth eeciency in the winter decreases much more than that in the fall (Davis and Warren, 1965).

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I n the winter, therefore, less metabolizable energy is available for growth, apparently because the animal cannot effectively utilize the amino acids supplied in the food, and as a result, greater losses through SDA occur. The capability to channel energy into growth may be under hormonal control. From these examples it appears that there is some control of the distribution of energy over anabolism and catabolism ; this distribution can be described in terms of food intake, growth and metabolism. Studies on the oxygen consumption rate in fish revealed that the total is a function of body weight ( W ): T = uWb. The metabolic rate ( T ) value of b is about 0.8, and is remarkably stable. The value of u varies considerably, and depends on activity, feeding level and temperature. This equation can also be used in food-growth studies if conversion is applied. Metabolism, which is expressed in mg O,/fish. h, can be expressed in calories, assuming that 1 litre of oxygen consumed corresponds to 4.8 calories of energy. Feeding rate (R)equals total metabolic rate (T) plus growth rate (G): r;R = T+G. Since the ration ( R )is not completely metabolizable due to losses via faeces and excretion, it is necessary to apply the coefficient p , which was estimated by Winberg (1956) to have a value of about 0.8. Paloheimo and Dickie (1965) combine the two equations: T = uWb = 0.8R - G. They point out that knowledge of u permits the calculation of R for various fish sizes. The importance of this equation is that it contains the constant value of b : " The constancy of b suggests a complex interaction of resting and active metabolism with the food energy supply, and implies some homeostatic mechanism operating on the dynamic energy system " (Paloheimo and Dickie, 1966). Gross growth efficiency (= gross efficiency of food conversion) is the ratio of growth to total food intake, and is affected by the size of the fish, the food consumption rate, the type of food, and the temperature. An accurate description of the relation between feeding rate, growth rate and temperature has been given for fingerling sockeye salmon by Brett et al. (1969), who showed that temperature has as much effect as feeding rate on conversion efficiency. The relations between feeding rate, growth rate and temperature reflect the regulation of the energy distribution in the total energy system. Some criticism on these considerations has been put forward. Kerr (1971a, b) points out that laboratory experiments on growth cannot simply be applied to field conditions, because abundance, mobility and size of prey can be expected to exert a greater influence on the growth efficiency of the predator than appears from feeding experi-

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ments in the laboratory. On the other hand, Carline and Hall (1973), working on coho salmon, obtained results suggesting that laboratory growth data can provide reliable estimates of food consumption in nature. See also Weatherly (1972). Cowey and Sargent (1972) draw attention to the fact that a fish, held at maintenance ration, differs in chemical composition from a growing fish. The non-growing fish has enhanced water and lowered fat and protein contents. Therefore, the maintenance ration of a nongrowing fish does not represent that of a growing fish. This question needs clarification to enhance the reliability of the calculation of net efficiency of food conversion. XI. CONCLUSIONS I n view of the different foods taken by teleosts and their feeding habits several types should be recognized, i.e. plankton feeders, herbivores, omnivores, carnivores and specialists. The various degrees of specialization in feeding habits leads to the distinction of europhags, stenophags and monophags. There is some adaptation of the structure of the alimentary tract to the diet, although the structure of the digestive apparatus is mainly related to phylogeny and to body form. The relative length of the gut is well associated with the feeding habits : fishes consuming food with a high proportion of undigestible material (microphags and herbivores) have a relatively longer gut than carnivores. The mouth, its form and position, dentition, and the occurrence of gill-rakers, is adapted to the food and to the feeding habits. A number of structures may be involved in the functioning of the mouth and pharynx as organs for food ingestion: lips, buccal valves, " lamellar organs ", palatine cushions, the tongue, pharyngeal glands and valves, epibranchial organs, pharyngeal pads and cushions, buccopharyngeal teeth, gill rakers, mucous glands, and taste buds. The inner lining of the oesophagus may be smooth or folded, densely packed with mucous cells or covered by a protecting cuticula ; it may contain simple or branched tubular or alveolar glands; it may even bear teeth which project into the cavity of a sac-like oesophageal widening. These oesophageal sacs store and triturate food. In some cases the oesophageal wall contains gastric-type glands. The glands in the gastric mucosa are of a simple or branched tubular type and are often confined to the cardiac part of the stomach. The glands secreting gastric juice contain only one type of secretory cell. Several fish (e.g. Mugil) have a pyloric stomach with a thick muscularis and a keratinized inner lining forming a masticatory gizzard. Many carnivorous fish have their stomach wall strengthened by a so-called

208

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a. KAPOOR,

H. SMIT AND I. A . VERIGHINA

stratum compactum, composed of dense collagenous connective tissue, or the wall has a very thick muscularis. A stratum granulosum is situated between the stratum compactum and the muscularis mucosae. Various functions are ascribed to these granular cells. Stomachless fishes, such as many Labridae and Cyprinidae, lack gastric glands. This absence is considered to be secondary, the fore-gut being often enlarged to form a so-called intestinal bulb, which functions as a reservoir, just as does a true stomach, or there is no intestinal bulb and the whole gut acts as a large reservoir, as in some microphags. The intestinal mucosa is lined with a columnar absorbing epithelium provided with a brush-border and contains numerous mucus secreting goblet cells, which are especially abundant in the rectum. I n several fish it has been observed that the histological appearance of the intestinal mucosal lining shows seasonal changes in the amount of cytoplasm in the epithelial cells, their RNA and lipid content, the number of vacuoles in these cells, and in the size of the goblet cells. I n Misgumus, part of the intestine has a respiratory function; then the epithelial cells are flattened and the subepithelial capillaries and lymphatics are cram-full. The pyloric caeca, occurring in many teleosts, are histologically almost identical with the intestine. The caeca increase the intestinal surface area and supplement the digestive functions of the alimentary canal. Many cell types of the teleost digestive tract have been electronmicroscopically investigated : oral epithelial cells, so-called chloride cells, scattered chemosensory cells, the cells of taste buds, intestinal goblet cells and epithelium cells, and also oesophageal striated muscle fibres. Histo- and cyto-chemical techniques have been used in the study of the teleostean alimentary canal. Since the inner lining of this canal is mucified, attention has been paid to the mucus-secreting cells, which appear to contain either neutral or acidic mucopolysaccharides. Histochemical demonstration of pepsinogen in the gast,ric glandular cells, and the formation of HC1 by the lining cells of the gastric glands indicate that the pepsinogen and HC1 forming cells are histologically identical. I n many teleosts alkaline phosphatase and acid phosphatase activity has been detected in the brush-border of intestinal and caecal epithelia. Lipase activity has been histochemically demonstrated in the intestinal epithelium of Cyprinidae ; also fat absorption by intestinal epithelium cells has been demonstrated by histochemical techniques. 5-hydroxytryptamine containing enterochromaffin cells have been shown to occur throughout the teleostean digestive tract, but Paneth and argentaffin cells appear to be lacking.

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The wall of the teleostean gut contains several nerve plexuses connected with the extrinsic vagus and splanchnic nerves, i.e. subepithelial, submucous, myenteric and subserous plexuses. These contain excitatory and inhibitory cholinergic fibres, and inhibitory adrenergic and purinergic nerve fibres. These intramural nerves play a role in gastric and intestinal motility, and probably also in the regulation of gastric secretion. Feeding rates have been measured by observing food intake under laboratory conditions with restricted or excess rations. I n the laboratory as well as under field conditions, feeding rates can be determined by measuring stomach contents either after killing the fish or by use of a stomach pump. Stomach contents are expressed as volume or as dry weight. An indirect method of estimating food intake relies on the relationship between food intake and growth, increased nitrogen content of the fish serving as a measure of nitrogen consumption. Application of this method requires a thorough knowledge of the effects of environmental factors on the energy balance of the species under study. Although fluctuations in feeding rate are observed within a species, the species can nevertheless be characterized by the average amount of food it consumes. Apparently, food intake is well regulated. Many factors influencing the feeding rate have been recognized : food supply, temperature, season, condition of the .fish, locomotory activity, digestibility of the food, relative proportion of the nutrients in the food, size of the fish, sexual cycle, etc. These (unequal) factors are interdependent in their action and effects; for example, the activity of a fish is influenced by food density, migration, ambient oxygen concentration, speed of the water current, and ambient temperature. Maintenance requirements, i.e. the energy needed for routine activity when the growth rate is zero, are satisfied by the maintenance ration. The fish is able to adapt t o a changing maintenance ration by adjusting its level of routine activity. If activity level is constant, the maintenance ration increases semilogarithmically with rising temperatures. When environmental conditions are kept constant, changes in feeding rates may reflect an annual physiological cycle. When the daily feeding period is short, gut capacity limits the amount of food consumed. When the fish has free access to food, the capacity of the fore-gut is not limiting, since the fish consumes a certain amount of calories rather than bulk. If the calorific value of the food is lowered, the fish takes in a greater volume of food. The rate of feeding is governed by hunger, which depends on a metabolic deficit. Hunger cannot accurately be described in terms of stomach contents

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B. Q. KAPOOR, II. SMIT AND

I. A.

VERIGHINA

and eagerness of feeding, since it can increase when the stomach is empty and the feeding response can be depressed by means other than food intake, so that the degree of filling of the stomach and eagerness of feeding can vary independently of each other. When the feeding response was not inhibited, eagerness of food consumption was found to depend on the glucose and amino acid level of the blood. The digestion rate in fish has been estimated by measuring the time interval between food intake and defaecation and by measuring the stomach contents at various time intervals after feeding; a third method makes use of X-rays for observing the progress of digestion with time. An unequivocal description of the time-course of gastric emptying cannot be formulated from the data available in the literature. The rate of gastric emptying depends on the quantity of the food, the rate of gastric secretion, the gastric motility, and the capacity of the intestine. Gastric secretion and motility are both influenced by the quantity of the food, since distension of the stomach wall enhances gastric functioning. Digestive rates generally increase when food intake increases; rate of digestion also depends on the digestibility of the food; small fish exhibit higher digestive rates than bigger fish. Temperature has a strong influence on the digestion rate ; a temperature rise of 10 degrees results in an increased rate of digestion by a factor of three and more. Temperature affects the digestion of food through its effect on feeding rate, rate of secretion of digestive enzymes, activity of digestive enzymes, motility of the gastro-intestinal tract, and intestinal absorption. The digestive enzymes of fish closely resemble those of mammals in their action and site of secretion. The enzymes secreted into the alimentary canal of fish originate from the mucosae of the stomach, intestine and pyloric caeca, and from the pancreas. Probably in all fish possessing a stomach, the gastric proteolytic enzyme is a pepsin that has maximal activity at a pH value of about 2 and often exhibits another maximum between pH 3 and pH 4. Tryptic activity, with its maximum between pH 7 and pH 9, has been detected in the pancreas, in which carbohydrase and lipase activity have also been demonstrated. The intestinal mucosa produces probably oligosaccharidases, exopeptidases, and enterokinase. However, the exact site of secretion of these enzymes has not yet been elucidated. There is evidence that gastric juice secretion is partly under vagal control. Distension of the stomach wall has been proved to be a secretory stimulus, for both acid and pepsin, acting through a neural mechanism, but a hormonal mechanism may also be involved. The gastric secretory rate is strongly temperature-dependent, having a

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distinct maximal rate at a given temperature. The secretory rate declines when temperature is either higher or lower than the optimal temperature. The gastric secretory rate has also been found to compensate partially for the effect of temperatures deviating from the acclimation level. Digestibility of the food depends on its quality and the quantity consumed. Generally, the digestibility of proteins is very high and that of fats somewhat lower, whereas some carbohydrates have high and others low absorption efficiencies. The nutritive value of the food depends on the relative proportions of proteins, carbohydrates and fats in the food. As an approximation, it has been estimated that 80% of the energy content of the food is available for metabolism and growth. The distribution of this energy over metabolism and growth depends on a number of extrinsic and intrinsic factors : temperature, ambient oxygen, feeding rate, activity, standard metabolism, specific dynamic action and hormone levels. The interdependence of these factors tends to obscure the role of each of them in controlling the direction of the energy flow. For example, if food density is low, activity may increase so that feeding rate can be kept a t the desired level. Activity may also be increased by a rise in the temperature ; the feeding rate will now increase, but the growth may decrease, because the rate of total metabolism rises. The metabolic capacity of the fish and its capability to adjust its metabolism to the environmental temperature can be considered to be of crucial importance for the obtaining and consumption of food and its transformation into fish substance.

XII. ACKNOWLEDGEMENTS B. G. Kapoor thanks Professor Dr S. D. Misra, Department of Zoology, University of Jodhpur and Dr M. L. Bhatia, retired Professor of Zoology, University of Delhi for encouragement.

XIII. REFERENCES AganoviE, M. and VukoviE, T. (1966). Odnos duaine crevnog trakta i duiine tijela kod tri lokalne populacije ostrulja (AuZopigehiigelii Heck.). Ribarstwo Jugeslavije, 21, 8-1 1. Agrawal, V. P. and Bala, V. (1967). Studies on the morphology and physiology of alimentary canal of Mugil corsula (Ham.). Agra University Journal of Research (Science),16, 107-120. Agrawal, V. P. and Sharma, U. (1966). Morpho-histological studies of the digestive tract of Mystus vittatus (Bloch). Proceedings of the National Academy of Sciences, India, B36, 441-456.

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Agrawal, V. P. and Singh, H. M. (1964). Functional morphology of the rectal caecum of Notopterus notopterus Pallas. Current Science, 33, 53-54. Agrawal, V. P. and Verma, S. R. (1966). The digestive physiology of the stomach of a few freshwater teleosts. Zoologische Jahrbucher, 72, 309-315. Albright, J. T. and Skobe, Z. (1965). Comparative ultrastructure of oral epithelium in fish and Amphibia. Archives of Oral Biology, 10, 921-927. Alexander, R. McN. (1966). The functions and mechanisms of the protrusible upper jaws of two species of cyprinid fish. Journal of Zoology, London, 149, 288-296. Alexander, R . McN. (1967a). The funetions and mechanisms of the protrusible upper jaws of some acanthopterygian fish. Journal of Zoology, London, 151, 43-64. Alexander, R . McN. (196713). Mechanisms of the jaws of some atheriniform fish. Journal of Zoology, London, 151, 233-255. Alexander, R. McN. (1969). Mechanics of the feeding action of a cyprinid fish. Journal of Zoology, London, 159, 1-15. Alexander, R. McN. (1970). Mechanics of the feeding action of various teleost fishes. Journal of Zoology, London, 162, 145-156. Al-Hamed, M. I. (1965). On the morphology of the alimentary tract of three cyprinid fishes of Iraq. Bulletin of the Iraq Natural History Museum (University of Baghdad), 3, 1-25. Al-Hussaini, A. H. (1945). The anatomy and histology of the alimentary tract of the coral feeding fish Scarus sordidus (Klunz.). Bulletin de l’lnstitut d’dgypte, 27, 349-377. Al-Hussaini, A. H. (1946). The anatomy and histology of the alimentary tract of the bottom-feeder, Mulloides auriflarnma (Forsk.). Journal of Morphology, 78, 121-153. Al-Hussaini, A. H. (1947a). The anatomy and histology of the alimentary tract of the plankton-feeder, Atherina forskali Rupp. Journal of Morphology 80, 251-286. Al-Hussaini, A. H. (1947b). The feeding habits and the morphology of the alimentary tract of some teleosts living in the neighbourhood of the Marine Biological Station, Ghardaqa, Red Sea. Publications of the Marine Biological Station, Ghardaqa (Red S ea ) , no. 5, 4-61. Al-Hussaini, A. H. (1948). Alkaline phosphatase in fish gut. Nature, London, 161, 274. Al-Hussaini, A. H. (1949a). On the functional morphology of the alimentary tract of some fish in relation to differences in their feeding habits : anatomy and histology. Quarterly Journal of Microscopical Science, 90, 109-139. Al-Hussaini, A. H. (1949b). On the functional morphology of the alimentary tract of some fish in relation to differences in their feeding habits : cytology and physiology. Quarterly Journal of Microscopical Science, 90, 323-354. -41-Hussaini, A. H. (1964). On the nature of certain pear-shaped cells in the intestinal epithelium of fish. Bulletin de l’lnstitut d’dgypte, 40, 23-32. Al-Hussaini, A. H. and Kholy, A. A. (1953). On the functional morphology of the alimentary tract of some omnivorous teleost fish. Proceedings of the Egyptian Academy of Sciences, Cairo, 9, 17-39. Angelescu, V. and Gneri, F. S. (1949). Adaptaciones del aparto digestivo a1 regimen alimenticio en algunos peces del Rio Uruguay y del Rio de La Plata. Revista del Instituto Nacional de Investigacion de la Ciencias Natureles anexo a1

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Museo Argentino de Ciencias Natura les “ Bernard0 Rivadavia ”, Buenos Aires, Ciencias Zooldgicas, I , 161-272. Aronson, L. R. (1963). The central nervous system of sharks and bony fishes with special reference to sensory and integrative mechanisms. I n “ Sharks and Survival ” (P. W. Gilbert, ed.), Ch. 6, pp. 165-241. D. C. Heath & Co., Boston. Arvy, L. (1962). Histichimie des enzymes impliques dans la digestion dans la sBrie animale. In “ Handbuch der Histochemie ” Vol. VII, pp. 154-303. G. Fischer Verlag, Stuttgart. Ashir, A. R. M. (1967). Gastric secretion in the bullheads Ictalurus melas and Ictalurw natalis. Dissertation Abstracts, 278, 2538-2539. Babkin, B. P. and Bowie, D. J. (1928). The digestive system and its function in Fun,dulus heteroclitus. Biological Bulletin, 54, 254-277. Bajkov, A. D. (1935). How to estimate the daily food consumption of fish under natural conditions. Transactions of the American Fisheries Society, 65, 288-289. Baldwin, N. S. (1956). Food consumption and growth of brook trout a t different temperatures. Transactions of the American Fisheries Society, 86, 323-328. Barber, W. E. and Minckley (1971). Summer foods of the cyprinid fish Semotilus atromaculatus. Transactions of the American Fisheries Society, 100, 283-289. Barbetta, F. (1962). Cellule mucose e mucoidi nell’epitelio gastric0 dei pesci. Annales d’aistochimie, 7, 25-32. Bardach, J. E. and Atema, J. (1971). The sense of taste in fishes. I n “ Handbook of Sensory Physiology ’’ (H. Autrum, R. Jung, W. R. Loewenstein, D. M. MacKay, H. L. Teuber, eds.) Vol. IV. Chemical senses, Part 2, Taste. Ch. 14, pp. 293-336. Springer-Verlag, Berlin, Heidelberg, New York. Barrington, E. J. W. (1942). Gastric digestion in the lower vertebrates. Biological Reviews, 17, 1-27. Barrington, E. J. W. (1957). The alimentary canal and digestion. I n “ The Physiology of Fishes” (M. E. Brown, ed.), Vol. I, Ch. 3, pp. 109-161. Academic Press, New York. Baumgarten, H. G. ( 1 9 6 7 4 . Vorkommen und Verteilung adrenerger Nervenfasern im Darm der Schleie ( T i n ca vulgaris Cuv.). Zeitschrift fur Ze22forschung und mikroskopische Anatomie, 76, 248-259. Baumgarten, H. G. (1967b). Uber die Verteilung von Catecholaminen im Darm des Menschen. Zeitschrift f u r Zellforschung und mikroskopische Anatomie, 83, 133-146. Bayliss, L. E. (1935). Digestion in the plaice. Journal of the Marine Biological Association of the United Kingdom, 20, 73-91. Beamish, F. W. H. (1972). Ration size and digestion in largemouth bass, Micropterus salmoides LacBpBde. Canadian Journal of Zoology, 50, 153-164. Beamish, F. W. H. and Dickie, L. M. (1967). Metabolism and biological production in fish. I n “ The Biological Basis of Freshwater Fish Production ” (S. D. Gerking, ed.), pp. 215-242. Blackwell Scientific Publications, Oxford. Bellisio, N. B. (1962). Anatomia e Histologia del tracto digestivo de algunos Pimelodidos argentinos. An a i s do Segundo Congresso Latino-American0 de Zoologia, Sdo Paulo, 2, 107-123. Belonozhko, R. A. (1966). On seasonal changes of histostructure of the digestive tract of roach. I n “ Voprosy fiziologii i morfologii ”, pp. 17-18. Rostovna-Donu. (In Russian.)

214

B. G. KAPOOR, H. SMIT AND I. A. VERIGHINA

Belonozhko, R. A. (1967a). A study of the process of adaptation of the gut to seasonal changes of diet. I n “ Fiziologiya i patologiya organov pischevareniya ”, pp. 28-30. Yaroslavl. (In Russian.) Belonozhko, R. A. (196713). Some histo- and cytochemical changes in the gut of the bream (Abramis brama) and the pike (Esox lucius) from lake Nero in dependence on the seasonal changes in diet. I n “ Morfologicheskiye issledouaniya adaptatsij ”, pp. 29-35. Materialy k I11 Vsesoyusnomu Soveschaniyu PO ecologicheskoi fiziologii, biokhimii i morfologii Novosibirsk. (In Russian.) Bergot, P. and FlBchon, J.-E. (1970a). Forme et voie d’absorption intestinale des acides gras a chaine longue chez la truite arc-en-ciel (Salmo gairdnerii Rich.). I. Lipides en particules. Annales de Biologie animale, Biochimie, Biophysique, 10, 459-472. Bergot, P. and FlBchon, J.-E. (1970b). Forme et voie d’absorption intestinale des acides gras a chaine longue chez la truite arc-en-ciel (Salmo gairdnerii Rich.). 11. Lipides “ &ales ”. Annales de Biologie animale, Biochimie, Biophysique, 10, 473-480. Berman, S. A. and Salenitse, J. K. (1966). Membrane digestion in fish. Voprosy ikhtiologii, 6, 41, 720-724. (In Russian.) Bernard, F. (1949-50). Anatomie compar6e des caecums pyloriques chez les Salmonid& Travaux du Laboratoire d’Hydrobiologie et de Pisciculture de 1’Universitk de Grenoble, 41-42, 25-42. Berry, P. Y. and Low, M. P. (1970). Comparative studies on some aspects of the morphology and histology of Ctenopharyngodon idellus, Aristichthys nobilis and their hybrid (Cyprinidae). Copeoeia, no. 4, 708-726. Bertmar, G. (1973). Epibranchialorgan en anpassning till planktonupptagning hos benfiskar. Zoologick Revy, 35, 5-10. Bertmar, G., Kapoor, B. G. and Miller, R. V. (1969). Epibranchial organs in lower teleostean fishes-an example of structural adaptation. I n “ International Review of General and Experimental Zoology ’’ (W. J. L. Felts and R. J. Harrison, eds.), Vol. IV, pp. 1-48. Academic Press, New York and London. Beukema, J. J. (1968). Predation by the three-spined stickleback (Gasterosteus aculeatus L.) : the influence of hunger and experience. Thesis, Groningen. Birkett, L. (1970). Experimental determination of food conversion and its application to ecology. I n “ Marine Food Chains ” (J. H. Steele, ed.), pp. 261-264. University of California Press, Berkeley. Bishop, C. and Odense, P. H. (1966). Morphology of the digestive tract of the cod, Gadus morhua. Journal of the Fisheries Research Board of Canada, 23, 1607-1015. Blain, A. W. and Campbell, K. N. (1942). A study of digestive phenomena in snakes with the aid of the Roentgen ray. American Journal of Roentgenology, 48, 229-239. Blake, I. H. (1936). Studies on the comparative histology of the digestive tube of certain teleost fishes. 111. A bottom-feeding fish, the sea robin (Prionotus carolinus). Journal of Morphology, 60, 77-102. Bogachik, T. A. (1969). Morphological adaptations of the digestive apparatus in some Labridae. I n “Biologiya morya” (Marine biology), 16, pp. 82-101. Kiyev. Naukova dumka. (In Russian.)

215

THE ALIMENTARY CANAL AND DIGESTION IN TELEOSTS

Bokova, E. (1938). Daily food consumption and digestive rate in Rutilus rutilus. Rybnoje Khosyajstvo no. 6. (In Russian.) Bolton, L. L. (1933). Basophilic (mast) cells in the aliment'ary canal of salmonoid fishes. Journal of Morphology, 54, 549-591. Bondi, A. and Spandorf, A. (1954). The action of the digestive enzymes of the carp. British Journal of Nutrition, 8, 240-246.. Borutsky, E . V. (1950). On the feeding of Xenocypris macrolepis B1. Trudy Amurskoi ikhtiologicheskoi expeditsii, 1, 31 9-330. (In Russian.) Bramstedt, F. (1949). Die Bedeutung der katheptischen Fermente fur die proteolytische Verdauung im Tierreich. Zoologischer Anzeiger, Leipzig, 14, Supplement Verhandlungen der Deutsclien Zoologischen Gesellschaft, 1 73-1 82. Branch, G. M. (1966). Contributions to the functional morphology of fishes. 111. The feeding mechanism of Syngnathus acus L. Zoologica Africana, 2, 69-89. Branson, B. A. and Hake, P. (1972). Observations on an accessory breathing mechanism in Piaractus nigripinnis (Cope) (Characidae). Zoologischer Anzeiger, Leipzig, 189, 292-297. Bremer, H. (1972). Einige Untersuchungen zur Histochemie der sezernierenden Elemente der Teleostier-Epidermis. Acta histochemica, 43, 28-40. Brett, J. R . (1971a). Energetic responses of salmon to temperature. A study of some thermal relations in the physiology and freshwater ecology of sockeye salmon (Oncorhynchus nerka). Am.erican Zoologist, 11, 99-1 13. Brett, J. It. (1971b). Satiation time? appetite and maximum food intake of sockeye salmon (Oncorhynchus nerka). Journal of the Fisheries Research Board of Canada, 28, 409 -415. Brett, J . R. and Higgs, D. A. (1970). Effect of temperature on the rate of gastric digestion in fingerling sockeye salmon, Oncorhynchus nerka. Journal of the Fisheries Research Board of Canada, 27, 1767-1779. Brett, J. R., Shelbourn, J. E . and Shoop, C. T. (1969). Growth rate and body composition of fingerling sockeye salmon, Oncorhynchus nerka, in relation to temperature and ra,tion size. Jou,rna,l of the Fisheries Research Board of Canada, 26, 2363-2394. Brockerhoff, H. (1966). Digestion of fat by cod. Journal of the Fisheries Research Board of Canada, 23, 1835-1839. Brody, S. (1945), Bioenergetics and growth. 1023 pp. Reinhold, New York. Bromlej, G. (1936). Nutrition of silver carp. Rybnoje Khosyajstvo, no. 6. (In Russian.) Brown, M. E. (1946). The growth of brown trout (Salmo trutta L.). 111. The effect of temperature on the growth of two-year-old trout. Journal of Experimental Biology, 22, 145-155. Brown, M. E . (1951). The growth of brown trout (Salmo trutta L . ) . IV. The effect of food and temperature on the survival and growth of fry. Journal of Experimental Biology, 28, 473-491. Brown, M. E. (1957). Experimental studies on growth. I n " The Physiology of Fishes " (M. E. Brown, ed.), Vol. I, Ch. IX, pp. 361-400. Academic Press, New York. Buchs, S. (1954). Die Proteolyse im Tiermagen. Zeitschrift f u r vergleichende Physioloqie, 36, 165-175. A.llI.B.-13

a

216

B. G . KAPOOR, H. SMIT AND I. A. VERIGHINA

Bucke, D. (1971). The anatomy and histology of the alimentary tract of the carnivorous fish the pike Esox lucius L. Joumal of F k h Biology, 3,421-431. Bullock, W. L. (1963). Intestinal histology of some salmonid fishes with particular reference to the histopathology of acanthocephalan infections. Journal of Morphology, 112, 23-44. Bullock, W. L. (1967). The intestinal histology of the mosquito fish, Gambusia a@nb (Baird and Girard). Acta Zoologica, Stockholm, 48, 1-17. Burnstock, G. (1959a). The morphology of the gut of the brown trout (Salmo trutta). Quarterly Journal of Microscopical Science, 100, 183-198. Burnstock, G. (195913). The innervation of the gut of the brown trout (Salmo trutta). Quarterly Journal of Microscopical Science, 100, 199-220. Burnstock, G. (1972). Purinergic nerves. Pharmacological Reviews, 24,509-581. Campbell, G. (1970). Autonomic nervous systems. I n “ Fish physiology ” (W. S. Hoar and D. J. Randall, eds.),Vol. IV, pp. 109-132. Academic Press, New York and London. Campbell, G. and Burnstock, G. (1968). Comparative physiology of gastrointestinal motility. I n “ Handbook of Physiology ”. Section 6. Alimentary canal. (C. F. Code, ed.), Vol. IV, Ch. 107, pp. 2213-2266. American Physiological Society, Washington, D.C. Carline, R . F. and Hall, J. D. (1973). Evaluation of a method for estimating food consumption rates of fish. Journal of the Fisheries Research Board of Canada, 30, 623-629. Castro, N. M., Sasso, W. S. and Katchburian, E. (1961). A histological and histochemical study of the gizzard of the Mugil sp. Acta Anatornica, 45, 155-163. Catton, W. T. (1948). Coarse granulocytes in epithelial tissues of teleost fishes. Nature, London, 162, 894. Catton, W. T. (1951). Blood cell formation in certain teleost fishes. Blood, The Journal of Hematology, 6, 39-60. Chan, V. M. (1941). The histology of the alimentary tract of the deep-water gurnard Paristedion longispatha (Goode & Bean). University of Nebraska Stdies, Lincoln, 41, 7-30. Chandy, M. (1956). On the oesophagus of the milk-fish Chanos chanos (Forskid). Journal of the Zoological Society of India, 8, 79-84. Chandy, M. and George, M. G. (1960). Further studies on the alimentary tract of the milk-fish Chanos in relation to its food and feeding habits. Proceedings of the National Institute of Sciences of India, B26, 126-134. Chaudhry, H. S. and Khandelwal, 0. P. (1961). The anatomy and histology of the alimentary tract of Oreinus plagiostomus (Heckel). Annotaliones Zoologicae Japonenses, 34, 139-152. Chepik, L. (1964). Activity of carp digestive enzymes a t different seasons of the year. Biological Abstracts, 41 (1966), 60747. Chesley, L. C. (1934). The concentrations of proteases, amylase and lipase in certain marine fishes. Bwlogioal Bulletin, 66, 133-144. Chu, Y. T. (1935). Comparative studies on the scales and on the pharyngeals and their teeth in Chinese cyprinids, with particular reference to taxonomy and evolution. Biological Bulletin of St John’s University, Shanghai, China, no. 2, 1-225.

THE ALIMENTARY CANAL AND DIGESTION I N TELEOSTS

217

Cowey, C. B. and Sargent, J. R. (1972). Fish nutrition. I n “ Advances in Marine Biology ” (F. S. Russell and C. M. Yonge, eds.), Vol. X, pp. 383-492. Academic Press, London and New York. Croston, C. B. (1960). Tryptic enzymes of chinook salmon. Archives of Biochemistry and Biophysics, 89, 202-206. Curry, E. (1939). The histology of the digestive tube of the carp (Cyprinus carpio communis). Journal of Morphology, 65, 53-78. Daan, N. (1973). A quantitative analysis of the food intake of North Sea cod, Gadus morhua. Netherlands Journal of Sea Research, 6, 479-517. Daget, J. (1960). Le genre Xenocharaz (Characiformes). Revue de Zoologie et de Botanique africaines, 61, 35-48. Daget, J. (1962). Le genre Citharinus (Characiformes). Revue de Zoologie et de Botanique africaines, 66, 81-106. Daget, J. (1967). Le genre Ichthyoborus (Characiformes). Cahiers d’OBce de la Recherche scienti3que et technique Outre-Mer, ser. Hydrobiologie, 1, 139-154. Dalela, R. C. (1969). Morpho-histological studies of the alimentary tract in the mastacembelid eel, Macrognathus aculeatus (Bloch). Journal of the Zoological Society of India, 21, 117-128. Darnell, R. M. and Meierotto, R. R. (1962). Determination of feeding chronology in fishes. Transactions of the American Fisheries Society, 91, 313-320. Das, S. M. and Moitra, S. K. (1963). Studies on the food and feeding habits of some freshwater fishes of India, Part IV. A review on the food and feeding habits, with general conclusions. Ichthyologica, 2, 107-1 15. Davis, B. J. and Miller, R. J. (1967). Brain patterns in minnows of the genus Hybopsis in relation to feeding habits and habitat. Copeia, no. 1, 1-39. Davis, G. E. and Warren, C. E. (1965). Trophic relations of a sculpin in laboratory stream communities. Journal of Wildlqe Management, 29, 846-87 1. Dawes, B. (1929). The histology of the alimentary tract of the plaice (Pleuronectes plateasa). Quarterly Journal of Microscopical Science, 73, 243-274. Dawson, I. (1970). The endocrine cells of the gastrointestinal tract. Htktochemie, 2, 527-549. Dixit, R. K. and Bisht, J. S. (1972). Histomorphology of the alimentary canal of a hill-stream teleost, Schizothoraz richardsonii (Gray and Hard). Zoologische Beitrlige, 18, 321-338. Dorier, A. and Bellon, G. (1952). Sur l’organe paletin des cyprinid6s. Travaux du Laboratoire d’Hydrobiologie et de Pisciculture de l’Universit6 de Grenoble, 43 and 44, 47-60. Doudoroff, P. and Shumway, D. L. (1970). Dissolved oxygen requirements of freshwater fishes. PA0 Fisheries Technical Paper, no. 86, FAO, Rome, 291 pp. Dumitru, M. and Mihai, P. (1962). Anatomia macro-@microscopic&a tubului digestiv la Rhodeus sericeus amarus (Bloch) yi particularit&tile acestuia in functie de regimul alimentar. Analele UniversitGJii Bucuregti, Seria ptiintelor Naturalii Biologie, 11, 277-287. Duthie, E. S. (1939). The origin, development and function of the blood cells in certain marine teleosts. I. Morphology. Journal of Anatomy, London, 73, 396-4 1 2. Eastman, J . T. (1971). The pharyngeal bone musculature of the carp, Cyprinus carpio. Journal of Morphology, 134, 131-140.

218

B . G . KAPQOR, H. SMIT AND I. A. VERIGIIINA

Eastman, J. T. and Underhill, J. C. (1973). Intraspecific variation in the pharyngeal tooth formulae of some cyprinid fishes. Copeia, no. 1, 45-53. Edwards, D. J. (1971). Effect of temperature on rate of passage of food through the alimentary canal of the plaice Pleuronectes platessa L. Journal of Fish Biology, 3, 433-439. Edwards, L. F. (1929). The origin of the pharyngeal teeth of the carp (Cyprinus carpio L.). Ohio Journal ofScience, 29, 93-130. Elliott, J. M. (1972). Rates of gastric evacuation in brown trout, Salmo trutta L. Freshwater Biology, 2, 1-18. Erspamer, V. (1954). Pharmacology of indolealkylamines. Pharmacological Reviews, 6, 425-487. Evans, H. E. and Duebler, E. E . (1955). Pharyngeal tooth replacement in Semotilus atromaculatus and Clinostomus elongatus, two species of cyprinid fishes. Copeia, no. 1 , 31-41. FBbiBn, G., Moln&rand Tolg, I. (1963). Comparative data and enzyme kinetic calculations on changes caused by temperature in the duration of gastric digestion of some predatory fishes. Acta Biologica Academiae Scientiarum Hungaricae, 14, 123-129. Fange, R . (1962). Pharmacology of poikilothermic vertebrates and invertebrates. Phaimacological Reviews, 14, 281-31 6. Field, J. G. (1966). Contributions to the functional morphology of fishes. 11. The feeding mechanism of the angler-fish, Lophius piscatorius L. Zoologica africana, 2, 45-67. Fish, G. R. (1951). Digestion in Tilapia esculenta. Nature, London, 167, 900. Fish, G. R. (1960). The comparative activity of some digestive enzymes in the alimentary canal of Tilapia and perch. Hydrobiologia, 15, 161-178. Fontana, N. (1941). Modificazioni del tubo digerente nelle anguille pialle sottoposte a digiuno prolungato fino all’estremo esaurimento. Rivista di Biologia, 31, 3-26. Foxx, R. M. and Martin, P. L. (1970). Food consumption rate as a function of temperature in the red-bellied piranha (Serrasalmus nattereri). Communications in Behavioral Biology, A5, 85-87. Frantsuzova, G. P. (1971). Afferent innervation of the digestive tract in Stenodus lewichthys. Arlchiv Anatomii Gistologii i Embriologii, 60, 3 G 4 1 . (In Russian.) Fry, F. E . J. (1947). Effects of the environment on animal activity. Publications of the Ontario Fisheries Research Laboratory, Toronto, no. 68, 61 pp. Fry, F. E. J. (1967). Responses of vertebrate poikilotherms to temperature. I n “ Thermobiology ” (A. H. Rose, ed.), pp. 375-409. Academic Press, New York and London. Fry, F. E. J. and Hochachka, P. W. (1970). Fish. I n “ Comparative Physiology of Thermoregulation ” (G. Causey Whittow, ed.), Vol. I. Invertebrates and nonmammalian vertebrates, pp. 79-1 34. Academic Press, New York and London. Fryer, G. and Iles, T. D. (1972). The Cichlid fishes of the Great Lakes of Africa. Their Biology and Evolution. 641 pp, Oliver and Boyd, Edinburgh. Fukusho, K. (1969). Notes on the intestinal convolution of the fishes of the Pomacentridae (Perciformes). Japanese Journal of Ichthyology, 16, 135-1 42. Fukusho, K. (1972). Organogenesis of digestive system in the mullet, Liza haem atocheila, with special reference to gizzard. Japanese Journal of Ichthyology, 19, 283-294. (In Japanese with English summary.)

THE ALIMENTARY CANAL AND DIGESTION I N TELEOSTY

219

Guuthier, G. F. and Landis, S. C. (1972). The relationship of ultrastriictiiral and cytochemical features to absorptive activity in the goldfish intestine. Anatomical Record, 172, 675-702. Geilenkirchen, W. L. M. and Elbers, P. F. (1951). Digestion of edestan and some other protein-substances by pig stomach extract. Enzymologia, 14, 304-3 10. Geistdoerfer, P. (1973). Sur quelques particularitks histologiques de l’intestin de Chalinura mediterranea (Macrouridae, Gadiformes). Cornptes rendus des dances de 1’Acadthie des Sciences, Paris, 276, 331-333. Gerking, S. D. (1954). The food turnover of a bluegill population. Ecology, 35, 490-498. Gerking, S. D. (1955). Influence of rate of feeding on body composition and protein metabolism of bluegill sunfish. Physiological Zoology, 28, 267-282. Gerking, S. D. (1962). Production and food utilization in a population of bluegill sunfish. Ecological Monographs, 32, 31-78. Gerking, S. D. (1971). Influence of rate of feeding and body weight on protein metabolism of bluegill sunfish. Physiological Zoology, 44, 9-19. Ghazzawi, F. M. (1935). The pharynx and intestinal tract of the Egyptian mullets Mugil cephalus and Mugil capito. Part 11. On the morphology and histology of the alimentary canal in Mugil capito (Tobar). Coastguards and Fisheries Service, Fisheries Research Directorate, Notes and Memoirs, Cairo, 110. 6, 1-31. Girgis, S. (1952a). The bucco-pharyngeal feeding mechanism in an herbivorous bottom-feeding cyprinoid, Labeo horie (Cuvier). Journal of Morphology, 90 281-316. Girgis, S. (1952b). On the anatomy and histology of the alimentary tract of an herbivorous bottom-feeding cyprinoid fish, Labeo horie (Cuvier). Journal of Morphology, 90, 317-362. Godinho, H., Tokumaru, M. and Ferri, A. G. (1970). Histologia do trato digestivo de Pimelodus maculatus LacBpBde, 1803 (Pisces, Siluroidei). Revista Brasiliera de Biologica, Ri o de Janeiro, 30, 583-593. Goel, K. A. and Sastry, K. V. (1973). Distribution of alkaline phosphatase in the digestive system of a few teleost fishes. Acta histochemica, 47, 8-14. Gohar, H.A. F. and Latif, A. F. A. (1959). Morphological studies on the gut of some scarid and labrid fishes. Publications of the Marine Biological Station, Al-Ghardaqa ( R e d S ea ) , no. 10, 145-190. Gohar, H. A. F. and Latif, A. F. A. (1961). The histology of the alimentary tract in representative scarid and labrid fishes (from the Red Sea). Publications of the Marine Biological Station, Al-Ghardaqa (Red Se a), no. 1 1 , 95-126. Gohar, H. A. F. and Latif, A. F. A. (1963). Gastric and intestinal absorption of olive oil and oleic acid in Clarias lazera C. & V. Publications of the Marine Biological Station, Al-Ghardaqa (Red S ea ) , no. 12, 44-62. Gomazkov, 0. A. and Krayukhin, B. V. (1963). The role of the vagus nerve in the regulation of digestion in fish. Byuleten Instituta Biologii Vodokhranilishch Akademii N a u k. SSSR, 8, 124-131. (In Russian.) Greene, C. W. (1912). Anatomy and histology of the alimentary tract of the king salmon. Bulletin of the United States Bureau of Fisheries, Washington, D.C. 32, 73-100. Greenwood, P. H. (1953). Feeding mechanism of the cichlid fish, Tilapia esculenta Graham. Nature, London, 172, 207- 208.

220

B. 0 . KAPOOR, H. SMIT AND I. A. VERIOHINA

Greenwood, P. H. (1964). Explosive speciation in African lakes. Proceedings of the Royal Institution of Great Britain, 40, 256-269. Gregory, W. K. (1933). Fish skulls: a study of the evolution of natural mechanisms. Transactions of the American Philosophical Society, Philadelphia, 23, 75-481. Grib, A. V. and Krasyukova, Z. V. (1949). Alimentary canal of some cyprinoid fishes. Uchonye Zapiski Leningradskogo ordena Lenina gosudarstvennogo Universiteta, seriyn Biologicheskaya, no. 21, 419-433. Groenewald, A. A. J. v. (1964). Observations on the food habits of Clariaa gariepinus Burchell, the South African freshwater barbel in Transvaal. Hydrobiologia, 23, 287-291. Groot, S. J. de (1969). Digestive system and sensorial factors in relation to the feeding behaviour of flatfish (Pleuronectifonnes). Journal du Conseil international pour I’Exploration de la Mer, Copenhague, 32, 385-394. Gupta, 0. P. (1971). Studies on the morphology, histology and the swallowing mechanism of the digestive tract of a carnivorous fish, Xenentodon cancila (Ham.). Okajimas Folia Anatomica Japonica, 48, 29-51. Hale, P. A. (1965). The morphology and histology of the digestive systems of two freshwater teleosts, Poecilia reticulata and Gasterosteus aculeatus. Journal of Zoology, London, 146, 132-149. Halver, J. E., ed. (1972). “ Fish Nutrition ”, 713 pp. Academic Press, New York and London. Ham, T. J. (1971). Chemoreception. I n “ Fish Physiology ” (W. S. Hoar and D. J. Randall, eds.) Vol. V, pp. 79-120. Academic Press, New York and London. Harder, W. ( 1960). Vergleichende Untersuchungen zur Morphologie des Darmes bei Clupeoidea. Zeitschrift fur wissenschaftliche Zoologie, 163, 65-167. Hastings, W. H. (1969). Nutritional score. In “ Fish in Research ” (0. W. Neuhaus and J. E. Halver, eds.), pp. 263-292. Academic Press, New York and London. Hathaway, E. S. (1927). The relation of temperature to the quantity of food consumed by fishes. Ecology, 8, 428-434. Hellawell, J. M. and Abel, R. (1971). A rapid volumetric method for the analysis of the food of fishes. Journal of Fish Biology, 3, 29-37. Henrikson, R. C. and Matoltsy, A. G. (1968). The fine structure of teleost epidermis. 111. Club cells and other cell types. Journal of Ultrastructure Research, 21, 222-232. Hermann, R. B., Warren, C. E. and Doudoroff, P. (1962). Influence of oxygen concentration on the growth of juvenile coho salmon. Transactions of the American Fisheries Society, 91, 155-167. Herold, R. C. (1970a). Vasodentine and mantle dentine in teleost fish teeth. A comparative microradiographic analysis. Archives of Oral Biology, 15, 71-85. Herold, R.C. (1970b). The fine structure of vasodentine in the teeth of the white hake, Urophycis tenuis (Pisces, Gadidae). Archives of Oral Biology, 15, 311-322. Herold, R. C. (19714. Osteodentinogenesis. An ultrastructural study of tooth formation in the pike, Esox lucius. Zeitschrift fur ZelEforschung und mikroskopische Anatomie, 112, 1-14.

THE ALIMENTARY CANAL AND DIGESTION IN TELEOSTS

221

Herold, R. C. (1971b). The development and mature structure of dentine in the pike, Esox lucius, analysed by microradiography. Archives of Oral Biology, 16, 29-41. Herold, R. C. and Landino, L. (1970). The development and mature structure of dentine in the pike, Esox lucius, analyzed by bright field, phase and polarization microscopy. Archives of Oral Biology, 15, 747-760. Hickling, C. F. (1966). On the feeding process in the White Amur Ctenopharyngodon idella. Journal of Zoology, London, 148, 408-418. Hirata, Y.(1966). Fine structure of the terminal buds on the barbels of some fishes. Archivum histologicurn japonicum, 26, 507-523. Hirsch, G. C. (1950). Magenlose Fische. Versuch einer typenmiissigen Erkliirung. I n " Neue Ergebnisse und Probleme der Zoologie ", pp. 302-326. Akademische Verlagsgesellschaft Geest & Portig, K. G., Leipzig. Hollands, B. C. S. and Smith, M. W. (1964). Phosphatases of the goldfish intestine. Journal of Physiology, 175, 31-37. Holstvoogd, C. (1965). The pharyngeal bones and muscles in Teleostei, a taxonomic study. Koninklijke Nederlandse Akademie van Wetenschappen, Amsterdam, Serie C,68, 209-218. Hopkins, A. (1966). The pattern of gastric emptying: a new view of old results. Journal of Physiology, 182, 144-149. Hotta, H.and Tung, I. S. (1966). Identification of fishes of the family Mugilidae based on the pyloric caeca and the position of inserted first interneural spine. Japanese Journal of Ichthyology, 14, 62-66. (In Japanese with English summary.) Hotta, H. Y. and Nakashima, J. (1969). Experimental study of the feeding activity of jack-mackerel, Trachurus japonicus. Biological Abstracts, 50, 108069. Hunt, B. P. (1960). Digestion rate and food consumption of Florida gar, warmouth and largemouth bass. Transactions of the American Fisheries Society, 89, 206-21 1. Ishibashi, T. (1956). A comparative histological study of teeth, the fixation of dentine in particular, in fish. Igaku Kenkyu (Acta Medica), 26, 955-976. (In Japanese with English summary.) Ishida, J. (1935). The stomach of Mugil cephalus and its digestive enzymes. Annotationes Zoologicae Japonemes, 15, 182-1 89. Ishida, J. (1936). Distribution of the enzymes in the digestive system of stomachless fishes. Annotationes Zoologicae Japonenses, 15, 263-284. Ishida, M. and Satti, M. (1960). The anatomical and histological observations of the alimentary tract of a catfish, Parasilurus asotus (L.). Science Reports of the Hirosaki University, Hirosaki, Japan, 7, 57-63. Ishiwata, N. (1969). Ecological studies on the feeding of fishes. Bulletin of the Japanese Society of Scientijc Fisheries, 35, 979-984. Islam Ahsan-ul. (1951). The comparative histology of tha alimentary canal of certain fresh water teleost fishes. Proceedings of the Indian Academy of Sciences, B33, 297-321. Isokawa, S., Onuma, H. and Yoshida, H. (1959). Pharyngeal teeth of porgies. Journal of Nihon University School of Dentistry, Tokyo, 2, 86-90. Isokawa, S., Van Huysen, G. and Kosakai, T. (1964). Historadiography of tubular enamel and dentin of osseous piscine teeth. Journal of Nihon University School of Dentistry, Tokyo, 6, 79-87.

222

B. G. KAPOOR, H. SMIT A N D I. A . VERIGHINA

Isokawa, S., Kubota, K., Kosakai, T. et al. (1965). Some contributions to study of esophageal sacs and teeth of fishes. Journal of Nihon University School of Dentistry, Tokyo, 7, 103-111. Isokawa, S., Kodama, N., Katsumata, A. et al. (1968). Scanning electron microscopic views of tubular enamel in a fish (Samicossyphusreticulatus). Journal of Nihon University School of Dentistry, Tokyo, 10, 136-139. Isokawa, S., Satomura, I., Yamaguchi, K. et al. (1970). Historadiographic observations on the outer dentin in certain osseous fishes. Journal of Nihon University School of Dentistry, Tokyo, 12, 1-5. Ito, Y. and Kuriyama, H. (1971). Nervous control of the motility of the alimentary canal of the silver carp. Journal of Ezperimental Biology, 55, 469-487. Iwai, T. (1962). Studies on the Plecoglossus altivelis problems : embryology and histophysiology of digestive and osmoregulatory organs. Bulletin of the Misaki Marine Biological Institute, Kyoto University, no. 2, 1-101. Iwai, T. (1963). Taste buds on the gill rakers and gill arches of the sea catfish, Plotosus anguillaris (LacBpBde). Copeia, no. 2, 271-274. Iwai, T . (1964). A comparative study of the taste buds in gill rakers and gill arches of teleostean fishes. Bulletin of the Misaki Marine Biological Institute, Kyoto Uniuersity, no. 7, 19-34. Iwai, T. (1968). Notes on the pear-shaped cell (rodlet-cell) in the epithelium of the digestive tract of fishes. Bulletin of the Japrmese Society of Scienti$c Fisheries, 34, 133-137. (In Japanese with English Summary.) Jacobshagen, E . (1911). Untersuchungen iiber das Darmsystem der Fische und Dipnoer. I. Beitrage zur Charakteristik des Vorder-, Mittel- und Enddarms der Fische und Dipnoer. Jenaische Zeitschrift fiir Naturwissenschaft, 47, 529-568. Jacobshagen, E. (1913). Untersuchungen iiber das Darmsystem der Fische und Dipnoer. 11. Materialien zur vergleichenden Anatomie des Darmkanals der Teleostomen nebst einer einleitenden Uebersicht. Jenaische Zeitmhrift f u r Naturwissenschaft, 49, 373-810. Jacobshagen, E . (1915). Untersuchungen iiber das Darmsystem der Fischc und Dipnoer. 111. Ueber die Appendices pyloricae, nebst Bemerkungen zur Anatomie und Morphologie des Rumpfdarmes. Jenaische Zeitschrift f u r Naturwissenschaft, 53, 445-556. Jacobshagen, E. (1937). Darmsystem. IV. Mittel- und Enddarm. Rumpfdarm. In " Handbuch der vergleichenden Anatomie der Wirbeltiere " (L. Bolk, E. Goppert, E . Kallius and W. Lubosch, eds.), Vol. 111, pp. 563-724. Urban und Schwarzenberg, Berlin und Wien. Jansson, B.-0. and Olsson, R . (1960). The cytology of the caecal epithelial cells of Perca. Acta Zoologica, Stockholm, 41, 267-276. Jam, Z.(1957). On the morphology and function of the so-called palatal organ in the carp (Cyprinus carpio L.). Przeglad Zoologiczn!j, 1, 110-112. Jearld, A. and Brown, B. E. (1971). Food of the channel catfish (Ictalurus punctatus). American Midland Naturalist, 86, 110-1 15. Jeuken, M. (1957). A study of the respiration of Misgurnus fossilis (L.), the pond loach. Thesis, Leiden, 114 pp. Jirge, S. K. (1970). Mucopolysaccharide histochemistry of the stomach of fishes with different food habits. Folia Histochemica et Cytochemica, 8, 275-280.

THE ALIMENTARY CANAL AND DIGESTION IN TELEOSTS

223

Johansen, K. (1970). Air breathing in fishes. I n " Fish Physiology " (W. S. Hoar and D. J. Randall, eds.), Vol. IV, pp. 361-411. Academic Press, New York and London. Kandyuk, R. P. (1967). Comparative evaluation of the activity and thermal stability of digestive enzymes of some fish in the northwestern part of the Black Sea. Chemical Abstracts, 69, (1968) 1001 n. Kandyuk, R. P. (1968). On alkaline phosphatase and enterokinase in the digestive canal of some fishes in the northwestern part of the Black Sea. Gidrobiologiche.skij Zh.urna1, 5, 81-84. Kapoor, B. G. (1953). The anatomy and histology of the alimentary canal in relation to its feeding habits of a siluroid fish, Wallago attu (Bl. & Schn.). Journal of the Zoological Society of I n d i a , 5, 191-210. Kapoor, B. G. (1957a). Oral valves of teleosts. Japanese Journal of Ichthyology, 5, 127-131. Kapoor, B. G. (195713). The callous pad of the pharyngeal masticatory apparatus in Indian carps. Japanese Journal of Ichthyology, 6, 26-30. Kapoor, B. G. (1957~).The digestive tube of an omnivorous cyprinoid fish, Barbus stigma (Cuv. & Val.). Japanese Journal of Ichthyology, 6, 48-53. Kapoor, B. G. (1957d). A study on the tongue of fishes. Japanese Journal of Ichthyology, 6, 82-86. Kapoor, B. G. (1958a). The morphology and histology of the alimentary tract of a plankton-feeder, Gadusia chapra (Hamilton). Annuli del Museo Civico d i Storia Naturale d i Genova, 70, 8-32. Kapoor, B. G. (1958b). The anatomy and histology of the digestive tract of a cyprinoid fish, Catla catla (Hamilton). An n uli del Museo Civico d i Storia Naturale d i Genova, 70, 100-115. Kapoor, B. G. (1965). Gill rakers of a few Indian freshwater fishes. Annuli de2 Museo Civico d i Storia Naturale di Genova, 75, 126-143. Kariya, T. (1969). The relationship of food intake to the amount of stomach contents in Sebastes inermis. Biological Abstracts, 51, (1970) 35650. Karpevitch, A. F. (1936). On changes of the digestive juice reaction in marine fishes. Fiziologicheskij Zhurnal, 30, 100-123. (In Russian.) Karpevitch, A. F. and Bolrova, E. N. (1936). The rate of digestion in marine fishes. Pt. I, Zoologicheskij Zhurnal, 15, 143-168. (In Russian.) (English translation by Z. Kabata, 1965. Department of Agriculture and Fisheries for Scotland, Aberdeen. Translation 1004, 1-5.) Karpevitch, A. F. and Bokova, E. N. (1937). The rate of digestion in marine fishes. Pt. 11, Zoologicheskij Zhurnal, 16, 21-44. (In Russian with English summary.) Kato, K. (1935). On the intestinal epithelium of Nomeus gronovii. Annolationes Zoologicae Japonenses, 15, 190-1 93. Kawai, S. and Ikeda, S. (1971). Studies on digestive enzymes of fishes. I. Carbohydrases in digestive organs of several fishes. Bulletin of the Japanese Society of Scientific Fisheries, 37, 333-337. Kawamoto, N. and Higashi, T. (1965). Studies on the structure and function of the pharyngeal organ in the mullet, Mugil cephalus L. Bulletin qf College of Agriculture andveterinary Medicine, N i h o n University, Tokyo, no. 21, 1-8. Kazansky, V. I. (1964). Specific differences in the construction of gill rakers in Cyprinidae. Voprosy ikhtiologii, 4, 45-60. (In Russian.)

224

B. 0. KAPOOR, H. SMIT AND I . A. VERIGHINA

Kelso, J. R. M. (1972). Conversion, maintenance and assimilation for walleye, Stizostedion vitreum vitreum, as affected by size, diet and temperature. Journal of the Fisheries Research Board of Canada, 29, 1181-1192. Kenyon, W. A. (1925). Digestive enzymes in poikilothermal vertebrates. An investigation of enzymes in fishes, with comparative studies on those of amphibians, reptiles, and mammals. Bulletin of the United States Bureau of Fisheries, Washington, 41, 181-200. Kerr, S. R. (1971a). Analysis of laboratory experiments on growth efficiency of fishes. Journal of the Fisheries Research Board of Canada, 28, 801-808. Kerr, S. R. (1971b). Prediction of fish growth efficiency in nature. Journal of the Fisheries Research Board of Canada, 28, 809-814. Kevern, N. R. (1966). Feeding rate of carp estimated by a radioisotopic method. Transactions of the American Fisheries Society, 95, 363-37 1. Khalilov, F. Kh. (1969). " Materials on morphology and histochemistry of the digestive system in teleosts ", 131 pp. Maktap, Alma Ata. (In Russian.) Khalilov, F. Kh., Inyushin, V. M. and Vorobjov, N. A. (1963). On morphology and histochemistry of the gut of fishes. Izcestia Akademii Nauk Kazakhskoj SSR. no. 2, seriya Biologicheskaya, 82-89. (In Russian.) Khanna, S. S. (1959). Structure of the tongue in some fresh-water teleosts. Proceedings of the First All-India Congress of Zoology, part 2, 157-161. Khanna, S. S. (1961). Alimentary canal in some teleostean fishes. Journal of the Zoological Society of India, 13, 206-219. Khanna, S. S. (1962). A study of bucco-pharyngeal region in some fishes. Indian Journal of Zootomy, 3, 21-48. Khanna, S. S. (1964). Histology of the digestive tract of a teleost, Clarias batrachus (L.). Journal of the Zoological Society of India, 16, 63-58. Khanna, S.S. and Mehrotra, B. K. (1970). Histomorphology of the buccopharynx in relation to feeding habits in teleosts. Proceedings of the National Academy of Sciences, India, B40, 61-80. Khanna, S. S. and Mehrotra, B. K. (1971). Morphology and histology of the teleostean intestine. Anatomischer Anzeiger, 129, 1-18. Khanna, S. S. and Pant, M. C. (1964). On the digestive tract and the feeding habits of some teleostean fishes. Agra University Journal of Research (Science), 13, 15-30. Khawaja, D. K. and Jafri, A. K. (1968). Distribution of acid and alkaline phosphatase activity in the gastro-intestinal tract of the freshwater murrel Ophicephalus punctatus Bloch. Enzymologia, 34, 63-66. Kilarski, W. and Bigaj, J. (1971). The fine structure of striated muscle fibres of tunica muscularis of the intestine in some teleosts. Zeitschrift fiir Zellforschung und mikroskopische Anatomie, 113, 472-489. Kimura, N. (1973). Fine structure of pear-shaped cells and " vesicle-rich cells " in pyloric caeca of rainbow trout. Japanese Journal of Ichthyology, 20, 94-106. (In Japanese with English summary.) Kitamikado, M. and Tachino, S. (1960). Digestive enzymes of rainbow trout. I. Carbohydrases. Chemical Abstracts, 55 (1961), 5789. Kitchell, J. F. and Windell, J. T. (1968). Rate of gastric digestion in pumpkinseed sunfish, Lepomis gibbosus. Transactions of the American Fisheries Society, 97, 489-492.

THE ALIMENTARY CANAL AND DIGESTION I N TELEOSTS

225

Klust, G. (1939). Ueber Entwicklung, Bau und Funktion des Darmes beim Karpfen (Cyprinus carpio L.). Internationale Revue der Cfesamten Hydrobiologie und Hydrographie, 39, 498-536. Kolehmainen, S. E. (1974). Daily feeding rates of bluegill (Lepomis macrochirus) determined by a refined radioisotope method. Journal of the Fisheries Research Board of Canada, 31, 67-74. Konfal, E . (1966). Beitrag zur vergleichenden mikroskopischen Anatomie der Verdauungsrohre der Fische. Acta Facultatis Rerum Naturalium Universitatis Comenianae, 12, Zoologia, Publ. 13, 259-267. Konfal, E. (1970). Mikroskopische Anatomie der Verdauungsrohre bei Umbra krameri Walbaum, 1792. Bioldgia (Bratislava),25, 875-886. Korovina, V. M. (1973). On the spiral fold in the gut of Salmo irideus Gibbons. Doklady Akademii N a u k SSSR, 209, 500-503. (In Russian.) Korovina, V. M. and Vasilieva, N. E. (1971). A comparative histological study of the mid-gut in some Salmonidae. Voprosy ikhtiologii, 11, 502-508. Krayukhin, B. V. (1958). The regulatory mechanism of secretion of digestive juices in fishes. Trudy Soveshchanya Ikhtiologicheskoj Komissii Akademii N a u k SSSR, 8, 179-185. Krayukhin, B. V. (1959). Effect of food swallowing on the intensity of digestive processes in fishes. Voprosy ikhtiologii, 12, 133-137. (In Russian.) Krayukhin, B. V. (1963). Physiology of digestion in some fresh-water teleosts. 138 pp. Akademia Nauk S.S.S.R. Moscow. (In Russian.) Kudinsky, 0. Yu. (1966). Microscopical anatomy of the digestive tract of fry of king salmon (Xalmo salar L.). T r u d y Murmanskogo biologicheskogo Instituta, no. 12, 112-119. ( I n Russian.) Kuz’mina, V. V. (1966). The influence of humoral factors on the feeding reaction rate in fish. Biological Abstracts, 48 (1967), 115075. Lal, M. B. (1968). Studies on the anatomy and histology of the alimentary canal of a carp, Tor putitora (Ham.). Proceedings of the National Academy of Sciences, India, B38, 127-136. Lal, M.B., Bhatnagar, A. N. and Kaile, R. K. (1964a). Studies on the morphology and histology of the digestive tract and associated structures of Chagunius chagunio (Hamilton). Proceedings of the National Academy of Sciences, India, B34, 160-172. Lal, M. B., Bhatnagar, A. N. and Oberoi, S. (1964b). Bucco-pharyngeal region of Labeo dero (Hamilton). Proceedings of the National Academy of Sciences, India, B34, 419-428. Lange, N. 0. (1962). Development of the intestine in Rutilus rutilus (L.). Voprosy ikhtiologii, 2, 336-349. (In Russian.) Lange, N. 0. (1966). Structure and development of the pharyngeal teeth in roach, Caspian roach and Cubanian roach. I n “ Morfoekologicheskij analis rasvitiya ryb ”, pp. 163-177. Nauka. (In Russian.) Liem, K. F. (1967). Functional morphology of the integumentary, respiratory, and digestive systems of the synbranchoid fish Monopterus albw. Copeia, no. 2, 375-388. Linss, W. (1969a). Elektronenmikroskopische Untersuchungen am Oesophagus des Hechtes (Esoz lucius L.). 11. Die Feinstruktur der Becherzellen. Anatomischer Anzeiger, 125, 73-87. Linss, W. (1969b). Elektronenmikroskopisclle Untersuchungen am Oesophagus des Hechtes (Esox lucius L.). 111.Die Feinstruktur der indifferenten Zellen des Epithels. Anatom,ischer Anzeiger, 125, 113-127.

226

B. G . KAPOOB, H. SMIT AND I. A. VERIGHINA

Linss, W. and Geyer, G. (1968). Elektronenmikroskopische Untersuchungen am Oesophagus des Hcchtes (Esox lucius L.). I . Die Feinstruktur der Einkornzellen. Anatomischer Anzeiger, 123, 423-438. Lipsliaya, N. Y. (1959). Duration of digestion in the Black Sea surmullet (Mullus barbatus ponticus). Biological Abstracts, 48 (1967), 26852. L6pez, R . B. and De Carlo, J. M. (1959). Descripci6n anat6mica e histol6gica del aparato digestivo del puyen (Galazias attenuatus) (Teleostomi, Galaxiidae). Actas y Trabajos del Primer Congreso Sudamericano de Zoologda, ( L a Plata), 5, 339-356. Luppa, H. (1966). Ein Beitrag zur Funktion der Appendices pyloricae der Fische. Morphologische, histochemisctie und elektronenoptische Untersuchungen . Morphologisches Jahrbuch , 109, 315-3 39. Lutfy, R. G. (1964). Studies on the epidermis of the catfish Synodontis schall B1. Schn. Ain Shams Science Bulletin, Cairo, no. 10, 153-163. MacKay, M. E. (1929). The digestive system of the eel-pout (Zoarces anguillaris). Biological Bulletin, 56, 8-23. Maggese, M. C. I. (1967). Consideraciones anatomo-histologicas sobre el tract digestivo del “ papamoscas ” Cheilodactylus bergi (Teleostomi, Cheilodactylidae). Physis, Buenos Aires, 27, 111-124. Mahadcvan, S. (1950). The digestive system of Caranx djedaba (Forsk.) and Trichiurus haumela (Forsk.). Journal of the Madras University, B20, 25-48. Mahadevan, S. (1954). The digestive system of Mugil crenilabis (Forsk.)-a plankton feeder. Journal of the Madras University, B24, 143-160. Magnuson, J. J. (1969). Digestion and food consumption by skipjack tuna (Katsuwonus pelamis). Transactions of the American Fisheries Society, 98, 379-392. Majumdar, N. N. (1952). On the anatomy and histology of the palate of Cirrhina mrigala (Hamilton), with special reference to the papillae present on it together with comments on their possible respiratory function. Journal of the Zoological Society of I n d i a , 3, 255-265. Majnmdar, N. N. and Saxena, B. P. (1961). On the palatal organs of Labeo dero (Hamilton). Proceedings of the National Academy of Sciences, I n d i a , B31, 109-1 16. Manfredi Romanini M. G. (1959). I Lipidi nella cellula ghiandolare gastrica dei vertebrati. Acta histochemica, 8, 495-503. Mart’in,N. V. and Sandercock, F. K. (1967). Pyloric cacca and gill raker development in lake trout, Salvelinus namaycush, in Algonquin Park, Ontario. Journal of the Fisheries Research Board of Canada, 24, 965-974. Matthes, H. (1963). A comparative study of the feeding mechanisms of some African Cyprinidae. Bijdragen tot de Dierkunde, 33, 3-35. Maynard, L. A. and Loosli, J . K. (1962). “ Animal Nutrition ”, 533 pp. McGrawHill, New York. McGeachin, R. L. and Debnam, J. W. (1960). Amylase in freshwater fish. Proceedings of the Society for Experimental Biology and Medicine, 103, 814-815. Medeiros, L. O., Ferri, S., Godinho, H. and Medeiros, L. F. (1970a). Proteins and polysaccharides of the club-shaped cells in the lining epithelium of fish (Pimelodus maculatus) digestive tract : histochemical study. Annales d’aistochimie, 15, 181-186.

THE ALIMENTARY CANAL AND DIGESTION I N TELEOSTS

227

Medeiros, L. O., Ferri, S., Longhi, L. and Worsmann, T. U. (1970b). Histochemical study of protein in epithelial tissue of the digestive tract of Pimelodus maculatus LacBpi.de, 1803. Acta histochemica, 37, 113-1 17. Mehrotra, B. K. and Khanna, S. S. (1969). Histomorphology of the oesophagus and the stomach in some Indian teleosts with inference on their adaptational features. Zoologische Beitruge, 15, 375-391. Mennega, A. M. W. (1938). Waterstofionenconcentratie en vertering in de maag van enige vertebraten. Thesis, Utrecht. Mester, L. (1971). Studiul cavitbt,iibuco-faringiene la Noemacheilus barbatulus L. (Pisces, Cobitidae). Studii ~icercetary de Biologie, Seria Zoologie, Bucareyti, 23, 439-444. Megter, R., Scripcariu, D. and Mepter, L. (1972). The distribution of some enzymes in the mucosa of the intestinal tract from loach Misgurnusfossilis L. Revue Roumaine de biologie, Zoologie, 17, 413-418. Mikuriya, B. A. (1972). The gross anatomy and microscopic anatomy of the tongue and lower jaw of Gnathonemus petersii (Gthr. 1862) (Mormyridae, Teleostei). Zeitschrift fur Morphologie der Tiere, 73, 195-208. Miles, A. E. W. and Poole, D. F. G. (1967). The history and general organization of dentitions. I n " Structural and Chemical Organization of Teeth " (A. E. W. Miles, ed.), Vol. I, Ch. 1, pp. 3-44. Academic Press, New York. Miller, R. J. and Evans, H. E. (1965). External morphology of the brain and lips in catostomid fishes. Copeia, no. 4, 467-487. Miller, R. V. (1969). Constancy of epibranchial organs and fourth epibranchial bones within species groups of clupeid fishes. Copeia, no. 2, 308-312. Mittal, A. K. and Munshi, J. S. D. (1969). Histochemical and autoradiographic studies of skin glands of Rita rita (Ham.) (Bagridae, Pisces). Mikroskopie, 24, 193-205. Mohsin, S. M. (1961). The morphology and histology of the alimentary canal of Glossogobius giuris (Ham.). Canadian Journal of Zoology, 39, 605-613. Mohsin, S. M. (1962). Comparative morphology and histology of the alimentary canals in certain groups of Indian teleosts. Acta Zoologica, Stockholm, 43, 79-133. Moitra, S . K.(1956). On the food-habitsof certain fishes in Lucknow. Proceedings of the Zoological Society, Calcutta, 9, 89-91. Moitra, S. K. and Bhowmik, M. L. (1967). Functional histology of the alimentary canal of the young Catla catla (Ham.) an omnivorous surface-feeding fish of Indian fresh-waters. V&tnZk Ceskoslovenskd spole6nosti zoologickd, 31, 41-50. Moitra, S. K. and Das, K. M. (1967). Influence of environment on the digestive enzymes of a fish, Tilapia mossambica (Peters). Current Science, 36, 381-382. Moitra, S. K. and Sinha, G. M. (1971). Studies on the morpho-histology of the alimentary canal of a carp, Chagunius chagunio (Hamilton) with reference to the nature of taste buds and mucous cells. Journal of the Inland Fisheries Society of India, 3, 44-56. MolnBr, G. and Tolg, I. (1962). Experiments concerning gastric digestion of pike perch (Lucioperca lucioperca L.) in relation to water temperature. .4 cta Biologica Academiae Scientiarum Hungaricae, 13, 231- 239.

228

B. G. KAPOOR, H. SMIT A N D I . A . VERIGHINA

MoInAr, G., Tamhssy, E. and Tolg, I. (1967). The gastric digestion of living, predatory fish. I n " The Biological Basis of Freshwater Fish Production " (S. D. Gerking, ed.), pp. 135-149. Blackwell Scientific Publications, Oxford. Mookerjee, H. K. and Ganguly, D. N. (1951). Modification of the facial structures in the major carps of India in relation to their feeding habits. Anatomischer Anzeiger, 98, 137-147. Moore, W. G. (1941). Studies on the feeding habits of fishes. Ecology, 22, 91-96. Moriarty, C. M. and Moriarty, D. J. W. (1973). Quantitative estimation of the daily ingestion of phytoplankton by Tilapia nilotica and Haplochromis nigripinnis in Lake George, Uganda. Journal of Zoology, London, 171, 15-23.

Moriarty, D. J. W. (1973). The physiology of digestion of blue-green algae in the cichlid fish, Tilapia nilotica. Journal of Zoology, London, 171, 25-39. Morishita, T., Noda, H., Kitamikado, M. et al. (1964). On the activity of the digestive enzymes in cultured fish. Journal of the Paculty of Fisheries, Prefectural University of Mie, T s u , 6, 239-246. Muir, B. S. and Niimi, A. J. (1972). Oxygen consumption of the euryhaline fish aholehole (Kuhlia sandvicensis) with reference to salinity, swimming and food consumption. Journal of the Fisheries Research Board of Canada, 29, 67-77.

Nagar, S. K. and Khan, W. M. (1958). The anatomy and histology of the alimentary canal of Mastacembelus armatua (LacBpBde). Proceedings of the Indian Academy of Sciences, B47, 173-187. Nagar, S. K., Khan, W. M. and Ahmed, S. (1961). The anatomy and histology of tho alimentary canal of the grey mullet Mugil corsula (Ham.). Annuli del Museo Civic0 di Storia Naturale di Genova, 72, 47-68. Nagase, 0. (1964). Contribution to the physiology of digestion in Tilapia mossambica: digestive enzymes and the effects of diets on their activity. Zeitschr+ fiir vergleichende Physiologie, 49, 270-284. Nelson, G. J. (1967). Epibranchial organs in lower teleostean fishes. Journal of Zoology, London, 153, 71-89. Nicholls, J. V. V. (1933). The influence of temperature on digestion in Fundulus heteroclitus. Contributions to Canadian Biology and Fisheries, 7, 47-55. Nicolaides, N. and Woodall, A. N. (1962). Impaired pigmentation in chinook salmon fed diets deficient in essential fatty acids. Journal of Nutrition, 78, 431-437.

Niimi, A. J. and Beamish, F. W. H. (1974.) Bioenergetics and the growth of largemouth bass (Micropterus salmoides) in relation to body weight and temperature, Canadian Journal of Zoology, 52, 447-456. Nikolskaya, N. G. and Verighina, I. A. (1974). Peculiarities of the structure of feeding and digestive organs in three flatfish species of the White Sea associated with the nature of food consumed by them. Voprosy ikhtiologii, 14, 117-128. (In Russian.) Nikolsky, G. V. (1963). " The Ecology of Fishes ", 352 pp. Academic Press, London and New York. Nikolsky, G. V. (1971). " Tshasnaya ikhtiologia ", 471 pp. Vysshaya Shkola. Moscow. Nikolsky, G. V. (1974). " Ekologiya ryb ", 367 pp. Vysshaya Schkola. Moscow. (In Russian.)

