Arctic Charr Aquaculture

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Arctic Charr Aquaculture Gavin Johnston Northern Biomes Ltd British Columbia, Canada

Arctic Charr Aquaculture Gavin Johnston Northern Biomes Ltd British Columbia, Canada

© 2002 William Gavin Johnston

First published 2002

Fishing News Books, a division of Blackwell Publishing Editorial Ofﬁces: Osney Mead, Oxford OX2 0EL, UK Tel: +44 (0)1865 206206 Blackwell Science, Inc., 350 Main Street, Malden, MA 02148 5018, USA Tel: +1 781 388 8250 Iowa State Press, a Blackwell Publishing Company, 2121 State Avenue, Ames, Iowa 50014–8300, USA Tel: +1 515 292 0140 Blackwell Science Asia Pty, 54 University Street, Carlton, Victoria 3053, Australia Tel: +61 (0)3 9347 0300 Blackwell Wissenschafts Verlag, Kurfürstendamm 57, 10707 Berlin, Germany Tel: +49 (0)30 32 79 060

Library of Congress Cataloging-in-Publication Data is available

The right of the Author to be identiﬁed as the Author of this Work has been asserted in accordance with the Copyright, Designs and Patents Act 1988. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, except as permitted by the UK Copyright, Designs and Patents Act 1988, without the prior permission of the publisher.

ISBN 0-85238-272-3 A catalogue record for this title is available from the British Library Set in 10/13 pt Times by Sparks Computer Solutions Ltd, Oxford http://www.sparks.co.uk Printed and bound in Great Britain by MPG Books Ltd, Bodmin, Cornwall For further information on Blackwell Science, visit our website: www.blackwell-science.com

For my father, Pat Johnston, who believed it was possible, and to C.G., wherever she may be.

Contents

Foreword by Dr Lionel Johnson Preface Acknowledgments

xi xiii xiv

Section I The Basic Requirements for Culture 1 An Introduction to Arctic Charr Use of Arctic charr by indigenous peoples Commercial exploitation The Canadian Arctic ﬁshery The Labrador ﬁshery Greenland, Ireland, Great Britain, and European ﬁsheries Development of Arctic charr aquaculture Production levels of cultured Arctic charr

1 3 4 6 6 7 9 10 13

2 Wild Arctic Charr: Basic Attributes Important to Culture Geographic distribution Taxonomy Morphology: the outward appearance Arctic charr forms and morphs Anadromous form Resident form Morphs Growth, size, and age at maturity Matters of fecundity Behavior: aggression, shoaling, and inter-species competition Food habits

16 16 17 19 21 21 24 25 27 31 33 35

3 The Rearing Environment: Chemical, Physical and Biological Water: the environment of Arctic charr Incoming source water Rearing water Outﬂow water Chemical parameters of water quality

37 37 38 39 40 41

vi

Contents

Oxygen Fish activity and oxygen consumption Food intake and oxygen consumption Water temperature and daily patterns of oxygen consumption Fish size and oxygen consumption Carbon dioxide Total gas pressure and gas supersaturation pH Ammonia-N Effect of pH and temperature on ammonia toxicity Safe levels of ammonia Nitrite and nitrate Salinity, seawater tolerance, and smoltiﬁcation Alkalinity and hardness Suspended solids Physical parameters of water quality Temperature Recommended temperatures Light Rearing densities Biological aspects: stress and disease-causing organisms Infectious disease and pathogens Infectious pancreatic necrosis virus (IPNV) Infectious hematopoietic necrosis virus (IHNV) Viral hemorrhagic septicemia virus (VHSV) Furunculosis Bacterial kidney disease (BKD) Vibriosis Saprolegniasis Proliferative kidney disease (PKD) Metazoan parasites – tapeworms and roundworms Gyrodactylid monogenean parasites – ﬂukes Sea lice Other non-infectious disease agents Toxicity of chemical compounds and construction materials Swim bladder stress syndrome (SBSS) Summary 4 Growth, Nutrition and Feeding Growth in Arctic charr Measuring growth performance Growth rate (R) Condition factor Food conversion ratio (FCR) Factors affecting patterns and rates of growth

41 43 43 46 48 48 49 49 50 51 51 53 53 55 56 56 56 57 58 59 60 63 64 65 65 65 66 67 68 68 69 70 70 71 71 71 72 74 74 75 75 78 79 81

Contents

Water temperature and its effect on growth Body size and growth Size variation, dominance, and growth Seasonal and daily rhythms in growth The effect of sexual maturation on growth and market size Compensatory growth Nutritional requirements Protein requirements Essential amino acids Lipids and essential fatty acids Lipid as an energy source Essential fatty acids Dietary carbohydrate Vitamin requirements Minerals and other trace elements Carotenoid pigments Levels of pigment required Prepared diets and manufactured feeds Investigations of Arctic charr diets The ideal Arctic charr diet Manufactured feeds for Arctic charr Feeding Arctic charr Setting daily ration levels Feed sizes Feeding strategies Satiation, restricted, or compensatory feeding Optimum feeding times Spatial distribution and feeding frequency Feed delivery methods Feed monitoring Section II Husbandry 5 The Standard Arctic Charr The attributes for culture Attributes of existing strains used for commercial culture The Norwegian Hammerfest and Svalbard strains The Swedish Hornavan strain The Icelandic Grenlækur and Ölvesvatn strains The Canadian Fraser strain The Canadian Nauyuk strain Potential for improving attributes of existing strains Heritability of growth-related traits Heritability of other traits Breeding strategies for improving commercial stocks The standard Arctic charr

vii

81 82 83 84 88 91 92 92 93 94 94 95 97 97 99 99 102 103 104 106 107 108 109 110 111 111 114 114 115 117 119 123 123 125 125 126 126 127 127 128 130 131 132 133

viii

Contents

6 Brood Operations: Keeping Brood, Egg Collection, and Incubation Spawning The spawning window Ovulation and spermatogenesis Methods for sexing and assessing ripeness Sorting brood ﬁsh prior to spawning Careful handling of spawning ﬁsh Egg collection Management and organization of the egg-take Preparation of equipment for egg-take and incubation Anesthetizing Arctic charr brood Techniques for taking eggs The dry fertilization method of egg taking Removing eggs Removing milt Fertilizing eggs Loading incubation trays After spawning Egg incubation Effect of temperature on embryo development and mortality Husbandry techniques in the egg room Monitoring egg development and inventory control Monitoring and controlling fungal growth Egg shocking and picking techniques Hatching Methods for receiving and transporting eyed ova

136 139 139 140 141 142 144 145 146 148 149 151 151 151 153 154 154 156 156 158 159 159 160 160 161 162

7 Raising Alevin, Fry, and Fingerlings From larval alevin to free-swimming fry Preparing the ponding environment Moving alevins to ponding tanks First-feeding techniques Types and sizes of starter diets Methods for delivering starter diets Ponding tank maintenance: good health or mortality Into larger tanks: rearing ﬁngerlings Light levels and photoperiod control Feeding ﬁngerling Arctic charr Size-grading, sorting, and splitting Arctic charr lots Grading techniques From the hatchery to grow-out facilities

164 164 167 170 170 171 172 173 174 175 176 178 179 181

Section III The Business of Production 8 Production of Arctic Charr for the Consumer Different production strategies for on-growing

