1 2
3
4
5 6
Plate 1. Adult captive gharials at the Madras Crocodile Bank. Note the ghara, the nasal excrescence, of the male gharial. Plate 2. The right gonad, macroscopically undifferentiated, of a juvenile Nile crocodile can be seen between the spleen and the right kidney. The left gonad is hidden by the mesentery. The yellowish adrenals are almost completely obscured by the paler gonads. Plate 3. The dark-brown right thyroid situated laterally of the right bronchus. The pale right parathyroid is visible slightly caudally of the thyroid on the right aortic arch, medially of the precaval vein. Plate 4. Fighting male Nile crocodiles on a crocodile farm in South Africa. Plate 5. Oral cavity, gular valve and pharynx exposed after the ventral skin has been removed and the tongue has been cut loose from the mandibles. Plate 6. Cutting lines for a belly skin.
7 8
9 10
11 12
Plate 7. Spectacled caiman hatchling with the greyish-white crusty lesions of caiman pox on the dorsal and lateral surfaces of head, body, tail and limbs. Plate 8. Nile crocodile hatchling with ventral, dark-brown crocodile pox lesions in patterns suggesting bite marks. Plate 9. Reddening of the ventral skin of the hind legs and around the cloaca of a juvenile Nile crocodile with septicaemia. Plate 10. Right elbow joint of a juvenile Nile crocodile with exudative arthritis. Plate 11. Heart of an adult Nile crocodile with exudative epicarditis. Plate 12. Hepatozoon sp. gametocyte in a red blood cell of a Nile crocodile.
13 14
15 16
17 18
Plate Plate Plate Plate Plate Plate
13. Ascaridoids in the stomach of an adult wild-caught Nile crocodile. 14. Juvenile Nile crocodile with fat necrosis involving the thoracic and abdominal fat deposits. 15. Fat necrosis: hardened yellow fat between the tail muscles of a Nile crocodile. 16. Renal gout in a juvenile Nile crocodile with deposits of uric acid in the pelvic portions of the renal folds. 17. Close-up of winter sores on the ventral surface of the tail of a juvenile Nile crocodile. 18. Advanced case of stress dermatitis with lesions affecting all parts of the body.
19 20
21
22
23 24
Plate Plate Plate Plate Plate Plate
19. Large fungal granuloma on the right hind foot of an adult captive Indo-Pacific crocodile. 20. Exudative enteritis causing the intestine to be grossly distended by the fibrinous exudate. 21. Haemorrhagic enteritis in a juvenile Nile crocodile. 22. Tonsillitis in a juvenile Nile crocodile. 23. Laryngitis in a juvenile Nile crocodile. 24. Lacrimal cyst under the eye of a captive Nile crocodile (photo Marc Gansuana).
Crocodiles
Biology, Husbandry and Diseases
Crocodiles Biology, Husbandry and Diseases
F.W. Huchzermeyer Onderstepoort Veterinary Institute, South Africa
CABI Publishing
CABI Publishing is a division of CAB International CABI Publishing CAB International Wallingford Oxon OX10 8DE UK Tel: +44 (0)1491 832111 Fax: +44 (0)1491 833508 E-mail:
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CABI Publishing 44 Brattle Street 4th Floor Cambridge, MA 02138 USA Tel: +1 617 395 4056 Fax: +1 617 354 6875 E-mail:
[email protected]
© CAB International 2003. All rights reserved. No part of this publication may be reproduced in any form or by any means, electronically, mechanically, by photocopying, recording or otherwise, without the prior permission of the copyright owners. A catalogue record for this book is available from the British Library, London, UK. Library of Congress Cataloging-in-Publication Data Huchzermeyer, F. W. (Fritz W.) Crocodiles : biology, husbandry and diseases / by F. W. Huchzermeyer. p. cm. Includes bibliographical references (p. ). ISBN 0-85199-656-6 1. Crocodile farming. 2. Crocodiles. 3. Captive reptiles. I. Title. SF515.5.C75 H83 2003 639.3982--dc21 2002013734 ISBN 0 85199 656 6 Typeset in Palatino by Columns Design Ltd, Reading. Printed and bound in the UK by Biddles Ltd, Guildford and King’s Lynn.
Contents
Foreword Disclaimer
vii viii
Introduction
ix
1
Crocodiles and Alligators The Species of Crocodilians Crocodilian Anatomy Crocodilian Physiology Crocodilian Biochemistry Crocodilian Behaviour
1 1 6 32 47 52
2
Examination of Crocodiles and Clinical Procedures Clinical Examination Post-mortem Examination Medication Surgical Interventions
57 57 75 86 91
3
Important Aspects of Crocodile Farming Nutrition Incubation of Crocodile Eggs Rearing Breeding Slaughter Crocodiles in Zoos and Private Collections Animal Welfare
98 98 102 107 118 123 133 136
4
Diseases of Eggs and Hatchlings Diseases of the Egg Diseases of the Yolk-sac Hatchling Diseases Congenital Malformations
139 139 142 145 148
5
Transmissible Diseases Viral Infections Bacterial Infections Fungal Infections Parasitic Protozoa Metazoan Endoparasites Ectoparasites
157 157 163 176 182 192 203 v
vi
Contents
6
Non-transmissible Diseases Nutritional Diseases Poisoning Multifactorial Diseases
211 211 221 226
7
Organ Diseases and Miscellaneous Conditions Skin Diseases Eye Diseases Diseases of the Digestive System Diseases of the Urogenital System Diseases of the Nervous System Diseases of the Circulatory System Diseases of the Respiratory System Diseases of the Skeletal–Muscular System Diseases of the Endocrine System Miscellaneous Pathological Conditions
240 240 245 247 263 266 268 270 272 274 277
References
292
Index
323
Foreword
Crocodilians have been the subject of international study for hundreds of years. Research on their biology began appearing in the literature during the 1800s, increased considerably in the 1920s and then really took off after the mid-1950s, when funding for academic research became more readily available. These early studies concentrated on various aspects of population dynamics of the species in the wild, and of crocodilians kept in display centres and zoos. Husbandry and diseases of crocodiles received early attention by zoo veterinarians and keepers, but interest in these matters took a dramatic turn upwards once ranching and farming of the species became a serious business, worth hundreds of millions of dollars. I well remember some 25 years ago how at meetings of the Crocodile Specialist Group (CSG), someone would mention seeing blemishes on crocodile skins and how this would drastically decrease the value of the skins. Soon dozens of husbandry problems and diseases came to the fore and it became imperative that the issues be looked at in a systematic and deliberate fashion. More and more researchers became interested in the field, and by the year 2000 the CSG had decided to establish, with the encouragement and leadership by Dr Fritz Huchzermeyer, a veterinary group within the CSG. I am delighted to see that Dr Huchzermeyer has put pen to paper and produced this most important and valuable book on husbandry and diseases of crocodilians. It will have many avid readers. Professor Harry Messel Chairman, CSG
vii
Disclaimer
Although every effort has been made in the collection and presentation of facts the author cannot accept any responsibility for damages arising from actions based on information contained in this book.
viii
Introduction
This book has been written for veterinarians, scientists, wildlife officials, students and crocodile farmers. The knowledge was gained mainly by my work over many years with farmed Nile crocodiles, some work with wild and wild-caught African dwarf crocodiles in the Congo Republic and, in addition, by the study of the available literature, which embraces most of the other crocodilian species as well. I believe this to be the first comprehensive book on crocodile diseases. Being a pathologist, poultry pathologist, and not a clinician, I placed the emphasis in this book on the diagnosis and treatment, or rather prevention, of diseases as they occur on crocodile farms. However, an effort has been made to cover all clinical aspects as well. I believe that my avian background has helped me to grasp the peculiarities of crocodilian physiology and pathology, while my poultry background has guided me towards a herd health approach. Diseases cannot be understood without a background knowledge of normal body functions, nor without knowledge of farming conditions. These are therefore treated in a somewhat introductory fashion in the first and third part, without any claim of completeness. Wherever possible, common names have been used as well as scientific names, in an effort to make the book more accessible. Unless emphasized specifically the term ‘crocodiles’ is used to denote all crocodilians (see Chapter 1). Basically we know very little about crocodiles and their diseases. Research into their biology is carried out and funded in the course of normal biological studies and conservation efforts. However, most veterinary research is centred on domestic animals and may at best involve some of the major wildlife species, possibly stimulated by a need to protect the inhabitants of national parks and zoological gardens. The crocodile farming and ranching industries in the various countries are in competition with each other and are most unlikely to be able to provide funding for a concerted and specialized veterinary research effort. There are no catastrophic crocodile diseases, and consequently veterinary research will always be regarded as not so important. I had the good fortune that the Poultry Section of the Onderstepoort Veterinary Institute (OVI) was closed a few years before my retirement and that I was allowed then to devote all my time to crocodile work. For some years I had some nearby crocodile farms submit practically all their mortalities. The many post-mortems carried out during that time and the generous permission to make full use of the Institute’s library, even up to the present, have laid a foundation of knowledge, on which I became confident to tackle writing this book. The past and present directors of the OVI, Dr D.W. Verwoerd, Dr G.R. Thomson, Dr S.T. Cornelius and Dr F.T. Potgieter, are thanked for the provision of an office for my use and continued access to the Institute’s infrastructure since my retirement, as well as for their continued interest in my work. The secretary of the now also defunct Pathology Section of the OVI, Mrs Mara Stoltz, has always been at hand to solve computer and program problems ix
x
Introduction
most speedily and efficiently, and Mr D. Swanepoel of the Institute’s library and his staff have been most helpful in trying to procure even the most obscure items of literature. Over the years I have been most fortunate in having been able to draw on the knowledge of many colleagues, for which I want to express my gratitude. Many crocodile farmers in southern Africa have welcomed me on their farms and have allowed me to study their animals in their environment. Dr Jenny Turton and Dr Jane Walker reviewed parts of the manuscript and helped me to overcome some of my language problems. To all go my heartfelt thanks. And, last but not least, I have to thank my wife Hildegard, who not only put up with my periods of withdrawal while writing, but always showed a keen interest in my work and encouraged me to carry on. F.W. Huchzermeyer Pretoria June 2002
Chapter 1 Crocodiles and Alligators
The Species of Crocodilians The crocodilians are classified as reptiles, together with lizards, snakes, tuataras and chelonians (tortoises, terrapins and turtles – note that the Americans use the term ‘turtles’ for all chelonians), because of their exothermia and their skin architecture. However, many features, particularly behaviour (vocalizations and parental care), heart morphology and fat body, clearly separate them from the other reptiles. All living crocodilians are grouped in the family Crocodylidae. They occur in a broad band around the globe in the tropics and subtropics of the Old and New World. At present the distinctions between subfamilies, genera and species are based mainly on anatomical features, particularly of the skull, and on scale patterns of the skin. DNA analyses may, in the near future, add new information and cause some revisions (Densmore and Owen, 1989; Ray et al., 2001; White and Densmore, 2001). The following details were taken mainly from Ross and Magnusson (1989). Please note that several common names can be in use for any one species. An effort has been made in this book to use only one common name per species, as listed below. Many synonyms of the scientific names can be found in the older literature. Where this
literature is cited, these synonyms have been replaced in most cases by the current names.
Crocodiles The subfamily Crocodylinae contains three genera: Crocodylus (the true crocodiles, with 13 species), Osteolaemus and Tomistoma (each with one species). The genus Crocodylus: C. rhombifer C. moreletii C. acutus C. cataphractus
C. niloticus C. intermedius C. porosus C. johnsoni C. palustris
Cuban crocodile Morelet’s crocodile American crocodile African slendersnouted crocodile (Fig. 1.1) Nile crocodile (see Fig. 1.7) Orinoco crocodile Indo-Pacific crocodile Johnston’s crocodile Mugger (Fig. 1.2)
C. siamensis Siamese crocodile C. mindorensis Philippine crocodile C. novaeguineae New Guinea crocodile C. raninus Bornean crocodile
© CAB International 2003. Crocodiles: Biology, Husbandry and Diseases (F.W. Huchzermeyer)
Cuba Central America Central America Africa
Africa and Madagascar South America Asia and Australia Australia Indian subcontinent Asia Philippines New Guinea Borneo (see Ross, 1990; Ross et al., 1998) 1
2
Chapter 1
Due to a consistent spelling error in its original description, the scientific name of Johnston’s crocodile is C. johnsoni. As the rules of nomenclature do not allow a subsequent correction, the original spelling of the scientific name must be retained. The wide distribution of C. porosus in the
Indo-Pacific area, C. niloticus throughout Africa and Madagascar, and C. acutus in Central America is probably due to their ability to tolerate varying degrees of salinity. This has allowed them to spread to different river systems and even islands, unlike more localized species that do not have any salt
Fig. 1.1. Captive Crocodylus cataphractus at the St Lucia Crocodile Centre.
Fig. 1.2. Captive Crocodylus palustris at the Madras Crocodile Bank.
Crocodiles and Alligators
tolerance. It therefore appears to be incorrect to use the names saltwater and freshwater crocodiles for C. porosus and C. johnsoni, respectively, outside Australia.
Dwarf crocodile
The genus Tomistoma: T. schlegelii
False gharial (Fig. 1.5)
Asia
Alligators
The genus Osteolaemus: O. tetraspis
3
Africa
This has two subspecies, as follows: O. t. tetraspis from coastal West Africa (Fig. 1.3); and O. t. osborni from the Congo basin (Fig. 1.4).
The subfamily Alligatorinae contains four genera: Alligator (the true alligators, with two species), Caiman (the caimans, with two species), Palaeosuchus (the dwarf caimans,
Fig. 1.3. Captive juvenile Osteolaemus tetraspis tetraspis at the St Lucia Crocodile Centre. Their colouring is yellow and black, while that of O. t. osborni hatchlings is green and black.
Fig. 1.4. Young adult wild-caught Osteolaemus tetraspis osborni trussed up for transport to the market.
4
Chapter 1
Fig. 1.5. Captive Tomistoma schlegelii on a farm in Kuching, East Malaysia.
with two species) and Melanosuchus (the black caiman, with only one species).
The genus Caiman:
The genus Alligator:
C. crocodilus
A. mississippiensis A. sinensis
American alligator USA Chinese alligator China
C. latirostris
Broad-snouted caiman Common caiman (Fig. 1.6)
Fig. 1.6. Juvenile Caiman crocodilus on a farm in São Paulo State, Brazil.
South America South America
Crocodiles and Alligators
The genus Palaeosuchus: P. palpebrosus P. trigonatus
Cuvier’s dwarf caiman Schneider’s dwarf caiman
South America South America
The genus Melanosuchus: M. niger
Black caiman
South America
Gharials The subfamily Gavialinae only has one genus, Gavialis, with a single species.
5
live further north than caimans and crocodiles in both North America and in China. 2. In alligators and caimans the teeth of the lower jaw fit into pits in the upper jaw, consequently when the mouth is closed no mandibular teeth are visible. In crocodiles the fourth mandibular tooth fits into a notch in the upper jaw and thus remains visible when the mouth is closed (Fig. 1.7). 3. Crocodiles and gharials have sensory pits in the ventral scales (Fig. 1.8). These are absent in alligators and caimans. This is one of the important features used in the species identification of goods made from crocodilian leather.
The genus Gavialis: G. gangeticus
Gharial (Plate 1)
Indian subcontinent
Differences between crocodiles and alligators This question is asked quite regularly. There are many anatomical and physiological differences, but for the purposes of this book it will suffice to name only three reasonably obvious ones: 1. Alligators are more cold resistant than caimans and crocodiles. They can therefore
Wild or captive? This refers to the description of the different ways in which the crocodiles are living or kept. Wild Crocodiles in the wild may be either left entirely to their own devices or subjected to a certain degree of management. They are hardly ever seen to be suffering from disease
Fig. 1.7. Adult Nile crocodile on a farm in South Africa. Note the visible fourth mandibular tooth in its maxillar notch.
6
Chapter 1
Fig. 1.8. Sensory pits in the ventral skin of Crocodylus palustris.
or dying, and often they live in such remote areas that suitable specimens rarely reach the laboratory (see also p. 239). Captive Crocodiles kept in zoos and other collections without a productive goal are referred to as captive. They may be bred or exhibited only, but they may also be subjected to scientific studies. Wild-caught Crocodiles caught in the wild and kept for a short period restrained for the purpose of sample collection or transported alive to a market, where they are slaughtered. They are under very severe stress which may affect many of their physiological and biochemical parameters. Such animals should be referred to as wild-caught. Ranched Crocodiles kept on farms for commercial (productive) purposes, but either hatched from eggs collected in the wild or having been collected as hatchlings, are referred to as ranched. Their diseases are substantially
the same as those of farmed crocodiles, except for their closer contact with wild populations, which may constitute a natural reservoir of crocodile-specific infectious agents. Farmed Crocodiles hatched from eggs laid by breeding stock kept on a farm for commercial purposes are called farmed crocodiles. The on-farm breeding of these crocodiles allows the genetic selection for certain productive parameters. These animals no longer have a direct link to the wild. Their only contribution to the conservation of wild crocodiles may be to keep commodity prices low, thereby lowering the incentive for poaching. However, they may also provide a substantial additional gene pool. Where such crocodiles are farmed far away from wild crocodile populations the incidence of crocodile-specific infectious diseases is usually very low.
Crocodilian Anatomy The aim of this section is to provide sufficient information for the normal functions of
Crocodiles and Alligators
the body to be understood and for the recognition of the organs during post-mortem examinations. This information is based largely on my own experience with Nile crocodiles. For a reasonably detailed and accurate study of the anatomy of the American alligator see Chiasson (1962). We are still waiting for a standard textbook on crocodilian anatomy. A dissection guide for post-mortem examinations is given in Chapter 2 (p. 75).
The skeleton Skull The pitted appearance of the dorsal skull surface (Fig. 1.9) is due to its fusion with the skin. There are three pairs of foramina dorsally on the skull: the external nares opening into one nasal orifice, the orbits and the supertemporal fossae (Fig. 1.9). On the ventral aspect, almost at the same level, are the anterior palatine foramina (foramen), the posterior palatine foramina and, partially hidden, the internal nares (Fig. 1.10). The cranium, which houses the brain, lies
7
roughly between the orbits and the supertemporal fossae. The articulation of the jaw is caudal to the atlanto-occipital joint, allowing the jaws to open extremely widely (Fig. 1.11). Vertebrae The cervical and thoracic vertebrae have ribs. The cervical ribs lie alongside the vertebral column pointing caudally, but only the thoracic ribs connect with the sternum. A cartilaginous portion in the midrib allows flexibility for collapsing the thorax during deep diving. The lumbar vertebrae do not have ribs, but the sacral ones do. Dorsally all the vertebrae bear neural spines; and ventrally, chevron bones, which point in an obliquely caudal direction, are attached to the caudal vertebrae. A fibrous membrane bearing abdominal ribs (gastralia) connects the sternum with the os pubis and supports the abdominal viscera. Legs The pectoral girdle, consisting of the scapula, coracoid and sternum, together with the first
Fig. 1.9. Pitted appearance of the skull bones of a mature Nile crocodile, dorsal aspect.
8
Chapter 1
Fig. 1.10. Ventral aspect of the skull of an adult Nile crocodile.
Fig. 1.11. Lateral aspect of the skull of a juvenile Nile crocodile.
thoracic ribs, surrounds the wide cranial aperture of the thorax. This allows large masses to be swallowed. The bones of the forelimb (humerus, radius and ulna) are shorter than their counterparts in the hind limb. The front feet have five digits, the first three carrying claws. The pelvic girdle consists of an os ileum, an os ischium directed caudoventrally and an os pubis pointing cranially. The hind limbs are twice as long as the forelimbs, allowing
for a galloping action. Femur, tibia and fibula are well developed. The foot has four digits, the first three carrying claws (Fig. 1.12). The skin Scales and osteoderms Crocodile skin, like that of all reptiles, is covered with scales or scutes and is devoid of sweat glands. On the head the skin is fused
Crocodiles and Alligators
9
Fig. 1.12. Claws on the left hind foot of an adult Tomistoma schlegelii at Singapore Zoological Gardens (photo P. Martelli).
to the bones of the skull. The large scales on the back, and in some species some of the ventral scales also, contain bony plates, the osteoderms. Muscles connect the ossified dorsal scales with the vertebral column, and when the muscles contract this results in a dorso-ventrally rigid, beam-like structure that allows the crocodile to keep its back and tail straight when walking or running (Frey, 1988a,b). In this context it is interesting to note that recent mitochondrial DNA analyses, as well as studies of nuclear genes, suggested a close relationship between crocodilians and chelonians (tortoises and turtles). The latter also have osteoderms and both dorsal and ventral armour (Hedges and Poling, 1999).
parenchymal cells contain lipid droplets (Weldon and Sampson, 1987). For the analysis of the aromatic secreta of these glands, see p. 52. In some species there are also rudimentary dorsal glands – in the Chinese alligator beneath the second row of scales from the dorsal midline, but in various positions from the 2nd to the 15th transverse row (Chen et al., 1991).
Skin glands
Pigmentation
Crocodilians have a few holocrine skin glands. The cloacal (paracloacal) glands are situated laterally within the lips of the cloaca. The mandibular (gular) glands are in the skin under the tongue, between the mandibles (Fig. 1.13). The septa of the gular glands are lined with melanocytes, giving the gland tissue its black appearance (Weldon and Sampson, 1988). The paracloacal gland is a single secretory sac with a single duct and a single lumen. The
Hatchlings of many species have light and dark transverse striations, which in some species are maintained almost into adulthood. These striations mimic rippling shadows in shallow water (see Fig. 1.3). The chromatophores in the skin can contract and expand following nervous impulses from the eyes via the brain. Blind crocodiles and those kept in complete darkness usually display lighter colours than those exposed to bright daylight.
Identification The patterns of scales, both dorsal and ventral, are species specific, although some slight individual variations may occur. A key for the identification of tanned whole crocodilian skins can be found in Brazaitis (1987).
10
Chapter 1
Fig. 1.13. Mandibular (gular) glands of a juvenile Nile crocodile.
The muscles There are no external muscles on the head because the skin adheres to the skull. The powerful jaw muscles are all on the median aspect of the mandible, thus broadening the posterior skull. Sphincters close the external
nares and depressors close the auricular flap over the tympanum for diving. The long dorsal muscles of the trunk extend into the tail. These muscles, plus the ventral tail muscles, musculus (m.) caudofemoralis medially and m. ilioischiocaudalis externally (Frey, 1988a), provide the power for swimming (Fig. 1.14).
Fig. 1.14. Schematic drawing of a cross-section of the tail of a Nile crocodile: 1, musculus (m.) longissimus dorsi; 2, m. caudofemoralis; 3, m. ilioischiocaudalis.
Crocodiles and Alligators
The respiratory system Respiratory tract The external nares are slightly raised above the level of the upper jaw, allowing the crocodile to surface and breathe when most of its body is submerged. Adult male gharials develop a large nasal excrescence, the ghara (see Plate 1), which is thought to function as a vocal resonator (Whitaker and Basu, 1983).
11
In the long nasal passage the olfactory nerve endings are exposed to the air. Except when swallowing, bellowing or yawning, the posterior part of the mouth is closed by the gular valve, consisting of the dorsal flap of the tongue and the palatal flap (velum palati) extending from the soft palate (Putterill and Soley, 1998a) (Fig. 1.15). The Eustachian tubes enter the pharynx in a joined opening just caudally of the internal nares (Colbert, 1946) (Fig. 1.16). Their func-
Fig. 1.15. Schematic drawing of the oral and pharyngeal cavities of the crocodile: 1, gular valve; 2, tongue; 3, larynx and trachea; 4, oesophagus; 5, internal nares; 6, tonsils; 7, Eustachian tubes; 8, nasal passages.
Fig. 1.16. Tonsils of the crocodile caudally of the internal nares.
12
Chapter 1
tion is to equalize the pressure on the two sides of the tympanum (the ear membrane). Close to the opening of the Eustachian tubes into the pharynx there are two mucosal folds, one on either side and extending caudally, which contain tonsillar tissue (Putterill and Soley, 2001) (Fig. 1.16). The glottis has two soft lips (Fig. 1.17) which close when the crocodile swallows. In crocodiles (but not in alligators) the trachea bends to the left inside the thorax before its bifurcation, a substantial distance before entering the lungs (Fig. 1.18). This allows large chunks of prey to be swallowed without exerting any pressure on the trachea or bronchi. Lungs The lungs are multi-cameral sac-like structures, highly vascularized but with thicker walls than a mammalian lung. These thick walls may be necessary to counteract the outside pressure during diving. The lungs lie in pleural chambers which are separated by
a complete mediastinum. The posterior part of the lungs is connected tightly to the anterior transverse membrane (postpulmonary membrane). In crocodiles the remainder of the lungs lies loosely in the thoracic cavity, not as described by Duncker (1989), while in the caiman the lungs are fused to the ventral wall of the thorax. For a detailed study of lung morphology of the Nile crocodile, see Perry (1988). Respiratory muscles The thorax is divided from the abdomen by two transverse membranes. The postpulmonary membrane separates the lungs from the liver, and its ventral third is muscular. The posthepatic (posterior transverse) membrane is attached to a sheet of muscle (m. diaphragmaticus) which extends to the os pubis (Van der Merwe and Kotzé, 1993). Together, the two membranes, with their muscular components, act like a diaphragm, pulling the liver in a caudal direction for inspiration.
Fig. 1.17. Tongue and ventral aspect of the pharyngeal cavity with protruding glottis; juvenile Nile crocodile.
Crocodiles and Alligators
13
Fig. 1.18. Tracheal loop in the thorax of Crocodylus palustris.
Voice organ? Crocodiles can produce a range of sounds, but have neither vocal cords (like mammals) nor a syrinx with tympaniform membranes (like birds). It is believed that sounds are produced by forcing the air through the compressed lips of the glottis (Fig. 1.17), much as sounds are produced by human lips in the mouthpiece of a trumpet.
The digestive system Teeth Crocodilian teeth are pointed, very sharp and are constantly replaced throughout life. The replacement rate varies with the growth rate and slows down as the animal becomes older. In small American alligators (<1.5 m) the estimated replacement rate varied from 3 to 4 months (Erickson, 1996a). Early in life, tooth replacement occurs in waves, passing along alternately numbered tooth series from back to front, while later in life the direction is reversed (Edmund, 1962). Although very old, toothless individuals are sometimes found, this may be due to accumulated damage to the alveoli (Erickson, 1996b) (see p. 247).
While crocodilian teeth are homomorphic, they may be categorized by their position in the maxilla and mandible. Kieser et al. (1993) group the teeth of the Nile crocodile as follows (Fig. 1.19): ● maxilla: 5 incisors – gap – 5 canines – gap – 5 molars; ● mandible: 3 incisors – gap – 5 canines – gap – 7 molars. The first mandibular canine is the longest and often extends above the dorsal plane of the snout (Fig. 1.20). This can cause damage to belly skins when frightened young crocodiles pile in the corner of their pen (see also pp. 114 and 241). In some individuals the two mandibular incisors 1 on each side sometimes penetrate the maxilla behind the maxillary incisors and produce openings in the upper lips in front of the nostrils, which could be called ‘false nostrils’ (Figs 1.9 and 1.21; see also p. 153). Tongue The tongue occupies the floor of the mouth cavity. It is not free but is held in place laterally by a folded membrane. The dorsal surface of the tongue contains mucus glands which are associated with lymphoid tissue,
14
Chapter 1
Fig. 1.19. Dentition of a juvenile Nile crocodile.
Fig. 1.20. The protruding first mandibular canine causes scratches when the crocodiles pile up in the corner of their pen.
forming ‘lingual tonsils’, while sensory organs are found along the sides of the tongue (Putterill and Soley, 1998b). In crocodiles the dorsal surface also contains salt glands (Taplin and Grigg, 1981; Franklin and Grigg, 1993). Oesophagus The oesophagus extends from the epihyal cartilage of the larynx to the clearly defined gastro-oesophageal junction. It has many longitudinal folds, allowing distension when the crocodile swallows large chunks. The entire epithelial surface contains many
goblet cells that function as an intra-epithelial gland (Putterill et al., 1991). Stomach The stomach lies to the left, immediately behind the left lobe of the liver and the posterior transverse membrane. Its junction with the oesophagus (cardia) is defined by a welldeveloped sphincter muscle. The pyloric exit also lies in the cranial aspect, slightly to the right of the cardia, and is defined by a small bulbus, the pyloric antrum, which in turn opens into the duodenum (Figs 1.22–1.24). The entire interior surface of the stomach is
Crocodiles and Alligators
15
Fig. 1.21. ‘False nostrils’ in a captive Crocodylus palustris.
lined uniformly by mucosal glands. Gastrin and somatostatin cells are found only in the glands of the pyloric antrum (Rawdon et al., 1980; Dimaline et al., 1982). The pyloric opening to the duodenum is very small, thus preventing the escape of accidentally swallowed foreign bodies (see p. 254). The gastric wall is strongly muscularized over the fundus, which gives the crocodilian stomach a somewhat gizzard-like appear-
ance. However, the internal glandular lining would not be able to protect the mucosa from a strong chewing action, as the koilin layer does in the avian gizzard. The function of the gastroliths that are often found in crocodilian stomachs, i.e. whether they are ballast, have a chewing function as in birds or have been taken in accidentally, is the subject of an ongoing debate (Steel, 1989) (see also pp. 36 and 290). The fact that stomachs of crocodiles
Fig. 1.22. Overview of the gastrointestinal tract, oesophagus to cloaca, of a Nile crocodile hatchling.