THE ALIMENTARY CANAL AND DIUESTION IN TELEOSTS

229

Nilsson, S. and Fiinge, R. (1967). Adrenergic receptors in the swimbladder and gut of a teleost (Anguilla anguilla). Comparative Biochemistry and Physiology 23, 661-664. Nilsson, S. and Fiinge, R. (1969). Adrenergic and cholinergic vagal effects on the stomach of a teleost (Gadus morhua). Comparative Biochemistry and Physiology, 30, 691-694. Noaillac-Depeyre, J. and Gas, N. (1973). Mise en evidence d’une zone adapt6 au transport des ions dans l’intestin de la carpe commune (Cyprinus carpio L.). Comptes rendus des Sdancm de 1’Acaddmie des Sciences, Paris, 276, 773-776. Nordlie, F. G. (1966). Thermal acclimation and peptic digestive capacity in the black bullhead, Ictalurus melas. American Midland Naturalist, 75, 41 6-424. Norris, E. R. and Elam, D. W. (1940). Preparation and properties of crystalline salmon pepsin. Journal of Biological Chemistry, 134, 443-454. Norris, E. R. and Mathies, J. C. (1953). Preparation, properties and crystallization of tuna pepsin. Journal of Biological Chemistry, 204, 673-680. Norris, J. g., Norris, D. 0. and Windell, J. T. (1973). Effect of simulated meal size on gastric acid and pepsin secretory rates in bluegill (Lepomh macrochirus). Journal of the Fisheries Research Board of Canada, 30, 201-204. Odense, P. H. and Bishop, C. M. (1966). The ultrastructure of the epithelial border of the ileum, pyloric caeca, and rectum of the cod, cfadus morhua. Journal of the Fisheries Research Board of Canada, 23, 1841-1843. Ohnesorge, F. K. and Rauch, R. (1968). Untersuchungen iiber Peristaltik am Darm der Schleie ( Tinca vulgaris). Zeitschrift fiir vergleichende Physiologie, 58, 153-170. Ohnesorge, F. K. and Schmitz, G. (1968). Einfluss der Badtemperatur und der Adaptationstemperatur auf die Kontraktionen des isolierten Darmes der Schleie (Tincavulgaris). Zeitschrift fiir vergleichende Physiologie, 58,171-184. Okutani, K., Sawada, T. and Kimata, M. (1967). Studies on chitinolytic enzyme present in aquatic animals. VI. The chitinolytic enzyme present in rainbow trout. Bulletin of the Japanese Society of Scientific Fisheries, 33, 952-955. (In Japanese with English summary.) Okutani, K. and Kitada, H. (1968). Studies on chitin-decomposing bacteria present in the digestive tract of aquatic animals. 111.Formation of organic acids. Bulletin of the Japanese Society of Scientific Fisheries, 34, 1141-1 146. Ooshiro, Z. (1971). Studies on proteinase in the pyloric caeca of fishes. 11.Some properties of proteinase purified from the pyloric caeca of mackerel. Bulletin of the Japanese Society of Scientific Fisheries, 37, 145-148. (In Japanese with English summary.) Oppenheimer, J. R. (1970). Mouthbreeding in fishes. Animal Behaviour, 18, 493-503. Osse, J. W. M. (1969). Functional morphology of the head of the perch (Perca $uviatilis L.) : an electromyographic study. Netherlands Journal of Zoology, 19, 289-392. Owen, T. G. and Wiggs, A. J. (1971). Thermal compensation in the stomach of the brook trout. Comparative Biochemistry and Physiology, B40, 465-473. Ozaki, N. (1965). Some observations on the fine structure of the intestinal epithelium in some marine teleosts. Archivum histologicum japonicum, 26, 23-38. (In Japanese with English summary.) Paloheimo, J. E. and Dickie, L. M. (1965). Food and growth of fishes. I. A growth curve derived from experimental data. Journal of the Fisheries Research Board of Canada, 22, 521-542.

230

B. C . KAPOOR, H. SMIT AND I. A. VERIGHINA

Paloheirno, J. E. and Dickie, L. M. (1966). Food and growth of fishes. 11, 111. Journal of the Fisheries Research Board of Canada, 23, 869-908 ; 1209-1248. Pandian, T. J. (1967). Intake, digestion, absorption and conversion of food in the fishes Megalops cyprinoides and Ophiocephalus striatus. Marine Biology, 1, 16-32. Pasha, S. M. Kamal (1964a). The anatomy and histology of the alimentary canal of an omnivorous fish Mystus (Macrones) gulio (Ham.). Proceedings of the Indian Academy of Sciences, B59, 211-221. Pasha, S. M. Kamal (1964b). The anatomy and histology of the alimentary canal of a herbivorous fish Tilapia mossambica (Peters). Proceedings of the I n d i a n Academy of Sciences, B59, 340-349. Pasha, S. M. Kamal ( 1 9 6 4 ~ ) . The anatomy and histology of the alimentary canal of a carnivorous fish Megalops cyprinoides (Brouss). Proceedings of the I n d i a n Academy of Sciences, B60, 107-115. Pearse, A. S. (1924). Amount of food eaten by four species of freshwater fishes. Ecology, 5, 254-258. Pegel, V. A. (1950). " Digestive physiology of fishes ". 199 pp. Tomskij gosudarstvennyj Universitet Tomsk. (In Russian.) Pessah, E. and Powles, P. M. (1974). Effect of constant temperature on growth rates of pumkinseed sunfish (Lepomis gibbosus). Journal of the Fisheries Research Board of Canada, 31, 1678-1682. Pevzner, R. A. (1962). Cyto-histochemical studies of taste buds in bony fishes (Cyprinus carpi0 and Carassius caraasius). Doklady Akademii Nauk SSSR, 147, 1187-1192. (In Russian.) Pevzner, R. A. (1964). Distribution of succinate dehydrogenase activity in the taste buds of some vertebrates. Doklady Akademii N a u k SSSR, 155, 191-196. (In Russian.) Pevzner, R. A. (1969). Structural and cytochemical bases of the mechanism of taste buds function. Uspekhi sovremennoi biologii, 67, 53-67. Pfeiffer, W., Sasse, D. and Arnold, M. (1971). Die Schreckstoffzellen von Phoxinus phoxinus und Morulius chrysophakedion (Cyprinidae, Pisces). Histochemische und elektronenmikroskopische Untersuchungen. Zeitschrift fur Zellforschung und mikroskopische Anatornie, 118, 203-213. Phillips, A. M. (1969). Nutrition, digestion, and energy utilization. I n " Fish Physiology " (W. S. Hoar and D. J. Randall, eds.), Vol. I , pp. 391-432. Academic Press, New York and London. Philpott, C. W. and Copeland, D. E. (1963). Fine structure of chloride cells from three species of Fundulus. Journal of Cell Biology, 18, 389-404. Piavaux, A. (1972). Intestinal laminarinasc of a vertebrate : Tilapia macrochir Boulenger. Lqe Sciences, 11, 185-190. Pierce, E. L. (1936). Rates of digestion in the yellowtail (Ocyurus chrysurus) and the white grunt (Haemulon plumieri). Copeia, no. 2, 123-124. Pillay, T. V. R . (1953). Studies on the food, feeding habits and alimentary tract of the grey mullet, Mugil tade ForskB1. Proceedings of the National Institute of Sciences of I n d i a , 19, 777-827. Poole, D. F. G. (1967). Phylogeny of tooth tissues : enameloid and enamel in recent vertebrates, with a note on the history of cementum. I n " Structural and Chemical Organization of Teeth " (A. E. W. Miles, ed.), Vol. I , pp. 111-149. Academic Press, New York.

THE ALIMENTARY CANAL AND DIGESTION I N TELEOSTS

23 1

Prakash, A. (1961). Distribution and differentiation of alkaline phospliatase in the gastro-intestinal tract of steelhead trout. Journal of Erperimental Zoology, 146, 237-251. Prasada Rao, P. D. (1967). Studies on the structural variations in the brain of teleosts and their significance. Acta Anatomica, 68, 379-399. Precht, H. ( 1 964). Anpassungen wechselwarmer Tiere im normalen Temperaturbereich und ihre Ursachen. Naturwissenschaftliche Rundschau, 17, 438-442. Purrmann, G. (1963). Histochemische Untersuchungen am Verdauungsrohr von Fischen. Vortriige auf der 3 Tagung des Arbeitsgemeinschaft der Morphologie in der DDR. Rostoek. Quispel, A. ( 1 940). Gastric juice secretion in Ictalurus nebulosus. Unpublished Report. Leiden. Rahimullah, M. (1943). Contributions to our knowledge of the pyloric caeca in three families of fresh-water Indian fishes (Ophicephalidae,Notopteridae and Mastacembelidae), together with some remarks on their probable functions. Proceedings of the I n d i a n Academy of Sciences, B18, 83-96. Rahimullah, M. (1945). A comparative study of the morphology, histology and probable functions of the pyloric caeca in Indian fishes, together with a discussion on their homology. Proceedings of the Indian Academy of Sciences, B21, 1-37. Rajbanshi, V. K. and Tewari, H. B. (1969). Histochemical studies on the distribution of alkaline and acid phosphatases in the barbels of a fresh-water Acta Biologica Academiae Scientiarum teleost, Saccobranchus f ossilis. Hungaricae,20, 1-9. Read, J. B. and Burnstock, G. (19G8). Fluorescent histochemical studies on the mucosa of the vertebrate gastrointestinal tract. Histochemie, 16, 324-332. Reid, M. J. and Atz, J. W. (1958). Oral incubation in the cichlid fish Geophagus jurupari Heckel. Zoologica, 43, 77-88. Reshetnikov, Yu. (1961). On the connection between the amount of gill rakers and the nature of feeding in chars of the genus Salvelinus. Zoologicheskij Zhurnal, 40. 1574-1576. (In Russian.) Reuttar, K. (1971). Die Geschmacksknospen des Zwergwelses Ameirus nebulosus (LeSueur). Morphologische und histochemische Untersuchungen. Zeitschrift fiir Zellforschung und mikroskopische Anatomie, 120, 280-308. Reznik, G. K. (1958). On microstructure of digestive organs of some Gadidae. Nauchnye doklady vysshej shkoly. Biologicheskiye nauki, no. 2, 46-52. (In Russian.) Riddle, 0. (1909). The rate of digestion in cold-blooded vertebrates. The influence of season and temperature. American Journal of Physiology, 24, 447-458. Rosenthal, H. and Hempel, G. (1970). Experimental studies in feeding and food requirement of herring larvae. I n " Marine Food Chains " (J. H. Steele, ed.), pp. 344-364. University of California Press, Berkeley. Rosenthal, H. and Paffenhofer, G.-A. (1972). On the digestion rate and calorific content of food and feces in young gar fish. Naturwissenschaften, 59, 274-275. Rowntree, W. S. (1903). On some points in the visceral anatomy of the Characinidaa, with an enquiry into the relations of the ductus pneumaticus in the Physiostomi generally. Transactions of the Linnean Society of London, 2nd ser., Zoology, 9, 47-81.

232

B. 0. KAPOOR, H. SMIT AND I. A. VERIGHINA

Rozin, P. and Mayer, J. (1961). Regulation of food intake in the goldfish. American Journal of Physiology, 201, 968-974. Rozin, P.and Mayer, J. (1964). Some factors influencing short-term food intake of the goldfish. American Journal of Physiology, 206, 1430-1436. Ruiter, L. de (1968). Feeding behaviour of vertebrates in the natural environment. I n " Handbook o f Physiology Section 6. Alimentary canal. (C. F. Code, ed.), Vol. I , Control of Food and Water Intake. Ch. 7, pp. 97-116. American Physiological Society, Washington. Saddler, J. B. and Ashley, L. M. (1960). Comparative histology of the pyloric caeca of certain teleost fish. Walla Walla College Publications of the Department of Biological Sciences and the Biological Station, Washington, no. 27,

".

1-21.

Yanta, V. and Pollingher, U. (1955). Anatomia macro Ti microscopic&a tubului digestiv la map. Revista Universit&$i C. I . Parhon pi a Politechwicii, Bucaresti, no. 8, 179-188. Sarbahi, D. S. (1939). The alimentary canal of Labeo rohita (Hamilton). Journal of the Royal Asiatic Society of Bengal, Science, 5, 87-116. Sarbahi, D. S. (1951). Studies of the digestive tracts and the digestive enzymes of the goldfish and the largemouth black bass. Biological Bulletin, 100, 244-257.

Sarkar, H. L.(1959). Studies on the morpho-histology of the digestive system in relation to the food and feeding habits in a siluroid fish Mystus (Osteobagrus) seenghala (Sykes). Proceedings of the Zoological Society, Calcutta, 12, 97-109. Sastry, K. V. (1972). Amino tripeptidase activity in three teleost fishes. Proceedings of the Indian Academy of Sciences, B76, 251-257. Sat& M. and Sannohe, N. (1967). Light and electron microscopical observations on the clavate cells in the skin epidermis of the loach, Misgurnus anguillicaudatus. Zoological Magazine (Dobutsugaku Zasshi), 76,339-343. (In Japanese with English abstract.) Savitz, J. (1971). Nitrogen excretion and protein consumption of the bluegill sunfish (Lepomis macrochirus). Journal of the Fisheries Research Board of Canada, 28, 449-451. Sawaya, P. and De Petrini, L. M. (1960). Sabre a presenqa de cloaca e respirqitso intestinal no cascudo (Loricariidae: Plecostomua plecostomus (Linn.)). Boletina da la Faculdade de Filosofia, Cidncias e Letras, Universidade de Sdo-Paulo, Zoologia, Brasil, 1, no. 23, 5-20. Saxena, D. B. (1958). Oral breathing valves in some freshwater fishes of India.

Science and Culture, 25, 318-319. Scheuring, L. ( 1928). Beziehungen zwischen Temperatur und Verdauungsgeschwindigkeit bei Fischen. Zeitschrijt f u r Fischerei, 26, 231-235. Schmitz, E.H. and Baker, C. D. (1969). Digestive anatomy of the gizzard shad, Dorosoma cepedianum, and the thread& shad, D. petenewe. Transactions of the American Microscopical Society, 88, 525-546. Schulte, E. and Holl, A. (1971). Untersuchungen an den Geschmacksknospen der Barbeln von Corydoras paleatus Jenyns. I. Feinstruktur der Geschmacksknospen. Zeihchrijt f u r Zellforschung und mikroskopische Anatomie, 120, 450-462. Schwartz, F. J. and Dutcher, B. W. (1962). Tooth replacement and food of the cyprinid Notropw cerasinus from the Roanoke River, Virginia. American Midland Naturalist, 68, 369-375.

THE ALIMENTARY CANAL AND DIGESTION I N TELEOBTS

233

Seaberg, K. G. and Moyle, J. B. (1964). Feeding habits, digestion rates, and growth of some Minnesota warmwater fishes. Transactions of the American Fisheries Society, 93, 269-285. Sehgal, P. (1960). The anatomy and histology of the alimentary canal of Mystus seenghala (Sykes) with a note on its feeding habits. Research Bulletin (N.S.) of the Panjab University, 11, 77-86. Sehgal, P. (1966a). Anatomy and histology of the alimentary canal of Labeo calbasu (Hamilton). Research Bulletin (N.S.) of the Panjab University, 17, 257-266. Sehgal, P.(1966b). Food and feeding habits of Labeo calbasu. Biological Abstracts, 48 (1967), 84218. Sehgal, P. and Salaria, J. (1970). Functional anatomy and histology of the digestive organs of Cirrhina mrigala (Cuvier and Val.). Proceedings of the National Academy of Sciences, India, B40, 212-222. Seshadri, B. (1967). Amylase in murrel and mullets. Indian Journal of Experimental Biology, 5, 175-176. Shcherbina, M. (1964). Determination of the digestibility of artificial food in pond fish with the aid of an inert substance. Voprosy ikhtiologii, 4, 672-678. (In Russian.) Shrable, J. B.,Tiemeier, 0.W.and Deyoe, C. W. (1969). Effects of temperature on rate of digestion by channel catfish. Progressive Fish-Culturist, 31, 131-138. Shuljak, 0. S. (1968). On morphology of the gut of silver carp. Gidrobiologicheskii Zhurnal, 4, 30-38. ( I n Russian.) Siankowa, L. (1966). The surface area of the intestinal mucosa in bream-Abramis brarna (L.). Studia Societatis Scientiarum Torunensis, Toruh-Polonia, Sectio E (Zoologia),8, 1-53. Singh, R. (1966). Morpho-histological studies on the alimentary canal of Bagarius bagarius Ham. Agra University Journal of Research (Science), 15, 69-82. Singh, It. (1967a). Studies on the morphology and histology of alimentary canal of Ophicephalus marulius. Agra University Journal of Research (Science), 16, 27-38. Singh, R. (196713). Studies on the anatomy and histology of the alimentary canal of some fresh water teleosts in relation to their feeding habits. Agra University Journal of Research (Science),16, 165-168. Sivadas, P. (1965). Absorption of fat in the alimentary canal of Tilapia mossambica (Peters) (Teleostei). Journal of Cellular and Comparative Physiology, 65, 249-254. Sivadas, P. and Govindan, P. (1966-69). Histology of the gastro-intestinal tract in Tilapia mossambica (Peters). Journal of Annamalai University, Science, 27, 169-178. Sivadas, P. and Govindan, P. (1970). Distribution of alkaline phosphatase in the gastro-intestinal tract with reference to absorption of fat in Tilapia mossambica (Peters). Journal of Animal Morphology and Physiology, 17, 131-136. Smit, H. (1967). Influence of temperature on the rate of gastric juice secretion in the brown bullhead, Ictalurus nebulosus. Comparative Biochemistry and Physiology, 21, 125-132.

234

B. G. KAPOOR, H. SMIT AND I. A. VERIGHINA

Smit, H. (1968). Gastric secretion in the lower vertebrates and birds. I n " Handbook of Physiology Section 6: Alimentary Canal, (C. F. Code ed.), Vol. V, Ch. 135, pp. 2791-2805. American Physiological Society Washington. Smith, C. L., Atz, E. H. and Tyler, J. C . (1971). Aspects of oral brooding in the nardinalfish Cheilodipterus a f l n i s Poey (Apogonidae). American Museum Nouitates, no. 2456, 1-11. Soule, J. D. (1969a). Tooth attachment by means of a periodontium in the trigger-fish (Balistidae). Journal of Morphology, 127, 1-6. Soule, J. D. (1969b). Amelogenesis in the trigger-fish Balistidae. Bulletin of the Southern Calijornia Academy of Sciences, Los Angeles, Calqornia, 68, 64-71. Spanovskaya, V. D. (1961). Stenophagy and euryphagy in fishes of the subfamily Gobioninae. Zoologicheskij Zhurnal, 40, 151G-1531. (In Russian with English summary.) Srivastava, A. K. (1966). Alkaline phosphatase and glycogen in the intestine of certain freshwater teleosts. Current Science, 35, 154-155. Srivastava, P. N. (1958). Primitive features in the alimentary canal of Gadusia chapra (Hamilton). Current Science, 27, 144-145. Sriwastwa, V. M. S. (1970a). Functional anatomy of digestive organs of a fresh-water fish Rhynchobdella aculeata (Ham.). IA, Morphology. VcZstnik seskoslovenskd spoleEnosti zoologickd, 34, 129--135. Sriwastwa, V. M. S. (1970b.) Functional anatomy of digestive organs of a fresh water fish Rhynchobdella aculeata (Ham.). IB, Histology. Vibtnik Ceskoslovenskd spoleEnosti zoologicke', 34, 136-142. Stern, J. A. and Lockhart, E. E. (1953). Proteolytic activity of the pyloric caeca of redfish. Journal of the Fisheries Research Board of Canada, 10, 590-598. Steward, N. E. (1962). Quoted from Warren and Davis, 1967. Storch, V. N. and Welsch, U. N. (1970). Electron microscopic observations on the taste-buds of some bony fishes. Archivum histologicum japonicum, 32, 145-153. Stroganov, N. G. and Buzinova, N. S. (1969). Proteolytic enzymes of the grass carp Ctenopharyngodon idella. Chemical Abstracts, 72 (1970) 1078 e. Stroganov, N. G. and Buzinova, N. S. (1971). Seasonal and age-related changes in the liver and intestines of the grass carp (Ctenopharyngodon idella) and silver carp (Hypophthalmichthys molitrix). Nauchnye doklady vysshej shkoly, biologicheskiye N a u k i , 14, 5-10. Sublette, M. S. (1956). The morphology of the post-pharyngeal alimentary canal of the white bass, Morone chysops (Rafinesque). Texas Journal of Science, 8, 444-462. Sutterlin, A. M. and Sutterlin, N. (1970). Taste responses in Atlantic salmon (Salmo salar) parr. Journal of the Fisheries Research Board of Canada, 27, 1927-1942. Suvorova, E. G. and Treschuk, L. I. (1973). The morphology and histochemistry of the gastrointestinal tract of the white Baical grayling Thymallus arcticus baicalensis Dyb. Voprosy ikhtiologii, 13, 523-534. (InRussian.) Suyehiro, Y. (1942). A study on-the digestive system and feeding habits of fish. Japanese Journal of Zoology, 10, 1-303.

".

THE ALIMENTARY CANAL AND DIGESTION I N TELEOSTS

235

Suzuki, Y. (1956). A histological study of the granular processes o n the lips of scythe fish Pseudogobio esocinus (T. et S.). Japanese Journal of Ichthyology, 5, 12-14. (In Japanese with English summary.) Suzuki, Y . , Osada, M. and Watanabe, A. (1963). Cytologic and electron microscopic studies on the intestinal respiration of the loach (Misgurnus anguillicaudatus). Archivum histologicum japonicum, 23, 43 1-446. (In Japanese with English summary.) Svetovidov, A. N. (1934). On the dependence between the feeding habits and the amount of pyloric caeca in fishes. Doklady Akademii N a u k SSSR, 3 67-72. ( I n Russian.) Svetovidov, A. N. and Skvorzowa, T. A. (1968). The structure and functional significance of pharyngeal organs in clupeoid fishes. Trudy Zoologicheskogo Instituta Akademii N a u k SSSR, Leningrad, 46, 169-189. (InRussian.) Swarup, K. (1959). The morphology and histology of the alimentary tract of Hilsa ilisha (Hamilton). Proceedings of the National Academy of Sciences, India, B29, 109-126. Swenson, W. A. and Smith, H. H. (1973). Gastric digestion, food consumption, and food conversion efficiency in walleye (Stizostedion vitreum vitreum). .Journal of the Fisheries Research Board of Canada, 30, 1327-1336. Szarski, H. (1956). Causes of the absence of a stomach in Cyprinidae. Bulletin de l’ilcaddmie Polonaise des Sciences, Cl. 11 Zoology, 4, 155-156. Szarski, H., Delewska, E., Leja, S., et al. (1956). The digestive system of the bream (Abramis brama L.). Studia Societatis Scientiarum Torunensis, (In Polish with English Toruh-Polonia, Sectio E . (Zoologia), 3, 1-34. summary.) Tamura, E. and Honma, Y. (1971).Histological changes in the organs and tissues of the gobiid fishes throughout the life-span-IV. Digestive organs of the icegoby. Bulletin of the Japanese Society of Scienti$c Fisheries, 37, 831-839. Tandon, K. K. and Goswami, S. C. (1968). A comparative study of the digestive system of Channa species. Research Bulletin (N.S.) of the Panjab University, 19, 13-31. Taylor, W. H. (1959). Studies on gastric proteolysis. Biochemical Journal, 71, 72-83 ; 373-388. Taylor, W. H. (1962). Proteinases of the stomach in health and disease. Physiological Reviews, 42, 519-553. Taylor, W. H. (1968). Biochemistry of pepsins. I n “ Handbook of Physiology Section 6: Alimentary Canal (C. F. Code, ed.), Vol. V, Ch. 120, pp. 25672587. American Physiological Society, Washington. Tewari, H. B. and Rajbanshi, V. K. (1969). Histochemical studies on the distribution of alkaline phosphatase in the cutaneous gustatory epithelia of fresh-water teleosts. Acta Biologica Academiae Scientiarum Hungaricae, 20, 269-279. Tewari, H. B. and Rajbanshi, V. K. (1971). Histochemical studies on the distribution of a few hydrolytic enzymes in cutaneous gustatory epithelia of a freshwater teleost, Saccobranchus fossilis. Annales d’aistochimie, 16, 255-264. Thomson, J. M. (1954). The organs of feeding and the food of some Australian mullet. Australian Journal of Marine and Freshwater Research, 5, 469-485. Tortonese, E. (1952). Anatomi-a e istologia del tubo digerente di Coris julis L. (Pisces Labriformes) in rapport0 a1 regime alimentare. Archivio Zoologic0 Italiano, 37, 1-27.

”.

236

B. 0 . KAPOOR, H . SMIT AND I. A. VERIOHINA

Trent, L. and Hassler, W. W. (1966). Feeding behavior of adult striped bass, Roccus sexatilis, in relation to stages of sexual maturity. Chesepeake Science, 7, 189-192. Turpayev, T. M. (1941). Contribution on the adaptation of the digestive system of fishes to their feeding habits. Bulletin of Experimental Biology and Medicine, Moscow, 12, 46-48. (In Russian.) Tyler, A. V. (1970). Rates of gastric emptying in young cod. Journal of the Fisheries Research Board of Canada, 27, 1177-1189. Uga, S. and Hama, K. (1967). Electron microscopic studies on the synaptic region of the taste organ of carps and frogs. Journal of Electron Microscopy, 16, 269-276. Unnithan, R. R. (1965). On the mucosal coefficient of a few Indian fresh water fishes. Science and Culture, 31, 387-388. Ushiyama, H., Fujimori, T., et al. (1965). Carbohydrases in the pyloric caeca of Oncorhynchus keta. Chemical Abstracts, 64, (1966) 709211. Vanajakshi, T. P. (1938). Histology of the digestive tract of Saccobranchus fossilis and Macrones vittatus. Proceedings of the Indian Academy of Sciences, B7, 61-79. Varute, A. T. and Jirge, S. K. (1971). Histochemical analysis of mucosubstances in oral mucosa of mouthbreeding cichlid fish and seasonal variations in them. Histochemie, 25, 91-102. Vasilieva, N. E. and Korovina, V. M. (1968). The dependence of histological structure of the middle intestine of teleostean fishes on phylogenetic and ecological factors. Trudy Zoologicheskogo Instituta Akadernii Nauk SSSR, Leningrad, 46, 190-206. Vasilieva, N. E. and Melnikova, M. N. (1965). Changes in the intestinal epithelium in king salmon (Salmo salar L.) in spawning period. Nauchnye doklady vysshej shkoly. Biologicheskiye nauki, no. 4, 32-35. (In Russian.) Vasisht, H. S. (1959). Relation of the basioccipital pad with the food in fishes. Science and Culture, 24, 579-580. Vegas-Velez, M. (1972). La structure histologique typique du tube digestif des poissons tilbosteens. Tethys, 4, 163-174. Venkateswarlu, T. (1962). A comparative study of the food, feeding habits and alimentary canal of some gobiids from Porto-Novo, S. India. Proceedings of the Second All-India Congress of Zoology, Varanasi, part 2, 465-471. Verighina, I. A. (1961). Histological structure of the gut of silver carp and white amur. Sbornik trudov Zoologicheskogo Museya Moscowskogo Universiteta, 8, 189-195. (In Russian.) Verighina, I. A. (1963). Morphological and histological structure of the intestine in two cyprinid species Erythroculter erythropterus (Bas.) and Elopichthys bambusa (Rich.). Nauchnye doklady vysshej shkoly. Biologicheskie nauki, no. 1, 38-42. (In Russian.) Verighina, I. A. (1965). Structure of alimentary tract of banded cat-fish (Pseudobagrus fulwidraco (Rich.))and Ussurian cat-fish (Liocassis ussuriensis (Dyb.)) Boprosy ikhtiologii, 5, 141-148. (In Russian.) Verighina, I. A. (1967). The structure of the alimentary tract in plant-eating fishes of the Cichlidae family. Voprosy ikhtiologii, 7,362-371. (In Russian.) Verighina, I. A. (1969a). The structure of the digestive tract of Varicorhynus capoeta sewangi (Filippi.). Voprosy ibhtiologii, 9, 539-545. (In Russian.)

THE ALIMENTARY CANAL AND DIGESTION I N TELEOSTS

237

Verighina, I. A. (1969b). Ecologo-morphological peculiarities of the alimentary tract of some Cypriniformes. I n “ Itogi nauki, Zoology, 1968 ”, pp. 79-109. Institut nauchnoi informatsii Akademii Nauk SSSR. (In Russian.) Verighina, I. A. (1971). The structure of the digestive tract of the Volga undermouth Chondrostoma nasus variabile Jak. Voprosy ikhtiologii, 11, 31 1-318. (In Russian.) Verighina, I. A. (1972). Histological structure of the opibranchial organ of silver carp Hypophthalmichthys molitrix (Val.). Sbornik trudov Zoologicheskogo Museya Moscowskogo Universiteta, 12, 182-190. (In Russian.) Verighina, I. A. and Medani, J. I. (1968). The structure of the digestive tract in Distichodus niloticus (L.) and Distichodus rostratus (Giinth.) in relation to feeding habits. Voprosy ikhtiologii, 8, 710-721. (In Russian.) Verighina, I. A. and Savvaitova, K. A. (1974). The structure of the alimentary tract in some chars (g. Salvelinus) from sympatric populations of Lake Azabachje (Kamchatka). Voprosy ikhtiologii, 14,466-476. (In Russian.) Verigin, B. V. (1957). Structure of the gill apparatus and superbranchial (epibranchial) organ of Hypophthalmichthys rnolitrix (Val.)Zoologicheskij Zhurnal, 36, 595-602. (In Russian with English summary.) Verma, S. R., Dalela, R. C., et al. (1974a). A study of the alimentary canal and physiology of digestion in Gadusia. Zoologische Jahrbucher, 92, 445-452. Verma, S. R. and Tyagi, M. P. (1974b).A comparative histological study of the stomach of a few teleost fishes. Gegenbaurs morphologisches Jahrbuch, 120, 244-253. Verma, S. R., Tyagi, M. P. and Dalela, R. C. (19740). Morphological variations in the stomach of few teleost fishes in relation to food and feeding habits. Gegenbuurs morphologisches Jahrbuch, 120, 367-380. Vickers, T. (1962). A study of the intestinal epithelium of the goldfish Carassius auratus : its normal structure, the dynamics of cell replacement, and the changes induced by salts of cobalt and manganese. Quarterly Journal of Microscopical Science, 103, 93-1 10. Volya, G. (1966). Some data on digestive enzymes in some Black Sea fishes and a micromodification of a method for the identification of trypsin, amylase and lipase. I n “ Fisiologia morskikhyzhitvotnykh.” Nauka. (In Russian.) Vonk, H. J. (1927). Die Verdauung bei den Fischen. ZeiMchrift fur vergleichende Physiologie, 5, 445-546. Vonk, H. J. (1929). Das Pepsin verschiedener Vertebraten. Die pH-Optima und die Wasserstoffionenkonzentration des Mageninhaltes. Zeitschrift fur vergleichende Physiologie, 9, 685-702. Vonk, H. J. (1937). The specificity and collaboration of digestive enzymes in Metazoa. Biological Reviews, 12, 245-284. Vonk, H. J. (1941). Die Verdauung bei den niederen Vertebraten. I n “ Advances in Enzymology Vol. I, pp. 371-417. Interscience, New York. Vrba, E. S. (1968). Contributions to the functional morphology of fishes. V. The feeding mechanism of Elops saurus L. Zoologica Africana, 3,211-236. VukoviF, T. (1966). DuBina crevnog trakta sapaEa (Barbua meridionalis petenii (Heck.) i krukusa (Gobio gobio L.) iz razliEitiha lokaliteta. Ribarstvo Yugoslavia, 21, 132-133. Ware, D. M. (1972). Predation by rainbow trout (Salmo gairdneri) :the influence of hunger, prey density, and prey size. Journal of the Fisheries Research Board of Can.ada, 29, 1193-1201.

”.

238

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Warren, C. E. and Davis, G. E . (1967). Laboratory studies on the feeding. bioenergetics, and growth of fish. I n “ The Biological Basis of Freshwater Fish Production ” (S. D. Gerking, ed.), pp. 175-214. Blackwell Scientific Publications, Oxford. Weatherly, A. H. (1972). “ Growth and Ecology of Fish Populations ”, 293 pp. Academic Press, London and New York. Weinreb, E. L. and Bilstad, N. M. (1955). Histology of the digestive tract and adjacent structures of the rainbow trout, Salmo gairdneri irideus. Copeia, no. 3, 194-304. Weisel, G. F. (1962). Comparative study of the digestive tract of a sucker, Catostomus catostomus, and a predaceous minnow, Ptychocheilus oregonense. American Midland Naturalist, 68, 334-346. Weisel, G. F. (1973). Anatomy and histology of the digestive system of the paddlefish (Polyodon spathula). Journal of Morphology, 140, 243-256. Western, J. R. H. (1969). Studies on the diet, feeding mechanism and alimentary tract in two closely related teleosts, the fresh-water Cottus gobio L. and the marine Parenophrys bubalis Euphrasen. Acta Zoologica, Stockholm, 50, 185-205. Western, J. R. H. (1971). Feeding and digestion in two cottid fishes, the freshwater Cottus,gobio L. and the marine Enophrys bubalis (Euphrasen).Journal Of Fish Biology, 3, 225-246. Western, J. R. H. and Jennings, J. B. (1970). Histochemical demonstration of hydrochloric acid in the gastric tubules of teleosts using an in vico Prussian blue technique. Comparative Biochemistry and Physiology, 35, 879-884. Wetzig, H. and Bruchmuller, W. (1967). Histologische und histochemische Untersuchungen am Epithel des Kopfdarmes schaumnestbauender Anabantidae. Acta histochemica, 28, 243-251. Whitear, M. (1971). Cell specialization and sensory function in fish epidermis. Journal of Zoology, London, 163, 237-264. Whitmore, D. H. and Goldberg, E. (1972a). Trout intestinal alkaline phosphatases. I. Some physical-chemical characteristics. Journal of Experimental Zoology, 182, 47-58. Whitmore, D. H. and Goldberg, E. (1972b). Trout intestinal alkaline phosphatases. 11. The effect of temperature upon enzymatic activity in vitro and in vivo. Journal of Experimental Zoology, 182, 59-68. Wier, H. C. and Churchill, E . P. (1945). The anatomy and histology of the digestive system of the gizzard shad Dorosoma cepedianum (LeSueur). Proceedings of the South {Dakota Academy of Science, Vermillion, 25, 34-43. Wilamovski, A. (1972). Structure of the gill apparatus and suprabranchial organ of Hypophthalmichthys molitrix (Val.) (Silver carp). “ Bamidgeh ”, 24, 87-98. Wilke, H. (1972). Das Wachstum der Drusenzellen in der Teleosteerepidermis. Ein Ergebnis von Zellfusionen? Zoologischer Anzeiger, Leipzig, 189,281-291. Winberg, G. 0. (1956). Rate of metabolism and food requirements of fishes. Belorussian State University, Minsk. Fisheries Research Board of Canada Translation Ser. no. 194, 253 pp. Windell, J. T. (1967). Rates of digestion in fishes. I n “ T h e Biological Basis of Freshwater Fish Production ” (S. D. Gerking, ed.), pp. 151-173. Blackwell Scientific Publications, Oxford.

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Windell, J. T. (1969). Digestive response of rainbow trout to pellet diets. Journal of the Fisheries Research Board of Canada, 26, 1801-1812. Windell, J. T. and Norris, D. 0. (1969a). Dynamics of gastric evacuation in rainbow trout, Salmo gairdneri. American Zoologist, 9, 584. Windell, J. T. and Norris, D. 0. (1969b). Gastric digestion and evacuation in rainbow trout. Progressive Fish-Culturist, 31, 20-26. Wu, H. W. and Chang, H-w. (1945). On the structures of the intestine of the Chinese pond loach with special reference to its adaptation for aerial respiration. Sinensia, 16, 1-8. Yamagishi, I., Nagumo, N., Oshiro, S. et al. (1969). Electron microscopic observation the absorptive epithelium of eel intestine. Journal of the Medical Society of Toho University, Tokyo, Japan, 16,101-108. Yamamoto, T. (1966). An electron microscope study of the columnar epithelial cell in the intestine of fresh water teleosts : goldfish (Carassius auratus) and rainbow trout (Salmo irideus). Zeitschrift fur Zellforschung und mikrosbopische Anatomie, 72, 66-87. Yoshida, Y. (1967). On the feeding mechanisms of plankton-feeders. Information Bulletin on Planktology i n Japan. Commemoration Number of Dr. Y. Matsue. 271-278. (In Japanese with English summary.) Young, R . T. and Fox, D. L. (1936). The structure and function of the gut in surf perches (Embiotocidae) with reference to their carotenoid metabolism. Biological Bulletin, 71, 217-237. Zambriborsch, F. S. (1953). On the histomorphology of the alimentary canal in mullet (Mugil). Sbomik Biologicheskogo fakulteta Odesskogo Universiteta, 6, 107-118. (In Russian.)

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Adv. mar. Biol., Vol. 13, 1975, pp. 241-355

PHYSIOLOGICAL MECHANISMS IN THE MIGRATION OF MARINE A N D AMPHIHALINE FISH M. FONTAINE Physiologie ge'ne'rale et compare'e, Muse'um national d'Histoirc naturelle, Paris France I. Introduction .. .. .. .. 11. Ionic and Osmotic Regulation . . .. 111. Thermopreferendum and Thermoregulation IV. Some Functions Involved in Migrations A. Respiratory Function .. .. B. Circulation. . .. .. .. C. Excretion . . *. .. .. D. Reproduction .. .. E. Metabolism .. . . .. V. Integration Mechanisms .. .. A. Endocrine Glands. . .. .. B. The Nervous System .. .. VI . Sense Organs .. .. *. .. A. Rheotropism .. .. .. B. Thermoreception . . .. .. C. Vision . . .. D. Chemical Reception .. .. E. Electro- and Magnetoreceptors . . VII. Conclusion .. . . .. *. VIII. Acknowledgements .. . . .. IX. References .. .. ..

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I. INTRODUCTION Many species of marine fish are migratory. But, as with other biological characteristics of this very diversified class, these migrations present varied aspects. Until now, migrations have been classified according to descriptive criteria, born of naturalists' observations, behaviour patterns specific to these migrations or again to their apparent purpose. Some are termed according to their direction (vertical for instance), others according to their rhythm (circadian when their periodicity is approximately twenty-four hours) ; such movements are those of certain Scaridae (Ogden and Buckman, 1973 ; Hobson, 1973) carrying out a daily migration from shallow water where they feed to deeper waters where they rest a t night, the migratory paths being constant. Some are termed according to their obvious purpose (the search for nutritious conditions allowing rapid 241

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growth and the accumulation of energetic reserves for the migratory stage which follows, a type of migration called trophic as opposed t o reproductive migration). Others should be called " amphibiotic )' when a change of environment is involved and if, a t regular intervals, the fish pass from an aquatic to a terrestrial environment. Such is the case with the grunion (Leuresthes tenuis) which during certain spring and summer months-at the lunar periods corresponding to the highest tides-lays and fertilizes its eggs in the sand. The adults are then carried out to sea by the waves. Admittedly, the amphibiotic migration of these mature adults is very short-lived, but if we consider the whole life cycle of the species, the use of this term is justified, for an entire development phase of the eggs takes place in the wet sand, outside the aquatic environment proper. We know also that, in tropical regions, many fish frequently leave the water and crawl or walk about on land. These changes of abode are not generally regarded as migrations, but rather as a sign of erratic behaviour,though they almost certainly have a physiological cause: the need to insure a supply of oxygen to the tissues, a normal excretion of carbon dioxide and to maintain a suitable blood pH as well as a hydromineral equilibrium. These movements do not occur, however, with sufficient regularity to be termed migrations, since the urgency of this amphibiosis depends greatly on the fish's activity in its temporary environment and the climatic conditions of the moment. Finally, there are many species which while remaining in the aquatic environment pass periodically, a t well defined stages of their life cycle, from salt to fresh water and vice versa. These species we have termed amphihaline* as opposed to those holohaline species whose migrations are carried out in the same environment as far as salinity is concerned (salt or fresh water). The expression " same environment " does not of course mean complete uniformity for naturally the salinity is never exactly the same either in the different types of fresh water or the different masses of sea water. These species are said to be amphihaline potamotocous when they reproduce in fresh water (as is the case with the majority of the species of both Atlantic and Pacific salmon) and amphihaline thalassotocous when they reproduce in sea water (as do eels). We should indeed bear in mind t8heetymological meaning of the terms catadromous and anadromous and speak of a catadromous migration when the animal goes downstream and of anadromous migration when it takes an upstream course. These qualifications and others similar are valid and prudent, *'Note that the term amphihaline is not synonymous with euryhaline (capable of withstanding the salinity change between sea and fresh water).

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for they do not presume the mechanisms controlling these migrations. Yet, we have become progressively more aware that neither certain purposes inherent in the need for fish t o accomplish their life cycle nor environmental factors can alone account for a migratory behaviour. Research has been made in an attempt t o understand the physiological modifications occurring before and during migration in relation to the relatively sedentary stages of the fish’s life and thus, we seek to explain on a physiological basis the why and how of the starting and the accomplishment of these migrations. We shall consider only certain wide ranging migrations where enough physiological research has been done to permit relatively satisfactory interpretations. We shall not deal with daily vertical migrations, which are widespread and involve a variety of factors (search for food, sensitivity to light, temperature or substances released by plankton). Often, several stimuli are involved. Thus, for herring in the Gulf of Finland, temperature and light seem t o play a role concurrently. The deep waters which are the habitat of the herring’s favourite food, copepods, in particular Limnocalanus grimaldii, are too cold for its thermopreferendum. So the fish descend for a few hours only per day and during daylight when they can hunt their prey. At night, they return to the warmer surface waters better suited to them (Bitinkov, 1959). Internal stimuli are also involved. For example, a cold water anchovy is more attracted by light when it is hungry than when it is sated. Undoubtedly light corresponds to the fish’s best food hunting possibilities. The gonads probably intervene also in these vertical migrations for it has been observed that a t the time of reproduction, fish surface more often during the day. The physiological mechanism involved is not yet clear (perhaps a diminution of the appetite) but we may suppose that the stimulation by light of the hypothalamo-pituitary axis aids in the maturation of the reproductive organs (Zousser, 1958). We shall therefore successively consider those physiological mechanisms which appear most likely t o be involved in the triggering off and accomplishment of the great horizontal migrations (which moreover may be associated with vertical migrations a t certain stages). This approach has the disadvantage-which we do not underestimate-of dissociating functions which in the organism are more or less interdependent in determining the behaviour of the individual or of the shoal. But although fully aware of this disadvantage, I think it is worthwhile to attempt such an analysis whereas until now such mechanisms have generally been studied in close conjunction with the migrations of a particular species.

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I believe it is useful, for example, to bring together in the same section (iono- and osmoregulation) the results concerning this function in three species : one amphihaline potamotocous (salmon), another amphihaline thalassotocous (eel) and the third, a holohaline marine species (cod). I would of course never go so far as to say that one type of migration results from the fluctuations of one specific physiological function, another type resulting from the changes in another function, for I think that each type presents several stages, each depending on modifications in various functions and in their integration mechanisms -modifications often related to changes in the surrounding environment, the whole process seeming to be the most often an accentuation of this conflict from which the fish is led to escape, or again as an effort to obtain a collaboration between the animal and the environment which suits it best at a given time, each stage presenting different physiological patterns corresponding to different media. None of the sections which follow (classified according to physiological mechanisms) claims to explain fully a particular migration, but only to show that these mechanisms intervene or are capable of intervening during certain migratory phases. I n fact, if the implication of one or another physiological process in the determinism* of a particular migration is in certain cases based on well-known facts concerning the migratory fish themselves, in other cases we must extrapolate from incomplete data on the migrating fish or from results obtained in other groups. For we feel that it is as interesting to suggest certain possible advances of tomorrow as to note past progress. The examples to be given will be taken from among amphihaline rather than marine holohaline fish, for the former have been much less accessible than the latter in certain phases of their migration and above all because some of them are accessible under conditions much closer to their normal physiology than their holohaline counterparts. It is regrettable, for example, that so little exploitable data is available on the neuroendocrinology of tuna, but this is hardly surprising when we consider the stress represented by the capture of a bluefin tuna in a tunny-net or in the course of its trophic or reproductive migrations and the highly important ethological change undergone by such a fish kept in an aquarium, even though its size earns it the name of oceanarium. The improved conditions of capture and teletransmission of certain data with the help of fixed apparatus *I call determinism all the factors determining a phenomenon, in this case migratory behaviour.

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on the fish, in conditions of the least possible stress, is certainly one of the important practical factors which will advance our knowledge on the physiology of great migrators. 11.

IONIC AND OSMOTICREUULATION

We must now take into consideration not only fish but certain Cyclostomata as well, for it is in this group that we have found the first indications that the functions examined here most probably play some role. This is shown in the work done on sea lamprey, Petromyzontidae, whose biology is similar to that of the amphihaline potamotocous teleosts, such as the salmon and the shad. Let us first recall that the conditions of osmoregulation in lower vertebrates differ greatly with each order. The Myxinoidea, lowest in the zoological scale, are poecilosmotic, like most invertebrates, i.e. the osmotic pressure (O.P.) of the internal milieu (I.M.) follows fairly closely the variations in the O.P. of the external environment (E.E.). The Petromyzonoidea, more advanced Cyclostomata, apart from a few critical phases to be discussed later, have, in a marine environment, an osmoregulation apparently as efficient as that of marine teleosts but whose mechanisms are much less well known. In the marine teleosts, the 02.of the I.M. being much lower than that of the E.E., there is a continual loss of water by osmosis and penetration by passive diffusion following the ion concentration gradients at the level of certain surfaces. The marine teleost must therefore contend with a constant water loss by osmosis, for which it compensates by drinking abundantly. However, as it drinks mostly to make up for the loss of water, diuresis is slight. Besides, the kidneys of certain species have no glomeruli, and when these exist, they are fewer in number and less developed than in freshwater teleosts. The fact that a large intake of sea water is indispensable for marine teleosts can be proved by obstructing the oesophagus and thus preventing the fish from drinking; this leads to a rapid loss in weight, followed by death. But how do the fish turn sea water into a salt solution isotonic with blood, which is about three times less concentrated than sea water? A selection takes place first in the intestine. A large number of bivalent ions do not penetrate the I.M. and are eliminated by the intestine; those that penetrate are excreted by the kidneys. Monovalent ions, most of which penetrate the I.M., are eliminated chiefly by the gills, which work actively against a salinity gradient. On the other hand, freshwater teleosts, like the Selachii of the same environment, having an I.M. hypertonic to the environment,

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undergo an influx of water mainly through the gills, but also by way of the mucous membranes of the mouth and gills and even, for certain teleosts, through the skin. Being constantly invaded by water, these fish have little need to drink, although they do occasionally, and they are perfectly able to survive for a long time with the oesophagus obstructed. The kidney eliminates this flow of endosmotic water by excreting a large amount of very diluted urine. However, despite a reabsorption of salts in the tubules, this urine is richer in salts than the E.E. There is therefore a continual loss of ions through the urine, in addition to the losses by diffusion a t the level of the teguments and especially the gills. Ions must be brought in from the E.E. to compensate. This is accomplished by various mechanisms : absorption of ions by the intestine after feeding-this mechanism seems particularly important for certain fish like the perch-and also an absorption of ions by the gills for very many species. There seems to be a relationship between the fish’s ecology and the threshold above which the gills can perform this ion pumping. Trout, for example, which can live in waters of very low mineral content, have a particularly low threshold for C1- absorption. With the great amphihaline migrators such as salmon, a profound modification of the physiological mechanisms of iono- and osmoregulation is called for, according to whether the animal is living in salt or fresh water. We may well wonder if it is not a structural and functional biochemical modification of certain organs and tissues involved in these mechanisms, beginning in a given environment, which sets off the complex migratory mechanism which will lead the fish to a new environment better suited to the new physiological condition resulting from this modification. Let us review the evidence that has led to this idea. I n 1930, wishing to complete, by research on the Cyclostomata, a study of Elasmobranchii and teleosts on the modification of the I.M. in terms of the variations in salt concentration of the ambient environment, a biologist caught some sea lampreys in the Lower Loire River during their anadromous reproductive migration ; they were coming from the sea and heading for their spawning grounds. The biologist wished to determine how the molecular concentration of their I.M. would evolve when the lampreys were replaced in sea water. Now, although the lampreys had left the ocean only a few days or weeks earlier, all efforts, however gradual, to reaccustom them to sea water resulted in death. A study of the blood’s freezing point shows that it rises rapidly with the increasing salinity of the ambient environment. The A,

a

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which was on the average - 0°54C for lampreys kept in fresh water, descended to 0'77C twenty-four hours after the E.E. had been brought to a A of - l'OOC by gradual addition of salt water. When this A reached - 1'96C, that is, close to the value for sea water, the blood of the lamprey sacrificed after 4 hours only in the new environment when it was already dying had a A of - l0O8C, a value clearly incompatible with survival (Fontaine, 1930). If we compare these data with those of Burian (1910) which give a A of - 0'59 C for a sea lamprey caught in the Mediterranean in an environment whose A was around - 2"30C, it appears that the osmoregulatory mechanism of the sea lampreys examined a t the beginning of their anadromous migration is much less efficient in regard to a hypertonic environment than that observed in the same cyclostome caught during its marine phase. The idea then arose that a modification of osmoregulatory capacities appearing at a precise stage in the life cycle may be the factor, or one of the factors, determining certain migrations. Especially in salmon returning from sea water to fresh water, the migration to fresh water may be guided by a change in osmoregulatory mechanisms with regard to a hypertonic environment, these mechanisms tending to readjust to a hypotonic environment. Let us see if we can find documentary evidence to support this notion ; we shall first consider a genus of teleost fish, Oncorhynchus, amphihaline and potamotocous like the sea lamprey. According to Kubo (1960), a t the moment when 0. m a w (Brevoort), still at sea, approaches the coasts to begin its fluvial anadromous migration, a clear increase in the molecular concentration of its blood can be observed, indicating a deterioration of the osmoregulatory mechanisms faced with a hypertonic environment. But there is more to it than that. I n 0. nerka (Walbaum), Zaks and Sokolova (1961) found phenomena entirely similar to those seen in the sea lamprey. Fish of this species having begun their upstream migration, cannot be put back into the sea water they have just left without succumbing, which is also true for 0. keta (Kashiwagi, 1971), and examination of the osmotic pressure of their blood reveals a dangerous increase. Even with osmotic pressures of the environment much lower than those of sea water and blood (A = - 0'18 C) the O.P. of the I.M. rises significantly. This fact led these authors to believe that the gill mechanisms which pump ions in a freshwater environment and excrete them in a marine environment are, among the adult fish during anadromous migration, orientated without possible return towards the pumping of salts ; even if the salmon were to be put back into sea water, these mechanisms could not be reversed and the fish would be unable to return to A.N.B.-13

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conditions under which they lived for many long months during their marine phase.* Let us now consider the young European eel as it approaches the coast following its metamorphosis from a leptocephalus larva to an elver t o start a fluvial anadromous migration which is not reproductive, as in the preceding examples, but trophic. J. Schmidt (1935) has studied the weight loss which occurs during metamorphosis in terms of wet and dry weight. Between the first and the fifth stage, there is a 77% weight loss in wet weight, but only a 17% t o 38% loss in dry weight. I n other words, the amount of dry matter diminishes much less than the water content, which in the leptocephalus averages 93% but drops to 79-7y0 in the elver (Callamand, 1943). There is therefore a link between metamorphosis and a sudden rapid reduction of the water content. It is possible to allege that this loss is not only due t o a decreased water content in the soft tissues, but also to a change in the ratio between the hard parts (skeleton) and the soft ones. This is why, in the elvers, we determined the water content of the muscle tissue only and here we found a value of 77% (Chartier and Fontaine, 1974). It is perhaps a t first surprising that this figure is lower than that for the entire animal (including bones) but in the whole animal the intestinal fluid must be counted in the total calculations. I n any case, it seems probable that a decrease of the water content of tissues does occur in the course of metamorphosis. This phenomenon has in fact been noted in frogs by Schaper and Cohen (1905) and Rey (1937), but it seems more pronounced in the elver, which may have something to do with its life in a hypertonic environment whereas the metamorphosing tadpole lives in hypotonic surroundings. On the other hand, the thyroid has shown an increased activity during metamorphosis of the eel (Murr and Sklower, 1928) as well as of the frog, and one might suppose that this hyperfunctioning of the thyroid perturbs osmoregulation with regard t o a hypertonic environment. Indeed, if we compare two lots of elvers in sea water (C1Na 32 g p.l.), one in normal sea water, the other in sea water to which has been added thyroxine (1-8 mg p.1.) and triiodothyronin (0.18 mg p.l.), we notice that the osmotic pressure of body juice is 9.60 for the second lot as against 8.17 for the first lot, a result indicating that the thyroid hormones have reduced the osmoregulatory capacities of elvers in sea water (Fontaine and Chartier, 1974). However, the fact that the osmoregulatory mechanisms become less *However, according to Donaldson (and quoted by Idler, 1973), it might be possible to obtain the survival of these salmon by a gradual return to sea water.

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effective seems less dangerous for the elver than for the lamprey, for it is possible to transfer elvers a t all times from fresh water to sea water without causing death. Moreover, a certain percentage of the elver population remains in our coastal waters. They seem nevertheless, when in a marine environment, to reach the extreme limit of their molecular concentration regulating capacities. If we draw a curve of the freezing point of the juice extracted from the elver in terms of the freezing point of the E.E., we note that the zone where osmoregulation is truly effective does not go below - 2OC (A approximately equal to that of our Atlantic coastal waters) (Fig. 1). Beyond this, that is, in hypertonic environments, t8hevery sharp slope of the straight line indicates a marked deficiency in osmoregulation (Boucher-Firly, 1935).

A o f the environment

17rr;. 1. A of (crushed)elver tissues in terms of the A of the environment.

One may therefore wonder whether it is not the reduced efficiency of osmoregulatory mechanisms in a hypertonic environment that incites the elver, like the salmon, t o seek less salty waters. Certain observations or experiments on the elver favour this hypothesis. For Iong past, it has been emphasized that the entry of elvers into the lagoons is triggered by an attraction to fresh water. The case of the pumps a t Mex, near Alexandria, has often been cited. These pumps do not function continually but periodically, when they release an enormous amount of water, over three millions tons per day, and these pumps are in action when the elvers come upstream. But these observations, made in natural conditions, although very significant, are not proof, for the aflux of fresh water is associated with a more or less violent current and it may be alleged that the elvers respond to a rheotropism rather than t o a chemotropism. However, the very simple experiment made by Sylvest (1931) tends to show that fresh water does exert an attraction. Sylvest put some elvers and two bottles, one filled with fresh water and one with sea water, into a tank containing salt water.

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Although each bottle was placed in very varied positions for the different experiments, Sylvest noticed that the elvers always went towards and into the bottle of fresh water ; the tank’s population was soon inside the freshwater bottle. No doubt it is a t the level of the mouth of the freshwater bottle, and here only, that currents will result from the differences in density between the water inside and outside the bottle. But there are two opposite currents, one of outgoing fresh water and the other of incoming sea water. And whereas elvers may be positively rheotropic for an outward flow of fresh water, they are not so in regard to an incoming flow of sea water. They therefore do seem attracted by fresh water. We performed a similar experiment with two tanks that communicated a t their base. One was filled with sea water, the other with fresh water. Elvers were placed in one or the other and communication established. The seawater tank always lost its population to the freshwater tank. We eliminated all possible influence of pH or water oxygenation differences and were led to conclude that the important factor was the hypotonicity of the water (Fontaine and Callamand? 1941).

However, certain reservations have been expressed. Deelder ( 1958) has observed that at the beginning of their migration toward continental waters, elvers swim at night, individually, with no tendency toward shoaling, avoiding all bright light, and that they are not attracted by fresh water. A significant percentage of elvers may even flee from this environment. Later, their behaviour changes-they group together in shoals ; stronger and stronger light is necessary before signs of their negative phototropism appear, and at this time they are undoubtedly attracted towards fresh water. From such observations, however, we cannot categorically deny that the first stage of migration towards the coast is also partly conditioned by a need for progressive osmoregulation. If we introduce fresh water into a marine environment containing elvers a t the beginning of their migration towards the coast and if they shun this fresh water, it is possibly because they are not yet prepared to stand such a strong hypotonicity, whereas if these animals were exposed to water just slightly more hypotonic than the sea water in which they live, the response would possibly be different. Certain facts observed by Creutzberg (1958) can undoubtedly be explained by the need for an osmoregulation progressively adapted to less and less salty waters. This author indeed observed that the young elvers are carried towards the continent by the rising ride and that a t ebb tide they settle on the bottom. They do not pursue their

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surface course towards inland waters until the next rising tide. I n attempting to understand this behaviour, we should remember that the elvers’ energy reserves are relatively low and that osmoregulation requires a certain energy expenditure. When the elver advances with the rising tide, in the sea or brackish water masses to which it is already adapted, the energy required for osmoregulation is limited, and the fish can swim freely, using all the metabolic resources of the moment for motor activity, in addition, of course, to its basic metabolism expenditure. But a t ebb tide, that is, with the arrival of fresh waters, the osmoregulatory processes must function very actively, and the elver could not meet motor activity requirements a t the same time. It therefore settles on the bottom and may even sink into it and directs its metabolism more specifically toward osmoregulatory needs until these being satisfied, water of lower salinity stimulates elvers hidden in the sand to achieve swimming. Creutzberg (1961) made another reservation on the r61e of the low salinity factor in the attraction of elvers by fresh water. He has in fact observed that elvers attracted by the fresh water of certain rivers are not attracted by tap water, nor by the same river water if it has been charcoal-filtered. He believes therefore that elvers a t a certain stage are attracted by some, as yet, hypothetical substance. We have repeated the experiments described above (Fontaine and Callamand, 1941), basing our work on that of Creutzberg. We filled one tank with fresh tap water filtered on a column of activated charcoal and another with natural sea water. We then placed 50 elvers in the sea water tank and noted 17 hours later that only 20 out of the 50 elvers had gone into the fresh water. The freshwater attraction first observed is therefore no longer present when the water has been charcoal-treated. However, if we first charcoal-filter both sea and fresh water, the attractive value of fresh water reappears (46 elvers in fresh water and 4 in sea water after the same period). Everything happens as though there is interference of the two actions, hypotonicity on the one hand, and an ordinary organic substance or an attraction group of organic substances, which is found in both fresh water and sea water, on the other. It has not so far been demonstrated moveover that this attraction is olfactive. I n any event, the weak tonicity factor clearly reappears in this experiment. We must ask ourselves now if in the case of migratory amphihaline fish on their fluvial catadromous migration (going from fresh water to the sea), an alteration of osmoregulatory mechanisms can also be found. When examining eels migrating a t night in a large river like the Loire, a t certain phases of the moon and in the winter, the

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passive aspect of their migrtttion is very strikirig. An engineer of the French Water and Forestry Department, who is particularly wellacquainted with the biology of the eels of France, writes: “ They are almost inert bodies drifting down with the current, and simple wirenetting, wooden fencing or large bag nets placed against the current to filter the water are sufficient to capture enormous quantities a t a time.” We deterrnined the blood

chloride content of these eels and found

highly variable figures, from 2.05 g t o 4-9 g, while yellow eels showed values over 5 g. Could there be a link between this low chloride content and the eels’ passivity? We took very active silver eels and placed them in frequently renewed distilled water without food. We then noted a striking decrease in the reactions to capture, which became even more pronounced if accompanied by a lowering of the temperature. as is the case in natural conditions a t the time of the downstream migrations. Thus it does seem possible t o associate the asthenia observed with a demineralization of the organism, all the more so if we take one of these almost inert eels and place it in a balanced salt solution, for example in sea water diluted t o one-fourth ; we observe a veritable resurrection, t,he eel regaining all its agility. This pronounced demineralization of the blood, most likely the result of a long period of fasting in water of low mineral content, can undoubtedly be explained by the fact that the eel does not seem t o possess any mechanism for chloride absorption from environments of low mineral content (Krogh, 1937, confirmed by Motais, 1967)) that the animal therefore depends solely on its food supply to make up the inevitable mineral deficiency after life in fresh water, and that silver eels fast. However, asthenia and the fall in the chloride content are not evident in all groups of silver eels. I n some cases, their blood chloride level is not significantly lower than that of yellow eels. Nevertheless, the mineral content of the muscle as a percentage of the water recalculated from Callamand’s data (Fontaine and Koch, 1950) is about 15% lower for the silver eels than for the yellow eels. McCance (1944) finds an osmolar concentration that is about 9% lower. Fontaine and Koch therefore concluded that the silver eel leaves fresh water a t the moment when a demineralization phenomenon begins. I n fact, from the ionic regulation point of view, a large number of data go t o show that downstream migration is associated with an alteration of ion regulatory processes, which is not always revealed by an examination of the I.M., certain tissues like muscle, and probably connective tissue as well, being capable of releasing ihto the I.M. these ions temporarily lacking and thus re-establishing

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equilibrium, but which does generally appear a t the muscle tissue level. What is more, behaviour during migration seems linked to the mineralization of the I.M. It should be emphasized, however, that this catadromous migration cannot simply be attributed to the fact that the animal, no longer able to ensure its ion regulation in fresh water, as a result of fasting and a new endocrine condition (which will be discussed later), is chased from the freshwater environment, for we observe modifications that we cannot help considering as a preparation for life in the deep seas. Indeed eels caught in the Atlantic a t an appreciable distance from the coast, have been found a t about a hundred metres deep and they probably spawn a t a depth of several hundred metres. Preparation for marine life is apparent in a thickening of the layers of skin (Fosi, 1934) which obviously helps to isolate the fish in strongly hypertonic surroundings, and an appreciable increase in the number of gill tissue cells secreting chlorides (Colombo and Cecchini, 1959); these cells will enable the eel to resist the salt invasion that threatens it, once in the marine environment. Moreover, a few days after entry into sea water, a hypertrophy of these chloride cells is noticed and new cells differentiate and multiply, an observation which strongly suggests the existence of a preadaptation phenomenon in the fresh water silver eel, preadaptation which accentuates when the fish reaches the sea water by an adaptation phenomenon. According t o Colombo (1961), application of the histochemical chloride test to the acidophil cells gives a positive, though weak, result for freshwater and seawater yellow eels, a negative result for silver eels in fresh water, and a strongly positive one for those silver eels which have passed into sea water. These results tally with the biochemical data referred to above and indicate that catadromous migration corresponds to the silver eel’s total incapacity for absorbing chlorides a t the very weak concentration found in fresh water, but to its increased aptitude t o excrete these ions from the blood from a certain threshold and to regulate the salinity of the I.M. better than the yellow eel. This superior salinity regulation had been demonstrated by the fluctuations of serum A observed simultaneously in yellow and silver eels transferred from fresh water to sea water: the serum A of the silver eels reverted after a few days to a value observed in fresh water more quickly than that of yellow eels of the same sex (Boucher-Firly and Fontaine, 1933). The Japanese school (Utida et al., 1967) also showed that the Japanese silver eel in catadromous migration shows a higher rate of intestinal water flux and a lower rate of sodium penetration through the gill than those observed in the yellow eel in

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fresh water, traits which must also be considered as preparation for a change of environment which will bring about modifications of a similar nature. Another characteristic of the silver eel which may be considered as a sign of preadaptation to life in deep waters is the change in the colour of the retina. In the yellow eel, the retina is crimson and contains a mixture of prophyropsin and rhodopsin, whereas when the yellow eel changes into a silver eel, the colour most often becomes golden (Carlisle and Denton, 1959) with the appearance of a pigment termed chrysopsin by Denton and Warren (1956). Now this coloration is found in numerous deep-sea fish and undoubtedly has a functional significance. Indeed, the observed colour change causes a shift of the absorption maximum toward the shorter wavelengths of the visible spectrum. This shift favours vision in oceanic water several hundred metres deep, where maximum light penetration is about 480 nm. Finally, an increase in the size of the red body of the swimbladder can also be observed (Schreiber, 1938),and this author believes that the development of this gas-secreting organ is related to the eel’s penetration into deep-sea waters, which involves a more active regulation of the gases contained in the swimbladder. Let us now turn to the modifications in osmoregulation in connection with a catadromous trophic migration, that of the young Salmo salar L.,which is born in fresh water and spends several years in these surroundings before leaving for its feeding grounds. It is only after having undergone important morphological, biochemical and physiological modifications which transform the parr into the smolt that the young European salmon undertakes its catadromous migration (Fontaine, 1960).* First of all we should consider the most obvious sign of this “ smoltification ” which is the fish’s silvery tint, resulting from an important deposit of the crystalline purines, guanine and hypoxanthine both beneath the scales and in a second deep derma layer (Johnston and Eales, 1967, 1968), and examine in particular the phenomena concerning iono- or osmoregulation. It was first observed that the smolt developed a more pronounced euryhalinity than the parr, a fact *If, as a rule, in the Adour Basin, smoltifioation occurs only shortly (a few days or weeks) before migration which takes place in the spring, in certain regions (Canada) smolts may be found a t all seasons. I n fact, most salmon smoltify in autumn and they do not migrate (the majority of them but probably not ~ 1 1 )until June or July of the following year (corresponding in the region concerned-Northern Canada-to our springtime). We believe this to be a further proof of the interaction of internal and external factors in the setting off and carrying out of migrations (Power, 1958).

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which is explained today by the increase in the number of chloride cells in the gills (Hoar, 1951), by the ultrastructural modifications of these cells and of those of the pseudogill (Threadgold and Houston, 1964), affecting in particular the abundance and form of the mitochondria, by enzymatic modifications (increase in succinodehydrogenase activity (Zaks and Sokolova, 1961) and of the salt linked ATPase in the gills (Giles, 1969; Zaugg and McLain, 1972). These enzymes are localized above all in the chloride cells. All these phenomena permit elimination of the excess salt brought through the

400-

-u)

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5

-- 350E

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-0 0

E 0

E

2 v)

300-

i

f

I

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I

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8

24

I

1

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96

Hours in S W

FIG.2. Variations of serum osmolality (m Osmols) of paws and smolts of Oncorhynehzis maau during transfer from fresh water to sea water. (Utida S., personal oommunioation.)

digestive tract when the fish enters the sea and account for the two very different variations of the osmolality presented by the parr and the smolt during the passage from fresh water to sea water (Utida, 1974) (Fig. 2). According to Zaks and Sokolova (1961), smolts transferred into hypertonic surroundings behave, as far as blood and the volume of excreted urine are concerned, like marine and not freshwater fish. We are dealing once again with preadaptive phenomena, since in various species of euryhaline fish it has been shown that the passage from fresh water to sea water increases the number

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of chloride cells and N a f K + ATPase activity in the gills (Conte and Lin, 1967 ; Utida et al., 1971) as well as succinodehydrogenasic activity (Natochin and Bocharov, 1962). These preadaptive phenomena are, however, only temporary for, if the smolts are kept in fresh water, they disappear (Evropeitzeva, 1962). A sharp drop was then noticed in the quantity of C1- ions in the muscle tissue of the smolt compared with the parr (Fontaine, 1951). This observation led t o research on the possible differences between parr and smolt concerning their respective capacities for absorbing C1- ions from the weakly mineralized water in which they live. It was then observed that, all other things being equal, the parr gains these ions, while the smolt loses them (Chartier-Baraduc, 1959). Later research was to show that losses of Na + are increased by smoltification (Chartier-Baraduc, unpublished results). The observed changes affect not only NaC1, but also the K concentration, which rises in both muscles and brain during smoltification (Chartier-Baraduc, 1960). This variation undoubtedly brings about certain modifications in excitability and therefore in behaviour, especially as they are most often associated in muscle tissue with a drop in calcium concentration. Data for the blood reveal a phase of instability in its mineral composition during smoltification. I n Oncorhynchus masu, Kubo ( 1955) has noticed, during this time, a period when the blood A rises, followed, just before migration, by a period when i t drops. For Houston and Threadgold (1963), working on Salmo salar, there is a drop in plasma chlorides a t the beginning of smoltification, but this value increases with the attainment of the silvery parr stage. From Parry’s data (1961) on the same species, a somewhat similar fluctuation seems to appear concerning osmotic pressure. We will not mention all the data on this subject, but we should note that Koch et al. (1959) have observed great differences in the regulation of blood sodium between the parr, the smolt raised in captivity and the smolt in catadromous migration, by transferring them directly from fresh water t o sea water. The parrs succumbed rapidly, after having shown a marked, abrupt rise in blood sodium content; the hatchery smolts, caught when not in their migratory period, resisted perfectly, the sodium concentration in their blood remaining nearly constant in the days following the transfer. These differences between parr and smolt demonstrate well the fish’s preadaptation t o its future environment. But the smolts trapped on their downstream migration did not stand up so well to this transfer as the non-migratory hatchery smoIts ; some succumbed, others showed great distress. The concentration of sodium in the blood rose considerably during the first two days, but returned to its normal

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level after four or five days. This difference between migrating and non-migrating smolts is not a t all surprising. Migration implies continuous motor activity, which requires a large consumption of oxygen, and if, as we believe, the energy necessary for osmoregulation comes from aerobic processes, it is understandable that the migrating animal would have difficulty in increasing its ion regulatory expenditure. I n addition, migration represents a real stress for the organism, to which is then added the direct transfer into pure sea water. Finally, in nature the transfer is never abrupt, but takes place progressively in the estuaries.* These examples taken between two migratory amphihaline teleosts can leave hardly any doubt as to the existence, just before migration, of alterations in osmo- or ionoregulatory mechanisms in regard to a present biotope and of processes of preadaptation to the future environment. But we may question whether such processes really play a part in the migration of holohaline fish living in sea water of an almost constant salinity. I n fact, oceanographers know that these migrators can be found in water of varying salinity and temperature and that these two factors influence density, osmotic pressure, viscosity, speed of sound propagation, coefficients of gas absorption, ion diffusion rates, etc., all important factors in the physiology and behaviour of marine animals. It is moreover such considerations that led Sakamoto (1962) to speak of the T-C1 character of oceanic water masses affecting the movements of shoals of migrating marine fishes. Bull (1938) has also shown that certain teleosts are capable of distinguishing very slight differences in salinity-of the order of 0.06%, for sea water containing about 30 g of NaCl per litre. But it is not impossible that wideranging holohaline migrators may have a much higher degree of sensitivity a t certain times in their migratory cycle and be more sensitive t o a concomitant variation of temperature and salinity, rather than to a variation in salinity alone. It therefore seems reasonable to explain certain migrations of holohaline fish by the modifications in their osmoregulatory capacities ; Mr and Mrs Woodhead have tried to do this with cod from the Barents Sea (Woodhead and Woodhead, 1958; 1965a,b; Woodhead, 1959,a,b,c.) I n the summer, these fish are found in shallow waters in the north of the Barents Sea where they feed abundantly. I n the autumn, *However, by taking great precautions which he describes, Koch (1968) was able to carry out an abrupt transfer of freshwater smolts into sea water without any apparent disadvant.age and very slight and transitory modifications in the internal milieu.