185 187 187

Contents

Holding structures Stocking density for growing Arctic charr in lakes Stocking density when growing Arctic charr in tanks Production cycles Light manipulation and growth Feeding strategies Ration size Feed delivery Diet Sorting and other ﬁsh husbandry practices Harvesting and processing Harvesting Pre-harvest preparation Harvesting methods Reaching sexual maturity before harvest Processing 9 Marketing and Market Economics Marketing Arctic charr Quality in Arctic charr products Product forms best suited for Arctic charr Price of Arctic charr products Marketing strategies Distribution channels Market economics of raising Arctic charr Capital costs Fixed operating costs Variable operating costs Proﬁtability and contribution margin Harvest size and proﬁtability Market price and proﬁtability Other variables 10 Managing Culture Facilities Business management of commercial culture facilities Operations management Environmental monitoring Fish health management Water-quality monitoring Managing downstream water Importance of good mechanical systems management Emergency preparedness: alarms and back-up systems Production management The operations manual A ﬁnal word

ix

188 189 190 192 198 198 199 200 201 202 205 205 206 207 208 209 210 210 211 212 214 215 216 219 219 220 220 222 224 224 226 227 227 230 230 231 233 234 237 239 241 243 244

x

Contents

Appendix: Protozoan and Metazoan Parasites of Wild and Cultured Arctic Charr

245

Bibliography Index

249 265

Foreword

Nauyuk Lake was selected in the early 1970s as a suitable location for the establishment of a research station devoted to the study of Arctic charr, certainly one of the most important native species for the inhabitants of Arctic Canada. Nauyuk Lake is situated at the southern tip of the Kent Peninsula in the central Arctic, approximately 150 kilometres from Cambridge Bay, Nunavut, Canada. The surrounding land is of great natural beauty with majestic cliffs along the western and southern shorelines. It is connected to the Arctic Ocean by a short river, some 150 metres long, that cuts between cliffs which turn red in the low August sun when the charr are returning from their summer in the sea. Nauyuk is Inukituk for ‘sea gull’ and the lake is so called because of a colony of Thayer’s gulls which nest on the cliffs overlooking the lake. Close to the mouth of the river, there is a small summer encampment of Inuit composed, at the time we were there, of Peter and Doris Aglegoetok, Charley and Mona Kioyok, their children and their dogs. Charley Kioyok was a great help in those early days in showing us poor Kabluna where the spawning grounds were and how the pre-spawning charr passed up through a small stream to a tributary lake, Willow Lake, where they spent the summer before spawning and then the winter afterwards. As soon as the ice goes out, seaward migration out of Nauyuk Lake begins, with the largest charr invariably leading the way. At Nauyuk Lake, these ﬁsh are almost entirely non-spawners going to the sea to feed on the brieﬂy abundant small ﬁsh and crustaceans. At the same time the spawners move up Willow Creek into Willow Lake and the spawners of the previous year, now in a weakened condition having spent 22 months in fresh water without feeding, move down Willow Creek, across Nauyuk Lake and so to the sea. After ﬁve to six weeks in the sea they return to Nauyuk Lake, having made a particularly good recovery from their post-spawning emaciation. All the returning charr spend the winter in Nauyuk Lake for they are prevented from entering the lake by the very low stream ﬂow at this time of the year. That Nauyuk Arctic charr would become the best strain for commercial culture came about by chance. We decided to collect some eggs of the anadromous and resident forms, and their respective crosses, for investigation in the laboratory of the Freshwater Institute in Winnipeg. It was hoped that laboratory studies would help to elucidate the breeding pattern and determine whether the two forms were independent populations, although this seemed unlikely as both stocks intermingle on the spawning grounds and ripen at the same time. In 1978, after the summer crew had left at the end of August, Andy Dwilow, a ﬁsh health specialist, and I stayed on in an attempt to collect fertilized eggs. Nauyuk Lake Arctic charr

xii

Foreword

spawn in mid-September as the ice cover is forming but before it is thick enough to bear the weight of a man. This means cold air temperatures and rapid freezing of wet gloves and garments. It was cold work. A trap net was established on the spawning grounds prior to ice formation and monitored daily from the ﬁrst of September. For the ﬁrst few days there was little sign of ripe ﬁsh, but by the end of the ﬁrst week we began to collect ﬁsh showing signs of ripening although not quite ready for egg removal. We decided to collect some of both the anadromous and resident charr and hold them in a pen until they were ripe and running. Two anadromous males and two females, each between three and four kilograms in weight, were caught after considerable effort and transferred to a small ﬂoating pen, and similarly with several resident ﬁsh. There they stayed for two days without reaching the ‘running’ condition. Then things began to happen rapidly. The following morning on reaching the pen we found the ﬂoor covered with eggs and the ﬁrst thought was that we were too late. The next blow was that when the cage was opened one of the large males won out on a wrestling match as he was being removed and immediately headed back to the preferred delights of his natural spawning grounds. This left us with one anadromous male and two females as well as three or four residents. From this point on things took a turn for the better and, within the meagre protection of a small tent, we managed to proceed with stripping the remaining eggs and carrying out the planned crossing program. It was somewhat disappointing to have collected such a small number of specimens but at least we had succeeded to some extent. The next problem was to transport this precious cargo 1500 miles south without killing them through overheating or asphyxiation. This involved three ﬂights and at least one night in a hotel, apart from the possibility of being stranded at Nauyuk Lake due to bad weather while waiting for the charter aircraft to arrive to take us home. However, all went well and we reached the Freshwater Institute without further mishap. The eggs were immediately placed in incubators and carefully nursed until they hatched the following spring. These alevins ultimately became the founding fathers and mothers of the Nauyuk Lake Arctic charr aquaculture stock. Dr Lionel Johnson

Preface

This book is divided into three sections, with each section containing a number of chapters arranged around common themes in Arctic charr aquaculture. In the ﬁrst section, Arctic charr interactions with humans and the charr’s biological requirements for culture are reviewed. Chapter 1, the overview, introduces Arctic charr and describes the species’ history of interaction with humans and reviews the development of Arctic charr aquaculture over the last hundred years. Chapter 2 reviews the biology and ecology of wild Arctic charr, which is important in setting the stage for growing Arctic charr under culture conditions. Chapter 3 reviews the chemical, physical and biological requirements for rearing Arctic charr and Chapter 4 details various aspects of growth, nutrition, and feeding requirements of Arctic charr. The middle section is a practical guide to the art and science of early-rearing Arctic charr, a hands-on application of current knowledge in Arctic charr aquaculture. Chapter 5 reviews the current strains of Arctic charr used for culture and suggests various improvements that can be made for developing a better charr for aquaculture. Based on a synthesis of current knowledge and my own experience, I have outlined the most successful ways of raising Arctic charr through to grow-out in Chapters 6 and 7. One common theme agreed upon by people with experience in early-rearing Arctic charr is that charr are different than salmon and trout, requiring different culture techniques. The last section focusses on the commercial production of Arctic charr, beginning with the grow-out phase. This phase is the point where rearing skills for live ﬁsh are combined with the business and marketing skills needed to bring high-quality Arctic charr products to the consumer. Chapter 8 discusses aspects of on-growing Arctic charr and methods for processing them into ﬁsh products – the great live ﬁsh/dead ﬁsh divide. In Chapter 9, marketing and economic issues of importance to Arctic charr production and marketing are discussed. The ﬁnal chapter is devoted to the skills needed to manage the various technical systems that keep a commercial operation proﬁtable.

Acknowledgments

Many people helped in the research and preparation of this book, with some help extending back ﬁfteen years to the beginning. I thank them all, though they are too numerous to mention them all by name. I am especially indebted to David Petkovich, one of the pioneers of commercial Arctic charr culture, for the hundreds of hours of discussion and hard work over the years in developing ideas and methods for growing Arctic charr. Thanks to Eric Allen, Ethan Allen, Susan Thompson, and Kevin Neufeld for sharing their ideas and experiences growing Arctic charr in the Yukon; Keith Alexander for sharing his thoughts about processing and marketing wild and farmed Arctic charr; Phil Millerd for discussing and modeling many of the cost factors related to production of Arctic charr, and for the many evenings spent discussing the ethical issues of rearing salmonids in tanks and net-pens. Northern Biomes Ltd supplied ﬁnancial support and technical assistance throughout the production of the book and Arctic Ova allowed me access to their brood stock facility and databases. I would like to thank many people within the academic and commercial research community who shared their knowledge and sent me technical papers and data on many different aspects of Arctic charr biology and culture. In particular, I thank: Dr Jim Reist, Dr Rich Moccia, Dr J.F. Leatherland, Dr Jim Johnson, Dr Willie Davidson, Dr Julie Bebak, Dr George Iwama, Greg Deacon, and Joey Johansen; Dr Jean Brouard and Dr Sally Johns for clarifying issues of genetics and heritability; Dr Neil Bass for supplying information on growing Arctic charr in Ireland; Sally Goldes and Dorithee Kaiser for sharing information on ﬁsh health issues and on virus transmission in salmonid eggs; Kerry Finley for the photograph used on page 5, the information on wild Arctic charr habitat use, and for introducing me, many years ago, to the traditional use of Irkalukvik by the Innuit in the Canadian Arctic; Gary Chapman for his tour of a high-tech recirculation facility and for numerous discussions about growing Arctic charr in lake cages; Gary Wilton, Roddie Milton, Kevin Jarrett, and Mark Pemberton for allowing me to tour their respective Arctic charr facilities; Bernie and Hans Lehman for telling me about their experience growing charr and trout; David Fletcher for the history of Arctic charr use in Wales; Dr Eunice Lam for the slimy thumb story and what makes a good hatchery worker. My appreciation to Jennifer Peterson for long hours of literature searches, reviewing technical papers, and preparing tables and ﬁgures; Shannon Gregg for literature reviews and ﬁgure preparation; Audrey McClellan for careful editing of manuscript drafts and removing the jargon; Donald Gunn for his many ﬁne drawings and his artistic interpretation of many of the technical concepts of charr culture; Charlie Wood for formatting and preparing tables and