16
Chapter 1
Fig. 1.23. Stomach and duodenal antrum of a Nile crocodile. The strong musculature and the central tendinous plate create a gizzard-like impression.
Fig. 1.24. Opened stomach and duodenal antrum of a Nile crocodile. Note the clear demarcation between oesophageal and gastric mucosa.
in the Okawango swamps in Botswana contain increasing amounts of plant material, such as papyrus roots and palm tree seeds, with increasing body length (Blomberg, 1976) tends to indicate accidental ingestion. Intestine The looped duodenum starts from the pyloric antrum and extends to the end of the loop. In many crocodile species the duode-
num folds over again, forming a double loop, although this is apparently not the case in alligators. Both forms occur in different populations of Osteolaemus tetraspis (Huchzermeyer et al., 1995; Huchzermeyer, 1996b). Part of the pancreas is embedded between the limbs of this loop (see Fig. 1.26). From the end of the loop the jejunum runs initially straight along the dorsal aspect of the abdominal cavity, then becomes suspended in loose coils by the mesentery to the
Crocodiles and Alligators
point at which the cranial mesenteric artery meets the intestine (van der Merwe and Kotze, 1993). From this point the ileum extends in similar coils to the very short rectum, which in turn enters into the cloaca (Hunter, 1861) (Fig. 1.22). The rectum is suspended by a short mesentery and lies between, and ventral to, the two kidneys. The internal surface of the intestine does not have villi, but a system of complex zigzagging, ridge-like folds, which alternate with each other and are oriented longitudinally (Kotzé et al., 1992; Kotzé and Soley, 1995) (Fig. 1.25).
17
Pancreas The proximal (ventral) pancreas lies between the limbs of the duodenal loop, while the distal (dorsal) part surrounds the cranial aspect of the spleen (Miller and Lagios, 1970; Huchzermeyer, 1995) (Fig. 1.26).
Liver The liver lies between the two transverse membranes in the hepatic coelom and has two lobes of almost equal size – the right lobe being slightly larger than the left. The
Fig. 1.25. Zigzagging intestinal folds, adult Nile crocodile.
Fig. 1.26. The pancreas between the duodenal loops and extending towards the spleen in a juvenile Nile crocodile.
18
Chapter 1
heart separates these two lobes. In some species the lobes are completely separate, while in others they are joined by a dorsal bridge of liver tissue. Substantial collagenous trabeculae have been found in the liver of American alligators and to a lesser extent in Caiman crocodilus (Beresford, 1992). Storch et al. (1989) found abundant Kupffer cells, as well as fat-storing cells, in the sinusoidal lining of the liver of O. tetraspis. Numerous Kupffer cells are also present in Nile crocodile livers. The gall bladder lies between the two liver lobes within the hepatic coelom, and receives bile from both. The bile duct enters the intestine in the proximal duodenum (Van der Merwe and Kotzé, 1993). In most of the American alligators examined by Xu et al. (1997) the right and left hepatic ducts were interconnected, the right duct entering the gall bladder while the left duct continued through the pancreas directly into the duodenum.
The urinary system The two kidneys are firmly attached to the dorsal abdominal wall in the most posterior part of the abdomen. As in birds, they are not embedded in perirenal fat and lack a capsule. The renal tissue, consisting of cortical and pelvic layers, is folded over, in a sin-
Fig. 1.27. Kidney of a Nile crocodile.
gle fold in the African dwarf crocodile and in multiple folds in other crocodile species. These folds continue to grow as the crocodile grows. These multiple folds give the kidney of the Nile crocodile a triangular shape on transverse section, while the kidney of the African dwarf crocodile appears flattened. The folding patterns appear to be species specific (Figs 1.27–1.29). Crocodilians do not have a urinary bladder. The two ureters open into the cloaca. However, urine may be stored in the rectum (Fig. 1.30). The reproductive organs Female Two ovaries are attached to the dorsal body wall cranioventrally to the kidneys, and are partially attached to the cranial part of the kidneys. The ovaries are elongate, and in very young animals they are difficult to differentiate macroscopically from testes. In larger juveniles the follicular structure becomes evident. In adult crocodiles all the follicles mature at the same time (Fig. 1.31). The ovarian histology of the American alligator was studied by Uribe and Guillette (2000). In adult female American alligators the corpora lutea form after ovulation. Their morphology is similar to that in birds and their size can be used to judge whether a female had laid eggs during the preceding season, recent corpora
Crocodiles and Alligators
19
Fig. 1.28. Kidney of Crocodylus palustris.
Fig. 1.29. Kidney of Caiman crocodilus.
lutea having a minimum diameter of 0.4 cm (Guillette et al., 1995b). The ostium of the oviduct lies close to the cranial apex of each ovary. The oviducts are convoluted and increase in size with maturity and sexual activity. They enter the uteri (the glandular part), followed by the vaginae, where the eggs are stored before laying (Fig. 1.32). The vaginae join the cloaca, caudally to the ureters. A small clitoral appendage, which resembles the male penis in shape, is situated ventrally in the cloaca.
Male The slightly flattened testes are situated in the same position as the ovaries in the female (Plate 2). A convoluted deferent duct runs along the caudolateral border of each testis and enters the cloaca close to the base of the copulatory organ. This crocodilian penis is folded around a ventral seminal groove (Fig. 1.33). Note that crocodiles and tortoises have only one penis, while lizards and snakes have paired hemipenises.
20
Chapter 1
Fig. 1.30. Rectum filled with urine, juvenile Nile crocodile.
Fig. 1.31. Nile crocodile ovary, with mature follicles.
Crocodiles and Alligators
21
Fig. 1.32. Ovaries, oviducts, uteri and vaginae of Osteolaemus tetraspis.
Fig. 1.33. Everted penis of an adult Nile crocodile.
The endocrine organs Pituitary The pituitary gland lies on the ventral aspect of the brain, at the level of the optic lobes (Fig. 2.26) (Chiasson, 1962).
Thymus The thymus gland consists of a series of lobules of varying sizes on both sides of the trachea along the neck and in the thorax to the base of the heart. In well-nourished crocodiles these glands are embedded in fatty
22
Chapter 1
tissue, which is almost the same colour. This makes it difficult to differentiate the individual lobules. Note that Huchzermeyer’s (1995) description of the thymus glands of the Nile crocodile was based on emaciated individuals for improved visibility. Consequenly the lobules had vanished from the necks of these animals. However, lobules were subsequently seen in the neck of healthier Nile crocodiles as described previously from other crocodile species (Gegenbauer, 1901; Bockman, 1970). It is believed that in crocodilians the thymus remains active throughout life. For a discussion of the striated muscle cells occasionally found in the reptilian thymus, see Raviola and Raviola (1967). Thyroids While some crocodilians have a single thyroid gland with two well-defined lobes on either side of the trachea, connected by a narrow isthmus (Lynn, 1970), other species have two separate lobes. They are recognized by their dark-brown colour. In the Nile crocodile these are situated not on either side of the trachea, but on the lateral side of each of the two bronchi and medially of the common carotid artery, the right one closer to the entrance of the right bronchus into the lung and the left one closer to the bifurcation of the trachea (Plate 3) (Huchzermeyer, 1995). Parathyroids The two parathyroid glands are normally hidden by thymus tissue and difficult to see. In the Nile crocodile they are situated caudolaterally of the thyroid glands on each side, between the precaval vein and the common carotid artery, immediately cranially of the dorsal bend of the aortic arch (Plate 3 and Fig. 1.35) (Huchzermeyer, 1995). The situation appears to be similar in C. crocodilus, apart from the fact that additional (accessory) parathyroid glands occasionally occur (Oguro and Sasayama, 1976). Adrenals The two adrenal glands are found in the abdominal cavity adhering to the dorsal
body wall. Ventrally they partially overlap the proximal part of the kidneys. They extend cranially beyond the two kidneys and somewhat laterally of the midline (Plate 2) (Huchzermeyer, 1995). Pancreas and intestinal tract The topography of the pancreas has been described above. In the Nile crocodile the islets of Langerhans appear to be present in the distal (dorsal) pancreas only (Huchzermeyer, 1995). A similar distribution was found in the American alligator, in which smaller groups were also found in the ventral (proximal) portion (Jackintell and Lance, 1994). Endocrine cells have also been found in the pyloric part of the stomach and in the intestine of crocodiles (Rawdon et al., 1980; Dimaline et al., 1982; van Aswegen et al., 1992).
The circulatory system and blood cells Heart In the Nile crocodile the heart is situated between the 4th and 8th thoracic ribs (Van der Merwe and Kotzé, 1993) and between the two lobes of the liver (Fig. 1.34). The situation is similar in the other crocodilians. A ligament at its apex, the gubernaculum cordis (Webb, 1979), connects it to the pericardial sac and beyond this to the postpulmonary transverse membrane. There is no fat in the coronary groove. The two auricles stretch caudally on either side halfway along the ventricles, the larger right auricle sometimes further. The four chambers are completely separated. Circulation The major blood vessels leaving the heart of the Nile crocodile are identified in Fig. 1.35. Crocodiles have two aortic arches like other reptiles. The left aortic arch leaves the right ventricle alongside the pulmonary artery and becomes the coeliac artery; this supplies the digestive organs of the abdomen. The
Crocodiles and Alligators
23
Fig. 1.34. The heart is situated between the lungs and the two lobes of the liver; juvenile Nile crocodile.
Fig. 1.35. Schematic drawing of the heart and major blood vessels of the Nile crocodile, ventral aspect. 1, trachea; 2, thyroid; 3, carotid artery; 4, precaval vein; 5, parathyroid; 6, aortic arch; 7, left auricle; 8, left ventricle; 9, bifurcation of the trachea; 10, carotid artery; 11, thyroid; 12, precaval vein; 13, parathyroid; 14, aortic arch; 15, right auricle; 16, right ventricle.
right aortic arch emerges from the left ventricle and runs posteriorly as the dorsal aorta. The left and right aortic arches communicate in two places: the foramen of Panizza and the anastomosis (Axelsson and Franklin,
1997). The foramen of Panizza is located at the base of the heart within the aortic arch valves (Webb, 1979), and the anastomosis is a short vessel connecting the two aortic arches. In American alligators of length 1–2 m, the foramen of Panizza had a diameter of
24
Chapter 1
1–2 mm (Greenfield and Morrow, 1961). During systole it is completely covered by the aortic valves, thus allowing an exchange of blood during diastole only (Axelsson and Franklin, 1997). As in all reptiles and birds, part of the venous blood of the caudal half of the body is drained through the renal portal system. According to Chiasson (1962) this appears to be bypassed partially by the ventral abdominal veins which, together with the mesenteric vein, enter the hepatic portal system. Superficial veins I have been unable to identify any large, easily accessible superficial veins for intravenous injections. Blood can be drawn from the dorsal and ventral vertebral veins of the neck and tail (see p. 64). The statement about drawing blood from the temporal vein, which lies just below the temporal muscle on the dorsal aspect of the head (Lance, quoted by Samour et al., 1984), is in error. Such a technique has never been used or described by Lance (personal communication, V.A. Lance, San Diego, 1999). Tonsils In the Nile crocodile the tonsils are situated in the roof of the pharynx (Putterill and Soley, 2001) (see above, Fig. 1.16). Spleen The pear-shaped spleen lies dorsally in the mesentery, close to the base of the duodenal loop (Plate 2). Its broad cranial end is embedded in the caudal limb of the pancreas. The spleen is covered by a strong capsule. The histology and vascular architecture of the spleen of the American alligator were studied by Tanaka and Elsey (1997). Lymphatics The lymphatic system was studied by McCauley (1956). There are no subcutaneous lymph vessels and no lymph nodes. Lymph vessels from the head and the anterior limbs, thorax and abdomen anastomose with the
external jugular vein just proximal to the juncture with the subclavian vein. The lymph from the caudal and pelvic regions is pumped by the posterior lymph hearts into small vessels which empty into the pelvic venous plexus. These lymph hearts are single-chambered muscular structures, measuring 3 5–7 mm in alligators 50–75 cm long. They are situated superficially at the junction of the hind limb with the pelvis, below the superficial layer of the deep fascia in the triangle formed by the m. longissimus caudae, the crest of the ileum and the m. flexor caudae. In the absence of lymph nodes, the thymus (see above), tonsils, spleen and numerous lymphoid masses in the walls of the digestive tract act as reservoirs of lymphocytes. Blood volume The total blood volume of one juvenile American alligator was 4.2% of body mass (Coulson et al., 1950), of another two alligators 5.1% and 5.5% (Andersen, 1961), and that of 3.5-year-old Cuban crocodiles (n = 19) was 4.0 ± 0.3% for males and 3.6 ± 0.2% for females (Carmena-Suero et al., 1979). Blood cells All crocodilian blood cells are nucleated. The erythrocytes are oval in shape with round or oval nuclei. The dimensions of the red blood cells of some crocodilian species are given in Table 1.1. The following descriptions of the various blood cells were taken from Mateo et al. (1984b) and refer to the American alligator. Detailed descriptions of the blood cells of Crocodylus porosus and Crocodylus johnsoni are given by Canfield (1985). See also Hawkey and Dennett (1989). However, there is some confusion in the literature, with different authors using different definitions for the different leucocytes. THROMBOCYTES. Length 14.3 m, oval or elliptical with smooth cell borders, smooth pale blue or almost colourless cytoplasm that often contains numerous clear confluent
Crocodiles and Alligators
25
Table 1.1. Erythrocyte dimensions (means). Species Alligator mississippiensis A. mississippiensis A. mississippiensis A. mississippiensis Caiman latirostris C. latirostris Caiman crocodilus A. mississippiensis C. latirostris C. crocodilus
Length (m)
Width (m)
References
14.8–22.0 17.5 23.2 23.0 21.3 19.5 23.8 20.8 17.0 17.0
8.1–12.8 9.7 12.1 14.3 10.9 10.8 13.3 11.1 9.0 9.0
1 4 5 6 2 2 3 3 7 7
1, Reese (1917); 2, Gulliver (1840) (cited by Reese, 1917); 3, Milne-Edwards (1856) (cited by Reese, 1917); 4, Glassman et al. (1981); 5, Wintrobe (1933); 6, Mateo et al. (1984); 7, Troiano et al. (1998). Note the nomenclature used in the older papers: Alligator lucius = Alligator mississippiensis; Alligator sclerops = Caiman crocodilus; Caiman fissipes = Caiman latirostris.
vacuoles with poorly demarcated borders. The uniform oval nuclei are located centrally and oriented longitudinally, staining intensely dark purple, with coarsely condensed chromatin. A phagocytic function of avian thrombocytes was discovered recently (Wigley et al., 1999) and the same function may be postulated for reptilian thrombocytes. The functions of the other blood cells are presumed to be the same as in mammals and birds. Heterophils, or type I granulocytes (Canfield, 1985), are round to oval cells with mean diameters of 17.3 m and distinct smooth cytoplasmic borders. The nuclei are lenticular, oval or, rarely, bilobed, with indistinctly clumped purple chromatin, usually eccentrically located at one pole of the cell. The cytoplasm contains abundant, 3–4 m long, fusiform refractile granules, occasionally arranged in perinuclear radially symmetrical star-like configurations (Fig. 1.36).
HETEROPHILS.
EOSINOPHILS. Eosinophils, or type II granulocytes (Canfield, 1985), are oval or occasionally round, with a mean diameter of 14.9 m and smooth cytoplasmic outlines. The lenticular or oval nuclei are purple with promi-
nent coarsely clumped chromatin and very sharply demarcated borders, usually located at one pole of the cell, often causing a slight outward bulge of the cell outline. Some nuclei are located more centrally. The paleblue, smooth cytoplasm is visible only as a thin rim surrounding the many bright pink plump granules measuring 2–3 m (Fig. 1.37). Often a few granules are present on the face of the nucleus. BASOPHILS. Basophils, or type III granulocytes (Canfield, 1985), are round cells with irregular external ‘cobblestone’ contours and a diameter of 12.8 m. Abundant, dark-purple to purplish-red, round granules measuring 0.1–0.5 m pack the cell to the point where they frequently obscure the nucleus. Sometimes the granules are arranged in a peripheral rim with a central cluster over the nucleus.
Lymphocytes are generally round or oval, with a diameter of 10.7 m, but irregular, polygonal forms are also seen. A large nucleus, with smooth outlines and following the cell contours, almost fills the cell. The nucleus is pale violet with finely clumped chromatin. The cytoplasm is visible only as a thin, slate-grey or pale-blue rim
LYMPHOCYTES.
26
Chapter 1
Fig. 1.36. Heterophil (h) of a Nile crocodile.
Fig. 1.37. Two eosinophils, Nile crocodile.
bordering the nucleus. Occasionally dustlike red granules and/or a few clear vacuoles, 1 m in diameter, are scattered through the cytoplasm. External cell borders range from smooth to ragged, frequently with bleb-like protrusions of cytoplasm. MONOCYTES. Monocytes are oval or round with a diameter of 14.3 m, with somewhat
indistinct external cell borders and numerous delicate cytoplasmic projections. The abundant grey-blue cytoplasm sometimes contains a few clear, refractile vacuoles, measuring 1.2 m. Many cells have fine dust-like granules, usually arranged in crescentic perinuclear aggregates. The plump, oval nucleus, measuring 7.1 m, is usually located centrally, but is sometimes eccentri-
Crocodiles and Alligators
cally situated adjacent to one pole of the cell. The nucleus is homogeneous light purple with finely stippled chromatin (Fig. 1.38). In addition to these typical monocytes, large cells, up to 20 m in diameter, with undulating borders, pale-blue cytoplasm with few inclusions, and prominent, indented or even horseshoe-shaped nuclei are seen occasionally. Details of crocodilian haematology are given in Chapter 2.
27
between the hemispheres and the relatively small cerebellum. The base is formed by a relatively broad medulla oblongata. Spinal cord The spinal cord extends almost to the tip of the tail. There is no cauda equina, as each pair of caudal nerves leaves the cord at the site of exit from the vertebral column (Chiasson, 1962). Peripheral nerves
Chromosomes The chromosomes of 21 species of crocodilians were studied by Cohen and Gans (1970) and of five species and several crossings by Chavananikul et al. (1994). The number of chromosomes ranges from 30 to 42 and the fundamental number from 56 to 62, for details see Table 1.2. There are no sex chromosomes.
The nervous system and sensory organs Brain The most striking features of the crocodilian brain are the two olfactory bulbs, which extend anteriorly far beyond the two cerebral hemispheres. The optic lobes are exposed
Fig. 1.38. Monocyte (m) of a Nile crocodile.
The peripheral nerves exit the spinal cord in pairs. At the level of the pectoral and pelvic girdles they are organized into a brachial and lumbo-sacral plexus, respectively. For a detailed description see Chiasson (1962). Autonomic nervous system Like higher vertebrates, crocodiles also have an autonomous nervous system, consisting of two components. The vagus nerve starts as the tenth cranial nerve and runs along the jugular to the thoracic and abdominal viscera. The sympathetic trunk runs parallel to the spinal cord and communicates with each spinal nerve, thickening at each site of communication in the form of a sympathetic ganglion (Chiasson, 1962).
28
Chapter 1
Table 1.2. The chromosomes of crocodiles. Cohen and Gans (1970) Species
2n
NF
Palaeosuchus trigonatus P. palpebrosus Melanosuchus niger Caiman latirostris C. crocodilus Alligator mississippiensis A. sinensis Gavialis gangeticus Crocodylus siamensis C. porosus C. moreletii C. johnsoni C. acutus C. intermedius C. niloticus C. novaeguineae C. cataphractus C. rhombifer C. palustris Osteolaemus tetraspis Tomistoma schlegelii
42 42 42 42 42 32 32 32 34 34 32 32 32 32 32 32 30 30 30 38 32
58 58 60 60 62 60 60 60 58 58 56 58 58 58 58 58 58 58 58 58 58
Chavananikul et al. (1994) 2n
NF
Amavet et al. (2000) 2n
42 42
30 34
58 58
32 32
58 58
30
58
2n, Diploid number; NF, fundamental number.
Ear The ear has two sensory functions, hearing and spatial orientation. The tympanic membrane of the ear is protected by a fibrous flap which closes when diving. In the middle ear the columella is attached to the tympanic membrane and at the other end it has a large basal plate set in the fenestra ovalis of the inner ear.
HEARING.
SPATIAL ORIENTATION. The membranous labyrinth consists of three semicircular canals, each with an ampulla, the utriculus and its ventral extension, the lagena, all enclosed in bone.
Both functions are served by the acoustic nerve (eighth cranial nerve) (Chiasson, 1962). Eye The eye is protected by three eyelids. The third eyelid is the nictitating membrane,
which is optically clear and protects the cornea during diving. A special muscle can retract the eye into the orbital fossa. A reflecting layer behind the retina improves night vision and causes crocodile eyes to light up at night in the beam of a torch (Fig. 1.39). There is no night vision in complete darkness without a minimum of residual light. Fat storage Fat body Being exothermic, crocodiles do not need fat for insulation. In fact, subcutaneous fat deposits would impede thermoregulation (see p. 44). Also, crocodiles do not store fat in the coronary groove of the heart. In mammals, there is growing evidence that the heart uses mainly fat as a source of energy (Medeiros and Wildman, 1997). It is believed that this is also the case in crocodiles, and that the fat supply for the heart is stored in the abdominal fat body, for which I propose the anatomical name the steatotheca (Greek stear = fat;
Crocodiles and Alligators
29
Fig. 1.39. Light of the photographic flash reflected by the eyes of the juvenile Nile crocodiles on a farm in South Africa (photo A. Brieger).
th\k\ = container, store). This organ is located in a mesenteric fold close to the right abdominal wall, immediately posterior to the liver (Fig. 1.40) (Vorstman, 1939; Mushonga and Horowitz, 1996). Its volume varies with the state of nutrition, while its shape varies from species to species (Fig. 1.41). The fat cells have large nuclei, demonstrating their ability to activate the stored fat rapidly (Fig. 1.42).
Somatic fat Additional fat may be stored in somatic fat cells with small nuclei: in the mediastinum of the thorax, under the peritoneum and between muscles, particularly ventrally in the tail between the inner (caudofemoralis) and external (ilioischiocaudalis) muscles.
Fig. 1.40. The abdominal fat body of a juvenile Nile crocodile, caudally of the right lobe of the liver and partially hidden by the duodenal loop.
30
Chapter 1
Fig. 1.41. Abdominal fat body of Osteolaemus tetraspis.
Fig. 1.42. Histology of an almost depleted abdominal fat body of a Nile crocodile hatchling. Note the large nuclei of the fat cells.
The egg Crocodilian eggs are elongate elliptical and have a hard shell. The size of the egg varies with the species, with the age of the female that lays the egg – young females laying smaller eggs than mature females – and indi-
vidually between females. Larger eggs produce stronger and more viable hatchlings, which rapidly outgrow hatchlings from smaller eggs. Parameters of American alligator eggs were determined by Cardeilhac et al. (1999b) and are summarized in Table 1.3.
Crocodiles and Alligators
Table 1.3. Summary of mean parameters of eggs of three different populations of American alligators (after Cardeilhac et al., 1999b). Parameter
Result
Egg length (cm) Egg width (cm) Egg mass (g) Length/width ratio Shell thickness (mm) Shell density Shell mass (g) Shell mass (% of egg mass) Yolk mass (g) Yolk mass (% of egg mass) Membrane mass (% of egg mass)
7.25–7.57 4.079–4.47 68.85–86.0 1.684–1.766 0.43–0.45 2.10–2.14 7.39–8.89 10.57–11.14 31.9–36.2 44–48 1.06–1.08
Eggshell The calcareous shell consists of an outer, densely calcified layer, in which the calcite crystals are stacked vertically; a honeycomb layer of horizontally stacked crystals; an organic layer, which contains a higher percentage of organic matrix; and a mammillary layer. Pores penetrate the shell surface and end between the mammillae. These pores are most frequent in the opaque zone (Ferguson, 1982). A thin, organic, probably mucinous, layer was found to cover the outer surface of some newly laid eggs and was believed to consist of the remnants of oviductal secretions. This layer was no longer present after 2 weeks of incubation. It is therefore not an equivalent
31
of the wax cuticle present on most avian eggs (Ferguson, 1982). Under the calcareous shell lies the eggshell membrane, consisting of two layers, a fibrous membrane facing the shell and a limiting membrane facing the embryo. The limiting membrane contains a large number of tiny pores and fewer large pores. Most of these pores are closed at the onset of incubation and others open up as incubation proceeds. Consequently, the shell membrane is less permeable to oxygen than the calcareous shell (Kern and Ferguson, 1997). The opaque band around the lesser circumference of the egg develops during incubation in parallel with the expansion of the chorioallantoic membrane and the mobilization of calcium out of the shell for use by the embryo (Fig. 1.43). At the same time, an extrinsic acidic degradation of the outer shell occurs due to microbial action in the nest. This produces erosion craters around the pores and increases the permeability of the shell (Ferguson, 1982). Unlike the avian egg, the crocodile egg does not have an air chamber between the shell and the shell membrane (Ferguson, 1982). Internal components The yolk, with the embryonic disc floating on top, is surrounded by a large quantity of thin albumen, which in turn is contained in a
Fig. 1.43. A banded Nile crocodile egg after removal of its contents.
32
Chapter 1
layer of thick albumen separating it from the shell (Magnusson and Taylor, 1980). If the egg is turned during laying, gravity causes the yolk with the embryo to rotate. Within 24 h of laying, the developing vitelline membrane and the embryo adhere to the shell membrane, displacing the albumen towards the poles of the egg (Webb et al., 1987). The embryo From the start of embryonic development in the oviduct, water is drawn from the albumen and secreted beneath the embryo on the inside of the vitelline membrane, where it forms the subembryonic fluid. After laying, the volume of subembryonic fluid increases rapidly, causing the volume within the vitelline membrane (containing embryo, subembryonic fluid and yolk) to expand (Webb et al., 1987). Albumen dehydration and the production of subembryonic fluid peak at the time of the expansion of the allantois. Along the shell the allantois fuses with the chorion and forms the chorioallantois (Webb et al., 1987), which becomes highly vascularized and takes on the gas-exchange function until hatching, when the lungs are able to fill with air. The different embryonic membranes and spaces are shown schematically in Fig. 1.44.
Crocodilian Physiology Yolk-sac resorption Just before hatching, the yolk-sac is drawn into the abdominal cavity and the body wall closes around the navel. At this point gas exchange can no longer take place via the membranes and the young pre-hatchling has to start using its lungs. The yolk-sac has already provided nutrition during embryonic and fetal development, and (in American alligators) has lost 25% of its mass (Fischer et al., 1991), but still contains sufficient nutrients (75% of its contents in American alligators) for the first few weeks, until the hatchling is strong enough to find its own food (Fischer et al., 1991). The contents of the yolk-sac are resorbed in two distinct ways: (i) direct resorption into the bloodstream via a capillary bed which has developed in the wall of the yolk-sac; and (ii) voiding via the vitello-intestinal duct into the intestine, digestion there and finally resorption through the intestinal mucosa. The open vitello-intestinal duct is also a major pathway for infection of the yolk-sac with intestinal bacteria, depending on intestinal colonization and peristaltic movements (see p. 142). The vitelline duct connecting the yolk-sac to the intestine is shown
Fig. 1.44. Schematic drawing of a crocodile embryo and its membranes at 45 days of incubation; ca, chorioallantois; m, shell membrane; s, shell; y, yolk-sac (after Webb et al., 1987).
Crocodiles and Alligators
in Fig. 1.45. Unlike the situation in birds, the crocodilian yolk-sac does not appear to be anchored to the navel. There do not appear to be any reports about the time it takes for the yolk-sac to be completely resorbed under normal circumstances. It is probably 3–4 weeks. This would be temperature dependent, with a slower rate of resorption at lower (suboptimal) temperatures. Infection of the vitello-intestinal duct can lead to its closure and, in this case, the yolk-sac will remain unresorbed (see p. 143).
33
enzyme in the synthesis of oestrogen. Oestrogen then binds to the oestrogen receptor, the expression of which is also modulated by the incubation temperature. Via this cascade of events low incubation temperatures favour the development of ovaries, while at high temperatures testes are produced. However, this cascade can easily be influenced, or even disrupted, by the action of external steroids (see p. 223).