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they leave these fishing banks and go south. The mature individuals migrate to the spawning zone near the Lofoten Islands, off the north coast of Norway. Spawning takes place in March and April. Then the fish, spent, disperse northwards and return to deep waters where they find their food. The eggs and young larvae are then transported to the same zones by the surface currents. This cod is rarely captured a t temperatures under 2"C, except in the summer from July to September, when it feeds abundantly and there is more light. Knowing that cod's body temperature cannot exceed by more than a few tenths of a degree that of the ambient environment (Britton, 1924), and drawing his inspiration from Doudoroff's work (1945) on Fundulus (research tending to show that death following a drop in temperature is caused by a disturbance in osmoregulation), the Woodheads supposed that too low temperatures led either to an excessive uptake of a ions into the I.M. or to a deficient elimination of these ions, or both ; the threat of this osmotic disturbance would be the limiting factor. The extreme temperature would vary according to the fish's physiological state : it would be lower in the summer, a period when the fish feeds abundantly and when it is probably best able t o cope with the threat which hypertonic surroundings may present for it. Using these results as a working hypothesis, the Woodheads suppose that a t temperatures below 2"C, the ionic and osmotic equilibrium of the I.M. is upset. These authors measure the blood plasma A and its chloride, sodium and potassium concentrations. They find, for cod captured on spring and winter expeditions in waters of 2", 4" and 5"C, that values are relatively well grouped and can surely be considered as physiological standards. But cod captured in waters whose temperature was lower than 2°C showed a significant percentage of values (for osmotic pressure and mineral content of the blood) above the normal values; in other words, the difference which normally exists concerning the molecular and ionic concentration between the I.M. and the external sea water environment is reduced. There seems to be a decrease in osmoregulatory ability in a hypertonic medium. On the other hand, in cod caught during the summer, not much difference is found between cod caught in waters whose temperature is higher than 2°C and those caught in water lower than 2°C. Woodhead and Woodhead (1965a) made a histological study of the gills and found, for individuals in a state of osmotic upset, a depletion of mucus and an increase in the number and size of chloride-secreting cells. According to them, the depletion of mucus permits the more rapid uptake of salts from the ambient environment into the I.M., and the changes observed in the chloride cells suggest an increase in their

+

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secretory activity to compensate for the rise in the blood sodium concentration. The facts thus seem to confirm the hypothesis. Which phenomena are capable of explaining the change in the limiting temperature observed in the course of the annual cycle? Feeding undoubtedly plays some part, for the aptitude of cod to form large schools in waters where the temperature has dropped to 0°C only appears after the copious summer feeding has begun. But it is very probable that the thyroid enters into play, as we shall see in the section on the endocrine glands and hormones. I n any event, these facts are of real importance for the problems faced by fishery technicians. Now we can understand the heavy mortality of cod observed in particularly severe winters and when they are overtaken by the cold current of the Arctic waters. Everything happens then as though they succumb before the physiological behaviour mechanisms had been able to lead them back to waters of a more suitable temperature. These observations also make it possible to explain changes in the distribution of shoals of cod and in their size, for when a penetration occurs into the Arctic waters from the Atlantic, as was observed some years back, this permits a geographical expansion of the cod northward, affecting the size of the fish by providing an abundant nourishment. Finally Hanaoka and Chu (1972) who have followed the routes of several pelagic migrators, Thunnus maccoyi Castelnau, Colalabis saira (Brevoort), Scomber japonicus Houttuyn, Trachurus japonicus and Decapterus muroadsi (Temminck and Schlegel) come to the conclusion that the O.P. of sea water plays an important r81e in their movements. They seem to migrate in waters of a certain level of O.P. which is proper to each kind of fish and may change as their maturity progresses. As far as the mackerel Scomber japonicus and the Jack mackerel Trachurus japonicus (Temminck and Schlegel) are concerned, in particular those studied in the China Sea (Chu and Hanaoka, 1973), it has been shown on the one hand that the O.P. of serum rises significantly as the maturity of the fish progresses, showing a maximal value averaging 12 Atms at the time of spawning. This value remained unchanged until the ripe eggs had completely disappeared from the ovaries, but then dropped gradually to 6 Atms. Correlatively to the rise in the O.P. of the serum, the fish move in the direction of saltier and warmer waters, but the O.P. of the E.E. rises much less than that of the body fluids, 'the least difference between the two occurring at spawning times. As many studies have proved a deterioration of the osmoregulatory mechanisms a t the time of spawning, it would seem that this condition thus reached, which

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requires a lesser osmoregulatory effort, is favourable. But to what extent does the search for a suitable osmotic pressure orientate migration? It is a t present impossible t o reply to this question. Whatever may be, a certain number of facts go to show the existence in several teleosts of modifications concerning certain iono- and osmoregulatory processes both preceding and during migration. Some of these are undeniable ; others require more thorough study or confirmation. But what allows us to suppose that we have here one of the most important and most general mechanisms of the physiological determinism of migrations, a t least amphihaline migrations, is that phenomena of a similar nature to these have been described in invertebrates. For example, Pannikar (1940, 1968) pointed out relationships which, according to him, seemed to exist between the migratory habits of certain prawns, Leander serratus Pennant (which live, during their life cycle, in waters of very different salinities) and their osmoregulatory aptitudes. I n addition, this author emphasized the importance of temperature in osmoregulation ; we are again faced with the temperature/salinity/osmoregulation trilogy described in the migration of the cod. Broekema (1941-2) suggested an explanation for the migration of the shrimp, Crangon crangon L., as the need to maintain satisfactory osmoregulation, and this has been discussed by various authors, Verwey (1957) in particular who, experimenting with other species of crustaceans, found temperature-salinity correlations different from those observed by Broekema ( 1 941-2). Physiological experimental data on a large number of species, studied until now mostly from an ecological viewpoint, are not yet sufficient t o permit a definitive interpretation. But from the work of Schwabe (1933), Scholles (1933)) Widman (1936)) Kamps (1937), Koch and Heuts (1944), it seems clear that the catadromous migration of an amphihaline crustacean, Briocheir sinensis H. Milne-Edwards, is linked with an alteration of osmoregulation in regard to hypotonic surroundings, an alteration which takes place a t the time of genital maturation and probably leads the crab to leave fresh water for the sea. Such a convergence of results for both invertebrates and vertebrates can but confirm the idea that periodic modifications of ion or osmoregulation intervene in determining the migration of many marine animals, but this is probably only one link in a very complex chain.

111. THERMOPREFERENDUM AND THERMOREGULATION It is an accepted fact that fish respond to a temperature gradient by choosing a given temperature (thermopreferendum) which appea,rs

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to be the optimal one for a given physiological state and, according to Brett (1971), there exists, a t least in the sockeye salmon (Oncorhynchus nerka), a behavioural thermoregulation, the consequence of which is to ensure a maximal bioenergetic yield. Many authors allow that this selection explains the distribution of fish in nature. But with many migratory fish which, during their migration, pass through water masses of fairly or even very differing temperatures, it is obvious that, a t certain moments of their cycle, they respond to more imperative factors than temperature, so that they no longer seek an optimal temperature but put up with the surrounding temperature which is not their thermopreferendum ; or else their thermopreferendum undergoes rapid adaptive reactions to environmental conditions; or again it varies with a physiological condition which, we know, fluctuates enormously in certain migratory fish ; or finally the fish manage to maintain an important difference between their body temperature atnd that of their environment, and this is the case for certain tunas and sharks, as we shall see later. But first let us point out that it seems obvious that a farranging migrator requires, during migration, a conduction speed of the nervous influx and a rapid muscular contraction ensuring its swimming speed and orientation which depend upon the body temperature. Speed of conduction of the nervous influx is also necessary for a rapid transmission to the nerve centres of information received by the peripheric sensorial receptors. The range of the convenient temperature varies not only according to genetic factors, but also to the water temperatures in which the fish lived previously (many studies have pointed out the importance of the temperatures of acclimatation on the optimal temperature of many vital manifestations) and according to physiological rhythms among which the distinction between exogenous and endogenous rhythms is still difficult, although we know that, in certain cases a t least, the photoperiod intervenes. Numerous investigations have shown that adjustments may be not only reactionary, that is t o say in response to changes in environmental temperature, in particular in the enzyme field, but also anticipatory of changes in temperature, just as we have seen preadaptations of the osmoregulatory function t o a change in salinity which occurs as though programmed in the life cycle of the species. NO doubt this is generally attributed to a correlation existing between a physiological character, basically biochemical or biophysical, and an external factor such as lighting. But for certain migrations, it seems that this factor cannot be concerned and future research should try to determine whether some endogenous rhythm does not exist in certain migratory species.

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But let us go back to the diverse hypotheses that we considered earlier concerning the interpretation of migratory movements in water masses of very different temperatures. I n the chapter on osmoregulation, we have seen that shoals of cod could suffer considerably high mortalities when caught during certain winters in masses of very cold water. It is doubtless at this moment that the mechanisms of reactionary adjustment are overwhelmed. But when the front of the cold water masses appears, why do the thermoreceptors not incite the cod to escape them? Several hypotheses can be put forward. One of them is that at the level of this front, prey particularly sought after by the cod-and themselves in difficult physiological condition because of their arrival in cold waters-liberate attractive ectocrine substances whose influence on the cod’s behaviour prevails over flight reactions provoked a t the nerve centre level by impulses received from the thermoreceptors. This is just one hypothesis among others, which has at least the merit of being susceptible to experimentation in stations equipped for the study of the behaviour of cod. A second hypothesis explaining the faculty of certain migratory fish for passing through environments of different temperatures is that of reactionary adjustment. Such a phenomenon has been revealed in numerous fish. It is connected with certain behaviours (swimming), certain functions (breathing), certain cellular mechanisms (enzymatic), the optimal affinity temperature of the enzyme for the substrate, and also other characteristics such as the stability of the enzyme, the dissociation rate of the enzyme-substrate complex, the enzyme’s affinity towards the stimulants and the inhibitors capable of varying according to the temperature of the environment which would be likely to bring about a modification of the steric composition of the enzymes. But usually these adaptive reactions require a certain time, a t least in species in which they have been studied, and if they may easily be assumed in certain migrators changing only very progressively from one given environmental temperature to a different one, they are more difficult to admit in long-distance migrators with a considerable speed of movement, passing very rapidly through water masses of quite different temperatures. It would be interesting to investigate here whether the speed of adaptive reaction is particularly fast, at least of the suitable stage of the migratory cycle. For the thermopreferendum can vary according to the physiological state of the organism and migrators are precisely characterized by especially vast fluctuations of diverse physiological functions. We shall come back to this point a t greater length in our conclusions. There is

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left the last eventuality, which is the fact that certain migrators are able to acquire a certain independence as far as their body temperature is concerned regarding the external environment. This eventuality has proved true, in particular thanks to remarkable studies made by Carey and Teal (1966, 1969b) who have demonstrated the capacity of certain long-distance migrators to maintain their body temperature within a much narrower temperature gap than that of the waters they have passed through. I n fact, it has been known for some time that certain tunnies can present a much higher body temperature than that of the waters in which they are caught. This difference is noticeable by a mere touch of the hand, and as early as 1835 Davy found that the temperature of Thynnuspelamis was 10°C higher than the temperature of water in which it lived. However, certain authors have thought that this phenomenon was due to violent muscular contractions made by the tunny floundering about when they emerge. But experiments made by curarizing fish and ensuring hematosis by a current of water at the level of the gills has shown that, under these conditions, an important difference remains between the body temperature and that of the ambient environment. Yet it was granted that fish cannot have a body temperature very much higher than that of the ambient environment because blood passes through the gills before reaching the tissues and that, at this level where gaseous exchanges take place, thermal diffusion being ten times as rapid as molecular diffusion, the internal milieu temperature and that of the external environment should become approximately equal. It is certain, however, that the metabolic heat warms the blood as it reaches the tissues, but the intensity of the metabolism is itself limited by the oxygen rate transported by the blood and calculations made tend to show that it is hardly likely that the body temperature of the fish can rise more than one degree above that of the environment. Since certain tunnies present differences in temperature of over 20°C with the ambient environment when this is pretty cold (a tunny has been found with a temperature of 28'8C in water a t 7 O C ) , we must allow that tunnies no doubt have some particular mechanism for preserving their metabolic heat. It seems, according to Carey and Teal, that this particularity is due to a device called counter-current present in the lateral red muscles and composed of an extensive rete receiving oxygenated blood from the lateral artery whereas the venous blood flows towards the lateral vein. This rete forms an efficient counter-currentheat exchanger. In certain tunnies, there is probably

not only a lateral rete, but also a dorsal and even a visceral rete (Kishinouye, 1923). A similar device has been described in lamnid

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sharks (Carey and Teal, 1969a), which while possessing a less important thermoregulation than the bluefin can ensure a temperature gap of 10°C between the body and water. The heat preserved by the rete warms the muscular mass, probably by conduction, as temperature gradients observed tend to prove (Fig. 3). The heating of the arterial blood, before it arrives in the tissues using it, can have the disadvantage of reducing the supply of oxygen to the tissues and even

FIG.3. Temperature distribution in cross section of a bluefin tuna. Temperatures were measured with thermistor probes a t positions indicated by curves. Heavy curves are isotherms plotted at 2°C intervals. Dark muscle is indicated by hatching. (After Carey and Teal, 1969.)

of creating a dangerous bubbling out of the blood if the warmed plasma was supersaturated. But this danger is avoided by the fact that, for the haemoglobins of bluefin, and no doubt for those of other tunnies, temperature has only a very slight effect on the P,, values (Rossi-Fanelli and Antonini, 1960). I n this species, the oxygen release a t the tissue level is most likely caused by a strong Bohr effect. All tunnies have not the same thermoregulatory capacity, as appears in Fig. 4, and we remark that the importance of the body mass is a favourable factor. Naturally, the ratio surface/weight being less in a bluefin tunny than in a skipjack, the heat loss is slower and thermo-

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regulation much better. However, it does not seem that this thermoregulation should be linked exclusively to an anatomical device and not to fluctuations of thermogenesis, as Fry and Hochachka (1970) have written. They base their affirmation on the fact that fish having struggled on the line for long periods show a lower temperature than that of fish caught in traps. No doubt, during the motor agitation exerted by the fish trying t o escape from t'he hook, there is an intensive muscular work, but this stress no doubt entails an acceleration of the

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W n : u temp " C

FIG.4. Temperatures of skipjack and yellowfin tuna; data from Barrett and Hester (1964) and from Messrs. Jones and Mather. Although able to keep their muscle warmer than the water, these fish do not appear to thermoregulate. Bluefin tuna (heavy line) are included for comparison. (After Carey and Teal, 1969.)

heart rhythm, a release of adrenalin causing dilatation of the gill vessels, so that the heat loss is greater. Moreover, the red muscle is thought to play the main r61e in normal swimming, whereas during periods of violent swimming such as those we have spoken of here, it would be above all the white muscle which comes into play, utilizing glycogen by anaerobic processes. From all we know about cellular structure, biochemistry and the metabolism of the red muscle,* which have led certain authors to attribute to it metabolic functions similar *We should emphasize above all the large quantity of mitochondria in its cells, a higher glycogen content than that of the white muscle, its great activities in the oxydation of fatty acids and sucoinic dehydrogenasic.

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to those of the mammal's liver (Bilinski, 1968), it is possible that it, rather than the white muscle, is the source of heat and as the latter is primarily concerned when the fish flounders on the end of a line, the result mentioned above, a t first view rather paradoxical, is easier to understand. Moreover, it is a question of long periods of agitation. Now the spent muscle can produce less calories than the normal muscle. For these reasons and also when noting the very wide variations in the temperature gap between the body and the water according to whether it is cold or warm, we believe that a real thermoregulation may result from several mechanisms, physiological and not only anatomical : heat production by the muscles and especially the red muscle, rate of circulation, state of dilatation or constriction of certain vascular territories, endocrine activities, etc. We should point out, however, that if we have made a clear distinction between the red and the white muscle, nevertheless a metabolic interdependence of the two muscle tissues seems to exist, even in a resting state and in particular a glucose transfer from the red to white muscle (Wittenberger, 1973). We should also note that the brain temperature of a skipjack (Kutsuwonus pelamis (L.)),even though it regulates its body temperature much less than Thunnus thynnus (L.), is 4'5 higher than that of the ambient environment when this is a t 25"6c. Considering that the brain is irrigated by blood coming from the gills and therefore at a temperature probably very close to that of the water, Stevens and Fry (1971) concluded that the brain of this tunny possesses its own heat conserving system. One single anatomical device would not be supple enough, in my opinion, to ensure a thermoregulation as remarkable as that presented by Thunnus thynnus; I think we must take it that it is associated with a physiological condition allowing the bluefin to adapt its thermogenesis and perhaps its thermolysis to the different environments it passes through. Let us recall indeed that a tunny like this one can go, in under 50 days, from the waters of the Bahamas which are close to 30°C to waters of the Norwegian coasts a t about 6°C. In all these waters, it swims rapidly, possesses its rete, yet the body temperature may be between 20°C and about 0°C higher than that of the environment. That is why we believe that in a fish of this type, its movements are linked, a t least in part, to present thermogenetic capacities. For example, the bluefin tunny found in Western Europe comes back for the season of reproduction from the northern waters into relatively warm waters and it may be supposed that, as a consequence of this vast transport of metabolites from diverse tissues or organs to the ripening gonads, thermogenetic capacities decrease. This hypothesis is not inaccessible to experimentation. Gordon (1968) has shown that

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in adult tunnies Katsuwonus pelamis and Thunnus obesus Lowe, ratios of mean metabolic rates for red muscles to those of white muscles averaged 6.2 a t five temperatures over the range of 5" to 35°C ; but what happens to the metabolisms of these muscles and their thermogenetic faculty at the moment of reproduction? As far as I know, we have no idea. But it is not unlikely to suppose a drop in both of them, a drop which would encourage the bluefin to look for warmer waters. I n the same way, we believe that specific variations of this thermogenetic capacity of diverse species of tunnies or even the intraspecific variations observed in populations of the same species (Aloncle and Delaporte, 1974) can explain, a t least partially, the great differences in eurythermia noted during their migrations. Thus thermoregulation should be included in the group of physiological regulations playing a role in migrations of certain teleost fish and perhaps of some selachians. IV. SOMEFUNCTIONS INVOLVED IN MIGRATIONS A. Respiratory function Fish migrating far show, a t least for a good part of their life cycle, great motor activity requiring an important respiratory metabolism. It may also be-and this opinion holds good for certain migratory fish such as mackerel-that the high metabolism of fish (genetic and ethologic character) obliges it to swim constantly in order to ensure a rapid renewal of water a t gill level. But continuous, rapid swimming is not sufficient to characterize a migratory behaviour, which must be orientated-at least a t certain times in the cycle. However, this great activity of migratory fish has led several authors to suppose that they were looking for waters either specially rich in oxygen (e.g. R o d e (1914, 1920) studying salmon on anadromous migration), or a t low CO, levels, this search resulting from an increase in tension in the internal milieu (Powers, 1940, 1941 ; Powers and Clark, 1943). However, the observations arising from these investigations do not make it possible to consider either the oxygen content of the water or the CO, level as factors guiding migrations of fish in a general way. They can be looked upon only as factors limiting geographical expansion when their levels fall below or rise above a certain threshold or subsequently deflecting the main directions of migration. These considerations in no way minimize the importance of the respiratory function, which is of course high for migratory fish and we have proof of this in the adaptation and preadaptation phenomena which have

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been revealed a t this phase in preparing the organism for the passage from fresh water to sea water (smoltification). Let us recall that smoltification of Salmo salar is accompanied by an increased respiratory metabolism (Baraduc and Fontaine, 1955) and that the migratory forms of Coregonus sardinella Berg in marine waters have higher oxygen consumption (respiratory) rates and higher metabolism rates over the body weights, temperature and activity ranges studied than do the same species isolated in a freshwater lake (Wohlschag, 1957). A preadaptation of haemoglobins t o the respiratory function a t sea is favourably envisaged by Vanstone et al. (1964), since, according to these authors, salmon present this particularity t o synthesize, in the adult, two haemoglobins already indicated by Eguchi et al. (1960) and which present higher oxygen affinities than embryonic or larval haemoglobins. Now the passage from highly oxygenated fresh water t o marine waters which are less so, makes the fish, in the latter environment, draw benefit from respiratory pigments of higher oxygen affinity. Their distribution into two classes with different physical properties would assure adequate transport and unloading over a wider range of environmental conditions than if only one class were present. Since these investigations, Koch et al. (1968), using the isoelectric focusing methods, have found in the blood of a sexually mature salmon as many as 25 haemoglobins a t extremely varied isoelectric points, for the p H went between 5.9 to 9. The plasticity of the rates of these diverse haemoglobins during a lifetime favours the hypothesis that this great capacity for qualitative and quantitative variations is an adaptation factor of the respiratory function to conditions in very varied environments. Numerous haemoglobins have also been found in the eel by Poluhowich (1972), which can have the same meaning ; however, this author points out that many haemoglobins exist in nonmigrating species, so that this is not a particular trait of migratory species, but more probably a mechanism functioning during times of metabolic stress and which may serve as a buffer against marked changes in the properties of the respiratory pigment during various seasonal variations in the aquatic environment. We should also note that respiratory metabolism rises during smoltification, even in sedentary fish. This capacity for a high respiratory metabolism is doubtless useful to ensure, on the one hand, the accelerated growth observed during smoltification, on the other, the metabolic expenditure required by migratory motor activity, and lastly the osmoregulatory expenditure imposed by the coming change of environment. Finally, if numerous authors have not observed an accelerative action on

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respiratory metabolism of teleosts of thyroid hormones or T.S.H., many authors have noticed such an action and that the thyroid hyperfunctioning particular to smoltification in Salmo salar may be, a t least in part, responsible for this increase in respiratory metabolism. When a fish crosses a zone where oxygen content is below the threshold ensuring normal respiration (the case of the salmon in waters of certain estuaries where 0, concentration is slight as a result of organic pollutions), it may, as Smith et al. (1972) have shown with Oncorhynchus kisutch (Walbaum),have recourse to anaerobic metabolism and contract a debt in oxygen allowing it to maintain its swimming and make its respiratory and cardiovascular functions able to adapt to this low level of oxygen. But if the oxygen level is too low for this adaptation to be sufficiently rapid and if the insufficiently oxygenated water mass is too wide to cross, then the fish will be in a critical situation owing to the increase in the lactic acid level in the blood, causing a drop in p H and therefore affecting the oxygen binding capacity of the blood. No doubt in this case the kidneys can excrete lactate, but the excretion rate may not be sufficient to avoid a fall in pH and moreover this lactate loss represents an energy leak. The depletion of anaerobic stores of energy (glycogen) in the muscle (Stevens and Black, 1966) causes fatigue. The fish can no longer detoxify ammonia, nor excrete it through the gills, There is every reason to believe then that the fish slows down its swimming or rests on the bottom (and that is no doubt why, in certain polluted estuaries, the migration speed is seen to slow down in comparison with clean estuaries), or it lets itself be carried by the current into marine waters without obeying the homing commands, however imperious they may be; and this is why perhaps, in certain overpolluted rivers, salmon have disappeared. I n certain cases, it is’ possible that the fish avoids underoxygenated waters, even before entering them. These are the avoidance reactions studied experimentally, particularly by Whitmore et al. (1960). Thus the requirements of the respiratory function in the presence of certain environmental conditions can modify migratory behaviour. On the other hand, migratory behaviour modifies respiratory intensity and if active swimming increases it, schooling decreases it (Parker, 1973). Thus the respiratory function does play an important rBle in migration, but I do not believe it either instigates it nor orientates it. It can, however, give a certain character to migratory behaviour. For example, it is no doubt to induce a better haematosis at the gill level that smolts on catadromous migration often descend, a t least in the Pyrenean streams, their head facing upstream.

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B. Circulation Circulation is a function which certainly intervenes too in migratory behaviour, at the periphery (gills, kidney), at the tissue level and in particular with the red muscle in exchange mechanisms of heat. We know that adrenalin dilates the gill vessels since it diminishes the resistance to the blood flow through the gills (Krawkow, 1913 ; Keys and Bateman, 1932), which proves that this hormone certainly intervenes in exchanges at the level of this tissue and the increase of adrenalin in the blood of the s m o l b i n comparison with the parr-speeds up haematosis and consequently facilitates the higher respiratory metabolism of the smolt. But it also increases the surface of exchange of salts and may play a rBle in the deteriorations of ionoregulation mentioned above. I n the following section, we shall see how this action can be compensated by the neuropituitary hormones. I n any event, the rise in blood pressure in the dorsal aorta and the cardiac rhythm after an injection of adrenalin (Randall and Stevens, 1967) in the salmon shows that the rises of physiological adrenalin content such as those observed in the course of the migratory cycle, particularly during smoltification, certainly facilitates migratory behaviour. Some modifications of the circulatory function can therefore participate in the preparation for the migratory stage, but nothing permits us to assert that this is the prime mover.

C . Excretion Excretion is a function which, without doubt, plays an important part in the physiology of migrators, but we cannot be sure that it contributes to determining migration. We should recall, however, that when amphihaline teleosts are preparing for their catadromous migration, everything occurs as though the gill was preparing itself to carry out the functions of ion excretion in the sea environment (see preceding section). The kidney behaves likewise. We know indeed that diuresis is lower in seawater fish than freshwater ones and this is considered to be due to the fact that freshwater fish live in a hypotonic environment and are constantly invaded by water ; seawater fish, living in a hypertonic environment, are threatened, on the contrary, by water losses. But, curiously enough, the smolt of the migrant Oncorhynchus nerka shows a remarkably low diuresis (in comparison with freshwater fish) and an exceptionally high salt content of the urine (Zaks and Sokolova, 1961). Similarly, the smolt of Salmo gairdneri Richardson, a euryhaline fish, has a diuresis

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(ml/h/kg) of 1.6 as against 3.8 at the pre-smolt stage (Holmes and Stainer, 1966). Now the smolt stage is the one which in many euryhaline salmonids is the sign of catadromous migration. Even before having left its environment, diuresis decreases. This may be due to the fact that smoltification is accompanied by a decreased permeability of the gills which can itself be caused partly by an increase in the activity of Stannius corpuscles, as their ablation seems to bring about an increased gill permeability. As for the increase in the elimination of salts by urine, it explains the reduced chloride content of the smolt muscles mentioned in the preceding chapter. If furthermore the young 0. nerka caught during their catadromous migration, are kept in fresh water, their diuresis, which is slight to begin with, increases, however, as the osmotic pressure of urine decreases, that is to say that its urine elimination characteristics, which were becoming in the migrant smolt like those of a seawater fish, revert to those of a freshwater fish, when the catadromous migration is stopped (Zaks and Sokolova, 1965). Let us note that excretion can play a r61e in the marking of a territory and a water mass and also has a part in the homing phenomena examined in the section on " Sense Organs ", but we have no reason to be sure that it is a kidney excretion; it may be a cutaneous one.

D. Reproduction It may seem surprising that we have not devoted a section to the function of reproduction in this article, although so many migrations are so-called reproductive. But even if everything occurs as though reproduction appears to be the aim of certain migratory stages and of a programme in which many functions are at play (accumulation, followed by utilization, of reserves to ensure the inevitable energetic expenditure occasioned by a long displacement and to supply the material necessary for the evolution of the gonads ; biosynthesis, then release, of diverse hormones of a protide and steroid nature to bring about the maturing of the gonads; neurohormonal elaboration of a reproductory behaviour ensuring the act of reproduction itself, etc.), we do not possess any proof that the said function intervenes in a primordial fashion in the physiological determinism of a migration, albeit reproductive. Sexual maturing often begins a t the same time, but often after modifications of other physiological functions and in particular integration mechanisms which play a more direct r d e in the setting off and the course of migrations. It is therefore impossible at present to a e r m that the reproductive function directly conditions the preparation and setting

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off of great migratory stages. It should not, however, be deduced from this that no interactions exist between preparation for reproduction and migration. It is evident that this would be a serious error. It is probable for example that the decrease in thyroid activity, in certain fish approaching reproduction, results, a t least partly, in a reduced biosynthesis in the pituitary of a glycoprotein with a thyrotropic effect, a reduction which makes it possible t o use certain elements necessary t o this synthesis for the increased elaboration of another glycoprotein hormone partially different from the gonadotropic hormone. Likewise the hypothesis may be put forward that the use of lipids during migration and the fast preceding reproduction in numerous species can cause an inhibition of certain stages of sexual maturing. Neither can the effect of sexual hormones be excluded on the motor activity characteristic of certain stages (Hoar et al., 1955) and on certain sensitiveness allowing recognition of the spawning grounds (see p. 315). But if the capacity for ensuring reproduction-and so the perennity of the species-seems inevitably to be the justification of so-called reproductive migrations, the reproductive function has not so far brought sufficient light to enable us to explain them.

E. Metabolism Certain characteristics of various metabolisms and in particular lipid metabolism doubtless play an important part in the migrations of fish-as they do moreover in the migrations of birds-but it seems that this r d e is permissive rather than the instigation of migration and that is why we shall not go into any detail about it here. We should point out however that great migrators are fish which constitute a t a certain moment of their life cycle important lipid reserves and note the remarkable correlation existing in the shad of the Caspian Sea (Table I) between the percentage lipid content of the various species and the length of the anadromous migration that they must make in the Volga t o reach the spawning grounds (Nikolsky, 1963). Idler and Bitners (1958, 1959, 1960), in the course of a very complete study on Oncorhynchus nerka, have moreover shown that fats and protein provide the major part of the energy necessary for anadromous migration during the synchonic fast (Mislin, 1941) accompanying the maturation of the gonads. A relatively small part of the fats is used t o elaborate the gonads (8% for the 9 and 0.5% for the 3). The major part together with the proteins covers the energy expenditure required by constant muscular activity and that is no doubt why, with the great migrators, most of the lipids are found in contact with the muscular tissue itself, being close to the place

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where they are used, making it easier for the muscles to draw on the reserves for their activity. It was thought for a long time that the adult anchovy Engraulis encrasicholus (L.) left the Azov Sea in autumn only because of a sudden fall in the temperature of the water, but then it was found that this migration could begin a t various temperatures, some of them relatively high. Later it was shown that the anchovy could not start its migration before reaching a certain degree of fattening (Lebedev, 1940). Those migrating first are the fattest, followed by others less so. Migrations involving %he highest number of fish are those of animals with the highest lipid rate. Less fatty fish migrate in small shoals, few TABLEI. PERCENTAGE FATCONTENTIN THE FLESH,AND LENGTH OF MIGRATIONUP THE VOLGA, OF VARIOUS SPECIESOB CASPIAN SHADS

Name of j s h

Blackback, Caspialosa kessleri Grimm Volga shad, Caspialosa volgensis Berg Caspian shad, Caspialosa caspia (Eichw.) Large-eyed shad, Caspialosa saposhnikovi

Per cent f a t content

Approximate maximal length of course u p river ( k m )

16.0

1000

8.71

500

748

100

5.61

0

(Grimm)

in number. So long as the fish has not accumulated a suficient quantity of lipids, i t does not start its migration, remaining in the Azov Sea where it may perish from very low temperatures. The higher the fatty level, the more the fish is able t o set out on its migration following a slight drop in temperature, for example in waters a t a temperature of 19°C. Lower fatty rates require more important drops in temperature (waters of 14" t o 9°C) so that the anchovy can migrate. I n this example then the interaction of external and internal factors in setting off migration is seen clearly as also in behavioural modalities. We do not believe, however, that it is the accumulation rate of lipids related t o a given temperature which is directly responsible for setting off migration, but rather certain elements of a physiological condition corresponding t o this fatty

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state in terms of a particular temperature, a condition of hyperphagy and an especially high aptitude to develop fatty reserves, not only from lipids, but also from proteins and glucids in food. These data are very important for fisheries in predicting the size of shoals leaving the detroit and the time of their departure. That is why fishery services pay the greatest attention both to weather forecasts and to the fattening process (Shulman, 1972). Similar facts have been described for other species in different areas and have demonstrated that the external factor intervening in the start of migration may not necessarily be temperature-or a t any rate, temperature alone-but also a change in the direction or force of the currents, the level or transparency of the waters, the disappearance or decrease of food. Signals triggering off migration can therefore be varied and this probably ensures a better regulation of migratory behaviour and tends to protect fish from situations which could be critical. We should note that the migration of young anchovies from the Azov Sea appears to depend on mechanisms very different from those of adults. It occurs 6 to 9 weeks before adult migration, in waters of high temperature and with relatively low lipid reserves. It seems to Shulman that the decrease in the quantity of food available-to be shared with the adults who are now feeding intensivelyis an important factor in this migration of the young. I n other types of migration, the catadromous migration of the young smolt or the young sturgeon, it is the fall in fatty reserves which corresponds to the preparation for migratory behaviour, and in Oncorhynchus nerka, for example, the young fish having fattened the least leave first (Akulin, 1966). Thus lipid metabolism appears involved in a certain number of migrations but no doubt only in so far as it depends on internal factors (neuroendocrine states), some of which intervene directly in setting off migratory behaviour, together with certain external factors (temperature, currents). We shall return to this point, arising here in a study of lipid metabolism, in a more general manner in our conclusions. Let us now call attention to the fact that everything occurs as though the intermediary metabolism showed adaptive reactions to long migrations. Thus in the case of starvation imposed on the eel, the activities of the glycolytic, the citric acid cycle and especially the hexose monophosphate shunt enzymes decrease in the muscle. However, although the silver eel does not feed, it shows a higher activity level of the hexose monophosphate shunt and an enhanced metabolism as a whole, compared to the yellow eel. The higher activity values of the oxidative enzymes in both red and white

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muscle of the silver eel compared to those of the yellow eel resemble the differences between a trained and an untrained muscle. Holloszy (1967) and Kraus and Kirsten (1969) have shown that the activity levels of oxidative and respiratory enzymes increase while those of the glycolytic enzymes remain constant as a result of training. The mitochondria were more numerous and larger, with more densely packed cristae, as was found by Gollnick and King (1969). The succinate dehydrogenase activities of isolated mitochondria1 fractions of white muscle in the yellow and silver eel were measured by Bostrom and Johansson (1972). The higher value found for the silver eel indicates that its mitochondria have a greater oxidative capacity. Also the silver eel has several times more red muscle than the yellow eel and this red muscle will no doubt be very useful to the silver eel in its prolonged and unflagging swim that it will accomplish-probably without taking nourishment-up to the laying area. The red muscle generally contains more lipids and glycogen than the white muscle. It possesses a larger number of mitochondria and a higher vascularization. Bilinski (1963, 1968) has shown that the red muscles of the salmonids possess a far more active fatty acid oxydating system than the white muscle and several authors agree that the red muscle produces the continuous swimming movements to maintain the fish a t its cruising speed, the white muscle being used €or short bursts of vigorous activity, but this distinction is still questioned (Johnston et al., 1972; Gatz, 1973). Barnard et al. (1970) has shown that training increases the amount of red fibres, but this change requires a fairly long lapse of time. Is the increase in motor activity, which we believe is determined in the silver eel by the thyroid and interrenal hyperfunctioning and which causes at the same time the silvering, sufficient to explain this increase of the red muscle mass? It would be imprudent to reply affirmatively to this question. But whatever the case, the differences described by Bostrom and Johansson between the enzyme activity patterns in white and red muscle of the yellow and the silver eel tend to indicate a pre-adaptation to the long migration awaiting the silver eel. Glucids certainly play an important r61e in fish migration. I n the Salmo salar, during anadromous migration, glycogen losses undergone by the liver between the start of migration and spawning are approximately equal to the quantity of glycogen accumulated in the gonads. If we think of the considerable muscular energy expenditure that this migration represents and the active life led by the salmon until reproduction, we are bound to infer that this muscular activity draws its strength directly from the lipids or in the

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gluconeogenesis arising from certain lipids and amino acids coming from muscular reduction or more probably from the coexistence of these diverse mechanisms. As glycogen concentration and stocks remain more or less constant in the organism during this synchonic fast of several months, it may be supposed that in salmon mechanisms exist remarkably adapted to regulating gluconeogenesis on a probably important glycogenolysis. Simizu (1948) points out that the arginine and histidine content in the muscle is particularly high in migrators and Cowey and Parry (1963) find in the muscle of Xalmo salar an important increase of creatine a t the passage from the parr t o the smolt stage and they interpret this phenomenon as a greater availability of phosphagen (a phosphoryl creatine) for endergonic reactions involved in the long voyage the young salmon will make to reach the fattening grounds. Besides this remarkable aptitude, we must emphasize the excellent energy output of all reserves used, all the more so that protids take an important place among them and that they are considered less efficient than lipids and glucids. The metabolisms of various migrators seem then well adapted to requirements of diverse types of migration. They are essential to the accomplishment of these migrations, but there is no ground for believing that they instigate and guide them. They merely allow them t o take place and that is why we have treated them rather summarily.

V. INTEGRATION MECHANISMS A. Endocrine glands These mechanisms most probably play an important r81e in the preparation, the setting off and the accomplishment of migration. We may assume this from certain facts concerning endocrine glands and the neuroendocrine system. First of all we shall take a look at those relating t o two glands that endocrinologists used t o call dynamogenic for they appeared to play a particularly important part in the dynamism, the vitality of individuals, and although this term has now been abandoned and seems today rather out-of-date, the study of migrators gives it some justification. They are the thyroid and the adrenal glands. I n fact, in the teleost migrators that we are studying above all here, the thyroid does not appear in the shape of a well individualized gland, but in the form of islets, dispersed along the ventral aorta. As for the adrenal, the two essential parts distinguished in higher vertebrates (adrenal cortex and medulla) are

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here dissociated and dispersed in cellular agglomerations, of two types, one corresponding bo the cortex, called interrenal (for they are found in the form of one or several masses between the kidneys in certain selachians), the other called chromaffin tissue (medulla). 1. Thyroid The most important observations regarding the r61e of this glandular formation and the hormones it secretes in migratory behaviour concern catadromous migration of amphihaline teleosts. As early as 1939, Hoar pointed out an active hyperplasia of the thyroid during the smolt stage and Callamand and Fontaine (1942) showed that in the silvery eel the thyroid is, according to histological criteria, more active than in the sedentary yellow eel. Since then, as a result of histological, chemical and radiobiological research, various studies have confirmed and defined this stimulation of the thyroid function during transformation preparing the freshwater fish for marine life (cf. in particular Fontaine, 1956). I n the young Salmo salar having spent one or several years in the river and having already changed to a silvery colouring, thyroid iodine in its diverse forms (mineral, organic, thyroxin) rises significantly a t the start of smoltification, goes through a maximal stage, then diminishes to reach, in the migrating smolt, very inferior values t o those observed in the parr. I n the blood, iodine content is correlatively maximal in the smolt, but without increase of thyroxine iodine and with a drop in the relation of protein iodine to total iodine; the excretion of radioiodine increases. Moreover the ratio t/s (1311 total in the thyroid/1311 t o 100 mg of blood) determined in a fish whose intrathyroid organic liaison of iodine has been previously inhibited by an antithyroid represents rather closely, as has been shown, the concentration power of iodines by the thyroid. Now this ratio increases in the course of smoltification and reaches its maximal value in the smolt. The secretion rate of the thyroid hormone is 0.058 pg hormonal iodine per lOOg body weight per day in the parr, 0.084 in the silver parr and 0.140 in the migrating smolt (Leloup and Fontaine, 1960). Thus it is possible t o conclude from these investigations and histological observations that during smoltification, a stimulation of the thyroid by the thyreotropic-pituitary hormone occurs, bringing about a release of thyroid hormone. This thyroid hormone is moreover responsible-at least in p a r t f o r the silvering of the young salmon. We say in part, for if the action of thyroid hormones on the smoltification of salmonidae has been clearly shown by several authors

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(Landgrebe, 1941 ; Robertson, 1948; Laroche et d.,1950; Fontaine and Baraduc, 1954), cortisol, whose content rises in the smolt’s blood, also intervenes in the deposit of guanine in the scales, as has been proved by experiments of injection of cortisol in trout, followed by a dosage of guanine in the scales (Fontaine and Martelly, 1974). This excess of thyroid hormone is rapidly catabolized because of the high metabolism of the smolt. Under the influence of T.S.H., the synthesis of the thyroglobulin is more intense, but its proteolysis is even more so, so that the gland loses thyroglobulin as the histological pictures and chemical dosages show. In the smolt then, we are in the presence of a hyperstimulated thyroid, this hyperstimulation probably reaching a maximum during migration since the struggle against the current stimulates thyroid activity (Fontaine and Leloup, 1959). Thus it may be assumed that at first a rise in the secretion of the thyroid hormone increases motor activity in the smolt (Hoar et aZ., 1955), but that later T.S.H. may intervene more or less directly as it is supposed to do in the states described in man by Bier and Roman (1931), Mahaux (1947))states of motor upset, of hypermotivity and tachycardia observed in patients showing, as in smolts, a drop in the relation of organic iodine to total iodine in the blood. The T.S.H. causes moreover a significantly increased swimming in the stickleback (Baggerman, 1964). This endocrine disturbance lessens or disappears when the smolt reaches sea water (Fontaine et al., 1952). Moreover, we should note that by ingestion of iodated casein or by a thyroxine wash, a pseudo-smoltification ” of the trout can be obtained, that is to say morphological modifications-in particular a silveringwhich is very like smoltification. Now these trout thus ‘‘ smoltified ” show an increase in euryhalinity (Fontaine and Baraduc, 1954). It may be supposed then that thyroid activity which sets off-or contributes to setting off-smoltification must also, at least in part, be responsible for the increase in euryhalinity towards hypertonic environments, which is observed in the passage of the parr to the smolt. These results must also be compared with those obtained by Baggerman (1963) showing that T.S.H. administered to young Oncorhynchus kisatch brought on a modification of their halotropism which from being negative became positive. But we believe that the particularly intensive motor activity engaged upon and sustained until arriving in the estuary is an essential factor in migration. Indeed the parr remained on the look-out in the gravel, always swimming close to the bed. The smolt leaves the gravel, rises midway towards the surface, swimming vigorously, even leaping (I

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frequently out of the water and this is how the spring floods carry it down to the sea. Once having left the uneven bed of the mountain torrents, it no longer finds the relatively calm zones where, hiding under stones, it could shelter from the current, often violent, of the spring floods. This description concerns the Salrno salar of the Adour basin in France and is quite striking. However, it is not clear whether this fact is common in the amphihaline salmonids, for if Oncorhynchus kisutch and 0. nerka show a definite smoltification phase with increased activity of the thyroid, some authors have described certain Oncorhynchus which descended t o the sea very soon after hatching without any conspicuous change in colouring. But Zueva (1965) has returned t o the problem of 0. keta (Walbaum) which descends to the sea about a month after having emerged from the bed and 0. gorbuscha (Walbaum) which goes out to sea immediately after having left the niche. 0. keta, a t the beginning of its life has in fact variegated colouring, but when descending it becomes silvery. As for 0. gorbuscha, it was long thought that it underwent no smoltification, because it did not present the characteristic colouring of the parr. But Zueva has shown that this arises from the fact that it develops within a very short lapse of time. True, there is a preliminary melanose pigmentation producing certain patches corresponding to those, more marked, of the Salmo salar parr, followed a t once by a deposit of guanine. And certain modifications of the histological picture of the thyroid are interpreted by Zueva as a sign of increased activity in the thyroid. It seems therefore that all salmonids can be said to have probably passed through a more or less marked stage of thyroid hyperactivity, first appearing before the first catadromous migration and being more or less precocious and prolonged. We should point out that thyroid hormones may intervene in determining the high proportion of porphyropsin present in the visual pigments of the young salmon Oncorhynchus kisutch when it nears the smolt stage and during this stage (Beatty, 1966, 1969). Moreover it has been shown (Beatty, 1972) that in 0. nerka the administration of T, or T,, as also T.S.H.-and under certain lighting conditions-brings about an increase of porphyropsin (an effect contrary to that observed in the frog (Wilt, 1959; Ohtsu et al., 1964). Cristy (1974) has been able to show the positive effect on this phenomenon in Salmo gairdneri not only of thyroxine, but of prolactin. As for the second catadromous migration of the mended* Salmo salar, and although histology reveals in the thyroid, alongside patches *Mended : a salmon having spawned, but having regained its silvery colouring and on the point or in the course of descending t o the ma. A.31.U.-13

10

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of disorganized tissues, groups of active and budding follicles, signs that the gland regenerates, thyroid secretion is low (Fontaine and Leloup, 1962). It may be that this secretion (much slighter than in the smolt) (Leloup and Fontaine, 1960) is related t o the facts that on the one hand the mended fish is at the end of its long fastand starvation in the salmonid diminishes the thyroid function (Fontaine and Fontaine, 1956)-on the other hand that the mended fish’s migration is accomplished with much less motor activity than in the smolt. Thyroid secretion definitely increases some days after arrival in sea water and this fact should be considered in conjunction with the rapidly recuperated muscle activity seen in the mended fish when it reaches the sea (Jones, 1959). One point remains t o be cleared up: is the recovery of the silvery colouring, when the kelt* becomes mended, due t o a phase of thyroid activity? We can give no answer to this question as we were unable to examine a salmon kelt in the process of silvering, but we shall come back later t o this point. The stimulation of the thyroid of the eel, during transformation of the yellow eel into the silver eel, observed histologically by Callamand and Fontaine (1942) and Bernardi (1958) has been confirmed by chemical studies (Leloup, 1959). However, the histological, biochemical and radiobiological study of the thyroid function should be made a t different times during migration so as t o understand clearly the differences in migratory behaviour of the smolt and the eel. Indeed, whereas the former shows constant activity during the whole of its downstream course, the silver eel only gives signs of great activity in the initial stage of its migration when it leaves the ponds, for example, to join the streams and rivers leading it t o the sea. At this moment, this activity is evident, depending at the same time on internal factors, among which is thyroid activity, and external ones t o which the fish is probably sensitized, no doubt owing t o its neuroendocrine condition. This is so true that, in certain regions, fishermen keep eels captive and watch their activity in order t o find out which night they should cast their net a t the exit of the pond, when they do not have a t their disposal a permanent capture chamber. It is also known that in autumn, silver eels placed in an aquarium at certain moments make repeated efforts to leave the water environment and that in the wild it is not rare t o find, in the morning, eels running across the damp fields. This tendency to amphibiosis may also be justified by a hyperthyroidism, as a result *Kelt : a salmon having spawned, but not yet having become silvery.

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of Harms’ observations following a histological study of the thyroids of gobies and blennies (aquatic ancestors of the amphibious Periophtalmids and Salarias, the latter composing for some authors a family, that of the Salaridae, whereas for others they are included in that of the Bleniidae). Harms’ observations (1935) show indeed a considerable transformation of thyroid formations with the passage of aquatic larvae to adult amphibians, a transformation which he interprets in the sense of a more intensive functioning. But it is above all his experimentation which is interesting. Several species of Periophtalrnus do in fact exist, very varyingly adapted to amphibiosis. Now Harms has worked on species scarcely adapted to terrestrial life, such as P . chrysospilos and P . schlosseri and he has treated them with the thyroid hormone, either by adding thyroid extracts to the water, or nourishing them with some thyroid, or by transplantation of the thyroid of the mouse. And he has seen these animals leave the water, spend several hours emerged, become progressively amphibians and even acquiring the morphological characteristics of P . argentilineatus Cuvier and Valenciennes, a species in which amphibiosis is most marked. Harms has even been able to bring about amphibiosis in a typically marine species, Blennius ocellatus, by feeding it with thyroid. This blenny left the water completely, breathing air for eight hours a t a time, then diving back for a moment into the water, after which it took up its place once more on a totally emerged stone for several hours. These are the facts which suggest that this tendency to amphibiosis in eels which occurs right a t the beginning of this catadromous migration may be attributed to the thyroid function.* The hypothesis has been put forward that thyroid stimulation taking place before or right a t the beginning of migration may be responsible for changes in pigmentation observed a t this time in the retina of the eel. I n fact, we must remember that in silver eels porphyropsin disappears and only rhodopsin remains (Bridges, 1972). But whereas in certain silver eels a h max around 500 nm is found, as might be expected, in others the h max is situated a t 487 nm, close to the typical position of special rhodopsins (or chrysopsins) of deep-sea fishes. Thus two transformations of the visual pigments seem to occur in the eel, the first involving the replacement of porphyropsin by rhodopsin, the second of rhodopsin by chrysopsin, of a wavelength more appropriate to the blue colours of the future *However, Bliim et al. (1972) do not believe the thyroid is responsible for the change of habitat in Blennius pawo Risso, although it affects the multiplication of mucous cells by means of T.S.H. and with prolactin.

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environment. As in the frog, Rana ccctesbiana (Wilt, 1959 ; Ohtsu et al., 1964), the administration of thyroxine brings about a large increase in the proportion of rhodopsin in the ocular pigments, it has been possible t o put forward the hypothesis expressed above. But it would be necessary t o experiment on the eel itself, for we have seen that the action of thyroid hormones on the composition of the said pigments in salmonids is very different. Moreover the change mechanism from rhodopsin to chrysopsin remains unknown. Where does this hyperthyroidism itself come from? Probably from a pituitary stimulation as we shall see later. The triggering off of this or these endocrine stimulations can be looked for in osmo- and ionoreceptors, since we have seen earlier that catadromous migration was preceded by a deterioration of certain ionoregulatory mechanisms and that in higher vertebrates the administration of thyroid hormones can compensate for the increased loss of sodium caused by hypothyroidism or thyroidectomy, whereas in the toad, thyroxine determines an increase of the intake of Na from the environment and of the resorption of ions a t the vesical level. Thus a feedback mechanism may be supposed. Amphibiosis can likewise be considered as a behavioural reaction with the effect of diminishing the drop in certain tissues of certain ions. However, Koch and Heuts (1942) point out that freshwater sticklebacks fed on thyroid powder mixed with breadcrumbs show much lower values of total osmotic pressure and chloride contents than those of the test sticklebacks. If in the eel hyperthyroidism produced a similar phenomenon, then it would no longer appear as a mechanism of hydromineral regulation but as a factor of the deterioration of this regulation, and therefore as one of the causes of migration. I n certain mammals moreover, Zaimis et al. (1969) believe that a treatment with thyroxine is responsible for a perturbation of the cellular membrane linked with an inhibition of the active transport of certain ions. But, in the eel, after this first phase of great motor activity, comes, a t least in certain of our rivers, a phase of reduced activity in the course of which everything happens as though the eels let themselves be dragged by the current (see p. 2 5 2 ) . Is there a t this moment a drop in thyroid activity? It is possible and this could be due to the low temperature of the river waters, since this phenomenon appears in autumn and winter, but t o our knowledge, the intensity of the thyroid function in this precise phase of migratory behaviour has not been measured. Another species, Mugil cephalus L., has been studied in the course of its catadromous migration (Leray, 1968). I n the immature young,

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this author finds an active thyroid, but it is much less so in older animals accomplishing their reproductive migration. If the thyroid activity of young mullet can be compared with that of smolts, that of mullets nearing reproduction is no doubt more comparable with that of the mended fish, in the two latter cases, most of the glycoprotein syntheses in the pituitary being or having been orientated to the biosynthesis of the gonadotrope hormone rather than to that of T.S.H. Whatever may be, it is certain that the thyroid gland plays an important r61e in certain aspects of catadromous migrations, whether of thalassotocous* or potamotocous** amphihalines. It probably intervenes too in anadromous migrations. As far as the young European eel is concerned, we should recall that when nearing the continental shelf, the leptocephali are metamorphosed into elvers. From an examination of the thyroid a t the time of this phenomenon, Sklower (1930) concludes that the metamorphosis mechanism is for a large part of a thyroid nature, for he notices a stimulation of the thyroid during this metamorphosis. But since then, other authors have noticed phases of thyroid activity later than this metamorphosis, for Von Hagen (1936), a t the moment when it passes from sea water to fresh water, for Franqois (1941), during pigmentation. We have seen earlier (p. 248) how the thyroid function can intervene by way of an alteration of the osmoregulatory function. But it also intervenes by its effect on the positive rheotropism, which is reduced by the action of an antithyroid drug. Vilter (1944) observing that a population of elvers in an anadromous migration in a small Mediterranean river showed various types of thyroid activity, deduced that the thyroid gland took no part in migration. It is rather a hasty conclusion. It should be emphasized that if elvers manifest the same behaviour a t the precise moment of capture and sampling, they will not do so the following days. It seems evident then that if the thyroid plays a r61e, as we believe, in positive rheotropism, individuals of a same strand must be a t varied thyroid stages, since this strand decreases from day to day, leaving the elvers sedentary all along its path. We must remember indeed that thyroid hormones seem to exercise a relatively slow influence on the poikilotherms and that their span of life is definitely longer than in mammals of the same weight, particularly in cold water as is the case in the rivers of our regions that the elvers reach in winter or a t the beginning of spring. It is thus possible to imagine the existence in elvers of a thyroid with limited activity, whereas the action of a preceding *Thalassotocous : spawning in sea water. **Potamotocous : spawning in fresh water.

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depletion of the gland still exercises some influence a t the surface. It is probable that in a strand, the elvers of different thyroid activities-according to histological criteria-correspond t o individuals ascending more or less far up the river. I n the same way, the behaviour of elvers remaining in coastal waters can no doubt be explained in part by a lesser thyroid activity. Facts are found in various papers supporting this idea. Let us recall that according to Bellini (1907), elvers reaching the continent a t Comacchio could be divided into three groups according t o their length: elvers of 56 to 61 mm, others of 63 to 73 mm and finally those of 78 to 84 mm. Bellini having reared them separately in basins situated inside a pond, noticed that the small elvers produce only males, the medium and large ones only females. This distinction between the three groups of elvers appeared arbitrary and has been criticized, but the general result remains and the experiments undertaken later, in particular those of Rodolico (1933), clearly confirm this notion that the small elvers produce a majority of males, those larger a majority of females. Now it is known that the thyroid hormone is an important factor in growth in fish as well as in mammals, and all other factors apart, males of slower growth thus appear hypothyroid in relation t o the females. On the other hand, it must be emphasized that thyroxine is considered by endocrinologists to be a feminizing hormone stimulating production of folliculin. And this notion fits perfectly in the framework of our hypothesis, since the majority of males meet around the estuaries, whereas the majority of females swim farther up the rivers. I n certain basins, it even seems that the percentage of the female sex increases fairly regularly with the distance from the ocean. Thyroid activity would therefore seem linked t o positive rheotropism and to an inclination towards the female sex. Of course certain exceptions can be put forward to refute this law of the distribution of the sexes in terms of distance from the sea. One finds, in certain coastal waters, an almost equal percentage of females and males and in some inland waters the male sex dominates. As far as the first exception is concerned, it apparently occurs above all in coastal waters which do not communicate-or only in a very limited fashion-with inland waters, so that everything happens as though eels with high thyroid activity, destined t o become female, find themselves incapable of swimming up t o inland waters. D'Ancona (1946) has clearly expressed this opinion regarding the coastal waters of the Adriatic : " I n the coastal ' sacchi ' ", he writes, '' and in open lagoons, there is a predominance of males, for

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the small eels destined t o become females escape to penetrate into the ‘ valli ’ and the rivers descending from inland. I n this migration, the small potentially female eels continue their ascent until they reach some insurmountable obstacles. Consequently the valli which are better closed on the side of inland waters will give a higher proportion of females, whereas those which are more permeable in the direction of inland fresh waters will produce smaller eels of the male sex.” As for populations with a male majority found several hundred kilometres from the sea, it may be supposed they come from elvers of female potentiality and which have therefore penetrated far up into the inland waters, but which, as a result of particular conditions (physical and chemical characteristics of the water, food) have developed into a sex different from the one to which they belonged genetically. Experiments made by d’Ancona, Tesch, Gandolfi-Hornyold (see Bertin, 1942), consisting in the transfer of eel populations from an environment, whose sex ratio is known, into another one quite different where a considerable modification of this sex ratio will be seen, prove the likelihood of such an interpretation. Let us point out too that the tendency shown by the elvers during their ascent, t o escape from the aquatic environment, also agrees with the hypothesis of an active thyroid functioning, as we mentioned earlier in connection with Harms’ experiments. As for the potamotocous amphihaline teleosts (Atlantic salmon, sea trout, Alosa) whose thyroid function we have examined in fresh water at the start of their anadromous migration, we have always found a very active thyroid function by histological, chemical and radiobiological methods. And this activity decreases considerably when we investigate individuals captured on the spawning grounds a t the time of reproduction. We believe then that this thyroid activity has a part in the positive rheotropic manifestation and this opinion is borne out by the experiment consisting in separating a given population of elvers into two lots and estimating the intensity of their rheotropism when they mount an inclined surface over which runs a current of water feeding the aquarium in which they are kept. Now it is found that a preliminary treatment by thiourea, an inhibitor of the thyroid hormone synthesis, decreases this rheotropism very significantly. This thyroid activity at the time of the upstream migration is not necessarily a consequence of the passage from sea t o fresh water. Indeed, Lahaye (1966) has noticed, both in holohaline freshwater populations of Alosa alosa L. and in the amphihaline populations of the same species, that ana-

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dromous migration corresponds t o a definite increase in thyroid activity. Another rather important thyroid activity is also found in immature young about to descend t o the sea. Thus the relation between thyroid activity and migratory behaviour seems (Lahaye’s data are only histological) rather comparable t o that observed in the salmon. The thyroid gland very probably plays a r81e in the migratory mechanism of holohaline fish. The Woodheads (1959) have observed in the course of the Barents Sea cod’s cycle, which was mentioned earlier (p. 257), that the thyroid gland becomes active in autumn, a t the moment when the temperature limit rises to 2°C and slows down in spring, some weeks before the fall of the temperature limit. This thyroid activity corresponds to the migration period from the banks of the Barents Sea t o the spawning zone in the Lofoten Islands and is probably an important physiological element, since the Woodheads have shown that fish treated with thyroxine swim faster (35%) than the test ones. Let us note also that during the sardine’s metamorphosis, BuserLahaye and Ruivo (1954) have noted a sudden and considerable increase in the whole volume of thyroid follicles; once metamorphosis is accomplished, the relation of the volume of the thyroid to the weight of the body lowers. Now to this metamorphosis of the larval form of young fry corresponds a profound change in ecological behaviour. The larvae which until now have led a pelagic life in waters of the open seas, come t o the coast into warmer and sometimes less salty waters. The thyroid of tuna has been studied by diverse authors (Honma, 1956 ; Olivereau, 1957). The authors’ descriptions indicate an active, highly hyperemiazed gland ; but in the absence of data concerning both diverse phases of the cycle and biochemical studies, it is difficult t o attribute t o it with certitude the role it probably plays in the accomplishment of these immense migrations. Obviously more numerous data, a t different stages of the migratory cycle would be necessary, together with biochemical measurements, but there seems t o be hardly any doubt that the thyroid plays an important role in the migration of marine and amphihaline fish, and in a general manner by increasing the excitability of the central nervous system (Timiras and Woodbury, 1956) and by facilitating the accomplishment of a great physical effort (Ardeleanu, 1971). But i t is known that, a t least in mammals, thyroid hormones increase the excitability of the central nervous system by a double mechanism : direct stimulation and indirect stimulation by means of an increase

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in the secretion of hormones of the adrenal cortex and medulla. Let us first take a look a t the counterpart of the adrenal cortex of highly developed higher vertebrates, that is to say the interrenal. 2. Interrenal The interrenal is another glandular formation which clearly seems to intervene in the determinism of these migrations. Indeed both in course of smoltification in the salmon and during silvering of the eel, a hyperplasia of the interrenal is seen and a hypersecretion of adrenal cortex steroids. Let us take the case of smoltification: we see, during the transformation of the parr into the smolt, a considerable increase in volume of the interrenal, since it doubles in size, and obvious cytological signs of hyperactivity. At the same time, the plasmatic rate of the hydrocorticosteroids increases considerably and, as well as cortisol (a steroid normally present in the parr), cortisone appears. This appearance of cortisone results probably from such a stimulation of the interrenal that the 11-hydroxylasic capacities of this tissue become insufficient for secreting only hydrocortisone. The highest secretory activity seems t o be reached a t the parr-smolt stage, before it has commenced migration. Thus, although swimming against the current causes in the trout a stimulation of the interrenal (Fontaine and Leloup, 1959), the stimulation seen during smoltification has nothing t o do with migratory activity, for the young salmon is sedentary a t this time. This internal stimulation has no doubt some connection with hyperthyroidism noted earlier and with a hypersecretion of the growth hormone which itself may be assumed from the speeded growth evident in the smolt and pituitary cytology examination (Fontaine and Olivereau, 1949). It seems then that metabolic expenditure increases greatly. Indeed, although the smolts feed abundantly, glycogenic stocks are drawn upon from the liver. It appears therefore that exogenous energetic provisions are insufficient t o cover the energetic expenditure of the smolt and the organism may call upon a hypersecretion of corticosteroid to promote the process of gluconeogenesis indispensable for maintaining the energetic equilibrium of the migrator, thanks to a hormonal action synergy (not only action of the thyroid hormones, but also potentialization by the growth hormone of ACTH action). This increase of corticosteroids probably intervenes to facilitate adaptation when passing into the sea, for administration of adrenocortical steroids to salt loaded specimens of rainbow trout increased the excretion of sodium (Holmes, 1959), whereas corticosterone

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reduces the glomerular filtration rate of this species in fresh water (Holmes and McBean, 1963). Let us consider now the transformation of the yellow eel into the silvery eel. I n this case too, the mass of interrenal cells which form quite a sheath around the lumen of the anterior cardinal vein develops very distinctly and the cortisol rate in the blood rises (Leloup-Hatey, 1964). Recently Lewander et al. (1974) published results which seemed a t first to differ somewhat from those of Leloup, but in fact this may be explained by the very different experimental conditions of the two experiments. I n fact, the samplings of the Swedish authors were made on eels captured in brackish water of 6 to 7%,, transported into sea water of 30%,,then sacrificed after 10 days in this environment, whereas the experiments made by Leloup concerned yellow or silvery eels from fresh water. Now yellow eels probably suffer from osmotic stress for much longer than silvery eels preadapted t o the passage from fresh water to the sea. Thus a week after the change of environment, the silvery eels present a plasma whose osmotic pressure has reverted to its initial freshwater value, whereas yellow eels are very far from having recovered this initial value after 13 days in sea water. At this moment, the molecular concentration of their blood is still far below its preliminary value (Boucher-Firly, 1935). One may suppose therefore that the yellow eel is still in a state of osmotic stress inducing the secretion of cortisol, whereas silver eels have gone beyond this stage and have adapted themselves. Whatever the case, it would certainly be desirable not to limit the comparisons made between silver and yellow eels, and between parrs and smolts to cortisol content, but apply them to speeds of secretion and metabolic clearance of cortisol, these measures being now possible (Leloup-Hatey, 1974). Let us note that this cortisol, together with the thyroid hormones, no doubt plays a r8le in the appearance of silvering, since Epstein et al. (1971) have shown that injections of this hormone (400 pg per 100 g per day) in yellow eels for 7 to 10 days change their colouring to that of eels in catadromous migration. These eels, transported without transition into pure sea water, show a smaller rise in chloride content than the non treated yellow eels. Moreover, it has been shown that cortisol in interrenalectomized eels placed in sea water makes survival possible, ensuring a net flux of Na excretion a t the gills level so that a relatively constant Na plasmatic concentration is maintained (Mayer et al., 1967). Cortisol also plays a r81e in adaptation to sea water by increasing the absorption of water a t the intestine

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level, a water movement associated with the active transfer of ions, especially C1 ions (Utida et al., 1972) and at the level of the urinary bladder (Hirano et al., 1973). Let us point out too that the injection of cortisol (Epstein et al., 1971 ; Kamyia, 1972) induces a rise in Na-K ATPase specific activity in the gill filaments and intestinal mucus. Now these two phenomena have been observed when transporting eels from fresh water to sea water. It should be emphasized then that here once again in the eel, adaptation mechanisms precede change of environment. However, we may also recall that the injection of cortisol increases the influx of sodium in the hypophysectomized freshwater eel and that this increase in interrenal activity observed in silver eels may be a defensive reaction against demineralization which is setting in. To resume, cortisol seems to react favourably against threats of osmotic unbalance in fresh water as in sea water, stimulating in particular the displacement of sodium in a direction favourable to homoestasis. Cortisol probably takes an important part in this catadromous migration by promoting the processes of lipid transformationsparticularly abundant in the silver eel-and of protid into glucids. The silver eel is fasting; it will accomplish a very long migration comprising a relatively passive stage, swimming downstream, after which probably, when reaching the ocean, it will show motor activity and find in the glucids the necessary metabolites to ensure this activity. The glucocorticoids secreted by the interrenal stimulate glucogenesis and thus allow the eel to maintain its glucid reserves, in particular hepatic glycogen. Besides, if hypophysectomy is performed on the eel, thus putting the interrenal to rest, we observe a decrease in the glucocorticoids circulating in the blood and correlatively a decrease in the liver glycogen. We have no data demonstrating that the interrenal plays a r61e in anadromous migration but as cortisol encourages ion absorption in fish in fresh water, this hormone can intervene favourably in adaptation during the passage from sea water to fresh water. But the activities of these two glands, thyroid and interrenal, are evidently under hypothalamo-pituitary control ; the fact has now been well established in teleosts as in higher vertebrates. It is therefore probable that signs will be found of modification in the activity of this axis during preparation for migratory behaviour. 3. Hypophysis

Already Evans (1940) has noted an important increase in the size of the two glandular and nervous lobes of the eel’s pituitary during

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the two months preceding catadromous migration and, in the glandular lobe, a hyperemia and an increase in the number of eosinophil cells. He came to the conclusion that activity increased in the adenohypophysis. Bernardi (1948) has observed, in the course of transformation of' the yellow eel into the silver eel, the formation of follicles and the presence of colloid in the adenohypophysis, and in the middle glandular region, an increase in the number of basophil cells. I n the purs neruosu, she points out the presence of large ependymary vacuoles. This double series of studies shows that important modifications exist in the functioning of this gland during this migratory period and simultaneously an important thyroid activity, a preliminary development stage of gonads and an interrenal stimulation leading to suppose that the cells secreting glycoproteic hormones (gonadotrope and thyreotrope) as well as the corticotrope cells are more active and/or more numerous. Knowles and Vollrath (1966a) have indicated that thyreotrope cells are highly active in the silver eel ; they believe on the other hand (1966b) they have observed a vacuolization of gonadotropic cells during the passage of the yellow to the silver eel; but Olivereau (1967) has criticized this and has not seen any definite modification. However it is clear that these studies should be resumed using the most recent techniques and in particular immunocytochemistry and radioimmunoassay, a t any rate if sufficiently purified fish hormones are available to be able t o use these techniques with a certain reliability. As far as the preparation for catadromous migration in the young Salmo salar is concerned, cytological observations made on the hypophysis of this fish when it passes from the parr state to that of the smoIt allow us t o believe that the hypophysis stimulates the target glands whose hyperactivity we have seen earlier (Olivereau, 1954). The degranulation of the cyanophil cells called delta, which are thyreotropic, suggests a release of T.S.H. which is responsible for the stimulation of the thyroid modifying, a few days later, the halopreferendum of young salmon. It is known in fact that the juvenile Pacific salmon, on its seaward migration in spring is associated with a change from fresh to sea water preference (Houston, 1957 ; Baggerman, 1960; McInerney, 1961). Now Baggerman (1963) has shown that underyearling coho salmon treated with T.S.H. showed a change from fresh to salt water preference, which was correlated with an increase in thyroid activity (as measured by the amount of radioiodine taken up by the gland and the conversion ratio). The treatment by thiourea shows a change from salt water to fresh water preference, which was accompanied by a decrease in thyroid activity. So the

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secretory activity of the thyroid gland (itself brought on by T.S.H.) is intimately involved in the induction of changes in salinity preference. In the threespined stickleback which lives in winter in the sea or in brackish water and migrates to fresh water in spring, then a t the end of the breeding season migrates back to the sea, Baggerman (1957) has noted that thyroxine induces a freshwater preference in animals initially preferring salt water, whereas thiourea (a thyroid inhibitor) induces a saltwater preference in fish initially preferring fresh water. All these facts show clearly the importance of the pituitary-thyroid axis in amphihaline migrations. I n the young Salmo salar in course of smoltification, the increase in the percentage of fuchsinophil cells and their degranulation allow us t o suppose an increased production of ACTH which accounts for the stimulation of the interrenal and therefore for some action on ionoregulation by way of the Na and K activated ATPase (Milne et al., 1971), and which can also play a r81e in the memorization of feelings allowing homing, sincs Murphy and Miller (1955), Miller and Ogawa (1962) have shown that the administration of ACTH to rats results in resistance to extinction of a conditioned avoidance response. But the hypophysis does not act through its target glands alone. It very probably secretes at this moment the growth hormone in greater abundance for the cells to which this function devolves become much more numerous and we know that smoltification corresponds to a phase of accelerated growth. This secretion acts on migration by potentializing the influence of ACTH on the interrenal and by increasing the salinity tolerance, as Smith (1956) has shown in trout, and by inducing a preference €or sea water in stream-resident underyearling coho. It is still difficult to reply to this question as to whether S.T.H. acts directly or by the intermediary of the interrenal. But this stimulation by S.T.H. secretion is probably linked to the increased motor activity (Schriider and Pfeiffer, 1973) which is evident during smoltification, reaching a maximum a t the time of migration itself. It would appear that prolactin above all plays an active part in anadromous migration, for it reduces the loss of Na and chlorides in freshwater fish and maintains the water balance by increasing the urine output. The general effect of prolactin is evident in particular a t the level of the gills, the kidney and the urinary bladder and, a t least in some cases, of the gut (Stanley and Fleming, 1966, 1967; Lam and Leatherland, 1969; Utida et al., 1972; Hirano et al., 1973.) This action is connected with the variations of the (Na+ K f ) dependent ATPase (Picliford et al., 1970). Prolactin is indispensable to several marine

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euryhaline fish such as Fundulus (Pickford and Phillips, 1959; Nagahama et al., 197 3) or amphihaline ones with a limited migration (Gasterosteus( (Lam, 1972), for their survival in fresh water. However, the great amphihaline migrators, such as salmon and the adult eel do not seem so dependent on prolactin as the smaller species just mentioned. Thus, the hypophysectomized eel bears up very well to the passage from sea water to fresh water and vice versa (Fontaine et al., 1949). Nevertheless, prolactin cells appear more active in the elvers entering fresh water than the adult eel moving from the river into the sea (Knowles and Vollrath, 1966 ; Vollrath, 1966), so that it may be supposed that this hormone plays a r6le in maintaining hydromineral equilibrium during the passage from sea water to fresh water occurring in the course of the elver’s anadromous migration and no doubt by acting on diverse effectors. This is how, in the starry flounder, Plutichthys stellatus (L.), prolactin intervenes at the urinary bladder level in reducing osmotic permeability to water and increasing sodium and chloride absorption (Hirano et al., 1973). As for salmon, McKeown and Overbeeke (1 972) notice no definite change in the granulations of prolactin cells during the passage from sea water to fresh water of Oncorhynchus nerka during its anadromous migration. In several other salmonids, prolactin cells have been described as being notably active in sea water and important quantities of this hormone have been determined in the hypophysis of 0. nerka and Mugil cephalus captured in ,sea water. We believe then that prolactin can exercise one or several physiological influences other than this one, so spectacular in certain fish, discovered by Pickford and Phillips and that its intervention does not seem essential in the sea to freshwater migration of salmon. Nevertheless, i t appears that this hormone may play a r81e in the migration upstream of the ayu, Plecoglossus altivelis Temminck and Schlegel (Honma and Yoshie, 1974) since, in the course of this migration from sea to fresh water, which occurs immediately after spawning, a hypertrophy and degranulation of prolactin-producing cells are seen whereas these cells in the fish kept in sea water showed only a few of these changes. It probably intervenes too in reproductive migration from fresh water to sea water of Mugil cephalus and probably other mugilids (Abraham, 1974). Indeed several studies suggest an antagonistic action between prolactin and gonadotropin. Thus certain observations made by Grant and Pickford (1959) on some species of teleosts indicate a decrease in pituitary prolactin at the start of spawning. Bliim (1966) has noticed that gonadotrope cells are inhibited by prolactin. Abraham et al. (1966) and Blanc-Livni and

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Abraham (1970) have observed in mullets kept in freshwater ponds and consequently without any possibility of returning to the sea, an increase in prolactin secretion and a decrease in gonadotrope activity. Priihs (1973), after experimental studies on Xiphophorus helleri, came t o the conclusion that prolactin inhibits the secretion of gonadotropins and provokes in the ovaries an increase of corpora atretica. Thus Abraham supposes that prolactin secretion diminishes a t the time immediately preceding the thalassotocous migration, imposing on the one hand the passage into sea water and on the other allowing the synthesis of gonadotropins. But the obvious activity of prolactin cells in the salmon or the mullet in sea water proves that it plays a rhle. Though these hypotheses do not exclude others, it seems that prolactin participates in water economy in Platichthys stellatus in sea water by stimulating water reabsorption from urine (Hirano et al., 1971) and in Anguilla japonica Temminck and Schlegel by reducing the absorption of water and salts a t the gut level (experiments made on the isolated gut) (Utida et al., 1972). It promotes mucous secretion (Lemoine and Olivereau, 1973), a mucus probably intervening in osmoregulation mechanisms and necessary to the defence of the organism against diverse attacks. Lastly, it promotes lipid deposit for this is one of the most generally recognized influences exercised by this hormone in teleosts under certain conditions (Joseph and Meier, 1971), and also birds and mammals (Bern and Nicoll, 1968). I n this case, it plays an important preparatory part in migration, permitting the accumulation of energy reserves in poikilotherms and in homeotherms. But prolactin certainly has an important effect on the anadromous migration of Gasterosteus aculeatus L. trachurus form, as Lam (1972) has demonstrated with several arguments t o corroborate this. It is striking t o note how the importance of prolactin in the aptitude t o pass from sea water t o fresh water decreases with the size of the animal. Perhaps the ratio exchange surfaces/body weight being greater in small individuals than in large ones, prolactin is more essential to the former. This hypothesis seems to receive confirmation in the work done by Sage (1973), showing that in Mugil cephalus transferred from sea water t o fresh water, a negative correlation is observed between pituitary prolactin content and body weight. Perhaps too the eel finds in its abundant mucous secretion a slowing down factor of exchanges making the effect of prolactin less essential, although the effect of this hormone on hydromineral exchanges in this species has been demonstrated also. We may wonder too whether on the other hand the hydromineral unbalance preceding and accompanying downstream migrations could

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not be compensated for following an insufficient secretion of prolactin or the ineffciency of prolactin in this state. This last hypothesis may be envisaged, for Umminger (1973) has noticed that prolactin in goldfish cannot compensate for the perturbed hydromineral regulation resulting from a stress and that migration can be considered a stress. We also feel we cannot exclude a role of M.S.H. in the physiology of migrations, considering the part now assigned t o this hormone in the functioning of the nervous system, particularly in memorization phenomena. We may recall that as early as 1960, Guillemin and Krikov showed that, in the mammal, M.S.H. increases the amplitude of the evoked potentials a t the level of a monosynaptic reflex arc and causes a facilitation effect. A release of M.S.H. being suspected during smoltification (blackening of certain regions of the body in the course of this transformation), it seemed t o us interesting to see whether differences could be revealed in this connection between parr and smolt. NOW we have obtained, in young hatchery Salmo salar, results in favour of the hypothesis of increased biosynthesis and release of M.S.H. in the smolt in comparison with the parr. Indeed, if we compare, a t both stages, the M.S.H. content of the hypophysis* of individuals kept on a white background under a constant light for 4 days-that is to say very pale-with individuals kept in total darkness during the same period and very dark, we obtain for the parrs the following values, expressed in unity p.mg. dry weight of the hypophysis: light 2 435-3 050, darkness 1 400-1 215, and for smoltified individuals : light 4 255-4 556, darkness 708-781. Each value is obtained on a pool of hypophyses of 6 individuals and the differences between parr and smolt in the same lighting conditions are significant, as also, a t a given stage of evolution (parr or smolt), the differences obtained between light and darkness. Thus, in the parr, when the release of M.S.H. is blocked or considerably slowed down by exposure t o bright light, an increase of about 110% in M.S.H. content of the hypophysis is obtained. I n the smolt under the same conditions, this increase is 492%. This fact bears out the hypothesis of a more important M.S.H. biosynthesis in the smolt. Moreover the much lower content in the smolt’s hypophysis in the dark, despite an increased biosynthesis by smoltification, leads us to suppose a more important hormone release than in the parr. The whole M.S.H. metabolism turnover seems thus accelerated in the smolt. De Wied and Bohus (1966) seem t o have been the first t o draw attention t o the r6le played by u M.S.H. (and ACTH) on the retention *Technique of Shizume et al. (1954),modified by Kastin et al. (1969).