Acknowledgments

xv

ﬁgures into their ﬁnal form; John Lammers and Cate McEwen for reviewing the manuscript and offering encouragement and support throughout the process of researching and writing. A special thank you to Jennifer Winter, for editing many drafts of the book, for preparing the bibliography, ﬁgures, and tables, obtaining permissions, and for bringing all the elements together into a coherent, ﬁnal manuscript. I would also like to thank Nigel Balmforth and Josie Severn, my editors at Blackwell, and Heather Addison and Deirdre Prinsen for seeing the book through the copy-editing and layout processes to ﬁnal completion. Deboragh Gainer created and painted the building mural for Arctic Ova which is used on the cover of the book. My greatest thank you to my family: Seanna, Liam, and Cate for their support and understanding during the long writing process. Gavin Johnston 220 Holmes Road Salt Spring Island BC Canada V8K 1T6 Email: [email protected]

Section I

The Basic Requirements for Culture

Chapter 1

An Introduction to Arctic Charr

Irkalukvik, l’omble chevalier, Salvelinus alpinus, Røye, Bleikja, by whatever name we know it, the Arctic charr lives under extreme circumstance, pushed up against the cold waters of the northern ice edge. Wild Arctic charr occur in the circumpolar regions of Canada’s High Arctic, along the coastline of Greenland, Iceland, northern Scandinavia, Russia, and around the many small islands dotting the rim of the Arctic seas. They are creatures of light and dark, short bright summers and long black winters. An enigma, they live at extreme temperatures but have no special physiological adaptations for cold. At low density they are aggressive with one another, but when crowded are extremely docile. Unlike most other salmonids, they are long-lived, repeat spawners with many populations spawning only every second or third year. Arctic charr cannot survive the winter in sea water. They are anadromous only in the sense that some populations move between fresh water and sea water – going to sea during the short Arctic summer, feasting on marine resources of a diverse nature, then returning to a long winter famine in freshwater lakes or rivers. Arctic charr and humans have a long association that reaches back into glacial times. Throughout the Canadian Arctic, wherever there are rivers that run with anadromous charr, there are signs of ﬁshing. Saputits (stone weirs to trap ﬁsh), built by the Inuit, are evident across the shallows, and old stone caches remain along the banks. Before the advent of mechanized travel, Arctic charr were an important food source for sled dogs and, during certain times of year, the primary source of food for the people of that region. Indigenous people scattered about the polar regions consumed Arctic charr fresh, dried, shaved in thin frozen slices, boiled, or smoked almost stiff. In the seventeenth and eighteenth centuries, Arctic charr sold fresh or preserved from Windermere, England, was considered a status symbol. A processed product known as Windermere charr, consisting of cooked Arctic charr and spices laid in a pastry casing sealed with butter, was shipped to London as a delicacy. Visitors to Windermere purchased potted Windermere charr, which was sold in small pots decorated with painted pictures of charr as novelty gifts (Kipling 1984). Today, Arctic charr is still served to royalty and heads of state, and to friends when they visit Canada. They are tasty ﬁsh with a delicate salmon ﬂavour, high in fat and of ﬁrm texture amenable to many forms of preparation. In Canada, Arctic charr represents the Arctic Ocean just as sockeye salmon (Oncorhynchus nerka) stands for the West Coast and lobster (Homarus americanus) for the cold Atlantic. Arctic charr has taken the place of Atlantic salmon

4

Arctic Charr Aquaculture

(Salmo salar) as the rare salmonid of excellent ﬂavour, ﬁt for consumption as lox, sushi, fresh ﬁllets, or steaks. Even today, throughout the circumpolar regions, Arctic charr is an important food resource for indigenous people who live close to the land. My ﬁrst contact with Arctic charr was at a camp of Inuit in the High Arctic islands of Canada. Guided by a man called Idlout, a small group of Inuit from Resolute Bay had returned to the land to live in a traditional way along the shores of Creswell Bay near the mouth of the Union River. I ﬂew in to visit a biologist friend in mid-August, when darkness was beginning to return and the fat sea-run charr, Irkalukvik, was returning upriver to the lake. With the charr migrating, the camp was full of excitement. I saw split Arctic charr, dull red in color, hung to dry on racks, and a stone cache full of fresh ﬁsh, just harvested with leisters (ﬁshing spears) near a point where the Union River narrowed to a few meters. Everywhere about the bay and river mouth were signs of long use: rock caches, whalebone skulls and ribs, and tent rings of stone. The people living a traditional life in a tiny oasis of rich resources surrounded by bleak tundra and sea ice gave me a sense of wonder at how short the distance was between subsistence living and the Twin Otter aircraft parked a few hundred feet away. Even in aquaculture, Arctic charr remain ﬁrmly connected to their wild brethren. Though this book moves a long way from that wilderness world, this theme of wildness is never far away.

Use of Arctic charr by indigenous peoples Over the past 5000 to 6000 years, the relation of humans to Arctic charr has been constant and predatory, ranging from relatively benign subsistence use of local charr populations by small indigenous groups to heavy commercial harvest for export to European cities. The use of anadromous Arctic charr by the Arviligjuarmiut Inuit of the Canadian central Arctic exempliﬁes the importance of this ﬁsh in the annual subsistence cycle of living off the land. The Arviligjuarmiut traditionally survived by ﬁshing, hunting caribou, and sealing in a yearly cycle that revolved around the presence or absence of sea ice. During the short openwater summer period, they hunted and ﬁshed charr from land-based camps, while in the winter they moved onto the sea ice to hunt seals. Harvested at traditional river sites and along the coastline during the open-water season, anadromous Arctic charr may have represented more than half of their total yearly food supply (Balikci 1980). After a long winter of eating seal and not much else, everyone in camp anticipated the ﬁrst harvests of Arctic charr, which coincided with the return of open water, ﬂowing rivers, and sunshine. This was the beginning of the summer season, and charr were a predictable and dependable resource in a land offering little at this time of year. They could be harvested in the river as they migrated to the sea from lakes where they had overwintered. Fishermen used harpoons or leisters. Harvesting also continued into the river estuaries and tidal ﬂats, where hunters stood on nearshore rocks, spearing individual ﬁsh from schools of feeding charr. Fishing with the harpoon and leister required a great deal of skill and provided only enough food for daily needs. It was not until August, when summer was ending and Arctic charr migrated in large numbers on their return to the lakes and could be trapped and harvested with leisters in the saputits, that enough were caught to allow the Arviligjuarmiut to preserve ﬁsh for future use.

An Introduction to Arctic Charr

5

Fig. 1.1 A traditional leister used for capturing Arctic charr.