Growth Sex differentiation Crocodiles do not have sex chromosomes (see above). Instead, the sex of the embryo is determined by the incubation temperature. Recently, Crews and Ross (1998) reviewed current knowledge about the mechanisms involved, as follows. At the temperature-sensitive stage early in embryonic development, temperature influences the expression of stereogenic factor 1, which in turn upregulates the expression of the gene for aromatase, the critical
Factors influencing growth The growth of juvenile crocodiles depends mainly on the environmental temperature conditions and on nutrition, although genetic and clutch-related factors probably also play a role (Garnett and Murray, 1986). The most important clutch-related factor is egg size and consequently hatchling size, as small hatchlings are generally poor growers. Stress caused by high stocking density can depress the growth rate (Elsey et al., 1990a) (see also pp. 116 and 280).
Fig. 1.45. One-day-old gharial hatchling, showing the yolk-sac connected to the intestines by the vitelline duct. Note the double duodenal loop of this species.
34
Chapter 1
Metabolic rate The metabolic rate of crocodiles depends on their size and activity, and the temperature (Baldwin et al., 1995; Munns et al., 1998). At 28°C a 70 kg American alligator produces about 72 kcal day1, i.e. about 4% of that of a person of equal mass. At 32°C the rate doubles. However, a hatchling at 28°C has half the human metabolic rate (Coulson et al., 1989). Stress-related reduction of the growth rate – runting – of some individuals is a common occurrence on crocodile farms (see p. 234). A positive influence of sunlight on the growth rate was found by Zilber et al. (1991), but the small number of individuals involved, the poor overall growth rates achieved and the high mortality in the experimental groups severely limit the usefulness and credibility of their results. Generally, growth rates, particularly weights, achieved on farms exceed those in the wild. One-year-old wild IndoPacific crocodiles attained 0.73 m and 0.87 kg, while farmed ones of the same age averaged 0.75 m and 1.36 kg (Webb et al., 1991). Crocodiles may continue growing throughout their life, males faster than females. The growth of adult females is further reduced by reproductive demands. With increasing age the growth in length slows down and is replaced by growth in width, leading to a maximum length, at least in American alligators, which might not be exceeded (Woodward et al., 1995). Young females lay smaller eggs and smaller clutches than older ones. There is also some indication that, in individual females, egg size and clutch size are inversely related.
Allometry Allometric studies have shown that the body and tail grow faster than the head and legs, although at some stage the snout length grows faster than any other part measured. These changes in the proportions of the different parts of the body allow the growing crocodiles to adjust to the different demands made by the environment on crocodiles of different sizes (Kramer and Medem, 1955; Junprasert and Youngprapakorn, 1994).
The correlation between myocardial mass, i.e. the mass of the two ventricles of the heart, and body length of Nile crocodiles was examined by Huchzermeyer (1994). The ventricular mass can be used as a standard for the evaluation of other more variable organs, particularly the fat body and spleen (see p. 85). Bone rings In most crocodilian species growth is seasonal and this is reflected by bone deposition. Such growth rings can be detected histologically and are used to estimate the age of the crocodile in question (de Buffrénil, 1980a,b; de Buffrénil and Buffetaud, 1981; Wagner et al., 1990). Experimentally, this method can be enhanced by feeding tetracycline which is deposited in the bone in the form of visible, stained rings (Roberts et al., 1988). The growth rate of crocodilians is limited by the slow deposition of lamellar bone. This was the case even in the giant crocodile Deinosuchus of the Late Cretaceous period of North America (up to 10 m in length), which is estimated to have taken 35 years to reach adult size (Erickson and Brochu, 1999). Age–length–weight relations The age–length relation depends on the growth rate, while the length–weight relation depends on the actual state of nutrition. Consequently these relations differ between wild and farmed crocodiles, the latter growing faster and being fatter. There are also individual differences. Some examples of such relations in American alligators, Nile crocodiles and African dwarf crocodiles are given in Tables 1.4 to 1.6. Further length–weight relations for Nile crocodiles can be found in Table 2.10. Mathematical approaches to length–mass relationships of crocodilians were explored by Wilkinson et al. (1997). Longevity While captive American alligators may live for up to 70 years, they do not appear to
Crocodiles and Alligators
35
Table 1.4. Age–length–weight relations of marked and released American alligators (McIlhenny, 1934). Age 1 day 32 days 10 months 12 months 15 months 20 months 21 months 2 years 1 month 2 years 8 months 3 years 2 months 3 years 10 months 4 years 2 months 6 years 6 years 9 years 9 years 10 years 10 years 11 years
Sex
Length (m)
Weight (kg) 0.071–0.085
Female Male Female Male Female Male Male
0.23–0.24 0.34–0.37 0.45 0.67 0.69–0.81 0.75 0.79–0.82 0.99–1.20 1.09–1.14 1.27–1.50 1.18–1.73 1.58–1.71 1.61–1.75 1.75–2.39 2.01–2.08 2.35–2.68 2.17–2.21 2.69–2.87 2.64–3.07
0.24 1.84 1.93–2.37 1.41 1.64–1.84 4.35–5.64 3.66–4.54 7.83–9.57 5.06–13.3 8.85–17.5 13.6–17.3 18.9–56.6 38.2–40.4 57.0–67.6 49.9–52.8 80.7–132.2 76.9–160.6
Table 1.5. Age–length–weight relations in farmed Nile crocodiles (Loveridge and Blake, 1972). Age
Sex
N
Length (m)
Weight (kg)
19–20 months 32 months 32–33 months 46–47 months 51–54 months
Female Male Female Female Female Female Male
5 4 4 2 2 2 1
0.91–1.18 1.18–1.33 0.98–1.40 1.18–1.75 1.91 2.82 3.92
1.75–5.3 5.5–8.9 3.2–9.7 5.9–25.4 32.6–33.5 125 312
Table 1.6. Age–length–weight relations of two African dwarf crocodiles reared in captivity (Helfenberger, 1982). Age
Length (m)
Weight (kg)
10 weeks 6 months 1 year 2 years
0.26–0.31 0.36–0.41 0.63 0.77–0.78
0.08–0.14 0.23–0.40 1.29–1.40 2.01–2.70
reach more than 50 years in the wild (Woodward et al., 1995). Similar ages may be attained by individuals of other crocodilian species. However, estimates may be far out. An American crocodile with an estimated age of 100 years was mentioned by Jasmin and Baucom (1967).
Locomotion Swimming The crocodilian body is designed primarily for swimming. During this action the front legs are held parallel to the thorax, while the hind legs are partially spread out to act as rudders. Sideways movements of the tail provide the propelling force for both slow and rapid swimming. Rapid swimming can be extremely fast and can catapult the crocodile out of the water at a very high speed when it attacks a prey on land close to the water. At lower temperatures the swimming speed is reduced. In juvenile American alligators the swimming speed increased at
36
Chapter 1
temperatures from 15°C to 20°C, but not between 20°C and 30°C (Gatten et al., 1991). Sliding Sliding occurs when the body is not lifted off the ground. This kind of motion is used over short distances on land and always when going into water. Sometimes referred to as ‘sprawling’, it is also seen in the transition from stationary to ‘high walk’ (Elias and Reilley, 1996). On farms sliding can damage the chin, the belly skin and the soles of the feet if the floor of the pen consists of concrete that is not absolutely smooth or covered with a protective paint. Gharials cannot walk. On land they slide, moving their body forward with all four legs acting simultaneously. Walking When walking the crocodile lifts its whole body off the ground. In this way it can move over rough terrain without getting scratched or torn. It is a stately motion, similar to that of a tortoise when walking. It is also referred to as ‘high walk’. Running A faster way of moving on land is running, which is a kind of galloping motion. This can be quite fast, but can only be sustained over short distances. Jumping Hatchlings and yearlings of the African dwarf crocodile have an additional mode of locomotion. They use their relatively strong hind legs to jump in a frog-like fashion when frightened while on land. Each jump propels the hatchling forward by up to 1 m and it may jump several times in succession. Crocodiles can also jump out of deep water to catch prey high above the water or out on land. To achieve this they gather speed under water before surfacing.
Digestion Ingestion Small prey is swallowed whole, though it is at least punctured during the act of catching and killing. Larger prey is masticated for a while before deglutination (Diefenbach, 1975a). However, crocodiles do not reduce the size of the morsels by prolonged chewing. Excessively large prey is reduced by worrying and ripping off bits or limbs by rapid rotation around the longitudinal axis of the crocodile. Ripping is facilitated when several crocodiles feed from the same carcass. Small bits are taken off the ground by holding the head sideways (see Fig. 3.20). Reduction In the stomach the swallowed food is exposed to the action of hydrochloric acid (HCl) and peptic proteolysis. Their secretion is stimulated by the presence of the food, while penetration into the food is facilitated by the puncturing and chewing that has taken place before swallowing. Gastric pH drops as low as 1.2 and in fasting animals even stays below 2.5 (Diefenbach, 1975a). Gastric contractions mixing the stomach contents take place 2–3 times per minute when the stomach is full (Diefenbach, 1975b). At 30°C complete emptying of the stomach took 99 h on average and at 15°C 315 h (Diefenbach, 1975b). However, Kanui et al. (1991) recorded gastrointestinal passage times in 12-week-old Nile crocodiles as 35 h at 30°C and 44 h at 25°C. Lithophagy Stones (gastroliths) are often found among crocodilian stomach contents. The question remains whether these stones are needed to grind the ingested food, similar to the situation in an avian gizzard, whether they are needed as ballast, or whether they are swallowed accidentally (Sokol, 1971) (see also p. 15). Here it should be noted that predatory (carnivorous) birds do not use stones in their gizzards. Fitch-Snyder and Lance (1993)
Crocodiles and Alligators
37
observed captive juvenile American alligators actively seeking out and swallowing gravel. However, this could have been due to a behavioural disturbance similar to the frequently seen ingestion of foreign objects by stressed farmed or captive ostriches (Huchzermeyer, 1996a) (see also pp. 281 and 290).
they were kept at a constant temperature. It is unclear whether this response was triggered by diminishing daylength or whether it might be governed by a built-in body clock. This phenomenon has also been observed in captive Nile crocodiles (personal communication, L. Fougeirol, Pierrelatte, 2002).
Regurgitation
Normal oral flora
When American alligators eat hairy prey, the indigestible hair forms hair balls, which are then regurgitated. Smaller foreign bodies may also become incorporated in these hair balls and regurgitated as well. Even radio collars attached to released juvenile alligators have been found regurgitated after the bearers had been cannibalized (Chabreck, 1996; Chabreck et al., 1996). Digestion The combined action of pepsin and HCl in the stomach digests most of the protein in the food and dissolves the bones of the prey. Further protein, glycogen and fats are digested in the upper small intestine under the action of bile and pancreatic secretions. There is some evidence that frequent filling of the stomach reduces the digestive efficiency of the system (Webb et al., 1991). There is a suspicion that excess fat in the diet might interfere with proteolytic activity and therefore Webb et al. (1991) recommend a maximum of 9% fat in crocodile rations.
Identification of the oral flora of crocodilians is important for the treatment of bite wounds. The work done on American alligators can be taken as representative for all crocodilian species. Doering et al. (1971) isolated Clostridium spp., Citrobacter, Enterococcus spp. ‘and others’ from two American alligators. Flandry et al. (1989) examined ten alligators from three different locations and found both aerobic and anaerobic bacteria in all of them, but isolated fungi from only seven individuals (Tables 1.7–1.9). The bacterial oral flora of 19 farmed spectacled caimans in Brazil comprised the genera Citrobacter, Providencia, Escherichia, Proteus, Morganella, Serratia, Edwardsiella, Aeromonas, Acinetobacter, Staphylococcus, Streptococcus and Bacillus (Matushima and Ramos, 1993). Table 1.7. Oral anaerobic bacterial flora of ten American alligators (Flandry et al., 1989). Genus
Species
N
Bacteroides
asaccharolyticus bivius loeschei/denticola oralis sordellii thetaiotamicron vulgatus bifermentans clostridioforme limosum sordellii tetani nucleatum varium magnus prevotii
2 3 2 3 1 1 1 3 1 1 2 1 2 3 1 3
Assimilation Assimilation is the uptake of the digested food from the intestine either into the venous circulation and hence into the liver, or via the lymph directly into the general circulation. This takes place throughout the length of the small intestine (duodenum, jejunum and ileum). Seasonal suppression of appetite Coulson et al. (1950) observed that captive American alligators practically stopped feeding during autumn and winter, although
Clostridium
Fusobacterium Peptococcus
N, number of isolates.
38
Chapter 1
Table 1.8. Oral aerobic bacterial flora of ten American alligators (Flandry et al., 1989).
Flora of the gular and paracloacal glands
Genus
Species
N
Acinetobacter Aerobacter Aeromonas Citrobacter Corynebacterium Diphtheroides Enterobacter Klebsiella Moraxella Morganella Pasteurella
calcoaceticus var. wolffi radiobacter hydrophila freundii sp. sp. cloacae oxytoca sp. morganii haemolytica sp. vulgaris cepacia fluorescens pickettii odorifera
1 3 9 4 1 2 2 1 1 1 1 1 7 2 1 1 1
Proteus Pseudomonas
Serratia
N, number of isolates.
Table 1.9. Oral fungal flora of ten American alligators (Flandry et al., 1989). Genus
Species
N
Aspergillus Candida
flavipes humicola lipolytica rugosa zeylansides sp. sp. sp. sp. sp. sp. sp. rubra sp. beigelii sp.
1 1 1 2 1 1 1 1 1 2 1 1 2 2 2 1 6
Cladosporium Curvularia Drechsleria Epicoccum Fusarium Penicillium Rhodotorula Trichoderma Trichosporon Torulopsis Unidentified moulds
N, number of isolates.
Williams et al. (1990) isolated the following aquatic and intestinal bacteria from either or both pairs of the exocrine skin glands of 23 adult American alligators: Acinetobacter anitratus, A. wolffi, Aeromonas hydrophila, Bacillus sp., Citrobacter amalonaticus, C. freundii, Corynebacterium sp., Enterobacter agglomerans, E. cloacae, Edwardsiella tarda, Escherichia coli, E. hermanii, Flavobacterium indoltheticum, F. gleum, F. multivorum, Hafnia alvei, Klebsiella pneumoniae, Proteus mirabilis, Pseudomonas cepacia, P. maltophila, Serratia marcescens and Yersinia enterocolitica.
Normal intestinal flora The intestinal flora plays an important protective role by occupying the available attachment sites and thereby displacing pathogenic intruders, a phenomenon referred to as competitive exclusion. Intensively reared crocodiles often have a single-species flora, an abnormal situation that makes them prone to intestinal infection. Despite its importance, this appears to be a neglected subject, probably partly due to the difficulty of obtaining specimens from animals in the wild, since they are usually in remote places. Most of the published results are from captive crocodiles and it is doubtful that they are representative of a normal intestinal flora. Campylobacter fetus subspecies jejuni serotype 23 was isolated from a captive African dwarf crocodile (Luechtefeld et al., 1981). Misra et al. (1993) examined cloacal swabs of 23 captive gharials and the results are shown in Table 1.10. Table 1.10. Aerobic bacterial intestinal flora of captive gharials, N = 23 (Misra et al., 1993). Organism
Crocodiles, particularly in captive or farm situations, tend to contaminate their aquatic environment with faecal bacteria and fungi. Thus it is not surprising that the oral flora should be similar to that of the intestine.
Staphylococcus sp. Aeromonas hydrophila Citrobacter sp. Edwardsiella tarda Haffnia alvei Escherichia coli
Pure
Mixed
4 1 – 3 1 2
10 6 6 – – 7
Crocodiles and Alligators
Roggendorf and Müller (1976) isolated Citrobacter sp., Escherichia coli, Proteus mirabilis, P. vulgaris and Aeromonas hydrophila from the faeces of one captive Nile crocodile and Citrobacter sp., Providentia rettgeri and Aeromonas hydrophila from the faeces of a C. crocodilus. Huchzermeyer and Agnagna (1994) reported the isolation of aerobic bacteria and fungi from 21 wild-caught and severely stressed African dwarf crocodiles which were sampled when they were slaughtered at markets in Brazzaville, Congo Republic. These and subsequently published isolations from samples collected during a second expedition in 1995 (Huchzermeyer
39
et al., 1999) are shown in Tables 1.11 and 1.12. Respiration Ventilation There are two types of ventilatory movements, pharyngeal and thoraco-abdominal. Pharyngeal ventilation does not contribute to the air flow to the lung. It only serves to move air through the nasal passages for olfaction. Thoraco-abdominal movements involve the diaphragmatic muscles for inhalation and the intercostal and abdominal muscles for exhalation (Gans and Clark, 1976).
Table 1.11. Aerobic bacterial intestinal flora of African dwarf crocodiles (Huchzermeyer et al., 2000). Genus
Species
Alcaligenes Bacillus
faecalis alvei cereus circulans coagulans amalonaticus freundii nishinomyaensis agglomerans cloacae gergoviae caecorum durans faecalis faecium pseudoavium solitarius coli balustinum odoratum oxytoca varians gibsonii sp. luteus mirabilis serovars odorifera chromogenes epidermidis xylosus salivarius sp.
Citrobacter Dermacoccus Enterobacter
Enterococcus
Escherichia Flavobacterium Klebsiella Kocuria Kurthia Lactobacillus Micrococcus Proteus Salmonella Serratia Staphylococcus
Streptococcus Streptomyces N, number of isolates.
N (1993)
11 1 1 1 3 1 7
10
N (1995) 2 1 4
1 1 1 1 1 1 1 7 1
8 1 2
1 4 6 3 1
1 2 1 3
2
4 1 2 1 1
40
Chapter 1
Table 1.12. Fungal intestinal flora of African dwarf crocodiles (Huchzermeyer et al., 2000). Genus
Species
Acremonium Arthrinium Aspergillus
sp. sp. clavatus flavus niger sp. guillermondii krusei sp. lipolytica luteolus sp. sp. candidum sp. sp. sp. sp. beigelii capitatum
Beauveria Candida Chrysosporium Cryptococcus Curvularia Fusarium Geotrichum Paecilomyces Penicillium Phoma Trichoderma Trichosporon
N (1993) 1 1 5 2 2 3 2 1 3 3 1 1
N (1995)
2
3
1 4 2 7 2
2 1
2 1
N, number of isolates.
Respiratory rate Respiration takes place in cycles of two to three rapid movements followed by a longer pause (Gans and Clark, 1976). The respiratory rate depends on the size of the animal, decreasing with increasing body mass (Gans and Clark, 1976). It is also influenced by temperature, increasing with increasing body temperature (Campos, 1964; Smith, 1976), with lower rates during warming than during cooling (Smith, 1976). There appeared to be a low correlation between the metabolic rate and the respiratory rate (Huggins et al., 1971). Respiratory rates for different sized crocodiles are given in Table 1.13. The respiratory rate of 123 crocodiles of 27.4 min1 reported by Sigler (1991) falls entirely outside the range of all the other observations and may possibly include pharyngeal (gular) movements. Diving The following is based on work with IndoPacific crocodiles by Wright (1987). Most voluntary dives are short, only lasting ±5 min. During these dives the metabolism stays aero-
bic. Forced dives occur when the crocodile is disturbed and can last for up to 1 h. During these dives the metabolism slows down and becomes anaerobic as an oxygen debt develops. A crocodile disturbed during a voluntary dive immediately changes its metabolism. The diversion of the arterial blood flow away from muscles during forced diving conserves oxygen reserves for the functioning of the brain. Lactic acid accumulated in the muscles enters the circulation only after the crocodile emerges (Andersen, 1961). Oxygen consumption In both American alligators and Nile crocodiles, the oxygen consumption of inactive animals was found to increase as the temperature rose. However, in Nile crocodiles it was found to decrease between 25 and 30°C and then rise again steeply to 35°C (Brown and Loveridge, 1981; Lewis and Gatten, 1985). The decrease is seen as an adaptation to nocturnal activity, which is usually at lower temperatures (Brown and Loveridge, 1981). In the American alligator values ranging from 0.08 to 0.2 ml g1 h1 correspond
Crocodiles and Alligators
41
Table 1.13. Respiratory rates of crocodiles. Species
Mass (kg)
Breaths per min
Temperature (°C)
Reference
Caiman crocodilus
0.18 0.29 0.65 4.8 4.8 5.0 1.15–8.78 0.46–1.31
0.58 0.63 0.57 0.25 0.14 0.17 3.3a:1.5b 0.39–4.95
23–25
1 1 1 1 1 1 2 3
Alligator mississippiensis
23–25
a During
cooling. warming. 1, Gans and Clark (1976); 2, Smith (1976); 3, Huggins et al. (1971).
b During
with those cited from a number of reports (Lewis and Gatten, 1985). Similar values were established for the Nile crocodile (Brown and Loveridge, 1981). Non-respiratory CO2 excretion A relatively low respiratory quotient in crocodilians is explained by the excretion of large amounts of ammonium bicarbonate in the urine (Coulson and Hernandez, 1964; Grigg, 1978), while Davies (1978) suggested cutaneous CO2 loss as an explanation (see also below). Acid–base balance In American alligators and in Indo-Pacific crocodiles, arterial pH decreased with rising body temperature, while arterial PCO2 increased (Davies, 1978; Davies et al., 1982; Seymour et al., 1985; Douse and Mitchell, 1991). Respiratory regulation In progressively anaesthetized American alligators it was shown that central chemoreceptors play a significant role in ventilatory regulation (Branco and Wood, 1993).
and uric acid in their urine, but when they are fed maximally the excretion of ammonia increases while the proportion of uric acid in the urine decreases. This decrease in uric acid clearance leads to increased plasma uric acid levels, predisposing the animals to gout (see p. 230). Only negligible amounts of urea are produced (Khalil and Hagagg, 1958; Herbert, 1981). The white deposits in crocodile urine consist mainly of uric acid crystals (Khalil and Hagagg, 1958). The glomerular filtration rate remains fairly constant under different conditions, and the tubules have little capacity to regulate the osmolality of the urine. However, cloacal absorption varies with the salt load (Schmidt-Nielsen and Skadhauge, 1967). Salt lost into the freshwater environment is replaced constantly by the salt contained in the prey. Excess salt is excreted by specialized salt glands, as is the case in other marine reptiles (Schmidt-Nielsen and Fange, 1958) (see also p. 14). Ammonia is thought to be excreted in the form of NH4HCO3 which may be responsible for a substantial deficit in respiratory CO2 (Schmidt-Nielsen and Skadhauge, 1967; Grigg, 1978) (see above).
Responses to high salinity Excretion Fasting crocodiles and alligators produce approximately equal quantities of ammonia
All alligatorines and most crocodiles are freshwater species with poor salt tolerance. However, four crocodile species (C. porosus, C. johnsoni, C. niloticus and C. acutus) have
42
Chapter 1
estuarine populations. Large specimens of C. acutus lose weight more slowly in sea water than small ones, and NaCl loading causes a reduction in cloacal flow rate, thus conserving body water (Ellis, 1981). Alligators osmoregulate by keeping a low body sodium turnover, by the low permeability of the skin to sodium and even by keeping a relatively low water turnover. Estuarine crocodiles add to that effect by the excreting of excess salt through the lingual salt glands (p. 14). Freshwater species of crocodiles also have these salt glands and may use them in aestivation during drought periods (Mazzotti and Dunson, 1989). Water loss through the skin when it is exposed to dry air may be considerable and the lost water can only be replaced by drinking, not absorbed through the skin (Cloudesley-Thompson, 1968).
Reproduction Laying cycle Crocodiles reproduce by laying eggs, as the temperature control of sex determination does not allow internal incubation (ovovivipary) as occurs in some snakes and lizards. Most species lay only one clutch of eggs per year, the mugger being the exception, with two cycles per year occurring regularly (Whitaker and Whitaker, 1984). However, many females in the wild do not reproduce every year, probably depending on their nutritional state (Lance, 1987; Kofron, 1990). Clutch and egg size Egg size and egg number per clutch are species dependent but increase with the size and age of the female, with younger females laying small eggs from which fewer, smaller and more slowly growing hatchlings are produced. Hormonal control The hormonal control of the reproductive cycle and factors influencing this control
have been described by Lance (1987). A sexsteroid-binding protein, seasonally present in the plasma of female American alligators and probably other crocodiles as well, prevents the delivery of free steroid to target organs outside the breeding season (Ho et al., 1987). Ovulation All follicles are normally ovulated together over a period of a few hours (personal communication, V.A. Lance, San Diego, 2000), but according to Youngprapakorn (1990b) sometimes some follicles ovulate prematurely and proceed through the oviduct to the uterus in advance of the others. Fertilization takes place in the infundibulum or upper oviduct before the albumen and shell are secreted in the glandular part of the oviduct (uterus). The eggs are then stored in the muscular part (vagina) until they are laid. In the American alligator the eggs are stored in the vagina for 3–3.5 weeks before they are laid (Lance, 1989). During this time, before oviposition, initial embryonic development is already taking place, to the 15–17 somite stage and occasionally further (personal communication, V.A. Lance, San Diego, 2000). Oestradiol liberated during ovulation increases plasma calcium levels for the production of the eggshells, but, unlike birds, crocodiles do not deposit calcium in their bones before ovulation (Elsey and Wink, 1986). Nesting and incubation Nesting habits vary from species to species. Forest-dwelling species build nest mounds from leaves scooped up from the forest floor and depend on the heat produced by composting, rather than on the sun, to incubate the eggs. Swamp dwellers make nest mounts from swamp vegetation and rely on composting heat as well as on the sun for the incubation of the eggs, while crocodiles living in rivers nest in the sandy banks above the flood level and rely on the sun for incubation heat. All eggs in the clutch are deposited into the nest at the same time and covered again with nesting material. The
Crocodiles and Alligators
incubation period depends on the species as well as on incubation temperature, decreasing with rising temperature, and ranges roughly from 60 to 90 days.
43
6.3 ml and a circulation time of 27 min (Coulson et al., 1989). Bradycardia
Cross-breeding Several species of crocodiles cross-breed voluntarily, producing fertile hybrids (Youngprapakorn, 1990a; Thang, 1994). As these hybrids tend to be more vigorous, they are sought after by some farmers. Escaped hybrids, however, can pollute existing wild populations and this constitutes a considerable danger to the conservation of certain crocodile populations.
Diving bradycardia occurs when crocodiles dive after a sudden fright. Under these circumstances the heart rate decreases from around 30 beats per minute to 2–5 beats per minute, but not during voluntary (shortterm) dives (Gaunt and Gans, 1969; Smith et al., 1974). During bradycardia the blood pressure is maintained by peripheral vasoconstriction (Jones and Shelton, 1993). Shunt
Circulation Blood flow The flow of blood transports oxygen and nutrients to the organs and tissues, and CO2 and end-products of metabolism from the organs and tissues to the lungs and kidneys. In addition, it can speed up the transport of heat from the skin to the internal organs when the crocodile is basking, move white blood cells and antibodies to infection sites, and hormones to targeted organs. A 70 kg American alligator at 28°C has a blood flow of 0.2 l min1, a stroke volume of 6.3 ml, a circulation time of 27 min and 4% of the metabolic rate of a person of equal mass (Coulson et al., 1989). Heart rate The heart rate depends on the size of the animal and on the temperature. In 57- to 78-cmlong American alligators at an ambient temperature of 22–25°C it was 18.7 beats per minute (Huggins et al., 1971). In anaesthetized American alligators from 1.5 to 4.3 kg live mass it ranged from 10 beats per minute at 10°C to 30 beats per minute at 30°C (Campos, 1964). At 38°C and above irreversible damage occurred through overheating (Wilber, 1960). At 28°C a 70 kg American alligator had a blood flow of 0.2 l min1, a stroke volume of
Under certain conditions, venous (deoxygenated) blood can become mixed with arterial (oxygenated) blood through the foramen of Panizza, through direct release into the right aorta and through the anastomoses between the right and left aortas (see p. 23). This mixing of venous and arterial blood is referred to as a left-to-right shunt. Jones and Shelton (1993) described a biphasic systolic pressure curve in the right ventricle of resting crocodiles in which the first phase supplies the pulmonary artery and the second phase supplies the right aorta. This shunt diverted 15–25% of the venous blood away from the pulmonary circulation. They speculated that in addition to the respiratory requirements for a shunt during forced diving, the alkaline wave caused by the production of HCl in the stomach after a meal also necessitated a flow of venous (acidic) blood to the digestive viscera. Vasoconstriction Vasoconstriction is mediated hormonally and by nervous stimuli and can occur locally, e.g. as a response in thermoregulation (see below), or systemically. Adrenaline was found to produce a stronger vasoconstriction in the American alligator than noradrenaline (Akers and Peiss, 1963). Angiotensin I of the American alligator was found to be closely related to that of the chicken (Takei et al., 1993).