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of a conditioned behaviour in a mammal. This result has given rise to many studies. I n particular, owing to the fact that Sandman et al. (1969) noticed that administration of M.S.H. t o rats causes rebention of a learned appetitive task, which implied an effect on the persistence of memory, that other experimental studies have shown that M.S.H. determines in man an increase in the average soinatosensory cortical evoked response and improvement in the performance of the Benton visual retention test, results suggesting an effect on the processes of attention (Kastin et al., 1971), that adaptive responses in rats having received M.S.H. (De Wied et al., 1968; Sandman et al., 1969, 1971 ; Kastin et al,, 1973) seem t o be explicable only by an increased visual attention and their reproduction with greater fidelity and less error, it is possible t o imagine that this increased M.S.H. production in the smolt plays a r61e in the process of attention and memorization that the acquisition of physiological and biochemical conditions permitting homing must imply. It would of course be most interesting t o look for the effect of M.S.H. not only concerning the retention of a conditioned behaviour but also, in the case of a positive response, on cerebral R.N.A. and peptides (see Nervous system, p. 301). It must also be emphasized that, according to Segawa et al. (1973), mice treated with M.S.H. show an increased sensitivity to external stimuli, a phenomenon which would tally with the fact that the smolts are apparently very meteorosensitive and sympathicotonic. Perhaps we should not completely rule out the part played by M.S.H. in the increased Na loss in the smolt, since in a rat, hypophysectomized or surrenalectomized, overloaded with water, a natriuretic effect of M.S.H. has been revealed (Orias and McCann, 1972). It would be worthwhile looking for such an effect in fish. Aldinger et al. (1971) have also described in the dog, under the influence of this hormone, an increase of ventricular contractile force and heart rate. This phenomenon, if confirmed in fish, could play a role in migratory behaviour. As far as the gonadotropic hormone is concerned and although many migrations are called reproductive because everything occurs as if their object is the accomplishment of the reproductive act in the most favourable conditions, it does not appear as though its r61e in triggering off or accomplishing migration is indubitably evident. When the Salmo salar reach the mouth of the Adour to carry out their anadromous reproductory migration, their gonadosomatic relation is generally no higher than that of the smolt when it leaves fresh water for its feeding grounds. I n certain cases however, rather rare for we have never witnessed one, females have been seen with eggs already

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developed, but this is exceptional. Pituitary cytology seems moreover to confirm that there is no important gonadotropic activity a t the beginning of the ascent. Bsrannikova’s observations (1957, 1965) are similar as far as the anadromous autumn migrations of acipenserids and salmonids are concerned. However, it would be interesting to find out by more sensitive methods (for example, uptake of P32 by gonads in waters on the feeding grounds compared with those near the estuary) if the ripening process has not started when the salmon begins its anadromous migration. We should remember too that several species of Oncorhynchus arrive in the estuaries, coming from the Pacific, with genital glands already considerably developed. It would be interesting t o see in these individuals if gonadectomy inhibits or not upstream migration. As far as the catadromous migration of smolts is concerned, female individuals are apparently in a genital state of rest, as they were during their whole juvenile life in fresh water. It is more interesting t o look a t male smolts, for it is known that an important percentage has reached genital maturity and these individuals have fertilized adult female eggs on the spawning grounds in December. Now, amongst these, the majority present testes having reverted t o a relative state of rest, greater than that of individuals leaving for migration without having reproduced and which are filiform, but which do not present the latescent aspect of the ripe testis. However, we have been able to observe smolts on catadromous migration which were still latescent. We have written still latescent, for we suppose them t o be fish having reached genital maturity on the spawning grounds and having maintained it until migration t o the sea. We cannot therefore write, like Evropeitzeva (1960), that the processes of smoltification and migration on the one hand and of genital maturation on the other are incompatible processes, biologically opposed. It is none the less true that, in the majority of cases, smoltification occurs in individuals who either have never been sexually ripe or who have been ripe in December to January, but whose testes have reverted or are in course of reverting t o a quiescent state. This is fairly understandable today, in the light of what we know of the great chemical similarity of gonadotropic and thyrotropic hormones. It is probable that the important quantity of T.S.H. necessary in the preparation for migration can only be produced if the glycoproteins are not mobilized t o elaborate the gonadotropic hormone. Whatever these hypotheses may be, the fact remains that this migration can take place a t very varied stages in the ripening of gonads. The gonadotropic hormone cannot therefore be considered a factor either favouring or slowing down migration. Besides, Bagger-

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man (1957)) when observing the migrations of an amphihaline stickleback, although apparently linked to the reproductive cycle, also came to the conclusion that the gonadotropic hormone does not play a primary r6le in the causation of migration. However, as far as the eel on its downstream course is concerned, the intervention of the gonadotropic hormone is more likely, for it is known that during the eel’s change from yellow to silver, a primary phase of the development of the gonad has taken place, which is not negligible, for the gonadosomatic ratio can, in certain cases, double or more. But this evolution seems to have been undergone progressively, and to have been stopped a t the moment when the eel leaves for migration. It is known that if it is kept in fresh water, no development of the gonads is observed, Moreover, pituitary cytology shows no really significant difference, regarding gonadotropic cells, between the yellow and the silver eel, which allows us to attribute a change in behaviour to the corresponding hormone (Olivereau, 1967).

We have therefore no reason to suppose that, in the abovementioned migrations, the gonadotropic hormone plays an important r61e. Our stand is very different concerning certain holohaline migrations during which the gonads begin to ripen before migration and continue simultaneously. I n this case, it would be interesting to find out whether the blocking of the gonadotropic function modifies migratory behaviour. Moreover certain experiments carried out by Idler (1973) give reason to believe that the fluctuations of a sexual steroid in the internal milieu could intervene in the choice of an environment during amphihaline migrations. Indeed Atlantic salmon kelts were acclimatized to brackish and then to sea water. During the ensuing months, they resumed feeding and were vigorous and active. However, when they were then injected with long-lasting oestrogen, they died within a few days and there was a considerable loss in weight. A few fish that were transferred to fresh water survived the oestrogen treatment. This observation suggests various hypotheses and experiments. It would be particularly interesting to compare the oestradiol contents of the blood of wild amphihaline salmon reproducing in fresh water and of salmon bred and reared until reproduction in sea water. As far as the hormones of the nervous lobe are concerned, as their elaboration is closely linked to neurosecretory phenomena, their possible r6le will be discussed with that of the nervous system.

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We would also like t o point out tha,t medullary adrenal tissue is stimulated during smoltification of the young salmon. Indeed, the adrenalin contents of the blood rise (Fontaine et al., 1963) a t this stage and it is moreover possible that this phenomenon plays a part in the previously observed thyroid stimulation, as it has been seen in mammals that adrenalin and noradrenalin provoke a release of thyroid hormones by the intermediary of thyroid receptors, similar or identical to adrenergic receptors (Melander, 1970) and this phenomenon contributes, together with silvering and the thyroid hyperfunctioning, motor behaviour having increased, t o support the diagnosis of a more accentuated sympathicotony than in the parr. Now sympathicotonics are particularly meteorosensitive individuals. This state can therefore explain the very high sensitivity to these meteorological or hydrodynamic fluctuations which seemed to us minor but which however, in springtime, when the fish are physiologically prepared, bring about a massive drop. Moreover the high adrenalemia of the smolt, by diverting the circulation to preferential circuits in the lamellae, to the detriment of the central compartment of the filament, facilitates oxygenation of the blood, but also increases the passive movements of water and electrolytes and can contribute t o a demineralization of certain tissues of the smolt. It now remains, to close this section on endocrine glands, for us t o imagine the possibility of a r61e played by the small glands situated on one side of the kidney, the Stannius corpuscles, which affect the permeability of certain cells, and thereby osmo- and ionoregulatory phenomena. Indeed, when the young salmon smoltifies and when the yellow eel transforms into a silver eel, a very definite stimulation of these corpuscles is observed, a stimulation marked by numerous mitoses, an increase in nuclear diameter and a holocrine melting of secretory cells. How far is this stimulation a part of the stimulation mechanism just described? If we perform an ablation of the Stannius corpuscles on an eel, we note, during the days following the operation, a progressive reduction in motor activity, a reduction which can be stopped by injecting Stannius corpuscles. These glands are therefore doubtless more or less directly associated with the dynamogenic stimulation of the thyroid, the interrenal and chromaffin tissue. On the other hand, following an ablation of Stannius corpuscles, a fall in sodium and chlorine content and a rise in calcium and potassium content in the blood are observed. These modifications react on the ionic ratios of the muscle and brain. For five K Na weeks after the ablation of the corpuscles, the ratio drops Ca

+

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progressively in both these tissues, the

Na ~

299

+ K ratio also undergoing

+

-

Ca Mg a significant drop, though less so (Fontaine and Poncet, 1969). Now we know that neuromuscular excitability is related to this ratio, decreasing and increasing a t the same time as it does. We may imagine then that the variations in these ratios are a possible and partial explanation of the influence of Stannius corpuscles on motor activity This stimulation of Stannius corpuscles may be also considered a reaction t o drops in Na and C1 increasing in the smolt. On the other hand, we know the passage from fresh water t o sea water of an eel causes a stimulation of Stannius corpuscles. So the stimulation observed in the smolt and silver eel may be interpreted as a preadaptive reaction regarding calcium like those we have already mentioned concerning, for example, chloride cells or the ATPase content of the gill. Indeed, the ablation of Stannius corpuscles brings about, as we have seen, a rise in calcium content, which results from an increase of the net flux of Ca. Stannius corpuscle extracts constitute a barrier t o these phenomena. We may therefore suppose that during the passage from fresh water to sea water, active Stannius corpuscles fight against an abnormal rise in calcium content in the organism. We have besides noted (Fontaine and Chartier, 1974) that when placed in a bath of CaClz a t 18 g per litre, eels deprived of Stannius corpuscles die much more rapidly than sham-operated. Following immersion in the bath for 98 hours, we have 0% mortality for sham-operated and 50% for those deprived of Stannius corpuscles ; 140 hours afterwards, 50% mortality in sham-operated and 100% in the tests. On the other hand, Pang and Pang (1974) showed recently that Stannius corpuscles of Ictalurus punctatus (Rafinesque) are richer in the hypocalcemizing factor (hypocalcin) in fish adapted to calcium enriched fresh water than those from catfish adapted t o low calcium fresh water. Johnson (1972) has observed, in Mugil cephalus, a greater interrenal activity in fresh water than in sea water and vice versa for Stannius corpuscles. However, it is impossible to conclude from this data alone that the interrenal and Stannius corpuscles affect the determinism of migratory behaviour, all the more so that different fishing techniques are used a t sea (beach seine) than in fresh water (gill net) and that the corresponding stresses were probably different and may have intervened in the histological differences noted. I n conclusion, we should emphasize the participation of numerous glands or endocrine formations in setting off migratory motor activity and the accomplishment of migration, and draw attention to the

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fact that the relative importance of these diverse glands can probably vary according to the species, the phase of migration, diverse internal and external factors, so that the fact that a dynamogenic gland is seen to rest in a given migratory condition does not mean either that the mechanism is not partly endocrine, or that this gland does not intervene at another stage or in another species in a predominant manner.

B. The nervous system The nervous system, another integration apparatus, certainly acts on migratory behaviour, if only by the information it receives from the sense organs in the form of messages transmitted by sensorial or sensitive nerves and the messages it transmits itself in diverse sectors of the organism, either in the form of nervous influx, or in the form of neurosecretions, sometimes in response to occasional external or internal stimuli, or resulting from exogenous or endogenous rhythmic phenomena (biological clock). Data a t the moment are too fragmentary for a satisfactory synthesis to be made of the r61e of the nervous system in the preparation, start and accomplishment of migrations ; they demonstrate however that the nervous system intervenes in migratory behaviour, which in turn intervenes in the functioning of the nervous system. Concerning this latter point then, let us recall that the study of total amino acids of the brain has not revealed differences between parr and smolts, but in free amino acids a significant increase of threonine and glutamin has been observed following smoltification (Fontaine and Marchelidon, 1971). The increase in glutamin may be supposed t o have some connexion with the increase of motor activity in the young salmon during smoltification, for such a correlation has been observed in the mammal (Vrba, 1956). Concerning the increase in threonine, we should remember that smolts differ from parrs in that they have a high level of adrenalin in the blood and a very wide variability of glycemia (Fontaine and Hatey, 1963). Therefore the peaks of adrenalinic hyperglycemia probably involve discontinuous insulin releases-with glycemic fluctuations-and insulin being known t o produce in mammals an important increase of threonine in the brain (Okumura et al., 1959), such a mechanism in this case may well be a reasonable explanation of the increased concentration from parr to smolt. The growth hormone can also be involved in this mechanism since it stimulates insulin secretion in mammals (Engel et al., 1958) and smoltification corresponds to the phase of growth acceleration.

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Let us recall too some studies having shown the interaction of both systems, endocrine and nervous, in fish and first of all those revealing the influence of certain hormones on the nervous system. The transport of 35S1 methionin and its incorporation in the protein of the brain are significantly stimulated in the trout having become hyperthyroid by a diet rich in iodated casein and in a hypophysectomized eel treated with thyroxine. This incorporation is more important in the smolt than in the parr, in the silver eel than in the yellow, a phenomenon which can be explained in the light of results previously indicated, by the hyperthyroidism of silver fish in comparison with preceding stages (Leloup et al., 1972). We must also remember that a number of studies have correlated the high rates of R.N.A. and protein synthesis in the brain with the acquisition and retention of a learned behaviour (Shashoua, 1968). Domagk and Zippel (1971) have produced facts supporting the idea of the peptidic nature of the material responsible for the transfer phenomenon of acquired information from trained goldfish into naive recipient animals. I n fact, according to Ungar and Fjerdingstad (1971) both the R.N.A. and peptide extracts of brain can transfer learned behaviour. It is likely that these peptides exist in two forms: the R.N.A. bound form, probably present in the cytoplasm, and the free form, perhaps partly bound t o acidic substances that may be located on the surface of the cell, especially a t synaptic junctions. The importance of R.N.A. in these memorization phenomena is demonstrated by the experiment of Neale et al. (1973) who showed that camptothecin, a vegetable alcaloid blocking the A.R.N. synthesis in the eukaryotic cells, blocks the incorporation of uridin 3H in the A.R.N. of the brain of Carassius auratus (L.) and, administered in the 90' following training, provokes a great memory decline. Now it is a t the moment when the young salmon must, because of homing, fix the memory of places it will leave, and perhaps of those it will cross during its migratory behaviour, that a faster synthesis of cerebral proteins occurs. It would be interesting to look for the biosynthesis of a new R.N.A. and some new peptids in the smolt. Recently, by intracranial injection of a brain extract of adult chinook salmon, migrating to the spawning grounds, into other chinook salmon, Hahn et al. (1974) have been able to increase the magnitude of the EEG evoked in the olfactory bulb by a non-home test water, a fact that tends to show, if confirmed, the role of cerebral chemical biosynthesis in the acquisition of homing, a complex phenomenon probably bringing into play not only the sensitivity of chemoreceptors (see Sense organs p. 316), but also a certa.in neuroendocrine condition of the subject

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favouring imprinting in the young salmon preparing for catadromous migration. Let us also point out that thyroxin in goldfish reduces the latency time of the optical tectum response to a luminous stimulation, reduces the time needed t o obtain the maximal response and increases its amplitude (Hara et al., 1965). This action can be useful during migration. Other hormones certainly intervene on the nervous system. Thus prolactin is capable of modifying the electric activity of the front brain neurons of certain teleosts (Fielder and Blum, 1972) and can therefore influence certain types of behaviour that seem t o be controlled by this part of the brain. Let us look now a t the influence of the nervous system on endocrine glands. The path which has been the subject of most studies is that passing through the hypothalamic centres and which is the seat of neurosecretion phenomena. There is little doubt that these intervene in migratory behaviour when we see the important modifications appearing, a t the level of the hypothalamus, a t the moment of smoltification of the young Salmo salar. I n the young parr, neurosecretory cells of the preoptic nucleus are still small in size and the intensity of the neurosecretory phenomena is fairly slight there. Secretion aspects become gradually clearer as the animal grows, but the pictures of the axonal path taken by this product remain rather hazy and the digitations of the neurohypophysis are relatively poor in neurosecretat. Now the preparations for the first catadromous migration go together with the important movement of the neurosecretion product in the proximodistal direction. This movement is already quite appreciable in the parr-smolt, that is t o say a t the preliminary preparation for migratory behaviour, but it reaches full strength in the smolt. The neurosecretory cells of the preoptic nucleus are much poorer in the neurosecretory product in smolts (captured in fresh water) than in parrs. The pictures of the axonal path of the neurosecretion product are on the contrary much clearer in smolts than in parrs and the neurohypophysis is much richer in the neurosecretion product which can be stained by paraldehyde fuchsin in animals getting ready to migrate. The indigence of neurosecretory cells of the preoptic nucleus is even more accentuated when we examine smolts having passed into sea water several days earlier. The phenomenon just described occurring during smoltification corresponds t o a phenomenon observed in diverse fish undergoing an osmotic stimulation by the passage from fresh water t o a solution hypertonic t o the body fluid and it is likely that it plays a r81e in

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the capacity to adapt to sea water. We are therefore once again here in the presence of a preadaptation phenomenon. It is probable that the thyroid plays a r61e in these modifications concerning hypothalamic neurosecretion, for the thyroid hormones administered 60 the trout bring about changes like those just described during smoltification, but it is unlikely that they act alone (Arvy et al., 1959). It has been demonstrated in the mouse (Srebro and Szirmai, 1972) that the neurosecretory hypothalamic centres of animals submitted to periods of forced swimming present an increased secretory activity. The hypothesis can then be put forward that the intensive motor activity deployed during migration causes a hyperfunctioning of these centres or of certain among them, just as it brings about certain endocrine hyperfunctionings. However, it must be remembered that it is precisely the countercurrent swimming of the trout that causes a thyroid hyperactivity which can itself intervene in the displacement of the neurosecretion product. Huve (1974), when studying bioelectric activity of the neurosecretion cells of the preoptic nucleus in the salmon a t the different stages of parr, parr-smolt, smolt, observed that in the parr the number of cslls without spontaneous activity is much higher than for the animals in course of smoltification. It is a t this stage (parrsmolt) that the number of cells with a spontaneous activity a t the unitary level reaches its maximal value. Thus, it is a t the moment of preparation for catadromous migration that the bioelectric spontaneous activity of the preoptic nucleus of the young salmon is maximal and this fact seems t o bring a new argument in favour of the r d e played by this part of the nervous system in the preparation for migration. By what mechanism can the displacement of this neurosecretat of the preoptic nucleus towards the neurohypophysis facilitate the change of environment? A certain number of experiments have been made with mammal neurohypophysary synthesis hormones, which have given interesting results, but we shall not consider them for we know that these hormones are not identical in fish and in mammals. I n the migratory teleosts we are examining here, the hormones present, up till now described and revealed by Acher (1971) are arginine-vasotocine and isotocine. From the fact that arginine-vasotocine increases the outflux of sodium in the euryhaline flounder, Platichthys $esus L., transferred from fresh water t o sea water (Motais and Maetz, 1967), and that the neurohypophysial and hypophysial extracts in the freshwater goldfish stimulate the influx of sodium, the outflux not being noticeably modified, whence an increase in the net flux (Maetz and Julien, 1961), and that isotocine produces a stimulation of the sodium influx

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by the gills, without increasing the outflux (Maetz et al., 1964), it seems that this neuro-hormone may be an agent as effective in fresh water as in sea water. This could explain why Barannikova (1964) observed in salmonids (Oncorhynchus) which had just passed from the Barents Sea into the rivers, an intense neurosecretion, most of the preoptic nucleus cells being empty and the transfer of the neurosecretion product towards the hypophysis being important, and that she noticed the same phenomenon during catadromous migration as we did in the Atlantic salmon when the fish were still in fresh water. We should point out that the preparation for the second catadromous migration, that of the mended fish, involves modifications, similar to those accompanying smoltification. The cells of the preoptic nucleus are emptied of their secretion product, the pictures of the axonal path are very clear and the neurohypophysis of the mended fish is literally inundated with a product which can be stained by chromic haematoxylin and paraldehyde fuchsin. Thus the neurosecretion of the preoptic nucleus appears as an emergency hormone during a change of osmotic environment and, if this is so, we can understand the need for a particularly large accumulation in the mended fish just a few days before the change of environment, considering the particularly deficient general physiological condition of this animal which has often been fasting for about one year and has lost much weight, finding itself especially vulnerable to any perturbation-in this case, osmotic. We have seen that during downstream migration of the smolt, an increase in adrenalin content in the blood must dilate the gill vessels, which may be beneficial for respiratory exchanges, but dangerous for ionoregulation. The neurohypophysial hormones accumulated a t this moment in the hypophysis (vasotocine and isotocine) are ready t o intervene a t the moment of salinity change t o reduce the exchange surface and no doubt fight against the loss of water by an antidiuretic effect, since many studies have shown, in the eel in fresh water and in the sea, and in salmonids in fresh water, an antidiuretic effect of A.V.T., and also that this hormone exercises on blood pressure an opposite effect t o that of adrenalin, so that a reduction of the surface exchange a t gill level increases ventral aortic pressure almost without interfering with the dorsal pressure (Maetz and Rankin, 1969; Chan and Chester Jones, 1969 ; Rankin and Maetz, 1971 ; Babikker and Rankin, 1972; Hammond, 1972). It is perhaps because the release of these hormones, when the smolts arrive in brackish water, ensures the predominance of their action on the catecholamines, that the less active smolts may be seen in the estuaries t o constitute easy

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prey for the sea birds. Neurohypophysial hormones, by decreasing the exchanges of respiratory gas at gill level, whereas osmoregulatory expenditures may require more energy, could limit the motor activity of the smolts. This could be resumed in full vigour once adaptation has come about. I n the Mugil cephalus captured in various environments (fresh water, sea and hypersaline lagoon), Leray (1968), Abraham (1971, 1974) have contributed very interesting data on structural and ultrastructural modifications observed a t the level of the preoptic hypophysial system in various environments. Unfortunately we have no data concerning preparation for migration and this can be explained by the fact that it is not accompanied by such a spectacular change of colour as with the young Salmo salar. We may wonder whether the neurosecretat of the neurosecretory caudal system is not likely to play a r61e too in the adaptation to a change in environment, according t o observations of Enami et al. (1956), Takasugi and Bern (1962), Maetz et al. (1964) and other authors. Without doubt, urophysial extracts act on gill and kidney excretion in Carassius auratus in fresh water t o bring about a gain in sodium by the organism and, from the osmoregulation point of view, a certain similarity exists between the action of uro- and neurohypophysial extracts. Moreover, Lacanilao (1972) believes that in the urophysis a factor exists, identical or very similar t o A.V.T. Many other various activities have been attributed to urohypophysial extracts : increase of blood pressure in eels (Bern et al., 1967), presence of a teleost bladder-contracting substance (Lederis, 1969). For Chan (1974), the urohypophysis could secrete two peptids : the hypertensive urotensine I in the eel could stimulate, a t the level of the kidney tubules, the excretion of bivalent cations and would therefore be very useful for adaptation to sea water. Urotensine 11, which is also hypertensive in fish, could increase the glomerular filtration rate as well as urinary elimination and Na, K, Mg, Ca excretion rates. The interest of this second substance appears less clear, as the fish passing into sea water has to restrict its water losses. It is questionable whether these substances really play a hormonal physiological role. Honma and Tamura (1967) suppose, following a study of anatomy and comparative histology, that the caudal neurosecretory system might play a r61e in certain migrations (not in all, however, since it is not found in Acipenser (Bern and Takasugi, 1962) and that no secretory material is recognized in the elver until several weeks after its entry into the river (Imai, 1965)) but, to our knowledge, no formal proof has been given of this and it

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would probably be only a secondary r61e in comparison with the hypothalamus. It is probable that the pineal organ intervenes too in the determinism of migrations. Indeed, either by its influence, demonstrated in mammals on the potassium contents of the central nervous system (Quay, 1965), or by the rhythm of its secretion of serotonin (5 HT) or of melatonin, which according t o Hafeez (1970) could modulate the swimming activity of rainbow trout, or again by its sensitiveness to environmental illumination which certainly reacts on central neurovegetative activities and secondarily on various peripheral targets, it seems to us fairly sure that the epiphysis fits into the complex integration mechanisms that we have just examined. When looking a t the epiphyses of salmon at the start of migration and on the spawning grounds, we have observed important differences in the morphological aspect and weight. A histological, biochemical and physiological study of this organ a t diverse stages of migration would probably be fruitful. The bovine and ovine epiphysis containing important amounts of T.R.H. (White et al., 1974), it would be very interesting to investigate whether this is true in fish and, if so, the r81e that it can play in determining migration, in particular by way of the thyroid. Certain characteristics, endocrine (thyroid, interrenal and chromaffin activity), humoral (higher content in the blood of adrenalin, increased glucose content and globular volume) and behavioural (greater motor activity) contribute to making us believe the smolt is more sympathicotonic than the parr and this nervous system condition no doubt plays an important r61e in the fish’s sensitiveness to certain meteorological and hydrological factors, that is t o say in the starting of migration and perhaps too in the irnprinting which ensures homing. Finally we should remember that several physiologists have looked for the influence of certain ablations and other lesions on different behaviours (learning in a labyrinth situation, aggressive sexual and parental behaviour) and have obtained interesting results. Unfortunately migratory behaviour does not appear t o have been the subject of studies of this nature-the experimental methods being no doubt more difficult t o carry out than in the preceding examples. However, these difficulties are not insurmountable and this approach is worth trying.

VI. SENSEORGANS The characteristic of migration is t o be orientated. Long-distance journeys which are not orientated are erratic. However, the very nature

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of this orientation has often been discussed. For example, regarding the reproductory migration of the European eel and following tagging of the silver eel by Maar (1947) in the Baltic, Deelder (1949) came to the conclusion that eels possess a sense of direction and that they follow a route a t a constant angle to the meridians, the loxodromic line. Some captures of migratory eels in the North Atlantic bear out this idea concerning eels from countries neighbouring the Baltic. But if all European eels assemble in the Sargasso Sea (and we adhere to this conception, Tucker’s thesis (1 959) having been submitted to numerous and justified objections), we should have to admit the existence of many geographical races of eels, reproducing in neighbouring spawning areas, yet nevertheless distinct, and born with real cape compasses set in different directions. However, we cannot conceive that the eels of the Iberian peninsular take the same direction for the Sargasso Sea as the eels from Scandinavia, or again that this sense of direction is a character acquired in the course of the larval life and the first transocean migration, both these hypotheses encountering serious difficulties. This mechanism could be dependent on the vestibular system, the closest counterpart of the sensory components of man-made navigation systems, but this conception remains hypothetical. We have seen a certain number of physiological functions which could be involved in setting off migration and in the choice of an environment of a temperature and salinity different from those in which fish find themselves at a given stage in the life cycle, but which do not explain an orientation sometimes operating over thousands of kilometres and able to arrive a t a very narrowly localized zone. This is the case of homing found in many species and particularly in certain amphihaline potamotocous species such as the salmon and shad, regarding the return t o the native river after a very long journey in marine waters. A. Rheotropism The earliest hypothesis on the orientation of migrations and which is still valid in some cases, invokes the direction of currents, whether the fish follows more or less the direction of the currents, downstream or downcurrent migration, or that it swims countercurrent, upstream or upcurrent. It is an accepted fact that many migrations of larval and juvenile fish are the most often denatant, that is to say that the fish drift with the current and that certain stages in migration of adult fish, particularly fish exhausted by spawning, are also denatant. All these migrations involve a passive drift.

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However, in one and the same fish, such as the herring, passive phases exist in succession and others during which the fish swims against the current. This latter behaviour is generally the case of the phase immediately preceding the ripening of the gonads and during this phase, whereas after spawning the fish becomes denatant. It should be emphasized that this explanation does not exclude of course the participation of physiological mechanisms determining whether the fish is, a t one phase of its life cycle, denatant and a t another, contranatant. I n a general way, it seems that the negative rheotropic phase of an adult fish corresponds to a certain physical exhaustion with some endocrine dysfunctionings comprising in particular certain hormonal insufficiencies, whereas the positive rheotropic phase corresponds to the existence, a t the beginning, of important energetic reserves and of their progressive utilization, together with a particularly active functioning of the dynamogenic endocrine glands. The rheotropic response of fish to the current seems to depend on a very complex mechanism (visual clues, rheotactic receptors of the skin and the lateral line, electrical clues resulting from the induction of an electromotive force induced by a flow moving horizontally across the vertical component of the earth’s magnetic field and by the movements themselves of the animal). The importance of these diverse mechanisms varies according to the transparency of the water, the position of the fish with regard to the visual clues, the nature of the current and the swirls (see Harden Jones, 1968) and the behaviour of the fish itself. If certain facts still tally with this conception of an extremely important r61e played by the currents, others have led, in order to accept this idea, to very risky hypotheses on the unproved existence of unidirectional currents characterizing certain water masses, within which are found shoals of fish-over a long distance. For example, to admit that the Atlantic salmon of the Adour Basin depends upon such a mechanism for its journey to the feeding grounds of the Baffin Sea, and on a similar mechanism, but in the other direction, t o return to its spawning grounds, these migrations being proved by taggings, would be a highly gratuitous hypothesis. Other similar examples could be mentioned. B. Thermoreception

It has also long been known that the temperature of certain water masses clearly seems to constitute a direct or indirect factor in the gathering together in shoals of certain migratory fish and the thermometer is usefully employed in fisheries oceanography.

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Various experiments (Murray, 1971) have, moreover, shown that certain marine fish can be trained t o respond to temperature changes of several hundredths of a degree. It has long been thought that the lateral line was the seat of this thermoreception, but it is accepted today that these thermal receptions are scattered over the body surface and they are probably innervated by spinal nerves. No doubt a fish is able to detect certain temperature gradients comparable to those observed in some zones of marine waters. For example, a t the level of a thermic front between polar and Atlantic water, a thermic gradient measured by thermistor was in the region of OOO1/m. Now, working on the basis of Bull's data (1936) on various marine species and in particular a gadoid, it was possible to calculate that a fish of 50 cm, cruising a t a speed of 10 m/s. was able to detect gradients of the order of 0-03 t o 0.003"C/m. Thus a t the level of such a front and probably even in less sharp gradients, a gadoid can be guided by its thermoreceptors. Obviously the sensitiveness of the response also depends on the speed a t which the fish crosses the isotherms and fish such as tuna, €or example, seem particularly apt a t guiding themselves, when they arrive in the neighbourhood of an especially abrupt thermocline, on a temperature gradient. This mechanism cannot however operate throughout a migration of several hundred or thousand kilometres, but only in special zones and in particular a t the level of thermoclines. The same observation may be made regarding halotropism, which we have discussed earlier and which plays a r61e in estuarine zones and at the level of haloclines, but which cannot explain the whole of a long migration. Besides, even for fish like tuna, which were considered particularly dependent on waters of given temperatures, many authors have made some reservations on this rather too categorical opinion. Without doubt the germ0 or long finned tunny, Germo ulalungu Bonnaterre, is generally found off the European coasts and a t the time when it is caught, in waters the temperature of which is above 14OC. But, on the one hand this tuna is not found in all waters of a temperature higher than 14OC (there are therefore other motivations for selection) and, on the other hand, it seems clear that its thermic optimum varies in the course of the diverse stages of its life cycle. I n the Pacific too, it was generally considered that the movements of tuna were determined essentially by temperature. Nakamura (1969) has made some justified reservations on this point, showing that numerous observations are difficult to interpret by water temperature alone. Nakamura believes the fish lives first and foremost in waters of an oceanic current which constitutes its ecological sphere corresponding t o a given physiological state.

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A change in the physiological state in the course of the life cycle can bring about a change of current. But how do tuna detect the frontiers of water masses? By thermoreceptors intervening at the level of thermoclines, reply those who maintain the importance of temperature in the migrations of tuna. Perhaps by electroreceptors capable of guiding fish along a particularly marked electric gradient a t the level of rheoclines", is what other scientists suppose (see below). Whatever may be, and to take another example, although eels generally reproduce in waters of relatively high temperature and salinity, it is very difficult to admit the existence of a regular gradient of temperature or salinity between the European coasts and the Sargasso Sea, along the route followed by the eels, and, even if this were so, it is difficult, knowing on the one hand the thermic sensitiveness of fish in general (of the order of a hundredth of a degree) and on the other the difference in temperature between a European estuary and the water of the Sargasso Sea-around 10'Ct o admit that this difference in temperature-spread over several thousand kilometres-can constitute a sufficient gradient for the eel to direct itself on a relatively short distance. Consequently numerous questions have arisen about other sensorial mechanisms and other clues which could intervene t o ensure this orientation.

C. Vision

It is normal that the first sense to come t o mind is that of vision, for it is known that many vertical migrations are nycthemeral. No doubt phenomena of sensitiveness t o light concerning the dermis, the pineal area and certain parts of the diencephalus have been described and their intervention cannot be excluded, but the eye however seems t o be an organ the most capable of explaining a t the same time orientation by light or by a luminous patch, recognition of bottom features and detection of movement across the rheocline. Regarding the two latter points, these mechanisms can only operate during the day, or certain nights, unless phenomena of bioluminescence make them possible in darkness. Moreover they are greatly dependent on the transparency of water, bottom features or the presence of targets drifting at a suitable distance. It seems clear that a sedentary fish living on or close t o the bottom is capable of recognizing a particular biotope and that it finds here landmarks *Rheocline : discontinuity i n the velocity or the detection of the currents.

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allowing it to maintain its position, despite a more or less violent current. This is the case, for example, with the parr of Salmo salar. But when an increased motor activity corresponding to smoltification makes the young salmon rise halfway to the surface and swim frequently against the current, it no longer has a t its disposal landmarks allowing it to know whether it remains in the same biotope, all the more so, that, in our region a t least, the most important migrations occur a t the time of the spring floods, that is to say when the water becomes more turbid, contributing to the difficulty in perceiving the landmarks. This concerns one of the causes of the setting off of a migration, involving, as we have seen, endocrine factors. Moreover, it has been observed that this catadromous migration occurs in the juvenile Pacific salmon a t a rather precise period of the night and that this is probably due to an imperfect adaptation of the eye to darkness and to a period of night blindness (Hoar, 1958). Indeed, an examination of retinae from several species of Oncorhynchus has revealed an incompletely dark-adapted condition of the retinae a t the time of most active downstream migration (Brett and Ali, 1958). Ali and Hoar (1959) consider that the nocturnal catadromous migration is initiated when visual contact with the environment is reduced or impaired. As far as the accomplishment of migration is concerned with the arrival on the spawning grounds or the feeding grounds, vision can intervene, in the first case, either by recognition of a bottom favourable to spawning, or in the case of salmon for example, which are considered by some authors, with facts to back them up, to return, not to any spawning ground, but to their native spawning ground, on recognition of a very particular biotope. This latter mechanism implies of course a very long-lasting memorization in which, as we have seen previously, endocrine mechanisms may be involved. Regarding the feeding ground, vision can play a r61e in the recognition either of a suitable bottom for fish feeding on bottom-living organisms or in the mud like sturgeons, or again of prey sought after by pelagic fish. But as we shall see, in all these phenomena, olfaction can also play an important r61e. As far as orientation by a luminous patch is concerned, essentially the sun, it seems to be quite true for certain fish. Indeed the remarkable experiments made by Hasler et al. (1958) on lake fish prove that they can use a sun compass mechanism, a capacity confirmed by other authors (Schwassmann, 1973). No doubt to compensate for the changing solar azimuth, these fish must also possess a " biological clock ", a circadian time sense that is kept in phase by the times of sunrise and sunset, but while the mechanism A.M.B.-13

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representing this aptitude t o measure time remains controversial, it is nevertheless very widespread in the living world. Probably the photoperiodic control of this mechanism adjusts the orientation capacity t o annual changes of the sun’s azimuth movement and the rate of change in the sun’s altitude determines the angular horizontal compensation a t different geographical latitudes. Do great migrators possess and utilize such a mechanism? That they possess it is very probable, since Groot (1965) in particular has found it in a young Pacific salmon, but that this sense is sufficient explanation for long distance migrations is highly improbable. First the weather is not always clear and Hasler (1971) has shown that the mechanism does not appear with a grey sky. We must admit then that the fish can only orientate itself on sunny days. Many migrations occur a t night. They cannot therefore be oriented by the sun and this very variable discontinuity in time and according to the weather ill suits the speeds of migrations of certain fish, calculated from the tagging t o the capture point and which remain, from year t o year, fairly comparable despite different climatic conditions. Certain fish moreover accomplish important migrations during the polar night, for example Arctic cod moving from Bear Island towards their spawning grounds a t Lofoten. But if the sun always appears in clear weather in the form of a brilliant disc, it is not so for the moon and, because of the lunar rhythm, it is still less constant than the sun. Furthermore, no proof has been found of a moon compass mechanism. Another objection against orientation by the sun is the depth a t which migrations take place. No doubt the fish can guide itself by direct vision when moving within the first few metres below the surface of the sea (the depth varies considerably moreover, according t o the transparency and agitation of the water) beyond which it can do so by radiance distribution which depends (1) on refraction a t the air-water interface, (2) not only on refraction but also on the scatterance, reflectance and absorptance in the submarine light path (Waterman, 1974), and this is possible down to a depth of some thirty metres in the sea near Woods Hole, for example. Below this it is supposed that it may be guided by underwater polarization patterns, and Waterman (1972, 1974) produced facts which tend to show that certain fish (Zenarchopterus in particular) can perceive the e-vector of linearly polarized light by which it can guide itself (polarotaxis). Similar results have been obtained by Kleerekoper et al. (1973) for the goldfish. But, t o our knowledge, this fact has not been demonstrated for great migrators. It is

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probable however, although no direct demonstration has been made of the actual application of this capacity in the sea or in other natural bodies of water. Finally, the degree of polarization in natural waters is diminished by turbidity as well as by depth. Certain migrations occur a t depths which make if difficult-or even impossible-to admit orientation by celestial bodies. Let us cite, for example, the reproductive migration of the European eel. Some trawlers have caught eels 20 miles off the coast of Cornwall, 80 to 100 metres deep, which, from their morphological and anatomical features, were eels going in the direction of the Sargasso Sea (Cligny, 1912). The research vessel " Anton Dohrn " caught, 700 metres deep on the Rosemary Bank, some Hora moro (Risso) and Aphanopus carbo Lowe which had just swallowed some silver eels (given the excellent state of the prey) (Reinsch, 1968). These facts lead one t o believe that the eel carries out its migration a t depths where orientation by celestial landmarks is impossible. And there is more still. Another apodal teleost a t great depth, the Synaphobranchus pinnatus (Gray), spawns in the Sargasso Sea, but adults are found in the abyssal zone near the coasts of Europe. As no catch was made between these two zones in surface or not very deep waters, we are bound to admit that adult individuals carry out their migration returning to the spawning grounds a t a very great depth and it seems impossible to allow that they are oriented by light from the sky. It is found then that if orientation by vision, a biological clock and celestial landmarks cannot be excluded in certain cases, it cannot explain everything. Groot (1965-1967), moreover, has come to the conclusion in his research that if Oncorhynchus nerka can orientate itself by the sun and certain celestial landmarks, it also shows a sense of orientation beyond all sight of light from the sky. Likewise, Miles (1968b) has shown that Anguilla rostrata (Le Sueur), caught on their catadromous migration, kept their southward orientation (direction of the supposed breeding area), even if they were deprived of a view of the sky. Thus the eel seems capable of noncelestial orientation. It is however curious that this direction is perturbed if the eels are not submitted t o a diurnal light-dark rhythm, for if they navigate several hundred metres deep, this rhythm, if by chance it exists, is extremely mitigated. Finally let us note that the r6le of sight is also important in the mechanisms of schooling, a behaviour so characteristic a t certain stages of migration. Whatever may be, it seems clear from these data that other sensorial receptors and other stimuli must be examined.

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D. Chemical reception Chemical receptions are divided into three categories : olfaction (smell), gustation (tasting) and common chemical senses. We easily distinguish between smells and tastes, the former being transmitted at a distance by way of air, the latter requiring contact with a solid or a liquid. But in fish, as the means of transport for all chemical stimuli is water, a t least for species with which we are concerned here, for some reserve must be made regarding amphibian fish, the distinction can only be established on anatomical and experimental physiological bases. If we want to know the nature of the way in which a chemical stimulus has set up a reaction, we have to section the nerves transmitting the influxes born of such or such a type of receptor or register their action potential. Olfactory organs are innervated by the first cranial nerve which contains the axonal extensions of the primary receptor cells to the olfactory bulb. Taste buds which lie either in the mouth and pharynx or in the gill cavity or appendages (barbels and fins) or on the external surface of the body are innervated by the VIIth, IXth and Xth cranial nerves. The common chemical sense is assured by free nerve endings supplied by the spinal nerves and located on the external surface of the body. The existence of palatal chemoreceptors responding specifically to diluted salt solutions (in particular 0.005-0.0005 M for NaC1) has been shown in the carp. The nasal barbels of catfish are also sensitive to variations in concentrations of NaCl (Hara, 1971). It is therefore not excluded that chemoreceptors other than olfactory organs play a r61e in certain migratory stages and in particular in those occurring in steep gradients of salinity. Nevertheless the fact that fish in general are capable of distinguishing slight differences in salinity does not suffice to prove that they can be guided by salinity gradients in certain migratory stages when this mechanism could however be favourably envisaged. For example, it has been demonstrated that the smoltification of salmon is accompanied by a positive halotropism that the parr did not show and it could be thought that migration from the spawning grounds to the sea was directed along an increasing salinity gradient. Yet in the rivers we have studied (Oloron River, Gaves dunis, Adour River), a smolt cannot be guided throughout its downstream freshwater migration by a salinity gradient, for this gradient is inversed when meeting a tributary whose waters are rich in salt (Fontaine and Vibert, 1952). I n the estuarine waters, this possibility must be considered more

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favourably (McInerney, 1964) although this author does not hide the difficulties arising from the comparison between the fishes’ sensitivity to salts and the very slight steepness of the considered estuarine salinity gradients (0~0000035%, salinity/cm). In mammals, it has been displayed that the olfactive channel is much more sensitive than the other two and although similar experiments have not been done on fish, it appears that smell can attain considerable sensitivity, much greater than taste, with the exception of the sensitivity of Phoxinus to eugenol and /3 phenyl alcohol on the one hand (smell) and to hydrochloride quinine on the other (taste) (Bardach and Atema, 1971). Thus, in the European eel, regarding /3 phenyl ethylalcohol, the lowest threshold was a dilution of 3.5 x 10-19. It is above all in certain homing phenomena that the importance has been revealed of the olfactive path in guidance to-and recognition of-the privileged sites. But we must point out that authors often refer, by the name of homing, to rather different phenomena, for example the return to its natural habitat of a sedentary fish captured in its natural habitat, then displaced, but which returns after a certain length of time, more or less prolonged, to its home ; or again the fact that the normal life cycle of a migratory fish involves, a t a given moment, the return to its native spawning grounds. We shall consider above all this last aspect of homing which has been well displayed for the shad and different salmon (Salmo and Oncorhynchus). These are salmon having been the subject of the most extensive research, tending to show that the final phase of the orientation of this homing is mediated through olfaction and so we shall look a t salmonids here. I n fact, the suggestion that the salmon can be guided in its return migration to its native river by the smell of the water of this river is a very old idea (Buckland, 1880), but it seems that the first experiment to support in some way this hypothesis was that made by Craigie (1926), who released 500 sockeye salmon, in half of which the olfactory nerves had been cut. Judging from later recaptures of the tagged normal and operated fish, it was evident that the migratory behaviour of the latter had been somewhat interfered with. Later, Wisby and Hasler (1954) captured sexually ripe coho salmon a t two branches of the Issaquah River (Washington State) and returned them downstream below the fork, to make the run and selection of the stream again. I n half of them, the nasal sac was plugged with cotton. The majority of normal fish again selected the stream of first choice, while the plugged-nose fish returned in nearly random fashion. These experiments suggest the important r d e that the functional olfactory system has in orientation. However, laboratory experiments were to provide

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definitive proof. They were of two types, first regarding the fish’s behaviour in waters of various rivers, then electrophysiological. By a combination of differential conditioned response and surgical operations (removing olfactory membranes, stitching up the anterior nares), many authors have displayed the great olfactive sensitivity of fish of diverse species. Brett and MacKinnon (1952) were the first to show the extreme sensitivity of the ascending coho salmon towards a substance presented on human hands and acting as a repellent. But what was important, to try t o explain the homing of fish of one species by olfaction, was to show that different streams have characteristic odours which the fish can detect and that it is able to discriminate between such odours if they do exist. The first set of experiments on the bluntnose minnow showed that it could be trained to discriminate between chemical differences of two Wisconsin creeks. The experiment was repeated in the salmon fry and after a short period of training it was evident that it too could discriminate between odours of two Wisconsin creeks (Hasler, 1954). A second approach to the problem is the recording of electric activities of different parts of the brains of salmon (Oncorhynchus tschawytscha (Walbaum) and 0. kisutch). When the adults arrive a t their home pond in order to spawn, the activities in the olfactory bulb and in the posterior cerebellum had a much higher amplitude than those of other parts : amplitudes of potentials in the optic lobes were especially low (Hara et al., 1965). Spontaneous electric records were also made from brains of a non-migratory salmonid, adult rainbow trout. E.E.G. activity in the olfactory bulbs was relatively low while that of the optic lobes was much higher than in the above mentioned salmon. Infusion of water from spawning grounds into the nasal cavity of adult salmon produced a stimulation in E.E.G. patterns recorded from the olfactory bulb ; various natural waters from other neighbouring sources produced virtually no response. But it was very important to find out whether the response was really specific to water from the proper spawning grounds of the salmon studied and if it could not be obtained equally well with water from other spawning grounds of salmon populations of the same species. Experiments made by Ueda et al. (1967), Oshima et al. (1969b) replied t o this question by showing that the response was indeed specific t o water from the spawning grounds of the population under study. These results implied that each spawning area has its own specific attracting substance, or specific combination of these substances recognized by the corresponding population of salmon. As weaker but definite response could be evoked by waters traversed by the salmon migrating

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towards the spawning grounds, it may be supposed that a population of mature salmon, coming from the sea, is guided t o its proper spawning grounds by a characteristic odour. Does this odour come from the biotope or the biocoenosis characterizing this river or this zone of a river? Does it come from the population itself which may emit one or several attracting substances? It is still difficult t o decide finally among these different hypotheses, but the second is supported by Solomon (1973) concerning Atlantic salmon as it has been previously by Nordeng (1971) for Salvelinus alpinus (L.), then by Hoglund and Astrand (1973). I n this case, it seems unlikely that the metabolisms of very numerous populations of salmon differ so much that each emits a different substance, but rather a catabolite complex, of which the different relations constitute a signal and this is no doubt what makes it so difficult to identify the signal. Yet this would be a very important fact, not only from the fundamental point of view but also applied. As t o the conditioning of salmon to these chemical signals, we must accept that this occurs during the life of the young salmon in the zone in which it is born and in the course of its downstream migration, for eggs or young salmon whose parents come from river A and which are transported to river B become smolts and, after their sea life, return to river B and not t o river A. This imprinting mechanism implies durable internal modifications in which the synthesis of an R.N.A. is probably involved. Indeed intracranial injection of antimetabolites, puromycine, actynomycine D or cycloheximide, in the chinook salmon inhibited olfactory bulbar discrimination between home water and water of other origins (Oshima et al., 1969a), and earlier, Rappoport and Daginawala (1968) showed that olfactory stimulation with morpholine induced an increase in brain nuclear R.N.A. and a change in base ratio in marine catfish Galeichthys felis. It therefore seems likely that a R.N.A. synthesis is part of the mechanism ensuring the olfactive memory and probably other types of memorization. As to the possibility of preserving this imprinting, according t o Hasler (1971) it seems that the younger the fish was imprinted, the longer this will last. I n 0. nerka, there would even seem t o be an age limit for this memorization faculty ( 1 8 months) (Shirahata, 1971). Hara (1971) has discussed the question as to how the fish’s orientation takes place and he comes to the conclusion that it is probably by trial and error. However, according to Ueda et al. (1971), a non-migratory fish such as Cyprinus carpio L. could distinguish the stream waters as well as a migratory salmon. This aptitude might not then be a privilege of great migrators. Considering the great olfactive sensitiveness of the eel, it was normal that the

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possibility should be sought of this species being guided by olfactive clues. However, indubitable proof of this mechanism, in the case of European eels transplanted over a long distance, up to a few hundred kilometres off the coast (Tesch, 1967, 1970; Deelder and Tesch, 1970), has not been found. Besides, we should note that here we have a nonreproductory homing, thus very different from that of the salmon in a period of synchonic fasting. As far as the natural migrations of this species are concerned, experiments made by Creutzberg (1961, 1963) and Miles (1968a) show thiLt substances attractive t o elvers of Anguilla anguilla (L.) and Anguilla rostrata are present in fresh water, but as described above (p. 249), attractive substances probably exist also in coastal waters and the displacement of eels from the sea to fresh water is much more complex than was initially supposed. This results on the one hand from the action of attractive substances present in sea and fresh water, probably in different concentrations and ratios, and on the other hand from an osmotic factor, the importance of which reappears when both waters (fresh and sea water) are treated with carbon. If, in alignment with most authors, we allow that these attractive substances are pheromones, why would not some exist in the sea waters off the French coasts, those which we have used, since these coastal waters are often inhabited by quite large populations of eels which, as they do not ascend the rivers, accomplish their growth there, and at the time of the ascent of the elvers in particular these waters are crossed by important shoals of silver eels just having ended their downstream migration and making for the spawning area? A supposition has been made (Bachelier, 1972), following observations concerning the settlement of eels in new fluvial zones, that eels return to the fresh waters in which their parents have lived. This hypothesis is founded on disturbing facts, but comes up against a certain number of objections. First of all, the male and female eels do not usually have the same habitat. It is true that the 9 and 8 of a same river basin and the corresponding estuary have perhaps a means of recognition. Perhaps they migrate together in a shoal towards the spawning area of the Sargasso Sea. But once arrived there, we ought to allow that each fluvial area has its distinct spawning ground. It is true that homing could be transmitted only by 9 sex. At any rate it would be a mechanism very different from that which the salmon is supposed to have, for it cannot consist of an imprinting but of an inheritance. Yet the European eel, like most Atlantic salmon, leave behind them in the ocean, a t a distance of several thousand kilometres, the waters which conditioned their homing. The question of knowing at

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what distance the chemical clues of home streams can be detected has been discussed by various authors and in particular by Harden Jones (1968). In truth it seems very difficult to come to a general conclusion in face of conditions which can be so varied. This distance depends indeed above all on the flow of the river where the spawning grounds under consideration are to be found, on the concentration of attractive chemical substances and therefore, if it is really a case of pheromones, on the density of the salmon populations on this spawning ground, b u t jh SE~DB qz& out of tAe queKd%n &at an At(and& salmon rFom a small Breton river could smell from its feeding grounds (Baffin Sea ar neighbouring waters) the odour of its native spawning grounds. Let us reserve then this notion for great migrators, that olfaction very probably plays a r61e, but above all, no doubt, in the anadromous river phase of this migratory cycle. The question remains as to how holohaline migrators, such as cod, plaice, herring, can use olfactory clues to find the spawning grounds where they were born, if they do indeed obey to a homing instinct, which is not always certain, but which seems to be the case for certain herring populations. However, no solid data can allow us to affirm this at present; and it seems that any r61e they might have as local landmarks is probably restricted to the immediate vicinity of the spawning grounds. We may also wonder if, just as the ultimate phase of reproductory migration of amphihaline migrators may be guided by olfactive stimuli, the last stage of recognition of feeding grounds might not comprise an olfactive component. Indeed, during research on the feeding ground of Salmo salar, situated in the Baffin Sea*, Momzikoff (1973) noticed that this zone was characterized by concentrations of 7 hydroxybiopterine and of 6 carboxyisoxanthopterine higher than those of other waters. Experiments on behaviour should try t o find out if salmon smolts and post-smolts are attracted by these substances. We should recall that having fractioned the extract of a clam which evoked exploratory response in the Japanese eel Anguilla japonica, Hashimoto et al. (1968) and Konosu et al. (1968) found that the amino acids, taurine, aspartic acid, serin, threonine, glutamic acid, glycine and alanine were the main components responsible for activity, but that each of these amino acids was ineffective when *We should point out that according to Dunbar (1972), Atlantic salmon have probably been assembling in this area at a recent date only and that this could be the result of a climatic marine shift comparable to that which determined the changes in the distribution of the Atlantic cod and other species.

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tested individually. They suggest therefore that the stimulating activity of the extract is attributable mainly to the synergetic or additive interaction of these amino acids. It is of course impossible to deduce a migratory activity from an exploratory activity linked to feeding behaviour, but these results can incite us to look for the chemical clues in a mixture of these substances rather than in one alone. A hypothesis has been put forward that chemoreceptors, sensitive to certain substances emitted by their congeners, might be responsible for maintaining the cohesion of a school of fish in the absence of any light permitting sight to come into action. They might therefore intervene in this behaviour, so frequent in numerous migrators. On the other hand, whatever the case may be, olfaction can only explain certain phases of certain migrations and we must now contemplate other mechanisms, the magnetoreceptors intervening as electroreceptors or magnetoreceptors*.

E. Electro- and magnetoreceptors It is known that several species of fish are equipped with electroreceptor organs, thanks to which they can obtain information from natural electric fields. These organs were first described in electric fish, but found again in other non-electric fish. They are the ampullary organs and in particular the small pit organs which in the lateral line are apparently used as electroreceptors**. They are sensitive t o weak local potential changes occurring a t their external opening. Lissman and Machin (1958) have carried out experiments on the behaviour of Gymnarchus niloticus Cuvier which show that the fish discriminates changes of 0.03 pV cm -l in the electric field. Rommel and McCleave (1972) attribute to the eel in sea water a sensitivity of 0.067 pV cm-l. But certain authors believe that some non-electric fish may possess more sensitive electroreceptors. The natural electric fields that are possibly detected by electrosensitive animals can be classified into three main categories (Kalmijn, 1974) : (1) inanimate electric fields of physical and chemical origin (e.g. induction fields, streaming potentials) ; (2) bioelectric fields from electric organs ; (3) bioelectric fields from sources other than electric organs. *The neurons of the lateral line react in fact equally to electrical and mechanical stimuli (Andrianov and Ilyinslry, 1973). **We do not take into consideration the tuberous receptors, found only in elecirio fish, which are not great migrators.

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For the problems of long-range orientation and navigation which interest us here, only first category natural electric fields can be used. They may be due to the fact that water, and particularly sea water, is an electrical conductor moving through the earth’s magnetic field. So the production of an electrical voltage could be expected. Stommel (1954) indeed found potential differences of 0.2 to 2.6 v across long distances in the Atlantic Ocean, and similar results have been contributed by several authors. It seems that the electrical gradient that might be available for navigational use is about 0.05 t o 0.5 pV cm -l, a value found close t o the surface in the Atlantic Ocean. As these voltages are directly related to the current and are polarized with respect to its direction, electrical clues seem to be a possible navigational device for the eel (Deelder, 1952) and salmon on the high seas (Royce et al., 1968). However, if, as we have seen, the eel in sea water manifests a high sensitivity to the voltage gradient, we should note that it responds to perpendicular fields, but not parallel with the body axis, which would enable the animals to align themselves with the direction of the ocean streams which, according t o certain authors, they follow during reproductory migration. But this behaviour is quite hypothetical and therefore this consideration should not be taken as a major obstacle t o guidance by an electric gradient. Besides, having discovered in the American eel and the Atlantic salmon a conditioned cardiac deceleration response to electric fields which are of the magnitude normally occurring in oc4an currents, Rommel and McCleave (1972, 1973a,b,) believe that this sensitivity makes it possible for a migratory fish to align itself upstream or downstream in an ocean current in the absence of fixed references. However, the demonstration of this interesting hypothesis has not yet been made. Nevertheless the feasibility of fish orientating in uniform electric fields has recently been demonstrated by Kalmijn and Bernal, who succseded in training a freshwater electrosensitive fish Sternopygris, when released in the middle of a weak field, to turn and swim t o the right or to the left, depending on whether the electric current was either head on or tail on, coming from the right or coming from the left (Kalmijn, 1974). If electro-orientation by the natural electric fields of ocean streams seems feasible in non-equatorial waters, it comes up against certain difficulties, however. I n part,icular, the top layer of the ocean is electrically rather noisy and other types of electric fields (for example, fields due to shoals of fishes swimming, to the passage of ships) can ~ p 3 e information t springing from natural physical conditions.

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Some recent experiments give reason to believe that certain electroreceptors may act as magnetoreceptors, the fish being guided by the gradient of the terrestrial magnetic field. After the hypotheses and preliminary informations given by Poddubnyj ( 1965), Mantejfel et al. (1965), we must above all mention the experiments on the eel made by Branover et al. (1971) and Ovchinnikov et al. (1973). Branover constructed a special labyrinth t o study the choice of direction by young eels in relation t o the geomagnetic field vector. He came to the conclusion that eels in the presence of this field chose a definite direction, varying according to the site (Leningrad, Kaliningrad (Province) or Odessa). There is no longer a choice when the labyrinth is placed inside Helmholtz coils which compensate the geomagnetic field. Ovchinnikov et al. worked on the same labyrinth with elvers and found orientation only if one of the axes of the labryinth was directed along the magnetic meridian. They also observed the disappearance of this orientation if elvers are taken from the terrestrial magnetic field. The fish, however, is no doubt sensitive not t o the terrestrial magnetic field itself, but to the electric field it creates by its own swimming in the magnetic field. There is then active self electro-orientation, the fish being informed of differences of potential existing at the level of its receptors, differences of potential the direction and importance of which vary according t o the direction swum in relation t o magnetic field lines. By this information, the fish would be able to feel the inclination of the earth’s magnetic field and thus know the latitude of its position on the globe. Recently Tesch (1974a) revealed the combined action of geomagnetism and salinity on migratory orientation of silver male eels. I n the female eels, the mean speed of migration was 2 to 2.6 km. The maximal speed sustained for one hour was 4.15 km/h in the silver eels and 6.22 km/h in the yellow eels. The directions taken by the silver eels and by the homing yellow eels were different, almost opposite (Tesch, 1974b). From his own studies and from those of Branover et al. (1971) and of Vasilyev and Gleiser (1973), he reaches the conclusion that in the eel, geomagnetic forces can influence directional choice or activity. Other sensorial systems have also been implicated in certain migrations, like audition. Some fish seem capable of being guided by the sound made by the sea breaking on the shore, but this could only be a very episodic factor in the great migrations we have in mind. Besides, according to Westenberg (1953), this capacity for orientation, a t least in fish in Indonesia which swim always a t about the same distance from the bottom, could be the consequence not of an auditive

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phenomenon, but a sensitiveness of the receptors of the lateral line to resonance phenomena coming from vibrations, produced a t the ruffled water surface, and which are reflected on the bottom of the sea. The acoustic system can also intervene in the detection of certain currents. But this system does not seem to be of major importance. The swim bladder seems clearly associated to audition and also plays a r61e in the vertical migration we are not studying here. To resume, it seems t o us probable that just as the setting off of a migration is not a simple but a very complex mechanism, so the orientation of a great migrator probably results from information received by diverse receptors, the importance of which may vary according to environmental conditions and the physiological state of the migrator a t each stage of migration (Fontaine, 1967; Stasko, 1971).

Moreover we know that the olfactive sensitivity of diverse vertebrates varies according to the endocrine activity of the genital glands and, in Carassius auratus, Hara (1967) has demonstrated that the administration of oestradiol increases the response (evoked potential) induced in the olfactive bulb by the action of a saline solution on the olfactive epithelium. We ourselves have shown (Cedard et al., 1961) that the oestradiol content in the blood of Xalmo salar increases as much in the male as in the female during its anadromous migration from the estuary to the spawning grounds. We can put forward the hypothesis that the olfactive sensitivity t o the odour of the native spawning ground increases therefore, allowing salmon the choice-often very subtle-between two tributaries transporting waters which are chemically very similar. It seems that the endocrine state may influence also the sense of direction of fish by other mechanisms than olfaction (Baggerman, 1964), but these preliminary results call for other research. It may be thought in particular that the secretion of prolactin controlling secretion of the epidermal mucous cells may also intervene in the secretion of pheromones and thus be one of the homing factors (Nordeng, 1971). The exquisite sensitivity of these mechanisms allows us to understand how, either by direct action on the sensorial receptors (lesions of the taste buds) in Ictalurus by detergents (Bardach et al., 1965), or by indirect action through the intermediary of other mechanisms, certain functions or integration mechanisms, diverse pollutants can gravely upset migrations. At a given stage of migration, many mechanisms may be concurrently a t play. Thus we hope to have shown that the sun compass is

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incapable on its own of explaining great migrations, but it seems that it can intervene, since as far as the populations of Oncorhynchus nerka in South Kamtchatka are concerned, night captures are of equal importance in whatever direction the nets are placed, whereas day captures increase in a direction according to the general direction of the fishes’ migration (Suzuki, 1970). It seems probable then that a t a given stage, there is intervention and integration of diverse guidance mechanisms and on which various environmental factors interact. Interactions were found in Atlantic salmon between temperature and the response to an electrical stimulus (Fisher and Elson, 1950), between temperature, light and rheotaxis in a few Oncorhynchus (Miles et al., 1954), and more recently between temperature and memorization in the goldfish (Riege and Cherkin, 1973). I n certain invertebrates, it has been possible t o show that the organism is able t o form an association between concurrent ambient vector patterns of light and such a pervasive ambient environmental component as geomagnetism (Brown and Park, 1967). Such associations should be more widely envisaged in migratory fish a t certain phases of their migration. VII. CONCLUSION I n the course of this article, we have analyzed the physiological mechanisms involved in the determinism of migrations, but they are only one aspect of determinism, the other being comprised of external factors. That external factors play an important r6le in the setting off, the accomplishment and the orientation of migrations is perfectly obvious, but we must, however, come back again t o this point, I think, all the more so that in the case of some of these factors we have no solid basis for deciding by which physiological mechanisms they act and that is why we have not mentioned them so far. The combination of external and internal factors is particularly evident in downstream migration, in our regions, of young Atlantic salmon. I n a given sector of a Pyrenean stream, young salmon acquire characteristics of the smolt, either a t the end of the first, the second or the third year, which clearly demonstrates the essential intervention of a physiological preparation, the speed a t which it occurs depending no doubt on genetic traits inherited from the parents, since they are apparently all submitted to the same environmental conditions. However, in the spring, if the level of the stream remains the same when smoltification has been accomplished, migration only occurs sporadically, individually or in small groups, but as soon as the water level rises, however slightly, as a result of a spring flood,

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then an absolute rush takes place, carrying down thousands of individuals*. The mechanism may be double-faced. The fish which are carried downstream have, as we saw, left their usual parr biotope and no longer dispose of landmarks allowing them to remain at the level of this biotope, all the more so that these spring floods are accompanied by an increase in the turbidity of the waters. But this mechanism can also depend upon a quite exceptional influence of certain environmental factors, an influence resulting from the state of excitability of the fish. Smolts present indeed the characters of sympathicotonic individuals and we know that these are specially meteorosensitive. We can therefore put forward the hypothesis that certain meteorological conditions which determine the spring flood and the spring flood itself intervene in a particularly sensitive nervous system t o “ s e t fire t o the powder ”. On the other hand, the anadromous migrations of salmon seem very slowed down, if not altogether stopped, when the spring floods take place after the melting of the snows, as though certain characteristics of this water acted as repellents t o the salmon. Similar facts are observed regarding the catadromous migration of silver eels which are singularly stimulated by the floods and atmospheric disturbances, particularly on moonless nights. Indeed, in this species, as several studies have displayed, an absolute lunar rhythm exists. Already in 1906, Petersen recorded that it was well known among fishermen that the silver eels migrate downstream almost entirely by night and on nights when the moon is not shining in the evening. Lowe (1952) insisted also on the light factor as inhibiting migration. Deelder (1954) found that, in the upper Rhine Valley, the peak of migration was prior t o the last quarter and comprised mostly females. I n the Baltic and in Dutch waters, migration was after the last quarter and involved mostly males. Deelder concluded that lunar influence is not exerted by light occurring a t migration, as the eels exhibit their lunar rhythm regardless of moonlight conditions, and heavy migrations are known on stormy nights. He suggested that the lunar light cycle may establish an endogenous rhythm so that migration occurs a t the appropriate time, regardless of night sky conditions prevailing on the night of migration. By means of a device making it possible to count eels escaping from the aquatic environment, throughout a nine months experiment, Boetius (1967) noted that the escape activity was shown t o be nocturnal, seasonal and related to the third quarter of the moon. For *In certain regions, it seems that the rise in temperature of the waters and a slight luminosity are favourable to the descent of the smolts (White, 1939).

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these reasons, escape activity was considered to equal the aquatic migratory activity of silver eels. The experiment was conducted in permanent darkness ; thus migratory activity of silver eels was shown to be independent of light, daylight as well as moonlight. It appears that the lunar rhythm of the European eel on the start of its catadromous migration really exists, but it remains unexplained so far. It is connected most certainly, however, with physiological mechanisms and that is why this problem had to be stressed here. To return, however, to the smoltification of young salmon, no doubt internal factors seem to us essential in this transformation, but we must not however exclude the intervention of external factors. At the time of this smoltification (at the end of winter and the beginning of spring, in France), there is increased illumination and we know the important influence of light in the stimulation of certain endocrine glands. It has been suggested (Hoar, 1953) that smoltification must be accelerated by lighting and this conception was supported by certain experiments (Kubo, 1959). However, I have often brought back to Paris young parr salmon from the spawning grounds of the Pyrenean streams. Now, when kept in covered basins, sheltered from the light, these young parrs acquire the main characteristics of the smolt and in particular the guanine deposit in the scales, at the same time as the young salmon remaining in their natural environment do. Saunders and Henderson (1970) have likewise noticed that the contrary of the natural photoperiod (decreasing day length in the spring) does not prevent the parr of Atlantic salmon from acquiring its silvery colouring and growing rapidly, and Zaugg and Wagner (1973) note that, if the onset of the smolting process is, in steelhead trout, influenced by the photoperiod, smolting occurs even if steelhead are reared in complete darkness. Everything happens then as though, initially, a seasonal rhythm was produced by external factors and as though this rhythm had become an innate behaviour, no longer depending completely on some of these manifestations of external conditions. Yet, Saunders and Henderson remark that these smolts, submitted to a decreasing day length in the spring, develop in fresh water higher conditions than normal smolts and, when transported into the sea, they eat less, grow more slowly and have lower efficiencies of food conversion than those subjected to a natural or constant photoperiod. Zaugg and Wagner note that the gill Na, K, ATPase was decreased and migration reduced when fish were subjected to temperatures of about 13OC or greater, or when the length of increasing photoperiods approximated that of the summer solstice. We should stress the fact that the

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smoltification processes of Salmo gairdneri, and in particular the increase of the Na-K-ATPase in the gills, are inhibited by a rise in temperature above a value situated between 10" and 15OC (Adams et al., 1973), for this point is very important with regard to the biological effects of thermic pollutions, especially those due to the functioning of power plants. Thus for certain characteristics the impact of external factors, not only light, but also temperature (Kubo, 1956, 1959; Johnston and Eales, 1968; Adams et al., 1973), is apparent. However, we must emphasize how certain other stages in the migration of salmon seem independent of external factors. Thus the anadromous migration of the Atlantic salmon occurs a t very different times of the year. We have been able to observe in the Adour Basin the upstream rise of salmon in the autumn, winter, spring, even sometimes in summer. We must admit then that the factor of individual preparation for reproductory migration prevails over external factors in this case, which can, however, modify certain aspects of upstream migration, in particular its length of time. Gard (1973) has shown, for example, that the season and rain affect the duration of the reproductory migration of Oncorhynchus nerka, as also the number of fish. These observations, like the phenomena of morphological, anatomical and physiological preadaptation that we have pointed out on different occasions and which occur a t definite stages in the life cycle of a migratory fish, evoke endogenous rhythms in which external synchronizers can intervene. But these rhythms are of a rather special type for, as we have seen, there are many which do not reproduce according to a well determined rhythm, reproductory and trophic migrations being capable of appearing at different ages in individuals, their periods presenting therefore a certain variability. Inversely, the annual spawning rhythm of the salmon seems extremely precise. It would be very desirable if chronobiologists, who until now have devoted the greater part of their activities to circadian rhythms, could study more closely, with the help of the resources offered by this science, which is now well advanced, migratory rhythms, which so far have received little attention. If, in the same way, there is interaction of external and internal mechanisms, so there is certainly interaction of physiological mechanisms. It has been demonstrated in mammals that there is interaction of ionoregulatory and endocrine mechanisms on the central nervous system. For example, the minimal strength of electroshock needed to produce convulsions (E.S.T.) in the rat depends at once on adrenocortical hormones and plasma content in certain electrolytes (Woodbury, 1954). Ionic modifications observed in the

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nervous system and the muscle in the course of smoltification (Chartier-Baraduc, 1960), the double hyperfunctioning of the interrenal and the thyroid are closely linked phenomena which no doubt have an impact on the excitability of the nervous system. Certain stages of migrations, and in particular the phases setting off catadromous migrations, may be considered types of normal physiological stress. Indeed stress (Selye) is a complex combination of nociceptive stimuli and of the reactions which they produce in the organism on which they act. For example, in the case of certain preparations for catadromous migrations examined above, following the weakening of iono- and osmoregulatory mechanisms in hypotonic environments, the hypotonicity of the water becomes nociceptive. Certain neuroendocrine and sympathicotonic activity peaks represent acrophases, according t o the terminology of chronobiologists, which contribute t o placing the organism in conflict with a given environment and inciting it t o change environments. Certain reactions appear t o act immediately as correctors, but others seem t o be a preparation for a new environment which the migrator will reach some days or weeks later. We cannot fail t o recall here Barcroft’s famous phrase: ‘‘ The stage must be set before the play commences ”, and these phenomena call forth the idea of a preestablished rhythm, remarkably adapted t o the ulterior phase of the life cycle. Thus whereas the European silver eels start off with visual pigments consisting for the most part of rhodopsin (A max = 500 nm) or chrysopsin (A = 487 nm), the young smolts begin with a visual pigment largely composed of porphyropsin (A = 523 nm). This difference in the absorption of luminous radiations is very probably related to the type of life immediately following the catadromous migrations of one and the other species, the eels diving down rapidly into the relatively deep layers of the ocean, the smolts carrying out the first part a t least of their trophic migration in the surface waters (several smolts tagged in the Pyrenean streams have been recaptured off the Breton coast in mackerel nets immerged in the surface waters). However, it seems clear that, a t the adult stage, salmon can dive down more deeply, and in adult Oncorhynchus caught a t sea, rhodopsin predominates. After that, porphyropsin gradually increases in the course of anadromous migration so that 3-4 dehydro derivatives of retinaldehyde can attain 90% of the visual pigment after spawning (Beatty, 1966). The determinism of these modifications of the visual pigment, although clarified by certain experiments involving hormones, is still not completely known and is certainly most complex. Nevertheless, this preparatory phase for a

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future environment, a t a given stage of development, can be stopped and can regress if environmental conditions different from the natural ones which should normally have occurred, are imposed on the migrator. Such is the case with smolts on migration, which, when kept in fresh water, go back to a colouring and type of osmoregulation of a freshwater fish different from that which they would have kept and accentuated if they had been able to carry out their natural migration. These stresses are no doubt made easier by the fact that migrators in general seem t o be species with more marked fluctuations in endocrine activity than sedentary ones (Fontaine, 1946 ; Fontaine and Leloup, 1952) and it is understandable that this phenomenon accentuates certain phases of unbalance between the organism and its environment. The idea that certain neuroendocrine activity phases are particularly intensive in great migrators corroborates the fact that these migratory species show much more important phases of accelerated growth than those of non-migratory species and much higher reproductory capacities. For example, in Salvelinus malma (Walbaum), if a migratory population is compared with a sedentary one, it is found that the sedentary produce 66 eggs on an average, whereas the migrators produce an average of 1880 eggs (Blackett, 1973). We notice that stress not only implies the intervention of exteroceptive agents, but also that of interoceptive agents like fasting which no doubt intervenes a t certain stages of migration (eel, salmon). To these aggressions correspond reactions constituting the adaptation syndrome comprising in particular a hypersympathicotony and an intensification of adrenalin secretion (the hormone of critical circumstances, according t o Cannon’s phrase), and a stimulation of the interrenal. This physiological stress that we have just mentioned and which occurs in migrators a t certain particular phases of the life cycle, not only results in contributing to the setting off of a migratory phase, but also-at least by certain actions-promotes preadaptation to a change of environment, for example in the parr smoltifying in fresh water, by causing a displacement of a neurosecretory product of the hypothalamus in the neurohypophysis, a phenomenon which, as we have seen previously, most probably plays a role in the adaptation t o a higher salinity. We should also draw attention to the fact that in a same genus, the relative importance of internal and external factors in setting off migration seems capable of variation. We have noted this regarding various Oncorhynchus species in which smoltification can be of very varying intensity, which probably implies certain endocrine hyperfunctionings of very differing importance. This is also true for eels. We have taken as

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examples in this study Anguilla anguilla and Anguilla rostrata. But it seems clear that in Anguilla nebulosa labiata, studied in East Africa by Van Someren (1962), the anatomical and morphological modifications characteristic of individuals of these two other species (early development of gonads, silvering, widening of the eyes) are lacking. No doubt a physiological study would be necessary to discover if a physiological preparation for migration really does not exist, but it is probably more modest than in both the other species mentioned above, since it does not bring about certain morphological modifications, evident in these. Consequently, the importance of external factors and in particular, according to Van Someren, turbidity of the water, would seem to prevail over internal factors in setting off migration. We have stressed the idea of conflict being capable of setting off migration, but life,is made up, as Claude Bernard wrote, not only of conflict but also of cooperation between the organism and its environment, and the arrival of a fish, on its catadromous migration, in the sea may be taken to represent, following a conflict, cooperation with the environment, since certain disequilibriums disappear. For example, when the smolt, which, in relation to the parr, shows a clear increase of K in the muscle and brain and a decrease in the Ca and Na content and of calcium concentration (Fontaine et al., 1969), reaches the sea, it is obvious that it has arrived a t an environment favourable to a return to this ionic equilibrium (Chartier-Baraduc, 1960) and, as a result, of its excitability. It seems that the need for a particularly close cooperation is specially evident a t the moment in the life cycle when the organism is most demanding regarding environmental conditions, in the course of the first development stages of the egg and during larval life. This is no doubt a necessity for the perennity of the species that the eels, whose larvae have been carried away, most likely by the currents, and often very far from the spawning grounds, return to them to spawn. Cooperation seems even closer with salmon, each population returning to its native river, although very diverse populations are found on the feeding grounds. To conclude, let us see how the physiological condition of great migrators fits into the evolution of the phylum of teleosts. All fish present cycles of endocrine glandular activity and the importance of their fluctuations seems more important, as we have already seen, in great migrators than in sedentary individuals of the same phylum. We may wonder consequently whether migrators do not descend from sedentary species by an orthogenetic evolution involving endo-

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crine and neuroendocrine hyperfunctionings. The study of orthogenetic series in mammals, and reptiles in particular, show clearly how small-sized ancestors have led progressively to larger types, both fossil or living. This evolution could not have been accomplished without a parallel functional evolution of the endocrine glands, an important factor in growth. Moreover, in certain cases (giant reptiles of the secondary era afflicted with acromegaly and consequently condemned to become extinct (Decugis, 1941) or, in general, great extinct fossil vertebrates (Edinger, 1944)), the volume of the pituitary seems to have increased, causing a disequilibrium between the organism and its environment. This hypothesis regarding great migrators is supported by several facts. Without doubt certain endocrine hyperfunctionings, normal for the species, reach peaks of intensity unknown in sedentary species, leading certain species to pathological states causing the death of individuals, once they have ensured survival of the species (for example, the Cushing syndrome in Oncorhynchus (Robertson and Wexler, 1959, 1960)). Now this could be the consequence of an orthogenetic evolution, as on the one hand, in a given phylum comprising sedentary and migratory species (in particular amphihalines), it is the latter which reach the largest size, and on the other hand certain anatomical and biochemical criteria allow us to consider salmonids, clupeids, pleuronectids and anguillids as particularly ancient families (Fontaine, 1946) and they all include amphihaline species. When we speak of endocrine hyperfunctionings of migratory species, we are not thinking of the hypothesis, no doubt over-simplified, of an endocrine hyperfunctioning having a bearing, in a very general way, on the whole of the endocrine system, but rather of a hyperfunctioning concerning certain sectors of the endocrine system, so that it is not only an increase of hormonal secretion which can bring about a disequilibrium between the organism and its environment, but also a modification in the ratio of these secretions. If this is so, we may consider that the physiology of a migratory behaviour represents a final stage in the physiological evolution of a phylum, Thus species which are migratory today might not always have been so and certain paleontological observations bear out this conception. If the Alosas of the tertiary era, for example, had been migratory, would it not be curious if they were only to be found in marine formations, to the exclusion of freshwater formations, such as those of Aix, in particular, whereas today a large majority of amphihaline Alosa succumb very rapidly in fresh water after reproduction? The hypothesis that certain species arrive gradually a t their migratory

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habits, following either a geographical or climatic evolution, or certain characteristics of biotopes (see Barannikova, 1975), or again physiological evolutions, or even a conibination of one or the other of these factors seems to be in accordance with the fact that even a t the present time, numerous families comprise, together with sedentary or holohaline species, migratory amphihaline species and that we observe, in the same genus, a whole gamet of behaviours from sedentarity to a far-reaching migration (for example, Salmo fario L., a stream trout, or river trout S . trutta L., and a sea trout, Salmo salar). Even within a typically migratory species (Salmo salar), certain individuals (parrs 6)can reach genital maturity (paedogenetic cycle) without having been compelled to migrate. Moreover, it has been possible to bring back certain populations of migrators t o a sedentary condition either by their natural isolation in lakes (landlocked fish-geographical or ecophysiological isolation (Ward, 1932)) or as a result of zootechnical demands (pisciculture). Others see certain stages of their migrations modified by important public works. This is the case for the Zuider Zee anchovy which, following the reclamation of land here, has adopted new spawning grounds (Russell, 1937). These are environmental conditions which modify the course of evolution. I n the landlocked condition, moreover, some of these populations still show a tendency to migrate by accomplishing a reduced migration in the river or rivers flowing into the lake, whereas others reproduce in the lake itself. It would be advisable to follow the physiological evolution of these migrators which have been brought back a t the present time, a t many points of the globe, t o sedentary conditions for reasons of pisciculture. Such studies would be of very great interest, not only for fundamental research, but also for applied science. VIII. ACKNOWLEDGEMENTS Our acknowledgements are due t o Madame Mary Delahaye, Librarian of the Institut oc&nographique, Paris, who is responsible for the translation of this article from the French original. IX. REFERENCES Abraham, M. ( 1 9 7 1 ) . The ultrastructure of the cell types and of the neurosecretory innervation in the pituitary of Mugil cephalus L. from fresh water, the sea and a hypersaline lagoon. General and Comparative Endocrinology, 17, 334-350. Abraham, M. (1974). L’ultrastructure de l’adbnohypophyse des Muges (TBlbostBens) adapt& aux biotopes da salinites diverses. Ann& biologique, I n press.