The three-pronged leister, shown in Fig. 1.1, was specially designed for capturing Arctic charr, and its working end is the ultimate tool for capturing such a strong-bodied, fast-moving ﬁsh. It consists of a central sharp bone point that impales the charr between two small sharp hooks of polar-bear bone mounted on prongs of musk ox horn that kept the ﬁsh from wriggling free. The saputits were barriers of stone built across rivers to block the upstream migration of returning Arctic charr. They consisted of long rock-and-boulder walls, pointed upriver in funnel fashion, that guided ﬁsh into a watery corral for easy spearing (see Fig. 1.2). By all accounts, ﬁshing at the saputits was the highlight of the year for the Arviligjuarmiut, and it involved everyone in some form or another. When a sufﬁcient number of migrating charr entered the circular trap, upon a signal everyone charged to the saputit and the best of the hunters speared ﬁsh with great excitement while women and children offered vocal encouragement. As each hunter speared a ﬁsh, he rapidly removed it from the leister and skewered it behind the gills with a sharp bone needle attached to a line of sealskin. The ﬁshing could last from a few minutes to over half an hour, a long time considering the water temperature was only a few degrees above zero. When the ﬁshing was ﬁnished, the men hauled their catch to the shore, where the ﬁsh were processed by the women. Some was consumed fresh or sometimes boiled. If the weather was dry, a portion of the catch, carefully gutted and split by the women, was spread on rocks or hung over lines for air-drying into pipsi. Quantities of pipsi were carefully packed into large stone cairns or caches built of rock, which held several hundred kilograms for use during the winter. Once the migration runs of charr were ﬁnished near the end of August, the people moved from the ﬁsh camps and turned their energies to fall caribou hunting. After freeze-up, which in the Pelly Bay region occurs in late September, the Arviligjuarmiut were in transition from summer hunting and ﬁshing to winter sealing. The sea ice had not yet

6

Arctic Charr Aquaculture

Fig. 1.2 Fishing Arctic charr at the saputit.

formed, but the lakes and rivers were solid in new ice, and the people relied on cached ﬁsh, caribou, and fresh Arctic charr. At this time, Arctic charr ﬁshing took place through small holes chipped in the newly formed river or lake ice. A lure, carved of white bone in the shape of a ﬁsh, was jigged in the water, and as charr approached to investigate, they were speared with the leister. Fishing charr through the ice remained practical until the ice grew too thick to see ﬁsh at the lure or until the ﬁsh moved themselves to deeper waters. By late November the sea ice formed and the camp moved onto the ice to hunt seals. Moving to the sealing grounds was in large part determined by the richness of the Arctic charr ﬁshing; if cached supplies were good, then the move to the sealing grounds might be delayed until February.

Commercial exploitation The Canadian Arctic ﬁshery The traditional life of the Arviligjuarmiut and their subsistence use of Arctic charr did not

An Introduction to Arctic Charr

7

long survive the arrival of Europeans in the Canadian central Arctic. Near the beginning of the last century the inﬂux of whalers, traders, missionaries, and the Royal Canadian Mounted Police (RCMP) gradually moved the people off the land and into relatively ﬁxed settlements in a pattern that was familiar from the Yukon to Labrador. With the introduction of gill-nets, Arctic charr were easily harvested in large numbers year-round in the open waters along the coast and under the lake ice during the winter. Hudson’s Bay Company traders, priests, and the RCMP accepted large quantities of Arctic charr for dog food in trade for ammunition, guns, and other trade goods the Inuit needed. In some locations, such as Coppermine River, this led to a shortage of Arctic charr, which forced the entire community of RCMP, Hudson’s Bay traders, and Inuit to relocate (Moshenko et al. 1984). Commercial export of Arctic charr from the Canadian Arctic began in earnest during the late 1940s, when the Shaw Steamship Company apparently harvested large amounts of ﬁsh from Frobisher Bay using gill-nets, with a portion of the catch salted and some canned for export. This ﬁshery did not exhaust the stocks as it only lasted a few years, but a commercial ﬁshery restarted in the late 1950s reduced stocks to the point where commercial ﬁshing was no longer feasible by 1966 (Kristofferson & Sopuck 1983). On the shores of Hudson Bay, a canning and smoking venture operated for a few years from Rankin Inlet but turned out to be unproﬁtable for a variety of reasons, mostly related to the difﬁculty of carrying out industrial food production in communities serviced only by small aircraft (Iredale 1984). The largest commercial harvest of Arctic charr, which continues to the present, occurs at Cambridge Bay, where net harvests from a number of rivers are processed and frozen in a commercial plant and shipped south by aircraft. The harvest varies from about 30 to 50 tonnes a year and requires tight management to prevent overharvest (Kristofferson et al. 1984). The ﬁshing industry in these areas came about, in part, due to the government’s attempt to create employment opportunities for local people now living modern, industrial lives. There was an abundance of Arctic charr and the ﬁsh had tremendous market appeal, so a commercial harvest seemed a proﬁtable venture. Unfortunately, the government did not take into account the detrimental effects unmonitored commercial exploitation has on Arctic charr. Hence it has been difﬁcult to sustain this venture in the Canadian High Arctic.

The Labrador ﬁshery This same pattern of subsistence harvest replaced by the commercial exploitation of anadromous Arctic charr occurred in Labrador as well, but commenced at a much earlier date. In 1771 the Moravian Church was given exclusive rights to convert the Labrador Inuit to Christianity and exploit the natural resources of the coastal area, a right maintained until the beginnings of the Great War. Moravians introduced gill-nets to the traditional method of Inuit ﬁshing, which expanded the Arctic charr ﬁshery to the open-water season and gave ﬁshermen a greater advantage in the rivers during Arctic charr migration. The Moravians purchased large quantities of dried Arctic charr from the Inuit and used it later to encourage conversion by offering it to Inuit who came to church and reselling it to the Inuit during food shortages of late winter. In 1860 the Moravians pickled two barrels of Arctic charr and salmon in heavy brine and shipped them to England, where they were received with enthusiasm. The venture was proﬁtable enough for the Moravians to purchase a schooner to collect pickled Arctic charr

8

Arctic Charr Aquaculture

from various ﬁsh camps along the coast and establish markets in Newfoundland, Boston, and England (Ledrew 1984). Although the Moravians had somewhat changed the Inuit system of ﬁshing with the introduction of trade, new technology, and their involvement in the harvesting of Arctic charr, they did not take over Arctic charr harvest in a way that excluded the Inuit, as up until the turn of the century much of the charr harvest was carried out by Inuit labour and resources. However, this changed when settlers came to the Labrador region with the cod ﬂeet and were forced by the Moravians to settle elsewhere. Many of the settlers inhabited areas bordering rivers that were abundant sources of Arctic charr and, in turn, excluded Inuit from these sites, eventually coming to dominate the Arctic charr ﬁshery. In some years the increased trade in pickled Arctic charr amounted to over 150 tonnes. This continued until the late 1960s, with annual harvested volumes changing dramatically in response to market prices for salted ﬁsh, the price of fur, and during the two World Wars. When the price of fur declined, the Arctic charr ﬁshery resumed; when the price of cod shot up, the charr ﬁshery declined (Ledrew 1984). In the late 1960s the Labrador Arctic charr ﬁshery slowly shifted to fresh-frozen and smoked sales into Canadian cities, notably Montreal, Halifax, and Winnipeg, the Canadian cities that still know Arctic charr well. Much as it did with the High Arctic ﬁshery, government assistance helped establish an infrastructure for the Labrador charr ﬁshery in the form of freezing and smoking facilities in Nain and by supplying gear directly to ﬁshermen. This was helpful in maintaining the local economy, but it initially overlooked the incapacity of Arctic charr to withstand high volumes of harvest and exploitation. Production volumes increased to over 200 tonnes per annum, and at this level regulations were imposed to prevent a detrimental decline in Arctic charr. In recent years, the total annual volume of Arctic charr harvested from both the Labrador and High Arctic ﬁsheries has declined to less than 120 tonnes (see Table 1.1). This is not because of a drop in market price of Arctic charr, but appears connected to a lack of market interest in wild Arctic charr unless it is of high quality. For example, because of its redder color and larger size, the High Arctic charr of Cambridge Bay sells for about twice the price of Labrador charr, and the overall quality of Arctic charr from the wild Labrador and High Arctic ﬁshery has not kept up with the quality of farmed Arctic charr and its year-round availability (Ledrew 1984; Kim 1993). Wild Arctic charr has high inherent quality upon capture in the fall, but quality declines due to poor harvesting and processing control. The lack of grading standards and poor attention to detail in processing and packaging are major concerns in selling wild Arctic charr. Table 1.1 Commercial catch from the wild ﬁshery of Arctic charr in Canada. Data from Stats Canada.