44
Chapter 1
Nervous activity The brain of the crocodile is larger and better organized than that of other reptiles, but it is still relatively small in relation to the crocodile’s body mass. Many functions are therefore delegated to centres in the spinal cord. During hypothermia (2–4°C) in restrained American alligators (size not stated, but probably large as their sex was stated), the electrical activity of cerebrum and optic lobes decreased, whereas it increased in the cerebellum (Parsons and Huggins, 1965). Compared with that of other reptiles, as well as with that of many birds and mammals, the hearing of crocodiles is very acute, particularly in the middle range but less so for high and low tones (Wever, 1971). On the farm, the crocodiles rely mainly on smell and hearing to recognize the person usually working with them. In nature they recognize each other by the excretions of their skin glands (see p. 52). Therefore, captive or farmed crocodiles may fail to recognize, and thus be disturbed by, people who occasionally wear perfume.
Thermoregulation Crocodiles are exothermic reptiles, unable to maintain a constant internal body temperature independently of the environment. However, they try to achieve and then maintain their temperature within a preferred range, and they do this by making use of thermogradients in the environment. These gradients exist between sun and shade, warm surface water and cool deep water. Some species also make use of burrows in which their rate of cooling during winter nights would be slower than in cold water (Pooley, 1962) or which protect them from heat and dehydration during aestivation (Christian et al., 1996). During cooling the blood circulation to the body surface is restricted, thus reducing the rate of cooling. During warming the blood flow to the skin is increased and the warmed blood transports the heat to the internal organs (Johnson, 1974; Grigg and Alchin, 1976; Johnson et al., 1976; Drane et al.,
1977; Johnson and Voigt, 1978; Smith and Adams, 1978; Smith et al., 1978; Smith, 1979). When basking in shallow water, the blood supply to the submersed skin is reduced, while it is increased to the skin exposed to the air and sun (Johnson, 1974). The osteoderms may also play a role in thermoregulation as heat collectors (Seidel, 1979). Gaping increases evaporation and thereby contributes to cooling, which at certain times of the day appears to be preferred to going into the water. However, gaping may also be used to increase the temperature-exchange surface. Consequently Nile crocodiles have been observed gaping while basking on a cold African winter morning (own observation). The preferred temperature depends on the crocodile’s activity: fasting crocodiles prefer cooler and feeding ones select higher temperatures (Lang, 1979). Endogenous (metabolic) heat plays a role only in very large crocodiles with a low surface area to mass ratio (Smith, 1979). In very cold winter weather American alligators remain close to the surface, with only the nostrils protruding from the water. In this position, called ‘icing’, they are safe from suffocation when the water freezes over (Hagan et al., 1983; Lee et al., 1997). However, even such specimens do not survive if their internal temperature falls below 4.5°C (Brisbin et al., 1982). A released American alligator in a swamp in Pennsylvania appears to have survived at least six cold winters before it was shot (Barton, 1955). Nile crocodiles tolerate a minimum internal temperature of 10°C. Exposing juvenile farmed crocodiles to varying temperature regimes, Turton et al. (1994) found that high temperatures are more stressful than lower ones, and that temperature changes are always accompanied by increased corticosterone levels. Certain farming conditions tend to expose the crocodiles periodically to overheating as well as to widely fluctuating day–night temperatures, a situation that is obviously to be avoided. It is my belief that for their well-being crocodiles need to be able to thermoregulate actively along a thermogradient within the range of preferred temperatures. They
Crocodiles and Alligators
should also be strictly protected from forced overheating, i.e. being exposed to high temperatures without any means of avoiding the heat or being able to cool down. The growth rate of juvenile crocodiles is closely related to the temperature at which they are kept, with the fastest growth seen in those kept closest to the preferred maximum temperature, and particularly in those with the highest preferred temperature (Lang, 1987). As the preferred temperature is influenced by the incubation temperature, one can actively select for a higher temperature preference, and thus for faster growth, by incubating at a higher temperature (Lang, 1987).
Immunity Crocodiles can react to infections by developing antibodies and thus becoming immune to the agent in question. The white blood cells that play a role in this system
45
have been described above (p. 25). In response to a stimulus, lymphocytes are produced in the thymus and spleen. An active spleen increases in size very rapidly, but as the tough fibrous capsule resists this rapid growth, the active tissue buds out through the capsule, giving the hypertrophic spleen an irregular, knobby appearance (Fig. 1.46). Unlike other reptiles, crocodiles are capable of an anamnestic response. Young American alligators immunized with 50 mg haemocyanin had antibodies in their blood after 20 days. However, when given a second injection of 2.5 mg, antibodies became detectable after only 2 days (Lerch at al., 1967). An immunoglobulin with two IgG-like light chains was isolated from American alligators by Saluk et al. (1970). Turton et al. (1994) isolated an immunoglobulin from juvenile Indo-Pacific crocodiles and identified it as IgG, with a molecular weight of 218 kDa and heavy and light chains of 57 and 27 kDa, respectively.
Fig. 1.46. ‘Budding’ hypertrophic spleens as a consequence of an immune response.
46
Chapter 1
American alligators did not have any isohaemagglutination, but their serum contained three agglutinins, one for all human cells, another similar to the -agglutinin and one similar to the -agglutinin of human serum (Bond, 1940).
ulocyte migration in the first 3 days. Later monocytic cells predominated, including vacuolated macrophages. From 14 days onwards zones of necrotic debris (most likely exudate, see above) were surrounded by palisades of vacuolated multinucleated giant cells and capillary-laden immature fibrous connective tissue.
Inflammation Exudation Inflammation is a reaction by the body to localize, isolate and fight a local infection or other injury. The first step is a congestion of the local capillaries, allowing serum to seep into the tissue and cause oedema. In mammals, the liquid from this oedema is filtered with the lymph through lymph nodes, but crocodiles, like birds, lack lymph nodes. To prevent the drainage of pathogens away from the inflammation site directly into the general circulation, they exude fibrin into the inflamed site, which immobilizes all the pathogens and prevents their escape. This is a very successful strategy, with the result that crocodiles and birds rarely contract septicaemia from wound infections. However, if the inflammatory cells are unable to remove the invading pathogens, the exudation process continues and ultimately can lead to serious problems. Abscess, fibriscess Fibrin also inhibits the movement of leucocytes and prevents the liquefaction of necrotic tissue, with the result that true abscesses filled with liquid pus cannot be formed. Hard swellings forming at the site of an infected wound consist of sheets of fibrin between the tissues and these are extremely difficult to remove surgically. Veterinarians often refer to this exudate erroneously as ‘inspissated pus’. Since such a fibrin-filled swelling cannot be classified as a true abscess, it should rather be called fibriscess (Huchzermeyer and Cooper, 2000). Cellular reactions After subcutaneous injection of turpentine into juvenile American alligators, Mateo et al. (1984b) observed oedema followed by gran-
Fever Fever results from a higher setting in an animal’s thermoregulatory system in reaction to an infection or similar event. In endotherms the increase in temperature is achieved metabolically, but crocodiles, as ectotherms, have to adjust their temperature behaviourally by selecting a higher temperature on the environmental gradient (Lang, 1987) (see p. 44).
Disease In a holistic view, a healthy animal lives in a state of balance with its natural environment. Within certain ranges it can respond to all physical, chemical and biological challenges. These challenges may act singly or in combination (Fig. 1.47). The responses are the defences. An animal that is unable to defend itself adequately against any such single or combined challenge slides into a state of imbalance that is referred to as disease (Wedemeyer et al., 1976). Captive, farming and ranching conditions are usually different from natural conditions and often far from ideal. Often they increase the severity of the challenges while limiting the animal’s ability to respond. Such conditions can easily cause an animal to become imbalanced and diseased. From the holistic definition of disease it is clear that such a state cannot be diagnosed merely by examining the affected animal alone, nor by the laboratory analysis of certain specimens taken from the diseased or deceased animal. In addition, all factors in the environment, as well as nutrition, have to be taken into consideration. Equally, all contributing environmental and other factors must also be considered when formulating a
Crocodiles and Alligators
47
Fig. 1.47. Schematic drawing of the physical, chemical and biological challenges countered by the appropriate responses of the crocodile in a state of balance.
course of treatment or a prophylactic programme. It is for this reason that chapters on behaviour, nutrition and farming practices have been included in this book. It is of little use if in a diagnosis the terms ‘stress’ and ‘poor management’ are used without clarifying the exact circumstances involved in the particular case, nor does the isolation of a pathogen from a crocodile necessarily mean that this was the primary cause of disease or death. Also, none of the crocodile-specific pathogens (viruses, bacteria, etc.) are primary pathogens. All are opportunists, waiting for a weakened or stressed animal in which to produce the specific disease. In all such cases one should always ask: Why did this happen? One should always investigate the circumstances of the outbreak. In a way, it is unfortunate that in a book like this the individual diseases have to be discussed in relation to their causal agent, when in reality they are all influenced or even triggered by environmental factors.
Crocodilian Biochemistry This section concentrates on diagnostic biochemistry, trying to give normal values, as far as they are known.
Blood biochemistry Published values of the blood (serum, plasma) biochemistry of crocodilians are given in Tables 1.14 to 1.16. Since most of these values are from captive or farmed animals, there may be some doubt as to whether they can be taken as normal values. Species differences may play a role and the stress involved in immobilizing the animals for sampling might also affect the results. However, they may still give some guidance for the interpretation of results of clinical investigations. In addition, thyroxine values are given in Table 1.17. In juvenile American alligators the injection of alligator, turkey or bovine insulin caused a hypoglycaemia lasting from 12 to 120 h after the injection, and a much more rapid decrease in plasma amino acids lasting from 2 to 36 h after the injection (Lance et al., 1993). All blood chloride, bicarbonate, pH and sodium values should be determined on animals that have been fasting for at least 3 days. This is because far-ranging changes are brought about by the alkaline tide following the ingestion of food, with all the accompanying changes in blood electrolytes (Coulson et al., 1950).
48
Chapter 1
Table 1.14. Blood biochemistry of farmed and captive crocodiles. Parameter
Unit
Total protein Albumin Globulin Glucose
g dl1 g dl1 g dl1 mg dl1 mmol l1 mg dl1 mmol dl1 mg dl1 mmol dl1 mmol dl1 mmol dl1 mmol dl1 mmol dl1 mol dl1 mg dl1 mol dl1 mg dl1 mg dl1 mg dl1 mmol l1 mmol l1 mg dl1 mg dl1 mol dl1 IU l1 IU l1 IU l1 IU l1 IU l1 mg dl1 nmol l1 nmol l1 nmol l1 IU l1
Calcium Phosphorus Sodium Potassium Magnesium Chloride Total serum iron Uric acid Urea Bilirubin Cholesterol Triglyceride Creatinine GOT GPT ALP ALT AST BUN T4 T3 rT3 LDH
A.m.a 5.21 1.87 3.33 92.0
C.l.b
C.m.c 9.37
81.82
52.95
C.n.d 5.3 1.9 3.1 81.6
T.s.e
C.p.g
3.7
4.1–7.0 1.4–2.3 2.7–5
75.3 4.5–12.1
10.73
10.5
5.73
3.0
2.4–2.8f
10.2 2.41–3.45 3.4
144.2 3.71
155.9 4.4
104.2
120.0
3.03
8.17
4.1
1.2–2.9 143–161 3.8–7.2 0.8–1.4 88–127 1–19
3.2 167–988
3.8 0.16 120.8
0.47 110.5
231.5
1.1–7.2 0.1–8.8 46.2 0.21
1.06
20–51 16.6 13.1 30.03 46.05 223.5 0.99 4.95 0.2 0.7
18.0 20.2 17.8
31–180 11–51 23–157
1.45
426.2
A.m., Alligator mississippiensis; C.l., Caiman latirostris; C.m., Crocodylus moreletii; C.n., Crocodylus niloticus; T.s., Tomistoma schlegelii; C.p., Crocodylus porosus. a Barnett et al. (1998); b Tourn et al. (1994); c Sigler (1991); d Foggin (1987); e Siruntawineti and Ratanakorn (1994); f Morpurgo et al. (1992); g Millan et al. (1997a). GOT, glutamate oxaloacetate transaminase; GPT, alkaline phosphatase; ALP, alkaline phosphatase; ALT, alanine aminotransferase; AST, alanine transaminase; BUN, blood urea nitrogen; T4, thyroxine; T3, triiodothyronine; rT3, reverse triiodothyroxine; LDH, lactate dehydrogenase.
Urine biochemistry The nitrogenous wastes excreted by the kidneys consist of uric acid, urea and ammonia in the form of ammonium bicarbonate (NH4HCO3). Crocodile urine, like that of birds, consists of a liquid and a solid portion. Values determined from the liquid urine of fasting crocodiles are given in Table 1.18. The
urine solids of the Nile crocodile were composed of 6% ammonia and 88.6% uric acid; no urea was present (Khalil and Haggag, 1958). The full composition of the urine of fasting American alligators is given in Table 1.19. In a comparison between maximally fed American alligators (fed ad libitum five times per week) and those given a single large meal, it was found that uric acid excretion levels were sim-
Crocodiles and Alligators
Table 1.15. Clinical serum biochemistry: means of 2-year-old farmed Nile crocodiles (n = 5) (Thurman, 1990) and ranges of means of wild Nile crocodiles from three different rivers in the Kruger National Park, South Africa (Swanepoel et al., 2000). Parameter
Unit
Farmed
Albumin Globulin Glucose Na K Ca Mg SIP TSP LD ALP CK Lactate Cortisol Urea Creatinine Cl
g l1 g l1 mmol l1 mmol l1 mmol l1 mmol l1 mmol l1 mmol l1 g l1 IU l1 IU l1 IU l1 mol l1 nmol l1 mmol l1 mmol l1 mmol l1
5.9 153.8 3.8 2.97 0.52
Wild 9.8–16.38 30.7–47.35 3.2–11.45 141.5–154.5 2.53–5.35 2.60–3.98 1.51–2.24 0.88–1.96
50.2 301 64.2 211 22.1 <27
Table 1.16. Blood biochemistry of Caiman latirostris (means only). Unit
Calcium Creatinine Phosphate Glucose Urea Cholesterol GOT GPT LDH Total protein Albumin Globulin
mg dl1 mg dl1 mg dl1 mg dl1 mg dl1 g dl1 IU l1 IU l1 IU l1 g dl1 g dl1 g dl1
Thyroxine (ng ml1) Crocodylus niloticus (Morpurgo et al., 1992) Crocodylus johnsoni (Hulbert and Williams, 1988)
Troiano and Tourn et al. Althaus (1993) (1993)
1.63 2.5
Table 1.18. Percentage distribution of nitrogen in the liquid urine of fasting crocodiles.
Ammonia Urea Uric acid
SIP, serum inorganic phosphate; TSP, total serum protein; LD, lactatedehydrogenase; ALP, alkaline phosphatase; CK, creatine kinase.
Parameter
Table 1.17. Mean plasma thyroxine values of crocodiles.
Component
0.60–2.62 36.5–97.0 88.5–120.5
49
Crocodylus niloticus (Khalil and Haggag, 1958)
Alligator mississippiensis (Hopping, 1923)
66.8 12.5 2.3
66–81 0–17 7–19.8
Mineral values Plasma Plasma mineral values of wild and farmed male American alligators, lengths ranging from 185 to 325 cm (wild) and 230–326 cm (farmed) (Lance et al., 1983), are shown in Table 1.20. Organs
10.12 0.36 5.40 102.2 6.88
For organ mineral values of American alligators and Nile crocodiles see Tables 6.1 and 6.2. 2.315
163 19.67 1020 5.01 2.42 3.10
GOT, glutamate oxaloacetate transaminase; GPT, alkaline phosphatase; LDH, lactate dehydrogenase.
ilar in both groups, while the excretion of ammonia was low in the single-meal group. However, uric acid clearance was also low in the single-meal group, with high levels of plasma uric acid (Herbert, 1981) (see p. 41).
Bones The mean mineral composition of the ribs of three wild Nile crocodiles from the Kruger National Park, South Africa, was: Ca, 17.9%; P, 7.9%; Mg, 0.38%; F, 713 g g1 (Swanepoel et al., 2000). It is quite possible that the skull and legs of crocodiles have a higher density than the ribs.
Composition of crocodile fat The fatty acid composition of the plasma and of the body fat depend on the sources of fat in the food, but also varies according to the
50
Chapter 1
Table 1.19. Urine composition of fasting American alligators expressed per kg body mass per day (Coulson and Hernandez, 1964), unit abbreviations as used by the authors. Parameter
Unit
Volume pH OP NH2 K Na Ca + Mg CO2 as bicarbonate Cl P SO4 Uric acid N Creatinine
ml
Mean
Range
17 7.81 203 1.77 0.13 0.06 0.03 1.19 0.05 0.45 0.17 0.75 0.6
mOs l1 mEq l1 mEq l1 mEq l1 mEq l1 mEq l1 mEq l1 mEq l1 mEq l1 mM l1 (?) mg l1
6–28 7.6–7.93 157–247 0.67–2.4 0.01–0.26 0.01–0.1 0.02–0.05 0.46–1.47 Traces to 0.12 0.07–0.98 0.1–0.26 0.18–2.14 0.37–1.04
OP, osmotic pressure. Table 1.20. Plasma minerals of wild (n = 24) and farmed (n = 18–23) male American alligators (Lance et al., 1983). Parameter
Unit
Wild
Calcium Magnesium Zinc Copper Iron Selenium Protein Cholesterol Vitamin E
mmol l1 mmol l1 g ml1 g ml1 g ml1 g ml1 g l1 mg l1 g ml1
3.12 1.32 0.44 0.76 0.53 0.17 0.564 5.81 5.36
Farmed 2.87 1.06 0.42 0.60 0.54 0.2 0.553 5.02 5.25
Table 1.21. Lipid composition (%) of American alligator fat from two farms (Peplow et al., 1990). Triglyceride Diglyceride Monoglyceride Free fatty acids Cholesterol Phospholipid
Nutrient composition of crocodile eggs Yolk The lipid and fatty acid composition of American alligator eggs and the changes during incubation were described by Noble et al. (1993). The composition on day 8 of incubation is shown in Tables 1.27 and 1.28.
85.1 2.1 1.5 1.2 0.2 6.7
Table 1.22. Fatty acid composition (%) of American alligator fat from different trial groups and different farms (Peplow et al., 1990). Fatty acid
species of crocodile (Tables 1.21–1.26). The different crocodilian species may, in fact, have differing nutritional requirements for saturated and unsaturated fatty acids. A homeostatic mechanism may be lacking, but there may also be an age effect (Morpurgo et al., 1993a; Gelman and Morpurgo, 1994; Morpurgo and Gelman, 1995).
77.2 2.4 0.4 1.9 1.8 4.8
C14:0 C14:1 C16:0 C16:1 C18:0 C18:1 C18:2 C18:3 C20:1 C20:2 C20:5 C22:1 C22:6 C24:1
Low
High
1.3 0.00 19.9 4.4 3.1 33.2 3.4 0.9 1.1 0.01 0.1 0.00 0.7 0.00
3.3 0.19 22.1 7.7 8.4 44.4 19.3 3.4 2.8 0.17 4.0 0.98 11.1 0.14
Crocodiles and Alligators
51
Table 1.23. Fatty acid composition (%) in four groups of juvenile Indo-Pacific crocodiles (Garnett, 1985). Fatty acid C16:0 C18:0 C16:1 C18:1 C18:2 C18:3 C20:4 C20:5 C22:6
Newly hatched
Starved
Fed lean pork
Fed fatty pork
19.62 5.93 2.95 30.31 5.01 1.70 3.22 7.75 15.55
22.81 9.99 2.26 35.27 8.43 1.62 7.31 0.60 2.84
21.86 8.59 2.84 29.22 21.18 2.81 3.37 1.07 2.52
22.73 12.19 2.94 41.06 11.31 1.85 1.26 0.17 0.41
Table 1.24. Mean percentage plasma fatty acid composition in 3- and 8-year-old farmed and 3–6-yearold wild Nile crocodiles (Morpurgo et al., 1993a). Fatty acid
Farmed (3 years old)
Farmed (8 years old)
Wild
16:0 16:1 18:0 18:1 18:2 18:3+20:1 20:4 20:5 22:5 22:6
38.46 0.60 9.22 19.11 20.32 2.79 6.82 1.25 0.22 1.50
37.04 4.95 9.94 23.74 22.79 0.69 3.58 0.46 0.34 0.31
27.03 7.49 12.54 27.00 12.04 3.44 2.71 2.74 1.25 3.91
NB: The tables in the paper by Morpurgo and Gelman (1995), referring to the same results, appear to have been mixed up. Table 1.25. Fatty acid composition of crocodile meat (Crocodylus porosus and Crocodylus johnsoni), averages of 12 samples (Mitchell et al., 1995). C:n
Name
14:0 15:0 16:0 16:1 -9 16:1 -7 17:0 18:0 18:1 -9 18:2 -6 18:3 -3 18:4 -3 20:0 20:1 -9 20:4 -6 20:4 -3 20:5 -3 22:5 -6 22:5 -3 22:6 -3
Myristic Pentadecanoic Palmitic Palmitoleic Heptadecanoic Stearic Oleic Linoleic -Linolenic Arachidic Gondoic Arachidonic Eicosapentaenoic Docosapentaenoic Docosahexaenoic
% 1.1 0.2 22.5 0.4 5.1 0.5 7.4 33.1 15.2 4.8 0.1 < 0.1 0.5 3.6 0.3 0.5 0.4 1.5 1.3
Table 1.26. Fat profile of boiled tail meat of Alligator mississippiensis – means in % (Debyser and Zwart, 1991). Total fat content Saturated fat Mono-unsaturated fat Poly-unsaturated fat Cholesterol (mg/100 g)
2.9 29.1 46.5 24.0 64.8
Table 1.27. Mean yolk lipid composition (% of total lipid) of American alligator eggs incubated at 30°C on day 8 (Noble et al., 1993). Cholesteryl ethers Triacylglycerols Free fatty acids Free cholesterol Phospholipids
1.48 69.5 1.60 7.68 19.8
52
Chapter 1
Table 1.28. Mean fatty acid composition (% of total) of the cholesteryl esters, triacylglycerols and phospholipids of the yolks of incubated American alligator eggs on day 8 (Noble et al., 1993). Fatty acids
Cholesteryl esters
Triacylglycerols
Phospholipids
60.0 5.68 7.76 16.4 4.47 1.69 3.96 <1.0 <1.0
29.1 18.5 6.49 32.3 6.53 4.58 1.02 <1.0 <1.0
32.1 9.16 7.88 19.3 4.18 2.33 13.1 2.38 9.67
Palmitic Palmitoleic Stearic Oleic Linoleic Linolenic Arachidonic Docosapentaenoic Docosahexaenoic
Albumen The albumen of avian eggs consists largely of proteins with antibacterial properties. Crocodile egg albumen contains much fewer solids (3.6% against 12% in birds) and the main protein is a glycoprotein (Burley et al., 1987; Abrams et al., 1989; Rose et al., 1990). An 2-macroglobulin-like protease inhibitor was identified in the albumen of eggs of the Cuban crocodile (Ikai et al., 1983). The possibility that the proteins in crocodilian eggs have antibacterial properties has not yet been investigated.
Paracloacal and gular glands The secreta of the paracloacal and gular glands are used by all crocodilians for chemical signalling. This is important for the recognition of individuals, of the sex of any other individual and of conspecifics. The paracloacal glands of C. crocodilus and Caiman latirostris contained between 3.5 g and 34.5 g secreta. They consisted of fatty acids, particularly myristic and palmitic acid, nitrogenous bases, glycerol, cholesterol, traces of phosphorus-containing compounds and an eight-carbon alcohol, yacarol. This was later identified as D-citronellol and was characterized by its distinct rose-like scent (Fester and Bertuzzi, 1934; Fester et al., 1937). Citronellol was also found in the paracloacal gland secreta of Paleosuchus palpebrosus and P. trigonatus (Shafagati et al., 1989). The diterpene -springene that occurs in the paracloacal glands of P. trigonatus is also present in the secretions of a braconid wasp and of the
springbok antelope, as well as in tobacco leaves (Avery et al., 1993). Paracloacal secreta of 80 immature and 15 adult American alligators contained hexadecyl and other acetates and esters, but no free alcohols. There was a high degree of variation between age classes and sexes, but also individually (Weldon et al., 1988). The secreta of the gular glands of American alligators consist of C14, C16 and C18 fatty acids, squalene and -tocopherol, but contain no pheromone (Weldon et al., 1987). Lipids from the paracloacal glands of adult Chinese alligators of both sexes consisted of acetates, aliphatic alcohols, free fatty acids and waxes, primarily hexadecanoates. The male secretions also contained cholesterol, a diterpene hydrocarbon, cembrene A and a diterpene ketone (Dunn et al., 1993; Mattern et al., 1997). The secretions of the paracloacal glands of O. tetraspis contained an aromatic ketone, dianeackerone, and several aromatic steroidal esters (Whyte et al., 1999; Yang et al., 1999). A comparative chromatographic study of the secretions of gular and paracloacal glands of almost all crocodilian species, except C. novoguineae, was carried out by Weldon and Tanner (1991).
Crocodilian Behaviour Normal behaviour is characteristic of a healthy animal. Not to be able to act in accordance with its behavioural requirements in a captive or farm situation may severely stress an animal. Non-domesticated animals, par-
Crocodiles and Alligators
ticularly crocodiles, are very sensitive to this kind of stress. It is therefore important for crocodile farmers and veterinarians to be aware of the behaviour patterns and requirements of their crocodiles.
Embryonic learning It has been found that the food selection of Indo-Pacific crocodiles can be influenced by painting flavours on to the crocodile eggs during incubation (Sneddon et al., 1998). This kind of embryonic learning may also influence other aspects of hatchling behaviour. It is possible that by urinating on the nest the mother primes the hatchlings to recognize her when they hatch.
Parental care Parental care has been observed in many crocodile species and it is presumably the rule in all crocodilians. It includes guarding the nest, helping the hatchlings out of the egg, carrying them from the nest to the water, guarding them there, responding to the distress calls of young ones in danger and occasionally moving the pod to new nursery areas. All this is done mainly by the female, but, where the adults live in pairs or where the female has disappeared, males have been seen either helping or taking over the care of the hatchlings (Alvarez del Toro, 1968).
Imprinting Imprinting is known from birds, which at hatch are imprinted with the image of their mother and thereby recognize their parents and later in life choose their sexual mate in their parents’ image. Human imprinting in intensively reared ostrich chicks can lead to behavioural disturbances, sometimes with serious consequences (Huchzermeyer, 1996a). It is difficult to explain the complex hatchling–parent interactions of crocodilians without thinking of the possibility of imprinting. A suspected case of human imprinting of
53
farmed Nile crocodiles in South Africa was reported by Huchzermeyer (1998b). It is postulated that when the mother drives the hatchlings away before the new brood hatches (see below), a behavioural switch is operated, inducing the juveniles to avoid larger crocodiles from then on. When farmreared juvenile crocodiles are released into the wild, often many of them are eaten by older crocodiles. Possibly their lack of imprinting made them unable to see the danger posed by larger members of the same species.
Dispersal of the young Before the new clutch hatches, in some species possibly long before, the juveniles leave their mother, and there are some indications that, in fact, they are being actively chased away (Hunt, 1977; Hunt and Watanabe, 1982). After leaving their parents they may still stay together in pods, even pods consisting of several clutches (Allstead, 1994), or they may disperse individually. In many species the different age groups occupy different habitats, primarily for agespecific prey requirements, but also keeping the different sizes apart and thereby minimizing cannibalism.
Cannibalism Cannibalism occurs quite commonly in crocodiles and may be regarded as a population regulatory mechanism, allowing more juveniles to reach adulthood in a depleted adult population (Hutton, 1989). However, high losses of released juveniles (Rootes and Chabreck, 1993) could also be caused by the fact that the released farm-reared animals were non-imprinted and therefore did not have the behavioural switch enabling them to avoid larger members of the same species (see above). Where the size classes are segregated in the wild, it would be important to release juveniles into the correct habitat or niches to avoid excessive cannibalism. The fact that many sporulated coccidian sporocysts often become sequestered in dif-
54
Chapter 1
ferent organs of crocodiles (see p. 187) could also be an indication that cannibalism is a normal occurrence in crocodiles in the wild and that this parasite, at least, has adopted this as a mechanism for its transmission.
Hunting and feed selection Crocodiles are nocturnal animals and hunt or forage actively during the night. However, they will also take prey during the day if the opportunity should arise. How much their behaviour is affected by diurnal feeding in captive and farm situations is not known. However, crocodiles might become more interesting for zoo visitors to observe if they were shown in a night display. All crocodiles prefer live, moving food, but they easily adapt to inert feed, such as fresh or boiled mince. Under suitable stressfree conditions they also will take pelleted feed without any problems. While small fish, tadpoles, frogs and toads were readily recognized as prey by Nile crocodile hatchlings previously fed with mince, lizards (Agama stellio) were left untouched (Morpurgo et al., 1991).
Social behaviour Social interactions revolve around sexual, territorial and food competition, and the establishment of a ranking hierarchy in a population. For this the crocodiles use acoustic and visual signalling as well as aggression. The signals vary to some extent from species to species, and so does aggressiveness. In juvenile farmed Nile crocodiles, aggression was found to be linked to feeding and the type of feed, to stocking density and to size variation. Inert feed, low stocking density and removal of the larger individuals were all conducive to low aggression levels (Morpurgo et al., 1993b).