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Abraham, M., Blanc, N. and Yashouv, A. (1966). Oogenesis in five species of grey mullets (Teleostei, Mugilidae) from natural and landlocked habitats. Israel Journal of Zoology, 15, 155-172. Acher, R. (1971). I n “Biochemical Evolution and the Origin of Life” (E. Schoffeniels, ed.), pp. 43-51. North Holland Publishing, Amsterdam. Adarns, B. L., Zaugg, W. S. and McLain, L. R. (1973). Temperature effect on parr-smolt transformation in steelhead trout (Salmo gairdneri) as measured by gill sodium-potassium stimulated adenosine triphosphatase. Comparative Biochemistry and Biophysics, 44A, 1333-1339. Akulin, V. N. (1966). Les variations de l’engraissement chez des jeunes d’0ncorhynchus nerka en relation avec l’avalaison Rybnoe Khozjajstvo, 8, 11-12 (In Russian). Aldinger, E . E., Kastin, A. J., Schally, A. V., Hawley, W. D. (1971). Cardiovascular action of MSH in the dog. Clinical Research, 19, 18. Ali, M. A. and Hoar, W. S. (1959). Retinal responses of pink salmon associated with its downstream migration. Nature, London, 184, 106-107. Aloncle, H. and Delaporte, F. (1974). Recherches sur le germon. Campagnes 1973 de 1’I.S.T.P.M. dans 1’Atlantique N.-E. Science et Pe^che, Bulletin de I’Institut des Pe^chesmaritimes, no 235, 1-1 1. Andrianov, G. N. and Ilyinsky, 0. B. (1973). Some functional properties of central neurons connected with the lateral-line organs of the catfish (Ichtalurus nebulosus). Journal of Comparative Physiology, 86, 365-376. Ardeleanu, A. (1971). Importance du tonus thyroi‘dien dans l’effort physique. (Etudes exphrimentales). Revue Roumaine d’Endocrinologie, 8, 233-242. Arvy, L., Fontaine, M. and Gabe, M. (1959). La voie neuros6crhtrice hypothalamo-hypophysaire des Thlhosthens. Journal de Physiologie, Paris, 51, 1031-1085. Babikker, M. M. and Rankin, J. C. (1972). Effects of neurohypophysial hormones on renal function in the freshwater and sea water adapted eel (Anguilla anguilla L,). Journal of Endocrinology, 57, XI-XII. Bachelier, R. (1972). Le tropisme herhditaire des jeunes d’anguilles. Bulletin frangais de Pisciculture, no. 245, 151-163. Baggerman, B. (1957). An experimental study on the timing of breeding and migration in the threespined stickleback (Gasterosteus aculeatus L.). Archives nkerlandaises de Zoologie, 12, 105-3 17. Baggerman, B. (1960). Salinity preference, thyroid activity and the seaward migration of four species of Pacific salmon (Oncorhynchus). Journal of the Fisheries Research Board of Canada, 17, 295-322. Baggerman, B. (1963). The effect of TSH and antithyroid substances on salinity preference and thyroid activity in juvenile Pacific salmon. Canadian Journal of Zoology, 41, 307-319. Baggerman, B. (1964). On the endocrine background of stickIeback behaviour. Archives derlandaises de Zoologie, 16, 159-163. Baraduc, M. M. and Fontaine, M. (1955). Etude cornparhe du m6tabolisme respiratoire du jeune saumon shdentaire (parr) et migrateur (smolt). Comptes rendus des SBances de la Sociktk de Biologie, Paris, 149, 1327. Barannikova, I. A. (1957). La diffhrenciation biologique du banc de l’esturgeon Volga-Caspienne (en relation avec les problhmes de la pisciculture de production d’esturgeons dans le delta de la Volga). Uchenye zapiski Leningradskogo gosudarstvennogo universiteta imeni A . A . Zdanova, 228, 44, 57-72. (In Russian.)

334

M . FONTAINE

Barannikova, I. A. (1964). Das hypothalamo-hypophysare System und die Wanderungen der Salmoniden und Acipenseriden. Biologische Rundschau 1, 164-173. Barannikova, I. A. (1965). Les bases fonctionnelles du comportement migratoire de poissons anadromes. I n “ Biologischeskoe znachenie i funkcionalnaja determinacija migracionnogo povidenija zhivotnykh ”, pp. 32-53. Izdatelstro Nauka, Moscow-Leningrad. (In Russian.) Barannikova, I. A. (1975) “ Les bases foncionnellesdes migrations de poissons ”, 210pp. Izdatelstro Nauka, Leningrad. (In Russian.) Bardach, J. E. and Atema, J. (1971). The sense of taste in fishes. I n “ Handbook of Sensory Physiology,” Vol. 4, pp. 293-336. Springer-Verlag, Berlin. Bardach, J. E., Fujiya, M. and Holl, A. (1965). Detergents: effects on the chemical senses of the fish Ictalurus natalis (Le Sueur). Science, New York, 148, 1605-1607. Barnard, R. J., Edgerton, V. R. and Peter, J. B. (1970). Effect of exercise on skeletal muscle. I. Biochemical and histochemical properties. Journal of Applied Phylsiology, 28, 762-766. Beatty, D. D. (1966). A study of the succession of visual pigments in Pacific salmon (Oncorhynchus). Canadian Journal of Zoology, 44, 429-455. Beatty, D.D. (1969). Visual pigment changes in juvenile kokanee salmon in response to thyroid hormones. Vision Research, 9, 855-864. Beatty, D. D. (1972). Visual pigment changes in salmonid fishes in response to exogenous L-thyroxine, bovine T.S.H. and 3-dehydroratinal. Vision Research, 12, 1947-1960. Bellini, A. (1907). Expbriences sur 1’6lavage de l’ilnguille en stabulation 8. Comacchio. Bulletin de la Sociitte’ Centrale d’Aquiculture et de P&he, Paris, 19. Bern, H. A. and Nicoll, C. S. (1968). The comparative endocrinology of prolactin. Recent Progress i n Hormone Research, 24, 681-720. Bern, H. A. and Takasugi, N. (1962). The caudal neurosecretory system of fishes. General and Comparative Endocrinology, 2, 96-100. Bern, H. A,, Nishioka, R. S., Chester Jones, I., Chan, D. K. O., Rankin, J. C. and Ponniah, S. (1967). The urophysis of teleost fish. Journal of Endocrinology, 37, XI-XII. Bernardi, C. (1948). Correlazioni dell’ipofisi e della tiroid con lo stato di maturazione delle gonadi nelle anguille gialle e argentine. Rivista d i Biologia Italia, 40, 186-228. Bertin, L. (1942). “ Les Anguilles ”. Payot, Paris. Bier, A. and Roman, W. (1931). Das Wesen der postoperativen Reaktion bei Morbus Bassedowii nach Thyroydektomie. Zeitschrift. f u r Klinische Medizin, 118, 15. Bilinski, E. (1963). Utilization of lipids by fish. I. Fatty acid oxidation by tissue slices from dark and white muscle of rainbow trout (Salmo gairdnerii). Canadian Journal of Biochemistry and Physiology, 41, 107-1 12. Bilinski, E. (1968). Lipid catabolism in fish muscle. I n “Fish in Research ” (0.W. Neuhaus and J. E. Halver, ed.) pp. 135-151, Academic Press, New York. Bilinski. E. (1974). Biochemical aspects of fish swimming In “ Biochemical and Biophysical Perspectives in Marine Biology ” (D. C. Malins and J. R. Sargent, eds.), pp. 239-287. Academic Press, London and New York.

.

MIGRATION OF MARINE AND AMPHIHALINE FISH

335

Bitinkov, E. P. (1959). La question des migrations verticales journalihes de Clupea harengus. Doklady Akademii Nauk SSSR, 128, 179-182. (In Russian.) Blackett, R. F. (1973). Fecundity of resident and anadromous Dolly Varden (Salvelinus malma) in Southeastern Alaska. Journal of the Fisheries Research Board of Canada, 30, 543-548. Blanc-Livni, N. and Abraham, M. (1970). The influence of environmental salinity on the prolactin- and gonadotropin-secreting regions in the pituitary of Mugil (Teleostei). General and Comparative Endocrinology, 14, 184-197. Blum, V. (1966). Zur hormonalen Steuerung der Brutpflege einiger Cicliliden. Zoologische Jahrbiicher Abteilung fiir allgemeine Zoologie und Physiologic der Tiere, 76, 340-355. Blum, V., Machemer, L., Bartmann, W. D. (1972). Die Wirkung von T.S.H. und L.T.H. auf das Verhalten und auf die Histologie der Haut, der Schilddriise und der Gonaden beim Pfauenschleimfish Blennius pavo. Zoologishe Jahrbucher Abteilung f u r allgemeine Zoologie und Physiologie der Tiere, 72, 264-290. Boetius, J. (1967). Experimental indication of lunar activity in European silver eels Anquilla anquilla L. Meddelelser f r a Kommissionen for Dankmarks Fiskeri- og Havundersogelser, N.S., 6, 1-6. Bostrom, S.-L. and Johansson, R. G. (1972). Enzyme activity patterns in white and red muscle of the eel (Anguilla anquilla) at different developmental stages. Comparative Biochemistry and Physiology, 42B, 533-542.

Boucher-Firly, S. ( 1 935). Recherches biochimiques sup les TBleost6ens Apodes (Anguille, Congre, MurBne). Annales de -1 ’Institut ochnographique, 15, 2 17-3 27.

Boucher-Firly, S. and Fontaine, M. (1933). Rapports existant entre quelques stades de developpement de 1’Anguille et le point de congelation de son serum lors du passage en eau de mer. Comptes rendus des S h n c e s de la Socidte de Biologie, Paris, 112, 462. Branover, G. G., Vasil’yev, A. S., Gleiser, S. I. and Tsinober, A. B. (1971). A study of the behaviour of eels in natural and artificial magnetic fields and an analysis of its reception mechanism. Journal of Ichthyology, 11, 608-614.

Brett, J. R. (1971). Energetic responses of salmon to temperature. A study of some thermal relations in the physiology and freshwater ecology of sockeye salmon (Oncorhynchus nerka). American Zoologist, 11, 99-113.

Brett, J. R. and Ali, M. A. (1958). Some observations on the structure and photomechanical responses of the Pacific salmon retina. Journal of the Fisheries Research Board of Canada, 15, 815-829. Brett, J. R. and MacKinnon, D. (1952). Some observations on olfactory perception in migrating adult coho and spring salmon. Fisheries Research Board of Canada, Pacific Progress Report, no. 90, 21-23. Bridges, C. D. B. (1972). The rhodopsin-porphyropsin visual system. I n “Handbook of Sensory Physiology”. (H. J. A. Dartnall, ed.) Vol. 7, pp. 417-480 Springer Verlag, Berlin. Britton, S. W. (1924). The body temperature of fishes. Contributions to Canadian Biology. ( N ew Series) 1, 415-418.

336

M. FONTAINE

Broekema, M. M. M. (1941). Seasonal movements and the osmotic behaviour of the shrimp Crangon crangon. Archives ne‘erlandaises de Zoologie 6, 1-100. Brown, F. A. Jr and Park, Y. H. (1967). Association-formation between photic and subtle geophysical stimulus patterns. A new biological concept. Biological Bulletin, 132, 31 1-319. Buckland, F. (1880). “ Natural History of British Fishes 420 pp. Unwin, London. Bull, H. 0. (1936). Studies on conditioned responses in .fishes. VII. Temperature perception in Teleosts. Journal of the Marine Biological Association of the United Kingdom, 21, 1-27. Bull, H. 0. (1938). Studies on conditioned responses in fishes. VIII. Discrimination of salinity changes by marine teleosts. Report of the Dove Marine Laboratory, 5, 19-35. Burian, R. (1910). Funktion der Nierenglomeruli und Ultrafiltration. Pflugers Archiv fiir die gesamte Physiologie des Menschen und der Tiere, 136, 741. Buser-Lahaye, J. and Ruivo, M. (1954). Modifications du volume de la glande thyroide au cows de la metamorphose de Sardina pilchardus (Walb.) de la mer de Banyuls. Comptes rendus hebdomadaires des Se’ances de 1’Academie des Sciences, Paris, 239, 1691-1693. Callamand, 0. (1943). L’Anguille europ6enne (Anguilla anguilla L.) : les bases physiologiques de sa migration. Annales de l’lnstitut ockanographique, 21, 361-440. Callamand, 0. and Fontaine, M. (1942). Activit6 thyroldienne de 1’Anguille au cows de son d6veloppement. Archives de Zoologie ezpdrimentale el ge‘ndrale, 82, 129-136. Carey, F. G. and Teal, J. M. (1966). Heat conservation in tuna fish muscle. Proceedings of the National Academy of Science of the U.S.A., 56, 1464-1469. Carey, F. G. and Teal, J. M. (1969a). Mako and porbeagle: warm-bodied sharks. Comparative Biochemistry and Physiology, 28, 199-204. Carey, F. G. and Teal, J. M. (1969b). Regulation of body temperature by the bluefin tuna. Comparatice Biochemistry and Physiology, 28, 205-221. Carlisle, D. B. and Denton, E. J. (1959). On the metamorphosis of the visual pigments of Anguilla anguilla L. Journal of the Marine Biologicai Association of the United Kingdom, 38, 97-102. Cedard, L., Fontaine, M., Nomura, T. (1961). Sur la teneur en oestrogknes du sang du saumon adulte (Salmo salar L.) en eau douce. C’omptes rendus hebdomadaires des Sdances de I’Academie des Sciences, Paris, 252,2656-2657. Chan, D. K. 0. (1974). Renal effects of urotensin I and 11. General and Comparative Endocrinology, I n press. Chan, D. K. 0. and Chester Jones, I. (1969). Pressor effects of neurohypophysial peptides in the eel Anguilla anguilla L. with some reference t o their interaction with adrenergic and cholinergic receptors. Journal of Endocrinology, 45, 161-174. Chartier-Baraduc, M. M. (1959). Etude des echanges de l’ion chlore avec le milieu chez le jeune saumon (Salmo salar) sedentaire et migrateur. Comptes rendus des Se’ances de la Socie‘td de Biologie, Paris, 162, 1968-1973. Chartier-Baraduc, M. M. (1960). Etude de quelques aspects du metabolisme hydromineral chez Salmo salar au cours de la smoltification et de la’ migration catadrome. Bulletin d u Centre d’Etudes et de Re‘cherches Scienti$que, Biarritz, 3, 19-31.

”.

MIQRATION OF MARINE AND AMPHIHALINE FISH

337

Chartier, M. M. and Fontaine, M. (1974). Unpublished data. Chu, A. J. and Hanaolra, T. (1973). Studies on osmotic pressure of the 11. Changes environmental media and body fluids of marine fish. in the osmotic pressure of body fluid in pelagic marine fish related to their maturity. Bulletin of the Japanese Society of Scientific Fisheries, 39, 349-355. Cligny, A. (1912). Migration marine de l’anguille commune. Comptes rendus hebdomadaires des Skances de 1’Academie des Sciences, Paris, 154, 727- 729. Colombo, 0. (1961). Chloride-secreting cells in the gills of European eels. Nature, London, 190, 101. Colombo, G. and Cecchini, S. (1959). Ricerche sull’osmoregolazione nelle anguille gialle e nelle anguille argentine. Rendiconti delle sedute della Accademia ATazionale di Lincei, 27, 136-137. Conte, F. P. and Lin, D. H. Y. (1967). Kinetics of cellular morphogenesis in gill epithelium during sea water adaptation of Oncorhynchus (Walbaum). Comparative Biochemistry and Physiology, 23, 945-957. Cowey, C. B. and Parry, G. (1963). The non-protein nitrogenous constituents of the muscle of parr and smolt stages of the Atlantic salmon. Comparative Biochemistry and Physiology, 8, 47-51. Craigie, E. H. (1926). A preliminary experiment on the relation of the olfactory sense t o the migration of the sockeye salmon (Oncorhynchus nerka Wal.). Transactions of the Royal Society of Canada, 5, 215-224. Creutzberg, F. (1958). Use of tidal streams by migrating elvers (Anguilla vulgaris Turt.). Nature, London, 181, 857-858. Creutzberg, F. (1961). On the orientation of migrating elvers (Anguilla vulgaris Turt.) in a tidal area. Netherlands Journal of Sea Research, 1, 257-338. Creutzberg, F. (1963). The role of tidal streams in the navigation of migrating elvers (Anguilla vulgaris Turt .). Ergebnisse der Biologie, 26, 118-127. Cristy, M. (1974). Effects of prolactin and thyroxine on the visual pigments of trout, Salmo gairdneri. General and Comparative Endocrinology, 23, 58-62. D’Ancona, U. (1946). Observations sur la proportion des sexes chez les Anguilles des lagunes littorales de 1’Adriatique. Dodonea, XIII, Jaarbock, p. 261. Davy, J. (1835). On the To of some fishes of the genus Thynnus. Proceedings of the Royal Society, 3, 327-328. Decugis, H. (1941). “ Le vieillissement du monde vivant ’’. Masson, Paris. Deelder, C. L. (1949). On the orientation of migrating animals. Bijdragen tot de Dierkunde, 28, 503. Deelder, C. L. (1952). On the migration of the elver (Anguilla vulgaris) a t sea. Journal d u Conseil international pour I’Exploration de la Mer, 18, 187-21 8. Deelder, C. L. (1954). Factors affecting the migration of the silver eel in Dutch inland waters. Journal d u Conseil international pour Z’Exploration de la Mer, 20, 177-185. Deelder, C. L. (1958). On the behaviour of elvers (Anguilla vulgaris) migrating from the sea into fresh water. Journal d u Conseil international pour L’Exploration de la Mer, 24, 135-146.

338

M. FONTAINE

Deelder, C. L. and Tesch, F.-W. (1970). Heimfindevermogen von Aalen (Anguilla anguilla), die iiber grosse Entfernungen verpflanzt worden waren. Marine Biology, 6, 81-92. Denton, E. J. and Warren, F. J. (1956). Visual pigments of deep-sea fish. Nature, London, 178, 1059. De Wied, D. and Bohus, B. (1966). Long term and short term effects on retention of a conditioned avoidance response in rats by treatment with long acting pitressin and A-MSH. Nature, London, 212, 1484-1486. De Wied, D., Bohus, B. and Greven, H. M. (1968). Influence of pituitary and adrenocortical hormones on conditioned avoidance behaviour in rats. I n “ Endocrinology and Human Behaviour (R. P. Michael, ed.) pp. 188-196. Oxford University Press, London. Domagk, G. F. and Zippel, H. P. (1971). Chemical transfer of colour and taste discrimination in goldfish. Biology of Memory, Symposia biologica hungaria, 10, 185-189. Doudoroff, P. (1945). The resistance and acclimatization of marine fishes to temperature changes. Experiments with Pundulus and Atherinops. Biological Bulletin, 88, 194-206. Dunbar, M. J. (1972). The nature and definition of the marine subarctic with a note on the sea-life area of the Atlantic salmon. Transactions of the Royal Society of Canada (ser. 4),10, 249-257. Edinger, T. (1944). The pituitary body in giant animals fossil and living: a survey and a suggestion. Quarterly Review of Biology, 17, 31-45. Egnchi, H., Hashimoto, K., Matsuura, F. (1960). Comparative studies of two hemoglobins of salmon. 111. Amino acid composition. Bulletin of the Japanese Society of Scientific Fisheries, 26, 810-81 3. Enami, M., Miyashita, S. and Imai, K. (1956). Studies in neurosecretion. IX. Possibility of occurrence of a sodium regulating hormone in the caudal neurosecretory system in teleosts. Endocrinology, Japan, 3, 280-290. Engel, F. L., Albertson, T., Fredericks, J. and Lopez, E. (1958). Evidence for stimulation of insulin secretion by growth hormone in the rat. Endocrinology, 63, 99-105. Epstein, F. H., Cynamon, M. and McKay, W. (1971). Endocrine control of Na-K-ATPase and sea-water adaptation in Anguilla rostrata. General and Comparative Endocrinology, 16, 323-328. Evans, H. M. (1940). On some seasonal changes in the pituitary glands of the eel. British Medical Journal, 565. Evropeitzeva, N. V. (1960). Les corrhlations des processus du dhveloppement pr6coce des gonades et du passage tL 1’6tat de “descente” des mBles du saumon de la Baltique (Salmo sal5r L.) dans les conditions d’htangs. Akadernii nauk SSSR, Zoologicheskii Zurnal, 39, 777-778. (In Russian. ) Evropeitzeva, N. V. (1962). The comparative analysis of the desmoltification process in young specimens of various ecological forms of Atlantic salmon. Uchenye zapiski Leningradskogo gosudarstvennogo universiteta imeni A . A . Zdanova, 331, Serija biologischeskikh nauk, no. 48, 46-73. (In Russian.) Fiedler, K. and Blum, V. (1972). Prolactin sensitive neurons in the forebrain of some fishes. Experientia, 28, 1384-1385. Fisher, K. C. and Elson, P. F. (1950). The selected temperature of Atlantic salmon and speckled trout and the effect of temperature on the response to an electrical stimulus. Physiological Zoology, 23, 27-34.

”.

MIGRATION OF MARINE AND AMPHIHALINE FISH

339

Fontaine, M. (1930). Recherclies sur le milieu interieur de la Lamproie marine. Comptes rendus hebdomadaires des Sdances de l’rlcademie des Sciences, Paris, 191, 680. Fontaine, M. (1946). Vues actuelles sur les migrations. Experientia, 7 , 1-15. Fontaine, M. (1951). Sur la diminution de la teneur en chlore du muscle des jeunes Saumons (smolts) lors de la migration d’avalaison. Comptes rendus hebdomadaires des Sdances de I’Academie des Sciences, Paris, 232, 2477-2479. Fontaine, M. (1956). Analyse expbrimentale de I’instinct migrateur des poissons. I n “L’instinct dans le comportement des animaux et de l’homme Rapports du Colloque de la Fondation Singer-Polignac, pp. 151-175. Masson, Paris. Fontaine, M. (1960). Quelques problemes physiologiques poses par le Salmo salar. Inter& de l’btude de la smoltification, type de preparation au comportement migratoire. Experientia, 16, 433-438. Fontaine, M. (1967). Quelquss aspects des mbcanismes physiologiques dcs p h h o m h e s migratoires. I n “ La distribution temporelle des activitbs animales et humaines ”. (R. Chauvin, ed.) pp. 135-145. Masson, Paris. Fontaine, M. and Baraduc, M. M. (1954). Influence d’une thyroxinisation prolonghe sup l’euryhalinith d’un SalmonidB, la Truite arc-en-ciel (Salmo gairdnerii Rich.). Comptes rendus des Skances de la Socidtk de Biologie, Paris, 148, 1942. Fontaine, M. and Callamand, 0. (1941). Sur l’hydrotropisme des civelles. Bulletin de l’lnstitut ockanographique, 811, 1-6. Fontaine, M. and Chartier, M. M. (1974). Unpublished data. Fontaine, M. and Fontaine, Y. A. (1956). Determination du pouvoir thyreotrope de l’hypophyse et du milieu interieur des TBlbost6ens par mesure de fixation de l a l I par la thyroide de la Truite arc-en-ciel (Salmo gairdnerii L.). Journal de Physiologie, Paris, 48, 881-892. Fontaine, M. and Hatey, J. (1953). Contribution B 1’6tude du m6tabolisme glucidique du saumon (Salmo salar L.) ti diverses &apes de son developpement et de ses migrations. Physiologia comparata et oecologia, Den Haag, 3. 37-52. Fontaine, M. and Koch, H. (1950). Les variations d’euryhalinitb et d‘osmoregulation chez les poissons. Leur rapport possible avec le determinismo des migrations. Journal de Physiologie, 42, 287-318. Fontaine, M. and Leloup, J. (1952). Iodemie et thyroxinemie Blevees des poissons T611BostBens migrateurs. Comptes relzdus du Deuxibme Colzgris international de Chimie biologique, Paris, p. 53. Fontaine, M. and Leloup, J. (1959). Influence de la nage B contre-courant sur le metabolisme de l’iode et le fonctionnement thyroidien chez la truite arc-en-ciel (Salmogairdnerii Rich.). Comptes rendus hebdomadaires dea Skances de l’Academie des Sciences, Paris, 249, 343-347. Fontaine, M. and Leloup, J. (1962). Le fonctionnement thyroidien du Saumon adulte (Salmo salar L.) B quelques &apes de son cycle migratoire. General and Comparative Endocrinology, 2, 317-322. Fontaine, M. and Marchelidon, J. (1971). Modifications des teneurs en certains acides amin& libres du cerveau et du muscle du jeune Salmo salar L. au cours de la smoltification. Comptes r e d u s hebdomadaires des SLances de I’Academie des Scien.ces, Paris, 272, 94-97. Fontaine, M. and Martelly, E. (1974). Unpublished data.

”.

340

M. FONTAINE

Fontaine, M. and Olivereu, M. (1949). L’hypophyse du Saumon (Salmo salar L.) B diverses Btapes de sa migration. Comptes rendus hebdomadaires des Skances de 1’Academie des Sciences, Paris, 228, 772-774. Fontaine, M. and Poncet, M. (1969). Comportement de 1’Anguille privee de corpuscules de Stannius et rapports ioniques du cerveau et du muscle. General and Comparative Endocrinology, 13, 506. Fontaine, M. and Vibert, R. (1952). Migration fluviale anadrome du Saumon (Salmosalar L.) et gradient de salinit6. Annales de la Stalion centrale d’Hydrobiologie applique’e, 4, 339-346. Fontaine, M., Callamand, 0. and Olivereau, M. (1949). Hypophyse et euryhalinite chez 1’Anguille. Comptes rendus hebdomadaires des Skances de I’Academie des Sciences, Paris, 228, 513-514. Fontaine, M., Leloup, J . and Olivereau, M. (1952). La fonction thyroidienne du jeune Saumon Salmo salar L. et son intervention possible dans la migration d’avalaison. Archives des Sciences physiologique. Paris, 6, 83-104. Fontaine, M., Mazeaud, M. and Mazeaud, F. (1963). L’adrBnalinBmie du Salmo salar L. B quelques Btapes de son cycle vital et de ses migrations. Comptes rendus hebdomadaires des Xe‘ances de I’Academie des Sciences, Paris, 256, 4262-5265. Fontaine, M., Chartier-Baraduc, M. M., Deville, J., Lopez, E. and Poncet, M. (1969). Sur les variations de la calcBmie observBes chez Salmo salar L. B diverses Btapes de son cycle vital, leur determinisme endocrinien et leur intervention siir le comportement. Comptes rendus hebdomadaires des skances de 1’Academie des Sciences, Paris, 268, 1958-1961. Fosi, V. (1934). Le modificazioni istologische della pelle delle Anguille nell’acquisizionedell’abito di nozze. Archivo Zoologico italiano, 20, 285-302. Francois, Y. (1941). Evolution de la thyro‘ide chez la civelle. Comptes rendus des Travaux de la Faculte des Sciences de Marseille, (Ere sBr.), 1, 74-77. Fry, F. E. J. and Hochachlia, P. W. (1970). Fish. I n “ Comparative Physiology of Thermoregulation.” (G. Causey Whittow, ed.), pp. 79-134. Academic Press, London and New York. Gard, R. (1973). Travel time and influencing factors for migrating adult sockeye salmon in Karluk River, Alaska. Transactions of the American Fisheries Society, 102, 723-727. Gatz, A. J. Jr. (1973). Speed, stamina and muscles in fishes. Journal of the Fisheries Research Board of Canada, 30, 325-328. Giles, M. A. (1969). Changes in the ouabain-sensitive, sodium and potassium activated adenosine triphosphatase of the gills of coho salmon Oncorhynchus kisutch, during the fry to smolt stages of its life history and up on exposure to sea water. Thesis, University of British Columbia. Gollnick, P. D. and King, D. W. (1969). Effect of exercise and training on mitochondria of rat skeletal muscle. American Journal of Physiology, 216, 1502-1509. Gordon, M. S. (1968). Oxygen consumption of red and white muscles from tuna fishes. Science, New Y o r k , 159, 87-90. Grant, W. C. and Pickford, G. E . (1959). Presence of red eft water-drive factor prolactin in the pituitaries of teleosts. Biological Bulletin, 116, 4 29-43 5. Groot, C. (1965-1967). On the orientation of young sockeye salmon (Oncorhynchus nerka) during their seaward migration out of lakes. Behaviour (Stlppl.), 13-16, pp. 1-198.

MIORATION OF MAXINE AND AMPHIHALINE FISH

341

Guillemin, R. and Krikov, W. A. (1960). L'hormone m6lanophor6tique b-MSH joue-t-elle un r81e dans les fonctions du systbme nerveux central chez les Mamnifbres sup&ieurs? Comptes rendus hebdomadaires des Se'anccs de 1'Academie des Sciences, Paris, 250, 1117-1119. Hafeez, M. A. (1970). Effect of melatonin on body coloration and spontaneous swimming activity in rainbow trout, Salmo gairdneri. Comparative Biochemistry and Physiology, 36, 639-656. Hahn, W. E., Oshima, K. and Gorbman, A. (1974). Homing in salmon: a model for examining possibilities of chemical transfer of behaviour. Brief communication. Hammond. I n discussion paper by Sawyer, W. H. (1972). Neurohypophysial hormones and water and sodium excretion in the African lungfish. General and Comparative Endocrinology (suppl.), 3, 345-349. Hanaoka, T. and Chu, A. J. (1972). On the oceanographic conditions for Albacore in the Western South Pacific Ocean. Bulletin of the Japanese Society of Scientific Fisheries, 38, 1351-1356. Ham, T. J. (1967). Electrophysiological studies of the olfactory system of the goldfish Carassius auratus L. 111. Effects of sex hormones on olfactory activity. Comparative Biochemistry and Physiology, 22, 209-225. Hara, T. J. (1971). Chemoreception. I n " Fish Physiology ". (W. S. Hoar and D. J. Randall, eds.) vol. 5, pp. 79-120. Academic Press, New York. Hara, T . J., Ueda, K. and Gorbman, A. (1965a). Electroencephalographic studies of homing salmon. Science, New York, 149, 884-885. Hara, T . J., Ueda, K. and Gorbman, A. (1965b). Influences of thyroxine and sex hormones upon optically evoked potentials in the optic tectum of goldfish. General and Comparative Endocrinology, 5, 313-319. Harden Jones, F. R. (1968). " Fish migration". Edward Arnold Ltd., London 325 pp. Harms, J. W. (1935). Die Realisation von Genen und die consecutive Adaptation. IV. Mitteilung Experimentelle hervorgerufener Medienwechsel: Wasser zu Feuchtluft, b. z. w. zu Trockenluft bei Goiiformen (Gobius, Boleophtalmus und Periophtalmus). Zeitschrift fiir Wissenschaftliche Zooloyie 146, 417-463. Hashimoto, Y., Konosu, S., Fusetani, N. and Nose, T. (1968). Attractants for eels in the extracts of shortnecked clam. I. Survey of constituents eliciting feeding behaviour by the omission test. Bulletin of the Japanese Society of Scientific Fisheries, 34, 78-83. Hasler, A. D. (1954). Odour perception and orientation in fishes. Journal of the Fisheries Research Board of Canada, 11, 107-129. Hasler, A. D. (1971). Orientation and fish migration. I n " Fish Physiology ". (W. S. Hoar and D. J. RandalI, eds.). Vol. 6, pp. 429-528. Academic Press, New York. Hasler, A. D., Horrall, R. M., Wisby, W. J. and Braemer, W. (1958). SUN orientation and homing in fishes. Limnology and Oceanography, 3, 353-361. Hirano, T., Johnson, D. W. and Bern, H. A. (1971). Control of water movement in flounder urinary bladder by prolactin. Nature, London, 230, 469-471. Hirano, T., Johnson, D. W., Bern, H. A. and Utida, S. (1973). Studies on water and ion movements in the isolated urinary bladder of selected freshwater, marine and euryhaline teleosts. Comparative Biochemistry and Physiology, 45A, 629-540.

342

M. FONTAJXE

Hoar, W. S. (1939). The thyroid gland of the Atlantic salmon. Journal of Morphology, 65, 257-295. Hoar, W. S. (1951). Hormones in fish. Publication of the Ontario Fisheries Research Laboratory, 71, 1-51. Hoar, W.S. (1953). Control and timing of fish migration. Biological Review, 28, 437-452. Hoar, W. S. (1958). The evolution of migratory behaviour among juvenile salmon of the genus Oncorhynchus. Journal of the Fisheries Research Board of Canada, 15, 391-428. Hoar, W. S., Keenleyside, M. H. A. and Goodall, R . G. (1955). The effects of thyroxine and gonadal steroids on the activity of salmon and goldfish. Canadian Journal of Zoology, 33, 428-439. Hobson, E. S. (1973). Die1 feeding migrations in tropical reef fishes. Helgolander Wwsenachaftliche Meeresuntersuchungen, 24, 361-370. Hoglund, L. B. and listrand, M. (1973). Preference among juvenile char (Salvelinus alpinus L.) to intraspecific odours and water currents studied with the fluviarium technique. Institute of Freshwater Research, Report no. 53, 21-30. Holloszy, J. 0. (1967). Biochemical adaptation in muscle. Journal of Biological Chemistry, 242, 2278-2282. Holmes, W.N. (1959). Studies on the hormonal control of sodium metabolism in the rainbow trout (Salmo gairdneri). Acta Endocrinologica, Copenhagen, 31, 587-602. Holmes, W. N. and McBean, R. L. (1963). Studies on the glomerular filtration rate of rainbow trout (Salmo gairdneri). Journal of Experimental Biology, 40, 335-341. Holmes, W. N. and Stainer, I. M. (1966). Studies on the renal excretion of electrolytes by the trout (Salmo gairdneri). Journal of Experimental Biology, 44, 33-46. Honma, Y. (1956). The thyroid gland of the tuna. Thunnus thynnus (Limb). Bulletin of the Japanese Society of Scientific Fisheries, 21, 1011-1015. (In Japanese. ) Honma, Y. and Tamura, E. (1967). Studies on Japanese chars of the genus Salvelinus. The caudal neurosecretory system of the NikkB-iwana, Salvelinus leucomaenis pluvius (Hilgendorf). General and Comparative Endocrinology, 9, 1-9. Honma, Y. and Yoshie, S. (1974). Studies on the endocrine glands of a salmonoid fish, the ayu, Plecoglossus altivelis Temminck et Schlegel IX. Seasonal changes in the cells of the adenohypophysis, especially the prolactin producing cells. Archivum histologicum japonicurn, 36, 237-250. Houston, A. H. (1957). Responses of juvenile chum, pink and coho salmon to sharp sea-water gradients. Canadian Journal of Zoology, 35, 371-383. Houston, A. H. and Threadgold, L. T. (1963). Body fluid regulation in smolting Atlantic salmon. Journal of the Fisheries Research Board of Canada, 20, 1355-1369. Huve, J. L. (1974). Work in progress. Idler, D. R. (1973). Hormones in the life of the Atlantic salmon. International Atlantic Salmon Symposium 1973, pp. 43-53. The International Atlantic Salmon Foundation Publication.

343

MIGRATION OF MARINE AND AMPHIHALINE FISH

Idler, D. R. and Bitners, I. (1958). Biochemical studies on sockeye salmon during spawning migration. 11. Cholesterol, fat, protein and water in the flesh of standard fish. Canadian Journal of Biochemistry and Physiology, 36, 793-799. Idler, D. R. and Bitners, I. (1959). Biochemical studies on sockeye salmon during spawning migration. V. Cholesterol, fat, protein and water in the body of the standard fish. Journal of the Fisheries Research Board of Canada, 16, 235-241. Idler, D. R. and Bitners, I. (1960). Biochemical studies on sockeye salmon during spawning migration. IX. Fat, protein and water in the major internal organs and cholesterol in the liver and gonads of the standard fish. Journal of the Fisheries Research Board of Canada, 17, 113-122. Imai, K. (1965). Development of the caudal and hypothalamic neurosecretory systems of the eel, Anguilla japonica. Enabryologia, 9, 66-77. Johnson, D. W. (1972). Variations in the interrenal and corpuscles of Stannius of Mugil cephalus from the Colorado River and its estuary. General and Comparative Endocrinology, 19, 7-25. Johnston, C. E. and Eales, J. G. (1967). Purines in the integument of the Atlantic salmon (Salmo salar) during pan-smolt transformation. Journal of the Fisheries Research Board of Can,ada, 24, 953-964. Johnston, C . E. and Eales, J. G. (1968). Influence of temperature and photoperiod o n guanine and hypoxanthine levels in skin and scales of Atlantic salmon (Xalmo salar) during parr-smolt transformation. Journal of the Fisheries Research Board of Canada, 25, 1901-1909. Johnston, I. A,, Frearson, N. and Goldspinlr, G. (1972). Myofibrillar ATPase activities of red and white myotonal muscles of marine fish. Experientia, 28, 713-714. Jones, J. W. (1959). “ The Salmon ”. Collins, London, 129 pp. Joseph, M. M. and Meior, A. H. (1971). Daily variations in the fattening response to prolactin in Fundulus grandis held on different photoperiods. Journal of Experimental Zoology, 176, 59-62. Kalmijn, A. J. (1974). The detection of electric fields from inanimate and animate sources other than electric organs. I n “Handbook of Sensory Physiology ”. Springer-Verlag, Berlin. I n press. Kamiya, M. (1972). Hormonal effect on Na-K-ATPase activity in the gill of Japanese eel, Anguilla japonica, with special reference to seawater adaptation. Endocrinologia japonica, 19, 489-493. Kamps, L. P. (1937). De chineesche Wolhandkrab in Nederland. Groningen D issertatie. Kashiwagi, M. (1971). La migration de Oncorhynchus keta et la regulation de la pression osmotique. I n “ Symposium snr 1’6tude physiologique de la migration. 111. Salmonides”, Abstr., 25-26 nov. 1971. (S. Utida, ed.), p. 11. Institute of Oceanographic Research, University of Tokyo. (In Japanese.) Kastin, A. J., Miller, M. C. and Schally, A. V. (1969). Modified in vitro assay for melanocyte-stimulating hormone. Experientia, 25, 192-193. Kastin, A. J., Miller, L. H., Gonzalez-Barcena, D., Hawley, W. D., DysterAas, K . , Schally, A. V., Velasco de Parra, M. L. and Velasco, M. (1971). Psychophysiologic correlates of MSH activity in ma.n. Physiological Behaviour, 7, 893-896. a.M.B.-13

12

344

M. FONTAINE

Kastin, A. J . , Miller, L. H., Nockton, R., Sandman, C. A., Schally, A. V. and Stratton, L. 0. (1973). Behavioral aspects of melanocyte-stimulating hormone (MSH). Progress in B r a i n Research, 39, 461-470. Keys, A. and Bateman, J. B. (1932). Branchial responses to adrenalin and pitressin in the eel. Biological Bulletin of the Marine Biological Laboratory, Woods Hole, 63, 327-336. Kishinouye, K . (1923). Contributions to the comparative study of the so-called scombrid fishes. Journal of the College of Agriculture, Imperial University of Tokyo, 8, 293-497. Kleerekoper, H., Matis, J. H., Timms, A. M. and Gender, P. (1973). Locomotor response of the goldfish to polarized light and its e vector. Journal of Comparative Physiology, 86, 27-36. Knowles, F. and Vollrath, L. (1966a). Neurosecretory innervation of the pituitary of the eels Anguilla and Conger. 11. The structure and innervation of the pars distalis. Philosophic Transactions of the Royal Society, 250B, 329-342. Knowles, F. and Vollrath, L. (1966b). Cell types in the pituitary of the eel Anguilla anguilla L. a t different stages in the life cycle. Zeitschrift f u r Zellforschung, 69, 474-479. Koch, H. J. A. (1968). Migration. I n " Perspectives in Endocrinology (E. J.W. Barrington and C. Barker Jorgensen, eds.), pp. 305-349, Academic Press, London and New York. Koch, H. J. and Heuts, M. J. (1942). Influence de l'hormone thyroidienne sur la regulation osmotique chez Gasterosteus aculeatus L. forme gymnurus Cuv. Annales de la Socidtd royale zoologique de Belgique, 73, 165-172. Koch, H. J. and Heuts, M. J. (1944). Le cycle de la regulation osmotique et minerale du crabe chinois Eriocheir sinensis (Milne Edw.). Annales de la Socie'td royale zoologique de Belgique, 75, 87-90. Koch, H. J., Evans, J. C. and Bergstrom, E . (1959). Sodium regulation in the blood of parr and smolt stages of the Atlantic salmon. Nature, London, 184, 283. Koch, H. J., Bergstrom, E., Bowarde-Schmitz, E . and Evans, J. C. (1968). The separation of the haemoglobins of Salmo salar L. by means of isoelectric focusing. Mededelingen v a n de Koninklijke vlaamse academie voor wetenschappen, letteren en Schone kunste van Belgie, 30, 1-18. Konosu, S., Fusetani, N., Nose, T. and Hashimoto, Y . (1968). Attractants for eels in tho extracts of shortnecked clam. 11. Survey of constituents eliciting feeding behaviour by fractionation of the extracts. Bulletin of the Japanese Society of Scientific Fisheries, 34, 84-87. Kraus, H. and Kirsten, R. (1969). Die Wirkung von Schwimm- und Lauftraining auf die cellulare Funktion und Struktur des Muskels. PJTugers Archiv f u r die gesamte Physiologie des Menschen und der Tiere, 308, 57-59. Krawkow, N. P. (1913). Uber die Wirkung von Giften und die Gelasse isolierter Fischkiemen. PJTugers Archiv f u r die gesamte Physiologie des Menschen u n d der Tiere, 15, 583-603. Krogh, A. (1937). Osmotic regulation in freshwater fishes by active absorption of chloride ions. Zeitschrift f u r Vergleichende Physiologie, 24, 656-666. Kubo, T. (1955). Changes of some characterist'ics of blood of smolts of Oncorhynchus masu during seaward migration. Bulletin of the Faculty of Fisheries, Hokkaido University, 6, 201-207.

".

MIGRATION OF MARINE AND AMPHIHALINE FISH

345

Kubo, T. (1956). The effect of the control of light upon the rate of smoltification and the growth of body of juvenile masu salmon. Scientific Report of the Hokkaido F i s h Hatchery, 11, 19-23. Kubo, T. (1959). A preliminary study on the effects of cnvironmental factors upon the attainment of the smolt stage in juvenile masu salmon. Scient@c Report of the Holckaido Salmon Hatchery, 14, 19-23. Kubo, T. (1960). Notes on the blood of masu salmon during inshore migration with spccial reference to the osmoconceritration. Bulletin of the Faculty of Fisheries, Hokkaido University, 11, 15-19. Lacanilao, F. (1972). The urophysial hydrosmotic factor of fishes. I. Characteristics and similarity t o neurohypophysial hormones. General and Comparative Endocrinology, 19, 405-412. Lacanilao, F. (1972). The urophysial hydrosmotic factor of fishes. 11. Chromatographic and pharmacologic indications of similarity to arginin vasotooin. General and Comparative E n d o c k o l o g y , 19, 413-420. Lahaye, J. (1966). Variations cycliques de l’activit6 thyroidienne chez des Aloses migrant normalement en mer et chez des Aloses bloqubes en eau douce. Revue des Travaux de l’lnstitut des Pdches Maritimes, 30, 347-355. Lam, T. J. (1972). Prolactin and hydromineral regulation in fishes. General and Comparatioe Endocrinology, suppl. no. 3, 328-338. Lam, T. J. and Leatherland, J. F. (1969). Effects of prolactin on the glomerulus of the marine threespine stickleback, Gasterosteus aculeatus L. form trachurus after transfer from seawater to fresh water, during the late autumn and early winter. Canadian Journal of Zoology, 47, 245-250. Landgrebe, F. W. (1941). The role of the pituitary and the thyroid in the development of teleosts. Journal of Experimental Biology, 18, 162-1 69. Laroche, G., Leblond, C. P. and Prefontaine, G. (1950). Effets de l’hormone thyroidienne sup le saumon de l’iltlantique: stade parr. Revue Canadienne de Bioloyie, 9, 101-103. Lebedev, N. V. (1940). Possibilit6 de pronostic des d6lais de la migratio? d’anchois de la mer d’Azov (Engraulis encrasicholus). Zoologischeskij Zurnal, 19, 649-671. (In Russian.) Lederis, K. (1969). Teleostean urophysis : stimulation of contractions of bladder of the trout Salmo gairdnerii. Science, N e w York, 163, 1327-1338. Leloup, J. (1959). Iode thyroidien et Bvolution g6nitale chez l’ilnguille femelle. Journal de Physiologie, 51, 516. Leloup, J. and Fontaine, M. (1960). Iodine metabolism in lower vertebrates. Annal s of the N e w York Academy of Science, 86, 316-353. Leloup, J., Long, P. and Fontaine, M. (1972). Influence des hormones thyroidiennes sur la synthkse des prot6ines dans le cerveau des TBlBostBens. General and Comparative Endocrinology, 18, 603. Leloup-Hatey, J . (1964). Fonctionnement de l’interrhnal ant6rieur de deux T616ost6ens : le Saumon atlantique et 1’Anguille europBenne. Annales de l’lnstitut Oce‘anographique, 42, 224-337. Leloup-Hatey, J. (1975). MBthode de mesure des vitesses d’6puration mBtabolique et de s6crBtion du cortisol chez 1’Anguille(Anguilla anguilla L.). Canadian Journal of Physiology and Pharmacology, In press. Lemoine, A. M. and Olivereau, M. (1973). Action de la prolactine chez 1’Anguille intacte et hypophysectomis6e. IX. Effet sur la teneur en acide N-acBtyl-neuraminique de la peau en eau de mer. Acta Zoologica, 54, 223-228.

346

M. BONTAINE

Leray, C. (1968). Etude llistopliysiologique de l’hypopliyse chez le muge et la carpe. Ses corrdlations avec l’hypothalamus, la thyroi‘de et les gonades. These facult6 des Sciences, Aix-Marseille. Lewander, K., Dave, G., Joliansson, M. L., Larsson, A. and Lidman, U. (1974). Metabolic and hematologic studies on the yellow and silver phases of the European eel Anguilla anguilla L. I . Carbohydrate, lipid, protein and inorganic ion metabolism. Comparative Biochemistry and Physiology, 47B,571-581. Lissmann, H. W. and Machin, K. E. (1958). The mechanism of object location in Gymnarchus niloticus and similar fish. Journal of Experimental Biology, 35, 451-486. Lowe, R . H. (1952). The influence of light and other factors on the seaward migration of the silver eel (Anguilla angulilla L.). Journal of Animal Ecology, 21, 275-309. Maiir, A. (1947). Uber die Aalwanderungen im Baltisclien Meer auf Grund der Wanderaalmarkierungversucken im finnischen und livischen Meerbusen i.d.J. 1937-1 939. Meddelanden f r a n Xtatens undersoknings-och forsoksanstalt f’ir sotwattenfisket, 27, 56 pp. Maetz, J. and Julien, M. (1961). Action of neurohypopliysial hormones on sodium fluxes of a freshwater teleost. Nature, London, 189, 152-153. Maetz, J. and Rankin, J. C. (1969). Quelques aspects du rBle biologique des hormones neurohypophysaires chez les poissons. Collogues internationaux d u Centre National de la Rdcherche Scientifique, Paris, 177, 45-54 Maetz, J.,Bourguet, J. and Lahlouh, B. (1964). Urophyse et osmorbgulation chez Carassius auratus. General and Comparati.Lie Endocrinology, 4, 401-414. Mahaux, J. (1947). “ Essai de physiopathologie thyro-hypophysaire ”. 267 pp. Masson, Paris. Mantejfel, B. P., Naumov, N. P., Jakobi, V. E. (1965). L’orientation et la navigation dans le monde des animaux. I n “Bionika”, pp. 245-250. Moskva, Izdat. Nauka. (In Russian.) Mayor, N., Maetz, J., Chan, D. K. O., Forster, M. and Chester Jones, I. (1967). Cortisol, a sodium excreting factor in the eel (Anguilla anguilla L.) adapted to sea-water. Nature, London, 214, 11 18-1 120. McCance, R . A. (1944). The chemistry of growth and the food value of the common eel (Anguilla anguilla L.). Biochemical Journal, 38, 474-480. McInerney, J. E. (1961). An experimental study of salinity preference and related migratory behaviour of juvenile Pacific salmon. Thesis, University of British Columbia. McInerney, J. E. (1964). Salinity preference : an orientation mechanism in salmon migration. Journal of the Fisheries Research Board of Canada, 21, 995-1018. McKeown, B. A. and Van Overbeeke, A. P. (1972). Prolactin and growth hormone concentrations in the serum and pituitary gland of adult migratory sockeye salmon (Oncorhynchus nerka). Journal of the Fisheries Research Board of Canada, 29, 303-309. Melander, A. (1970). Amines and mouse thyroid activity: release of thyroid hormone by catecholamines and indole-amines and its inhibition by adrenergic blocking drugs. Acta Endocrinologica, 65, 371-384. Miles, S. G. (1968a). Rheotaxis of elvers of the American eel (Anguilla rostrata) in the laboratory to water from different streams of Nova Scotia. Journal of the Fiahteries Research Board of Canada, 25, 1591-1602.

MIGRATION OF MARINE AND AMPHIHALINE FISH

347

Miles, S. G. (1968b). Laboratory experiments on t h e orientation of the adult American eel, Anguilla rostrata. Journal of the Fisheries Research Board of Canada, 25, 2143-2155. Miles, H., Keenleyside, A. and Hoar, W. S. (1954). Effects of temperature on the responses of young salmon to water currents. Behaviour, 7, 77-87. Miller, R. E. and Ogawa, N. (1962). The effect of adrenocorticotropliic liormone (ACTH) on avoidance conditioning in the adrenalectomized rat. Journal of Comparative and Physiological Psychology, 55, 2 1 1-2 13. Milne, K. P., Ball, J. N. and Chester Jones. I, (1971). Effects of salinity, hypophysectomy and corticotrophin on branchial Na and K activated ATPase in the eel, Anguilla anguilla L. Journal of Endocrinology, 49, 177-178. Mislin, H. (1941). Der Phasenwechsel des Rheinlachses (Salmo salar) unter besonderer Berucksichtigung des Ernahrungsapparates. Revue Suisse de Zoologie (suppl.), 48, 1-181. Momzikoff, A. (1973). Unpublished data. Motais, R. (1967). Les m6canismes d’bchanges ioniques branchiaux chez les TBlBostBens. Leur r61e dans l’osmor6gulation. Annales de l’lnstitut ockanographique, 45, 1-84. Motais, R . and Mactz, J. (1967). Arginine vasotocine et Bvolution do 1& permBabilitB branchiale au sodium au cours du passage d’eau doucc en de mer chez le Flet. Journal de Physiologie, 59, 271. Murphy, A. V. and Miller, R. E. (1955). The effect of adronocorticotrophic Eiormone (ACTH) on avoidance conditioning in the rat. Journal of Comparative and Physiological Psychology, 48, 47-49. Murr, E. and Sklower, A. (1928). Untersuchungen uber die inkretorischen Organe der Fische. I. Das Verhalten der Schilddruso in der Metamorphose des Aales. Zeitschrift f u r vergleichende Physiologie, 7, 129. Murray, R . W. (1971). Temperature receptors. I n “ Fish Physiology ”. (W. S. Hoar and D. J. Randall, eds.) Vol. 5, pp. 121-132. Academic Press, New York. Nagahama, Y., Nishioka, R. S. and Bern, H. A. (1973). Responses of prolactin cells of two euryhaline marine fishes, GiZlichthys mirabilis and Platichthys stellatus, to environmental salinity. Zeitschrift f u r Zellforschung, 136, 153-167. Nakamura, H. (1969). “ Tuna distribution and migration ”. 76 pp. Fishing News (Books) London. Natochin, J U . V., Bocharov, G. D. (1962). Activation des cellules excr6trices do sodium dans les branchies d’Oncorhynchzrs gorbuscha et d’O. keta adapt& A la vie en eau de mer. Voprosy iktiologii, 2, 687-692. (In Russian.) Neale, J. H., Klinger, P. D., Agranoff, B. W. (1973). Camptothecin blocks memory of conditioned avoidance in the goldfish. Science, New Y o r k , 179, 1243-1246. Nikolsky, G. V. (1963). “ The Ecology of Fishes ”. Academic Press, New York. Nordeng, H. (1971). Is the local orientation of anadromous fish determined by pheromones? Nature, London, 233, 41 1-413. Ogden, J. C. and Buckman, N. S. (1973). Movements, foraging groups, and diurnal migrations of the striped parrotfish Scarus croicensis Bloch (Scaridae). Ecology, 54. 589-596. Ohtsu, K., Naito, K., Wilt, F. H. (1964). Metabolic basis of visual pigment conversion in metamorphosing Rana eatesbiana. Developmental Biology, 10, 216-232.

348

M. FONTAINE

Okumura, N., Otsuki, S. and Nasu, H. (1959). The influence of insulin hypoglycemic coma, repeated electroshocks and chlorpromazine or jphenylisopropylmethylamine administration on the free aminoacids in the brain. Journal of Biochemistry, 47, 207-247. Olivereau, M. (1954). Hypophyse et glande thyroide chez les Poissons. Etude histophysiologiqua de quelques corr6lations endocriniennes en particulier chez Salmo salar. L. These Fac. Sci. Paris (1953). Annales de Z’Institut ocdanographique, 29, 95-296. Olivereau, M. (1957). Etude anatomique et histologique de la glande thyroide du Thon (Thunnus thynnus L. et Germo alalunga). Bulletin de la Socidtd zoologique de Prance, 82, 401-417. Olivereau, M. ( 1 967). Observations sup l’hypophyse de 1’Anguille femelle, en particulier lors de la maturation sexuelle. Zeitschrift fiir Zellforschung, 80, 286-306. Orias, R. and McCann, S. M. (1972). Natriuretic effect of alpha melanocyte stimulating hormone (a-MSH) in hypophysectomized or adrenalectomized rats. Proceedings of the Society of Experimental Biology and Medicine, 139, 8 72-8 7 6. Oshima, K., Gorbman, A. and Shinada, H. (1969a). Memory blocking agents; effects on olfactory discrimination in homing salmon. Science, New York, 165, 86-88. Oshima, K., Hahn, W. E. and Gorbman, A. (1969b). Olfactory discrimination of natural waters of salmon. Journal of the Fisheries Research Board of Canada, 26, 2111-2121. Ovchinnikov, V. V., Glejzer, S. I. and Galaktionov, G. Z . (1973). Les particularit& de l’orientation de l’anguille europ6enne de rivikre Anguilla anguilla L. A certaines 6tapes de sa migration. Voprosy ilchtiologii, 13, 543-553. (In Russian.) Pang, P. K. T. and Pang, R. (1974). Environmental calcium and hypocalcin activity in the Stannius corpuscles of the channel catfish Ictalurus punctatus (Rafinesque). General and Comparative Endocrinology, 23, 239-241. Pannikar, N. K. (1940). Influence of temperature on osmotic behaviour of some Crustacea and its bearing on problems of animal distribution. Nature, London, 146, 366. Pannikar, N. K. (1968). Osmotic behaviour of shrimps and prawns in relation to their biology and culture. F.A.O. Fisheries Report, 2, 527-538. Parker, F.R. Jr (1973). Reduced metabolic rates in fishes as a result of induced schooling. Transactions of the American Fisheries Society, 102, 125-131. Parry, G. (1961). Osmotic and ionic changes in blood and muscle of migrating salmonids. Journal of Experimental Biology, 38, 41 1-427. Petersen, C. G. J. (1906). The influence of light on the migrations of the eel. Report of the Danish Biological Station, Copenhagen, 14, 1 . Pickford, G. E. and Phillips, J . G. (1959). Prolactin, a factor in promoting survival of hypophysectomized killifish in fresh water. Science, N e w Y o r k , 130, 454-455. Pickford, G. E., Griffith, R. W., Torretti, J., Hendlez. E., Epstein, F. H. (1970). Branchial reduction and renal stimulation of (Na+ K+)ATPase by prolactin in hypophysectomized killifish in fresh water. Nature, London, 228, 378-379. Poddubnyj, A. G. (1965). Quelques rBsultats sur les observations A distance effectuhes s u r le comportement des poissons migrateurs. I n “ Bionika ”, pp. 255-263. Moskva, Izdat. Nauka. (In Russian.)

MIGRATION OF MARINE A N D AMPHIHALINE FISH

349

Poluhowich, J. J. (1972). Adaptive significance of eel multiple hemoglobins. Physiological Zoology, 45, 215-222. Power, G. (1958). The evolution of the freshwater races of the Atlantic salmon Salmo salar L.) in Eastern North America. Arctic, Montreal, 11, 86-92. Powers, E.B. (1940). The spawning migration of the salmon. Science, New Y o r k , 92, 353-354. Powers, E.B. (1941). Physicochemical behaviours of waters as factors in the “ homing ” of the salmon. Ecology, 22, 1-16. Powers, E. B. and Clark, R. T. (1943). Further evidence on chemical factors affecting the migratory movements of fishes, especially the salmon. Ecology, 24, 109-113. Priihs, D. (1973). Der Einfluss von Prolaktin auf die Anzahl und die Verteilung der vershiedenen Stadien der “ Corpora atretica praeovulatoria ” im Ovarium des SchwerttrBgers Xiphophorus helleri (Heckel). pp. 1-46. Ph.D. Thesis, Bochum. Quay, W. B. (1965). Experimental evidence for pineal participation in homeostasis of brain composition. Progress in Brain Research, 10, 646-653. Randall, D. J. and Stevens, D. E. (1967). The role of adrenergic receptors in cardiovascular changes associated with exercise in salmon. Comparative Biochemistry and Physiology, 21, 415-424. Rankin, J. C. and Maetz, J. (1971). A perfused teleostean gill preparation: vascular actions of neurohypophysial hormones and catecholamines. Journal of Endocrinology, 51, 621-635. Rappoport, D. A. and Daginawala, H. F. (1968). Changes in nuclear RNA of brain induced by olfaction in catfish. Journal of Neurochemistry, 15, 9911006. Reinsch, H. H. (1968). Fund von Fluss-Aalen Anguilla anguilla L. in Nordatlantik. Archiv f u r Fischereiwissenschaft, 19, 62-63. Rey, P. (1937). Recherches exp6rimentale.e sur 1’6conomie do l’eau chez les Batraciens. Thkse, Paris. Annales de Physiologie et de Physicochimie bioZogique, 1937, 13, 1081-1144; 1938, 14, 1-66. Riege, W. H. and Cherkin, A. (1973). Retrograde enhancement of memory in goldfish by a time dependent temperature shift. Physiological Behaviour, 11, 555-561. Robertson, 0. H. (1948). The occurrence of increased activity of the thyroid gland in rainbow trout a t the time of transformation from parr to silvery smolt. Physiological Zoology, 21, 282-295. Robertson, 0. H. and Wexler, B. C. (1959). Hyperplasia of the adrenal cortical tissue in Pacific salmon (genus Oncorhynchus) and rainbow trout (Salmo gairdnerii) accompanying sexual maturation and spawning. Endocrinology, 65, 225-238. Robertson, 0. H. and Wexler, B. C. (1960). Histological changes in the organs and tissues of migrating and spawning Pacific salmon (genus Oncorhynchus). Endocrinology, 66, 222-239. Rodolico, A. (1933). Differenziamento dei sessi ed ovo-spermatogenesi nell Anguilla. Publicazioni della Stazione zoologia d i Napoli, 13. Rommel, S . A. J r and McLeave, J. D. (1972). Oceanic electric fields: perception by American eels? Science, New York, 176, 1233-1235.

350

M. FONTAINE

Rommel, S. A. J r and McLeave, J. D. (1973a). Sensitivity of American eels (Anguilla rostrata) and Atlantic salmon (Salmo salar) t o weak electric and magnetic fields. Journal of the Pisheries Research Board of Canada, 30, 657-663. Rommel, S. A . J r and McLeave, J. D. (1973b). Prediction of oceanic electric fields in relation t o fish migration. Journal d u Conseil international pour 1’Exploration de la Me r, 35, 27-31. Rossi-FanelIi, A. and Antonini, E. (1960). Oxygen equilibrium of haenioglobin from T hunnus thynnus. Nature, London, 186, 895-896. Itoule, L. (1914). Sur l’influence exercbe s u p la migration de montbe du Saumon (Salmo salar L.) par la proportion d’oxygbne dissous dans l’eau des fleuves. Comptes rendus hebdomadaires des Sdances de I’Acadkmie des Sciences, Paris, 158, 1364-1366. Roule, L.(1920). Etude sur le saumon des eaux douces de la France (considbrh au point de veu de son &at nature1 et d u repeuplement de nos rivihres). Ministere de l’Agriculture, Direction gbnbrale des Eaux e t ForBts, PBche et Pisciculture. Imprimerie nationale, Paris, 178 pp. Royce, W. F., Smith, L. S. and Harrt, A. C. (1968). Models of oceanic migrations of Pacific salmon and comments on guidance mechanisms. United States Fisheries Bulletin, 66, 441-462. Russell, E. S. (1937). Fish migrations. Biological Reviews, 12, 320-337. Sage, M. (1973). The relationship between the pituitary content of prolactin and blood sodium levels in Mullet (Mugil cephalus) transferred from sea water to freshwater. Contributions to Marine Science, 17, 163-167. Sakamoto, I. (1962). On the action mechanism of the osmotic balance regulated by the T-C1 character in the water masses upon the movements of the pelagic fish school. Journal of the Oceanographical Society of Japan. Twentieth Anniversary Volume, 1962. Sandman, C. A., Kastin, A. J. and Schally, A. V. (1969). Melanocytestimulating hormone and learned appetitive behaviour. Ezperientia, 25, 1001-1002. Sandman, C. A,, Kastin, A. J. and Schally, A. V. (1971). Behavioural inhibition as modified by melanocyte-stimulating hormone (MSH) and light-dark conditions. Physioloqical Behaviour, 6, 45-48. Saunders, R. L. and Henderson, E. B. (1970). Influence of photoperiod on smolt development and growth of Atlantic salmon (Salmo salar). Journal of the Fisheries Research Board of Canada, 27, 1295-1311. Beitrage zur Arialyse des tierischen Schaper, A. and Cohen, C. (1905). Wachstums. 11. Uber zellproliferatorische Wachstumzentren und deren Beziehungen zur Regeneration und Geschwultshildung. Archiv fur Entwicklungsmechanik der Organismen, 19, 348-445. Schmidt, J. (1935). “ Danish eels investigations during 25 years, 1905-1930 ”. Bianco Luno, Copenhagen. Scholles, 1%’. ( 1933). Ueber die mineral Regulation wasserbehender Evertebraten. Zeitschrijt fur vergleichende Physiologie, 19, 522-554. Schreiber, B . (1938). Correlazione fra occhio e carpo rosso della vescica natatoria in anguille della laguna Vah0t.a. Atti ddla Societa italiana Progr. sci., 1, 112-113. Schroder, K. E., Pfeiffer, E. F. (1973). Kurzdauernde Muskelarbeit als Stimulationtest dcr STH-Sekretion. Miinch. med. Wscher., 115, 456455.

MIGRATION O F MARINE AND AMPHLHALINE FISH

351

Schwabe, E. ( 1933). Ueber die osmoregulation verschiedener Krebse (Malacostracen). Zeitschrift fiir vergleichende Physiologie, 19, 183-236. Schwassmann, H. 0. (1973). Solar radiation as major factor in spatial and temporal orientation of fish. I n “ Le soleil au service de l’homme ”. B40, pp. 1-9. Unesco, Paris. Segawa, T., Kawasaki, K., Yajima, H. (1973). Synthetic melanocyte- stimulating hormone and mouse behaviour. Japanese Journal of Pharmacology, 23, 121-123. Shashoua, V. E. (1968). The relation of R.N.A. metabolism in the brain t o learning in the goldfish. I n “ The Central Nervous System and Fish Beliaviour.” (David Ingle, ed.) pp. 203-213. University of Chicago Press. Shirahata, S. (1971). Caract6res migratoires de Oncorhynchus nerka. Symp. sur 1’8tude physiologique des migrations, p. 1, Uchida S., Tokyo. Shizume, K., Lerner, A. B. and Fitzpatrick, T. B. (1954). I n vitro bioassay for the rnelanocyte-stimulating hormone. Endocrinology, 54, 553-560. Shulman, G. E. (1972). “ Les particularit& physio-biochimiques des cycles annuels des poissons ”. “ L’Industrie alimentaire ” publ., Moscou. ( I n Russian.) Simizu, W. (1948). Etudes sur le muscle des animaux marins. Bulletin of the Japanese Society of Scienti$c Fisheries, 15, 28-34. (In Japanese.) Sklower, A. (1930). Die Bedeutung der Schilddriise fur die Metamorphose des Aales und der Plattfische. Porschungen und Fortschritte, 6, 435-436. Smith, D. C. W. (1956). The role of endocrine organs in the salinity tolerance of trout. Memoirs of the Society of Endocrinology, 5, 83-101. Smith, L. S., Cardwell, R . D., Mearns, A. J., Newcomb, 7’. W. and Watters, K. W. J r (1972). Physiological changes experienced by Pacific salmon migrating through a polluted urban estuary. I n “ Marine Pollution and Sea Life ”. (F.A.O., ed.) pp. 322-325. Fishing News (Books)Ltd., London. Solomon. D. J. (1973). Evidence for pheromone-influenced homing by migrating Atlantic salmon, Salmo salar L. Nature, London, 244, 231-232. Srebro, Z.and Szirmai, E. (1972). Further research on neurosecretion in mice under forced exercise. Journal of the Institute of Nuclear Engineers, 13, 79-91. Stanley, J. G. and Fleming, W. R . (1966). Effect of hypophysectomy on the function of the kidney of the eiiryhaline teleost, Fundulus kansae. Biological Bulletin of the Marine Biological Laboratory, Woods Hole, 130, 430-441. Stanley, J. G. and Fleming, W. R . (1967). Effect of prolactin and ACTH on the serum and urine sodium levels of Fundulus kansae. Comparative Biochemistry and Physiology, 20, 199-208. Stasko, A. B. (1971). Review of field studies on fish orientation. Annals of the N e w York Academy of Science, 188, 12-29. Stevens, D. E. and Black, E . C. (1966). The effect of intermittcnt exercise on carbohydrate metabolism in rainbow trout, Salmo gairdneri. Journal of the Fisheries Research Board of Canada, 23, 471-485. Stevens, E. D. and Fry, F. E. J. (1971). Brain and muscle temperatures in ocean caught and captive skipjack tuna. Comparative Biochemistry and Physiology, 38A, 203-211. Stommel, H. (1954). Exploratory measurements of electrical potential differences between widely spaced points in the North Atlantic Ocean. Woods Hole Oceanographic Institution, collected reprints, contribution 693, pp. 292-304.