NWT Labrador Total Canada

NWT Labrador Total Canada

1981

1982

1983

1984

1985

1986

1987

1988

1989

1990

— 253 —

— 243 —

52 179 231

62 148 210

63 142 205

73 114 187

53 148 201

84 95 179

65 105 170

60 106 166

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

43 79 122

41 84 125

64 48 112

130 44 174

138 33 171

— 11 —

— 31 —

— 37 —

— 50 —

— 120 —

An Introduction to Arctic Charr

9

Greenland, Ireland, Great Britain, and European ﬁsheries In Greenland, Ireland, Great Britain, and other parts of Europe, the pattern of Arctic charr exploitation was slightly different, but the consequent problem of overexploitation and the eventual necessity for regulations were the same. In 1903 a commercial ﬁshery in central Greenland began harvesting anadromous Arctic charr with gill-nets, canning or salting the catch. A ﬁshery established in the Godthaab area in 1914 was shut down in 1917 due to decreases in Arctic charr numbers (MacCrimmon & Gots 1980). It reopened brieﬂy, with over 80 tonnes exported annually from the Godthaab region, but by 1960 only a small number of rivers sustained commercial ﬁshermen. Fishing of lake-resident Arctic charr in Ireland, Wales, and Scotland occurred throughout the last 400 years, and in each case slowly terminated due to overexploitation from commercial ﬁshing. This led to economic extinction, serious resource depletion, and in some places local destruction of Arctic charr stocks. In Northern Ireland, for example, Arctic charr were commercially harvested with nets in Lough Neagh until 1814, when harvest was no longer feasible due to the termination of Arctic charr stocks. In Scotland, St Mary’s Loch Arctic charr were harvested to near extinction by the mid-eighteenth century. The Windermere charr ﬁshery, one of the best-documented ﬁsheries in Europe, lasted almost 400 years without overly threatening the local charr population before succumbing to overharvesting from the use of longer nets of ﬁner mesh and increased sports ﬁshing in the late 1800s (Johnson 1984). The result of the switch from subsistence harvesting to commercial harvesting to meet consumer demand beyond the local community level has been moderate to serious decline and even catastrophic loss in many local Arctic charr populations. In large part, overexploitation is due to high demand and high prices for the ﬁsh. Humans have an almost pathological capacity to put intense pressure on a wild species of economic value, given very efﬁcient capture gear and disregard for biological limits to growth (Johnson 1984). On its own, high consumer demand does not result in overexploitation. Poor regulations, efﬁcient harvest methods, the extent and duration of harvest pressure placed on a population, ﬁsh growth and reproductive capacities, and size of populations all play a role. Arctic charr are easy to harvest and are highly susceptible to netting as they all return to the same lake via the same river. You can catch a high percentage of an anadromous Arctic charr population within a few weeks when ﬁshing with gill-nets. Anadromous wild Arctic charr are also slow growers, having only ﬁve weeks of the year to feed. This means they take a longer time to reach sexual maturity than other salmonids, in some populations taking more than 10 years to reach maturity. Commercial exploitation of wild Arctic charr continues, though it is now tightly controlled by government regulation to prevent the overharvests seen in the past. Production from the wild Arctic charr ﬁshery remains static and near its sustainable level. An alternative method articulated by a few biologists and ﬁsheries managers in Canada would see a further reduction in commercial ﬁshing. They feel there should be no commercial exploitation of Arctic charr from natural systems in Canada’s north other than by a regulated domestic and sports ﬁshery. The economic value of sports ﬁshing to a northern community is much higher than the value of a commercial catch of Arctic charr. Moreover, the volume of ﬁsh removed from the system by sports and domestic ﬁshing is considerably lower, giving each ﬁsh captured a much higher value than if it were processed and sold commercially (MacCrimmon & Gots 1980).

10

Arctic Charr Aquaculture

Given the state of the wild ﬁshery and the better value obtained from sports ﬁshing, supplying the market demand for Arctic charr with cultured ﬁsh makes good sense. Aquaculture could meet the high demand and alleviate the pressure placed on wild stocks. There have never been enough wild Arctic charr of quality to supply consumer demand, so market expansion could come from cultured production. The attractive market price, excellent consumer appeal, and certain traits of Arctic charr when kept under culture conditions make them ideal candidates for aquaculture.

Development of Arctic charr aquaculture The commercial culturing of Arctic charr is a relatively recent phenomenon, although stocking Arctic charr into lakes, which is a form of aquaculture, may go back a thousand years. Arctic charr was an important food resource for the Vikings who lived in Iceland and Greenland for over a thousand years. A researcher investigating genetic differences in Icelandic populations of Arctic charr hypothesized that Vikings or their descendants may have stocked small lakes adjacent to Thingvallavatn Lake. Although perhaps a leap, this theory may explain genetic differences he observed (Gydemo 1984).The dukes of Austria also managed a sophisticated ﬁshery in Tyrolean mountain lakes in the ﬁfteenth and sixteenth centuries, which involved stocking lakes with brown trout (Salmo trutta) and Arctic charr (Pechlaner 1984). There are written documents from that time detailing the organization of the charr ﬁshery in the high mountains. In a letter to ﬁshermen on the Achensee, a ﬁshery ofﬁcer asked them to supply charr fry, but not before autumn, to facilitate transportation at cooler temperatures. They had even developed special transportation kegs, which allowed the transport of live Arctic charr over distances requiring days of travel (see Fig. 1.3). In one case, instructions written by a sovereign for his ﬁshery director request the stocking of ﬁve ﬁshless lakes with Arctic charr and brown trout. There are also records detailing the construction of cages to hold live Arctic charr, and a ﬁshery ofﬁcer in 1527 ordered the construction of a special cage to hold small charr at Plansee (Pechlaner 1984). Techniques for artiﬁcial breeding and rearing salmonids from egg incubation onwards developed in the late 1800s in both Europe and North America. This predominantly involved brown trout and rainbow trout for the purpose of restocking natural water bodies and growing in earthen ponds. This early period of salmonid rearing saw the transportation and propagation of brown trout and rainbow trout all over the world, making rainbow trout the second most important cultured salmonid in the world, next only to the production of Atlantic salmon. The earliest reported rearing of Arctic charr in European hatcheries was in 1900, for restocking in Norway (Eriksson & Wiklund 1989). Fisheries scientists’ interest in propagating Arctic charr for enhancing or rejuvenating decimated lake-resident populations in Europe began in the mid-1970s. This was during a time when many lake-resident populations were being depleted as a result of overharvest, pollution, and acid rain. The mid1970s were a time of tremendous expansion and interest in Atlantic salmon net-pen farming in Norway. The interest in commercial Arctic charr aquaculture in Norway and Sweden came about when someone had the idea of using seawater net-pen technology for raising Arctic charr. It was hoped that Arctic charr could be an alternative or complementary species to Atlantic salmon, allowing an expansion of the farmed salmonid market.

An Introduction to Arctic Charr

11

Fig. 1.3 Engraving showing Arctic charr ﬁshing and live ﬁsh transportation methods of late medieval times. From the book Weisskunig of Kaiser Maximilian I (1459–1519). Source: Pechlaner 1984. Reprinted with permission.

A considerable body of scientiﬁc knowledge concerning the commercial rearing of other salmonids existed, and this inﬂuenced the direction of Arctic charr culture research. When growth trials were ﬁrst initiated in the mid-70s, only a handful of the approximately 1000 scientiﬁc papers on Arctic charr gave information that was applicable to cultivation (Jobling et al. 1993), so Arctic charr aquaculture was developed using existing rearing systems and husbandry techniques used for other species. Thus in Norway they made use of round tanks and seawater rearing in net-pens, while in Canada they began work with troughs, square tanks, raceways, and pond culture. Early research with various strains of Arctic charr showed great promise for commercial rearing: rapid growth, high-density stocking capacities, disease tolerance, and good marketability. The Norwegians and Swedes spent a great deal of research time and effort investigating seawater tolerance, trying to ﬁt Arctic charr into the Atlantic salmon rearing paradigm. Norwegian researchers concentrated on anadromous Arctic charr, as they believed these ﬁsh would have the seawater capabilities required for net-pen rearing. Unfortunately, even anadromous charr cannot tolerate overwintering in sea water.