Territoriality Territorial behaviour varies from species to species and is most marked in adult croco-
diles during the breeding season. In general, one can say that swamp-inhabiting crocodiles are stricter about establishing territories, while riverine species tend to be more gregarious or tolerant of a higher population density in a breeding area. This may have implications for the establishing of breeding colonies on crocodile farms. Although apparently severe wounds may be inflicted during territorial fights between males, the fights are more of a ritualized nature (Plate 4) and much less severe than those between females over nesting sites.
Sexual behaviour The sexual behaviour of crocodiles consists of courtship displays, mating and defending the ‘harem’. Here also the details differ from species to species. Often, while the dominant male is occupied with one particular female, some of the other females of his ‘harem’ will seek out and copulate with other males. This leads to multiple fatherhood of particular clutches and has the benefit of a wider spread of genes. In large breeding colonies on Nile crocodile farms one aims to provide distinct territories for several dominant males by the disposition of islands and other visual barriers (Fig. 1.48).
Nesting Depending on the characteristic habitat of the species, crocodiles either build nest mounds from the substrate (vegetation matter or sand) or dig holes in the sand. It is believed that the rotting vegetation in the nest mound contributes to the creation of the correct incubation temperature, particularly in dense forest, where the nest mounds cannot be exposed to the sun. In areas where flooding occurs, crocodiles choose high ground for their nesting sites. For this reason it is important when designing breeding colonies on Nile crocodile farms to have all the nesting sites at the same level, to avoid competition for the more elevated ones (Fig. 1.49).
Crocodiles and Alligators
55
Fig. 1.48. Breeding colony on a Nile crocodile farm with visual barriers to allow the establishment of several individual territories.
Fig. 1.49. Nesting sites all on the same level in a breeding colony for farmed Nile crocodiles.
Thermoregulation All crocodiles like to maintain a constant internal body temperature, depending somewhat on their activities and the time of day. To achieve this they make use of the environmental thermogradient, which consists of sun (radiation) and shade (air temperature), as well as warm surface and cool
deep water. To some extent they can also make use of evaporative cooling, although it is unlikely that that is the only purpose of gaping (Fig. 1.50). During gaping the gular valve remains closed, whereas it opens during yawning. Many species make use of burrows to escape excessive heat (aestivation) or excessive cold. This means of maintaining the
56
Chapter 1
Fig. 1.50. Gaping Nile crocodile on a farm in South Africa; gaping may facilitate evaporative cooling.
temperature is usually not provided on crocodile farms. In autumn, Chinese alligators dig particularly elaborate burrows, with one or two openings usually facing south, one or two tunnels, one to three chambers, a sleeping platform and a pool. They use their snout, fore limbs, body and tail for digging and moving the soil (Bihui et al., 1990). We also know the pleasures of thermoregulatory behaviour, lying on a beach and soaking up the warm sunshine, then diving into the cold water to cool down, and then back into the sun again and so on. Crocodiles lying in the sun the whole morning are not just lying there, they are busy thermoregulating. We should always keep in mind that to prevent crocodiles in a captive or farm situation from being able to thermoregulate and achieve their desired temperature can cause very severe stress. Optimal core temperatures are between 28 and 33°C. Temperatures above 35°C are lethal (once the internal temperature rises to those levels), and several systems cease to function below 25°C. However, American alligators are known to survive very low temperatures. If, during a cold spell, their water freezes over, they keep their nostrils out of the water (ice), while the rest of the body remains submerged. This behaviour is called ‘icing’ (Hagan et al., 1983; Lee et al., 1997) (see also p. 44).
Vocalization Crocodiles have a large repertoire of sounds that they use in their various interactions. This begins with the croaking of the hatchlings in the egg when they are ready to hatch, their frequent croaking to inform their mother and hatch mates of their whereabouts, and the distress call of a hatchling in danger. The same distress call is also used by older juvenile crocodiles. In some species vocalizations are added to the mating displays. Growling and bellowing are used to threaten off attackers or competitors. In the Congo Basin swamp forests, adult African dwarf crocodiles can be heard calling each other during the night (own unpublished observation). Britton (2001) has classified the calls of juvenile crocodilians as: ● ● ● ● ●
hatching calls; contact calls; threat calls; annoyance calls; distress calls.
Their vocal range includes infrasound, which may be audible to other crocodiles in the water over very long distances. The agitation of the water around the thorax of an American alligator producing this sound is shown in the cover photo of Volume 1 of the 1990 CSG Proceedings (CSG, 1990).
Chapter 2 Examination of Crocodiles and Clinical Procedures
Bare hands
Clinical Examination Capture and physical restraint Stress The capture of wild crocodiles falls outside the scope of this book. The subject here is the handling of captive and farmed crocodiles. All handling and physical restraint causes severe stress and should therefore be kept to the minimum. If it is ever necessary, the least violent methods should be employed.
Hatchlings can be caught by hand directly behind the head. Slightly larger juveniles are caught in the same way, but the tail is held with the other hand. A dustpan held over the crocodile to be caught will be accepted as shelter. The hatchling or juvenile will remain immobile under the shelter and can easily be apprehended by the free hand (Fig. 2.1). Specimens over 1 m in size are caught with a wet towel (Blake, 1993), the animal to be caught is separated from the others and a
Fig. 2.1. Holding a dustpan over the hatchling to be caught. © CAB International 2003. Crocodiles: Biology, Husbandry and Diseases (F.W. Huchzermeyer)
57
58
Chapter 2
wet towel or sack is thrown over its head (Fig. 2.2). The handler then grabs the caudal part of the head through the towel, while straddling the crocodile and holding its body between his knees (Fig. 2.3). With larger animals a second and third person may be needed to hold down the body and tail. Another assistant then secures the jaws with insulating tape, taking care not to block the nostrils. The muscles opening the jaws are relatively weak, so the crocodile will be unable to break the insulating tape.
Therefore, using rubber bands or string is not necessary and can cause needless discomfort. The animal can be further immobilized by tying it to a plank, pole or ladder (Fig. 2.3). In this way it can also be carried to another location (Fig. 2.4). Bending the body sideways and fastening the head to the tail prevents the crocodile from rolling in attempts to free itself. Pressing the eyes into the orbits and then taping the eyes shut appears to have a further calming effect (Fig. 2.5).
Fig. 2.2. A wet sack is thrown over the head of the roped crocodile.
Fig. 2.3. The crocodile is tied to a ladder, while one assistant sits on its head.
Examination of Crocodiles and Clinical Procedures
59
Fig. 2.4. The crocodile tied to a ladder can now be moved without danger to the assistants.
Fig. 2.5. Young Nile crocodile with jaws and eyes taped closed. Note that masking tape is not a suitable material as it is not water resistant.
Devices The above methods are very stressful for the animal and also dangerous for the handler(s) and it is better to use one of the handling devices described below. ● Hatchling and small juveniles (<1 m) are easily caught with snake tongs (Fig. 2.6) or Pillstrom tongs (McDaniel and Hord,
1990). This allows one to catch them from a distance without having to enter the rearing pen and thereby upsetting all the other hatchlings in the pen. ● A catching noose made from strong rope can be handled more easily if it is passed through a strong PVC pipe of adequate diameter and length (Fig. 2.7) (Fletcher and Trammel, 1989).
60
Chapter 2
Fig. 2.6. Snake tongs can be used to catch crocodile hatchlings out of their pen without causing disturbance.
Fig. 2.7. Catching noose fitted through a PVC pipe.
● PVC irrigation pipes of various diameters and lengths can be used to restrain and transport crocodiles after they have been caught with a noose around the neck and a second noose has been fitted around the body in front of the hind legs. The front noose is used to pull the crocodile into the pipe and the rear noose is then used to hold it back, preventing it from escaping through the front of the pipe (Fig. 2.8) (Jones and Hayes-Odum, 1994). Both ropes can be fastened through holes or notches drilled or cut into the pipe. ● A rigid PVC pipe of about 5–8 cm diameter is also useful for chasing away other crocodiles while working in the pen, e.g. when collecting eggs. Such a pipe produces a loud noise when hitting the
ground next to the crocodile that is to be chased away. This noise is very similar to the jaw clap used by crocodiles as a warning, and this is probably why it is so effective. Being lighter than a pole of similar dimensions, its impact is lighter and there is less danger of causing pain or injury when hitting the crocodile.
Physical examination Unrestrained crocodiles An unrestrained crocodile is examined from a distance in its enclosure. Its estimated length is noted and its nutritional state is judged mainly by the relative thickness of its
Examination of Crocodiles and Clinical Procedures
61
Fig. 2.8. Crocodile inside a large PVC pipe, held in place by two ropes which are fastened into notches in the pipe.
neck, a severely drawn-in neck being typical for an animal in a poor state (Fig. 2.9). Sunken muscles in the supertemporal fossae (see p. 7) also indicate a poor state of nutrition (Fig. 2.10). Nile crocodiles can be recognized individually by the distribution of dark spots on both sides of the tail, and the same probably holds true for some of the other crocodile species (Swanepoel, 1996) (see p. 74). The tail lying either erect or flat in a sideways posi-
tion is supposed to indicate the state of health, the latter position indicating poor health (Fig. 2.11), but this is rather doubtful. The animal is then examined for obvious abnormalities, wounds, other skin lesions or discoloration and also the state of its eyes. Restrained animals Restrained crocodiles can be examined more closely. They can also be turned over for a
Fig. 2.9. A drawn-in neck indicating a poor state of nutrition.
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Chapter 2
Fig. 2.10. Sunken supertemporal fossae on a captive Nile crocodile, indicating a poor nutritional state (photo Henri Lagasse).
Fig. 2.11. A tail lying flat on its side, supposedly indicating poor health.
close examination of the belly skin and cloaca. The eyes are difficult to examine, as they are retracted as soon as the lids are touched. However, it is possible to examine the pupil and its response to light, as well as the eyelids for any sign of conjunctivitis. A whitish dis-
coloration of the eyelids and the area around the nostrils sometimes occurs in chronic disease conditions (Fig. 2.12) (see p. 237). The whiteness of the teeth of hatchlings and older crocodiles indicates the state of calcium nutrition. Calcium-deficient croco-
Examination of Crocodiles and Clinical Procedures
63
Fig. 2.12. A whitish discoloration around the nose may indicate a chronic disease condition.
diles have clear, diaphanous, ‘glassy’ teeth (Fig. 2.13), and such hatchlings should be tested for the rigidity of their bones by gently trying to bend the upper jaw (‘rubber jaw’) (see pp. 148 and 211). In hatchlings the mouth can also be opened, by a gentle tap on the nose, to examine the gingivae, the tongue and the two flaps of the gular valve (see p. 11).
Diagnostic imaging While wild and farmed crocodiles can rarely be taken to imaging apparatus, this situation may be different in the case of captive animals, as many zoos and specialized city practices have well-equipped clinics and laboratories. However, the existing literature on this subject is still very limited:
Fig. 2.13. Diaphanous teeth in a calcium-deficient adult Nile crocodile.
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Chapter 2
● Radiography: radiographs were taken of the digital connective tissue masses of an American alligator at San Diego Zoo (Ensley et al., 1979). No technical details were given. ● Ultrasonography: ultrasound was used to evaluate follicle development in adult female broad-nosed caimans (Vac et al., 1992; Verdade, 1995). The authors used the ultrasonograph Aloka No 210-DX2 at 3.5 MHz. In larger animals the lateral approach was preferred, due to the presence of ventral osteoderms. ● EKG: an electrocardiogram was recorded from a 75 cm American alligator. Electrodes applied to the hide did not receive any deflections. When pins were inserted into both forelimbs and the left hind limb, deflections were recorded, none in lead I, but low deflections in leads II and III. The P waves were indistinct and the R wave in lead II measured 2.5 mm. In lead III it was lower and slightly slurred. The T waves were also poorly defined in both leads (Blackford, 1956). ● Gastric pressure: in chronically cannulated Caiman crocodilus, gastric pressure was recorded with a Beckman Model R Dynograph in relation to temperature and
fasting or feeding (Diefenbach, 1975b). However, this method is beyond the scope of normal clinical examination.
Sample collection Blood Blood can be obtained from several sites: ● The internal jugular vein runs dorsally within the vertebral column and can best be punctured at the junction of atlas and axis. Flexing the head slightly downwards may help in reaching the vein. Care should be taken not to injure the spinal cord (Olson et al., 1975). ● The caudal veins run ventrally and dorsally along the vertebral column (ventral and dorsal coccygeal veins). To access the ventral vein, the animal is held in dorsal recumbency. The best place is about onefifth of the distance from the cloaca to the tip of the tail. The needle should be long enough and inserted pointing craniad at an angle of 45° from vertical. Bending the tail slightly in the opposite direction helps by opening the space between the long chevron bones covering the haemal canal (Fig. 2.14) (Olson et al., 1975; Gorzula
Fig. 2.14. Taking a blood sample from the ventral tail vein.
Examination of Crocodiles and Clinical Procedures
et al., 1976; Samour et al., 1984). The dorsal vein can be reached at a similar distance from the base of the tail, and at a similar angle because of the dorsal spines (Fig. 2.15). This is also the preferred site for a lethal injection. ● Cardiac puncture: the heart can be found by holding the crocodile lying on its back and observing the slight rise and fall of the ventral wall that accompanies each heart beat (Hopping, 1923). In the American alligator, the heart lies in the midline at the level of the 11th and 12th row of scutes, counting back from the broad band above the forelimbs (Hopping, 1923; Jacobson, 1984). Because of differences in the size of scutes, the number of rows to be counted may differ from species to species. It may, therefore, be necessary to ascertain the heart’s exact position by first examining a dead specimen of the same species. The animal is held in dorsal recumbence and the needle is inserted slowly, until blood is encountered. ● Small quantities of blood for smears may be obtained by clipping the toe nails, the tips of the tail crests (Olson et al., 1975) or the tip of the tail (Coulson et al., 1950).
Fig. 2.15. Bleeding from the dorsal tail vein.
65
A small drop of blood is deposited at one end of a slide and the edge of a second slide or cover slip is dipped into it. The blood is then allowed to spread sideways right across the edge, before the slide or cover slip is pushed along the original slide, thus spreading the blood in a thin, even film. The frosted edge or the dried blood film itself can be marked with a pencil (Fig. 2.16). Crocodile red blood cells are nucleated, and these nuclei tend to obscure the stained blood smear if the blood film is too thick. Therefore, care should be taken to prepare very thin blood films. The blood film is allowed to dry in the air. It can be placed face down over two pencils to keep flies away from the blood. When dry, it is fixed by immersing it briefly in methanol and allowing it to dry again. For the preparation of permanent specimens the blood film should be stained with Giemsa stain.
TAKING A BLOOD FILM.
Urine In the coprodeum the urine is mixed with the faeces, making it impossible to collect clean urine for clinical examination. However, clean urine can be obtained for research purposes by catheterization of the ureters.
66
Chapter 2
Fig. 2.16. Preparing a thin blood film.
Faeces Faeces mixed with urine can be obtained from the cloaca of a crocodile held in dorsal recumbency. They can also be collected from the base of a clean container, in which a small crocodile is kept until it has defecated. For bacteriological sampling of faeces one can simply take a cloacal swab, which is then placed into a sterile container (tube), or a transport medium, and kept refrigerated until it can be examined in the laboratory. Sperm During the breeding season sperm can be obtained by swabbing the seminal groove of the externalized penis. For this the crocodile is immobilized and held in dorsal recumbency (see p. 70). Stomach contents Stomach contents can be sampled by scooping or by washing (Taylor et al., 1978). For
scooping, a piece of rubber-coated metal tube is tied into the opened mouth of the crocodile. A scoop is made from a stainlesssteel or brass rod shaped into a handle, with a loop at a right angle at its end and with a rubber finger, or glove, sewn on to the loop. This is lubricated with vegetable oil and passed through the tube then, with a twisting motion, through the basihyal valve into the oesophagus, and, with another twisting motion, through the pectoral girdle. When it is in the stomach, it can be felt by external palpation and positioned behind a suitable piece of food to be extracted. Throughout this operation the crocodile’s head is raised at an angle of about 30° to the axis of the body. Diameters and sizes of tubes and scoops vary with the length of the crocodiles to be sampled. These sizes are shown in Table 2.1. For stomach washing, a clear PVC tube is inserted through the mouth and oesophagus into the stomach. The crocodile is then held with its head above the level of its stomach
Examination of Crocodiles and Clinical Procedures
67
Table 2.1. Dimensions (in centimetres) of crocodiles (Crocodylus porosus) and recommended mouth cylinders, scoops and stomach tubes. The dimensions should be similar for other crocodile species. (After Taylor et al., 1978.) Cylinder
Crocodile length
Diameter
Length
28–35 35–50 50–120 120–130 130–140 140–180
3 4.5 5 5 9.5 9.5
2 2.5 3 3 5 5
Scoop diameter
2 3 3 4
and water is poured through a funnel into the tube until the abdomen is visibly distended. The abdomen is then squeezed and massaged gently to mix the water with the stomach contents until the water surges up in the tube. The crocodile then is turned with its head down, the free end of the tube is inserted into the collecting bottle and the tube is withdrawn from the mouth of the crocodile. Water and food then flow into the bottle. Three to four washes suffice to clear all the food from the stomach (Taylor et al., 1978). The diameters and lengths of tubes required for the different sizes of crocodiles are shown in Table 2.1. Biopsy Taking samples of diseased tissue from a live animal for laboratory examination may help to establish an accurate diagnosis. The sampling by excision, punches, suction needles or biopsy forceps employs the same techniques as are used in other species (Cooper, 1994).
Haematology Blood sampling has been discussed above (see p. 64). The best diluent for leucocyte and erythrocyte counts for reptiles is Shaw’s avian solution, which is prepared as follows (Otis, 1974): Solution A Neutral red Sodium chloride Distilled water
25.0 mg 0.9 mg 100.0 ml
Rod Length
40 60 60 80
Tube
Diameter
Diameter
Length
0.2 0.4 0.4 0.4
1 1 1.5 1.5 2 2
40 40 60 60 80 80
Solution B Crystal violet Sodium citrate Formaldehyde Distilled water
12.0 mg 3.8 g 0.4 ml 100.0 ml
Each solution is thoroughly mixed and filtered, then the two are added to each other and mixed again. The stain is now divided into 1.98 ml aliquots and can be kept frozen for up to 3 months. Heparinized blood (20 l) is added to one thawed aliquot and mixed gently for several minutes, resulting in a 1:100 dilution before filling the counting chamber. For the morphology of crocodilian leucocytes see Chapter 1 (p. 24). Haematological values have been reported from several different crocodilian species and are summarized in Tables 2.2–2.7. Individual and species values vary widely. Runting leads to the depression of many haematological values (Foggin, 1987). White blood cell counts in American alligators infected with Aeromonas hydrophila (see p. 173) increased considerably. In differential counts the heterophils increased from 37.4% to 72.9%, while the lymphocytes decreased from 50.6% to 16.0% (Glassman and Bennett, 1978; Glassman et al., 1981). Infestation of American alligators with the leech Placobdella multilineata (p. 203) resulted in an increase of eosinophils to 60%. After removal of the leeches, the eosinophil levels returned to normal within 6 weeks (Glassman and Bennett, 1978; Glassman et al., 1979). In Nile crocodiles stressed by blasting, the total leucocyte counts decreased, with a relative increase in lymphocytes (Watson, 1990) (see also p. 280).
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Chapter 2
Table 2.2. Mean haematological values of American alligators.
Parameter
Unit
Erythrocytes Leucocytes Haemoglobin Haematocrit Heterophils Lymphocytes Monocytes Eosinophils Basophils
106 l−1 103 l−1 g dl−1 % % % % % %
Barnett et al. (1998)
Mateo et al. (1984)
0.67 5.8 9.29 24.4 57.6 11.1 22.3 9.2 1.2
Glassman et al. (1981)
0.38 6.4
0.4 5.3 7.2 18.6 37.4 50.6 3.0 5.5 3.5
54.7 23.9 0.7 10.4 12.7
Table 2.3. Mean haematological values of Caiman latirostris (C.l.) and Caiman crocodilus (C.c.). Parameter
Unit
C.l.a
C.l.b
C.c.a
Haematocrit Haemoglobin Erythrocytes Leucocytes Lymphocytes Azurophils (?) Monocytes Basophils Eosinophils Heterophils
% g dl1 ×106 dl1 ×103 dl1 % % % % % %
22 9.4 0.56 22.7 65 8 5 1 19 3
19.5
27 12 0.69 16.4 60 9 5 0 21 5
aTroiano
et al. (1996a); b Tourn et al. (1994).
Table 2.4. Mean haematological values of Crocodylus niloticus (C.n.), C. rhombifer (C.r.) and C. moreletii (C.m.). Parameter
Unit
Haematocrit Haemoglobin Erythrocytes Leucocytes Neutrophils Lymphocytes Monocytes Eosinophils Basophils
% g dl1 106 l1 103 l1 % % % % %
C.n.a 24 7.8 0.60 4.0 6 73 1 2 20?g
C.n.b
C.r.c 23–26 8.1–8.9 2.4–2.9
C.m.d 24.5 7.75
C.n.e
C.r.f
22 7.4
21.7 7.5
50 21 5 2 22
a Makinde and Alemu (1991); b Thurman (1990); c Carmena-Suero et al. (1979); d Sigler (1991); e Foggin (1987); f Moliner et al. (2000a). g Apparently left out of the paper.
Examination of Crocodiles and Clinical Procedures
69
Table 2.5. Mean haematological values of Crocodylus porosus (C.p.) and Tomistoma schlegelii (T.s.). C.p.a
Parameter
Unit
Haematocrit Haemoglobin Erythrocytes Leucocytes Heterophils Lymphocytes Eosinophils Monocytes Basophils
% g dl1 106 l1 103 l1 % % % % %
a
C.p.b
19.2 4.9
T.s.c
24.8
15.2 7.1 0.34 4.35 64.9 24.1 8.5 3.9 0
Wells et al. (1991); b Grigg and Cairncross (1980); c Siruntawineti and Ratanakorn (1994).
Table 2.6. Ranges of haematological values from Crocodylus porosus yearlings (Millan et al., 1997a) and hatchlings (Turton et al., 1997). Parameter
Unit
Yearlings
Haematocrit Haemoglobin Erythrocytes Leucocytes Heterophils Lymphocytes Monocytes Eosinophils Basophils Thrombocytesa
% g dl1 106 l1 103 l1 103 l1 103 l1 103 l1 103 l1 103 l1 103 l1
17–41 4.7–12.2 0.6–1.3 6.4–25.7 0.8–7.4 4.5–21.6 0.0–1.2 0.0–0.7 0.0–0.4 4–71
Hatchlings
5.33 3.08 1.69 0.05 0.35 0.15
a
The diagnostic value of thrombocyte counts is still undetermined. In percentage counts they tend to upset the other values.
Table 2.7. Ranges of haematological values from 2–4-year-old captive Australian crocodiles, four Crocodylus porosus and four Crocodylus johnsoni (Canfield, 1985). Parameter
Unit
Haematocrit Total plasma protein Erythrocytes Haemoglobin Total leucocytes Thrombocytes Lymphocytes Monocytes Type I granulocytes Type II granulocytes Type III granulocytes Unidentified
% g l1 1012 l1 g l1 109 l1 % % % % % % %
C. porosus
C. johnsoni
0.20–0.22 48–70 0.86–0.98 62–77 39.6–44.2 72.2–95 0.6–9 0–3.0 1.6–14 0–0.8 0–4.8 0.2–0.8
0.18–0.21 33–69 0.71–0.93 57–75 26.4–48.8 76.5–87.7 4–8.5 2.2–11 3–8.6 0–0.5 0.8–2.8 0.4–0.8
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Chapter 2
Sexing Crocodiles do not show distinctive sexual bimorphism. American alligators have a differing pattern of scutes around the vent, with three rows of smaller scutes around the vent in males and four rows in females (Viosca, 1939). However, the penis and clitoris of crocodiles of all species and ages differ sufficiently in size and shape for an experienced operator to sex even hatchlings with a large measure of confidence (Brazaitis, 1969; Whitaker, 1973; Webb et al., 1984). In female hatchlings, the cliteropenis is small with a sharp extremity, while in the male it is large and tubular with a more bulbous extremity (Webb et al., 1984). For the examination of hatchlings, fine curved forceps or haemostats are inserted into the cloaca and spread, thus exposing the cliteropenis which is attached to the cranioventral wall of the cloaca (Webb et al., 1984). In large specimens the index finger is inserted into the cloaca, with the tip of the finger hooked cranially. It is then possible to feel the rigid male organ and to extrude it (Brazaitis, 1969) (see Fig. 1.33).
Cloacal examination As in the case of rectal examination of mammals, larger crocodiles can be examined via the cloaca by inserting a finger into the lower rectum. The animal is held in dorsal recumbency and pressure is applied to the abdomen to shift the organs to be examined towards the midline. In this way intestinal loops and ovarian follicles, as well as hardand soft-shelled eggs in the uterus and vagina, could be identified by palpation in Johnston’s crocodiles (Limpus, 1984).
Immobilization When larger crocodiles are to be handled, either for examination and other interventions, or to be moved, the safety of staff has to be considered just as much as the safety of the animal. Being caught and handled is
very stressful for all crocodiles, and this stress can have very deleterious consequences (see p. 278). While there are many instances where crocodiles have been handled and transported safely without chemical immobilization, there are also many cases where the animals have died a few months later from a stress-associated disease. If used at the correct dosage rates and handled properly by competent persons, preferably by veterinarians, immobilizing agents are very safe. The only major cause of mortality encountered in immobilized crocodiles is drowning, which occurs if they are released into water before they have fully recovered from immobilization or if they have been darted in the water (Loveridge, 1979). In this context the recommendation by Flamand et al. (1992) that crocodiles should be allowed access to water ‘once the immobilization is complete’ is misleading and dangerous. Rather, it should read, ‘once recovery from immobilization is complete’ (Brisbin, 1966; Loveridge and Blake, 1972; Messel and Stephens, 1980). It should also be noted that the dosages found to be safe and effective in one species may not be so in another (McClure, 1997), for instance, the effective dose of succinylcholine HCl in Crocodylus porosus was ten times that required for Crocodylus johnsoni (Messel and Stephens, 1980). Exploratory trials should always be undertaken and effective doses established before any of these drugs is used on a species for the first time. These drugs are either given by hand syringe, pole syringe or dart (Flamand et al., 1992). If a hand syringe is to be used, the animal must be restrained beforehand. The preferred sites of injection are the upper foreand hind limbs. The advantages of using these sites are that there are no fat deposits between the limb muscles, which could slow down the resorption of the drug, and that a larger quantity can be injected slowly, thus preventing the liquid from flowing out after withdrawal of the needle (Flamand et al., 1992). A pole syringe is safe for the handler, but the injection takes place very rapidly, with the risk of reflux through the puncture wound. The preferred injection site is the side of the
Examination of Crocodiles and Clinical Procedures
tail, close to its base. If the drug is injected into the fat deposits between the superficial and deep muscles (see p. 29), its resorption will be slow (Flamand et al., 1992). The same site is used for darting, and the same disadvantages apply. In addition there is great danger if the dart should strike an osteoderm obliquely and ricochet off (Flamand et al., 1992). The neck has also been used as a darting site in cases where the darts tended to bounce off the tail (Klide and Klein, 1973). Several drugs, mainly muscle relaxants, have been used for the immobilization of crocodiles. Those that have been reported are shown with their dosage ranges in Tables 2.8 and 2.9. In several species of Crocodylus, gallamine (Flaxedil®) has been found to be effective. Its action can be reversed rapidly by the injection of the antidote, neostigmine. While the immobilized crocodiles recover without the help of the antidote, it is essential to have it at hand whenever Flaxedil® is used, for the treatment of accidentally injected people (e.g. by a ricocheting dart!). It is also essential to use it when immobilized crocodiles cannot be prevented from entering the water before full recovery. In fact, a large number of transferred Nile crocodiles died on a crocodile farm in South Africa in 1998, when the drugged crocodiles were released into a pen with water, without first giving
71
them the antidote. The animals entered the water before having fully recovered and were found drowned the next morning. Many similar incidents have occurred. Recently, exploratory work has been undertaken on the combination of xylazine and ketamine (Seashole et al., 2000). The trial animals were given xylazine 1.5 mg kg1 body mass and, 20 min later, ketamine 20 mg kg1 body mass, both injected into the brachial muscles. Immobilization was profound in Crocodylus moreletii and Palaeosuchus palpebrosus, moderate in C. crocodilus, while there was no effect in Palaeosuchus trigonatus. The recommended doses for Flaxedil® and neostigmine are given in Table 2.10. However, at the time of writing, Flaxedil® has been taken off the market. While it has become available again locally in South Africa, this has opened the quest worldwide for other efficient and safe immobilizing agents for crocodiles. The names of the immobilizing drugs and their synonyms are shown in Table 2.11. The following precautions for crocodile handlers have been suggested by Blake (1993): ● Do not take chances when working with crocodiles, even small ones. ● Never work alone with crocodiles. ● Never use damaged or worn equipment.