352

M. FONTAINE

Suzuki, T. (1970). Swimming behaviour of chum salmon in the Southeastern area off Kamchatka Peninsula. Bulletin of the Japanese Society of Scientijo Fisheries, 36, 19-25 (In Japanese.) Sylvest, E . (1931). “ Om Betydningen af Kemotaxis og Rheotaxis for Clasaalenes Vandring ”. Naturens Verden, Copenhagen. Takasugi, N. and Bern, H. A. (1962). Experimental studies on the caudal neurosecretory system of Tilapia mossambica. Comparative Biochemistry and Physiology, 6, 289-303. Tesch, F. W. (1967). Homing of eels (Anguilla anguilla) in the southern North Sea. Marine Biology, 1, 2-9. Tesch, F. W. (1970). Heimfindevermogen von Aalen Anguilla anguilla nach Beeintrachtigung des Geruchssinnes, nach Adaptation oder nach Verpflanzung in ein Nachbar-Astuar. Marine Biology, 6, 148-157. Tesch, F. W. (1974a). Influence of geomagnetism and salinity on the directional choice of eels. Helgolander Wissenschaftliche Meeresuntersuchungen, 26, 382-3 95. Tesch, F. W. (1974b). Speed and direction of silver and yellow eels, Anguilla anguilla, released and tracked in the open North Sea. Berichte der Deutschen Wissenschaftlichen Kommission fur Meeresforschung, 23, 181-197. Threadgold, L. T. and Houston, A. H. (1964). An electron microscope study of the “ chloride cell ” of Salmo salar L. Experimental Cell Research, N e w York, 34, 1-23. Timiras, P. S. and Woodbury, D. M. (1956). Effect of thyroid activity on brain function and brain electrolyte distribution in rats. Endocrinology, 58, 181-192. Tucker, D. W. (1959). A new solution to the Atlantic eel problem. Nature, London, 183, 495-501. Ueda, K., Hara, T. J. and Gorbman, A. (1967). Electroencephalographic studies on olfactory discrimination in adult spawning salmon. Comparative Biochemistry and Physiology, 21, 133-144. Ueda, K., Hara, T. J., Satou, M. and Kaji, S. (1971). Electrophysiological studies of olfactory discrimination of natural waters by Him6 salmon, a land-locked Pacific salmon, Oncorhynchus nerka. Journal of the Faculty of Science, University of Tokyo, (sec. 4 ) , 12, no. 2. Umminger, B. L. (1973). Death induced by injection stress in cold-acclimated goldfish, Carassius auratus. Comparative Biochemistry and Physiology, 45A, 883-887. Ungar, G. and Fjerdingstad, E. J. (1971). Chemical nature of the transfer factors: RNA or protein? Symposia biologica hungarica, 10, 137-143. Utida, S. (1974). Unpublished data. Utida, S., Oide, M., Saishu, S. and Kamiya, M. (1967). Pr66tablissement du mkcanisme d’adaptation st l’eau de mer dans l’intestin et les branchies isol6s de 1’Anguille argentbe au cows de sa migration catadrome. Comptes rendus des SBances de la SociBtd de Biologie, Paris, 161, 1201. Utida, S., Kamiya, M. and Shirai, N. (1971). Relationship between the activity of Na+-K+-activated adenosinetriphosphatase and the number of chloride cells in eel gills with special reference to sea-water adaptation. Comparative Biochemistry and Physiology, 38A, 443-447. Utida, S., Hirano, T., Oide, H., Ando, M., Johnson, D. W. and Bern, H. A. (1972). Hormonal control of the intestine and urinary bladder in teleost osmoregulation. General and Cornparatiwe Endocrinology, (suppl.) 3, 31 7-327.

MIGRATION OF MARINE A N D AMPHIHALINE FISH

353

Van Heusden, G. P. H. (1943). De trek van de glasaal naar het Ijsselmeer. Thesis, University of Utrecht. Van Someren, V. D. (1962). The migration of fish in a small Kenya river. Revue de Zoologie et de Botanique Africaines, 66, 375-393. Vanstone, W. E., Roberts, E. and Tsuyuki, H. (1964). Changes in the multiple hemoglobin patterns of some Pacific salmon, genus Oncorhynchus, during Canadian Journal of Physiology and the parr-smolt transformation. Pharmacology, 42, 697-703. Vasilyev, A. S. and Gleiser, S. I. (1973). Changes in activity of Anguilla anguilla L. in magnetic fields. Voprosy Ikhtiologii, 13, 381-383. (In Russian.) Verwey, J. (1957). A plea for the study of temperature influence on osmotic regulation. Annales de Biologie, Paris, 33, 129-149. Vilter, V. (1944). Rht5otropisme de la civelle et activitt5 thyroidienne. Comptes rendus des Sdances de la Sociktt? de Biologie, Paris, 138, 668-669. Vollrath, L. (1966). The ultrastructure of the eel pituitary at the elver stage with special reference to its neurosecretory innervation. Zeitschrift f u r Zellforschung und mikroskopische Anatomie, 73, 107-131. Von Hagen, F. (1936). Die wichtigsten Endokrinen des Flussaals. Thyroidea, Thymus, und Hypophyse in Lebenszyklus des Flussaals (Anguilla vulgaris) nebst einigen Untersuchungen uber das chromophile und chromophobe Kolloid der Thyroidea. Zoologische Jahrbiicher (Abt. Anat.), 61, 467-538. Vrba, R. (1956). On the participation of the glutamic acid glutamine systcm in metabolic processes in the rat brain during physical exercise. Journal of Neurochemistry, 1, 12-1 7. Ward, H. B. (1932). The origin of the landlocked habit in Salmon. Proceedings of the National Academy of Science, 18, 569-580. Waterman, T. H. (1972). Visual direction finding by fishes. I n “Animal Orientation and Navigation ”. (S. R . Galler, K. Schmidt-Koenig, G. J . Jacobs and R. E. Belleville, eds.) pp. 437-456. National Aeronautics and Space Administration, Washington D.C. Waterman, T. H. (1974). Polarimeters in animals. I n “Planets, stars and nebulae studied with photopolarimetry ”. (T. Gehrels, ed.) pp. 472-494. University of Arizona Press, Tucson. Westenberg, J. ( 1 953). Acoustical aspects of some Indonesian fisheries. Journal d u Conseil international pour I’Exploration de la Mer, 18, 311-325. White, H.C. (1939). Factors influencing descent of Atlantic salmon smolts. Journal of the Fisheries Research Board of Canada, 4, 323-326. White, W. F., Hedlund, M. T., Weber, G. F., Rippel, R. H., Johnson, E. S., Wilber, J. F. (1974). The pineal gland: a supplemental source of hypothalamic-releasing hormone. Endocrinology, 94, 1422-1426. Whitmore, C. M., Warren, C. E. and Doudoroff, P. (1960). Avoidance reactions of salmonid and centrarchid fishes to low oxygen concentrations. Transactions of the American Fisheries Society, 89, 17-26. Widman, E. (1936). Osmoregulation bei einheimischen Wasser und Feuchtluftcrustaceen. Zeitschrift f u r wissenschaftliche Zoologie, 167, 132-169. Wilt, F. H. (1959). The organ specific action of thyroxin in visual pigment differentiation. Journal of Embryology and Experimental Morphology, 7, 556-563. Wisby, W. J. and Hasler, A. D. (1954). The effect of olfactory occlusion on migrating silver salmon (0. kisutch). Journal of the Fisheries Research Board of Canada, 11, 472-478.

354

M. FONTAINE

Wittenberger, C. (1973). Metabolic interaction between isolated white and red carp muscles. Revue Roumaine de Biologie, (ser. Zool.), 18, 71-76. Wohlschag, D. E. (1957). Differences in metabolic rates of migratory and resident freshwater forms of an Arctic whitefish. Ecology, 38, 502-510. Woodbury, D. M. (1954). Effect of hormones on brain excitability and electrolytes. Recent Progress in Hormone Research, 10, 65-107. Woodhead, A. D. (1959a). Variations in the activity of the thyroid gland of the cod, Gadus callarias L., in relation to its migrations in the Barents Sea. I. Seasonal changes. Journal of the Marine Biological Association of the United Kingdom, 38, 407-415. Woodhead, A. D. (195913). Variations of the activity of the thyroid gland of the cod, Gadus callarias L., in relation to its migrations in the Barents Sea. 11. The “Dummy r u n ” of the immature fish. Journal of the Marine Biological Association of the Un,ited Kingdom, 38, 417-422. Woodhead, A. D. and Fontaine, Y. A. (1959). Quelques donnkes sup le pouvoir thyrhotrope de I’hypophyse de morue (Gadus rnorrhua L.). Buttetin de l’lnstitut ockanogruphique, no. 1137, 1-6. Woodhead, A. D. and Woodhead, P. M. J. (1965). Seasonal changes in the physiology of the Barents Sea cod, Gadus morrhua L. in relation to its environment. I. Endocrine changes particularly affecting migration and maturation. Special Publication of the International Comm. N . W . Atlantic Fisheries, no. 6, 692-716. Woodhead, P. M. J. (1959). Effects of low temperature on the physiology and distribution of the cod Gadus morrhua in the Barents Sea. Proceeding8 of the Zoological Society, London, 133, 181-199. Woodhead, P. M. J. (1970). An effect of thyroxine upon the swimming of cod. Journal of the Fisheries Research Board of Canada, 27, 2337-2338. Woodhead, P. M; J. and Woodhead, A. D. (1958). Effect of low temperature on the osmoregulatory ability of the cod (Gadus callarias) in Arctic waters. Proceedings of the Linnean Society, London, 169, 63-64. Woodhead, P. M. J. and Woodhead, A. D. (1965). Seasonal changes in the physiology of the Barents Sea cod, Gadus morrhua L. in relation to its environment. 11. Physiological reactions to low temperature. Special Publication of the International Comm. N . W . Atlantic Fisheries, no. 6, 71 7-721. Zaimis, E., Papadaki, L., Ash, A. F., Larbi, E., Kakari, S. and Matthew, M. ( 1969). Cardiovascular effects of thyroxine. Cardiovascular Research, 3, 118-133. Zaks, M. G. and Sokolova, M. M. (1961). Les mhcanismes d’adaptation aux modifications de la salinith de l’eau chez le nerka ((Oncorhynchus nerka Walb.). Voprosy Ikhtiologii, 1, 333-346. ( I n Russian.) Zaks, M. G. and Sokolova, M. M. (1965). Modifications du type d’osmor8gulation aux diffhrentes phriodes du cycle migratoire du saumon rouge Oncorhynchm nerka (Walb.). Voprosy Ikhtiologii, 5, 331-337. (In Russian.) Zaugg, W. S. and McLain, L. R. (1972). Changes in gill adenosinetriphosphatase activity associated with parr-smolt transformation in steelhead trout, coho and spring chinook salmon. Journal of the Fisheries Research Board of Canada, 29, 167-1 7 1.

MIGRATION O F MARINE AND AMPHIHALINE F I S H

355

Zaugg, W. S. and Wagner, H. H. (1973). Gill ATPase activity related to parrsmolt transformation and migration in steelhead trout (Salmo gairdneri) : influence of photoperiod and temperature. Comparative Biochemistry and Physiology, 45B,955-965. Zousser, S. G. (1958). L'Btude des causes des migrations verticales journaliBres des poissons. Ikhtiol. Komiss. Tr. soce Lohania PO physiol. ryb., no. 8 , 115-120. Zueva, K. D. (1965). Presence du processus de smoltification chez Oncorhynchus gorbiischa (Walb.) avec absence du stade parr. F'oprosy Ikh,tiologii, 5, 324-331. (In Russian.)

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Adv. mar. Biol., Vol. 13, 1975, pp. 357-397

SPECIATION IN LIVING OYSTERS MUZAMMILAHMED Institute of Marine Biology, University of Karachi, Pakistan T. Introduction .. .. .. .. .. 11. Genera of Living Oysters .. .. .. 111. Generic Difforences in Ostrea and Crassostrea . . A. Bio-ecological Differences .. .. B. Cytological Differences . . . . .. IV. Physiological Races .. .. .. .. A. Crassostrea virginiea .. .. .. B. Ostrenedulis .. .. .. .. v , Subspecies .. .. .. .. .. VI. Speciation in the Southern Part of the Range. . A. Crassostrea virginica .. .. .. B. Ostrealurida .. .. .. .. VII. Superspecies-Semispecies .. .. .. A. Craasostreagigas . . . . .. .. B. Saccostrea cueeullata .. .. .. vrn. Hybridization . . .. .. .. .. A. Closely Related Species . . . . .. B. Distantly Related Species .. .. IS. Generic Divergence .. .. .. .. X. Discussion .. .. .. .. .. X I . Summary .. .. .. .. .. XII. Acknowledgements .. .. .. xm. References .. .. .. .. ..

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I. INTRODUCTION Ever since Stauber (1950) and Loosanoff and Nomejko (1951) produced evidence in support of physiological races in the American Oyster Crassostrea virginica (Gmelin) many oyster biologists have speculated that physiological races and even subspecies might also be found in other species of oysters. They have, however, referred t o such as forms, strains and varieties-terms which have no taxonomic or evolutionary significance. To many biologists speciation in the bivalve molluscs is purely of academic interest. To oyster growers it can have economic implications. Some of them might be interested in knowing exactly what subspecies or species of oyster they are cultivating, so that their product can be marketed with a specific name. This knowledge can have other practical applications, for instance, in assessing the hybrid potential of some controversial races, subspecies or species, in selective hybridization and in interpreting 357

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the significance of failures or successes of these (see Longwell and Stiles, 197313). I n the last 24 years since Stauber (1950) published his review on oysters (and snails) further information has accumulated regarding hybridization, genetics and cytogenetics of several commercial species of oysters (Imai and Sakai, 1961 ; Ahmed and Sparks, 1967 ; Longwell et al., 1967; Menzel, 1968, 1971; Longwell and Stiles, 1970, 1973a, 1973b ; Ahmed, 1973) and our understanding of their genetic systems and interrelationships has increased. Studies have also been made on what might be genetic differences between populations of oysters, using serological and chromatographic technique (Numachi, 1962 ; Hillman, 1964; Li et al., 1967). Also, a comprehensive treatise on oysters, both living and fossil, has appeared (Stenzel, 1971) in which the nomenclature of living oysters has been revised and some instances of oyster speciation cited. We are thus now better equipped to study oysters for generic differentiation and speciation. The present article reviews available information in support of physiological races of C. virginica along with other evidence suggesting that different levels of speciation exist in such well-known oysters as Ostrea lurida and Crassostrea gigas. There is also evidence to suggest that the many species of oysters which are normally placed in the genus Crassostrea by oyster biologists need to be assigned to more than one genus. 11. GENERAOF LIVINGOYSTERS The oyster family, Ostreidae, as known today, is comprised of three genera, Ostrea Linnaeus, Crassostrea Sacco and Pycnodonte Fisher de Waldheim (see Yonge, 1960; Galtsoff, 1964). This, of course, is the current view held by oyster biologists and zoologists (neontologists) and is a t variance with the classification proposed by the paleogeologist Stenzel (1947) who recognized twelve valid generic names of living oysters. Gunter (1950) recognized three valid generic names of living oysters namely, Ostrea, Crassostrea and Pycnodonte and three others Dendostrea, Alectryonia and Striostrea of doubtful validity. Ranson (1941, 1948b and 1960), basing his conclusions primarily on the structure of the prodissoconch shell, lumped the three doubtful genera of Gunter (1950) into Ostrea and recognized Crassostrea and Pycnodonte as well. Thomson (1954) made a thorough taxonomic study of the Australian oysters and also recognized the three genera Ostrea, Crassostrea and Pycnodonte. Evidence from morphological and biological studies of oysters seemed to support the recognition of these three genera (Galtsoff, 1964). The question of generic classific-

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ation of living oysters thus appeared to be settled. However, recent studies of oyster hybridization and cytogenetics have produced data which suggest that the genus Crassostrea may have undergone evolutionary changes and a t present contains an heterogenous assemblage of species some of which might belong to a different genus. I n his recently published, masterly treatise on oysters, living and fossil, Stenzel (1971) has also emended, to some extent, his original classification of oysters. He now recognizes the following eight genera of living oysters : Ostrea, Lopha, Alectryonella, Crassostrea, Saccostrea, Striostrea, Neopycnodonte and Hyotissa. Pycnodonte, the genus considered as living by oyster biologists, is regarded as fossil by Stenzel. Instead, he has created two new genera, Neopycnodonte and Hyotissa (of oysters living in the deep sea), to which he has assigned species which are normally included in Pycnodonte. Also, Stenzel places the genera Neopycnodonte and Hyotissa in the family Gryphaeidae, apart from Ostrea and Crassostrea which remain in the Ostreidae. Stenzel, for the first time, has suggested that the oysters are not a monophyletic family, as is commonly believed, but may very probably be diphyletic. For the needs of the present review it is necessary to restrict discussion t o the genera Ostrea and Crassostrea which present no controversy. Species belonging to these two genera are considerably better known than those of other oyster genera and provide reliable data for reasonable interpretations. These two genera include about a hundred or so edible and inedible species distributed throughout the world except in Antarctica (Hopkins, 1957). 111. GENERICDIFFERENCES IN OSTREAAND CRASSOSTREA It was Orton (1928) who first realized the existence of two natural groups within the oyster genus Ostrea in which all living oysters were placed a t that time. He enumerated several morphological and biological differences between these two groups and believed that a generic or subgeneric separation was warranted. This generic separation had to wait until Stenzel (1947) and Gunter (1950) indicated that the correct generic name for the American Oyster was Crassostrea virginica (Gmelin). Some of the important biological and ecological differences between the two genera will be outlined below. Other differences have only recently become known. The two genera are now known to differ in their chromosome cytology (Ahmed and Sparks, 1967; Ahmed, 1973). A brief discussion of the chromosome cytology and karyotypes will also be presented for an assessment of the potential of oysters for chromosomal evolution. A.M.B.-13

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MUZAMMIL AHMED

A. Bio-ecological differences As adults all oysters are sedentary and remain confined to the spot where the spat (juvenile oyster) happens to settle. Modifications of shape and sculpture result according to the nature of the substratum and possibly salinity. Dispersal occurs chiefly through a planktonic larval phase which is of shorter duration in Ostrea than in Crassostrea. Stenzel (1971) has pointed out that oysters in general have good dispersal and geologic rates of migration ; maximum distance for successful dispersal of an oyster species, through its planktonic larvae, in an ocean current is about 1 300 km. This high migration rate can explain the wide geographical distributions of such oysters as C. virginica, Ostrea edulis and Ostrea lurida. Species of Crassostrea are mostly estuarine and euryhaline and those of Ostrea are stenohaline. Salinity preference of larval forms may in fact become a limiting factor in dispersal as possibly in the case of Crassostrea virginica whose possible migration from North America to South America might have been halted by the absence of euryhaline conditions in the Caribbean Sea and its islands (Stenzel, 1971). Species of Crassostrea flourish in enclosed protected waters of bays and in the turbid conditions of backwaters and creeks. Species of Ostrea, on the other hand, live in less turbid cleaner waters. The presence of the promyal chamber, first noted by Nelson (1938), probably permits the extension of Crassostrea into the more turbid euryhaline conditions of estuaries (see Yonge, 1960 ; Galtsoff, 1964). Although considered as a primitive character by Stenzel (1971), the promyal chamber, which permits a greater flow of water through the mantle cavity, is certainly to be regarded as a specialized condition associated with elongation of the body and mantle cavity. The only other genus of bivalves in which it is known to occur is the exceptionally elongated Malleus (Yonge, 1968). The genus Crassostrea is mostly dioecious (with separate sexes) but once a year a certain percentage of its members change their sex; Ostrea is hermaphrodite, in which the relative quantity of sex cells of one or other type alternate periodically from male t o female and vice versa (see Galtsoff, 1964). Both genera spawn millions of eggs but Crassostrea is more prolific. Crassostrea discharges loose spermatozoa, but Ostrea produces sperm-balls. Unfertilized eggs (oocytes) or early embryos of Crassostrea are small in size, measuring about 35-55 p, but those of Ostrea are large and more than twice that size, that is, about 100-150 p. Eggs of Ostrea chilensis, occurring on the Pacific coast of Chile are exceptionally large for oysters, 323 x 264 p (Walne, 1963).

SPECUTION IN LIVING OYSTERS

361

Crassostrea is non-incubatory, that is, gametes are released into water and fertilization and complete larval development occurs in the sea, but Ostrea is incubatory and “larviparous”. Most bivalve molluscs are dioecious and non-incubatory, characteristics which Stenzel ( 1971) suggests, represent the original sexual condition among bivalves. Hermaphroditism and larval incubation are, in Stenzel’s opinion, specialized modes of life. On these counts, although not because of the absence of R promyal chamber, the genus Ostrez can be considered specialized and Crassostrea primitive. Generic differences are also seen in the size and morphology of the shell, which is more elongated and can attain huge dimensions in Crassostrea, characteristics of the adductor muscle scar, which is elongated and eccentric in Crassostrea where it may be variably pigmented or unpigmented whereas in Ostrea it is always unpigmented, and larval “ definitive ” prodissoconch (Ranson, 1941, 1948b, 1960). The two genera also differ in the presence or lack of tubercles or ridgelets on the inner lateral margins of the valves. These are present in Ostrea and absent in most species of Crassostrea. Stenzel (1971) has referred to these as chomata ; anachomata are tubercles or ridgelets on the right valve and catachomata are corresponding pits on the left valve for the reception of anachomata, both are generally restricted to the vicinity of the hinge but may encircle the whole valve. Stenzel (1971) considers chomata to be of taxonomic importance.

B. Cytological differences Ostrea and Crassostrea differ considerably in the cytology of the meiotic prophase of their oocytes. Ahmed and Sparlga (1967) reported “ lampbrush ” bivalents from the developing oocytes of Ostrea lurida. The ten bivalents of this species a t the diplotene stage are large and fuzzy because they “ spin out ” loops from the chromosome axis. They are also characteristically associated with vacuolated bodies resembling nucleoli. Diplotene bivalents of several species of Crassostrea are much smaller and loops from the chromosome axis are notably absent or very poorly developed. Evidently the diplotene nuclei of Ostrea are metabolically more active than those of Crassostrea. The loop formation is a manifestation of gene activation for the synthesis of RNA which in turn would be required for the production of larger quantities of yolk material in the oocytes of Ostrea. The eggs of Ostrea are much larger in size, twice or more, than those of Crassostrea and contain much greater quantities of yolk. This evidently is an adaptation directly related to incubation. The mitotic interphases of 4-8 cell embryos of both Ostrea lurida

362

MUZAMWL AHMED

FIQ.1. Twenty late mitotic prophase chromosomes of 0. Zurida from a third cleavage nucleus. One chromosome slightly out of focus. Phase contrast (from Ahmed and Sparks, 1967). FIG.2. Twenty mitotic metaphase chromosomes of 0. Zuridn from a third cleavage nucleus. Phase contrast (from Ahmed and Sparks, 1967)

and 0. edulis are characterized by the presence of several (f 20) nucleoli-like bodies interspersed in the chromatin material. At least 2-4 of these can sometimes still be seen in the late prophase and early metaphase plates. I n the several species of Crassostrea examined by me only 1-2 such bodies were observed in the mitotic prophases. At corresponding stages of the mitotic cycle, chromosomes of Ostrea are smaller than those of Crassostrea. For instance, in the third cleavage nuclei, chromosomes of Ostrea lurida measure 1.2 to

SPECIATION IN LIVINU OYSTERS

363

FIG. 3. Mitotic metaphane chromosomes of the Miyagi " variety " of G . gigas; at,ypicsl set with 23 chromosomes. Phase contrast (from Ahmed and Sparks, 1967). FIG.4. Twenty mitotic metaphase chromosomes of C . rivularis. Phase contrast (from Ahmed, 1973).

5.0 p and those of Crassostrea gigas 1.8 to 6.0 p (Ahmed and Sparks,

1967). While mitotic chromosomes of Ostrea are more strongly coiled and thicker in appearance, those of Crassostreame more slender and less strongly coiled (Figs 1 t o 4). Chromosome complements of Ostrea might have evolved from those of a Crassostrea-like ancestor through tighter coiling of the chromatin material and may thus be more specialized. The several species of Ostrea and Crassostrea which have so far been examined cytologically (Ahmed and Sparks, 1967 ; Longwell et al., 1967; Menzel, 1968; Ahmed, 1973) all possess a common diploid number of 20 (n = 10). Their genes are thus distributed in 10 linkage groups as in maize. Meiosis is chiasmate in males and females (Ahmed, 1973) to provide oysters with sufficient variation potential,

364

MUZAMMIL AHMED

through recombination, to cope with the changing estuarine conditions in which most oyster species thrive. Their karyotypes (Fig. 5 ) are composed of only metacentric and submetacentric chromosomes of much graded lengths which in most cases cannot be individually identified. A greater number of B-type submetacentrics (Table 1) seem to occur, however, in 0. lurida than in species of Crassostrea (Ahmed, 1973). Oysters, as most other bivalves, are cytologically conservative in that changes in chromosome number do not occur and conspicuous chromosome change seems to have played no role in their evolution. It has been proposed (see Jackson, 1971) that

1

2

3

4

5

6

1 9 Tf77

c \ ( I3

7

8

9

1

p9 ?7

0

-

Mffl

10 fi

FIG.5. Karyotypes of oysters. A, 0. lurida; B, Miyegi “veriety C, Kumamoto ‘‘ variety ” of C. gigas (from Ahmed, 1973).

”

of C . gigas;

conservative karyotypes are probably so because of lack of heterochromatin (inert chromatin material in which breaks can occur without attendant lethalities and can thus lead to repatterning of karyotypes). Presumably, therefore, oysters are cytologically conservative because of lack of heterochromatin in their chromosome complements. Among bivalves only marine mussels have shown chromosome polymorphism (for pericentric inversions) and thus some flexibility (Ahmed and Sparks, 1970). The genus Perna is dimorphic for chromosome number, having 2n = 28 and 30 (Ahmed, 1974). There is some evidence that karyotypes of oysters which are superficially alike may in fact possess different numbers and types of submetacentrics. Different species of Ostrea and Crassostrea could have been differentiated through short pericentric inversions which are normally difficult to detect (Ahmed, 1973). Such inversions can alter the position of the centromere within

365

SPECIATION I N LIVING OYSTERS

TABLEI. FREQUENCIES OF METACENTRICS (M) AND SUBMETACENTRICS A AND B (M A B) IN FOUR SPECIES OF OYSTERS(from Ahmed. 1973).

Species

No. specimens

.

-

~

A ~-

~

5

7

9

4 6

4 11 10

9 8 6 8

6 4

Submetacentriw

Melacentrics &I

.

~

Crassostrea rivularis C glomerata C . gigas Miyagi C . gigas Kumamoto Ostrea lurida

plates scored

9

45% 45%

11 9

40% 30%

12

55% 45% 60%

12

60%

40%

9

45%

B .- .___.

- 2 10% - 2 10% 3 15%

a chromosome and can possibly change the frequencies of different chromosome types (Table I).

IV. PHYSIOLOGICAL RACES The occurrence of temperature races in marine animals has been known for a long time (Mayr, 1963). Runnstrtjm (1936)had pointed out that physiological races of several marine invertebrates exist in the Eastern Atlantic. The case of the bivalve Chlamys opercularis was investigated by Ursin (1956) who found North Atlantic populations of this species living between 4" and 13°C and the Mediterranean subspecies thriving between 13" and 26°C. Recently Sastry (1970)reported variation in the timing of spawning in two latitudinally separated populations of the Bay Scallop Aequipecten irradians from the east coast of North America. He suggested that this variation has probably been favoured by selection as an adaptive response to geographical differences in temperature and time of abundant food production. Eco-physiological adaptation, with genetic basis, is generally considered synonymous with the beginning of the speciation process (see Mayr, 1963; Golikov, 1973). Uninterrupted isolation and selection over long periods of time could transform physiologically different populations of a species into incipient species. Among oysters Crassostrea virginica of the east coast of North America and Ostrea edulis of European shores are reputed to occur in several physiological races. The strength of both claims is evaluated in the following discussion. A. Crassostrea virginica The American Oyster, C. virginica (Gmelin) (Fig. 6), one of the most prolific of oysters (Gunter, 1951), occurs all along the east coast of

FIG.6. CTa8808tVW Virginica from the east coast of the U.S.A. (upper row) and, below, a C . t&@nica-likeoyster from the coast of Venezuela; right, exterior view; left, interior view.

SPECIATION I N LIVING OYSTERS

367

North America from the Gulf of St Lawrence in Canada to Key Biscayne, Florida, in the Gulf of Mexico (down to Yucatan in Central American Peninsula) and in the West Indies (see Galtsoff, 1964; Stenzel, 1971) (Fig. 8). South of Yucatan this species is replaced by C. rhizophorae (Fig. 7 ) which can withstand much higher salinities (Stenzel, 1971). Gunter (1951) had, however, indicated that C. virginica extends as far south as Brazil in the South American continent. I n any case, this constitutes a vash distributional range, some 5 000 miles north to south, an area of distribution in which a wide range of

Fra. 7. Crassostreu rhizophorue from the coast of Venezuela.

temperature conditions prevail. On the east coast of North America C . virginica is the only species of Crassostrea to occur because it can stand the prevailing low temperatures better than any other species of oyster found on the east coast (Stenzel, 1971). At least three species of Ostrea, 0. equestris, 0. permollis and 0. frons, occur on the eastern coast of North America but none of these extends as far north as Crassostrea virginica (see Galtsoff, 1964). C. virginica has been transplanted on t o the west coast of the U.S.A. and to Canada, Japan, Hawaii, Australia and the United Kingdom. It is possible that from these regions it could have spread to other areas. C. madrasensis (Preston) ( = C. cuttackensis Newton

368

MUZAMMIL AHMED

and Smith ; in Stenzel, 1971) one of the species occurring in Pakistan and India has been considered synonymous with C. virginica (Ahmed, 1971). It seems, therefore, that due to the efforts of man the species has now become more or less cosmopolitan.

FIQ.8. Distribution of C. virginica and 0. lurida and of their subspecies and related species on the east and west coasts of North America, respectiuely; solid black circles in the Gulf of California region, below San Diego, indicate the occurrence of three subspecies of 0. Zurida and four other species of Ostrea besides 0. lurida.

Several workers have drawn attention to the existence of physiologically distinct races in C. virginica on the east coast of North America (see Hillman, 1964). Stauber (1950), however, was the first to put the problem in a clear perspective by publishing a review of the subject. By analyzing the then available evidence he concluded that there exist three physiological races of this species which spawn at

SPECIATION IN LIVING OYSTERS

369

temperatures of 25", 20" and 16.4"C. This means that there is a difference of about 4-8'C in the minimum threshold temperature required for the initiation of spawning between oysters from northern and southern areas. Later Loosanoff and Nomejko (1951) confirmed experimentally the validity of these conclusions. Loosanoff and Nomejko (1951) transplanted young oysters 2-3 weeks old (spat) originating from different localities in southern and northern areas of the United States to Milford, Connecticut. A study of gamete formation and spawning behaviour and its physiology in oysters of the same age was made and the following results were obtained. The oysters which originated in Massachusetts or Long Island Sound, that is, in the more northern latitudes, spawned in Milford Harbour during the summer of 1950, discharging all their spawn. However, the majority of oysters that originated from warm regions, New Jersey or Virginia, either did not spawn at all or discharged only a portion of the accumulated spawn. This difference indicated that the breeding temperature requirements of the northern oysters were somewhat lower than those of the southern. Other studies which strengthen these conclusions are mentioned below. Additional evidence supporting the occurrence of physiological races in C. virginica was presented by Meneel (196.5). He found that under experimental conditions the ciliary activity of the gills of oysters from more northern areas persisted down to O'C, whereas all activity ceases a t temperatures of 5 6 ° C in oysters from the Gulf of Mexico. Also, northern oysters cease feeding a t a temperature of 30"C, a high temperature rarely encountered in the colder areas. I n the Gulf areas oysters feed a t 30°C and above as indicated by the presence of the crystalline style (which is only fully formed in actively feeding oysters). Two other studies have a bearing on this subject. Hillman (1964), using chromatographic technique, has demonstrated differences in the patterns of free amino acids or small peptides between two populations of C. virginica respectively indigenous to Long Island Sound and James River, Virginia. This is the first study actually to demonstrate genetic differences in separate stocks of C. virginica. Another study demonstrating such differences, this time using serological methods, is that of Li et al., (1967) who found antigenic differences in two populations of C. virginica occurring on the east coast of Canada. There is now, therefore, irrefutable evidence that C. virginica does exist in several races. But the differences seem to be only on the gene level. The chromosomes show no detectable differences from population to population (Longwell and Stiles, 1970 and 1973b). Different

3 70

MUZAMMIL AHMED

populations of this species have the same number, 2n. = 20. No centric fusions or fissions are known which could indicate chromosomal differentiation of populations. Moreover, all races of C. virginica are morphologically alike. Stauber (1950) had postulated that C. virginica formerly had a discontinuous distribution on the east, coast of North America. Reproductive isolation was practically complete in that different populations spawned a t different times because of adjustments to certain critical temperatures for spawning. He hypothesized that man, by changing the discontinuous distribution of C. virginica to a continuous one, has interrupted the process of speciation. This probably is truer today than ever before since oyster farmers keep moving their stocks from one region to another. Yet, despite all these stock mixings, an occasional population of C . virginica could still exist along the extensive eastern coastline of North America which might retain its genetic isolation. Such populations probably exist today in the State of Maine and on Long Island in the United States. For instance an incipient barrier may be developing between wild populations of C. virginica occurring in Long Island Sound and in Maine (Longwell and Stiles, 1973a ; Longwell, personal communication). I n about ten crosses made by Longwell and co-workers a t Milford, Connecticut, in a period of few days in one season, the average rate of fertilization was low. Some fertilization, nonetheless, did occur and some oyster spat settled. Longwell has pointed out that under conditions of artificial fertilization it would be surprising if such a barrier would be absolute (Longwell, personal communication). This preliminary finding is of much interest and the work needs to be repeated with a larger number of animals.

B. Ostrea edulis The European Flat Oyster 0. edulis Linnaeus has a wide geographical range from Norway to the coast of Morocco a distance of some 2 000 miles, as well as within the Mediterranean and the Black Sea (Yonge, 1960). Stenzel (1971) mentions that the summer temperature requirements of 0. edulis for reproduction are very low (12-16°C). For this reason 0. edulis is the one species that can survive on the coast of Europe north of France. I n northern Norway 0. edulis survives only in a few isolated and favourable localities.* These places have a " hot house " effect (Stenzel, 1971). They are narrow waters exposed to the full sun and protected by hills or mountains so that

* Notably in pools cut off at the heads of fjords by terminal moraines (Gaardner and Bjerkan, 1934; Yonge, 1960).

SPECIATION I N LIVING OYSTERS

371

the water temperature can rise while cold winds or water currents cannot reach them. There is evidence to suggest that this species also consists of several physiological spawning races (Korringa, 1958). Races of this species which spawn and swarm a t the highest temperatures occur a t the northern extremity of the distribution, while just about 2 000 miles south along the north coast of Spain live oysters with lower temperature requirements for spawning (see Yonge, 1960). The northern populations of this species require 15-16°C for spawning and the southern populations 12-13°C (Korringa, 1958). Along the coast of Spain the preferred spawning temperature is 12-14OC while near Bergen, Norway it is about 25°C. I n this species distribution of spawning races evidently does not follow latitudinal patterns as in Crassostrea virginica. No morphological forms or subspecies of Ostrea edulis have been described except that Korringa (1958) has cited Bompayre (1955) who mentioned the ‘‘ eking out ” of a special variety of 0. edulis called “gravette ’’ in the Bay of Arcachon when the original resident population of 0. edulis in this Bay had been wiped out by a disease. Although 0. edulis has great economic importance in Europe and has also been transplanted to some areas in North America it is not as well studied a species as C . virginica. Hence physiological, chromatographic and serological studies of different stocks have not been made which could have supported the claim for the existence of physiological races.

V. SUBSPECIES Ostrea lurida Carpenter, the California, Olympic or Pacific Native Oyster occurs from Sitka, Alaska (57” north latitude) to Cape San Lucas (22.5” north latitude) and Mexico (Hertlein, 1960) (Fig. 8), i.e. about 5 000 miles from north to south. This is a distributional range more or less equivalent of that of Crassostrea virginica on the east coast of North America. Stenzel (1971) mentions that Ostrea lurida has the lowest summer temperature requirements of any oyster on the Pacific coast of North America, and therefore, it is the only oyster able to survive north of San Diego, California. It is probably for this reason that no species of Crassostrea could ever establish here naturally.* Populations of C. gigas, C. rivularis, and C . virginica now occur along the west coast of North America but these resulted through transplantations from other areas.

* Except in regions of exceptional suitability, notably Pendrell Sound and elsewhere in the Straits of Georgia, British Columbia (Quayle, 1969).

372

MUZAMMIL AHMED

No suggestion that physiological races occur has ever been made for Ostrea lurida. They may, nevertheless, occur because wide temperature fluctuations and different hydrographical conditions occur over this extensive range. This species has been studied to an even lesser extent than the European Flat Oyster 0. edulis. Ostrea lurida is very variable morphologically, especially in the southern part of its range, and the multiplicity of forms assumed by it in this region has led to the proposal of names for three of its TABLE11. SPECIESAND SUBSPECIES OF Ostrea FOUND ON THE WESTCOAST OF NORTHAMERICA (prepared from the descriptions given in Hertlein, 1960) SpeciesSubspecies

Shape

0. lurida

flat shallow concave

0. 1. rufoides

thin umbo hollow flat round winged cupped winged wavy flat round thin

0. 1. expansa 0. 1. laticaudata 0. conchaphila

Colour

Colour

Exterior

Interior

yellow brown stripedyellow purplebrown

white olivegreen to purplebrown

Range Sitka, Alaska to Mexico

reddishbrown stripedbrown yellow

purplebrown yellowstriped

white olivaceous olivegreen purple olivegreen white

San Diego to Panama

forms : 0. lurida forma rufoides, forma expansa and forma laticaudata Carpenter (Hertlein, 1960). The three named " formas )' of 0. lurida were originally described by Carpenter who had also described the species lurida and the types of these " formas ') were illustrated by Hertlein (1960). I am suggesting that these ('formas " of 0.lurida be considered as subspecies as the terms formalvariety have no taxonomic validity and are obsolete. A subspecies can be defined as " an aggregate of local populations of a species, inhabiting a geographic subdivision of the range of the

SPECIATION IN LIVINU OYSTERS

373

species, and differing taxonomically from other populations of the species” (see Mayr, 1963). It is difficult to decide if these three r‘ formas ” have really attained subspecific differentiation or are merely ecophenotypes. Considerable overlapping of characters exists between these three “formas” and 0. lurida on the one hand and between them and another species of Ostrea, 0. conchaphila, on the other (Table 11). This latter species occurs only in the southernmost part of California (Hertlein, 1960). Certainly more information is needed about their population structure and genetic relationships before their taxonomic status can be finally confirmed. IN THE SOUTHERN PARTOF THE RANGE VI. SPECIATION Among oysters, perhaps the two most widely distributed species are Crassostrea virginica and Ostrea lurida which are native, respectively, to the east and west coasts of North America. Their vast range of distribution, some 5 000 miles north to south, encompasses cold temperate, subtropical and tropical waters. I n this range sharp changes in hydrographical conditions can be expected. Ecophysiological adaptations of oysters to local environmental conditions could result in the establishment of geographically isolated populations. A species would acquire a polytypic character if it produces morphologically and/or physiologically distinct geographical isolates. If gene flow stops and selection is favouring them the isolates would emerge as new species in due time. The parental species could thus split into one or more new species, itself remaining unchanged. Such a speciation process seems to have occurred in C. virginica and 0. lurida in the southern part of their respective ranges. This is discussed below.

A. Crassostrea virginica The physiological divergence of C . virginica populations along the east coast of North America has been unaccompanied by morphological divergence. Populations with preferences for certain critical spawning temperatures in different areas cannot be morphologically distinguished. However, some indication does exist that morphological divergence might have been initiated in the southernmost populations in the Caribbean Sea. For instance, a C. virginicu-like oyster (Fig. 6) owurs on the coast of Venezuela which differs from C. virginica in tlie pigmentation of its muscle scar ; instead of the black-brown or dark-blue scar which is characteristic of C. virginica this Venezuelan oyster possesses an unpigmented to slightly pigmented scar (Fig. 6). The oyster has been identified tentatively as C. guyenensis Ranson by

374

MUZAMMIL AHMED

Macsotay (1974) but from its shell characteristics it appears to be a subspecies of C. virginica. A second and larger oyster with an altogether unpigmented muscle scar also occurs in Venezuelan waters. Macsotay (1974) has identified this species as C. lacerata Hanley. A third oyster occurring on the coast of Venezuela and distributing over all the Caribbean Islands is the well-known Mangrove Oyster C. rhizophorae. The muscle scar of this species is less heavily pigmented than in C. virginica and in some individuals the pigmentation is entirely missing (Fig. 7). This species can be distinguished by some other shell characteristics, one being that the upper valve is uniformly depressed or set within the lower valve (Gunter, 1951). Also, C. rhizophorae lives in waters of somewhat higher salinity than C. virginica (Gunter, 1951). Stenzel (1971) mentions that, south of Yucatan, C. virginica is replaced by C. rhizophorae which can stand higher salinities better than C. virginica. Menzel (1968) has successfully crossed C. rhizophorae with C. virginica providing an indication Crassostrea that the two species are fairly closely related. rhizophorae and the other two species C. guyenensis and C . lacerata mentioned above occur near the southernmost periphery of the range of C. virginicri and might have descended from it. It would be very interesting t o know if the latter two species are compatible with C. virginica in experimental hybridization.

B. Ostrea lurida I n addition to the three " formas " or subspecies of 0. lurida which were shown to occur in California by Hertlein (1960) several other species of Ostrea are believed to occur in southern California and the Gulf of California on the coast of Mexico. Hertlein mentioned the presence of two species 0. conchaphila and 0. angelica in southernmost California and the Gulf of California, respectively. Granados and Sevilla (1965) have indicated the presence of two other species besides 0. angelica on the west coast of Mexico in the Gulf of California. These are 0. megadon and 0.jischerii. It is very interesting to note that from Sitka, Alaska t o Cape San Lucas there exists only one clear cut species, 0. lurida, but that three subspecies/formas of 0.lurida and four other species of Ostrea have been recorded from lower California and from the Gulf of California. Evidently, therefore, a burst of speciation seems t o have occurred near the southern periphery of the range of 0. lurida, making it in all probability the parental species. The genus Ostrea seems to be better suited for speciation than Crassostrea. I n Ostrea fertilization occurs internally and the larvae

SPECIATION I N L N I N G OYSTERS

375

are brooded until the straight-hinge stage after which they are released into the water. For this reason there are greater chances for the establishment of reproductive isolation between populations from different geographical locations. This is very much in conformation with Mayr’s suggestion (Mayr, 1963) that any factor, such as parental care, that reduces dispersal may facilitate speciation. By the time the larvae of Ostrea become independent they might become thoroughly habituated to the very localized niche of the parents and thus might result in a locally adapted population. VII. SUPERSPECIES-SEMISPECIES

A superspecies is composed of a monophyletic group of entirely or essentially allopatric species that are morphologically too different to be included in a single species (Mayr, 1963). According to Mayr the principal feature of a superspecies is that geographically i t presents essentially the picture of a polytypic species, but that the allopatric populations are so different, morphologically or otherwise, that reproductive isolation between them can be assumed. The allopatric species of which a superspecies is composed have been designated by Mayr as semispecies (see Mayr, 1963). Gene exchange is still possible between semispecies but not as freely as among conspecific populations. Superspecies are common among birds, fishes, land snails and marine animals (see Mayr, 1963). Superspecies seem to exist in oysters also. The outstanding case, in my opinion, is that of the Japanese oyster Crassostrea gigas, but Stenzel ( 1 97 1 ) has also emphasized that Saccostrea cuccullata ( = C. cuccullata), which is widely distributed in the Indo-Pacific waters, is a complex superspecies. Both cases will be discussed now. A. Crassostrea gigas Crassostrea gigas (Thunberg) is distributed all around Japan (Fig. 9) and Korea (Imai and Sakai, 1961) and off China and Asiatic Russia (Stenzel, 1971). It has also established itself on the west coast of the United States and Canada where shipments of its seed still arrive annually. I n the Japanese Islands this species is known to consist of four physiologically and to a great extent morphologically, welldefined forms which most contemporary workers tend to regard as only varieties (seeCahn, 1950 ;Imaiand Sakai, 1961 ;Numachi, 1962 ; Galtsoff, 1964; Quayle, 1969;Menzel, 1974).The four so-calledvarieties, Hokkaido, Miyagi, Hiroshima and Kumamoto are named after the geographical locality (prefecture) from where they originate (Fig. 9). These four

376

MUZAMMIL =ED

15'

40'

35c

10

30'

1

130'

FIG.9. Distribution of the four

"

I

I

135O

140'

varieties " of C. gigas in the Japanese Islands.

oysters have different morphological characters, growth rates, spawning temperatures, adaptibility to environmental conditions and flavour. Some of these differences are outlined in Table I11 and others of greater importance, from the point of view of speciation, are discussed below. Imai and Sakai (1961) had indicated that the northern oysters Hokkaido and Miyagi could easily be distinguished from the southern

377

SPECIATION IN LIVING OYSTERS

Hiroshima and Kumamoto through morphological differences. Further, the Hokkaido and Miyagi oysters can be told apart by shell form and colouration. The Kumamoto can be distinguished from the Hiroshima because the Kumamoto oyster is much smaller. I myself have seen that the Kumamoto oyster is so morphologically distinct from Miyagi (Fig. 10) and Hokkaido that it could never be confused with them, although the latter two oysters are sometimes difficult to tell apart from such clear cut species as C. virginica. TABLE111. SUMMARY OF THE COMPARISONS O F CHARACTERS AMONG OYSTERSOF DIFFERENT ORIQININ JAPAN (based on Imai and Sakai, 1961) Characters

Hokkaido

Shell size Shell colour

largest greyish white

Valve flatness Relative shell depth

flat shallow

Miyagi large intermediate bet. Hokkaido and Hiroshima slightly wavy intermediate bet. Hokkaido and Hiroshima low

Hiroshima

Kumamoto

small black purple

smallest black purple

very wavy deep

very wavy deep

highest Meat lowest weight index slow fast Growth very fast Mortality highest in the higher in the higher in the southern beds southern beds northern beds

high slowest low in all beds

Imai and Sakai (1961) found differences in the spawning of these four types of oyster while they were being observed for ten years in Onagawa Bay (Fig. 9) where they were brought from their respective areas of origin. Both Hokkaido and Miyagi oysters spawned in late August and early September when the water temperature begins to decline. The Hiroshima spawned a week or two later, in the first and second decades of September. Usually none of these three oysters carries ripe gonads during the winter. Kumamoto oysters show an altogether different mode of spawning. I n Onagawa Bay they usually spawn naturally in late July when temperatures reach 22 or 23°C and then resume ripening of the gonad so that they possess ripe gonads even in November and December. Such gonad formation in

FIG.10. Miyagi and Kumamoto ‘‘ varieties Kumamoto.

”

of C . gigas. Larger shells are those of Miyagi and smaller those of

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Kumamoto oysters at low temperatures was observed in Ohminato, Mangoku-ura, Hamajima, Kagamimachi and also on the west coast of the United States. In order to demonstrate genetic differences between the four oysters, Imai and Sakai (1961) performed a series of inbreeding and crossbreeding experiments. The larvae were reared under identical conditions and the spat obtained were transplanted to several oyster beds in Japan and the United States where they grew under identical conditions. Inbreeding of the four oysters for three generations indicated the specificity and hereditary nature of such characters as shell size, form and weight, flatness of shell valve, colouration, adaptability to environmental conditions and spawning. Hybridization of the four ‘‘ varieties ” resulted in offspring with characters intermediate between those of the crossed strains and with no evidence of segregation in the F, generation. Hybrid oysters showed a higher adaptability to environmental conditions than the inbred strains. The four oysters, Hokkaido, Miyagi, Hiroshima and Kumamoto, have been considered as only strains or varieties of C . gigas by Imai and Sakai (1961), and by others following them, because they yield viable hybrids in the laboratory. Cross fertility, however, does not prove conspecificity (Mayr, 1963). Many good species, including those of oysters, in which hybridization does not occur in nature have been shown to cross easily in the laboratory (see hybridization of oysters in this article, p. 382). Reproductive isolation in the four “ varieties ” is not complete in the sense that fertilization, cleavage and hybrids can be produced in the laboratory. It is complete, though, in the sense that they spawn in nature at different times and would not be expected to interbreed as noted elsewhere (Ahmed, 1973). Moreover, they maintain their specificity after generations of inbreeding. Two other studies indicate that genetic differentiation among the four oysters is great and that the various types cannot simply be regarded as varieties, strains or races. Numachi (1962) found some antigenic differences among the four “ races ” of C. gigas by the use of antisera prepared against different races and absorbed with the antigens of other races and these differences are “ . . . in accordance with the degree of their geographic isolation from each other”. Chromosome analysis of the Miyagi and Kumamoto oysters has shown that they differ in the frequencies of metacentrics and different kinds of submetacentrics (Table I) (Ahmed, 1973). As far back as 1930 Hirase had pointed out that the Miyagi and Hokkaido oysters constituted the true C. gigas (Thunberg). Hirase

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(1930) identified the Hiroshima oyster as C . laperousi (Schrenek) and Amemiya (1928) had named the Kumamoto oyster as C. gigas variety sikamea. I am of the opinion that the Kumamoto oyster is so morphologically and physiologically distinct from the other three oysters as to deserve full species rank. I wish to propose that the varietal name sikamea given to it by Amemiya in 1928 [Cahn (1950) refers to this variety as a subspecies C. gigas sikamea (Amemiya, 1928)] be retained as a species name. The Kumamoto oyster should then be designated as C. sikamea sp. n. (the oyster would be described as a new species elsewhere). I further propose that the species name laperousi given to the Hiroshima oyster by Schrenek in 1861 (see Cahn, 1950) be also restored. The Hiroshima oyster should then be designated as C. laperousi. The Hokkaido and Miyagi oysters are not so distinct, in my opinion, as to qualify for full species ranks. They resemble a t best the physiological races of C. virginica which have accumulated physiological differences but do not morphologically diverge. The oysters C. gigas ( = Hokkaido and Miyagi), C . laperousi ( = Hiroshima) and C. sikamea ( = Kumamoto) are like very closely related species or semispecies ; C. gigas in that case is a superspecies with two semispecies. The case of the C . gigas oysters has a very close parallel with Jaera marina, a benthic isopod. This is represented by six forms (four in the Roscoff area in France) which, since they interbreed only exceptionally in nature, have been considered as distinct species. On the other hand, their remarkable morphological resemblance, the parallelism of their genetic polymorphisms and the easy occurrence of hybridization in the laboratory indicate their close affinity so that Jaera marina has been classified as a superspecies (Bocquet, 1953). Similarly the tropical echinoid Tripneustis gratilla has been regarded as a superspecies with two semispecies T . ventricosus and 2'. depressus (Mayr, 1954). Speciation in C. gigas might have occurred in response to great temperature differences which prevail along the eastern coast of Japan. The islands receive warm water from the south by means of the ocean current Kuroshio whose main mass passes the south-eastern coast. East of Yokohama the Kuroshio leaves the coast and flows out into the open sea. Northern Japan is influenced by the cold Kurile current which comes from the north. The Japanese Islands can thus be divided into northern and southern Japan, the two belonging to different zoogeographical regions and having their southern and northern group of species (Ekman, 1952). The boundary between the two lies about 86"N latitude east of Tokyo and Yokohama. The Hokkaido and Miyagi oysters would thus belong to the northern group which is cold-

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temperate in character and the Hiroshima and Kumamoto to southern group which is subtropical in nature.

B. Saccostrea cuccullata Among oysters Crassostrea cuccullata (von Born, 1778) has also been considered a superspecies by Stenzel (1971) who, however, assigns this tuberculated or denticulated species and others like it to the genus Saccostrea (see later in this article). According to him the Sydney rock oyster Crassostrea commercialis is a subspecies of Saccostrea cuccullata. This introduces a new controversy in the field of oyster taxonomy. Iredale and Roughley (1933) had identified the Sydney rock oyster as a species of the genus Saxostrea, but Thomson (1954) placed it in the genus Crassostrea and ever since then the Sydney rock oyster has been known to oystermen and to biologists as C. commercialis. Thomson (1954) has also expressed doubt about the validity of the name cuccullata indicating that von Born (1778) had probably applied it incorrectly. Instead, Thomson (1954) identified the cuccullata-like oysters of Australia as C. tuberculata (Lamarck). Carreon (1968) accepted the name C. tuberculata for the cuccullata-like oysters of the Philippines and I have also identified the cuccullata-like oysters of Pakistan as C. tuberculata (Ahmed, 1971). Stenzel (1971), however, considers that Thomson’s (1954) suppression of the name cuccullata is an error. Saccostrea cuccullata occurs abundantly in the Indo-Pakistan subcontinent. It is a purely marine species never forming beds in backwaters and estuaries. On the coast of Sind in Pakistan this species occurs on elevated cliffs exposed to direct sunlight and gets submerged in the surfy waters only occasionally. The oyster attaches very firmly to rocks and almost blends with the colour of the substrate and is difficult to detach (Ahmed, 1971). The species has invaded the mangrove habitat in East Africa where it has been reported to occur in two distinct forms which Stenzel (1971) considers as ecomorphs. This species has been reported from north western Australia (Thomson, 1954), the Philippines (Carreon, 1968), East Africa (Sparks, 1965 in Ahmed, 1971 ; Stenzel, 1971), India (Awati and Rai, 1931) and Hawaii (Sparks, 1963 in Ahmed, 1971). Evidently 8. cuccullata is widely distributed in the Indo-Pacific tropics and subtropics. It will not be surprising to find variants or subspecies of this species in different parts of the world. For instance, there are the two ecomorphs of this species occurring in East Africa (Stenzel, 1971) and one subspecies commercialis in the Australian waters (as believed by Stenzel). To call S. cuccullata a

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complex superspecies, as does Stenzel (1971) is, however, not justified unless genetic differences and partial or complete reproductive isolation is demonstrated between different stocks of this species from different parts of the Indo-Pacific. To arrive a t such a conclusion, that is one favouring a superspecies grouping, studies such as those made on C. gigas oysters of Japan would be necessary. Merely a widespread distribution and morphological variability of the different stocks is not enough. The species may simply be polymorphic instead of being polytypic. VIII. HYBRIDIZATION Oysters of the family Ostreidae propagate through cross-fertilization. Because of their sedentary mode of life, however, they are not capable of selecting their mates. But this sedentary mode of life is not much of a handicap with regard to interbreeding between populations of the same species or of different species. This is so because species of Crassostrea release their gametes into the surrounding water (Ostrea retains the oocytes in the mantle cavity) where they could be transported for fairly long distances before their viability would be affected. The gametes of one species could thus become available to a relatively distant population of the same species or of a different species. Also, gamete discharge by one population could induce spontaneous spawning of another population of oysters. Both intra- and interspecific hybridization could thus easily come about in the natural environment. At least in the tropics and subtropics where a number of oyster species can occur in a small area (see Awati and Rai, 1931 ; Carreon, 1968 ; Ahmed, 1971)interspecific hybridization is a distinct possibility. There are, however, some factors which could prevent interspecific hybridization. For instance, the spawnings of different species might not coincide, or if they did, general incompatibility mechanisms would not permit hybridization (Ahmed, 1973). I n fact recent studies on experimental hybridizations of different species of Crassostrea, some coming from widely different parts of the world, have indicated the possible existence of incompatibility genes (Imai and Sakai, 1961 ; Menzel, 1968 ; Longwell and Stiles, 1970, 1973b ; Stiles, 1973). Longwell and Stiles (1970) have mentioned that incompatibility genes may have played a significant role in the evolution of present-day oysters by preventing self-fertilization in more primitive oysters which developed and spawned both eggs and sperm simultaneously. In fact the natural outbreeding nature of oysters must become reinforced by a system of gamete cross incompatibility (Longwell and Stiles, 1973a). Hybridize-

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tjon between spec& of O?&w and Ozwms6~eain nature or in the laboratory is not possible because of the outstanding differences in their modes of reproduction, morphology of their gametes and the cytology of their chromosomes (see earlier in this article). The successes and failures of experimental hybridization of various species of Crassostrea have shed considerable light on the nature of affinities between them. It has now become apparent that some species of oysters are more closely related to one another and others rather distantly so. A discussion of these relationships will now be presented.

A. Closely related species The Portuguese Oyster, C . angulata, has been shown t o cross easily with oysters of the superspecies C. gigas and to yield viable hybrids in the laboratory (Imai and Sakai, 1961). Menzel (1968) has also shown that these two species cross readily in the laboratory. Crassostrea angulata occurs along the east and southeast coasts of Portugal and Spain and has also been introduced into France and It England although it seldom breeds in the British waters. resembles C. gigas (Hokkaido and Miyagi oysters) in shell characteristics and the temperature a t which it breeds. The suggestion has been made that C . angulata may in fact be C. gigas which could have been introduced accidently into Portugal possibly attached to the underside of a vessel (Ranson, 1948a). Stenzel (1971) has, however, suggested that both C. gigas and C. angulata arose from the same parental species after the breaking up of the ancient Tethys Sea into various bays and gulfs due to tectonic events. A cross has recently been attempted by Stiles (1973) between C. virginica of North America and C. angulata which was obtained from Spain. Stiles found varying degrees of failure of cross-fertilization, meiotic and mitotic abnormalities, parthenogenesis and polyspermy. These anomalies were interpreted as evidence of gamete incompatibility between C. virginica and C. angulata. Unfortunately the larvae could not be reared because of lack of facilities for the rearing of exotic species and their hybrids (at Milford) so that the character of the hybrids between these two species remains unknown. Several attempts have been made to hybridize C. virginica with the Japanese oyster C. gigas. Galtsoff and Smith (1932) were the first to attempt the cross. They observed normal cell division in the hybrid embryos but could only obtain early veliger larvae. The same cross was attempted by Davis (1950) who also was unable to obtain hybrid oysters since all larvae died before reaching the umbo stage. I n Japan,

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'

Imai and Sakai (1961) obtained similar results from this cross. Recently, however, Menzel (1968) has succeeded in obtaining hybrid oysters from this cross. Some 12-18% fertilized eggs were obtaineda rather low percentage (see Menzel, 1971). It is not known if any of these oysters resulted from parthenogenetic eggs. The well-known oyster of the Caribbean Sea, Crassostrea rhizophorae, has been shown to hybridize readily with C. virginica in the laboratory as reported by Menzel (1968). There is evidently no genetic barrier between these two species. Menzel (1968) has suggested that the species C. angulata, C. gigas, C. virginica and C. rhizophorae are all fairly closely related because crosses between them result in fertilization, cleavage, larval development, metamorphosis and attachment of the hybrid oysters with apparently normal mitosis and meiosis in the F, and mitosis in the F, (in the cross C . gigm x C. virginica). It is possible that, as Menzel (1971) has indicated, some described species of oysters from certain areas are ecological variants of a species from another area. That C. angulata, C. gigas and C. virginica might be closely related can be interpreted from the work of Numachi (1962). He has shown that they share certain antigens. Almost all of these species occur in geographically remote areas and cannot be expected to interbreed in nature, yet hybridization studies have shown that their isolating mechanisms have not been perfected. Because of their geographical separation they only possess premating mechanisms (mechanisms which prevent interspecific crosses, such as seasonal and habitat isolation, ethological isolation and perhaps some mechanical isolation) while their postmating mechanisms (mechanisms which reduce full success of interspecific crosses such as gamete mortality, zygote mortality, hybrid inviability and hybrid sterility; see Mayr, 1963) break down to greater or less extent. Reproductive isolation seems to have reached an advanced stage between C. gigas and C. rivularis both of which are native to Japanese waters. Miyazaki (1939) obtained almost no cross-fertilization between them. He suggested, on the basis of experimental fertilization, that no interbreeding can be expected between these two species in nature. B. Distantly related species Menzel (1968) encountered several anomalies in mitotic complements of hybrid embryos between C. iredalei, from the Philippines, and the three species C. gigas, C. angulata and C. virginica with which he crossed this species. This suggests a distant affinity of C. iredaled with these oysters.

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Some data are also available on the failure of hybridization between the Sydney rock oyster, C . commercialis, and several other species of oysters from different parts of the world. For example, Galtsoff and Smith (1932) reported that this species could not cross-fertilize the American oyster C. virginica and also that the eggs of this Australian oyster had no effect in stimulating the spawning of ripe males of C. virginica. Menzel (1968) tried to cross C. commercialis with C . virginica, C . gigas, C. rhizophorae, C. angulata and C. iredalei. No fertilization and cleavage resulted suggesting complete incompatibility of their gametes. Crassostrea commercialis is a tuberculated or denticulated oyster but the others are not. Another tuberculated oyster, C . echinata (Quoy and Gaimard), which occurs commonly attached to rocks just below high tide level in the Japanese waters (Cahn, 1950) seems to be incompatible with C. gigas, the well-known Japanese oyster. Imai and Sakai (1961) crossed the Hokkaido " variety " of C. gigas with C. echinata. I n the cross C . gigass x C . echinata? only 16% eggs were fertilized, but 84% in the cross C. gigas? x C. echinatas. I n the first case development was very slow and some mortality occurred a t the 2-8 cell stage a few eggs reaching an abnormal early veliger stage. I n the reciprocal cross also abnormal looking veliger larvae were obtained most of which died within 5 h. Imai and Sakai (1961) concluded that crossfertilization could occur between C . gigas and C. echinata but not normal larval development.

IX. GENERICDIVERGENCE Oysters within the genus Crassostrea seem t o occur in two groups. Menzel (1968) has previously drawn attention to such a grouping. Group 1 Species belonging to this group occur on rocky platforms and cliffs exposed to the ocean surf. They possess a single row of well-defined small tubercles or ridgelets or small raised white teeth on the upper valve and corresponding depressions on the lower valve along the entire margin or part way through from the hinge (called anachomata and catachomata, see Stenzel, 1971). To this group belong such oysters as the Sydney rock oyster, C. commercialis, and C . amasa (Australia, Philippines), C . echinata (Japan, China, Australia) and C . tuberculata ( = C. cuccullata) (Pakistan, India, Australia, Philippines, East Africa) and C. margaritacea (East Africa, South Africa). All species mentioned here, except C. commercialis, are fully marine and seem to prefer oceanic conditions. Crassostrea commercialis

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mainly occurs in estuaries but sometimes on rocky headlands and on various parts of the Great Barrier Reef (Thomson, 1954).

Group 2 A majority of species of Crassostrea occur in protected turbidmuddy relatively calm estuarine waters and backwaters. I n these the lateral margins of both valves of shell on the inner side are devoid of tubercles or ridgelets. Representative oysters of this group are C. virginica, C. gigas, C. rivularis, C. angulata, C. rhizophorae and many others. I n my opinion the division of Crassostrea into tuberculated marine forms and non-tuberculated estuarine ones might have a n evolutionary significance. The importance of tubercles as a characteristic of taxonomic value (generic value) has been denied by Thomson (1954) for the reason that they are irregularly present or absent in various species of Ostrea and Crassostrea. He, nevertheless, mentioned that exposure to surf or heavy wash resulted in better developed marginal denticles. Hybridization experiments have demonstrated that the non-tuberculated oysters, C. virginica, C. gigas, C. angulata, C. rhizophorae and C. rivularis, may be crossed among themselves to a t least yield cleaved embryos (or hybrid oysters in most cases). The species that has not responded to them in this way is C. commercialis, 6 tuberculated oyster. Another tuberculated species which has shorn a more or less similar behaviour is C. echinata. Whether the failure of several workers (Galtsoff and Smith, 1932; Imai and Sakai, 1961; Menzel, 1968) to hybridize C. commercialis and C. echinata with nontuberculated oysters was due to a real genetic barrier between these oysters or simply because of technical procedures or immaturity of gametes available a t the time is difficult to say. Also, whether all tuberculated species of Crassostrea would behave similarly remains to be seen. Stenzel (1971) has placed the tuberculated oysters of Crassostrea in two different genera. He assigns C. cuccullata ( = C. tuberculata; see Thomson, 1954) and C. commercialis to the genus Saccostrea Dollfus and Deutzenberg, 1920. According to Stenzel Saccostrea differs from Crassostrea in the following characteristics : 1 . Its deeper umbonal cavity. 2. Strong chomata (tubercles and corresponding pits). 3. Tendency to form conical rudistiform or cornucopia-like shapes. I n my opinion these shell characteristics of Saccostrea are quite consistent and can be used to separate the tuberculated species of

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Crassostrea from the non-tuberculated ones. Moreover, the difference in habitat preference, that is, occurrence in oceanic surf-exposed conditions, and the evidence of a possible genetic barrier between tuberculated and non-tuberculated oysters make a strong case for splitting the genus Crassostrea. Iredale and Roughley (1933) had earlier placed C. commercialis in the genus Saxostrea but the genus Saccostrea, as shown by Stenzel (1971), merits nomenclatural priority. Stenzel’s (1971) placement of C. commercialis and cuccullata and tuberculata-like oysters in the genus Saccostrea is accepted here and it is hoped that it would find general acceptance among oyster biologists and oyster growers. Menzel (1968) has already suggested that C . commercialis probably belongs to a different taxon of generic level. Longwell and Stiles (1973b) seem also to have taken favourable notice of the change. Stenzel (1971) has placed another species of Crassostrea, C . margaritacea, which occurs in East and South Africa, in the genus Striostrea Vyalov 1936, of which it has been made the type species. According t o Stenzel, Striostrea differs from Crassostrea in the following characteristics : 1. Its reniform imprints of adductor muscle. 2. Presence of chomata. 3. Nacreous and irridescent interior. 4. Very foliaceous shell structure. 5. Rudistiform growth pattern. I n my opinion shape and size of the adductor muscle scar and the foliaceous nature of shell structure can hardly be characters of taxonomic importance. I n oysters size and shape of the muscle scar may be variable and often irregular and the texture of the shell can be influenced by environmental conditions (see Galtsoff, 1964). Chomata and rudistiform growth pattern characterize Saccostrea also. It would then seem that Crassostrea and Striostrea differ among themselves only in the nacreous lining of the shell, a difference which may not be considered enough to warrant recognition of Striostrea as a separate genus. All tuberculated species of Crassostrea should now be assigned to Saccostrea alone. It is believed that oysters have originated in euryhaline or stenohaline waters (see Yonge, 1960; Stenzel, 1971). Yonge (1960) has postulated a migration of oysters from clearer off-shore waters t o more turbid conditions inshore with a greater cupping of the valves, appearance of a promyal chamber, accompanied by displacement of the adductor and increased proportion of the quick muscle. This is

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supposed to have led to the separation of the genus Crassostrea from Ostrea and the successful conquest by its species of inshore waters laden with sediment but rich in food. It is possible that the several tuberculated species of Crassostrea, now to be assigned to the genus Saccostrea, which still occur in clear oceanic waters are there as a result of reinvasion of their original habitat or because a complete migration of Crassostrea to turbid conditions has not occurred. The promyal chamber of oysters is generally considered to be a character of taxonomic importance since it easily separates Ostrea from Crassostrea. It is supposed to be of advantage in turbid silt laden conditions. Yet it is interesting to note that it exists in tuberculated oceanic species of Crassostrea (that is in Saccostrea) as well as in deep-sea oysters of the genus Pycnodonte (or Neopycnodonte and Hyotissa as Stenzel, 1971 classifies them) (see Stenzel, 1971). Certainly turbidity and siltation would not be a problem to oysters in clear oceanic and deep waters. It is possible that some hitherto unknown advantage may be associated with the presence of the promyal chamber. No one has yet demonstrated experimentally and conclusively the exact function or functions of this chamber. Stenzel (1971) considers the oysters a diphyletic family instead of monophyletic. How is it then that the promyal chamber occurs in both families, Ostreidae and Gryphaeidae (as Stenzel classifies them)? Should it be assumed that the chamber evolved independently in both groups or does its presence in both families indicate a common heritage? The question of generic differentiation among incubatory oysters merits consideration here. Earlier in this article I have suggested that the genus Ostrea seems to be better suited to speciation than Crassostrea. One can thus expect to find other incubatory genera of oysters besides Ostrea. Neontologists, that is, oyster biologists and zoologists, have followed a simple classification of lumping with the justified argument that unless radical biological differences are not demonstrated new genera and species of oysters should not be designated. Yet biological research on non-commercial oysters is practically non-existent and not much optimism can be felt for the future. Thus an investigator interested in the taxonomic relationships of oysters has no choice but to make use of the conchological characters. Stenzel (1947) initially followed this procedure but in his recent treatise (1971) he adopted a somewhat interdisciplinary approach taking information from the fields of biology and paleontology. Yet his classification has resulted in the splitting of all oyster genera recognized by oyster biologists. Stenzel ( 197 1) recognizes three genera of incubatory

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oysters, namely, Ostrea, Lopha and Alectryonella, of which the first two show subgeneric differentiation also. One of the most characteristic features of Lopha and Alectryonella seems to be the sharp plications and crenulations of the shell margin which in some cases conform to a cockscomb shape. The sharp crenulations of the shell margins would be a poor character for distinguishing oyster genera as was noted by Galtsoff (1964). Recognition of the two genera Lopha and Alectryonella would be acceptable only after demonstration of biological and genetic differences. Experimental crossing of incubatory species of oysters would be difficult and might not even be possible so that the question of reproductive isolation may never be solved. The incubatory species could, however, be studied chromatographically, serologically and with other available techniques with a view t o demonstrating their genetic similarities and differences. It would also be worthwhile to examine their chromosome complements. Meiotic chromosomes from spermatocytes of Ostrea folium, (Lopha folium!), the cockscomb oyster occurring in Karachi, Pakistan, have already been examined to some extent (Ahmed, 1973) but comparable observations on other species of Ostrea have not been made. Stenzel(1971)shows the genera Lopha and Alectryonella to be mostly of tropical and partly subtropical distribution and Ostrea to be universally distributed outside the polar regions. The oysters 0. lurida, 0. edulis and 0 . chilensis-which differs from all other species of Ostrea in possessing eggs of very large size; so does it belong to a different genus or subgenus !-are mostly of temperate and subtropical distribution. It is possible that in the tropical and subtropical waters Ostrea may have been replaced by one or more related genera descendent from it. The speculation can be substantiated only by future biological and cytogenetic studies.