12

Arctic Charr Aquaculture

In Canada, researchers also concentrated on anadromous Arctic charr, starting two brood stocks based on collections from the north and east of the country. In 1978 there was a transfer of fertilized eggs to the Department of Fisheries and Oceans’ (DFO) Rockwood hatchery in Manitoba from Nauyuk Lake, NWT. In the east, Labrador stock were collected from the Fraser River of Labrador in 1980, 1981, and 1984. It was fortunate for future commercial growers that, in both regions, wild anadromous stocks were collected for rearing under culture conditions, because they generally grow larger than lake-resident populations. By blind luck, one of the two races of anadromous Arctic charr collected by Canadian DFO scientists, the Nauyuk strain, had attributes that make it one of the best brood stocks in the world. Researchers in Sweden, Norway, and Canada developed basic brood stocks from which eggs and ﬁngerlings were transferred to commercial growers in a ﬁrst wave of commercial development in the mid-1980s. There was something of a ‘gold rush’ mentality about growing Arctic charr within the research community and in commercial aquaculture circles, which was restricted only by the limited quantities of eggs available. Some researchers even left government institutions to start private companies supplying eyed ova and ﬁngerlings from pedigreed Arctic charr brood stock lines. Regional and national governments funded research programs into Arctic charr culturing methods, market studies, and commercial grow-out farms. The ﬁrst commercial wave was not large, but it generated much interest, and Arctic charr was the new darling species, always on the agenda at international aquaculture conferences and often written about in the aquaculture trade magazines. Starting in 1987, the Rockwood hatchery distributed Labrador-strain Arctic charr eggs and ﬁngerlings to more than 20 private sites across Canada. For reasons of expediency, most ﬁrst-wave commercial growers selected the Fraser race, and this almost caused the downfall of Arctic charr aquaculture. Fortuitously, a few commercial growers received Nauyuk Lake ﬁngerlings and eggs. David Petkovich and I were two of the ﬁrst commercial growers of Nauyuk Arctic charr, raising them in northern Canada’s Yukon in the harshest of conditions – −40 °C, long winters, short summers – but under a photoperiod and water temperature proﬁle similar to their natural Arctic abode. We acquired two strains – Fraser and Nauyuk – from DFO Rockwood and built a commercial-size facility based on the DFO’s pilot-scale commercial production tank system that showed feasibility, at least in a government hatchery. In our minds, the second Yukon gold rush was on. However, much like the Chechako miners of 1898 who moiled for gold and found few riches, it was not long before the downside of rearing Arctic charr began to emerge in our operation. The Fraser stock grew exceptionally well, but after about 18 months the ﬁrst mature jack males appeared, and not long thereafter the growth rates declined in the entire lot. They did not color to the prominent orange-red of wild charr, and many individuals showed uneven coloration. Furthermore, they proved barely marketable due to their small size, and there was little hope of ever reaching a market size of 2–3 kg without generating a considerable expense. The Nauyuk strain proved much better growers, reaching a large size with good orange/red coloration, but the size range within each lot of ﬁsh was large, so they required a lot of grading (sorting according to size). Feeding was difﬁcult; the feed tables based on rainbow trout were all wrong and the diets did not seem quite right. Both strains grew exceptionally well at high density, but the water systems design inherited from DFO and our inability to manage heavy loading rates led to repeated operational problems. A catastrophic loss of entire lots of ﬁsh

An Introduction to Arctic Charr

13

was not uncommon in the early days. They were tough ﬁsh just the same; sometimes an entire tank of ﬁsh would be belly up from a system failure, their gills just barely moving. We would boost the oxygen, ﬂood the tanks with new water, and slowly they all recovered. We gradually learned what Arctic charr were really all about under culture away from the controlled conditions of a research laboratory. Our problems were not unique, as growers in Sweden, Norway, and elsewhere in Canada experienced similar types of business-threatening problems. In Norway they could not adapt Arctic charr to seawater rearing; in Sweden the sea water was too warm, leading to stress and disease; and everywhere there was a shortage of good-quality eggs. In all places, except for those lucky enough to have the Nauyuk strain, the ﬁsh did not grow large enough to catch the best market prices. Arctic charr has been no exception to a common theme in aquaculture: those into the game ﬁrst with a new species shoulder the burdens of transforming the scientist’s optimistic experimental results to the commercial level. Scientists rarely see to the bottom line that ultimately governs every commercial business, while entrepreneurs rarely foresee the real costs of developing a new species’ commercial potential in terms of the husbandry and technology required, the high burn rate of cash, and the very steep learning curve. However, every new species, with a bit of luck and if it meets the basic criteria for culture, moves beyond the ﬁrst wave. Arctic charr have the basic attributes for commercial culture: they grow well at high density, they are resistant to disease, they grow well on commercial rations, and they command a high price if they are the right size and ﬂesh color. Researchers, although fewer now than in the ﬁrst heady days, are concentrating on problems pertinent to commercial charr production although some of the research approaches are still attempts to solve problems that should just be bypassed, such as working with strains that do not have basic attributes for culture or attempting to force Arctic charr into sea water (Tabachek & de March 1991).

Production levels of cultured Arctic charr Commercial production of cultured Arctic charr began in 1985 in Sweden with a yield of about 50 tonnes. Initially, world production increased exponentially with the ﬁrst wave of commercial production from growers in Sweden, Norway, and Canada. By 1993 many of the ﬁrst entrepreneurs in Arctic charr culture, particularly those working with strains other than Nauyuk, had fallen by the wayside, worn out by the struggle and bankrupt. Despite the reduction in the number of growers, those that survived produced larger volumes. World production at the turn of the century approached 3000 tonnes per annum (see Table 1.2). There are two or three main growers in Iceland and Canada, and small volumes of cultured Arctic charr are produced in France, Italy, Germany, Ireland, and Great Britain. While Norway, Iceland, Canada, and the United Kingdom have invested the most time and research into Arctic charr culture, there has been less intense work in other parts of the world such as Sweden, Germany, Italy, Austria, the United States, and Finland. Most countries that produce rainbow trout, brown trout, or Atlantic salmon would have suitable water conditions for growing Arctic charr. Even China is experimenting with the production of Arctic charr. Despite the tremendous interest in culturing Arctic charr, it has not met initial hopes and expectations. I think this reﬂects two main difﬁculties facing Arctic charr aquaculture today.

14

Arctic Charr Aquaculture

Table 1.2 World production levels of cultured Arctic charr. Data from Federation of European Aquaculture Producers. Year

Country Canada

1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000

7 12 24 75 100 150 150 160 175 200 300 400 700 720

Total Iceland

100 220 340 388 472 616 770 800 800 1100

Norway

100 300 250 200 600 289 200 344 200 626 430

Sweden

75 200 160 114 250 180 100 183 200 350 500

France

60 60 60 60 60 60

Italy

50 50 60 50 100 150

7 12 24 250 700 780 804 1398 1226 1226 1717 1710 2636 2960

For one, most Arctic charr grown for culture are less than 1 kg in size (rather than the preferred size of 2–3 kg) and have paler ﬂesh than the market demands. Small, pale-ﬂeshed Arctic charr command a lower price, but cost considerably more to produce. For example, in Norway, the small size of the Norwegian charr leads to high handling costs, particularly in slaughtering. High production costs are a real challenge to the survival of Arctic charr aquaculture, as there are already successful cost-effective alternatives, such as salmon rearing. The same problem is faced by Arctic charr aquaculturists everywhere – they are growing strains of Arctic charr that are too small. Again, small strains result in high production costs and poor market prices due to poor pigmentation, as the preferred consistent reddish-ﬂeshed Arctic charr is biologically difﬁcult to achieve with a small pan-size Arctic charr and, with some strains of charr, impossible at any body size. The other issue is that techniques for growing Arctic charr are not well understood (Glebe & Turner 1993). Misunderstandings of basic husbandry requirements for Arctic charr, particularly the skills needed to grow them to large size at high densities, is a continued hindrance to the success of Arctic charr operations. In their responses to culture, Arctic charr are deﬁnitely not rainbow trout and deﬁnitely not Atlantic salmon. This might sound discouraging but we are basically at the stage where Atlantic salmon farming was in the 1970s. Atlantic salmon farming saw the same types of difﬁculties in the early days of development, but now is a viable, fully developed industry (Gurure et al. 1995). Atlantic salmon operations are so economically viable and widespread that current difﬁculties tend not to be economical or operational, but have more to do with spreading public dissent, as seen in parts of Canada. This appears related to the perception and often the reality of poor environmental management around ocean net-pens, poor local community skills, and the perception of heavy drug and chemical use. Although Arctic charr farming is still in its infancy, it can manage these types of problems with an emphasis on growing ﬁsh within the bounds of the natural environment and in tune with local community needs. Growers are beginning to understand that Arctic charr are not the same as salmon or trout in their response to culture. They do not grow well in sea water, nor in net-pens or raceways.