Table 2.8. Immobilizing agents that have been tried in Alligatorinae (dosages in mg kg1 body mass). Alligator mississippiensis Agent
Dose
Effect
Tricaine
88–99
9h
Pentobarbitol
7.7–8.8
2–3 h
0.4
+
Phenylcyclidine Succinylcholine
11–22 3.0–5.0
6–7 h 7–9 h
Diazepam + succinylcholine
0.22–0.62 0.14–0.37
3h
Etorphine
Caiman crocodilus Dose
Effect
110
–
8.8 2.5–20a 0.5
– + –
0.33
35 min
Reference
+ Effective. – Not effective. a Hatchlings. 1, Brisbin (1966); 2, Klide and Klein (1973); 3, Wallach and Hoessle (1970); 4, Hinsch and Gandal (1969); 5, Spiegel et al. (1984).
1 2 1 2 3 4 1 1 2 5
72
Table 2.9. Immobilizing agents that have been tried in Crocodylinae (dosages in mg kg1 body mass). Crocodylus acutus Agent Succinylcholine
Zoletil® Suxathonium
Dose
Effect
Dose
Effect
9.2
2h
6
1h
*
+
Crocodylus porosus
Crocodylus johnsoni
Dose
Effect
Dose
Effect
3–17 * * *
+ − − +
0.8–3.6 * *
+ − −
Crocodylus niloticus Dose
0.5–0.6 0.64–4.0 1–1.25 5.0 *
−
*
−
Effect
+ + + +
References 1 2 2 2 3 4 5 6 7 2
* No dose stated. + Effective. − Not effective. 1, Klide and Klein (1973); 2, Messels and Stephens (1980); 3, Whitaker and Andrews (1989) (quoted by McClure, 1997); 4, Bonath et al. (1990); 5, Loveridge and Blake (1972); 6, Woodford (1972); 7, Haagner and Reynolds (1992).
Chapter 2
Tricaine Phenylcyclidine Gallamine
Crocodylus palustris
Examination of Crocodiles and Clinical Procedures
73
Table 2.10. Recommended doses for Flaxedil® and neostigmine in Nile crocodiles (Loveridge and Blake, 1972; Flamand et al., 1992). Weight (kg)
Length (m) 0.91 1.07 1.22 1.37 1.52 1.68 1.83 1.98 2.13 2.29 2.44 2.59 2.74 2.90 3.05 3.20 3.35 3.51 3.66 3.81 3.96 4.12 4.27 4.42 4.57 4.72 4.88 a b
Flamand et al. (1992)
Loveridge and Blake (1972)
Flaxedil®a (ml)
Neostigmineb (ml)
2 3 5 8 12 16 21 26 35 55 65 77 95 125 135 165 185 215 230 260 280 295 320 340 350 492 532
2 3 5 8 12 16 21 26 35 42 61 77 88 99 108 135 155 179 203 239 297 338 376 415 451 492 532
0.10 0.15 0.25 0.40 0.60 0.80 1.50 1.70 2.00 2.50 3.00 3.50 4.00 4.50 5.00 5.50 6.00 6.50 7.00 7.50 8.00 8.50 9.00 9.00 9.50 10.00 10.00
0.05 0.05 0.10 0.20 0.30 0.40 0.50 0.60 0.80 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00
Gallamine triethiodide 40 mg ml1. Neostigmine methylsulphate 2.5 mg ml1.
Table 2.11. Names and synonyms of immobilizing drugs as used in the cited literature. Technical
Commercial
Diazepam Etorphine Gallamine triethiodide Phenylcyclidine hydrochloride Sodium pentobarbital Succinylcholine chloride
Valium® M99® Flaxedil® Sernylan® Cap-Chur Barb® Anectine®, Scoline®, Sucostrin® Brevidil E® MS222®
Suxathonium bromide Tricaine methanosulphonate Zolazepam hydrochloride + tiletamine hydrochloride (1:1)
Zoletil®
● Do not leave drugged crocodiles unattended. ● Do not forget to remove the tape from the jaws before administering the antidote. ● Do not allow large, noisy audiences at a crocodile capture exercise. ● Do not allow the nostrils of the crocodile to be occluded while it is tied up or drugged – it will suffocate.
Pre-release screening There is concern about the introduction or spread of diseases where farm-reared, juvenile
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crocodiles are to be released back into the wild. However, habitats already occupied by wild crocodiles usually already harbour all the crocodile-specific pathogens of that species. One should also bear in mind that crocodiles are fortunate in being free from primary pathogens: none of the presently known crocodile-specific contagious agents can be classified as primary pathogens, as they all need triggering factors to precipitate outbreaks of disease. In fact, the presence of these pathogens at a low level in a wild population most likely ensures a state of immunity in the population. For this reason it is possibly not a good idea to release ‘clean’ juveniles into a new area, not inhabited by crocodiles, as the later introduction of a pathogen might have more serious consequences there. In any case, it is not possible to recommend a programme of rigorous serological screening, as there are no serological tests available for any of the crocodile-specific infections yet, except chlamydiosis. The only recommendation presently possible is to check the condition of the animals to be released, and only release healthy looking, well-nourished individuals, originating from a farm where no undue mortality has occurred in the preceding 12 months. The presently known crocodile-specific pathogens are: ● ● ● ● ● ●
crocodile poxvirus (p. 158); caiman poxvirus (p. 157); adenovirus (p. 160); Mycoplasma spp. (p. 167); Chlamydia sp. (p. 167); coccidia (as yet unnamed) (p. 183).
The only other pathogen that one should possibly consider is Mycobacterium avium (p. 170), which could be perpetuated in a wild population through cannibalism. However, this pathogen does occur in wild birds and has recently been involved in mass mortality in flamingos in Kenya (Kock et al., 1999). There may perhaps be a difference in pathogenicity for crocodiles between M. avium strains originating from pigs and those from birds. The mycobacteria may also need stress or other triggering factors to cause disease.
Tagging and identification Natural markings For many purposes it is useful to be able to recognize or mark individual animals. Nile crocodiles have dark spots on the sides of their tail which vary individually. Swanepoel (1996) used the markings on the last nine tail segments with horizontal scutes that precede the segment with the first single vertical scute (Fig. 2.17) on both sides of the tail (R and L). By numbering the segments 1–9 from caudal to cranial, and by recording the segments with markings, doubling the number for double markings, a code could be established. This could be further refined by distinguishing between black and grey markings, placing the code numbers for grey spots in brackets, and by adding a sketch of the side view to the record. Using nine rows of scales on either side of the tail of almost 300 crocodiles, Swanepoel (1996) found an accuracy of 95%. The degree of accuracy could be increased by using ten or even 12 rows. This method is applicable to wild populations as well as to farmed animals, e.g. in a breeding colony, and could also be applied to other species of crocodiles.
Clipping Several ways of marking crocodilians have been used. Toe clipping limits the number of individuals that can be marked, and the accidental amputation of a toe as a result of biting or fighting is quite common (Dixon and Yanowsky, 1993). Clipping the dorsal crest of the tail is difficult, if not impossible in hatchlings. As the marked individuals grow, the mark becomes smaller in relation to the overall size of the animal (Dixon and Yanowsky, 1993). Tags Web-tagging has been used widely, but tags are frequently lost, and limbs are also lost occasionally – leading to the loss of a record (Dixon and Yanowsky, 1993). Tags applied to one of the dorsal crests in adult crocodilians are often used. However, they occasionally
Examination of Crocodiles and Clinical Procedures
75
Fig. 2.17. Spots on the tail of a Nile crocodile used for identification (after Swanepoel, 1996). Reading from caudal to cranial, this crocodile would have the code R113346688.
get lost, and the numbers are not easy to read (Dixon and Yanowsky, 1993). On South African crocodile farms the colour of these tags is used to indicate the sex of the animal. None of these markings is acceptable for zoos and other tourist exhibits. Microchips Transponder chips or microchips have been used successfully in broad-snouted caimans (Dixon and Yanowsky, 1993). The chips were inserted into the left side of the tail base, and it was found that the microchips did not migrate from the site of implantation, nor was there any scarring of the skin. A serious disadvantage of this method is the fact that the reading device only works from a maximum distance of about 20 cm, forcing the operator to come dangerously near to the animal to read it, or to capture and restrain the animal first. The presence of the chip in the tail meat may also affect its acceptability in certain countries. Since 1997, the European community has required all crocodilians to be microchipped (as are all Annex A listed vertebrates) if used for commercial purposes such as sale, display, breeding, etc. (Redrobe et al., 1999). The British Veterinary Zoological Society advises
injection of the microchip in crocodilians dorsally into the neck, anterior to the nuchal cluster (Redrobe et al., 1999).
Post-mortem Examination Storage and transport of the carcass Dead crocodiles are usually found in a very warm environment and, at that temperature, tend to decompose very rapidly. Therefore, it is important to collect the dead animal as soon after death as possible and cool it down to about 4–10°C. Larger bodies cool more quickly if immersed in ice water. Freezing a carcass should be avoided as the formation of ice crystals destroys the cells and renders the carcass unsuitable for histopathological examination. However, when refrigerated, psychrophilic bacteria continue to multiply and may overgrow those pathogens potentially involved in causing the mortality. Thus freezing a few specimens purely to maintain the microbial flora for examination in the laboratory might be considered. In any case, the carcass should be taken to a diagnostic laboratory as soon as possible – remember that laboratory procedures also cause delays and that the usefulness of a
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Chapter 2
diagnosis decreases with the time lapsed after the death of the animal. The laboratory should be alerted and the carcass transported to the laboratory, size permitting, in an insulated container and on ice. The cost of an examination and investigation is usually small compared with the value of the animals lost. If there is a high mortality, several carcasses should be submitted, but a whole bagful of dead hatchlings may only tire the pathologist without contributing to the eventual diagnosis. At the laboratory the pathologist should be given as complete a history as possible, including the age and number of animals affected, and be provided with contact numbers (phone, fax and e-mail) and address. Most laboratories have forms for this purpose.
Humane killing Live specimens that have been submitted for post-mortem examination will have to be put down humanely. Larger crocodiles (>60 cm) are killed easily with a captive bolt stunning gun, as used for the slaughter of pigs or cattle. This destroys the brain of the crocodile completely, rendering the animal
immediately ready for further procedures. The spot to aim at is in the middle, between the orbits and the supertemporal fossae (Fig. 2.18). Small specimens can be given a lethal injection of a barbiturate either intraperitoneally (see p. 89), into the heart, the dorsal neck vein (see p. 64) or into the dorsal or ventral tail vein (Figs 2.14 and 2.15). Catto and Amato (1994b) used intracerebral injections of ethyl alcohol, but the route of injection and dosage rate were not given, nor did the authors comment on the effectiveness of this method.
Examination of head and skin Before opening the carcass, the head and skin are examined. The examination of the head includes the eyes (eyelids, nictitating membrane, cornea), the nostrils and the mouth (gingivae, teeth, tongue and gular valve). The skin of the whole body is checked for injuries, ulcers, swellings, abrasions (under the chin and the soles of the feet, see p. 242), pox (pp. 157 and 158) or pox-like lesions (p. 236) and any other abnormalities. Then the total length is measured, recorded and, if possible, the animal is weighed.
Fig. 2.18. Head of a farmed Nile crocodile killed with a captive bolt stunning gun. The correct spot to aim at is in the centre, between the orbits and the supertemporal fossae.
Examination of Crocodiles and Clinical Procedures
77
Opening the carcass
Neck, pharynx and oral cavity
The animal is placed on the table with its belly up and the skin is incised across the lower neck, just cranial to the row of large scales between the fore limbs (Fig. 2.19). From there the skin and body wall are cut along both sides of the body, first through the coracoid and then through the cartilaginous part of the ribs. The coracoids are very tough, and in adult animals it may be easier to cut through their cartilaginous junction, in the midline, before going to the ribs on either side. In larger specimens the skin is taken off prior to the removal of the ventral body wall (Fig. 2.20). The lateral cuts are continued beyond the ribs through the abdominal wall, taking care not to cut into any of the abdominal organs, particularly into the stomach which is attached to the left body wall. The pubic bone protrudes cranially from the pelvic girdle. In hatchlings it can be removed with a transverse cut, in older specimens it becomes extremely tough and can be left in place and the transverse cut made just cranially to it. The skin with the ventral body wall is now lifted and all adhesions are carefully dissected until the whole piece can be lifted off, exposing the thoracic and some of the abdominal organs (Fig. 2.21).
The lateral cuts are continued in a cranial direction to the maxillary joints, and then medially of the mandibles to the tip of the tongue. This flap of skin with the tongue is lifted off, exposing the hard and soft palate, with the dorsal flap of the gular valve, the internal nares, the ventral opening of the Eustachian tubes and the larynx (Plate 5) (see p. 11). Along both sides of the neck it may be possible to see the chains of thymus glands (p. 21). However, they are no longer present in emaciated animals.
Examination of the thoracic viscera The thoracic part of the trachea is inspected first. Then the various thoracic endocrine glands are located, which may be hidden in fat deposits: the multiple lobes of the thymus gland, the thyroid(s) and the parathyroids (see p. 22) (see Plate 3). The pericardial sac is opened, the heart is taken out, and the auricles separated from the ventricles. Note that crocodiles do not have fat in the coronary groove. The two lungs are then loosened from their attachments to the body wall and the prehepatic
Fig. 2.19. Line of incision across the lower neck and along the sides.
78
Chapter 2
Fig. 2.20. In larger specimens the ventral skin is taken off before removal of the ventral body wall.
Fig. 2.21. Opened carcass with the ventral body wall deflected caudally.
transverse membrane. These attachments are normal, but they vary in extent from species to species. The lungs can then be taken out for closer examination. This leaves the oesophagus, which is situated in the mediastinum and is attached dorsally to the body wall.
Examination of the abdominal viscera Before fully exposing the abdominal viscera it may be necessary to carefully remove the ventral diaphragmatic muscle, which runs from the cranial transversal membrane to the pubic bone. Its removal exposes the two
Examination of Crocodiles and Clinical Procedures
lobes of the liver, the stomach on the left side, the fat body on the right side and a few intestinal loops (Fig. 2.22). The duodenum is severed where it emerges from the pyloric antrum of the stomach, and the whole intestine is gently pulled loose from the mesentery and lifted out to the left side of the body. The fat body is then lifted out, giving access to the spleen dorsally in the mesentery (Fig. 2.23). The size of the fat body is a better indicator of the actual state of nutrition than any subperitoneal fat that may be present, as such fat is poorly metabolized, while the fat body is a very active fat storage organ, supplying the daily needs, particularly of the heart (see p. 28). Cranially the spleen is surrounded by the caudal pancreas, the cranial pancreas is found between the duodenal loops. The spleen is covered by a very strong fibrous membrane, which normally grows as the spleen itself grows but does not stretch when the spleen hypertrophies in response to an infection. In such cases, the spleen tissue buds through the capsule. Such a budding spleen is a clear sign of hypertrophy splenomegaly, indicating infection and septicaemia (Fig. 1.46) (Huchzermeyer, 1994). The stomach is severed from its attachment
79
to the left body wall and then lifted out with parts of the oesophagus. It is then opened and inspected for normal contents, foreign bodies (p. 254), parasites (pp. 192 and 194) and ulcers (p. 251). Next, the two lobes of the liver, together with the gall bladder, can be removed and examined. The intestine is then cut off at its most caudal accessible end. It is opened for closer examination, at least in parts. It is now possible to attempt a cut through the pubic bone towards the cloaca and excise the cloaca. This leaves the gonads partially covering the adrenals, the Muellerian ducts or the oviducts and finally the kidneys, attached to either side of the backbone in the caudal recesses of the abdominal cavity.
Tail, legs and feet The tail is cut across, not far from its base, to expose the fat deposits between the superficial and deep muscles (p. 10). The legs and the joints are examined for any swellings and, if necessary, the joints are opened to examine them for arthritis (p. 273) and gout (pp. 230 and 264) (Fig. 2.24). Any other swellings are also incised and examined.
Fig. 2.22. Abdominal organs exposed after removal of the diaphragmatic muscle: a, liver; b, stomach; c, fat body; d, duodenal loop; e, loops of jejunum and ileum.
80
Chapter 2
Fig. 2.23. The spleen in situ dorsally in the mesentery, cranially surrounded by the caudal pancreas.
Fig. 2.24. Opened carpal joint.
Brain and spinal cord In smaller specimens (<1.5 m) the skull can be split longitudinally in the midline from the ventral aspect (the head upside down) with the help of a strong knife and a hammer (Fig. 2.25). This gives access to the nasal cavi-
ties and both halves of the brain (Fig. 2.26). For mature specimens a saw has to be used to open the skull. Sections of the vertebral column can also be opened longitudinally with a knife and hammer, to expose the spinal cord. I have never been able to pull the spinal cord as is
Examination of Crocodiles and Clinical Procedures
81
Fig. 2.25. Splitting the skull of a juvenile Nile crocodile from the ventral aspect with a strong knife and a hammer.
Fig. 2.26. The split skull, exposing the nasal passages, the halves of the brain and the pituitary gland (p. 21) at the base of the brain (arrow).
82
Chapter 2
done with slaughtered dwarf crocodiles in the Congo Republic. There, the butcher ladies at the markets cut dorsally through the neck down to the vertebral column, bend the head down and grip the spinal cord between two fingers before severing it cranially. Then, while gently tapping the back with the blunt side of the machete, they slowly pull out the entire spinal cord (Fig. 2.27). They claim that the meat is inedible if the ‘black worm’ is left inside. Sample collection Blood If the animal is still alive, blood samples can be collected as explained above (p. 64). During post-mortem examination, blood can be collected from the auricles of the heart. Note, though, that the cells deteriorate after death, and that only the freshest carcasses will have blood that is still suitable for some of the laboratory tests. The method for the preparation of thin blood smears has been explained above (p. 65). The blood smears are air dried and then fixed by immersing them in methanol, or by letting methanol run over them. They are air dried again, and can
then be wrapped in tissue paper or placed in a container for dispatch to a laboratory. Bacteriology Samples for the isolation of bacteria should be taken with sterile instruments before the organs have been contaminated by handling, and should be placed in sterile containers. If they cannot be delivered to the laboratory immediately, they should preferably be frozen to prevent any further growth by contaminating bacteria. If sterilized instruments are not available, scissors and forceps can be immersed in a 10% formalin solution, such as is used for the preservation of histopathology specimens (see below). In the case of a generalized infection, all internal organs will contain the bacteria, as crocodiles have no lymph nodes and are therefore unable to localize an infection in a particular organ system. Therefore it is unnecessary to collect bacteriological specimens from all the organs, normally the liver suffices. In addition, one should sample specific lesions or organs that are visibly diseased. In cases of enteritis, either a piece of unopened intestine is collected or a small quantity of intestinal contents. The organ
Fig. 2.27. Pulling the spinal cord from a slaughtered wild-caught African dwarf crocodile at a market in Brazzaville.
Examination of Crocodiles and Clinical Procedures
samples should be taken in the form of small cubes, with a side length of 5–10 mm, and placed in separate containers. Viral isolation If a viral infection is suspected, first discuss with staff at the virology laboratory whether such a virus can be isolated at all (see p. 157). An alternative may be to demonstrate virus particles in fluids (intestinal contents) by negative staining and transmission electron microscopy (TEM) (Huchzermeyer et al., 1994b). Virus particles can also be detected by TEM in tissues that have been fixed in glutaraldehyde solution. The details would have to be discussed with the electron microscopist at the laboratory. Some viruses cause the formation of typical inclusion bodies, which are detected by histopathological examination (see below). Histopathology For histopathological examination, small cubes of tissue (5–10 mm side length) should be placed in 10% formalin solution. Formalin is normally sold as a 40% formaldehyde solution, which is regarded as 100% formalin (saturated solution). One part of this, diluted in nine parts of water gives the 10% formalin solution that is required. Laboratories prefer to dilute the formalin in buffered distilled water or in buffered saline solution. However, in an emergency, sufficiently good results can be obtained by using tap water as diluent. Note that the formalin becomes further diluted by the water in the tissues. Therefore, it is advisible to immerse the tissue cubes in about ten times more formalin solution than the actual mass of the tissues to be preserved (e.g. 10 g of tissues in 100 ml of solution). Formalin penetrates the tissues only very slowly, and this causes large pieces to rot inside while only the outer layers are fixed by the preservative, particularly under warm or hot climatic conditions. This is the main reason why small cubes of tissue should be used. It is wise to collect tissues from all organs and from all the different lesions encountered, but tissues from different animals
83
should be kept in separate containers. The histopathologist can then choose which organs to examine in each particular case. By limiting the number of organs collected, the ability of the pathologist to establish the correct diagnosis is also limited. Parasites Stomach and intestine are cut open in their whole length and placed in a screw-cap jar, which is filled to one half with water. The cap is tightened and the jar shaken vigorously. Then the contents are poured through a strainer (coffee strainer) and the contents of the strainer washed out into a dark plastic tray, in which the parasites can be found. Intestines from very large crocodiles may have to be processed in smaller sections. Parasites are best preserved in 70% ethyl alcohol. Roundworms tend to roll up into tight balls when placed in alcohol. They are then difficult to examine later under the microscope. It is better to place them in a test tube with saline solution, or even tap water, which is then heated over a flame to almost boiling. At that moment the parasite stretches out, and it remains stretched when placed in alcohol.
Collecting specimens in the field Required material Field work often takes place far away from the nearest laboratory, under difficult climatic conditions and usually also with severe restrictions regarding space and weight allowed for equipment and materials. The minimal requirements comprise the following instruments: ● ● ● ● ● ● ● ●
a knife; scissors (both good quality and sharp); forceps and razor blades; a number of very small (2–5 ml) and small (20–30 ml) plastic screw-cap jars; a few larger (±200 ml) screw-cap jars; one 500 ml screw-cap jar; a few 10 ml plastic syringes with needles; two test tubes;
84
Chapter 2
● ● ● ● ● ●
glass slides and cover slips; a coffee strainer; a small cutting plank; a plastic tray; a plastic measuring cylinder (±250 ml); 500 ml of formalin (40% formaldehyde solution – see above, p. 83), 500 ml of 70% ethanol and 500 ml of methanol, all three in sturdy plastic cool drink bottles; ● a few similar spare bottles for the solutions to be made up, and; ● an insulated box for the transport of frozen specimens. Also required are masking tape, a roll of toilet paper, a pencil, paper and a marking pen. Bacteriology and blood samples If there is no access to a freezer, bacteriological and serum samples cannot be taken. If a freezer is available, the bacteriological samples are taken as explained on p. 82, but in the smallest possible containers, marked on the outside with the specimen number and placed in the freezer as soon as possible. For serum samples, the blood is collected from the auricles, one drop of blood is placed on a glass slide for a blood smear (see p. 65) and the rest squirted gently into a 20 ml jar, marked on the outside and placed on its side in the shade, but not refrigerated, to allow the blood to coagulate in a slope (Fig. 2.28). Once the blood has coagulated, the jar is stood
upright again to allow the serum to collect at the bottom. After a few hours, the serum can be drawn off with a syringe and needle, squirted into a very small jar, marked on the outside again and placed in the freezer. The air-dried blood smears are marked with a pencil, either on the frosted end or on the thicker part of the smear. After fixing and drying they can be rolled into a short length of toilet paper (Fig. 2.29) and secured tightly with masking tape. Several blood smears rolled up tightly in toilet paper are fairly well protected from breakage.
Histopathology samples A 1:10 formalin solution is prepared with either tap or other drinking-quality water, using the measuring cylinder, and poured into one of the spare bottles. One of the 200 ml jars is roughly half-filled from this stock for the initial fixing of the histopathology samples, which are cut as small as possible and left in this jar for 24–48 h without refrigeration. The specimen number is written, with a pencil, on a small square of paper, and also placed into the jar. After 1 or 2 days of fixing, the contents of the jar are poured through the coffee strainer into a second jar. The fixed organ pieces are then placed into the plastic tray and are trimmed with a razor blade on the small cutting plank to the minimum size required for embedding (usually
Fig. 2.28. Jars lying on their side to allow the blood to coagulate in a slope.
Examination of Crocodiles and Clinical Procedures
Fig. 2.29. Several blood smears wrapped tightly in toilet paper are fairly secure from breakage.
3 mm thick pieces, about 5 10 mm wide and long, for details consult a pathologist). These pieces, together with the square of paper, now fit into one of the small jars, in which they are covered with some recycled formalin. They are now ready for storing at ambient temperature and eventual transport back to the laboratory. Do not refrigerate samples in formalin! If necessary, the remainder of the formalin can be used a second time for fixing another set of specimens. Parasites Stomach parasites can be picked directly out of the opened stomach, or the stomach contents can be poured out into the plastic tray in which the parasites become more visible. The intestine is cut open along its whole length and placed into the 500 ml jar. This is roughly half-filled with water, the cap is closed and the jar is shaken vigorously. The intestine is then taken out and the remaining contents of the jar poured through the coffee strainer. The contents of the strainer are then washed with a small amount of water into the tray, where the parasites can be collected. Fixation of the parasites with heat and in alcohol has been explained above (p. 83). For storing the parasites, use the smallest possible container and place a square of paper with the pencilled specimen number in the jar with the sample. Store at ambient temperature. Note that
85
writing in pencil on paper is not washed off by immersion in the liquid, while glued-on labels or writing with a marker pen easily come off if there is an accidental leak. Pentastomes (p. 205) are collected by deeply incising the lungs. If the parasites are still alive, they will come out into the air and can then be picked up easily. For a thorough search, the lungs should be cut into small pieces, washed in the 500 ml jar and the contents then examined in the tray. These are the absolute minimal requirements for the collection of standard specimens, tried on several Congo expeditions. If you can carry more, do so by all means. If there are any specific requirements, e.g. samples for toxicological investigations, you should ask the laboratory for detailed instructions.
Age determination Crocodiles do not have any outwardly visible markers that can be used to determine their age. Their growth also varies individually, for example runted 1-year-old yearlings can be the same size as 1-month-old hatchlings. Unless the date of hatch is known and stated, one should not attempt to guess a crocodile’s age, but rather record its length and weight. Crocodiles that are exposed to hot and cold seasons, as a rule, grow faster in the hot than in the cold season. In such crocodiles the bone is deposited in laminae of varying thickness, similar to tree rings. These bone rings can be visualized and counted in histological preparations (de Buffrénil, 1980a,b; de Buffrénil and Buffetaud, 1981; Hutton, 1986).
Organ morphometry In animals with very large variations in overall body size, it is often difficult to judge the relative size of a particular organ in an individual case. However, for a pathological diagnosis it is important to be able to determine whether an organ is hypotrophic, hypertrophic or normal. Huchzermeyer
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(1994) found a close relation in Nile crocodiles between the mass of the two ventricles of the heart (total ventricular mass, TV) and total body length, so TV is used as the standard against which the other organs are measured (Fig. 2.30). To make this comparison, the organ in question is weighed and so is the heart, without the auricles. The weight of the organ is then divided by the weight of the ventricles, resulting in the following ratios: ● spleen :heart ratio (SHR); ● fat body :heart ratio (FHR); ● kidney :heart ratio (KHR). The spleen :heart ratio indicates the state of activity of the spleen. The SHRs of normal and diseased Nile crocodiles are shown in Table 2.12. It must be borne in mind, though, that often the affected crocodiles die very slowly, and that after a long illness the spleen becomes hypotrophic again and could appear normal. The fat body :heart ratio indicates the actual state of nutrition. An FRH <0.5 indicates an animal in a very poor state, while an FRH >5 indicates an overfed animal (excess energy). The kidney:heart ratio was found to be of limited use, as there was little variation in relative kidney mass and visibly affected kidneys could be detected without weighing.
Examination of unhatched eggs On farms where poor hatching results are obtained, it may be necessary to open and examine all unhatched eggs, particularly those from nests with very poor results. If the eggs are to be submitted to a laboratory, they should be kept refrigerated, but not frozen, before and during transport. The eggs are cut open lengthwise with a small pair of scissors and the contents poured into a dish. After each egg has been examined, the contents of the dish are poured into a bucket for eventual disposal. Infertile eggs usually remain clear throughout the incubation period and no sign of banding or remains of an embryo can be found. If any contamination has penetrated into the egg, the contents become putrid, and in such an egg a small, dead embryo may have dissolved altogether. Consequently an infertile egg may be difficult to differentiate from one with early embryonic death. A microsatellite analysis procedure, based on parental DNA, has been described for the exact differentiation between infertile eggs and early embryonic death, but may not be applicable to routine farm investigations (Rotstein et al., 2002). Larger embryos can, however, be found and examined. From their state of development one can try to judge at which point during incubation the embryo has died. If contamination is found, or is suspected to be the problem, submit some swabs to a bacteriology laboratory (i.e. sterile swabs dipped into the liquid before it has been poured out of the egg).