X. DISCUSSION It is sometimes possible to find natural populations in various I n other words a hierarchy of stages of “becoming species ”. successive levels of speciation can be found. As Mayr (1963) has pointed out, ‘‘ in every actively evolving genus there are populations that are hardly different from each other, others that are as different as subspecies, populations which have almost reached species level, and finally still others that are full species; sometimes these are allopatric in other cases the most distinct ones may already have been able t o overlap the ranges of their closest relatives”. The

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responsible mechanism for such evolutionary changes has been termed geographic speciation or speciation by distance. Distance, therefore, as indicated by Wright (1943) and others, is the most powerful mechanism for achieving genetic divergence. Geographic speciation is believed to be the most common mode of speciation among animals. It leads to the isolation of a population from its parental species in the form of geographical isolates. The isolates then acquire during a long and continued period of isolation characters which promote or guarantee reproductive isolation when external barriers break down. Also, as a consequence, the isolates may acquire different degrees of divergence, genotypic, phenotypic or both. The evidence presented in this article clearly shows that speciation in living oysters has occurred due to geographic isolation. In Crassostrea virginica physiological and genetic differences have accumulated in different geographic populations but no morphological divergence has occurred. Evolutionary morphological changes are generally believed to follow physiological changes (see Golikov, 1973). Such morphological changes have occurred in the C. gigas oysters of Japan. The Kumamoto, Hiroshima, Miyagi and Hokkaido oysters must have passed through a stage in which they resembled the physiological races of C. virginica before achieving morphological divergence. It would seem that the C. gigas oysters had a longer history of uninterrupted isolation than C. virginica. The theory of geographic speciation envisages the formation of isolates towards the periphery of the species range (Mayr, 1963). I n fact semispecies like Kumamoto ( = C. silcamea) and Hiroshima ( = C. laperousi) of C. gigas and the subspecies of 0. lurida (rufoides, expansa and laticaudata) occur near the periphery of the ranges of the respective species. Similarly the nominal species of Ostrea occurring in southern California and on the west coast of Mexico are also found near the southern periphery of 0. lurida. The same may be said of oysters like Crassostrea rhizophorae and the two other tentatively identified oysters (C. guyenensis and C. lacerata) which occur on the coast of Venezuela. These exist in what might be the southernmost part of the range of C. virginica. Mayr (1963) mentioned that every widely distributed species that has been carefully examined has been found to contain geographically representative populations that differ from each other t o a lesser or greater extent in their ecology. This certainly is very true of the oyster species reviewed here. The species C. virginica, C. gigas, Ostrea edulis and 0. lurida are all widely distributed sometimes 2 000 to 5 000 miles in extent from north to south. Their physiological races,

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subspecies and semispecies seem to have been developed in response to selection over long and continued periods of isolation in different and fluctuating environmental conditions. Among molluscs there are a number of examples which help to prove that speciation is bound to occur in species which have widespread distributions. The oyster drill Urosalpinx cinereum, which has a distribution similar to that of Crassostrea virginica on the east coast of North America, is known to exist in several physiological races associated with different geographical locations (Stauber, 1950). The surf clam, Spisula solidissima, occurs on the east coast of North America from north of Cape Cod to northernmost coast of Mexico ; its southern populations vary in size and shell characteristics to such an extent that Merrill and Webster (1964) regard them as a subspecies, 8. solidissima raveneli. Jacobson and Old (1966) are of the opinion, however, that the southern populations of this species are sufficiently distinct to warrant specific recognition as S. raveneli. The northern quahog clam, Mercenaria mercenaria, ranges from the Gulf of St Lawrence to Florida and the Gulf of Mexico. I n the southern part of the range of this species (from the northern Gulf of Mexico) two subspecies M . mercenaria notata and M . m. texana, are known to occur (Abbott, 1954). However, Menzel (1968) believes that the subspecies M . m. notata has no validity. Several environmental factors influence the process of speciation in marine animals. Temperature by its influence on spawning seems t o become the single most important factor in imposing reproductive isolation in different geographical populations of a widespread species. Also ecological conditions resulting from changes in sea level sometimes form favourable and a t other times unfavourable habitats for a species and this might have been the case with Ostrea lurida occurring on the Pacific coast of North America (Hertlein, 1960). Moreover, benthic species, either in shallow waters or in the deep sea, have populations that are often split into isolates by geographic barriers (Mayr, 1954). Knox (in Harding and Tebble, 1962) while discussing speciation in bivalves off the coast of New Zealand has stressed the changes in the configuration of coastlines, fluctuations in the position of the subtropical convergence and changes in the current systems affecting the dispersal of larvae or adults. Stenzel (1971) has discussed some of the causes of speciation among oysters and has especially emphasized land barriers and tectonic events. He considers Crassostrea virginica, which occurs from the Gulf of S t Lawrence in Canada to Yucatan, and C. corteziensis, which ranges from the head of Gulf of California to Panama in the Pacific A.M.B.-IY

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Ocean, to be daughter species of a common Pacific-Atlantic ancestral species of the Miocene and Pliocene. The two species are believed to have evolved from a common ancestor due to geographical isolation of the ancestral populations. This isolation occurred after the emergence of the Central American land bridge following tectonic events. This land bridge is believed to be comparatively recent (Ekman, 1952 ; Stenzel, 1971) and might have affected the distribution of several other marine species which originally ranged from the Pacific to the Atlantic. According to another interesting hypothesis of Stenzel (1971) a widely distributed fossil oyster C. gryphoides of the ancient Tethys Sea split up into various populations which later evolved into such well-known modern oysters as C. gigas, C. angulata and C. cuttackensis. This occurred because of the breaking up of the Tethys Sea, in response to tectonic events, into separate sea basins, gulfs and bays which became inhabited by different populations of the original C. gryphoides. Crassostrea gryphoides, however, is considered to be a living species by several oyster biologists (see Awati and Rai, 1931 ; Ahmed, 1971). Generally, whenever subspecies or species have formed from parental species it has been in the southern periphery of the species range, that is, approaching the tropics or warm waters. It has been held that cold water conditions are not so suitable for speciation while the greater variety of tropical and subtropical biota due to diversity of environments provides greater possibilities for evolution (Hedgpeth 1957). The oysters have been no exception to this general rule. XI. SUMMARY Evidence has been presented to show that several levels of speciation occur in the oysters Crassostrea virginica, C. gigas, Ostrea edulis and 0. lurida. These species have widespread distributions, some 2 000 to 5 000 miles north to south. Physiological races, spawning at different temperatures in different localities, are known in Crassostrea virginica (on the east coast of North America) and Ostrea edulis (Europe), but these show no morphological divergence. Near the southern part of the range of Crassostrea virginica, a C. virginicalike oyster, differing from it in shell morphology to some extent, occurs on the coast of Venezuela and might be a subspecies. Two other oysters, C. rhizophorae and another tentatively identified as C. lacerata, are also found in Venezuela and the Carribbean Islands and it is probable that they might have evolved from C. virginica. A burst of speciation seems to have occurred in the southern part

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of the range of Ostrea lurida (on the Pacific coast of North America) since three subspecies and four species of Ostrea have been recorded from lower California and the coast of Mexico. 0. lurida in all probability is the parental species since it is the lone species of Ostrea occurring from Sitka, Alaska to Cape San Lucas, California. The Japanese oyster Crassostrea gigas has been considered as a superspecies with two semispecies C. sikamea (sp. n.) and C. laperousi which many contemporary workers regard as only races, varieties or strains Kumamoto and Hiroshima, respectively. The Kumamoto and Hiroshima " varieties '' and two others, Hokkaido and Miyagi of C. gigas do not interbreed in nature since they spawn a t different times. Judging from the results of interbreeding experiments the oysters C. gigas, C. angulata, C. virginica and C. rhizophorae have been considered as closely related species. Crassostrea rivularis and C. iredalei are probably related to these. All these species occur in turbid estuarine waters and are non-tuberculated or non-denticulated as are a majority of species of Crassostrea. A second group, consisting of tuberculated species which prefer clear oceanic waters, seems to exist in the genus Crassostrea. The results of experimental hybridization show two tuberculated species, C. commercialis and C. echinata, to be incompatible with non-tuberculated species. Stenzel (1 971) has placed the tuberculated oysters C. commercialis and C. cuccullata in a separate genus, Saccostrea Dollfus and Deutzenberg. This change is accepted here and it is recommended that all tuberculated species of Crassostrea should now be assigned to Saccostrea."

XII. ACKNOWLEDGEMENTS I am grateful to Sir Maurice Yonge for scrutinizing a draft of the present review and for his valuable comments and encouragement. Dr A. C. Longwell, Research Geneticist, Milford Laboratory, Connecticut, also read a draft of this review critically, offered useful suggestions, supplied literature and specimens of oysters. The several courtesies extended to me by Dr Longwell are gratefully acknowledged. I am thankful to Dr N. B. Nair, Visiting Professor at the Instituto Oceanografico, Cumana, who has been a consistent source of encouragement in the completion of the present review. Professor W. P. Breese of the Department of Fisheries and Wildlife, Oregon State University, is thanked for making available specimens of the Miyagi and Kumamoto oysters and Senior Quintana Molina of the Instituto Oceanografico, Cumana, for photographing the oysters.

*

See Note Added in proof, on page 397.

394

MUZAMRIIL AHMED

XIII. REFERENCES Abbott, R. T. (1954). “American Seashells”. 541 pp. D. Van Nostrand, New York. Ahmed, M. (1971). Oyster species of West Pakistan. Pakistan Journal o j Zoology, 3, 229-236. Ahmed, M. (1973). Cytogenetics of oysters. Cytologia, 38, 337-346. Ahmed, M. (1974). Chromosomes of two species of the marine mussel Perna (Mytilidae: Pelecypoda). Boletin del Instituto Oceanopafico, Venezuela. Ahmed, M. and Sparks, A. K. (1967). A preliminary study of chromosomes of two species of oysters (Ostrea lurida and Crassostrea gigas). Journal of the Fisheries Research Board of Canada, 24, 2155-2159. Ahmed, M. and Sparks, A. K. (1970). Chromosome number, structure and autosoma1 polymorphism in the marine mussels Mytilus edulis and M . californianus. Biological Bulletin of the Marine Biological Laboratory, Woods Hole, 138, 1-13. Amemiya, I. (1928). Ecological studies of Japanese oysters with special reference to the salinity of their habitats. Journal of the College of Agriculture, University of Tokyo, 9, 332-382. Awati, P. R. and Rai, H. S. (1931). “ Ostrea cuccullata” (The Bombay Oyster). I n d i a n Zoological Memoirs, 3, 1-107. Bocquet, C. (1953). RBcherches sur le polymorphisme des Jaera marina (Fabr.) (Isopodes, Assellotes). Archives Zoologique Expdrimentale et Gknirale, 90, 187-450. Cahn, A. R. (1950). Oyster culture in Japan. Fishery Leaflet, Fisheries and Wildlife Service, 383, 1-80. Carreon, J. A. (1968). The malacology of Philippine oysters of the genus Crassostrea and a review of their shell characters. Proceedings of the National Shellfisheries Association, 59, 104-1 15. Davis, H. C. (1950). Hybridization experiments in Ostrea. Science, N e w York, 111, 522. Ekman, S. (1952). “Zoogeography of the Sea”. 417 pp. Sidgwick and Jackson, London. Galtsoff, P. S. (1964). The American Oyster Crassostrea virginica Gmelin. Fishery Bulletilz of the Fisheries and Wildlife Service, of the U.S., 64, 480 pp. Galtsoff, P. S. and Smith, R. 0. (1932). Stimulation of spawning and crossfertilization between American and Japanese oysters. Science, N e w York, 76, 371-372. Gaardner, T. and Bjerkan, P. (1934). “Osters og osterskultur i Norge”. Bergen. Griegs, 96 pp. Golikov, A. N. (1973). Species and speciation in poikilothermal animals. Marine Biology, 21, 257-268. Granados, R. R. and Sevilla, M. L. (1965). Las ostras de Mexico. Publ. Instituto Nacional Investigacion Biologia Pesquera, 7, 1-100. Gunter, G. (1950). The generic status of living oysters and the scientific name of the common American species. American Midland Naturalist, 43, 438-449. Gunter, G. (1951). The species of oysters of Gulf, Caribbean and West Indian region. Bulletin of Marine Science of the Gulf and Caribbean, 1, 40-45.

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Harding, J. P. and Tebble, N. (1962). Speciation in the sea. Nature, London, 193, 2 P 2 6 . Hedgpeth, J. W. (1957). Marine biogeography. I n “ Treatise on Marine Ecology and Paleoecology ”. Vol. I. Ecology (J. W. Hedgpeth, ed.) Memoir 67, pp. 359-382. Geological Society of America. Hertlein, L. G. (1960). Notes on California oysters. Veliger, 2, 5-10. Hillman, R. E . (1964). Chromatographic evidence of intraspecific genetic differences in the Eastern Oyster Crassostrea virginica. Systematic Zoology, 13, 12-18. Hirase, S . (1930). On the classification of Japanese oysters. Japanese Journal of Zoology, 3, 1-65. Hopkins, S . H. (1957). Oysters. I n “Treatise on Marine Ecology and Paleoecology”. Vol. I. Ecology. (J. W. Hedgpeth, ed.). Memoir 67, pp. 1129-1 134. Geological Society of America. Study of breeding of Japanese oyster Imai, T. and Sakai, S. (1961). Crassostrea gigas. Tohoku Journal of Agricultural Research, 12, 125-171. Iredale, T. and Roughley, T. C. (1933). The scientific name of the commercial oyster of New South Wales. Proceedings of the Linnaean Society, New South Wales, 58, 278. Jackson, R . C. (1971). The karyotype in systematics. Annual Review of Ecology and Systematics, 2, 327-368. Jacobson, M. K. and Old, W. E. (1966). On the identity of Spisula sinailis (Say). American Malacological Union Inc., Annual Report, 30-31. Korringa, P. ( 1958). Water temperature and breeding throughout the geographical range of Ostrea edulis. Annie Biologique, 33, 109-1 16. Li, M. F., Flemming, C. and Stewart, J. E. (1967). Serological differences between two populations of oysters (Crassostrea virginica) from the Atlantic coast of Canada. Journal of the Fisheries Research Board of Canada, 24, 443-446. Longwell, A. C. and Stiles, S. S. (1970). The genetic system and breeding potential of the commercial American Oyster. Endeavour, 29, 94-99. Longwell, A. C. and Stiles, S. S. (1973a). Gamete cross incompatibility and inbreeding in the commercial American Oyster Crassostrea virginica Gmelin. Cytologia, 38, 521-533. Longwell, A. C. and Stiles, S. S. (197313). Oyster cytogenetics and the probable future role of genetics in aquaculture. Malacological Review, 6, 151-177.

Longwell, A. C., Stiles, S. S. and Smith, D. G. (1967). Chromosome complement of the American Oyster Crassostrea virginica as seen in meiotic and cleaving eggs. Canadian Journal of Genetics and Cytology, 9, 845-856.

Loosanoff, V. L. and Nomejko, C. A. (1951). Existence of physiologically different races of oysters, Crassostrea virginica. Biological Bulletin of the Marine Biological Laboratory, Woods Hole, 101, 151-156. Macsotay, 0. (1974). Estudios sobre especies de ostras del genero Crassostrea, fosiles y vivientes del Cenozoico a1 Reciente de Venezuela (MS). Mayr, E . (1954). Geographic speciation in tropical echinoids. Evolution, 8, 1-18. Mayr, E . (1963). “ Animal Species and Evolution ”. 797 pp. Belknap Press of Harvard University Press, Cambridge, Massachusetts. 14%

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Menzel, R. W. (1955). Some phases of the biology of Ostrea equestris Say and a comparison with Crassostrea virginica (Gmelin). Publications of the Institute of Marine Science, University of Texas, 4, 69-153. Menzel, R. W. (1968). Cytotaxonomy of species of clams (Mercenaria) and oysters (Crassostrea). Proceedings of the Symposium on Mollusca, Part I, 75-84. Menzel, R. W. (1971). Selective breeding in oysters. In “Artificial Propagation of Commercially Valuable Shellfish’ . 212 pp. Publ. Coll. Mar. Stud. University of Delaware, Newark, Delaware. Menzel, R. W. (1974). Portuguese and Japanese oysters are the same species. Journal of the Fisheries Research Board of Canada, 31. 453-456. Merrill, A. S. and Webster, J. R. (1964). Progress in surf clam biological research. Circular of the Fisheries and Wildlife Service of the U.S., 200, 38-47. Miyazaki, I. (1939). Some notes on the cross-fertilization of Japanese oysters. Bulletin of the Japanese Society of Scientific Fisheries, 7, 257-261. Nelson, T. C. (1938). The feeding mechanism of the oyster. I. On the pallium and branchial chambers of Ostrea virginica, 0. edulis and 0. angulata, with comparisons with other species of the genus. Journal of Morphology, 63, 1-61. Numachi, K. (1962). Serological studies of species and races in oysters. American Naturalist, 96, 211-217. Orton, J. H. (1928). The dominant species of Ostrea. Nature, London, 121, 320-321. Quayle, D.B. (1969). Pacific oyster culture in British Columbia. Bulletin of the Fisheries Research Board of Canada, 169, 1-192. Ranson, G. (1941). Les espbces actuelles et fossiles du genre Pycnodonta F. de W. I. Pycnodonta hyotis (L.). Bulletin d u MusBe d’Histoire naturelles Paris (series 2), 13, 82-92. Ranson, G. ( 1948a). ficologie e t repartition gbographique des ostreidks vivants. Revue de Science, Paris, 86, 469-473. Ranson, G. (194813). Prodissoconques et classification des OstrkidAs vivants. Bulletin d u MusBe Royale de l’aistoire naturelle de Belgue, 24, 1-12. Ranson, G. (1960). Les prodissoconques (coquilles larvaires) des ostreidbs vivants. Bulletin Institut Ockanographique, Monaco, No. 1, 1-41. Runnstrom, S. (1936). Die Anpassung der Fortpflanzung und Entwicklung mariner Tiere an die Temperaturverhaltnisse verschiedener Verbreitungsgebiete. Bergens Museums Arsberetning, 3, 1-36. Sastry, A. N. ( 1970). Reproductive physiological variation in latitudinally separated populations of the Bay Scallop Aequipecten irradians Lamarck. Biological Bulletin of the Marine Biological Laboratory, Woods Hole, 138, 56-65. Stauber, L. A. (1950). The problem of physiological species with special reference to oysters and oyster drills. Ecology, 31, 109-118. Stenzel, H. B. (1947). Nomenclatural synopsis of supraspecific groups of the family Ostreidae (Pelecypoda : Mollusca). Journal of Paleontology, 21, 165-185. Stenzel, H. B. (1971). Oysters. I n “ Treatise on Invertebrate Paleontology N 953-N 1224 pp. Part N, Vol. 3 (of 3), Mollusca 6, (K. C. Moore, ed.) Geological Society of America Inc. and the University of Kansas. Boulder, Colorado.

”.

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Stiles, S. S. (1973). Cytogenetic analysis of an attempted interspecies hybridization of the oyster. Incompatibility Newsletter, No. 3, 41-45. Thomson, J. M. (1954). The genera of oysters and the Australian species. Australian Journal of Marine and Freshwater Research, 5, 132-168. Ursin, E. (1956). Distribution and growth of queen, Chlamys opercularis (Lamellibranchiata) in Danish and Faroese waters. Meddelelser f r a Kommissionen f o r Danmarks Fiskeri og Havunders0gelser (n.s.), 1, 1-32. Walne, P. R. (1963). Breeding of the Chilean oyster (Ostrea chilensis Philippi) in the laboratory. Nature, London, 197, 676. Wright, S. (1943). Isolation by distance. Genetics, 28, 114-138. Yonge, C. M. (1960). “ Oysters ”. 209 pp. London, Collins. Yonge, C . M. (1968). Form and habit in species of Malleus (including the “ Hammer Oysters ”) with comparative observations on Isognomon isognomon. Biological Bulletin of the Marine Biological Laboratory, Woods Hole, 135, 378-405.

NOTEADDEDIN PROOF I n a recent note Menzel (1974) has emphasized that the Japanese oyster C . gigas (Thunberg, 1793) and the Portuguese C . angulata (Lamarck, 1819) are the same species because their prodissoconchs and adult shells are indistinguishable, they hybridize easily and their hybrids show normal chromosome behaviour. By rules of priority Menzel considers the Portuguese oyster as a subspecies of the .Japanese oyster and designates the two as C. gigas gigas and C. gigas angulata. He also refers to Stenzel’s (1971) hypothesis that C. gigas, C. angulata and C. cuttackensis (Newton and Smith) ( = C . madrasensis (Preston))of the Indian Ocean were all derived from C . gryphoides (von Schlotheim) during the Miocene. Stenzel’s hypothesis, Menzel points out, would require that C. gigas and C . angulata have remained morphologically and genetically unchanged during the 10 million or more years of geographic isolation. That such genetic stability would prevail for so long is highly improbable, especially since oysters have not been stagnant in speciation. If C . gigas and C. cuttackensis were derived from C . gryphoides, then it is to be pointed out that both species have undergone much morphological and genetic change during this period. I n its morphology, C . cuttackensis has now come to resemble C . virginica and has been identified as such (Ahmed, 1971), and C. gigas of the Japanese Islands has formed discrete “races” or “varieties”, for two of which full species ranks have been recommended in this review. The present disjunct distribution of the Japanese and Portuguese oysters is then probably due to accidental transportations either from Japan to Portugal (Ranson, 1948a) or the other way around as Menzel (1974) has now

suggested.

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Author Index Numbers in italics refer to poges on which the full reference ,isgiven,

A Abbott, R . T., 391, 394 Abel, R., 173, 220 Abraham, M., 292, 293, 305, 332, 333, 335 Acher, R., 303, 333 Adams, B. L., 327, 333 Afanasjev, M., 54, 9 2 Aganovii., M., 115, 211 Agranoff, B. W., 301, 347 Agrawal, V. P., 120, 123, 124, 134, 196, 211,212 Ahmed, M., 358, 359, 361, 362, 363, 364, 365, 368, 379, 381, 382, 389, 392, 394 Ahmed, S., 123, 124, 228 Airapetjanz, E. Soh., 5 5 , 9 2 Akulin, V. N., 274, 333 Albertson, T., 300, 338 Albright, J. T., 140, 141, 142, 212 Aldinger, E. E., 295, 333 Alexander, R. McN., 78, 9 2 , 119, 212 Al-Hamdd, M. I., 112, 117, 212 Al-Hussaini, A. H., 57, 77, 80, 92, 110, 111, 112, 119, 120, 121, 122, 123, 125, 126, 130, 131, 132, 133, 134, 135, 136, 137, 149, 150, 155, 166, 167, 168, 169, 212 Ali, M. A., 311, 333, 335 Aloncle, H., 267, 333 Amemiya, I., 380, 394 Ando, M., 289, 291, 293, 352 Andrianov, G. N., 320, 333 Andriashev, A. P., 89, 9 3 AngelescqV., 111, 118, 138, 212 Antonini, E., 264, 350 Arch, S. W., 12, 45, 50 Ardeleanu, A., 286, 333 Arnold, M., 144, 153, 154, 230 Aronov, M. P., 55, 89, 9 3 Aronson, L. R., 110, 169, 213 Arvanitaki, A., 14, 34, 47 389

Arvy, L., 151, 213, 303, 333 Ash, A. F., 282, 354 AshiT, A. R. M., 199, 213 Ashley, L. M., 139, 232 Astrand, M., 317, 342 Atema, J., 55, 81, 85, 89, 90, 93, 110, 145, 169, 213, 315, 334 Atz, E. H., 121, 234 A-tz, J. W., 121, 231 Awati, P. R., 381, 382, 392, 394

0 Babikker, M. M., 304, 333 Babkin, B. P., 195, 196, 21.1 Bachelier, R., 318, 333 Baecker, R., 78, 93 Baggerman, B., 278,290, 291, 297, 323, 333 Bajkov, A. D., 173, 180, 213 Baker, C. D., 81, 105, 111, 121, 122, 127, 131, 169, 232 Bala, V., 123, 124, 211 Baldwin, N. S., 175, 177, 213 Ball, J. N., 291, 347 Bannister, L. H., 9 3 Baraduc, M. M., 268, 278, 333, 339 Barannikova, I. A., 296, 304, 332, 333, 334 Barber, W. E., 176, 213 Barbetta, F., 151, 213 Bardach, J. E., 55, 79, 81, 89, 90, 91, 92, 9 3 , 94, 9G, 101, 110, 145, 169, 213, 315, 323, 334 Barnard, R. J., 275, 334 Barrington, E. J. W., 110, 130, 133, 213 Bartmann, W. D., 281, 335 Bateman, J. B., 270, 344 Bath, H., 80, 94 Baumgarten, H. G., 167, 171, 213

400

AUTHOR INDEX

Bayliss, L. E., 190, 192, 193, 195, 213 Beamish, F. W . H., 177, 182, 202, 213, 228 Beatty, D. D., 279, 328, 334 Bellini, A., 284, 334 Bellisio, N. B., 120, 213 Bellon, G., 79, 80, 96, 121, 217 Belonozhko, R. A., 138, 151, 166, 213, 214 Bennett, M. V. L., 91, 94 Bergot, P., 148, 150, 166, 167, 214 Bergstrom, E., 256, 268, 344 Berman, S. A., 197, 214 Bern, H. A., 289, 291, 292, 293, 305, 334, 341, 347, 352 Bernard, F., 139, 214 Bernardi, C., 280, 290, 334 Berry, P. Y . , 138, 214 Bertin, L., 285, 334 Bertmar, G., 80, 94, 122, 169, 214 Beukema, J. J., 179, 214 Bhargava, S. C., 80, 100 Bhatia, B., 78, 94 Bhatnagar, A. N . , 79, 101, 111, 121, 225 Bhatti, H. K., 80, 94 Bhatti, I. H., 57, 68, 94 Bhimacher, B. S., 88, 94 Bhowmik, M. L., 138, 227 Bier, A., 278, 334 Bigaj, J., 150, 224 Bijvank, 0. J., 59, 62, 95, 104 Bilinski, E., 266, 275, 334 Bilstad, N. M., 127, 130, 131, 132, 151, 153, 155, 162, 168, 169, 238 Birkett, L., 203, 214 Bishop, C. M . , 80, 94, 111, 121, 130, 132, 134, 136, 137, 147, 149, 151, 155, 167, 214, 229 Bisht, J. S., 125, 217 Bitinkov, E. P., 243, 335 Bitners, I., 272, 343 Bjerkan, P., 370, 394 Black, E. C., 269, 351 Blackett, R. F., 329, 335 Blain, A. W . , 183, 214 Blake, I. H . , 139, 214 Blanc, N., 292, 333 Blanc-Livni, N., 292, 335 Blum,V., 281,292,302,335,338

Bocharov, G. D., 256, 317 Bocquet, C., 380, 394 Bodrova, N. V., 80, 94 Boeke, J., 7 7 , 94 Boetius, J., 325, 335 Bogachik, T. A., 120, 214 Bohus, B., 294, 295, 338 Bokova, E., 175, 179, 180, 186, 187, 214, 223 Bolton, L. L., 168, 215 Boltt, R. E . , 25, 41, 47 Bondi, A., 192, 195, 215 Boone, L., 13, 47 Boolootian, R. A., 42, 47 Borutsky, E. V., 112, 215 Bostrom, S.-L., 275, 335 Boucher-Firly, S., 249, 253, 288, 335 Bourguet, J., 304, 305, 346 Bowarde-Schmitz, E., 268, 344 Bowie, D. J., 195, 196, 213 Braemer, W., 311, 341 Bramstedt, F., 191, 215 Branch, G. M., 120, 215 Branover, G. G., 322, 335 Branson, B. A., 78, 95, 120, 215 Breder, C. M., 77, 90, 95 Brehm, A. E., 13, 47 Breipohl, W., 59, 62, 95, 104 Bremer, H., 153, 215 Brett, J. R., 174, 176, 182, 183, 184, 187, 188, 204, 206, 215, 261, 311, 316, 335 Bridges, C. D. B., 281, 335 Britton, S. W., 258, 335 Brockerhoff, H., 195, 215 Brody, S., 203, 215 Broekema, M. M . M., 260, 336 Bromlej, G., 116, 215 Brown, B. E., 173, 222 Brown, F. A. Jr., 324, 336 Brown,M. E., 174, 175, 178, 205,215 Bruchmiiller, W., 151, 238 Buchs, S., 190, 191, 215 Bucke,D., 111, 124, 132, 138, 151, 215 Buckland, F., 315, 336 Buckman, N. S., 241, 347 Budker, P., 91, 95 Bull, H. O., 55, 95, 257, 309, 336 Bullock, T. H . , 90, 95

401

AUTHOR INDEX

Bullock, W. L., 132, 134, 135, 136, 137, 138, 151, 152, 155, 162, 168, 169, 216 Burian, R., 247, 336 Burnstock, G., 130, 132, 134, 139, 167, 168, 170, 171, 185, 216, 231 Buser-Lahaye, J., 286, 336 Buzinova, N. S . , 115, 193, 234

C Cahn, A. R., 375, 380, 385, 394 Callamand, O., 248, 250, 251, 277, 280, 292, 336, 339, 340 Campbell, A. C., 44, 47 Campbell, G , 185, 216 Campbell, K . N., 169, 171, 172, 183, 185, 214 Campos, H., 81, 95 Cardwell, R. D., 269, 351 Carey, F. G., 263, 264, 265, 336 Carline, R. F., 174, 207, 216 Carlisle, D. B., 254, 336 Carreon, J. A., 381, 382, 394 Case, J., 55, 79, 92, 93 Castro, N. M . , 131, 151, 152, 216 Catton, W. T., 137, 216 Cecchini, S., 253, 337 Cedard, L., 323, 336 Chagneux, R.,22, 47 Chagneux-Costa, H., 22, 47 Chalazonitis, N., 14, 22, 34, 47 Chan, D. K . O., 288, 304,305,334,336, 346 Chan, V. M., 130, 132, 216 Chandy, M., 78,105, 126, 127, 131, 216 Chang, H. W . , 139, 239 Chartier-Baraduc, M. M . , 248, 256, 328, 330, 336, 337, 339, 340 Chaudhry, H . S., 80, 95, 125, 216 Chauschesku, I., 55, 90, 102 Chepik, L., 182, 195, 216 Cherkin, A., 324, 349 Chesley,L. C., 193, 195, 197,216 Chester Jones, I., 288, 291, 304, 305, 334, 336, 346, 347 Chu, A. J., 259, 337, 341 Chu, Y . T., 124, 216 Churchill, E. P., 130, 131, 238 Clark, R. T., 267, 349

Cligny, A., 313, 337 Cobb, J. L. S., 24, 43, 50 Cohen, C., 248, 350 Coleman, R., 20, 22, 49 Colombo, G., 253, 337 Conte, F. B., 256, 337 Cook, M. H., 75, 77, 95 Copeland, D. E., 140, 230 Cordier, R., 55, 57, 68, 70, 95 Cornman, I., 45, 47 Cowey, C. B., 207, 216, 276, 337 Craigie, E. H . , 315, 337 Creuteberg, F., 250, 251, 318, 337 Crickmer, R., 55, 93 Cristy, M., 279, 337 Crosby, E. C., 82, 100 Croston, C. B., 193, 217 CuBnot, L., 13, 47 Curry, E., 57, 79, 95, 121, 217 Cynamon, M., 288, 289, 338

D Daan, N., 181, 217 Daget, J., 114, 217 Daginawala, H. F . , 317, 349 Dahlgren, U., 19, 47 Dambach, M., 7, 10, 11, 13, 15, 47, 51 Dalela, R. C., 111, 119, 217, 237 D’Ancona, U., 284, 337 Daniel, J. F., 77, 95 Darnell, R. M . , 173, 181, 217 Das, K. M., 197, 227 Das, S. M., 110, 217 Dave, G., 288, 346 Davis, B. J . , 80, 88, 95, 110, 217 Davis, G. E., 204, 205, 217, 237 Davis, H . C., 383, 394 Davy, J., 337 Dawes, B., 130, 134, 138, 167, 217 Dawson, I., 167, 217 Dayton, P. K., 13, 14, 47 Debnam, J . W . , 194, 196, 226 De Carlo, J . M., 126, 131, 226 Decugis, H., 331, 337 Deelder, C. L., 250, 307, 318, 321, 325, 337, 338 Delaporte, F., 267, 333 Delewska, E., 133, 235

401”

AUTHOIt INDEX

Denton, E. J . , 254, 336, 338 De Petrini, L. M., 138, 232 Desgranges, J.C., 55, 59, 65, 66, 67, 69, 70, 95, 96 Deville, J., 330, 340 De Wied, D., 294, 295, 338 Deyou, C. W., 182, 184, 188,233 Dickie, L. M., 177, 206, 213, 229, 230 Diebschlag, E., 2, 48 Disler, N. N . , 80, 96 Ditchburn, R. W., 46, 48 Dix, T. G., 12, 13, 14, 15, 48 Dixit, R. K., 125, 217 Dogiel, A. S . , 65, 96 Domagk, G. F., 90,108, 301,338 Dorier, A., 79, 80, 96, 121, 217 Doudoroff, P., 177, 205, 217, 220, 258, 269, 338, 353 Dubois, R., 15, 48 Ducros, C., 79, 96 Duebler, E. E., 124, 218 Dumitru, M., 115, 151, 217 Dunbar, M. J., 319, 338 Dutcher, B. W., 124, 232 Duthie, E. S., 217 DysterAas, K., 295, 343

E Eales, J. G., 254, 327, 343 Eastman, J. T . , 121, 124, 217 Ebner, V. von, 68, 96 Edgerton, V. R., 275, 334 Edinger, T., 331, 338 Edwards, D. J., 124, 183, 218 Edwards, L. F., 7 5 , 96 Eguchi, H., 268, 338 Ekman, S., 380, 392, 394 Elam, D. W., 190, 229 Elbers, P. F., 190, 219 Elliott, J. M., 183, 185, 218 Elson, P. F., 324, 338 Enami, M., 305, 338 Engel, F. L., 300, 338 Epstein, F. H., 288, 289, 291, 338, 348 Erspamer, V . , 167, 218 Evans, H. E., 77, 79, 80, 87, 88, 102, 121, 124, 218 Evans, H. M . , 88, 96, 289, 338

Evans, J. C., 256, 268, 344 Evropeitzeva, N. V . , 256, 296, 338 Ewer, D. W., 25, 41, 47

F Fabitin, G., 188, 189, 218 Fahrenholz, C., 7 5 , 96 FBhrmann, W., 68, 9G FBnge, R., 167, 171, 172, 218, 228 Farbman, A. I., 67, 68, 96 Ferner, H., 59, 103 Ferri, A. G., 151, 167, 219 Ferri, S., 120, 152, 153, 154, 164, 226 Fiedler, K., 302, 338 Field, J. G., 120, 218 Fish, G. R., 190, 191, 192, 194, 197, 201, 218 Fisher, K. C., 324, 338 Fitzpatrick, T. B., 294, 351 Fjerdingstad, E. J . , 301, 352 FIBchon, J.-E., 148, 150, 166, 167, 214 Fleming, W. It., 291, 351 Flemming, C., 358, 369, 395 Fontaine, M., 247, 248, 250, 251, 252, 353, 254, 256, 268, 277, 278, 280, 287, 292, 298, 299, 300, 301, 303, 314, 323, 329, 330, 331, 333, 335, 336, 339, 340, 345 Fontaine, Y. A., 280, 33.9, 354 B’ontana, N., 139, 218 Forster, M., 288, 346 Fosi, V., 253, 340 Fox, D. L., 138, 239 Fox, H. M., 3, 41, 42, 48 Foxx, R. M., 175, 218 Francois, Y., 283, 340 Frantsuzova, G. P., 171, 218 Frearson, N., 275, 343 Fredericks, J., 300, 338 Frisch, K. von, 90, 96 Fry, F. E. J., 187, 204, 218, 265, 266, 340, 351 Fryer, G., 111, 218 Fuji, A., 41, 48 Fujimori, T., 194, 196, 236 Fujiya, M., 55, 89, 92, 93, 96, 323, 334 Fukusho, K., 124, 131, 134, 218 Fusetani, N., 310, 341, 344

403

AUTHOR INDEX

G Gaardner, 'l'.,370, 394 Gabe, M., 303, 333 Galaktionov, G. Z., 322, 348 Galtsoff, P. S., 358, 360, 367, 375, 383, 385, 386, 387, 389, 394 Gamble, J. C., 15, 48 Ganguly, D. N., 88, 103, 110, 228 Gard, R., 327, 340 Gas, N., 147, 229 Gatz, A. J. Jr., 275, 340 Gauthier,G.F., 147, 148, 149, 151, 162, 165, 219 Geilenkirchen, W. L. M., 190, 219 Geistdoerfer, P., 134, 136, 219 Gensler, P., 312, 344 George, M. G., 127, 131, 216 Gerking, S. D., 174, 219 Geyer, G., 145, 146, 226 Ghazzawi, F. M., 111, 123, 126, 129, 131, 219 Giese, A. C., 42, 47 Giles, M. A., 255, 340 Girgis, S., 57, 79, 9 6 , 111, 112, 116, 120, 121, 124, 134, 219 Glaser, D., 73, 90, 96 Gleiser, S. I., 322, 335, 353 Glejzer, S. I., 322, 348 Gneri, F. S., 111, 118, 138, 212 Godinho, H . , 120, 151, 154, 167, 219, 226 Goel, K. A., 155, 219 Gohar, H. A. F., 110, 119, 122, 167, 219 Goldberg, E., 155, 238 Goldspink, G., 275, 343 Golikov, A. N., 365, 390, 394 Gollnick, P. D., 275, 340 Gomazkov, 0. A., 198, 219 Gonzalez-Barcena, D., 295, 345 Goodall, R. G., 272, 278, 342 Gorbman, A., 301, 302, 316, 317, 341, 348, 352 Gordon, M. S., 266, 340 Goswami, S. C . , 81,106, 121, 235 Govindan, P., 151, 155, 162, 233 G6z, H., 90, 97 Graberg, J., 68, 97 Granados, R. R., 374, 394

Grant, W. C., 292, 340 Gray, E. G., 70, 97 Gray, I. E., 3, 12, 13, 14, 15, 5 1 Graziadei, P. P. C., 55, 57, 59, 65, 70, 97 Gregory, R. L., 44, 48 Gregory, W. K., 110, 220 Greene, C. W., 130, 132, 139, 21.9 Greenwood, P. H., 111, 119, 120, 219, 220 Greven, H. M., 295, 338 Grib, A. V., 116, 220 Griffith, R. W., 291, 348 Grimm, R. J., 90, 97 Groenewald, A. A. J. v., 110, 220 Groot, C., 312, 313, 340 Groot, S. J. de, 110, 139, 220 Grzycki, S., 85, 97 Gudger, E. W., 79, 97 Guillemin, R., 294, 341 Gunter, G., 338, 359, 365, 367, 374, 394 Gupta, 0. P., 119, 138, 220

H Hafeez, M. A., 306, 311 Hahn, W. E., 301, 316, 341 Hale, P. A,, 136, 137, 167, 220 Hall, J. D., 174, 207, 216 Halver, J. E., 203, 220 Hake, P., 120, 215 Hama, K., 55, 57, 68, 70, 107, 169, 236 Hammond, 304, 341 Hanaoka, T., 259, 337, 341 Hara, T. J., 55, 85, 9 7 , 110, 145, 220, 302, 314, 316, 317, 323, 341, 352 Harden Jones, F. R., 308,319,341 Harder, W., 111, 220 Harding, J. P., 391, 395 Harms, J. W., 281, 311 Harrt, A. C., 321, 350 Hashimoto, K., 268, 338 Hashimoto, T., 55, 90, 100 Hashimoto, Y., 268, 319, 341, 344 Hasler, A. D., 56, 90, 9 7 , 311, 312, 315, 316, 317, 341, 353 Hassler, W. W.. 176, 235 Hastings, W. H., 201, 220 Hatey, J., 253, 339

404

AUTHOR INDEX

Hathaway, E. S., 175, 220 Hawley, W. D., 295, 333, 343 Hedgpeth, J. W., 392, 395 Hedlund, M. T., 306, 353 Heidenhain, M., 57, 68, 97 Hellawell, J. M., 173, 220 Hempel, G., 183, 186, 231 Henderson, E. B., 326, 350 Hendlez, E., 291, 348 Henrikson, R. C., 144, 153, 220 Hentschel, G., 13, 15, 47 Hermann, F., 57, 68, 97 Herold, R. C., 124, 220, 221 Hermann, R. B., 177, 205, 220 Herrick, C . L., 87, 97 Herrick, C . J., 54, 55, 78, 79, 82, 83, 84, 87, 92, 97, 98 Hertlein, L . G., 371, 372, 373, 374, 391, 395 Hess, C., 19, 48 Heuts, M. J., 260, 282, 344 Hiatt, R. W., 55, 98 Hickling, C. F., 117, 125, 221 Hidaka, I., 55, 80, 98, 101 Higashi, T., 80, 100, 123, 124, 223 Higgs, D. A., 182, 183, 184, 188, 215 Hillman, R. E., 358, 368, 369, 395 Hirano, T., 289, 291, 292, 293, 341 Hirase, S., 379, 396 Hirata, Y., 55, 57, 59, 60, 66, 67, 69, 70, 71, 98, 145, 169, 221 Hirsch, G. C., 133, 221 Hoagland, H., 55, 92, 98 Hoar, W. S., 255, 272, 278, 311, 324, 326, 333, 342, 347 Hobson, E. S., 241, 342 Hochachka, P. W., 187, 218, 265, 340 Hodgson, E. S., 55, 90, 98 Hoffmann, G., 68, 96 Hoglund, L. B., 317, 342 Holl, A., 55, 57, 59, 63, 89, 92, 93, 106, 145, 232, 323, 334 Hollands, B. C . S., 162, 221 Holloszy, J. O., 275, 342 Holmes, S. J., 3, 19, 48 Holmes, W. N., 271, 287, 288, 342 Holstvoogd, C., 124, 221 Honma, Y., 139, 235, 286, 292, 305, 342 Hopkins, A., 183, 221

Hopkins, S. H., 359, 395 Horrall, R. M., 311, 341 Hotta, H . Y . , 139, 176, 178, 221 Houston, A. H., 255, 256, 290,342, 352 Hubbs, C . L., 92, 98 Huber, G. C., 82, 100 Hughes-Games, L., 41, 49 Humbach, I., 90, 98 Hunt, B. P., 173, 176, 177, 181, 184, 185, 221 Huve, J. L., 303, 342

I Idler, D. R., 248, 272, 297, 342, 343 Iles, T . D., 111, 218 Ilyinsky, 0. B., 320, 333 Ikeda, S., 223 Imai, K., 305, 338, 345 Imai, T., 358, 375, 376, 377, 379, 382, 383, 384, 385, 386, 395 Inyushin, V. M., 126, 155, 224 Iredale, T., 381, 387, 395 Ishibashi, T., 124, 221 Ishida, J . , 120, 131, 192, 194, 195, 196, 221 Ishida, M., 77, 98 Ishiwata, N., 178, 221 Islam, Ahsan-ul-, 80, 98, 120, 126, 221 Isokawa, S., 124, 127, 129, 221, 222 Ito, Y . , 171, 222 Iwai, T., 57, 68, 73, 77, 79, 80, 98, 121, 125, 127, 136, 137, 150, 222

J Jackson, R. C., 364, 395 Jacobshagen, E., 75, 98, 114, 116, 133, 134, 222 Jacobson, F. W., 6, 7, 11, 48 Jacobson, M. K., 391, 395 Jafri, A. K., 162, 224 Jakobi, V. E., 322, 346 Jakubowski, M., 70, 78, 79, 98, 99 Jansson, B.-O., 147, 149, 150, 151,155, 162, 164, 166, 167, 222 Jara, Z., 121, 222 Jearld, A., 173, 222

AUTHOR INDEX

Jennings, H. S., 47, 48 Jennings, J. B., 130, 155, 157, 189, 191, 199, 238 Jeuken, M., 139, 222 Jirge, S. K., 125, 151, 152, 153, 162, 222, 236 Jobert, A., 55, 99 Johansen, K., 125, 138, 223 Johansson, M. L., 288, 346 Johansson, R. G., 275, 335 Johnson, D. W., 289, 291, 292, 293, 299, 341, 343, 352 Johnson, E . S., 306, 353 Johnson, G. H., 81, 93 Johnston, C. E., 254, 327, 343 Johnston, I. A., 275, 343 Johnston, J. B., 75, 85, 99 Jones, J. A., 14, 42, 50 Jones, J. W., 280, 343 Jordan, H., 92, 99 Joseph, M. M., 293, 343 Julien, M., 303, 346 Jutare, T., 14, 42, 50

K Kaile, R. K., 111, 225 Kaji, S., 317, 352 Kakari, S., 282, 354 Kalmijn, A. J., 91, 99, 320, 321, 343 Kamiya, M., 253, 256, 289, 343 Kamps, L. P., 260, 343 Kamrin, R. P., 85, 99 Kandyuk, R. P., 190,194,196,223 Kappers, C. U. A., 82, 100 Kapoor, B. G., 79, 80, 94, 99, 100, 105, 111, 116, 120, 121, 122, 125, 126, 131, 134, 169, 214, 223 Karamian, A. I., 87, 100 Kariya, T., 188, 223 Karpevitch, A. F., 133, 186, 187, 223 Kashiwagi, M., 247, 343 Kastin, A. J., 294, 295, 333, 343, 344, 350 Katchburian, E., 131, 151, 152, 216 Kato, K., 135, 223 Katsuki, Y., 55, 90, 91, 100 Katsumata, A., 124, 222 Kawamoto, N., 80, 100, 123, 124, 223 Kawai, S., 223

405

Kawasaki, K., 295, 351 Kazansky, V. I., 119, 125, 223 Keenleyside, M. H . A., 272, 278, 324, 342, 347 Kelso, J. R. M., 186, 224 Kendall, J. I., 55, 90, 91, 100, 106 Kennedy, D., 34, 48 Kennedy, G. Y . , 6, 48 Kenyon, W. A., 190, 191, 195, 224 Kerr, S. R., 206, 224 Kevern, N. R., 174, 224 Keys, A., 270, 344 Khalilov, F. Kh., 126, 154, 155, 166, 167, 224 Khan, W. M., 120, 123, 124, 228 Khandelwal, 0. P., 80, 95, 125, 216 Khanna,S. S., 79, 81, 88,100,111,117, 119, 120, 121, 124, 125, 126, 127, 129, 130, 139, 224, 227 Khawaja, D. K., 162, 224 Kholy, A. A., 57, 77, 92, 120, 130, 212 Kilarski, W., 150, 224 Kimata, M., 196, 229 Kimurta, N., 136, 150, 224 King, D. W., 275, 340 Kirsten, R., 275, 344 Kishinouye, K., 263, 344 Kitada, H., 201, 229 Kitamikado, M., 190, 192, 193, 194, 195, 196, 197, 224, 228 Kitchell, J. F., 184, 185, 224 Kleerekoper, H., 312, 344 Kleinholtz, L. H., 48 Klenk, F., 55, 100 Klinger, P. D., 301, 347 Klust, G., 137, 225 Knowles, F., 290, 292, 344 Kobayashi, N., 42, 48 Koch, H. J. A., 252, 256, 257, 268, 282, 260, 339, 344 Kock, L. L. de, 80, 100 Kodama, N., 124, 222 Kolehmainen, S. E., 174, 225 Kolmer, W., 54, 55, 66, 100 Konfal, E., 112, 130, 151, 152, 154, 155, 225 Konishi, J., 55, 80, 100, 101 Konosu, S., 319, 341, 344 Korovina, V . M., 134, 135, 137, 138, 166, 225, 236

406

AUTHOR INDEX

Korringa, P., 371, 395 Kosakai, T., 124, 127, 129, 221, 222 Krajuchin, B. V., 80, 94 Krasyukova, Z. V., 116, 230 Kraus, H., 275, 344 Krawkow, N. P., 270, 344 Krayukhin, B. V., 174, 176, 198, 199, 219, 225 Krikov, W. A., 294, 341 Kristensen, I., 48 Krogh, A., 252, 344 Kubo, T., 247, 256, 326, 327, 344, 346 Kubota, K., 127, 129, 222 Kudinsky, 0. Yu., 126, 225 Kulshreshtha, S. D., 73, 101 Kuriyama, H., 171, 222 Kuz’mina, V. V., 179, 225

L Lacanilao, F., 305, 34s Lagler, K. F., 92, 101 Lahaye, J., 285, 345 Lahlouh, B., 304, 305, 346 La1,M. B., 79, 101, 111, 121, 225 Lam, T. J., 291, 292, 293, 345 Landacre, F. L., 75, 85, 101 Landgrebe, F. W., 278, 345 Landino, L., 124, 221 Landis, S. C., 147, 148, 149, 151, 162, 165, 219 Lange, N. O., 115, 118, 125, 225 Larbi, E., 282, 354 Laroche, G., 278, 345 Larsson, A., 288, 340‘ Latif, A. F. A., 110, 119, 122, 167, 219 Lawrence, J. M., 41, 49 Leatherland, J. F . , 291, 345 Lebedev, N. V., 273, 345 Leblond, C. P., 278, 345 Lederis, K., 305, 345 Leja, S., 133, 235 Leloup, J., 277, 278, 280, 287, 301, 329, 339,345 Leloup-Hatey, J., 288, 345 Lemoine, A. M., 293, 345 LenhossBk, M. von, 68, 101 Leray, C., 282, 305, 346 Lerner, A. B., 294, 351

Lewander, K., 288, 346 Lewis, J. B., 13, 49 Leydig, F., 54, 66, 101 Li, M. F., 358, 369, 395 Lidman, U., 288, 346 Liem, K . F . , 80,101, 129, 137, 138,225 Lin, D. H. Y., 256, 337 Lindahl, P. E., 13, 49 Linss, W., 143, 145, 146, 225, 226 Lipskaya,N. Y., 185,186,188,226 Lissman, H. W., 320, 346 Lockhart, E. E., 193, 234 Loewenthal, L. A., 91, 93 Loosli, J. K., 186, 226 Long, P., 301, 345 Longhi, L., 151, 152, 153, 154, 164,226 Longwell, A. C., 358, 363, 369, 370,382, 387, 395 Loosanoff, V. L., 357, 369, 395 Lopez, E., 300, 330, 338, 340 Lbpez, R. B., 126, 131, 226 Lorenzo, A. J. de, 59, 101, 102 Low, M. P., 138, 214 Lowe, R. H., 325, 346 Lukowicz, M. von, 57, 78, 102 Luppa, H., 147, 149, 155, 165, 226 Lutfy, R. G., 80, 92, 144, 226

M Milar, A., 307, 346 MacBride, E. W., 13, 49 Machemer, L., 281, 335 Machin, K. E., 320, 346 Macsotay, O., 374, 395 Maetz, J., 288, 303, 304, 305, 346, 347, 349 McBean, R. L., 288, 342 McCance, R. A., 252, 346 McCann, S. M., 295, 348 McGeachin, R. L., 194, 196, 226 McInerney, J. E., 290, 315, 346 MacKay, M. E., 190, 195, 226 McKay, W., 288, 289, 338 McKeown, B. A., 292, 346 MacKinnon, D., 316, 335 McLain, L. R., 255, 327, 333, 354 McLeave, J. D., 320, 321, 349, 350 McPherson, B. F., 14, 42, 50

AUTHOR INDEX

407

Maggese, M. C . I., 121, 134, 226 Menzel, D. W., 91, 94 Magnus, B. E., 2, 45, 49 Menzel, R. W., 358, 363, 369, 382, 383, Magnuson, J. J., 179, 226 384, 385, 386, 387, 391, 396 Mahadevan, S., 123, 124, 129, 130, 131, Merkel, F., 55, 202 132, 226 Merrill, A. S., 391, 396 Mahajan, C. L., 79, 102 Mester, L., 120, 121, 144, 155, 163, 164, Mahaux, J., 278, 346 227 Majumdar, N. N., 79, 102, 121, 122, Mester, R., 155, 163, 164, 227 226 Mihai, P., 115, 151, 217 Maljukina, G. A., 55, 90, 102 Mikuriya, B. A., 121, 169, 227 Manfredi Romanini, M. G., 155, 226 Miles, A. E . W., 124, 227 Manly, B. M., 46, 49 Miles, H., 347 Mantejfel, B. P., 322, 346 Miles, S . G., 315, 318, 324, 346, 347 Marchelidon, J., 300, 339 Miller, L. H., 295, 343, 344 Marshall, N. B., 80, 102 Miller, M. C., 294, 343 Martelly, E., 278, 339 Miller, R. E., 291, 347 Martin, N. V., 125, 139, 226 Miller, R. J . , 77, 79, 80, 87, 88, 95, 102, Martin, P. L., 175, 218 110, 121,217, 227 Mathewson, R. F., 55, 90, 98 Miller, R.R., 92, 101 Mathies, J. C., 190, 229 Miller, R . V . , 80, 94, 122, 169, 214, 227 Matis, J. H., 312, 344 Milligan, H . N., 13, 49 Matoltsy, A. G., 144, 153, 220 Millott, N., 2, 5 , 6, 7, 8, 9, 10, 11, 12, Matsuda, H . , 55, 80, 101 13, 14, 15, 16, 18, 19, 20, 21, 22, Matsuura, F., 268, 338 25, 26, 28, 29, 30, 31, 33, 34, 36, Matthes, H., 116, 117, 120, 125, 134, 38, 39, 40, 42, 44, 46, 48, 49, 50, 226 52 Matthew, D. C., 55, 98 Milne, K. P., 291, 347 Matthew, M., 282, 354 Minckley, 176, 213 May, R. M., 85, 102 Mislin, H., 272, 347 Mayer, J., 175, 178, 179, 180, 232 Mitchell, E. G., 79, 102 Mayer, N., 288, 346 Mittal, A. K . , 153, 227 Maynard, L. A., 186, 226 Miyadi, D., 79, 102 Mayr, E., 365, 373, 375, 379, 380, 384, Miyashita, S., 305, 338 389, 390, 391, 395 Miyazaki, I., 384, 396 Mayser, P., 87, 102 Mohres, F. P., 92, 102 Mazeaud, F., 298, 340 Mohsin, S. M . , 57, 102, 111, 118, 124, Mazeaud, M., 298, 340 125, 127, 130, 132, 134, 138, 139, Mearns, A. J., 269, 351 227 Medani, J. I., 112, 113, 114, 129, 136, Moitra, S. K., 81, 103, 110, 126, 137, 197, 217, 227 237 Medeiros, L. O., 120, 152, 153, 154, 164, MolnBr, G., 183, 185, 188, 189, 218, 227, 226,227 228 Momzikoff, A., 319, 347 Medeiros, L. F., 120, 127, 154, 226 Mehrotra, B. K., 81, 100, 120, 125, 126, Mookerjee,H.K., 88,103,110,228 127, 129,139, 224, 227 Mookherji, P. S., 88, 103 Meier, A. H., 293, 343 Moore, G. A., 57, 77, 79, 90, 103 Meierotto, R. R., 173, 181, 217 Moore, H. B., 14, 42, 50 Melander, A., 298, 346 Moore, W. G., 173, 176, 228 Melnikova, M. N., 138, 236 Mori, Y., 55, 101 Mennega, A. M. W., 190, 191, 227 Moriarty, C . M., 186, 228

408

AUTHOR INDEX

Moriarty, D. J. W., 186, 191, 228 Moriehita, T., 190, 192, 194, 196, 197, 228 Mortensen, Th., 2, 13, 50 Motais, R., 252, 303, 347 Moyle, J. B., 182, 233 Muir, B. S., 205, 228 Munshi, J. S . D., 153, 227 Muraki, T., 135, 147, 148, 149, 239 Murphy, A. V., 291, 347 Murr, E., 248, 347 Murray, R. G., 55, 103 Murray, R. W., 90,103,309,347

N Nagahama, Y., 292, 347 Nagar, S. K., 120, 123, 124, 228 Nagase, G., 190, 191, 192, 194, 195, 228 Nagumo, N., 135, 147, 148, 149, 239 Naito, K., 279, 282, 347 Nakamura, H., 309, 347 Nakamura, K., 42, 48 Nakashima, J., 176, 178, 221 Nasu, H., 300, 348 Natochin, J u . V., 256, 347 Naughton, I. J., 55, 98 Naumov, N. P., 322, 346 Neal, H. V., 75, 77, 95 Neale, J. H., 301, 347 Nelson, G. J., 91, 106, 131, 228 Nelson, T. C., 360, 396 Nemetschek-Gander, H., 59, 103 Newcomb, T. W., 269, 351 Nicoll, C. S., 293, 334 Nicholls, J. V . V., 187, 188, 228 Nicolaides, N., 195, 228 Niimi, A. J., 202, 205, 228 Nikolskaya, N . G., 111, 130, 228 Nikolsky, G. V . , 110, 119,228, 272, 347 Nilsson, S., 171, 172, 228 Nishioka, R. S., 292, 305, 334, 347 Niwa, H., 55, 101 Noaillac-Depeyre, J., 147, 229 Nockton, R., 295, 344 Noda, H., 190, 192, 194, 196, 197, 228 Nomejko, C. A., 357, 369, 395 Nomura, T., 323, 336 Nordeng, H., 317, 323, 347 Nordlie, F. G., 190, 229

Norris, D. O., 181, 185, 186, 199, 229, 239 Norris, E. R., 190, 229 Norris, J. S., 199, 229 Nose, T., 319, 341, 344 Numachi, K., 358, 375, 379, 384, 396

0 Oberoi, S., 79,101, 111, 121, 225 Odense, P. H., 80, 94, 111, 121, 130, 132, 134, 136, 137, 147, 149, 151, 155, 167, 214, 229 Ogawa, N., 291, 347 Ogden, J. C., 241, 347 Ohnesorge, F. K., 172, 229 Ohtsu, K., 279, 282, 347 Oide, H., 253, 289, 291, 292, 352 Okumura, H., 28, 29, 30, 31, 50 Okumura, N., 300, 348 Okutani, K., 196, 201, 229 Old, W. E., 391, 395 Oliva, O., 79, 99 Olivereau, M., 278, 286, 287, 290, 292, 293, 297, 340, 345, 348 Olivo, 0 . M., 85, 103 Olmsted, J. M. D., 85, 103 Olsson, R., 147, 149, 150, 151, 155, 162, 164, 166, 167, 222 Onuma, H., 124, 221 OoshIro, Z., 193, 229 Oppenheimer, J. R., 122, 229 Orias, R., 295, 348 Orton, J. H . , 13, 50, 359, 396 Osada, M., 150, 167, 235 Oshima, K., 301, 316, 317, 341, 348 Oshiro, S., 135, 147, 148, 149, 239 Osse, J. W . M., 119, 229 Otsuki, S., 300, 348 Ovchinnikov, V. V . , 322, 348 Overbeeke, A. P. van, 292, 346 Owen, T. G., 200, 229 Oya, T., 135, 147, 148, 149, 239 Ozaki, N., 147, 148, 149, 150, 229

P Paffenhofer, G.-A,, 185, 231

409

AUTHOR INDEX

Paine, R. T., 13, 14, 47 Palay, S. L., 79, 105 Paloheimo, J. E . , 206, 229, 230 Pandian, T . J., 177, 181, 184, 202, 230 Pang, P. K. T., 299, 348 Pang, R., 299, 348 Pannikar, N. K., 260, 348 Pant,M. C., 79,100, 117, 119, 121, 224 Papadaki, L., 282, 354 Park, Y. H . , 324, 336 Parker, F. R. Jr., 269, 348 Parker, G. H., 50, 90, 103 Parry, G., 256, 276, 337, 348 Parzefall, J . , 81, 103 Pasha, S. M. Kamal, 120, 124, 133, 230 Pearse,A. S., 12,41,42,45, 50,172,177, 230 Pegel, V. A., 176, 179, 182, 186, 230 Pentraeth, V. W . , 24, 43, 50 PBquignat, E., 13, 51 Pessah, E., 204, 230 Peter, J. B., 275, 334 Petersen, C. G. J., 325, 348 Pevzner, R. A., 68, 7 1 , 1 0 3 , 154, 230 Pfefferkorn, G., 59, 62, 95 Pfeiffer, E. F., 291, 350 Pfeiffer, W., 144, 153, 154, 230 Phillips, A. M., 186, 194, 202, 230 Phillips, J. G., 292, 348 Pickford, G. E., 291, 292, 340, 348 Pictet, A., 65, 104 Philpott, C. W., 140, 230 Piavaux, A., 196, 230 Pierce, E. L., 184, 230 Pillay, T.V. R., 110, 111, 123, 124, 131, 132, 138, 230 Poddubnyj, A. G., 322, 348 Pollingher, U., 134, 232 Poluhowich, J. J., 268, 349 Poncet, M., 299, 330, 340 Ponniah, S., 305, 334 Poole, D. F . G., 124, 227, 230 Power, G., 254, 349 Powers, E. B., 267, 349 Powles, P. M . , 204, 230 Prakash, A., 155, 162, 169, 231 PrasadaRao, P. D., 87,104, 110,231 Precht, H., 187, 231 Prefontaine, G., 278, 345 Pruhs, D., 293, 349

Purmann, G., 145, 231

Q Quay, W. B., 306, 349 Quayle, D. B., 371, 375, 396 Quispel, A., 199, 231

R Raffin-Peyloz, R., 80, 104 Rahimullah, M . , 139, 231 Rai, H. S., 381, 382, 392, 394 Rajbanshi, V. K., 57, 69, 71, 104, 106, 154, 231, 235 Randall, D. J., 270, 349 Rankin, J. C., 304, 305, 333, 334, 346, 349 Ranson, G., 358, 361, 383, 396 Rappoport, D. A., 317, 349 Rasquin, P., 77, 90, 95 Rauch, R., 229 Raup, D. M . , 15, 43, 51 Read, J. B., 167, 168, 171, 231 Reid, M. J., 121, 231 Reinsch, H. H., 313, 349 Reshetnikov, Yu., 125, 139, 231 Retzius, G., 68, 104 Reutter, K., 5 5 , 57, 59, 65, 69, 70, 71, 75, 104, 145, 154, 169, 231 Rey, P., 248, 349 Reznik, G. K., 155, 166, 231 Riddle, O., 182, 231 Riege, W. H., 324, 349 Rippel, R. H., 306, 353 Rizhkov, L. P., 55, 104 Roberts, E., 268, 278, 353 Robertson, 0. H., 331, 349 Robilliard, G. A., 13, 14, 47 Rodolico, A., 284, 349 Roman, W., 278, 334 Rommel, S. A. Jr., 320,321, 349, 350 Roper, C . F . E., 14, 42, 50 Rosenthal, H., 183, 185, 186, 231 Rossi-Fanelli, A., 264, 350 Roughley, T. C., 381, 387, 395 Roule, L., 267, 350 Rowntree, W. S., 114, 231 Royce, W. F., 321, 350

410

AUTHOR INDEX

Rozin, P., 175, 178, 179, 180, 232 Ruiter, L. de, 179, 180, 232 Ruivo, M., 286, 336 Runnstrom, J., 13, 49 Runnstrom, S., 365, 396 Russell, E. S., 332, 350

S Saddler, J. B., 139, 232 Sage, M., 293, 350 Saishu, S., 253, 352 Sakai, S., 358, 375, 376, 377, 379, 382, 383, 384, 385, 386, 395 Sakamoto, I., 257, 350 Salaria, J., 111, 233 Salenitse, J. K., 197, 214 Sandercock, F. K., 125, 139,226 Sandman, C. A., 295, 344, 350 Sannohe, N . , 144, 153, 232 Santa, V., 134, 232 Sarasin, C. F., 20, 51 Sarasin, P. B., 20, 51 Sarbahi, D. S., 126, 138, 190, 193, 194, 195, 196, 232 Sarbini, D. S., 57, 104 Sargent, J. R., 207, 216 Sarkar, H. L., 80, 104, 120, 232 Sasse, D., 144, 153, 154, 230 Sasso, W. S., 131, 151, 152, 216 Sastry, A. N . , 365, 396 Sastry, K. V., 155, 195, 219, 232 SatB, M., 55, 77, 78, 79, 80, 85, 88, 90, 98, 104, 105, 120, 144, 153, 221, 232 Satomura, I., 124, 222 Satou, M., 317, 352 Saunders, R . L., 326, 350 Savitz, J., 204, 232 Savvaitova, K. A., 131, 237 Sawada, T., 196, 229 Sawaya, P., 138, 232 Sawyer, W. H., 341 Saxena, B. P., 79, 102, 121, 122, 226 Saxena, D. B., 120, 232 Saxena, S. C., 78, 105 Schally, A. V . , 294, 295, 333, 343, 344, 350 Schaper, A., 248, 350 Scharrer, E., 79, 105

Schemmel, C., 90, 105 Scheuring, L., 180, 186, 188,232 Schmidt, J., 248, 350 Schmitz, E. H., 81, 105, 111, 121, 122, 127, 131, 169, 232 Schmitz, G., 172, 229 Schnitzlein, H. N . , 88, 105 Scholles, W . , 260, 350 Schreiber, B., 254, 350 Schroder, K. E., 291, 350 Schtefanesku, M., 55, 90, 102 Schuchardt, E., 68, 96 Schulte, E., 55, 57, 59, 63, 105, 145, 232 Schulze, F . E., 54, 65, 105 Schwabe, E., 260, 351 Scliwartz, F. J . , 124, 232 Schwassmann, H. O., 311, 351 Scripcariu, D., 155, 163, 164, 227 Seaberg, K. G., 182, 233 Segawa, T., 295, 351 Sehgal, P., 111, 117, 120, 176, 233 Seshadri, B., 194, 233 Sevilla, M. L., 374, 394 Sharma, U., 120, 211 Sharp,D.T., 3, 12, 13, 14, 15, 51 Shashoua, V. E., 301, 351 Shcherbina, M., 201, 233 Shelbourn, J. E . , 174, 176, 204, 206, 215 Sheldon, R. E., 90, 105 Shinada, H., 317, 348 Shirahata, S., 317, 351 Shirai, N., 256, 352 Shizume, K., 294, 351 Shoop, C. T., 174, 176, 204, 206, 215 Shrable, J. B., 182, 184, 188, 233 Shuljak, G. S., 112, 115, 233 Shulman, G. E., 274, 351 Simizu, W., 276, 351 Shumway, D. L., 205, 217 Siankowa, L., 112, 135, 233 Singer, M., 85, 99 Singh, B . R., 80, 105 Singh, C. P., 80, 105 Singh, H . M., 134, 211 Singh, H. R., 88, 100 Singh, R., 120, 134, 233 Sinha, 0. M . , 81, 103, 126, 227 Sivadas, P., 151, 155, 162, 167, 233

41 1

AUTHOR INDEX

Sklower, A., 248, 283, 347 Skobe, Z., 140, 141, 142, 212 Skvorzowa, T. A., 122, 235 Smit, H., 130, 185, 187, 190, 191, 199, 200, 233, 234 Smith, C . L., 121, 234 Smith, D. C . W., 291, 351 Smith, D. G., 358, 363, 395 Smith, H. H., 182, 235 Smith, L. S., 269, 321, 350, 351 Smith, M . W., 162, 221 Smith, R.O., 383, 385, 386, 394 Smith, S. W., 79, 105 Sokolova, M. M . , 247, 255, 270, 271, 354 Solomon, D. J., 317, 351 Soule, J. D., 124, 234 Spandorf, A., 192, 196, 215 Spanovskaya, V. D., 115, 116, 117, 234 Sparks, A. K., 358, 359, 361, 362, 363, 364, 381, 394 Springer, S., 90, 106 Srebro, Z., 303, 351 Srivastava, A. K., 155, 162, 234 Srivastava, P. N., 126, 129, 234 Sriwastwa, V. M . S., 111, 234 Stainer, I. M . , 271, 342 Stanley, J. G., 291, 351 Stasko, A. B., 323, 351 Stauber, L. A., 357, 358, 368, 370, 391, 396 Stenzel, H. B., 358, 359, 360, 361, 367, 368, 370, 371, 374, 375, 381, 382, 383, 385, 386, 387, 388, 389, 391, 392, 393, 396 Stern, J. A., 193, 234 Steven, D. E., 269, 349 Steven, D. M., 2, 51 Stevens, E. D., 266, 270, 351 Steward, N. E., 177, 234 Stewart, J. E., 358, 369, 395 Stiles, S. S., 358, 363, 369, 370, 382, 383, 387, 395, 396 Stommel, H., 321, 351 Storch, V. N., 55, 57, 59, 65, 106, 107, 145, 169, 234 Stratton, L. O., 295, 344 Strieck, F., 55, 90, 106 Stroganov, N. G,, 115, 193, 234 Sublette, M. S., 130, 171, 234

Sutterlin, A. M., 55, 79, 80, 106, 121, 234 Sutterlin, N., 55, 79, 80, 106, 121, 234 Suvorova, E . G., 151, 152, 153, 234 Suyehiro, Y., 110, 111, 119, 234 Suzuki, T., 135, 147, 148, 149, 239, 324, 352 Suzuki, Y., 120, 150, 167, 235 Svetovidov, A. N., 122, 139, 235 Swamp, K., 7 3 , 1 0 6 , 126, 129, 131, 236 Swenson, W. A., 182, 235 Sylvest, E., 249, 352 Szarski, H., 133, 235 Szirmai, E., 303, 351

T Tachino, S., 190, 193, 194, 195, 196, 224 Takahashi, K., 20, 22, 36, 38, 39, 40, 50, 51 Takasugi, N., 305, 334, 351 TamBssy, E., 185, 228 Tamura, E., 139, 235, 305, 342 Tandon,K. K., 80,106,121,235 Tateda, H., 55, 106 Taylor, W . H., 190, 191, 235 Teal, J. M., 263, 264, 265, 336 Tebble, N., 391, 395 Teichmann, H., 55, 89, 90, 106 Tennant, D. H., 41, 51 Tesch, F.-W., 318, 322, 338, 352 Tester, A. L., 55, 90, 91, 100, 106 Tewari, H . B., 57, 69, 71, 106, 154, 231, 235 Thomson, J. M., 123, 124, 131, 235, 358, 381, 386, 397 Thornton, I. W . B., 2, 51 Threadgold, L. T., 255, 256,342, 352 Tiemeier, 0 .W., 182, 184, 188, 233 Timiras, P. S., 286, 352 Timms, A. M., 312, 344 Todd, J. H., 55, 81, 89, 93, 106 Tokumaru, M . , 151, 167, 219 Tolg, I., 183, 185, 188, 189, 218, 227, 228 Torretti, J., 291, 348 Torrey, T. W., 85, 106

412

AUTHOR INDEX

Tortonese, E., 119, 235 Toyota, M., 55, 80, 101 Trent, L., 176, 236 Treschuk, L. I., 151, 152, 153, 234 Trudel, P. J., 55, 107 Trujillo-Cenbz, O., 55, 65, 107 Tsinober, A. B., 322, 335 Tsuyuki, H., 268, 353 Tucker, D. W., 307, 352 Tung, I.-S., 139, 221 Turpayev, T., 197, 235 Tyagi, A. P., 130, 237 Tyagi, M. P., 111, 130, 237 Tyler, A. V., 182, 184, 185, 188, 236 Tyler, J. C., 121, 234

U Uchida, M., 55, 101 Uchihashi, K., 88, 107 Ueda, K., 302, 316, 317, 341, 352 Uga, S., 55, 57, 68, 70, 107, 169, 236 Umminger, B. L., 294, 352 Ungar, G., 301, 352 Underhill, J. C., 124, 217 Unnithan, R. R., 112, 236 Ursin, E., 365, 397 Ushiyama, H., 194, 196, 236 Utida, S., 253, 255, 256, 289, 291, 292, 293, 341, 352

v Vanajakshi, T. P., 120, 336 Van Heusden, G. P. H., 353 Van Husen, G., 124, 221 Van Someren, V. D., 330, 353 Vanstone, W. E., 268, 353 Varute, A. T., 125, 152, 236 Vasilevskaja, N. E., 55, 92 VasilIeva, N . E., 135, 137, 138, 166, 225, 236 Vasil'yev, A. S., 322, 335, 353 Vasisht, H. S., 125, 236 Vegas-Velez, M., 130, 151, 236 Velasco, M., 295, 343 Velasco, de Parra, M. L., 295, 343 Venkateswarlu, T., 124, 236

Verighina, 1. A., 111, 112, 113, 114, 115, 116, 117, 120, 122, 125, 127, 129, 130, 131, 133, 134, 135, 136, 151, 155, 165, 166, 228, 236, 237 Verigin, B. V., 122, 123, 125, 237 Verma, S. R., 111, 130, 196, 212, 237 Verwey, J., 260, 353 Vevers, H. G., 6, 48, 50 Vibert, R., 314, 340 Vickers, T., 112, 135, 137, 167, 171, 237 Vilter, V., 283, 353 Vollrath, L., 290, 292, 353 Volya, G., 197, 237 Von Hagen, F., 283, 353 Vonk, H. J . , 190, 194, 197, 237 von Uexkiill, J . , 2, 13, 15, 19, 51 Vorobjov, N. A., 126, 155, 224 Vrba, E. S., 120, 237 Vrba, R., 300, 353 Vukovi6, T., 115, 117, 211, 237

w Wagner, C. E . , 85, 107 Wagner, H . H., 326, 355 Walne, P. R., 360, 397 Ward, H. B., 332, 353 Ware, D. M., 174, 237 Warren, C. E., 177, 204, 205, 217, 220, 238, 269, 353 Warren, F. J., 254, 338 Watanabe, A., 150, 167, 235 Waterman, T. H., 312, 353 Watkins, K. C., 70, 97 Watters, K. W . Jr., 269, 351 Weatherly, A. H., 207, 238 Weber, E. H., 54, 79, lo?' Weber, G. F., 306, 353 Weber, H., 79, 92, 107 Weber, W., 7, 10, 51 Webster, J. R., 391, 396 Weinreb,E. L., 127, 130, 131, 132, 151, 153, 155, 162, 168, 169, 238 Weisel, G. F., 79, 81,107, 111, 112, 117, 121, 125, 134, 135, 150, 238 Welsch, U. N., 55, 57, 59, 65, 106, 107, 145, 169, 234 Westenberg, J., 322, 353

413

AUTHOR INDEX

Westerman, R. A., I07 Western, J. R. H., 81, 107, 125, 129, 130, 138, 151, 155, 157, 161, 162, 163, 189, 191, 199, 238 Wetzig, H., 151, 238 Wexler, B. C., 331, 349 White, H. C., 325, 353 White, W. F., 306, 353 Whitear, M., 55, 57, 59, 65, 70, 73, 79, 107, 140, 143, 145, 169, 238 Whitmore, C. M., 269, 353 Whitmore, D. H., 155, 238 Widman, E., 260, 353 Wier, H. C., 130, 131, 283 Wiggs, A. J . , 200, 229 Wilamovski, A., 122, 238 Wilber, J. F . , 306, 353 Willre, H., 144, 238 Wilson, J. A. F., 107 Wilt, E’. H., 279, 282, 347, 353 Winberg, G. G., 203, 206, 238 Windell, J. T., 181, 184, 185, 186, 199, 224, 229, 238, 239 Winn, H. E., 91, 94 Wisby, 147. d . , 311, 315, 341, 1353 Wittenberger, C., 266, 354 Wohlschag, D. E., 268, 354 Woodall, A. N . , 195, 228 Woodbury, D. M., 286, 327, 33’2, 354 Woodliead, A. D., 257, 258, 286, 354 Woodhead, P. M. J., 257, 258, 286, 354 V170rsmann, T. U . , 151, 152, 153, 154, 164, 227 Wright, R.R., 83, 107 Wright, S., 390, 397 Wu, H. W., 139, 239