An Introduction to Arctic Charr

15

There needs to be a paradigm shift towards growing large ﬁsh using specialized high-density rearing techniques or natural low-density rearing in pothole lakes that complements the natural culture attributes of Arctic charr. One thing that has been lacking is the dissemination of information among and between researchers and growers, and to those marketing Arctic charr. Although many research scientists share information openly, too often researchers and growers involved with the commercial sector do not. We are at a point in the development of the industry where information should ﬂow more freely. The market for Arctic charr is underdeveloped and will remain so until many more commercial producers get involved, and this will not happen without cooperation and an increase in knowledge and information sharing. I hope this book is one big step in that direction.

Chapter 2

Wild Arctic Charr: Basic Attributes Important to Culture

Cultured Arctic charr remain wild creatures and are in no sense domesticated, unlike Atlantic salmon and rainbow trout, which have a long history of selective breeding that has produced a domesticated ﬁsh far removed from its wild brethren. This is reﬂected in their phenotypic expressions of growth, body conformation, and ﬂesh color when under cultivation. Arctic charr are only a few generations from the wild and have yet to be bred to select attributes suited to commercial aquaculture. However, rather than basing Arctic charr husbandry practices on the physiological requirements unique to this species, current practice has often mistakably defaulted to the methods used for Atlantic salmon and rainbow trout culture. In any salmonid under culture, proper husbandry practices should arise from an understanding of the salmonid’s natural characteristics. A ﬁsh under culture that is pushed beyond its natural physiological limits cannot perform well. For example, cultured Arctic charr brood ﬁsh require cold water for proper egg development and for early incubation of eggs, similar to the temperature ranges found in their natural High Arctic environment. They must also return to fresh water in the fall, as their wild cousins have done for thousands of years. Pushing this physiological temperature limit a few degrees higher or forcing Arctic charr to overwinter in sea water can be disastrous. Similarly, it is almost impossible to develop the best strain for domestication without understanding the many biological attributes such as size at maturity, ﬂesh color, and fecundity of the different stocks of wild Arctic charr. Some stocks do not have the characteristics needed for commercial culture. The form, whether resident or anadromous, of Arctic charr will also determine the qualities or characteristics of the ﬁsh raised under culture. For example, if a resident form of Arctic charr is chosen for culture – that is one which spends its whole life in fresh water – it will grow rapidly, but growth will level off as it reaches sexual maturity at a young age, well before it reaches market size. On the other hand, anadromous forms may not initially grow as fast, but they will grow to a larger size before reaching maturity. To understand why Arctic charr behave the way they do under culture, it is valuable to review some aspects of their geographic distribution, ecology, and life-history patterns.

Geographic distribution Salmonids are the dominant ﬁsh family in the circumpolar, northern hemisphere fresh waters of Asia, North America, and Europe, ranging southwards almost to the Tropic of Cancer in moun-

Wild Arctic Charr: Basic Attributes Important to Culture

17

tainous areas of Europe (Scott & Crossman 1973). Arctic charr have the classic life-history pattern displayed by all members of the family Salmonidae, but no other salmonid ranges as far north as the Arctic charr. They are truly the salmon of the Arctic (see the distribution map in Fig. 2.1). The cold, extreme northern fresh waters, pressed up against the Arctic ice edge and frozen for 8 months of the year, are the habitat of Arctic charr alone. In the Canadian High Arctic of Nunavut, Arctic charr are often the only salmonid, and in a few freshwater habitats, such as Lake Hazen on Ellesmere Island and Charr Lake near Resolute Bay, it is the only ﬁsh species found (MacCallum & Regier 1984; Reist et al. 1995). Less successful at surviving in lakes and water systems shared by other species of ﬁsh, they have adapted to hostile regions unsuitable for other ﬁsh by becoming generalists (Johnson & Burns 1984). They will eat any living creature, provided it is small enough to ﬁt in their mouths. They have a wide size range, presumably to meet the different challenges of the Arctic environment. By following the retreating continental glaciers, they are able to take advantage of habitats unoccupied by species they would normally compete with. Arctic charr are so well adapted to the harsh northern environment that they only reach their maximum potential in the Arctic basin (Johnson 1980).

Taxonomy Until recently, the taxonomic status of Arctic charr within the Salmonidae subfamily was confused. Arctic charr were formally named by Linnaeus in 1758, based on a type specimen from Swedish Lapland (Scott & Crossman 1973).He classiﬁed it as a salmon, naming it Salmo alpinus. It was later reclassiﬁed in the genus Salvelinus. Original classiﬁcations were further complicated by the fact that Arctic charr show a great variation in body form and life-history, resulting in tremendous phenotypic variation, outwardly expressed in body shape and coloration. During the heyday of taxonomic exuberance, the high degree of phenotypic variation in ‘charr’ was taken as an indication that there were many species of the ‘Arctic charr type’, as opposed to variations of the same species. In Europe, thirteen species were listed from the British Isles: six species from Sweden, and at least seven from North America (Johnson 1980). Sir John Richardson identiﬁed four species from types he collected during his travels with Sir John Franklin to the Canadian Arctic in 1835, including two he named after Samuel Hearne and John Ross, previous explorers of the Canadian wilderness. Over the next 150 years the ‘lumpers,’ those taxonomists who prefer to gather different races or varieties under the same species name, regrouped many of the separate charr species as Salvelinus alpinus (Arctic charr) based on meristic (measurable body attributes), behavioral, and ecological characteristics that are recognized by most researchers today (see the chart in Plate 1). Difﬁculties in distinguishing Dolly Varden (S. malma) from Arctic charr also presented problems in the development of the current taxonomic status. Both species occupy similar habitats and are superﬁcially similar in morphology (external appearances). Arctic charr occupy the polar basin, with populations circumnavigating the coastlines of North America, Russia, and Europe, while Dolly Varden are more restricted to the North Paciﬁc and western Arctic regions of Alaska and eastern Russia. Behnke (1984) proposed that Arctic charr and Dolly Varden were separate species that probably split from a common ancestor during an early Pleistocene glacial period. In the 1990s, the ability to look at genetic differences based on electrophoretic markers such as mtDNA further clariﬁed Arctic charr systematics. As a

18 Arctic Charr Aquaculture

Fig. 2.1

Circumpolar distribution of wild Arctic charr.

Wild Arctic Charr: Basic Attributes Important to Culture

19

result, Reist et al. (1997) were able to substantiate, much to the consternation of the Alaskans and Yukoners, that river-dwelling charr (anadromous, resident, and isolated stream-resident forms) west of the Mackenzie River were Dolly Varden and that only a few lake-dwelling charr in Alaska were Arctic charr. Today, four subspecies of Arctic charr are recognized: Salvelinus alpinus alpinus, S. a. erythrinus, S. a. oquassa, and S. a. taranetzi, which in aquaculture circles are known respectively as European charr, Canadian High Arctic charr, Sunapee charr, and Kamchatka charr (Fig. 2.1). Another group of charr occurs in Labrador (Labrador charr) and is more similar in form to the European charr than to the Canadian High Arctic charr. The timing and locations of divergence of these four subspecies are confused, but all originated in the advance and retreat of glacial icesheets in the last 2 million years (Johnson & Burns 1984). Wilson et al. (1996) suggested that North American charr originated from two distinct lineages: an Arctic lineage from a northern glacial refugia (Yukon Beringia, continental Siberia, or among the Arctic islands), and an eastern Laurentian lineage from an eastern glacial refugia. These lines probably diverged about 1–1.6 million years ago during the early Pleistocene. All of the subspecies differ in geographic distribution and show subtle variation in morphology, particularly in body size at maturity, ﬂesh color, and age at sexual maturity. The Canadian High Arctic, Labrador, and European charr are used in commercial aquaculture with different levels of success.