Medication Administration of medication Mass medication
Fig. 2.30. The relative sizes of myocardium, fat body and spleen.
Mass medication is rarely given in the water, as only a small part of the water is consumed by the crocodiles. Medication of the water is suitable for the external treatment of skin infections and for a supportive treatment with salt (1 g l1). The salt is intended to
Examination of Crocodiles and Clinical Procedures
87
Table 2.12. Spleen : heart ratios (SHR) of Nile crocodiles in relation to different pathological conditions (Huchzermeyer, 1994). SHR values indicate the degree of splenomegaly. Condition
Range
n
No apparent infection Conjunctivitis, mostly chlamydial
0.19–0.72 0.11–2.12
77 40
Septicaemia
0.24–2.57
84
Salmonellosis Gastritis Enteritis
0.22–2.68 0.41–2.49 0.34–2.71
70 54 35
See also Chapter 5, p. 167; Chapter 7, p. 245 Chapter 5, p. 173; Chapter 6, p. 228 Chapter 5, p. 164 Chapter 7, p. 251 Chapter 6, p. 226; Chapter 7, p. 255
n, Number of cases.
replace salt lost into the fresh water by animals that have not eaten for a while, and thus have not been able to obtain salt from their food (see pp. 41 and 282). Antibacterials and anticoccidials can be administered via the food. Medicated pelleted rations will have to be prepared specially for the purpose. When medication is to be incorporated into wet rations based on meat or fish, only one-quarter of the dry ration dose should be used to compensate for the high moisture content of the ration. Mixing powders or liquids accurately into wet rations is extremely difficult and an even distribution of the medication is rarely achieved. If the mince is spread out in a thin layer on a tray, a liquid can be sprayed over it. Medication in powder form should first be mixed into bonemeal to increase its bulk, and only then be mixed into the mince. Individual dosing Small crocodiles that can be handled easily (hatchlings) can be dosed individually by mouth, in the following way. The liquid (0.2–0.5 ml) is drawn into a 1 ml plastic syringe. The crocodile is held in one hand, with the thumb and index finger holding the base of the mandible (Fig. 2.31). Tapping the hatchling’s nose lightly with a pen causes it to open its mouth, or the mouth is forced open gently with the tip of a finger of the other hand, and the entire syringe is slowly pushed into the mouth, past the gular valve and into the oesophagus, to the cardia of the stomach. Then the plunger is pushed down before the
syringe is withdrawn slowly. The crocodile is still held upright for a while, so that the liquid is not regurgitated. During the whole procedure care should be taken not to exert any pressure on the stomach. Larger crocodiles can be force-fed by stomach tube in the same way as for collecting stomach contents (see p. 66). It may be easier to use a flexible tube, threading it through a hole of appropriate size drilled through a long piece of wood, which can be held still by an assistant (Fig. 2.32). The method described for stomach washing (p. 66) can also be used for force-feeding. Larger, even very large crocodiles, particularly ones that have not eaten for a long time and need dosing with sugar to stimulate their hunger, can be dosed with a thick sugar syrup (e.g. treacle or honey), which can also be medicated with whatever is required. The syrup is rolled on to one end of a long stick (broomstick), and with another stick or plastic pipe the crocodile is tapped on its snout until it opens its mouth. The syrup then is slapped into the back of its mouth and wiped off on the tongue. From there it will be swallowed slowly by the crocodile. After dosing, the crocodile should be prevented from entering the water, so as not to wash the syrup out of its mouth (personal communication, P. Martelli, Singapore, 1994). Injections The resorption of injected medication is slower in reptiles than in mammals or birds because of the slower heart rate (p. 43). It is
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Chapter 2
Fig. 2.31. Dosing a hatchling with the help of a 1 ml syringe.
Fig. 2.32. Dosing by stomach tube.
also temperature dependent – slower at lower, and faster at higher temperatures. It is recommended not to inject oily solutions or emulsions, as their resorption is even slower (Kraft,
1978). Oils and emulsions may also elicit a local inflammatory response, and the exudation of fibrin may prevent the resorption of the injected substance entirely (see p. 46).
Examination of Crocodiles and Clinical Procedures
Because of the tight adherence of the skin and the many cutaneous muscles, it is hardly possible to give subcutaneous (sc) injections to crocodiles, except under the ventral skin, which is less accessible. When giving intramuscular (im) injections, one should try to avoid injecting into accumulations of body fat, which would slow down the resorption. This often happens with deep injections into the tail. The ideal sites for im injections are the muscles of the upper limbs. An injection with a pole syringe is best given caudolaterally into the junction of hind leg and tail. Intraperitoneal (ip) injections are given either in the ventral midline, cranial to the pubic bone, in small crocodiles that can be held in a belly-up position, or, in larger specimens, laterally on the right-hand side cranial to the knee. It is also possible to inject into masses of fat here, with a consequently reduced speed of resorption. The sites for intravenous (iv) injections are the same as those that are used for taking blood samples (see p. 64). However, it should be noted that all these sites only allow the needle to be placed in a perpendicular position to the vein and, therefore, some or even all of the liquid could well be injected paravenously, particularly if the animal struggles during the injection. A case of paravenous injection during an attempted blood transfusion into the supervertebral (internal jugular) vein in an African dwarf crocodile ended in the death of the crocodile due to compression of the spinal cord by blood entering the subarachnoid space (Heard et al., 1988). For future attempts of blood transfusion, the authors recommended using the tail veins, or the external jugular vein after surgical dissection. Tibial puncture An alternative to the iv route may be tibial puncture in the middle of the proximal third of the tibia. This allows the needle to be placed in the venous sinuses in the head of the tibia. The injected liquid will be transported very rapidly from this site. This may be the route of choice when a needle must be left in place for repeated injections or blood sampling, e.g. for pharmacokinetic studies. This method has
89
been adapted from paediatrics and has been used successfully in birds (Ritchie et al., 1990).
Drugs and dosages Generally, the same drugs that are used in poultry can be used in crocodiles. For a single dose, the same dosage should be used as in poultry. However, excretion is generally slower in crocodiles and, therefore, repeated administrations should be spaced accordingly. Normally, with drugs being given in the food, this evens out, as crocodiles tend to eat only every second day. The dosage should also take into account the relatively low feed intake of crocodiles. The dosage levels given in Table 2.13 have been calculated for the average feed intake. Another point to be taken into consideration with mass administration of medication is the possible effect on the environment. Many drugs are excreted unaltered and will be washed out with the water. They have the potential to pollute rivers or other natural water bodies into which the effluent from the crocodile farm is released. Some of the metabolites of commonly used drugs are also biologically active. The antibiotic sensitivity of bacteria isolated from crocodiles varies considerably. It is therefore recommended that antibacterials should be used only after the sensitivity of the bacteria in question has been established in a laboratory (see p. 91). The prolonged or repeated prophylactic use of antibiotics only serves to increase the level of resistance in all the bacteria exposed to the particular antibiotic. This resistance can even be passed on to other species of bacteria, creating problems when the same antibiotic could, or should, be used in a disease outbreak. This is the reason why the prophylactic use of antibiotics should be strictly avoided (see also p. 91). The commonly used drugs and their dosages have been collated in Table 2.13. Note that ivermectin is toxic to crocodiles (see p. 225). It causes paralysis when used at half the mammalian dose (personal communication, C.M. Foggin, Harare, 2000).
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Chapter 2
Table 2.13. Drugs and dosages commonly used in crocodiles. Drug
By mouth
im
In feed
75 mg kg1
Tetracyclinea
1.5 g kg1 10 mg kg1
10 mg kg1 0.5 g kg1
Tetracycline long actinga Kanamycina
20 mg kg1 20 mg kg1
Gentamycina
2.5mg kg1
Times
Refs
Single dose Daily for 10 days Daily for 9 days For 4–10 days Repeat after 3 days Every 2nd day for 8 days Every 3rd day for 15 days
1 1 3, 4 5 5 2
3 mg kg1 20 mg kg1
Chloramphenicola
10–30 mg kg1 Penicillinsa Danofloxacin (Advocin®)b Enrofloxacin (Baytril®)b Sulphachloropyrazine (ESB3)b
0.1 MIU kg1 1 g kg1 0.05–0.2 ml kg1 dilute 1:5, 5 ml kg1 10 g kg1 2 g kg1 1 g kg1 7 ml kg1
Amproliumb Toltrazuril (Baycox®)b Ketaconazolea
2 per day for 9 days Daily for 4 days Repeat after 2 days For 5 days
50 mg kg1
Mebendazolea
20 mg kg1
Piperazinea
50 mg kg1
Ca-borogluconate (250 mg ml1) Doramectin 1% NaCl
5 3, 4 5 5 6 5 5
2 ml kg1
For 4 days Daily for 7 days Continuously For 3 days 1 repeat after 2 weeks For 3 days
5 ml kg1
For 3 days
5
1 repeat after 2 weeks 1 repeat after 2 weeks 1 repeat after 2 weeks
4
50 mg kg1
Fenbendazole (100 mg ml1) Oxfendazole (22.6 mg ml1) Thiabendazolea
3, 4
ip, dilute 1:2, 3 ml kg1 1 ml 50 kg1
5 5 5 5 3, 4 5
4 4 5
In water 1 g l1
For 10 days
7 6
a
Active substance. As product. 1, Huchzermeyer et al. (1994a); 2, Huchzermeyer (1991a); 3, Verseput (1986); 4, Jacobson et al. (1983); 5, Foggin (1992a); 6, own recommendation; 7, C.M. Foggin, Harare (2000), personal communication.
b
Vaccines Vaccines are used to stimulate antibody production against specific pathogens. For the preparation of such vaccines it is necessary to culture and propagate the specific disease agents. Few vaccines have been used in crocodiles so far, as none of the crocodile-specific
viruses have yet been cultured. In an inactivated vaccine, the agent has been killed to prevent its further multiplication and spread, while a live vaccine allows the agent to multiply in the inoculated host. An autogenous crocodile pox vaccine was prepared and tested successfully by Horner (1988a). He macerated 1 g of pox crusts,
Examination of Crocodiles and Clinical Procedures
collected from the skin of affected crocodiles, in 10 ml of phosphate buffered saline, added 1 MIU penicillin and 1 g streptomycin, and left the suspension standing for 24 h, after which it was centrifuged at 180 g for 10 min. The trial hatchlings were inoculated with 0.5 ml of this vaccine sc between the hind leg and the base of the tail. Mohan et al. (1997) reported the vaccination of Nile crocodiles against Mycoplasma crocodyli. The vaccine was inactivated with formalin, and contained aluminium potassium sulphate as an adjuvant. The use of an inactivated calf paratyphoid vaccine as part of a range of therapeutic and preventive measures in an outbreak of salmonellosis in farmed Nile crocodile hatchlings was reported by Huchzermeyer (1991a).
Pharmacokinetics Pharmacokinetics deals with the fate of drugs in the body, their absorption, distribution, metabolization and, finally, their excretion. Hardly any work has been carried out in this field in crocodiles. We assume that, because of the slow circulation in crocodiles, the resorption, distribution and excretion of any drug are much slower than in birds and mammals, and that they are temperature dependent. We also assume that, because of the low metabolic rate of crocodiles, they are metabolized more slowly. Drug dosage rates (p. 89) have generally been calculated on the basis of these assumptions, and in certain cases have been corrected if and when signs of toxic effects occurred. There is no doubt that species differences might occur among the crocodilians regarding pharmacokinetics and drug tolerance. This is a very wide field of research that urgently needs attention. In this context, the paper by Coulson and Hernandez (1953), regarding glucose, insulin, adrenaline and ACTH in the American alligator, deserves particular mention. The authors found that injected glucose is removed from the bloodstream at a very slow rate. One unit of insulin per 1 g of body mass produced an immediate state of shock due to hyperglycaemia, which lasted for a
91
few hours. A second state of shock occurred more than a day later, and was due to hypoglycaemia. Large amounts of glucose promoted the formation of liver and body glycogen. For 2 h after the injection of adrenaline no effects on blood glucose or pupillary response were observed. After 2 h the pupils contracted to slits and blood glucose rose by several hundred mg ml1. Adrenaline reduced the glycogen stores of the liver to about one-third and the body glycogen to about one-half of normal values within 24 h. Prolonged daily injections of cortisone, 10 mg kg1 body mass, caused a moderate hyperglycaemia. Daily injections of ACTH, 5 mg kg1 body mass, had no effect.
Antibiotic resistance The antibiotic resistance of pathogenic bacteria depends on previous exposure to these substances. If crocodiles are fed the meat or whole carcases of farm mortalities, they acquire the pathogens of these animals, which will be resistant to any antibiotics to which they have been exposed previously. This is the case particularly if poultry or pigs are used as crocodile feed. As not all bacteria are killed during a course of treatment, the most resistant ones are likely to remain alive and pass on their genes for resistance to their progeny. Bacteria can also transfer these genes to other bacterial species, thereby causing a whole population of bacteria to become resistant very rapidly. Continuous use of antibacterials on the crocodiles themselves can obviously also stimulate antibiotic resistance and should therefore be avoided (see above).
Surgical Interventions Most of the procedures described in the following were designed for experimental surgery, used in physiology research. In cases in which clinical surgery becomes necessary, they may be able to give some guidance on how to access a particular organ.
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Anaesthesia Anaesthesia differs from immobilization (p. 70), in that it excludes the sensation of pain, which immobilization does not do. For any surgical procedure it is necessary to employ a local or general anaesthetic, possibly in addition to immobilization. Drugs and dosages used in the anaesthesia of crocodilians have been reviewed by Loveridge (1979) and Bennett (1991). Hypothermia Lowering the body temperature by packing the animal in ice, or even placing it in a freezer, reduces its ability to react and immobilizes the animal, but does not reduce its capability to perceive pain (Kennedy and Brockman, 1965; Hartman, 1976; Ensley et al., 1979). The procedure is very stressful, and may lead to post-recovery complications. It should, therefore, never be used, even in conjunction with local anaesthesia (Bonath, 1979; Nichols, 1986; Bennett, 1991). Inhalation anaesthesia Crocodiles, like all amphibious animals, can hold their breath for prolonged periods. This may make it difficult to induce inhalation anaesthesia (Jones, 1977). However, this may be overcome by removing the tape covering the eyes, which was found to stimulate respiration in a 2.2 m Crocodylus palustris (Russo, 1979). For the induction of anaesthesia, the animal’s head was placed in a clear plastic bag filled with a halothane–oxygen mixture from a vaporizer, operated at a 5.5% halothane concentration with a flow rate of 5 l min1. After 20 min the animal was thought to be sufficiently anaesthetized, the plastic bag was removed and its jaws were held open by the insertion of a wooden block. However, the animal started to react, so the plastic bag was replaced for another 15 min. After that, a cuffed endotracheal tube was inserted and connected to the anaesthetic machine, which was then operated at 2.5% halothane with 2 l min1 oxygen. After termination of the anaesthesia it took the animal 10 min to recover fully and walk back to
its pool (Russo, 1979). Apparently, the loss of the skin reflex is a better indicator of the depth of anaesthesia than the loss of other reflexes. This reflex is provoked by applying firm pressure with a key, in a linear stroke along the side of the crocodile (Russo, 1979). In juvenile American alligators of ±770 g body mass, anaesthesia was induced by 5% halothane and 95% oxygen and maintained with 3% halothane and 95% oxygen (Branco and Wood, 1993). In American alligators, Calderwood (1971) induced anaesthesia with 3% halothane in oxygen via a mask, which after intubation was continued with 1.5% halothane. General anaesthesia by injection A number of general anaesthetics have been used in crocodiles, including barbiturates, ketamine, phencyclidine and tricaine methane sulphonate. Their dosages are summarized in Tables 2.14–2.16. As most of these drugs are injected either im or ip, their resorption may take a long time. Recovery from this type of general anaesthesia may also be prolonged and barbiturate anaesthesia should be avoided, since recovery is especially protracted (Nichols, 1986). Local anaesthesia Local anaesthetics work best when used together with chemical restraint (see p. 70). In very small hatchlings there may be a danger of overdosing, as is the case in small birds. Lignocaine and procaine have been used for laparotomies in C. johnsoni and Crocodylus niloticus, respectively (Limpus, 1984; Kofron and Trembath, 1987) (see also below), and procaine, together with thiopental, in American alligators (Greenfield and Morrow, 1961). Xylocaine was used in conjunction with hypothermia in an American alligator, for the removal of fibro-granulomatous masses (Ensley et al., 1979) (see also p. 95).
Laparoscopy Limpus (1984) examined the ovaries of 23 mature Johnston’s crocodiles by laparoscopy
Examination of Crocodiles and Clinical Procedures
93
Table 2.14. The use of barbiturates for general anaesthesia in crocodiles. Species
Length (m)
Pentabarb Alligator mississippiensis A. mississippiensis A. mississippiensis
A. mississippiensis A. mississippiensis Caiman crocodilus C. crocodilus A. mississippiensis Thiopental A. mississippiensis
Mass (kg)
<2.3 90–180
Dose (mg kg1)
1–1.14
4.1–5.9
>43 11–14.5 11 14.8 14.8 3.7 9 7.8–8.9 15.5 8.9 20–30
1–1.2
7–30
15
3.35
135
Route
References
By mouth By mouth ipa;b By mouth ip ipa;b ip im imc imd ip
s s s
1
s s s u u s
1 2 3 4 4 6
ipe
s
5
1
a
+ Tubocurarine ip. + Postsurgically pentamethylene tetrazole half-hourly or hourly. c Split and given in three consecutive amounts. d During induced hyperthermia 35.6°C. e + Local anaesthesia with procaine. s, Satisfactory. u, Unsatisfactory. 1, Pleuger (1950); 2, Jones (1977); 3, Brisbin (1966); 4, Klide and Klein (1973); 5, Greenfield and Morrow (1961); 6, Xu et al. (1997). b
Table 2.15. The use of ketamine for general anaesthesia in crocodiles. Species Aligator mississippiensis Crocodylus niloticus A. mississippiensis C. niloticus
Length (m)
Mass (kg)
0.65–2.92
2.5–3 0.07 0.8–100
Dose (mg kg1) 125–150 59 40–100 22–44
Route
Comment
References
im
h d h, s s, r
1 2 3 4
im
h, Fine for handling only. d, Dead after 1 h. s, Satisfactory. r, Respiratory depression. 1, Jones (1977); 2, Cooper (1974); 3, Terpin and Dobson (1978); 4, Thurman (1990).
in the field. Each crocodile was strapped to a board to prevent movement. The abdominal cavity was tightly inflated with air from a compressed air cylinder, as used for underwater diving, delivered via a Veress pneumoperitoneum needle (10 cm) with a spring-loaded blunt stylet. This was inserted through the ventral body wall, two scale rows to the right of the midline and anterior to the pubic bone. A 7 mm OE trocar and
cannula with valve was inserted through the same incision, to provide an entry for the laparoscope, a Storz 26031B Hopkins telescope (OD 6.5 mm, forward-oblique viewing, 30E wide angle, incorporating fibre optics light transmission) connected to a Storz 482B cold light source. The following internal structures were seen and identified during laparoscopy: intestinal loops, hard-shelled eggs in the
94
Chapter 2
Table 2.16. Other agents used for general anaesthesia in crocodiles. Agent
Species
MS222®
Alligator mississippiensis Caiman crocodilus A. mississippiensis A. mississippiensis A. mississippiensis
Sernylan® Viadryl® Saffan® M99®
Crocodylus spp. C. crocodilus A. mississippiensis
Mass (kg)
1.4–4.3 Immature 10 0.112 1.5–6.7
Dose (mg kg1) 88–99 66–110 11–22 150 0.74 0.25 0.3–0.5 0.5–5 1–20
Route im im im iv iv im im
Comment References s, l u h, l s u s s s ss
1 2 1 3 4 4 5 6 6
MS222®, Tricaine methanosulphonate; Sernylan®, phenylcyclidine; Viadryl®, hydroxidione; Saffan®, alphaxolone/alphadolone; M99®, etorphine; s, satisfactory; l, long recovery; u, unsatisfactory; h, fine for handling only; ss, satisfactory in small individuals only. 1, Brisbin (1966); 2, Klide and Klein (1973); 3, Campos (1964); 4, Calderwood and Jacobson (1979); 5, Jones (1977); 6, Wallach and Hoessle (1970).
oviducts (vaginae), soft-shelled eggs in the oviducts (uteri) and the ovaries with small or large follicles.
Laparotomy Limpus (1984) performed laparotomies on five adult Johnston’s crocodiles to examine their ovaries. The manually restrained animals were held in dorsal recumbency, the skin around the site of the incision was scrubbed and disinfected, and the incision site was injected subcutaneously with a local anaesthetic (see also p. 92). The incisions were closed with surgical catgut, and coated with a sterile spray-on wound dressing. The crocodiles were kept dry and cool for 24 h after the surgery and then returned to the water. Kofron and Trembath (1987) describe laparotomies on adult female Nile crocodiles for the examination of their ovaries. The animals were restrained manually, their legs were tied together over their backs and their eyes were taped closed. Two animals were operated on in dorsal, and two in ventral recumbency, and it was found that the latter struggled less. For the animals in ventral recumbency, the abdomen was lifted somewhat on the side of the incision by placing a
block of wood underneath. The skin was scrubbed, disinfected and a local anaesthetic was injected at several points along the line of the intended incision, transversally between two rows of scales, halfway between the last rib and the leg (see also p. 92). The skin was incised ±10 cm and the different muscle layers each dissected bluntly. After the operation the peritoneum, the muscle layers and the fat layer were closed with continuous catgut sutures. The skin was closed with stainless-steel or nylon sutures. The incision was then sprayed with a plastic skin sealer containing neomycin and bacitracin, and each animal was given chloramphenicol by im injection into the base of the tail. The animals were released into the water 30 min after completion of the operation and were recaptured 1–3 months later, when the skin sutures were removed.
Clinical surgery Gastrotomy Pleuger (1950) describes the gastrotomy of an adult zoo ‘crocodile’ (species not indicated) that had been observed swallowing a Coca Cola bottle. The animal was anaes-
Examination of Crocodiles and Clinical Procedures
thetized with pentobarbitol (see p. 92). The abdominal skin was scrubbed, disinfected and a longitudinal 25 cm incision was made in the midline, between two rows of scales. The skin was held back by retractors, and the abdominal muscle was incised down to the peritoneum and also held back by retractors. The stomach itself was palpated and brought to the surface through a peritoneal incision. Then a 7.5 cm incision, made through the stomach wall along the line of its greatest curvature, exposed the neck of the Coca Cola bottle. This bottle, unbroken, was removed from the stomach, together with the major portions of five broken bottles, 39 stones, three marbles, two firearm shells, a plastic whistle and a porcelain elephant. The stomach mucosa was thoroughly sponged and the gastric incision was closed with surgical silk No. 0, which was also used to close the abdominal muscle and the subscutal skin. The skin was closed with No. 1 sutures, painted with collodion and covered with gauze sponges. The entire abdomen was then wrapped in a heavy muslin bandage. The crocodile was not allowed back into its pool for 3 weeks, after which the bandage was removed and the wound was found to have healed completely. Pleuger’s (1950) speculation about storage of swallowed matter in the lower oesophagus is wide off the mark: the stomach takes all the swallowed matter and the oesophagus does not act as a crop, as in fowls, or a proventriculus, as in the ostrich. While gastroliths are commonly found in crocodiles and their presence is regarded as normal, it is possible that the swallowing of large numbers of foreign bodies might be due to deranged, or stress, behaviour (see p. 290), similar to that commonly observed in ostriches (Huchzermeyer, 1998a). Whether the operation described above was in fact necessary is a debatable point; it may be the case that the bottles would have been either regurgitated or ground down. Regurgitation of hair balls and foreign objects has been observed in American alligators (Chabreck, 1996; Chabreck et al., 1996) (see p. 37). The bandage appears to have been entirely unnecessary, and the animal should have been returned to the water much earlier,
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probably within 3 or 4 days, to avoid unnecessary dehydration (see p. 283). Oral surgery Russo (1979) reports on the removal of a granulomatous polyp from the palatal fold in the pharynx of a 55 kg, 2.2 m C. palustris, at the New York Zoological Park. The animal was restrained manually and anaesthetized with halothane (see p. 92), while the mouth was held open by a wooden block inserted on one side, between the jaws. The polyp measured 5 3 1.5 cm and was easily excised from the underlying tissue. Two small vessels entering the growth were ligated and the incision was closed with simple interrupted sutures of polyglycolic acid (Dexon, American Cyanamid). Ten minutes after completion of surgery, the animal walked back into its pool. It resumed feeding on schedule and the surgical site healed without complication or recurrence. An open multiple fracture of the mandible of a 1.05 m long American crocodile was operated on under general and local anaesthesia (ketamine 50 mg kg1 and lidocaine 1%). A 1 cm piece of bone was taken out. The two ends of the fractured jaw bone were united with the help of a stainless-steel plate, stitched in place with surgical stainless-steel wire. During recovery, the lower jaw deviated towards the injured side by approximately 5° (RubioDelgado, 2000). Limb surgery Ensley et al. (1979) describe the removal of granulomatous masses from both forelimbs, plantar in the metacarpal area of a 128 kg American alligator, at San Diego Zoo. The animal was restrained physically and by hypothermia, and was given a local anaesthetic at the base of the growths. A circumferential incision was made at the base of each mass, the edge of this incision was undermined and dense fibrous connective tissue was excised from the centre of the surgical wound to facilitate its closure. Simple, interrupted sutures of 0.4 mm stainless-steel wire were used to close the skin. A gauze
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dressing, covered by elastic adhesive tape (Elastakon, Johnson & Johnson), was applied to each carpus, leaving the digits exposed. The operation lasted 2 h, and minimal bleeding was encountered. After the operation, the animal was housed for 6 weeks in a shaded enclosure on concrete. Dressings were changed each week and wound drainage was minimal. When the animal was returned to an aquatic exhibit, the stainless-steel sutures, with a small amount of adjacent tissue, were sloughing while being replaced by regenerating skin (Ensley et al., 1979). Yolk-sac excision The surgical removal of retained yolk-sacs has been described by Youngprapakorn and Junprasert (1994). For details, see Chapter 4 (p. 144).
Experimental surgery Gastric cannulation Sixteen C. crocodilus ranging from 30.5 to 96 cm total length were used in the experiments by Diefenbach (1975b). As repeated cannulation of the stomach, through the mouth, for the sampling of fluids was found to be too traumatic, a polyethylene tube was inserted via the mouth into the lumen of the stomach. The cranial end was then led outside through an incision in the floor of the pharynx, lateral to the basihyal cartilaginous plate of the larynx. The outside of the catheter was stoppered and strapped to the animal’s neck with surgical adhesive tape, which resisted immersion in water. Details of anaesthesia, if any, and suture were not given (Diefenbach, 1975b). Bile fistula Xu et al. (1997) implanted bile fistulas into seven juvenile American alligators, between 104 and 114 cm long and weighing 4.1–5.9 kg, for the study of bile salts. The animals were anaesthetized by the ip injection of pentobarbital, 20–30 mg kg1 live mass,
and deep anaesthesia followed within 1–2 h. The animals were taped to an operating table prior to surgery. A midline incision of about 8 cm was made just caudally of the rib cage. The gall bladder was mobilized from the mesoduodenum and the cystic duct, dissected and ligated. Cholecystotomy was performed by inserting silicone tubing into the gall bladder and fixing it with a purse-string suture. The tubing was exteriorized through a dorsal subcutaneous channel to an area near the hind legs of the animal, fixed in position with tape and inserted into a sterile, plastic sampling bag, which was also secured with tape. After three animals had been fistulated in this manner, the method was modified when it was found that the left hepatic duct in most alligators had a direct connection with the duodenum. After ligation of the cystic duct, the left hepatic duct was dissected in the mesoduodenum, double-ligated and cut between the ligations. Then the procedure for cholecystotomy and externalization of the bile drainage tubing was followed as before. The alligators were maintained in dry tanks for 5–7 days postoperatively and then placed in environmental chambers (Xu et al., 1997). Open-heart surgery Heart operations were carried out on 11 American alligators (1.1–1.5 m) by Kennedy and Brockman (1965). After immobilization by hypothermia (see p. 92), and scrubbing and disinfection of the site of incision, a midline cut between the scales was made from the distal end of the sternum, extending caudally for about 6 cm. Beneath the scales the thin, fibrous tissue and the muscle layer were exposed and incised to permit entry into the pericardium, which was lifted with forceps and incised longitudinally. The pericardial incision was large enough to permit delivery of the heart beyond the ventral abdominal wall. The gubernaculum cordis was clamped, cut and tied on the side of the pericardium. Near the apex of the heart, the clamp was left on the gubernaculum cordis and used for traction when manipulating the heart. After delivery of the heart, a cardiac
Examination of Crocodiles and Clinical Procedures
tourniquet, consisting of a heavy cotton string looped within a glass tube, was applied so as to encircle all the vessels near the base of the heart. Once the cardiac tourniquet was tightened, a time was set to measure the time of cardiac occlusion. The mean occlusion time for nine alligators was 22.5 min (range 16–30 min). The ventriculotomy began just caudal to the junction of the right ventricle, with the conus arteriosus longitudinally for about 1.5 cm, and avoided major coronary vessels. After completion of the experiments, the right ventriculotomy wound was closed in two layers with a continuous suture through the myocardium and through the epicardium. Shortly before closure, the ventricle was flooded with Ringer’s solution to reduce the risk of air embolism. The cardiac tourniquet was released immediately after the ventricle had been closed. The heart was observed through several beats to demonstrate adequate closure and, when necessary, one or two additional sutures were applied. Clotted blood was removed from the pericardial cavity and the cavity was closed loosely with interrupted fine silk sutures to allow
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drainage. The fibrous and muscle tissue cut during the initial midline incision was closed with an interrupted suture of No. 30 stainless-steel wire. Eastman 910 Monomer or collodion was applied to the sutured wound to strengthen and seal it. After the operation the alligator was left in a dry cage for up to 2 weeks to ensure that no infection or other problem had occurred. Five of the operated alligators died with a mean survival time of 35 days. All of them had an acute pericarditis, which the authors believed to have been due to insufficient closure of the skin wound. Sutures did rupture during violent movements of the alligators when they were caught for inspection of the wounds. Even sutures that remained intact caused local peripheral erosion around the suture of scales and subjacent tissue, with eventual disruption of the wound (Kennedy and Brockman, 1965). Another more likely reason for the high incidence of pericarditis after the operation may be stress septicaemia (p. 228) brought about by the lack of anaesthesia during hypothermia, by the hypothermia itself, by water deprivation or by the stress of frequent handling (p. 278).