Wunder, W., 79,89,90,107,108

Y Yajima, H., 295, 351 Yamagdii, I., 135, 147, 148, 149, 239 Yamaguchi, K., 124, 222 Yamaguchi, M., 88, 108 Yamamoto, T . , 147, 148, 149, 150, 239 Yamashita, E., 55, 108 Yanagisawa, K., 55, 91, 100 Yashouv, A., 292, 333 Yokota, S., 55, 80, 98 Yonge, C. M., 358, 360, 370, 371, 387, 397 Yoshie, S., 292, 342 Yoshida, H., 124, 221 Yoshida, M., 2, 3, 4, 7, 8, 10, 11, 12, 20, 21, 25, 26, 28, 29, 30, 33, 34, 36, 37, 42, 50, 51, 52 Yoshida, Y . , 123, 124, 239 Young, R. T., 138, 239

Z Zaimis, E., 282, 354 Zaks, M. G., 247, 255,270, 271,354 Zambriborsch, F. S., 131, 239 Zaugg, W. S., 255, 326, 327, 333, 354, 355 Zippel, H. P., 90, 108, 301, 338 Zotterman, Y., 55, 101 Zousser, S . G., 243, 355 Zueva, K. D., 279, 355

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Taxonomic Index A

Aspius, 197 Aulopige hugelii, 115

Abramis brama, 166 Acanthurus, 133 Acipenser, 305 ru,thenus, 78 Aequipecten irradians, 365 Alburnus, 197 alburnus, 188 Alectryonella, 359, 389 Alectryonia, 358 Alestes kotschyi, 114 macrolepidotus, 114 Alosa, 285, 331 alosa, 285 Amblypharyngodon mola, 117 Ameiurus, 78, 82, 85 melas, 75, 82 Amia calva, 182 Amiurus c a t w , 155 nebulosus, 59, 62, 63, 69, 73 Anabas testudineus, 130 Anchoviella, 184 Anguilla, 139, 144, 153 anguilla, 144, 172, 318, 330 japonica, 190, 293, 319 nebulosa labiata, 330 occidentalis australis, 167 rostrata, 313, 318, 330 Aphanopus carbo, 313 Aplysia, 22, 34 Arbacia, 7, 12, 19 lixula, 6 punctulata, 3 Arenicola, 203 Ariomma lurida, 127 A.M.B.-13

B Barbus, 196 grypus, 117 meriodionalis, 115 sharpeyi, 117 ticto, 117 tor, 117 Barilius, 134 moorei, 117 chrysti, 117 Belone belone, 185 Blennius ocellatus, 281 paro, 281 Blicca, 197 Brachymystax lenok, 126, 154, 166 Brevoortia, 193, 195

C Catotomus, 192, 194 Carassius, 87, 112, 153 auratus, 86, 135, 147, 148, 149, 150, 162, 165, 171, 301, 305, 323 auratus gibelio, 115 carassius, 56, 73 Carpiodes velifer, 87 Caspialosa caspia, 273 kessleri, 27 3 saposhnikovi, 273 volgensis, 273 Cassis

tuberoaa, 45 Catla catla, 116, 138 415

15

416

Catostomus commersoni, 87 Centrostephanus, 6, 7, 10, 19 coronatus, 41, 42 longispinus, 2, 7 Chaenobryttus gulosus, 173, 176, 184 Chalinura mediterranea, 136 Channa, 121 Chanos, 127 chanos, 126, 131 Chasmistes cujus, 78

Cheilodipterus afinis, 121 Chela bacaila, 117 Chelethiops elongatus, 117 Chlamys opercularis, 365 Chondrostoma nwus variable, 120, 135 Cirrhina mrigala, 79, 116, 121 Citharinus citharus, 114 congicus, 114 distichodoides, 114 gibboeus, 114 macrolepsis, 114 Clarias, 196 batrachus, 65 gariepinus, 110 Cobitis biwae, 56 Colalabis saira, 259 Colisa, 79, 196 Compostomabarbus wittei, 117 Coregonus autumnalis, 119 lavaretus pidschian, 119 sardinella, 119, 268 Corydoras, 153 hastcctus, 68 julii, 140, 141, 142 paleatus, 59, 60

TAXONOMIC INDEX

cottus gobio, 125, 129, 151, 157, 161, 162, 163, 191, 199

perplexus, 205 Crangon crangon, 260 Crassostrea, 358, 359, 360, 361, 362, 363, 364, 367, 371, 374, 381, 382, 383, 385, 386, 387, 388 amasa, 385 angulata, 383, 384, 385, 386 commercialis, 381, 385, 386, 387 cuccullata, 375, 381, 385, 386, 387 cuttackensis, 367 echinata, 385, 386 gigas, 358, 363, 364, 365, 371, 375, 376, 378, 379, 380, 382, 383, 384, 385, 386, 390 gigas sikamea, 380 glomerata, 365 guyenensis, 373, 374, 390 iredalei, 384, 385 lacerata, 374, 390 laperousi, 380, 390 madrasensis, 367 margaritacea, 385, 387 rhizophorae, 367, 374, 384, 385, 386, 390 rivularis, 363, 365, 371, 384, 386 sikamea, 380, 390 tuberculata, 381, 385, 386, 387 virginica, 357, 358, 359, 360, 365, 366, 367, 368, 369, 370, 371, 373, 374, 377, 380, 383, 384, 385, 386, 390, 391 Crenilabrus, 120 Ctenolabrus, 120

Ctenopharyngodon idella, 115, 117, 151, 152, 193 Cucumaria sykion, 43 Curimatus, 114 Cycleptus, 87 Cymatogmter aggregatus, 138 Cyprinus, 69, 80, 82, 85, 87, 197 carpio, 56, 73, 166, 169, 317

417

TAXONOMIC INDEX

D

G

Daphnia, 185 Decapterus muroadsi , 25 9 Dendostrea, 358 Diadema, 11, 12, 19, 20, 22, 25, 30, 36,

Gadus, 83, 84, 195 callarias, 82 morhua, 82, 111, 121, 132, 136, 149,

37, 41, 43, 44, 45, 46

antillarum, 2, 5, 6, 7, 8, 9, 10, 11, 12, 21, 22, 26, 27, 28, 29, 30, 31, 33, 34, 38, 39, 40, 41, 42, 45, 46 setosum, 2, 7, 8, 11, 22, 28, 29, 37, 41, 42, 45, 46 Distochodus, 112, 113, 129 niloticus, 112, 113, 114, 127, 129 rostratus, 112, 113, 114, 127, 129

Dorosoma cepedianum, 122, 127, 131 petenense, 121, 127

E Echinothrix calamaris, 41 Elopichthys, 112, 134 bambusa, 115, 117 Engraulicypris minutus, 117 Engraulis encrasicholus, 273 Enophrys bubalis, 751, 157, 161, 162, 163, 199 Eriocheir sinensis, 260 Erythroculter erythropterus, 117, 136 ESOX,182 lucius, 132, 143, 145, 146, 190 Evechinus, 14, 15 chloroticus, 12 Extrarius aestivalis tetranemus, 77

155, 171, 181, 184, 188

Galeichthys felis, 317 Cambwia, 181, 184

aBnis, 138, 151, 152, 162, 169 Cammarus, 188 Garra congolensis, 116 dembensis, 116 mullya, 78 Casterosteus, 7 3, 292 aculeatus, 59, 140, 143, 293 Geophagus jurpari, 121 Gepmo alalunga, 309 Ginglymostoma cirratum, 90 Glossogobius giuris, 125, 127, 130 Glyptothorax telchitta, 78 Gnathonernus petersii, 169 Gnathopogon biwae, 80 Gobio fluviatilis, 150, 151 gobio, 117, 121, 155, 166 Gobius, 133 minutus, 59 Gudusia, 196 chapra, 126, 129 Gymnarchus niloticus, 320 Gymnothorax moringa, 92 uicinus, 92 Gyrinocheilus aymonieri, 144

H

F Fundulus, 140, 195, 258, 292 heteroclitus, 188

Haemulon plumieri, 184

418

TAXONOMIC INDEX

Haplochromis, 111 cav$rons, 111 macrops, 111 parvidens, 111, 120 sauvagei, 111 Helioperca incisor, 173 Helostoma temmincki, 140 Hemicentrotus pulcherrimus, 3, 4 Hemigrammus caudovittatus, 73 Hepomis gibbosus, 204 Heterodontus, 77 Heteropneustes f ossilis, 162 Hilsa ilisha, 73, 126, 129 Hippocampus coronatus, 73 Hyatella, 181 Hybopsis, 88 gelida, 78 Hydrocyon Forskalii, 114 Hyotissa, 359, 388 Hypophthalmichthys, 112, 133 molitrix, 116, 118, 122, 123, 165, 166

I Ichthyoborus besse, 114 Ictalurus, 83, 89, 190, 199, 323 m el m, 69, 181 natalis, 173 nebulosus, 81, 85, 173, 174, 191, 198, 200 punctalus, 182, 184, 188, 299 Ictiobus bubalis, 87 Iticus pellucidus, 127

J Jaera marina, 380

K Katsuwonus pelamis, 266, 265 Kryptopterus bicirrhis, 65 Kuhlia sandvicensis, 205

L Labeo, 112, 133 calbasu, 117, 176 dero, 79, 121 horie, 79, 116, 120, 121 lineatus, 116 niloticus, 116 rohita, 126, 138 variegatus, 116 Ladislavia taczanowskii, 116 Leander serratus, 260 Lepidosteus platyrhincus, 173, 176 Lepomis cyanellus, 173, 176 gibbosus, 173, 175, 183, 184 incisor, 190 macrochirus, 174, 175, 183, 184, 199, 204 Leptocypris modestus, 117 Leuciscus leuciscus biacalensis, 182 Leucopsarion petersi, 139 Leuresthes tenuis, 242 Limnocalanus grimaldii, 243 Liza haemotocheila, 124, 131 Lopha, 359, 389 folium, 389 Lophiomus setigerus, 7 3 Lota lota, 198 Lucioperca lucioperca, 188

419

TAXONOMIC INDEX

Lytechinus, 12, 13, 14, 15, 16, 19, 42, 43 variegatus, 3, 12, 16, 18, 41

M Macronus, 68 Malleus, 360 Mastacembelus pancalus, 162 Megalops cyprinoides, 178, 181, 184, 202 Menidia thomasi, 84 Mespilia globulus, 42 Micropterus, 182 salmoides, 173, 175, 176, 177, 182, 188, 190 Misgurnus, 139 anguillicaudatus, 79, 150, 164 fossilis, 78, 188 Monopterus albus, 129, 138 Mora moro, 3 13 Morone chysops, 130, 171 Morulius chryophakedion, 154 Moxostoina ariomum, 77 Mugil, 123, 131, 152, 194, 197, 207 auratus, 123 capito, 126, 129 cephalus, 80, 123, 124, 282, 292, 293, 299, 305 crenilabis, 129, 132 tade, 132 Mulloides auri$amma, 132 Mullus, 197 barbatus, 185, 188 Mytilus, 203

N Negaprion brevirostris, 90 Neopycnodonte, 359, 388

Noemacheilus barbatulus, 79, 120, 144, 150, 151 Nomeus albula, 127 gronovii, 135 Notopterus notopterus, 73, 127

0 Ocycruis japonicus, 127 Ocyurus chryurus, 184 Oncorhynchus, 190, 194, 247, 279, 296, 304, 311, 315, 324, 328, 329, 331 gorbuscha, 274 keta, 196, 247, 279 kisutch, 174, 177, 269, 278, 279, 316 masu, 247, 255, 256 nerka, 174, 182, 184, 187, 188, 204, 247, 261, 270, 272, 274, 279, 292, 313, 317, 324, 327 tschawytscha, 3 16 Ophicephalus, 120, 194, 196 gachua, 130 punctatus, 162 striatus, 162, 178, 202 Orcinus sinuatus, 117 Ostrea, 358, 359, 360, 361, 362, 363, 364, 367, 368, 372, 373, 374, 375, 382, 383, 386, 388, 389, 390 angelica, 374 chilensis, 360, 389 conchaphila, 372, 373, 374 edulis, 360, 362, 365, 370, 371, 372, 389, 390 equestris, 367 Jischerii, 374 folium, 389 f r o m , 367 lurida, 358, 361, 362, 364, 365, 368, 371, 372, 373, 374, 389, 390 lurida expansa, 372, 390 lurida laticaudata, 372, 390 lurida rufoides, 372, 390 megadon, 374 permollis, 367

420

TAXONOMIC INDEX

P Pagrus major, 196 Pampus argenteus, 127 echinogaster, 127 Paracentrotus lividus, 15, 41 Parasilurus, 112 asotus, 56 Parechinus, 41, 43 angulosus, 25 Parenophrys bubalis, 125, 129 Perca, 197 jlavescens, 173 jluviatilis, 149, 150, 151, 155, 164, 165, 166, 167 Periophthalmus argentilineatus, 28 1 chrysospilos, 281 schlosseri, 281 Perna, 364 Peristedion longispatha, 130, 132 Phoxinus, 73, 315 phoxinus, 59, 61, 154 Piaractus nigripinnis, 120 Pimelodus maculatus, 152, 153, 154, 155, 164 Platichthys Jesus, 303 stellatus, 292, 293 Plecoglossus altivelis, 292 Plotosus anguillaris, 80 Plecoglossus, 196 altevelis, 121, 127, I96 Plecostomus plecostomus, 138 Pleuronectes, 197 platessa, 130, 138, 167, 190 Pomatoschistus minutus, 59 Pomoxis sparoides, 190 Prionotus, 79, 92, 193, 195

Pristiophorous japonicus, 78 Prochilodus, 114 lineatus, 111, 114, 118 Psammechinus, 12, 13, 14 miliaris, 2 Psenopsis anomala, 127 Pseudogobio esocinus, 120 Ptychocheilus, 112 oregonense, 111, 117 Ptyocheilus, 134 Pycnodonte, 358, 359, 388 Pyrrhulina $lamentosa, 114

R Rana, 199 catesbiana, 282 Rhinichthys atratulus, 86 Rhodeus sericeus amarus, 115 Roccus chrysops, 190 saxatilis, 176 Rostrogobio amurensis, 117 Rutilus, 115 rutilus, 118, 138, 151, 166, 169 rutilus caspius, 118, 175, 179, 180 rutilus heckeli, 118

S Saccobranchus fossilis, 70, 154 Saccostrea, 359, 381, 386, 387, 388 cuccullata, 375, 381 Salarias, 192, 194, 195, 281 Salmo, 132, 137, 315 fario, 332 gairdneri, 150, 167, 169, 190, 270, 279, 327 gairdneri irideus, 127, 130, 132, 153, 155, 162, 168 irideus, 149, 150, 155, 167, 196

421

TAXONOMIC INDEX

Salmo, salar, 126, 169, 254, 256, 268, 269, 275, 276, 277, 279, 290, 291, 294, 295, 302, 305, 311, 319, 323, 332 trutta, 132, 151, 167, 169, 170, 175, 199, 332 Salvelinus, 125, 137 alpinus, 317 fontinalis, 135, 169, 174, 175, 199 malma, 329 namaycush, 139 Scardinius, 197 Schirothorae richardsonii, 126 Scomber, 193, 195, 197 japonicus, 259 Scorpaena porcus, 130 scrofa, 155 Sebastes, 193 inermis, 188 Sepia, 14 Seriola, 192 quinqueradiata, 190 Serrasalmo, 1 14 Silurus soldatowi, 112 Sisor rabdophorus, 79 Spheroides, 192, 193, 194 stictonotus, 150 Spisula, 34, 36 solidissima, 391 solidissima raveneli, 391 Squalus acanthias, 77 Stenodus, 137 leucichthys, 171 Stenotomus, 195 Sterechinus neumayeri, 14 Sternopygris, 32 1 Stirostedion, 182 Stizostedion, 182, 186 Striostrea, 358, 359, 387 Strongylocentrotus intermedius, 4 1 purpuratus, 42 Synaphobranchus pinnutus, 313

S ynodontis schall, 144

T Temnopleurus toreumaticus, 3 Tetragonurus atlanticus, 127 cuvieri, 127 Thalassoma, 192, 194 Thunnus, 190 maccoyi, 259 obesus, 267 thynnus, 266 Thymallus areticus baicalensis, 152, 153 Thy nnus pelamis, 263 Tilapia, 186, 191, 192, 193, 194, 195, 197 esculenta, 201 macrochir, 196 mossambica, 112, 125, 130, 152, 153, 155, 162, 167, 190, 197 nilli, 155 nilotica, 191 zillii, 130 Tinca tinca, 150, 151 vulgaris, 167, 172 Trachurus, 197 japonicus, 73, 259 trachurus, 190 Trichiurus haumela, 130 Trichogaster, 79 trichopterus, 79 Trigla, 79 gurnardus, 130 lucerna, 59 Trigon pastinaca, 66, 68 Tripneustes depressus, 380 esculentus, 14 gratilla, 380 ventricosus, 380 Trutta fario, 190

422

SUBJECT INDEX

U Umbra krameri, 152, 154, 155 Upeneoides bensasi, 85 Urosalpinx cinereum, 391 Urticinopsis, 14

v Varicorhinus, 1 1 2, 133 capoeta sevangi, 116, 125 heratensis, 1 1 6 tanganicae, 1 16

X Xenocharax spilurus, 114 Xenocypris, 112, 133 Xiphophorus helleri, 74, 75, 293

Z Zenarchopterus, 3 12 Zoarces, 195 anguillaris, 190

Subject Index A Aboral feeding, echinoid, 14 Aboral spines, echinoid, 45, 46 Absorption efficiency, food, 202, 203 Acclimatation temperature, fish, 261 Acetylcholinesterases, taste buds, in, 71, 72, 73 Acid phosphatase goldfish gut, in, 162, 163 teleost gut, in, 158, 162, 165, 208 Acipenserids, anadromous migration, 296 ACTH hormone, 287, 291, 294 Actinopterygii, tongue, 121 Action spectra, echinoid spine responses, of, 28, 29 Activity level, fish food consumption, and, 176, 177 Adductor muscle scar, oyster, 387 Adenohypophysis, migratory fish, function in, 290 Adhesive organs, taste buds, 77, 78 Adrenalin haematosis, effect on, 270 thyroid stimulation, 298, 300 Adrenergic drugs, teleost stomach, effect on, 171, 172 Adrenergic receptors, teleost stomach, 171, 172 Aggregation behaviour, ecliinoid, 45 Agranular endoplasmic reticulum, 140, 142, 144, 148 Alarm substance cells, 154 Algae, 112, 116, 117, 118 blue-green, 191, 201 echinoid food, as, 14 green, 201 Alimentary canal, teleost, 109 et seq. Alkaline phosphatases, teleost gut, in, 154, 155, 158, 162, 169, 208 Ambulacral spines, echinoid photic response, 39, 40, 45 423

American oysters distribution, 365, 366, 367, 368, 370 physiological races, 357, 365-370 spawning behaviour, 369 transplantation, 367 Amino acids, migratory fish attraction by, 319 Amoebocytes, melanin synthesis, 6, 11 Amphibiotic migration, 242, 280, 281, 282 Amphihaline crustaceans, migration, 260 Amphihaline fish, migration, 241 et seq.

Amphipods, 181, 186 Ampullary organs, 320 Amylase activity, gastric miicosa, 193, 194, 196, 197 Anabantids, taste buds, 79 Anadromous migration, 242 metabolism during, 272 osmoregulatory mechanisms during, 246 Anaerobic metabolism, migratory fish, 269 Anarrhichadids, hydrochloric acid secretion, 133 Anchovy lipid metabolism, 273 migration, 273, 274 vertical migration, 243 Anemone, 14 Anterior intestine, teleost, 152 Antigenic differences, oysters, 379 Antimetabolites, olfactory inhibition by, 317 " Anton Dohrn " vessel, 313 Apical plasma membrane, teleost, 147, 148 Apical processes, 57, 59 receptor cells, of, 59, 60 Apogonids, 45 mouth, 121

424

SUBJECT INDEX

Arginine-vasotocine hormones, 303 A.R.N. hormone, 301 Asteroids, 1 Asthenia, eels, 252 Atlantic ocean, electric field, 321 Atlantic salmon-see Salmon Ampulae of Lorenzini, 91 Attractive chemical substances, migratory orientation by, 318, 319 Audition, migratory orientation by, 322 Auerbach’s plexus, 170, 172 Australian oysters genera, 358 hybridization, 385 Avoidance reactions, migratory fish, 269 A.V.T. hormone, 304, 305 Ayu, migration, 292

B Barbel taste buds, 55, 56 distal parts, on, 78 SEM micrographs, 59 shape, 56 structure, 58, 59, 60 Basal cells, taste bud, 56, 57 cytoplasm, 67 frog, of, 68, 69 histochemistry, 7 1 mitochondria, 67 rat, of, 68 secretory material, 154 shape, 67 stimulation, 69, 70 structure, 145 vesicles, 67 Basement membrane, taste bud, 67 Bass digestion rate, 181, 182, 183, 185, 189 food consumption, 176 Bay scallop, 365 Benton visual retention tests, 295 Bio-ecology, oysters, 360-361 Biological clock, 300, 311, 313 Bioluminescence, 310 Bivalve molluscs, speciation, 357 “ Becherformige Organe ”, 54

Blennies amphibiosis, 281 stomach, 133 thyroid function, 281 Blood freezing point, 246 iodine content, 277, 278 mineral composition, 256 Bluefin tuna body temperature, 264, 265 salinity effect, 246, 247 thermoregulation, 264, 265, 266 Bluegill sunfish digestion rate, 181 food consumption, 174 gastric mucosa, 194, 196, 199 specific dynamic action, 204 Bluntnose minnows-.see Minnows Body size, digestion rate, effect on, 186, 187 Body temperature, migratory fish, 263, 264, 265, 266 Brain, teleost diencephalon, 86 feeding behaviour, and, 88 mesencephalon, 86 metencephalon, 87 myelencephalon, 87 olfactory organs, 85, 86 telencephalon, 85-86 thalamus, 86 vagal lobe, 87 Brain temperature, thermoregulation, and, 226 Bream, intestine, 138 British cyprinids, brain pattern and feeding behaviour, 88 Brook trout digestion, 202 food consumption, 175, 177, 204 gastric mucosa, 194, 199, 200 Brown bullheads, taste buds, 81 Brown trout digestion rate, 183, 185 gastric mucosa, 199 growth rate, 205 gut peristalsis, 185 Buccal cavity, teleost, 119-126 Buccal valves, teleost, 120 Bucco-pharynx, teleost, 120, 121

SUBJECT INDEX

Bullhead digestion rate, 181 food consumption, 177 gastric mucosa, 198, 200, 201 Burbot, 198

C Caeca, teleost, 149, 151, 155 adrenergic receptors in, 172 secretory material, 155, 164 Caecal epithelium, teleost, 165 California oysters-see Oysters and Ostrea lurida Calorific value, food, 202 Carbohydrases, 193-1 94 Carbohydrate digestibility, 202 6-Carboxyisoxanthopterine,migratory fish attraction by, 319 Carp barbel taste buds, 56, 64, 69 brain, 87 digestion rate, 182, 198, 201 food absorption, 201 food consumption, 174, 179 gastric mucosa, 194, 195, 196, 197 oro-pharyngeal cavity, 75, 77, 87 palatal chemoreceptors, 314 taste buds, 54, 69, 75, 82, 85 Caspian roach, 118 digestion rate, 180 Catadromous migration, 242 osmoregulatory mechanisms during, 251 Catfish electroreception, 91 facial nerve, 83 hydrochloric acid secretion, 133 nasal barbels, 314 olfactory reception, 89, 317 taste buds, 59, 75, 78, 80, 82, 83, 85, 89 taste reception, 54, 89 Catostomids brain, 87, 88 cerebellum, 87 digestive apparatus, 111 facial lobe, 83 palatal organ, 121 taste buds, 79

425

Caudal neurosecretary system, migratory fish, 305 Celestial bodies, migratory Orientation by, 313 Cells, taste bud basal, 56, 57, 67-70 dark, 57 Golgi apparatus, 57, 63 light, 57 receptor, 56, 57, 59-65 sensory, 54, 55 shape, 57, 73 supporting, 56, 57, 61, 65-67 Cerebellum, teleost brain, 87 Channel catfish, digestion rate, 182 Chanoids, pyloric stomach, 131 Characinoids feeding habits, 112, 114, 125 gill rakers, 125 gut length, 112, 114 pyloric stomach, 131 stomach structure, 114 Chemical reception, migratory orientation by, 314-320 Chemical senses, fish, 55 Chemoreception, predator-prey relationship, in, 90 Chemoreceptor cells palatal organ, in, 79, 80 sensitivity, 80 teleost, 145 Chewing pad, teleost, 124, 125 Chinook salmon, 193 memorization processes, 301 olfactory orientation, 317 Chloride secreting cells, 253, 255, 256, 258 Chromaffin activity, 306 Chromatocytes, see Chromatophores Chromatoglyphs, 9 Chromatophores bodily displacement, 8, 11 degeneration, 9 echinoid, 10 effector mechanism, 11 histology, 9 humoral control, 11 melanin in, 6 nervous control, 11 pigment dispersion, 28, 29

426

SUBJECT INDEX

Chromatophores-continued properties, 8, 11 receptor mechanism, 11 response to light, 6 , 7, 8, 9, 10, 11 Chromosomes, oyster, 361, 362, 363, 364, 369, 379

Cichlids feeding habit adaptation, 111 gut length, 112 mouth, 120, 121 stomach, 133 Circulation, migratory fish, 270 Cladocera, 118 Club cells digestive tract, in, 154 ostariophysous fish, in, 144, 153 secretory material, 153, 154 skin, in, 144, 153 Clupeoidei, pyloric stomach, 131 Clypeastridei, migration, 2 Cobitids palatal organ, 121 stomach, 133 taste buds, 79 Cockscomb oysters-see Oysters Cod body temperature, 258, 259 chloride secreting cells, 258, 259 digestion rate, 181 exploratory organs, 83 feeding habit adaptation, 111 gastric mucosa, 194, 195 ionic regulation, 244, 258 limiting temperature, 259 migration, 257, 286 mortality, temperature effects on, 25Y, 262

olfactory orientation, 319 osmoregulation, 244, 257, 258 spawning, 258 taste buds, 82 thyroid function, 286 Coefficient of food utilization, 203 Coho salmon growth rate, 205, 207 hypophysis, 290 olfaction, 315, 316 Colour change, echinoderms, 5--12 Columnar cells, intestine, 135

Communis system, 54 cranial nerve, of, 82, 83 gustatory fibres, 83, 84 Conditioned behaviour, hormone function, 295 Copepods, 243 nauplii, 186 Coral, 122 Coregonids, mouth, 119 Corticotrope cells, 290 Cortisol adaptation to sea water, effect on, 288

lipid transformation by, 289 pigmentation, effect on, 288 Cottids, gastric mucosa, 199 Covering habit, urchins, 13, 14, 15, 16, 17, 19

Crab, 45 Cranial nerves, 314 facial, 82, 87 glossopharyngeal, 82, 84, 85, 87, 89 vagus, 82, 84, 85, 87, 89 Crappie, 191 Crassostrea generic diffcrences froin Ostrea, 359365

hybridization, 382, 383 non-tuberculated estuarine forms, 386

tuberculated marine forms, 386 Crassostrea gigas hybridization, 383 speciation, 375-381 Crassostrea virginica geographic speciation, 365, 373-374 hybridization, 383 physiological races, 365-370 Crayfish, 186 Cross-fertilization, oysters, 383 Crustaceans, neural photosensitivity, 43

Cubanian roach, 118 Current, rheotropic response to, 308 Cushing syndrome, 331 Cutaneous taste bude, 82, 83 Cyanophil cells, 290 Cyclostomes, 167 osmoregulation, 24 5

427

SUBJECT INDEX

Cyprinids alimentary canal, 133, 208 brain pattern and feeding behaviour, 88

carnivorous, 133, 134 classification based on diet, 110 digestive apparatus, 11 1 feeding habits, 112, 116, 117 gut, 155 gut length, 112, 116, 117 intestinal mucosal epithelium, 166, 208 paaatal organ, 121 stomachless, 133, 134 taste buds, 79, 83 Cyprinodonts, brain pattern and feeding behaviour, 88 Cytochemistry, alimentary canal, 151169, 208 Cytogenetics, oysters, 358, 359 Cytology, oysters, 361-365

D Damsel-fly, 184 Darters, 186 Defaecation, digestion rate determination by, 180, 210 Defensive mechanisms, echinoid, 45 Denatant migration, 307 Denticulated oysters, 385 " Dermal light sense ", echinoid, 22 Detritus, 80, 112, 116, 124 Development, taste buds, 75-82 Diadematid urchins colour change, 11 reproductive process, effect of light on, 42 Diatoms, 117, 126, 201 Diencephalon, teleost brain, 86 Diet, digestive enzyme relationship, 1YG198

Dietary components, digestion rate, effect on, 186 Digestibility, calculation, 201, 21 1 Digestion coefficient, derivation equation, 201 Digestion rate, fish, 180-189, 210 temperature, effect of, 199, 200, 201

Digestive enzymes, teleost, 189-198, 210 Digestive tract feeding habit, and, 112, 113 innervation, 171 Dioecious oysters, 360, 361 Dispersal, oysters, 360 Diuresis, migratory fish, 270 Diurnal rhythm, echinoid, 41, 44 physiological colour change, of, 8 Dogs conditioned behaviour, 295 gastric secretion control, 198

E Earthworms, 175, 186 Echinochrome, 5 , 6, 11, 28 photoreceptive function, 29 spectral absorption, 29 Echinoderms colour change, 5-1 2 movement of whole animal, 2-5 photosensitivity, 1 et seq. pigmentary system, 5-12 podia1 responses to light, 12-19 sensory adaptation, 2 spine responses to light, 19-41 Ectodermal genesis, taste buds, 75 Eggs, oyster, 360 Eels adaptation mechanisms, 289 adenohypophysis function, 290 amphibiosis, 281 anadromous migration, 248 asthenia, 252 blood chloride content, 252 catadromous migration, 251, 252, 253, 282, 328 chloride secreting cells, 253 electro-orientation, 320, 321 gastric mucosa, 194, 196 gonadotropic activity, 297 haemoglobins, 268 homing, 318 interrenal function, 289 intestinal epithelium, 149, 167 intestine mucosa, 168 ionic regulation, 244, 252, 253 lunar rhythm, 325, 326

428

SUBJECT INDEX

Eels-continued magneto-orientation, 322 marine life, preparation for, 253 metamorphosis, 248 mid-gut, 135 muscularis mucosa, 171 olfactory orientation, 317, 318 osmoregulation, 244, 248, 252 prolactin secretion, 293 reproductory migration, 313 retina coloration, 254 sense of direction, 307 sex distribution, 285 smell sense, 315 Stannius corpuscle function, 298, 299 stomach innervation, 171 swimbladder, 254 thermoreception, 3 10 thyroid function, 280, 282, 283 urophysis, 305 visual pigmentation, 281 " Einkornzellen ", 145 Elasmobranchs electroreception, 91 olfactory reception, 90 osmoregulation, 246 taste buds, 77, 89 taste reception, 89 Electric fields, migratory orientation by, 320, 321 Electron microscopy taste buds, of, 57, 59 alimentary canal, of, 140-151 Electroreception, fish, 310 migration orientation by 320-324 Electroreceptors, 91 Electrosensitive fish, 321 Elvers fresh water attraction, 249, 250, 251 geomagnetic orientation, 322 migration, 250, 283, 292 osmoregulation, 248, 249, 250, 251 prolactin function, anadromous migration, in, 292 sex distribution, 284, 285 thyroid function, 283, 284 Endocrine glands, migratory fish, 276300, 330, 331 nervous system influence on, 302

Endocrine hyperfunctionings, migratory fish, 330, 331 Endodermal genesis, taste buds, 75 Endogenous rhythm, migratory fish, 261 Energy balance, fish, 202, 203 Enterochromaffin cells, 167 Enterokinase activity, gastric mucosa, 196 Electrophoresis, gastric mucosa, 190 Enzyme activity, teleost gut, in, 158, 159, 160, 161 Eosinophilic inclusions, teleost miggut epithelium, in, 165, 166 Epibranchial organs, teleost, 122, 123 innervation, 169 Epiphyses, migratory fish, 306 Epithelial cells, echinoid, 43 Esterase activity, gastric mucosa, 195 Estuarine oysters, 360 European eels-see Eels European flat oyster distribution, 370 physiological races, 370-371 spawning behaviour, 371 European salmon catadromous migration, 254 chloride secretory cells, 255, 256 euryhalinity, 254 ionic regulation, 254 osmoregulation, 254 smoltification, 254 See also Salmon Euryhaline fish diuresis, 270 preoptic nucleus bioelectric activity, 303 Euryhaline oysters, 360 Euryphags, 110, 207 Evolution migratory fish, 330, 331 oysters, 382 Excretion, migratory fish, 270-271 Exogeneous rhythm, migratory fish, 261 Exopeptidase activity, gastric mucosa, 195

429

SUBJECT INDEX

F Facial nerve, 82, 83, 169 acoustico-lateralis system, 82 communis system, 82, 83 ramus lateralis accessorius, 83 transection, 85 Faeces, digestion rate determination by, 180 F a t absorption, teleost intestine, 166, 167 F a t digestibility, 202 Fats digestion rate, effect on, 186 digestive tract, in, 194, 195 Feeding action, teleost, 119 Feeding habits, fish brain pattern, and, 88 Feeding habits, teleost, 109, 207 Feeding rate, fish, 206, 209 Feeding reaction time, fish, 180 Feeding rhythm, echinoid, 41 Fertilization, oyster, 370, 374 Fibrils, pigment cells in, 9, 10, 11 Filter apparatus, teleost, 125 Fins, taste buds, 77, 79 Fish classification based on diet, 110 digestion rate, 180-189 digestive enzymes, 189-198 feeding habit adaptation, 110, 111 food consumption, 172-180 Flounder, 194 Fluorescent nerve fibres, 171 Food, teleost, 109-118 absorption and conversion, 201-207 intake, 172-180 Food absorption and conversion, fish, 201-207 Food consumption, fish, 172-180, 209 activity level, and, 176, 204 digestibility, and, 177 direct measurement, 17 2 field method estimation, 173 growth rate, and, 174 hunger level, and, 179 indirect measurement, 173, 174 " maintenance requirement," 174, 175, 176 nutritional state, and, 179

Food consumption, fish-continued radio-isotopic measurement, 174 regulating mechanisms, 178 seasonal fluctuations, 176 size, and, 177 temperature dependence, 174, 175, 179, 204 Force-feeding, fish, 182 Foregut, teleost, 151, 179 " Formas ", oyster, 372, 373, 374 Fluvial anadromous migration, osmoregulation in, 247, 248 Freshwater attraction, elvers, 249, 250, 251 Freshwater teleosts, osmoregulation, 245 Fright reaction, 144 Frogs metamorphosis, 248 taste buds, 68, 69 visual pigmentation, 282 Fuchsinophil cells, 291

G Gadoids intestine, 134 thermoreception, 309 Gametes, oyster, 361 cross incompatibility, 382 Gammarids, 186 Gar digestion rate, 181 food consumption, 176, 177 Gastric acid, teleost gut, in, 157 Gastric emptying, 183, 184, 185, 186, 189, 210 Gastric epithelium, teleost, 130, 153 fat absorption, 167 secretory material, 154 Gastric glands, teleost, 130, 153, 207 secretory material, 166 Gastric mucosa, teleost, 146, 147, 189 secretion control, 198-201 Gastric proteases carbohydrases, 193-194 lipase, 194-195 pepsin, 190-192 trypsin, 192-193

430

SUBJECT INDEX

Gastric secretion, regulation, 198-201, 210 Gastric teleosts, 132 Gill rakers feeding habits, and, 125 taste buds, 80 Gizzard, teleost, 131 mucoid plaque, 152 Genes, oyster, 363, 369 Genera, oysters, 358-359 Generic differences, oysters, 359-365, 379, 385-389 Genetics, oysters, 358 Genital maturity, anadromous migration, and, 296 Geographic speciation, oyster, 365, 373-375, 390, 391, 392 Geomagnetism, migratory orientation by, 322 Germ layer origin, taste buds, 75 Germon, thermoreception, 309 Gill arches, taste buds, 75 Gills, oyster ciliary activity, 369 Glossopharyngeal nerves, 82, 84, 85, 87, 89, 169 Glucid metabolism, migratory fish, 275, 289 Gluconeogenesis, 276, 287 Glycogen, taste buds, in, 71, 72, 73 Glycolytic enzymes, 275 Goat fish, 85 Great Plains minnow, taste buds, 78 Gobies pharyngeal organs, 124 thyroid function, 281 Goblet cells caeca, in, 151 intestine, in, 134, 135, 137, 149, 150, 151, 152 mucus, 151 oesophagus, in, 143 145, 152 oral epithelium, in,l 43 rectum, in, 137, 138, 139, 151 Goldfish brain, 87 chemoreception, 90 digestion rate, 180 food consumption, 175, 178, 179 gastric mucosa, 193, 194, 195, 196

Goldfish-continued intestine, 148, 149, 162, 163, 171 memorization processes, 301, 302 polarotaxis, 312 preoptic nucleus bioelectric activity, 303 prolactin secretion, 294 Golgi apparatus, 57, 63, 66, 144, 145, 149, 167 Gonadatropic hormones, migration, function in, 290, 295, 296, 297 Granular cells, digestive tract, in, 168, 169, 208 Grass carp, 193 Growth, fish efficiency, 204 energy requirements, 202, 203 gross rate, 206 hormones, 300 oxygen concentration, effect of, 205 rate, 174 seasonal variations, effect of, 205 thyroid function, and, 284 " Growth acclimation ", fish, 204 Grunion, amphibiotic migration, 242 Gryphaeidae genera, 359 promyal chamber, 388 Gudgeons, intestine, 115 Gurnards, taste buds, 79 Gustatory cells-see Receptor cells Gustatory fibres dorsal branch, 84 hyoid ramus, 84 hyomandibular trunk, 84 identification, 83, 84 infraorbital trunk, 84 mandibular ramus, 84 meningeal ramus, 84 ophthalmic ramus, 84 otic ramus, 84 posterior palatine branch, 84 pretrematic branch, 84 Gustatory system, fish, 53 et seq. Gut capacity, food consumption, and, 178, 179 Gut length, feeding habit, and, 112. 113, 114, 207 Gymnotids, electroreception, 91

431

SUBJECT INDEX

H

I

Haemoglobins, preadaptation to res- Iliophagous fish, feeding habit adaptapiratory function, 268 tion, 111 Incompatibility genes, oyster, 382 Hake, taste buds, 79 Incubatory genera, oyster, 388, 389 Haplocarotenoid proteins, 44 Index of feeding behaviour, 110 Head gut, taste buds, 74, 75, 80 Helmet conch, defensive mechanisms, Indian cyprinids, brain pattern and feeding behaviour, 88 45 Innervation Hermaphrodite oysters, 360 taste buds, 82-85, 169 Herring teleost alimentary canal, 169-172 contranatant migration, 308 Insulin secretion, 300 denatant migration, 308 Interrenal, migratory fish, 287-289, digestion rate, 183, 186 291 olfactory orientation, 319 Interspecific hybridization, oyster, 382 vertical migration, 243 Intestinal bulb, teleost, 134 Hind-gut, teleost, 163 functions, 139, 140 Hiroshima oysters-see Oysters and innervation, 17 1 Craasostrea gigas Intestinal caeca, teleost, 139, 149 Histochemistry Intestinal epithelium, teleost, 150, 166 alimentary canal, 151-169, 208 Intestinal microvilli, teleost, 163 taste buds, 71 Intestinal mucosa, teleost, 135, 164, Hokkaido oysters-see Oysters and 208 Crassostrea gigas Intestine Holohaline fish gastric fish, in, 134 migration, 257, 286 stomachless fish, in, 134 thyroid function, 286 Intestine, teleost, 134-137 Homing, migratory fish, 291, 295, 301, adrenergic receptors in, 172 306, 318, 319 age-related changes, 115, 118 Hormonal control, gastric secretion, basement membrane, 150 199 fat absorption, 166, 167 Hunger, fish, 179, 210 innervation, 170 Hybridization, oyster, 358, 359, 379, lamellar structures, 148 382-385 mucosal ridges, 147 closely related species, 383-384 peristaltic movement, 172 distantly related species, 384-385 seasonal changes, 115, 118 Hydrochloric acid, teleost gut, in, 155, secretory material, 155 156, 157 starvation-related changes, 138 Hydroids, 14 structure, 148, 149, 150 7-Hydroxybiopterine, migratory fish Intestine length attraction by, 319 feeding habit, and, 112, 114, 115 Hyperthyroidism, 280, 282, 287, 301 sexes variation, 115 species variation, 112, 115 Hypertonic environment undigestible material in diet, and, euryhalinity towards, 278 115, 118 osmoregulatary mechanisms in, 245, Intraspecific hybridization, oyster, 382 248, 249, 250 Ionic regulation, 245-260 Hypophysis, migratory fish, 289, 304 Hypothalmic neurosecretion, migra- Iridophores, echinoid, 46 tory fish, 302, 303 Isotocine hormones, 303

432

SUBJECT INDEX

J

L

Light microscopy, taste buds, 56-57, 65, 66 Light response, echinoderms, 1 et seq. Lipase, 194-195 Lipid metabolism, migratory fish, 272, 273, 274, 289 Lipolytic activity, gastric mucosa, 194, 195, 197 Lips taste buds, 79 teleost, 120 Liver, teleost age-related changes, 115, 118 seasonal changes, 115, 118 Loach, taste buds, 78 Location, taste buds, 75-82 Locomotion, echinoid response to light, 16, 17, 19, 14, 45 rhythm, 41, 45 Long finned tunnies-see Tunnies Loricarids, alimentary canal, 133 Lunar light cycle, migratory orientation by, 325 Lymphocytic wandering cells, 169

Labrids feeding mechanism, 120, 208 gastric mucosa, 195 Lamellar organ, taste buds, 79 Lamina propria, innervation, 171 Lamnid sharks lateral rete, 264 thermoregulation, 264 Lantern muscles, echinoid, 25, 41 Largemouth bass digestion rate, 182 food consumption, 177 growth rate, 205 gastric mucosa, 193, 194, 195, 196 Larvae, echinoderm aggregation, 5 distribution pattern, 4 light response, 3, 4, 5 migration, 3, 4, 5 Larval incubation, oyster, 361 Lateral rete, migratory fish, 263, 264 Leptocephalus larva, eel, 248 Leucine minopeptidase, teleost gut, in, 164, 165 Life cycle, osmoregulation modification during, 247

Mackerel gastric mucosa, 193, 194, 195, 196 migration, 259 osmoregulation, 259, 260 respiratory function, 267 Macrourids, intestine, 134 Maintenance requirement, food consumption, of, 174, 175, 176 Magnetic fields, migratory orientation by, 322 Magnetoreception, migratory orientation by, 320, 324 Mammalian taste buds, 68, 70 Mammals digestion rate, 183 gastric secretion control, 198, 199 olfactive channel, 315 Man attention processes, 295 digestion rate, 183 gastric mucosa, 190 Mangrove oyster--aee Oysters Marine ayu, 196

Japanese Islands, oyster speciation in, 375, 376 Japanese oysters-see Oysters and Crassostrea gigas Japanese silver eels-see Silver eels

K Karyotypes, oyster, 364 Kelt, thyroid function, 280 Killifish digestion rate, 186 gastric mucosa, 195, 196 King salmon, 132 " Kopfdarm ", teleost alimentary canal, 118 Kumamoto oysters-see Oysters and Crassostreagiga.s

M

SUBJECT INDEX

Marine fish, migration, 241 et seq. Meal size, digestion rate, and 185, Mealworms, 186 Meiotic prophase, oyster oocytes, 361 Meissner’s plexus, 170, 171 Memorization processes, migratory fish, 291, 295, 301, 317 Mended fish catadromous migration, 279 preoptic nucleus bioelectric activity, 304 thyroid function, 280, 283 Menhaden, 193, 195 Mesencephalon, teleost brain, 86 Metabolic heat, migratory fish, 263 Metabolic rate, fish, 206, 211 Metabolism, migratory fish, 272-276 Metacentric chromosomes, oyster, 364, 365, 379 Metamorphosis osmoregulation, and, 248 thyroid activity during, 248, 283 Metazoan, photoreceptive neurons, 43 Metencephalon, teleost brain, 87 Meteorological conditions, migratory orientation by, 325 Mette’s tubes, 182 Mexican characins, taste buds, 77 Mice conditioned behaviour, 295 hypothalmic neurosecretion, 303 Microbenthos, 124 Microphags, 112 alimentary canal, 133 intestinal bulb, 134 mud-feeding, 133 stomach, 133 Mid-gut, teleost, 135, 163, 165, 166, 189 Migration, marine and amphihaline fish, 241 et seq. caudal neurosecretory system function, 305 chemical reception function, 314-320 circulation function, 270 classification, 241 electroreception function, 320-324 excretion function, 270-271 hypophysis function, 289 interrenal function, 287-289 ionic regulation effect, 245

433

Migration, marine and amphihaline fish-continued magnetoreception function, 320-324 metabolic function, 272-276 nervous system function, 300-306 osmoregulation effect, 246 pineal organ function, 306 preoptic nucleus function, 303, 304 reproductive function, 271-272 respiratory function, 267 rheotropism function, 307-308 sense organs function, 306-324 thermopreferendum effect, 260 thermoreception function, 308-3 10 thermoregulation effect, 260 thyroid function, 276-287 urophysis function, 305 vision function, 310-313 Migration, oysters, 360, 387 Mineral composition, blood, 256 Minnows, 175, 182 facial lobe, 83 olfactory orientation, 316 taste buds, 73, 77, 83 Mitotic interphase chromosomes, oyster, 361, 362, 363 Miyagi oysters--see Oysters and Crassostrea gigas Molluscs geographic speciation, 391 photosensitivity, 22, 34, 43 Monoamine oxidase, taste buds, in, 71, 72, 73 Monophags, 110, 207 Moon compass mechanism, migratory orientation by, 312 Moray eels, touch reception, 92 Mormyrids, electroreception, 9 1 Morpholine, olfactory stimulation by, 317 Morphological colour change, urchins, 5, 6 Motor activity, thyroid function, 278, 282 Mouth, teleost, 119-126, 207 mucous cells, 153 M.S.H. hormone, 294, 295 Mucopolysaccharides, 152, 153, 154, 155, 169 Mucoproteins, 152

434

SUBJECT INDEX

Mucous epithelium, 151 Mucus, teleost, 151 et seq. Mugiloids, pyloric stomach, 131, 139 Mullets pharyngeal organs, 124 prolactin secretion, 293 thyroid function, 283 " Muskulose Faserzelle ", 66 Mussels, chromosomes, 364 Myelencephalon, teleost brain, 87 Myxinoidea, osmoregulation, 245

N Nerve cells, teleost digestive tract, in, 170, 171 Nerve supply, taste bud myelinated components, 70 unmyelinated components, 70 Nervous influx, conduction speed, 261 Nervous system echinoid, 46, 47 migratory fish, 300-306 Net growth efficiency, fish, 205 Neural photosensitivity, echinoid, 22, 43 Neuroendocrine system, migratory fish, 276-300 Neuroepithelial cells-see Receptor cells Neurohypophysial hormones, 303, 304, 305 Neuromasts, 54 Neurosecretion cells bioelectric activity, 303 migration, function in, 302 Non-electrosensitive fish, 320 Non-tuberculated oysters, 386 North American cyprinids, brain pattern and feeding behaviour, 88 Nucleic acids, taste buds, in, 71, 72, 7 3 Nutritive cells-see Supporting cells

0 Oesophageal epithelium, teleost, 145, 146 Oesophageal mucosa, teleost, 145 Oesophagus, teleost, 126-129, 207 adrenergic receptors in, 172

Oesopliagus, teleost-continued innervation, 171 mucous cells, 153 secretory material, 167 tunica muscularis, 150 Olfaction, migratory orientation by, 314, 315, 316, 317, 318, 319 Olfactory organs, 314 Olfactory receptors, 89, 90 Oligochaetes, 186, 188 Oligosaccharidase activity, gastric mucosa, 196 Olympic oysters-see Oysters and Ostrea lurida Oocytes, oyster, 361 Oral cavity, taste buds, 75, 77 Oral epithelium chloride cells, 140 goblet mucous cells, 143 surface layer cells, 143 taste bud, 56 teleost, 140, 143 Oral mucosa, teleost cells, 142 mucosubstances, 152 Origin, taste buds, 75-82 Oro-pharyngeal cavity, carp, 75, 77, 87 Oro-pharyngeal taste, 87 Osmoregulation, 245-260 Ostariophysous fish, club cells, 144, 153 Ostrea, generic differences from Crausostrea, 359-365 Ostrea edulis geographic speciation, 370 physiological races, 370-371 Ostrea lurida, geographic speciation, 374-375 Ostreidae genera, 358 hybridization, 382 promyal chamber, 388 Oxidative enzymes, 275 Oxygen concentration food consumption, effect on, 205 growth, effect on, 205 respiratory function, and, 269 Oyster drill, geographic speciation, 391 Oysters, speciation, 357 et seq.

SUBJECT INDEX

P Pacific native oysters-see Oysters and Ostrea lurida Pacific salmon-see Salmon Palade’s granules, 144 Palatal epithelium, teleost, 140 cells, 140, 141 Palatal organ, taste buds, 79, 84 Pancreas, teleost, carboliydrases secretion, 194 Paneth cells, 145 Pam, salmon blood composition, 256 chloride ion absorption, 256 Iiaematosis, 270 hypophysis, 290 illumination period, effect on, 326 paedogenetic cycle, 332 preadaptivo phenomenon, 255 serum osmolality, 255 thyroid function, 277 Pars nervosa, migratory fish, function in, 290 Parthenogenetic eggs, oyster, 384 “ Pear shaped ” cells, intestine, 136, 137, 150, 167 Pedicellariae, echinoid, 13 Pepsin, 190-192 Peptic activity, gastric mucosa p H effects, 190, 191 temperature effects, 190, 200 Perch, 182 alimentary canal, 133 digestion rate, 183 gastric mucosa, 191, 192, 194, 197 Periophthalmids, 281 Periphyton, 115, 116, 118 Peristaltic movement, teleost gut, 172, 185 Pctromyzontidae, osmoregulation, 245 PH peptic activity, effect on, 190, 191 tryptic activity, effect on, 192, 193 Phagocytic cells, digestive tract, in, 169 Pharyngeal glands, teleost, 122 Pharyngeal cavity, taste buds, 84 Pharyngeal organs, teleost, 123, 124 Pharyngeal teeth, teleost, 124, 125

435

Pharynx, teleost, 119-126 Phasic receptors, 01 Pheromones, 318 Photic response, echinoid primary spines, 38, 39, 45 Photography, digestion rate determination by, 183 Photoreception, echinoid integrative system, 29-41 spine rcflex, in, 20-29 Photoreceptive neurons, echinoid, 22, 43 Photoreceptive pigments, ecliinoid, 1 1 , 44 haplocarotenoid proteins, 44 spectral absorption, 26, 44 Photoreceptors, echinoid “ eyes ”, 20 nerve centres, 44 Photosensitivity, echinoderms, 1 et seq. Photosensitizing dyes, action in echinoids, 14 Phototaxis, urchins, 2, 3 Phylum evolution, migratory fish, 330 Physiological colour change, urchins, 6, 7 PhysioIogical mechanisms, migratory orientation, in, 324 Physiological races, oysters, 357, 36537 1 Phytoplankton, 116, 122, 201 Pigmentation interrenal function, and, 288 thyroid function, and, 279, 280 Pigmentary system, echinoid, 5-12 Pigments chromolipoid, 5 , 11 echinochromo, 5 , 6, 11 hydroxynaphthayuinone, 5 , 44 melanin, 5 , 6, 11 urchins, in, 5, 6 Pigs, gastric mucosa, 190 Pike gastric mucosa, 190, 191, 197 intest.ine, 138 oesophageal epithelium, 146 Pike perch, digestion rate, 183, 185, 188, 189 Pineal organ, migration, function in, 306

436

SUBJECT INDEX

Pinocytosis, 148 Piranha, food consumption, 175 Pit organs, 90, 91 Plaice digestion rate, 183 energy balance, 203 gastric mucosa, 190, 193, 194, 195, 196 olfactory orientation, 319 Plankton, 243 Planktonic larvae, oysters, 360 Pleuronectids, alimentary canal, 111 Podia, echinoid response to light, 12-19, 22 Podial ganglion, echinoid, 22, 24 Podial organ, echinoid, 22, 23, 24 Podial pit, echinoid, 22, 23, 24 epithelium lining, 27 superficial nerve layer, 24, 25, 26 Poikilotherms, digestion rate, 187 Polarotaxis, 312 Pollution, respiratory function, and, 269 Polychaetes, 186, 188 Polyzoans, 14 Pond loach, digestion rate, 180, 186, 188 Portuguese oysters--see Oysters Posterior intestine, teleost, 147, 148 secretory material, 165, 166 Potamodromous migration, 242 Prawns, 181, 184, 202 migration, 260 osmoregulation, 260 Preadaptation mechanisms, migratory fish, 256, 289, 303 Predators, echinoids, of, 45, 46 Predatory fish digestion rate, 183, 185 food consumption, 173, 174 Preoptic nucleus, migratory fish, function in, 302, 303, 304 Primary spines, echinoid innervation, 38 photic response, 38, 39, 40 Prodissoconch shell, 358 Prolactin hormone anadromous migration, function in, 291, 292, 293 nervous system, function in, 302

Prolactin hormone-continued thalassotocous migration, function in, 293 Promyal chamber, oyster, 360, 361, 387, 388 Protein digestibility, 202 Proteins, taste buds, in, 71, 72, 73 Proteolytic activity, gastric mucosa, 191, 192, 197 Protid metabolism, migratory fish, 276, 289 Puffer, 193 Pumpkinseed, food consumption, 177 Pyloric caeca, teleost, 139, 207, 208 enzyme secretion, 189 epithelium, 166 horizontal longitudinal section, 158, 159, 160, 161 secretory material, 158, 159, 160, 161 Pyramid lake sucker, taste buds, 78

Q Quahog clam, geographic speciation, 391

R Radial nerves, echinoid electrical stimulation, 30, 31, 32, 33 light response, 20, 21, 22, 30, 38, 39, 40 photosensitive elements, 20, 21, 22, 43 temperature response, 40 spatial interaction, effect of light under, 34, 35, 36 spectral sensitivity, 26, 27, 28 structure, 25 Radio-isotopes, food consumption determination, in, 174 Radiography, digestion rate determination by, 182 Rainbow trout digestion rate, 181, 185, 186 gastric mucosa, 193, 194, 195, 196 interrenal function, 287 intestine, 149, 193 olfaction, 316 swimming activity, 306

437

SUBJECT INDEX

Ramus laterals accessorius, 83 Rats conditioned behaviour, 291, 295, 327 taste buds, 67, 68, 70 Rayleigh scattering, 46 Rays, taste sense, 89 Reactionary adjustment, migratory fish, 262 Receptor cells, taste bud, 56, 57 apical process, 59, 60, 61, 144 chemoreceptive activity, 63 Golgi apparatus, 63, 144 histochemistry, 71 infranuclear cytoplasm, 64 secretory material, 154 shape, 59 structure, 144 supranuclear cytoplasm, 63 tubular structures, 60, 63 types, 144 vesicles, 60, 64, 65 Receptor pigment, echinoid, 44 Rectum, teleost, 137-140 enzyme activity, 161 Red muscle, metabolism, 265, 266, 267, 270, 275 Red Sea bream, 196 Red tuna, 244 Red tunny, thermoregulation, 264, 266 Reproductive activity, echinoid, 41, 42 Reproductive isolation, oyster, 370, 375 Reproductive migration, 242, 271-272 Respiratory enzymes, 275 Respiratory function, migratory fish, 2 6 7-26 9 Rheoclines, 310 Rheotropism migratory orientation by, 283, 307308 thyroid function, and, 283, 284 Rhythmic activity, echinoid, 41-42 R.N.A., learned behaviour, function in, 301, 317 Roach feeding habits, 118 food consumption, 175, 179 intestine length and undigestible matter, 115, 118 Rock bass, food consumption, 177

Rosefish, 193 Rotatoria, 118 “ Rumfdarm,” canal, 118

teleost

alimentary

S Saccostrea cuccullata, speciation, 381382 Salarids, 281 Salinity migratory orientation by, 246, 247, 250, 251, 257, 314 Salinity preference oysters, 360, 367 thyroid gland induction, 291 Salivary neurotoxin, 45 Salmon anadromous migration, 247, 267, 275, 295, 296, 325, 327 anaerobic metabolism, 269 annual spawning rhythm, 327 catadromous trophic migration, 254, 311 circulatory function, 270 epiphyses, 306 external chemoreceptors, 80 feeding habits, 125, 138 gastric mucosa, 196 gill rakers, 125 gonadotropic activity, 296 granular cells, 169 haemoglobins, 268 halotropism, 314 homing, 307, 315, 318 hypophysis, 290, 291, 292 intestine, 138, 162, 169 ionic regulation, 244, 246 memorization processes, 301 metabolism, 275 olfactory orientation, 315, 316, 317, 319 osmoregulation, 244, 245, 246, 247, 249 palatal organ, 121 pigmentation, 279 preadaptation mechanisms, 256 preoptic nucleus bioelectric activity, 303, 304 prolactin secretion, 293

438

SUBJECT INDEX

Salmon-continued spawning, 138, 139 stratum compactum, 132 taste buds, 79 thyroid function, 277, 279, 285 vision, 311 visual pigment modification, 328 Sardine metamorphosis, 286 thyroid function, 286 Satiety, fish, 179 Scanning electron microscopy, barbel taste buds, of, 59, 62 Schwann cell, 67 ‘‘ Scope for growth ” fish, 203, 204 Scototaxis, urchins, 45 Sculpins, growth rate, 205 Scup, 195 Sea lamprey anadromous migration, 246, 247 blood freezing point, 247 osmoregulation, 245, 246, 247 Sea trout, thyroid function, 285 Searobins gastric mucosa, 193, 195 taste buds, 79 touch reception, 92 Seasonal rhythm, echinoid, 44 Seasons, growth rate, effect on, 205,206 Secreting cells, teleost, 145, 146, 147 Selachians osmoregulation, 245 thermoregulation, 267 Self-fertilization, primitive oysters, 382 Semispecies, oyster, 375-382 Sense of taste, 54 Sense organs, migratory orientation by, 306324 Sensory cells cylindrical, 55 filiform, 55 See also Receptor cells Sensory receptors, 53 Serotonin, taste buds, in, 71, 72, 73 Sex distribution, fish coastal waters, in, 284, 285 thyroid function, and, 284 Sexual activity, echinoid, 42 Sexual hormones, migration, function in, 295, 296, 297, 298

Shad anadromous migration, 272 homing, 307, 315 lipid metabolism, 272, 273 osmoregulation, 245 Shadow response, echinoid, 27, 28, 29 electrical inhibition, 32, 33 illumination period, effect of, 34 inhibitory threshold, 36, 37 latent period, 36, 37 light inhibition, 30 light intensity changes, effect of, 34 nervous mechanism, 36, 46 Sharks body temperature, 261 chemoreception, 90 electroreception, 91 olfactory reception, 90 taste reception, 77, 89, 90 Sheat fish, digestion rate, 183 Shell, oyster, 361, 386, 387, 389 Sheltering habit, echinoid, 46 Shiners, 182 Shrimps, 45, 181, 182, 184, 188 migration, 260 osmoregulation, 260 Silurids alimentary canal, 133 electroreception, 91 innervation, 82 pharyngeal valve, 122 taste buds, 83 Silver eels amphibiosis, 280 asthenia, 252 catadromous migration, 253, 325 geomagnetic orientation, 322 hyperthyroidism, 301 interrenal function, 288, 289 lipid transformation, 289 metabolism, 274, 275 preadaptive phenomenon, 253, 254, 289 retina colour change, 254 salinity regulation, 253 thyroid function, 277, 280 Silvering, salmon interrenal function, and, 288 thyroid function, and, 277, 278

SUBJECT INDEX

Skin, echinoid photosensitivity, 25 spatial interaction, effect of light under, 34, 35, 36 Skipjack body temperature, 265, 266 brain temperature, 266 food consumption, 179 Smolt, salmon blood composition, 256 catadromous migration, 27 1, 274, 296 chloride ion absorption, 256 diuresis, 270, 271 haematosis, 270 migration, 257, 324 preadaptive phenomenon, 255 serum osmolality, 255 sympathicotonic behaviour, 306, 325 thyroid function, 277, 278 Smoltification blood composition, and, 256 illumination period, effect on, 326 interrenal function, and, 287 nervous system function, and, 300, 328 neurosecretion, and, 302 respiratory metabolism, and, 268, 269 thyroid function, and, 277 Snakes, digestion rate, 183 Sockeye salmon digestion rate, 182, 183, 187 food consumption, 176 growth rate, 206 migration pattern, 204 olfaction, 315 thermoregulation, 26 1 Southern range oyster speciation Crassostrea virginica, 373-374 Ostrea lurida, 374-375 Spawning echinoids, 42 oysters, 360, 369, 376, 377, 382 Speciation, oysters, 357 et seq. Specific dynamic action, fish energy loss through, 204, 205 oxygen consumption through, 205 Spectral absorption, echinochrome, 29

439

Spine reflex, echinoid action spectra, 28 directional movement, 38 electrical stimulation, 30, 31 integrative system, 29-41 light response, 15, 16, 19-41 photoreceptor identification, 20-29 spectral sensitivity, 26, 27, 28 spontaneous activity, 40 temperature response, 40 Sprats, 181, 196 Squid, 45 Stannius corpuscles, 271 nervous influx of, 261 migration, function in, 298, 299 Starry flounders,prolactin function, 292 Steelhead trout, 326 intestine, 162, 169 Stenohaline oysters, 360 Stenophags, 110, 207 S.T.H. hormone, 291 Sticklebacks, 278, 282 migration, 297 salinity preference, 291 Stomach disappearance in marine fishes, 133 motility, 185 Stomach, teleost, 129-134 contractive effects of drugs on, 171, 172 innervation, 170, 171 peptic activity, 190 relaxing effect of drugs on, 171, 172 sagittal section, 157 secretory material, 154, 156, 157, 167 transverse section, 156 Stomach contents, digestion rate determination in, 180-182 Stomachless teleosts, 132, 133, 171, 194, 208 Stone loach, taste buds, 79 Stratum compactum, teleost, 131, 132, 135, 169, 208 Stratum granulosum, teleost, 132, 208 Striped bass, food consumption, 176 Sturgeon catadromous migration, 274 taste buds, 78 vagus nerve, 85 vision, 311

440

SUBJECT INDEX

Sturgeon chub, taste buds, 78 " Stutzfibrillen ", 66 Submetacentric chromosomes, oyster, 364, 365, 379 Subspecies, oyster, 371-373 Sucker, brain, 87 Sun compass mechanism, migratory orientation by, 312 Sunfish, 181 digestion rate, 185, 186 gastric mucos, 191 growth rate, 204 Sunlight, echinoid locomotion stimulation by, 19 Superspecies, oyster, 375-382 Supporting cells, taste bud, 56, 57 apical process, 61, 65 basal portion, 64, 65 boundaries, 67 endoplasmic reticulum, 67 filaments, 66 function, 67 Golgi apparatus, 66 histochemistry, 71 infranuclear cytoplasm, 67 intracytoplasmic structure, 66 microvilli, 65 mitochondria, 67 ribosomes, 67 secretory material, 154 shape, 65 supranuclear cytoplasm, 66 vacuoles, 66, 67 Surmullet, digestion rate, 186 Sustentacular cells-see Supporting cells Sword-tails, head gut taste buds, 75 Sydney rock oysters-see Oysters and Saccostrea cuecullata Synapses, 65

T Tadpoles, metamorphosis, 248 Taste buds, 54 basal cells, 67-70, 144, 145, 154 development, 75-81 electron microscopic examination, 57 histochemistry, 71 innervation, 82-85, 169, 314

Taste buds-continued light microscopic examination, 56--57 location, 75-81 nerve supply, 70 origin, 75-81 receptor cells, 59-65, 144, 145, 154 schematic representation, 63 secretory material, 154 shape, 71, 73 size, 71 structure, 56-75 supporting cells, 65-67, 144, 145, 151 teleost, 125, 126, 145 vascular supply, 70-71 Taste receptors, 89, 90 Telencephalon, teleost brain, 85 Teleosts adrenal glands, 276 alimentary canal, 109 et seq. anadromous migration, 247 brain morphology, 85-89 chemoreception, 90 digestion, 109 et seq. ionic regulation, 260 osmoregulation, 245, 247, 2F0 phylum evolution, 330 respiratory metabolism, 269 taste buds, 75, 80 thermoregulation, 260 thyroid, 276 Temperature digestion rate, effect on, 187, 188, 199 food consumption, effect on, 174,175 gastric secretion rate, effect on, 199, 200, 201 migration, effect on, 258, 259 peptic activity, effect on, 192 Tench, gut, 166, 167, 171 Terminal taste buds, 54, 55 apical portion, 56 sensory cells, 54 shape, 56 Tethys Sea, 383, 392 Thalassodromous migration, 242 Thermogenetic capacity, migratory fish, 266, 267 Thermopreferendum, fish, 260-267 Thermoreception, migratory orientation by, 308-310

441

SUBJECT INDEX

Thermoregulation, fish, 260-267 Theutids, alimentary canal, 133 Three-spined stickleback, food consumption, 179 Threshold of taste, 73 Thyreotrope cells, 290 Thyroid migratory fish, function in, 277-287 osmoregulation control, 248, 259 preadaptation mechanisms, control by, 303 salinity preference, control by, 291 Time course, gastric digestion, 183, 184, 186 Tom-cod, taste buds, 79 Tongue, teleost, 121 innervation, 169 Tonic receptors, 91 Tonofibrils, 11 Touch corpuscles, 91, 92 Transparent fish, digestion rate, 183 T.R.H. hormone, 306 Trypsin, 192-193 Tryptic activity, gastric mucosa, 197 p H effects, 192, 193 Trophic migration, 242 Trout digestion, 186, 202 euryhalinity, 278 food consumption, 178 hyperthyroidism, 301 illumination period, effect on smoltification, 326 interrenal function, 287 intestine, 137, 149 osmoregulation, 246 salinity preference, 291 stomach innervation, 170, 171 thyroid function, 278 T.S.H. hormone, 278, 290, 296 Tuberculated oysters, 385, 386 Tunas body temperature, 261 capture, 244 electroreception, 310 food consumption, 179 thermoreception, 309, 310 thyroid function, 286 Tunnies body temperature, 263

Tunnies-continued lateral rete, 263 metabolic heat preservation, 263 muscle metabolism, 267 thermogenetic capacity, 266, 267 thermoreception, 309 thermoregulation, 264, 266 Turbidity, migratory orientation by, 330

U Ultra-violet radiation, ecliinoid locomotion stimulation by, 19 Urchins aboral feeding, 14 colour change, 3, 5 “covering” habit, 13, 14, 15, 16, 17, 19 light adaptation, 2, 3, 5 locomotion, 16, 17, 19 migration, 2 morphological colour change, 5 movement, 2 nervous organization, 43, 44 neural photosensitivity, 43, 44 photosensitivity, 3, 43, 44, 45 phototaxis, 2, 3 physiological colour change, 6, 7 pigmentary system, 5, 6 podia1 photosensitivity, 13, 15 reproductive activity, 41, 42 spawning rhythm, 42 spectral sensitivity, 27 Urine excretion, migratory fish, 270, 271 Urophysis, migratory fish, function in, 305 Urotensine, 305

V Vagus nerves, 82, 84, 85, 87, 89, 169, 171, 172 electrical stimulation, 172 gastric secretion, regulation by, 198, 199 Vascular supply, taste bud, 70-71 Venezuelan oysters-see Oysters Vertical migration, 243, 310

442

SUBJECT INDEX

Vision migratory orientation by, 313 schooling mechanisms, in, 313 urchins, of, 45 Visual pigmentation, thyroid function, and, 279, 281 von Uexkull’s Reflexrepublik, 1, 15, 46

w Walleyes, digestion rate, 186 Warmouth digestion rate, 181 food consumption, 176 “ Wechselsinneorgan ”, 55, 69 Weight loss, metamorphosis, in, 248 White bass, 191 White muscle, metabolism, 265, 266, 267, 275 Whitefish digestion rate, 180 food consumption, 173

X X-rays, digestion rate, determination by, 183

Y Yellow bullheads, taste buds, 81 Yellow eels, 252 adenohypophysis, 290 geomagnetic orientation, 322 interrenal function, 288 metabolism, 274, 275 pigmentation change, 288 retina colour change, 254 salinity regulation, 253 thyroid function, 277, 280 Yellowfin tuna, body temperature, 265 Yellowtail jack, 194, 196

Z Zooplankton, 117, 121 Zymogen granules, 134

Cumulative Index of Authors Allen, J. A., 9, 205 Ahmed, M., 13, 357 Arakawa, K. Y., 8, 307 Balakrishnan Nair, N., 9, 336 Blaxter, J. H. S., 1, 262 Boney, A. D., 3, 105 Bruun, A. F., 1, 137 Campbell, J. I., 10, 271 Carroz, J. E., 6, 1 Cheng, T. C., 5, 1 Clarke, M. R., 4, 93 Corner, E. D. S., 9, 102 Cowey, C. B., 10, 383 Cushing, D. H., 9, 255 Cushing, J. E., 2, 85 Davies, A. G., 9, 102 Davis, H. C., 1, 1 Dell, R. K., 10, 1 Denton, E. J., 11, 197 Evans, H. E., 13, 53 Fisher, L. R., 7, 1 Fontaine, M., 13, 248 Garrett, M. P., 9, 205 Ghirardelli, E., 6, 271 Gilpin-Brown, J. B., 11, 197 Goodbody, I., 12, 2 Gulland, J. A., 6, 1 Hickling, C. F., 8, 119 Holliday, F. G. T., 1, 262 Kapoor, B. G., 13, 53, 109

Loosanoff, V. L., 1, 1 Macnae, W., 6, 7 4 Marshall, S. M., 11, 57 Mawdesley-Thomas, L. E., 12, 151 Mauchline, J., 7, 1 Meadows, P. S., 10, 271 Millar, R . H., 9, 1 Millott, N., 13, 1 Moore, H. B., 10, 217 Naylor, E., 3, 63 Nelson-Smith, A., 8, 215 Nicol, J. A. C., 1, 171 Noble, E. R., 11, 121 Omori, M., 12, 233 Pevzner, R. A., 13, 53 Riley, G. A., 8, 1 Russell, F. E., 3, 256 Saraswathy, M., 9, 336 Sargent, J. R., 10, 383 Scholes, R . B., 2, 133 Shelbourne, J. E, 2, 1 Shewan, J. M., 2, 133 Sindermann, C. J., 4, 1 Smit, H., 13, 109 Sournia, A., 12, 236 Taylor, D. L., 11, 1 Verighina, I. A., 13, 109 Wells, M. J., 3, 1 Yonge, C. M., 1, 209

443

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Cumulative Index of Titles Alimentary canal and digestion in teleosts, 13, 109 Antarctic benthos, 10, 1 Artificial propagation of marine fish, 2, 1 Aspects of stress in the tropical marine environment, 10, 217 Aspects of the biology of seaweeds of economic importance, 3, 105 Behaviour and physiology of herring and other clupeids, 1, 262 Biology of ascidians, 9, 1 Biology of coral reefs, 1, 209 Biology of euphausiids, 7, 1 Biology of pelagic shrimps in the ocean, 12, 233 Biology of wood-boring teredinid molluscs, 9, 336 Blood groups of marine animals, 2, 85 Breeding of the North Atlantic freshwater eels, 1, 137 Circadian periodicities in natural populations of marine phytoplankton, 12, 326 Diseases of marine fishes, 4, 1 Effects of heated effluents upon marine and estuarine organisms, 3, 63 Estuarine fish farming, 8, 119 Fish nutrition, 10, 383 Floatation mechanisms in modern and fossil cephalopods, 11, 197 Gustatory system in fish, 13, 53 General account of the fauna and flora of mangrove swamps and forests in the Indo-West Pacific region, 6, 74 Interactions of algal-invertebrate symbiosis, 11, 1 Habitat selection by aquatic invertebrates, 10, 27 1 Learning by marine invertebrates, 3, 1 Management of fishery resources, 6, 1 Marine molluscs as hosts for symbioses, 5, 1 Marine toxins and venomous and poisonous marine animals, 3, 256 Methods of sampling the benthos, 2, 171 Parasites and fishes in a deep-sea environment, 11, 121 Particulate and organic matter in sea water, 8, 1 Photosensitivity of echinoids, 13, 1 Physiological mechanisms in the migration of marine and ampliikialine fish, 13, 248 Physiology of ascidians, 12, 2 Plankton as a factor in the nitrogen and phosphorus cycles in the sea, 9, 102 Present status of some aspects of marine microbiology, 2, 133 Problems of oil pollution of the sea, 8, 215 Rearing of bivalve mollusks, 1, 1 446

446

Cumulative Index of Titles

Respiration and feeding in copepods, 11, 57 Review of the systematics and ecology of oceanic squids, 4, 93 Scatological studies of the bivalvia (Mollusca), 8, 307 Some aspects of the bioIogy of the chaetognaths, 6, 271 Some aspects of neoplasia in marine animals, 12, 151 Some aspects of photoreception and vision in fishes, 1, 171 Speciation in living oysters, 13, 357 Taurine in marine invertebrates, 9, 205 Upwelling and production of fish, 9, 255