Chapter 3 Important Aspects of Crocodile Farming
The contents of this chapter are not intended to be a definitive guide to crocodile farming. However, most crocodile diseases are somehow related to, or caused by, management factors, and this cannot be made clear in the discussion of the diseases unless the principles of crocodile farming have been spelled out somewhere. As there is, at present, no textbook on this subject, it became necessary to collect and present the relevant facts in this book.
Nutrition In the wild The study of the nutrition of crocodiles in the wild is based mainly on the analysis of their stomach contents and only secondarily on the observation of their behaviour. Indigestible items, such as shells and fish scales, tend to accumulate in the stomach and may skew the results of such analyses. It is also logical to assume that prey size increases as the crocodile grows. The fact that fishes are the only known intermediate hosts of the internal parasites of crocodiles further indicates the important role of fish in the diet of all crocodilians. Hatchlings start feeding on small aquatic invertebrates such as insects, crustaceans and 98
snails, and later include tadpoles, small frogs and fish in their diet. As they grow, the proportion of fish increases and later birds and small mammals are also taken. Hippel (1946) examined 587 stomach contents of Nile crocodiles in Uganda, of which 141 were found to be empty apart from stones. Of the remaining stomachs, 73.1% contained fish, 14.8% amphibians and reptiles, including crocodile remains and crocodile eggs, 8.5% birds, 1.6% mammals, 0.7% insects and 36.3% plant material, the latter probably ingested accidentally. Stomach contents of Crocodylus porosus up to 180 cm in length consisted mainly of crustaceans and insects, with an increasing proportion of vertebrates (fish, reptiles, birds and small mammals) in animals longer than 120 cm (Taylor, 1979). Stomach contents of adult wild-caught dwarf crocodiles Osteolaemus tetraspis surveyed at markets in the Congo Republic comprised remains of beetles and other insects as well as spiders, scorpions and millipedes, also remains of fishes, frogs, lizards, snakes, birds and small mammals (Riley and Huchzermeyer, 2000).
Energy The metabolic rate is the rate at which energy is burned. In crocodiles, as in other
© CAB International 2003. Crocodiles: Biology, Husbandry and Diseases (F.W. Huchzermeyer)
Important Aspects of Crocodile Farming
reptiles, this is dependent on the body and environmental temperature and on the energy demands of certain activities. Thus it increases sharply during the digestion of a meal (Gatten, 1980). In American alligators it was found that acetate (from fat) was preferred to glucose as a source of energy, but the major pathways of energy utilization were the same as in mammals (Black et al., 1963). Lawrence and Loveridge (1988) demonstrated that a meat diet (ox heart plus bone meal) did not fulfil the energy requirements of juvenile Nile crocodiles. The addition of raw maize (corn) flour as an energy source to the rations of spectacled caimans reduced their performance (Avendaño et al., 1992), as crocodiles cannot digest raw starch. The supplementation of rations of American alligators with precooked (extruded) starch improved not only the growth performance of the alligators but also the digestibility of protein (Staton et al., 1990a,b, 1992). The same authors found a similar improvement by supplementing the rations with fat. However, fat supplementation alone of C. porosus diets did not reduce the use of protein as an energy source, but led to fat deposition instead. The digestibility of long-chain saturated fatty acids was less than that of unsaturated fatty acids, and C20:5 as well as C22:6 fatty acids were found to be essential for juvenile C. porosus (Garnett, 1985, 1988).
Protein While protein may be used partially as a source of energy, its main purpose in nutrition is to provide amino acids that are used in the synthesis of the body’s own proteins for the growth of body tissues. As predators, crocodiles in nature consume animal protein almost exclusively. However, in feed trials with American alligators, they have been shown to utilize isolated soybean protein equally well when it was incorporated as 40% of the total protein content of the ration (Staton et al., 1992). Total digestible protein comprising 42.5–48.7% of the rations gave the best performance (Staton et al., 1990b).
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Minerals There is no need to supply additional macrominerals if the crocodiles are fed meat with bones. In compounded rations the macrominerals are best supplied by the addition of bonemeal. Fish meal is a good source of many microminerals (trace elements). The composition of a micromineral premix used in South Africa (Feedmix, Johannesburg) is shown in Table 3.1. The quantities given are for inclusion into 1 t (1000 kg) of dry mixed ration. In a meat- or fish-based wet ration, only one-quarter of the amount should be used, because of the water content of the ration (see also Table 3.4). A trace mineral premix used in feeding trials with juvenile American alligators is shown in Table 3.2.
Vitamins There are hardly any experimental data concerning the vitamin requirements of Table 3.1. Mineral premix used for crocodiles in South Africa (Feedmix, Johannesburg), quantities per 1 t of complete ration. Availa-Zn Availa-Cu Availa-Mn Availa-Fe Choline Iron Copper Zinc Cobalt Manganese Iodine Selenium Chromium
40,000 mg 5,000 mg 40,000 mg 20,000 mg 600,000 mg 40,000 mg 7,000 mg 70,000 mg 500 mg 60,000 mg 1,500 mg 200 mg 200 mg
Availa, mineral in a metabolically available form. Table 3.2. Micromineral premix used in feeding trials with American alligators, inclusion per 1 kg of wet ration (Staton et al., 1992). Manganese Zinc Iron Copper Iodine Selenium (sodium selenite)
240 mg 200 mg 120 mg 20 mg 4.2 mg 0.1 mg
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crocodiles. Most of the recommendations are based on extrapolation from other species. A crocodile vitamin premix used in South Africa (Feedmix, Johannesburg) is shown in Table 3.3. The quantities given are for 1 t (1000 kg) of dry mixed ration. In a meat- or fish-based wet ration only one-quarter of the amount should be used. The composition of the vitamin supplement used by Cardeilhac et al. (1991) in breeding trials with American alligators is shown in Table 3.4 and the one used in feeding trials with juvenile American alligators by Staton et al. (1992) in Table 3.5.
Home-mixed rations Home-mixed rations are often based on farm mortalities – dead horses, cows, pigs or poultry. Meat from large animals usually is separated from the bones before mincing and thereby becomes deficient in macrominerals (see above), whereas poultry carcasses are minced usually with the bones. However, the bones in broiler carcasses may be deficient in calcium and phosphorus, as these birds are fed minimal mineral levels. Pig carcasses may provide excessive amounts of fat. The polyunsaturated fatty acids in fish oil may have become rancid if the fish is not entirely fresh when fed, and this can poison the Table 3.3. Vitamin premix for crocodiles used in South Africa (Feedmix, Johannesburg), quantities per 1 t of complete ration. Vitamin A Vitamin D3 Vitamin E Vitamin K3 Folic acid Niacin Pantothenic acid Vitamin B1 Vitamin B2 Vitamin B6 Vitamin B12 Biotin H2 Vitamin C Antioxidant Zinc bacitracina a
12,000,000 IU 2,000,000 IU 120,000 mg 15,000 mg 3,000 mg 100,000 mg 50,000 mg 15,000 mg 20,000 mg 15,000 mg 30 mg 1,000 mg 1,000,000 mg 3,500 mg 80,000 mg
Not a vitamin, but added as a growth promotor.
Table 3.4. Vitamin and micromineral supplements used in breeding trials with American alligators; rate of inclusion not stated, probably per kg wet ration (Cardeilhac et al., 1991). Vitamin A Vitamin D3 Vitamin C Vitamin E Menadione Riboflavin Niacin Pantothenic acid Folic acid Vitamin B12 Biotin Pyridoxine Thiamin Copper Manganese Iron Selenium Iodine
220,000 IU 55,000 IU 300 mg 14,500 IU 300 mg 132 mg 700 mg 220 mg 18 mg 0.22 mg 3.5 mg 88 mg 44 mg 18 mg 1,320 mg 176 mg 6 mg 18 mg
Table 3.5. Vitamin supplement used in feeding trials with juvenile American alligators, inclusion per 1 kg of wet ration (Staton et al., 1992). Vitamin A, all-trans-retinyl acetate 18,000 IU Vitamin D, cholecalciferol 2,000 IU Vitamin E, all-rac--tocopheryl acetate 150 IU Menadione sodium bisulphite 25 mg Thiamin 15 mg Riboflavin 15 mg Pyridoxine 25 mg Vitamin B12 0.042 mg Niacin 200 mg Calcium pantothenate 50 mg Folic acid 4 mg Biotin 1 mg Choline 1,500 mg Inositol 50 mg p-Amino-benzoic acid 50 mg Vitamin C 450 mg
crocodiles, causing steatitis and fat necrosis (see p. 219). Mince that is kept frozen, and thawed out and refrozen repeatedly, becomes depleted of biotin, with the resulting deficiency causing nervous symptoms (see p. 217). All farm mortalities, and even other fresh meats, may contain large numbers of bacteria, including pathogenic ones. These can be
Important Aspects of Crocodile Farming
eliminated by heating the mince, which is then allowed to cool down before vitamin and mineral premixes are added and the mix is minced a second time (Huchzermeyer, 1991a). The resulting food is a loose crumble, which does not compact on the floor of the pen as easily as fresh mince and therefore can be consumed much better by the crocodiles. Carbohydrate can be added to such a cooked ration easily by cooking a stiff maize (corn) porridge (polenta) which is added in approximately equal proportion to the cooked mince and the other ingredients (see above) before mincing the ration a second time.
Pellets Provided the crocodiles are kept under controlled thermal conditions, within a narrow range of their preferred temperature, and are protected from disturbances and other stress (see p. 277), they will accept dry pellets as food and can be fed pellets exclusively from hatch to slaughter. Dry pellets have the advantage that they are very hygienic and can be picked up easily from the floor by the crocodiles, thereby minimizing wastage. In South Africa several crocodile farmers prepare their own pellets in different sizes depending on the size of the young crocodiles. Other crocodile farmers have turned to commercial trout pellets, also with acceptable results. In the formulation of such pellets one should probably be guided by the results of Staton et al. (1990b), although these authors were feeding their rations in the form of a thick paste, which led to serious wastage problems. Their best results were obtained at levels of 42.5–48.7% digestible protein and 4367–4421 kcal kg1 digestible energy, with the inclusion of 6.3–18.8% precooked (extruded) maize (corn) and 15.8–27.4% fat. Note that the inclusion of such amounts of fat into dry pellets would create serious technical problems. The same authors gave 8.2–10.9 : 1 kcal g1 protein as an optimal digestible energy to crude protein ratio.
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Influence of temperature on nutrient utilization In Caiman crocodilus the amplitude and frequency of gastric contractions increases with temperature, while complete emptying of a full stomach takes an average of 315 h at 15°C and 99 h at 30°C (Diefenbach, 1975b) (see also p. 36). In the same species, peptic activity in the stomach also increases with temperature between 15°C and 35°C (Diefenbach, 1975a). While American alligators kept at 32°C had greater feed intake and body mass gains, their feed efficiency ratio was poorer than that of alligators kept at 28°C. However, the digestibility of protein appeared not to be affected by temperature (Staton et al., 1992). At 25°C the digestion of lean meat by juvenile American alligators was found to be incomplete (Coulson and Coulson, 1986).
Effect of nutrients on reproductive performance Cardeilhac et al. (1991) studied the influence of various nutrients on the reproductive performance of American alligators. They divided reproductive performance into nest rate, clutch size, per cent banding and embryo survival, and analysed the effects of protein, fat, highly unsaturated fat, vitamins (see Table 3.5) and a growth promoter (‘Gatorcillin’ containing 200 mg virginiamycin and 800 mg oxytetracycline). Nest rate was influenced by protein consumption, followed by total feed intake and highly unsaturated fat, and slightly by vitamin and antibiotic supplementation. Clutch size was affected by total fat in the diet, followed by protein and total feed. Percent banding was strongly correlated with vitamins and antibiotics, followed by highly unsaturated fat, while total fat consumption had a negative effect. Embryo survival was strongly affected by the mother’s age, and the effect of nutrients was estimated to be in the following order: total fat, vitamins, antibiotics, highly unsaturated fat, protein, total feed.
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A high incidence of shell defects was caused by low calcium levels in the ration of the breeding females. The addition of extra calcium in subsequent seasons eliminated the incidence of these defects almost completely (Hibberd, 1996) (see p. 139). Note that the long-term use of antibiotics in the feed leads to bacterial resistance, and should therefore be avoided (see p. 91). It may also leave antibiotic residues in the meat, which may then not be allowed to be exported to certain countries (see p. 130).
84 mg kg1 and oxytetracycline 300 mg kg1 of the ration. The South African crocodile premix contains 80 mg zinc bacitracin per kg of final ration (see Table 3.3). Note that there is growing concern about the stimulation of bacterial resistance due to the widespread use of antibiotics in animal feeds (see p. 91). Importing countries increasingly demand meats and meat products to be free of growth stimulant, hormone and antibiotic residues.
Incubation of Crocodile Eggs Growth stimulants Nesting behaviour and physiology Various growth stimulants have been tried in the different species of crocodiles. The anabolic steroid Laurobolin was given at a dose of 1 mg kg1 of live mass to poorly performing Morelet’s crocodiles by intramuscular (im) injection. The effect lasted for approximately 21 days and there was a marked improvement in growth and mass gains (Leon Ojeda et al., 1998). Similar results were obtained in Caiman crocodilus yacare that were injected at fortnightly intervals subcutaneously (sc) with nandrolone phenpropionate (Pelosi et al., 1944). Kanui et al. (1993) treated juvenile Nile crocodiles with weekly im injections of 0.325 mg kg1 recombinant bovine growth hormone and found that this treatment stimulated appetite and growth. The authors recommend this treatment for poorly performing crocodiles kept under less than ideal conditions. The addition of taurine, an extract of ox heart, at 0.1% to the diet of American alligators resulted in greater fat digestibility and improved weight gains (Staton et al., 1992). However, the addition of 0.025 mg day1 of L-thyroxine to the diet did not affect the growth of juvenile C. crocodilus (Avendaño et al., 1992). Antibacterials are often used as growth stimulants. A combination of virginiamycin 200 mg and oxytetracycline 800 mg is supplied under the name of ‘Gatorcillin’ (Cardeilhac et al., 1991). Avendaño et al. (1992) used a combination of virginiamycin
Crocodilians either lay their eggs in holes in the sand or build nest mounds into which they lay their eggs. While it has been speculated that these two forms of nesting have evolved during the evolution of the crocodilians themselves (Greer, 1970), it is also possible that they represent adaptations to particular environments. The hole nesters usually nest in sand above the flood level on river banks, while the mound nesters often inhabit swamps or plains without access to higher ground. Mounds made from plant material may produce incubation heat by bacterial action, and this may be beneficial in a forest (swamp forest) environment where the nests cannot be exposed to direct sunlight. Different nesting substrates differ in their water content and in their resistance to gas diffusion. American crocodile eggs in sand nests were found to lose up to 15% of their initial mass due to evaporation during incubation, without apparent ill effects to the embryo (Lutz and Dunbar-Cooper, 1984). On the farm the nesting areas should all be on the same level to avoid competition for the higher nesting sites, and they should be separated by walls to allow the undisturbed use of adjacent nests (Fig. 3.1). The females continue guarding their nests even when the eggs have been lifted, and remain aggressive towards other females in the vicinity of the nest.
Important Aspects of Crocodile Farming
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Fig. 3.1. Nesting sites all on the same level and with separating walls in a Nile crocodile breeding pen in South Africa.
Physical parameters of the egg Crocodile eggs have an oblong ovoid shape and a hard shell. The shell consists of an outer densely calcified layer of vertically stacked calcite crystals, a honeycomb layer of horizontally stacked crystals, an organic layer containing a higher proportion of organic matrix to calcite crystals and a mammillary layer. The latter is more pronounced in the central opaque region of the shell and is attached to the shell membrane, which has numerous pores and is separated from the albumen by an amorphous limiting membrane (Ferguson, 1982) (see also p. 30). Embryonic development starts before the eggs are laid. Within 24 h after the egg has been laid, the embryo, which is floating at the top of the yolk, attaches its membranes to the top of the egg. By displacing the watery albumen towards the poles of the egg, it causes the shell to dry out somewhat, and this changes the optical properties of the shell and produces the visible opaque banding (Ferguson, 1982), the band increasing in size with the growth of the embryo (see Fig. 1.43). Consequently, a banded egg can be regarded as a fertile egg and the size of the banded area can be used to estimate the age of the embryo (Webb et al., 1987).
During incubation, the outer crystalline layer of the egg undergoes a degradation process, due to the acidic metabolic products of the nest bacteria which cause the formation of erosion craters. At the same time, calcite from the organic layer is mobilized for the calcium requirements of the growing embryo. Both the extrinsic and the intrinsic action weaken the shell, which facilitates hatching (Ferguson, 1981, 1982). However, one wonders whether this really is an evolutionary necessity, as most crocodile parents assist the hatchlings to emerge from the eggs. During the last third of incubation the oxygen uptake of Nile crocodile eggs at 32°C is 8.11 ml h1 (Aulie et al., 1989).
Egg collection and transport On farms the eggs should be collected as soon after laying as possible. This is often impossible if eggs are collected from the wild. Collection should be done early in the morning or late in the afternoon, not in the heat of the day, and care should be taken not to expose the eggs to direct sunlight, which would cause overheating and rapid death. Early in the morning the nesting
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areas are checked for signs of nightly activity to determine where eggs might have been laid. On some farms nightly egg-laying activity is recorded by an automatic video camera, which comes on every few hours during the night – together with floodlights – and does one circular sweep of the nesting areas. In the morning the tape is played back and the nests in which activity occurred are noted. During collection of the eggs, one person must stand guard to fend off the female, which might want to defend the nest. The sand is gently removed from the top of the nest until the uppermost eggs are exposed. The top of each egg then is marked with a cross with felt-tipped pen, crayon or pencil and each egg is transferred in its position to the transport box. Even though the embryo normally attaches itself to the uppermost point of the shell within 24 h after laying only, it is good practice to mark the position of farm-laid eggs as well, as occasionally embryonic development has already commenced before the eggs have been laid (see p. 30); it certainly has to be done with all eggs that have started banding.
The transport box is a styrofoam box of the same type as is used for incubation, with holes punched in the bottom as well as the lid (Fig. 3.2). If the eggs have to be transported over long distances, they should be cushioned by placing them on a layer of moist vermiculite. The collected eggs remain separated by clutch, one clutch per box.
The incubator room Crocodile eggs can be, and have been, incubated in boxes filled with sand or even in sand mounds. This may cause hygiene problems, particularly fungal infections. In the following, the most successful techniques used on crocodile farms will be described. The incubation complex should consist of a storage area for the egg boxes and the vermiculite, a cleaning and packing area, the incubator room itself and a hatching room. The incubator room should be of sufficient size to accommodate all the clutches and allow for future increase in production. It should be well insulated and allow the
Fig. 3.2. Nile crocodile eggs and a styrofoam box with holes punched into lid and bottom.
Important Aspects of Crocodile Farming
required temperature and humidity to be maintained throughout the incubation period. The most even distribution of heat is achieved by under-floor heating controlled by a thermostat. Humidity of 97–99% is achieved with the help of a humidifier assisted by a fan. Covering the floor with water to achieve the necessary level of humidity can cause hygiene problems and should be avoided. Inside this room the egg boxes are stacked on stainless-steel racks, with passages between the racks for easy access (Fig. 3.3). Wood is prone to fungal growth under conditions of high humidity and the use of stainless steel is therefore recommended for all structures within the incubator room. Ventilation of the incubator room is usually provided through the door, which is opened from time to time when the operator enters and leaves. This is sufficient as the eggs consume very little oxygen (see
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above) and as the air volume in the room is very large in relation to the total mass of eggs being incubated. When incubation facilities on a farm in South Africa were not completed in time, eggs were incubated successfully in the passage between rearing pens in a space-heated rearing house (Fig. 3.4). In the cleaning and packing area, the collected eggs are cleaned under running tapwater and dipped in a mild disinfectant solution (e.g. the South African product, F10®, Health and Hygiene (Pty) Ltd), before they are packed into the incubation boxes. This area also contains the control panel monitoring the temperature and humidity in the incubator room. The hatching room should also have thermostatically controlled heating, should have a sink and tap for washing the hatchlings and some basins into which the hatchlings can be placed before they are transferred to the rearing house (see p. 107).
Incubation temperature The incubation temperature not only determines the sex of a hatchling (see p. 32), but also its preferred body temperature later in life. Consequently, crocodiles that are to be reared or kept in a cooler environment should be incubated at a lower temperature. As the metabolic rate depends on the body temperature, a higher rearing temperature will ensure faster growth and will therefore require a higher incubation temperature. The length of the incubation period also depends on the incubation temperature. All these factors have to be taken into consideration when choosing the temperature at which the incubator is to function, anywhere between 29°C and 33°C. In the last third of the incubation period the metabolic heat produced by the growing embryo can raise the temperature within the box, and this may have to be monitored if the incubator room is running at a high temperature. Fig. 3.3. Egg boxes stacked on racks in an incubator room.
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Fig. 3.4. Incubation in the passage of a space-heated rearing house on a farm in South Africa. The enterprise had been moved to new premises and the incubation room had not been completed before the beginning of the laying season.
Humidity The humidity in the incubator room should be held just below saturation point, 97–99%. Excessive moisture is absorbed by the eggs and leads to them swelling and bursting (see p. 139). Excessive moisture in the incubation medium also interferes with gas permeability and can lead to the suffocation of embryos at a fairly late stage, when their oxygen demand is at its highest. The vermiculite in the boxes should be soaked in water and then squeezed out, so that it just compacts but does not drip.
Incubation on trays Incubation on trays requires a particularly well-controlled environment. In this method the eggs lie open on plastic egg trays on shelves in the incubator room. This allows easy access to the eggs and the removal of infertile (not banded) eggs, reducing the danger of rotting and contamination, and it also prevents overheating from the metabolic heat produced by the
embryo. However, the eggs are exposed directly to fluctuations of temperature and humidity.
Incubation in a medium Incubation in a medium copies the situation in nature, where the egg is buried in the nest. While sand and other materials have been used, vermiculite has been found to be superior, as it is practically sterile on delivery and is capable of holding a large amount of moisture. However, experience has taught crocodile farmers not to re-use vermiculite, as it is difficult to sterilize or disinfect after it has been used. A layer of 2–3 cm moistened vermiculite is spread on the bottom of the incubation box. The eggs are stacked in a pyramid on top of this layer and then more vermiculite is added until the eggs are covered by a layer 1–2 cm thick. In a different method, the eggs are stacked on the moistened vermiculite, but no further vermiculite is added, leaving the eggs open to inspection once the lid of the box is lifted.
Important Aspects of Crocodile Farming
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Hatching
Hatchery hygiene
When the calculated hatching date approaches, the nest boxes are opened gently one by one. If the crocodiles in the eggs are ready to hatch they begin croaking, calling their mother. The boxes containing these eggs are taken to the hatching room, where the eggs are uncovered and those hatchlings that have hatched by themselves are taken out. The remaining eggs are examined and any further live hatchlings are assisted out of the shell. As they are taken from the box, the hatchlings are placed in a basin or bucket with clean warm water containing a mild disinfectant (F10®, Health and Hygiene (Pty) Ltd) for a first wash. They are then transferred to a nursery basin in which they remain for 1 or 2 days until their navels have closed completely, after which they are transferred to the rearing pens. The nursery basins should have sloping floors, allowing the hatchlings to come out of the water. They should also be partially covered to give the hatchlings the feeling of protection, as they do not realize that they are indoors and protected from predators (Fig. 3.5). These basins can be glass aquaria or plastic or metal basins. Some farms have a small nursery enclosure instead. However, from the point of view of cleaning and observation of individual hatchlings, smaller basins, one per clutch, are preferable. The water in the nursery basins should contain a mild disinfectant, such as a quaternary ammonium or F10® (Health and Hygiene (Pty) Ltd).
Before the start of the incubation season, the incubator room is cleaned thoroughly and disinfected, and the heating and humidifying equipment is checked. The incubation boxes are washed, disinfected and left in the sun to be dried and irradiated. The supply of vermiculite is also checked. The boxes used for the collection of the eggs from the nests are kept separately. They are re-used for the same purpose but never enter the incubator room. On arrival at the packing room, the eggs are rinsed under the tap in running water and may be immersed in a mild disinfectant solution (F10®, Health and Hygiene (Pty) Ltd), before they are stacked in the box. For the day’s clutches the vermiculite is soaked in clean water. Before placing it into the box the water is squeezed out that it no longer drips from the material held in the hand. As soon as the eggs have been packed in the box it is placed on the shelf in the incubator room. People working in the cleaning and packing room, the incubator room and the hatching room should wear clean gumboots and clean overalls. Visitors should not be allowed into the incubator room during the incubation season.
Rearing Farming conditions are a compromise between the perceived requirements of the farmed animals and economically feasible
Fig. 3.5. Nursery basin with sloping floor and partial cover.
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Chapter 3
solutions. Constraints are not only economic – our understanding of the requirements of crocodiles is still very limited. While domesticated species have been selected and bred to adapt to certain given conditions, animals taken from the wild are much less adaptable. The closer one can cater for the actual needs of the crocodiles, the more likely it is that the farming enterprise will be successful. Hatchlings and juvenile crocodiles not only need food, water and space, they have very strict hygiene and other needs and a range of behavioural requirements. Not meeting these needs causes stress, and stress often causes disease and death (see pp. 46 and 278).
Rearing outside Outdoor rearing is practised in tropical countries, often in the proximity of wild crocodile populations. The crocodiles are kept in relatively small concrete-lined pens with equal water and land areas and partially shaded. The water is usually 15–20 cm deep, and there are sloping sides to allow the
crocodiles to climb out of the water. Additional heating may be provided via hot water pipes which run submerged through the water areas of the pens (Fig. 3.6). While such a system is relatively cheap to build, it has several serious weaknesses. Although the additional heating may prevent cooling of the water during cool nights, there is no protection against overheating. When air (shade) temperatures climb above 36°C, and the sun shining on to the shallow water heats it up to a similar temperature while heating the concrete floor of the pen even more – the crocodiles have no way to escape overheating. Smaller crocodiles are more likely to suffer than larger ones, as their smaller mass heats up more quickly. This overheating is a very serious source of stress (see p. 278). The lack of temperature control also depresses the appetite to the point that crocodiles reared outdoors generally do not accept dry compound feeds (pellets). Hatchlings are instinctively afraid of any movement overhead, such as birds or even the shadow of a passing person. While these frequent disturbances could be prevented by the provision of hide boards, this is often not
Fig. 3.6. Partially shaded outdoor crocodile rearing pen with hot water pipes for additional heating on a farm in Zimbabwe.
Important Aspects of Crocodile Farming
done, exposing the hatchlings to a constant succession of stressful events. On such farms the alarm calls of the hatchlings can be heard frequently, indicating the degree of stress suffered by the animals. Further problems encountered in outdoor rearing are flies and rats attracted by leftover feed, as well as escapees, as young crocodiles are very good at climbing over separating walls and fences (Fig. 3.7). If outdoor rearing is to be attempted during the colder months, some protection against excessive cold or temperature fluctuations may have to be provided. Possible measures include: ● deeper water (>1 m), which will not cool down as rapidl