Morphology: the outward appearance Arctic charr are a beautiful bright ﬁsh with a large variation in body form and coloration depending on form and genetic stock. The main color characteristics of large anadromous adult Arctic charr are scattered white dots along bright red and/or silvery sides (see Plate 2). The back is usually dark in adult ﬁsh, with a few pale yellow vermiculations (worm-like spots, usually forming a pattern). A characteristic feature is the white leading edges of the paired ﬁns and anal ﬁn, which are often visible in water too dim to see the body proper. Until just prior to sexual maturity, 9 to 13 parr marks are clearly visible along the sides of the body. The back of sub-adults is often a mass of yellow spots and vermiculations. In the year before sexual maturity, at least in Nauyuk Arctic charr, the parr marks become very pale, there is an almost complete loss of yellow spots and vermiculations on the back, and the ﬂanks and belly darken to bronze or dull orange. In adult form during spawning season, there is no confusing a sexually mature male Arctic charr with any other salmonid. They display a brilliant red, and in some males the entire body, including the belly, will turn a bright, almost ﬂuorescent orange. Sexually mature females also brighten, showing bright leading edges on ﬁns, with the ﬂanks and bellies colored a bright bronze to pale red. The body form is similar to most other salmonids, slender and fusiform (cylindrical shape), while somewhat more rounded than trout or salmon. Compared to other salmonids, the small delicate head, large eyes, and shortness in body of Arctic charr is particularly noticeable (see Fig. 2.2). The tail is slightly forked, less than that of the lake charr but more than the brook charr or Dolly Varden. The head is short and forms 22% to 25% of the body length. The snout is rounded, mouth large, and the maxillary (upper jaw) extends beyond the posterior margin of the eye in anadromous forms but not in all freshwater forms. Teeth develop on upper

20

Arctic Charr Aquaculture

Fig. 2.2 External and internal anatomy of an Arctic charr.

and lower jaws and on the vomer or palate (Scott & Crossman 1973). At sexual maturity, the males in most races develop a distinctive kype (hooked jaw), sometimes with a ﬂeshy bulbous end, on the lower jaw. This makes the head look longer. They also become thinner from side to side in the body, and deeper from top to bottom. After the spawning season has ended, they revert to a more cylindrical body form and lose much of the prominent kype. Some females of Nauyuk and Svalbard charr also develop a much reduced but noticeable kype at maturity, but females never lose their cylindrical body form. In the year prior to spawning, males and

Wild Arctic Charr: Basic Attributes Important to Culture

21

females begin to develop the brighter plumage of adults, but are similar to each other in appearance until full sexual maturity is reached in the fall of their ﬁrst spawning.

Arctic charr forms and morphs Throughout their range and amongst all of the four subspecies, Arctic charr exhibit two broad life-history patterns: anadromous and resident forms. Anadromous Arctic charr spend brief periods in the ocean environment, feeding on the rich nearshore food resources of Arctic waters. Unlike other salmonids that may remain at sea for years, Arctic charr must return to fresh water after the short Arctic open-water summer, virtually not feeding again until the next year at sea (Gyselman 1984). Of all the salmonids, they are the least adapted for long-term tolerance of sea water (Johnson 1984). Most anadromous populations of Arctic charr overwinter and spawn in lakes, with a few Norwegian and Canadian populations entirely stream-resident upon their return to fresh water (Jensen 1994). Conversely, resident forms spend all their lives in a freshwater lake or river environment. Some resident populations are landlocked in lake systems without access to ocean water, while others remain resident by choice, even though they have easy access to the Arctic Ocean. In some lakes such as Nauyuk Lake in Nunavut, Canada, both anadromous and resident forms co-exist and may well arise from the same parental stocks (Johnson 1980).

Anadromous form Anadromous populations of Arctic charr occur in the more northerly regions around the periphery of the Arctic basin and the intervening islands, with a southern limit deﬁned by a line where summer seawater temperature rise too high for comfort. In Norway, Jensen suggested that seawater temperatures above 14 °C acted as a thermal barrier in the distribution of anadromous Arctic charr into southern waters (Jensen 1981).All of the anadromous populations occur in river/lake systems quite close to the seacoast, usually less than 25 km from tidewater. In Norway, where the North Atlantic Drift sweeps warm sea water northwards, the southern limit of anadromous Arctic charr is Latitude 65°. In eastern North America, the cold south-ﬂowing Labrador Current pushes the range of anadromy southwards to Latitude 49° in the vicinity of the Gander River, Labrador. Although all the major river systems ﬂowing into the Baltic Sea have Arctic charr populations, none are anadromous. As well, no anadromous stocks occur in the White Sea (Johnson 1980). Anadromous Arctic charr generally do not range far from their natal river/lake systems, preferring to stay in adjacent nearshore waters (Dempson 1984). However, each year some nonspawners from each cohort will travel from the ocean into other freshwater systems. Individual ﬁsh-tagging studies conducted on Nauyuk Arctic charr show migrations of up to 250 km to other river systems. These long migrations involved overwintering in river/lake systems other than natal waters, as recoveries of tagged ﬁsh occurred in the fall of the second year (see Fig. 2.3). The tagging work suggests a great deal of interchange between the Nauyuk Lake charr and charr from other river systems in the Coronation Gulf region since only 70% of seagoing ﬁsh return to the Nauyuk system each fall, with 30% of the total returning ﬁsh being new immigrants to the system each year (Gyselman 1984). Anadromous Arctic charr from northern Norway also show this tendency to make long coastal migrations and occasionally overwinter in non-

22

Arctic Charr Aquaculture

Fig. 2.3 Overwintering migrations of Nauyuk Arctic charr to other river systems. Source: Gyselman 1984. Reprinted with permission.

natal waters. A few Arctic charr tagged in the Vardnes River, Norway, moved more than 100 km away, with one individual that had previously been recaptured in the Vardnes River four times, recaptured 940 km away in the Tuloma River near Murmansk, Russia (Johnson 1980). Contrary to our narrow sense of time that suggests we are long clear of the ice ages, Arctic charr live in a world still driven by glacial forces. The presence or absence of ice cover is the driving force in the High Arctic, much as ﬁres are the driving force of the great boreal forests and wide-open prairies of central North America and Asia. It is uncharacteristic of other anadromous salmonids to stray from their natal streams and overwinter in foreign freshwater systems but it is a long-term necessity for the survival of Arctic charr. Since they exist in regions dominated by ice, subzero seawater temperatures in winter, and limited food resources, this ability to explore new freshwater environments by traversing a saltwater habitat intoler-

Wild Arctic Charr: Basic Attributes Important to Culture

23

able during the prolonged northern winter is their strategy to access new habitats that become exposed as glacial ice retreats. According to Johnson, homing to natal streams to spawn assures concentration of reproductive effort in an area known to work, while overwintering in foreign freshwater systems allows exploration of new habitats (Johnson 1980). If Arctic charr never strayed from their natal streams, they would not be able to expand their population to new areas, make use of other resource-rich water systems, or compensate for the long-term uncertainty of Arctic living. Little is known on this subject, but it is likely that Arctic charr spawn in the non-natal waters discovered and overwintered in if the habitat conditions are favorable. How else could Arctic charr invade and occupy new habitats as glacial ice sheets melt and new river systems form? Anadromous Arctic charr generally spend less than 15% of the total year at sea (see Fig. 2.4). They enter sea water during mid-to-late June and return upstream from mid-August to

Fig. 2.4 Relative amount of time Arctic charr of different ages spend in fresh water and sea water.

24

Arctic Charr Aquaculture

early September, living in sea water that rarely rises above 10 °C. For example, the nearshore areas used by Arctic charr in Labrador average 7.6 °C during mid-July, and fall to nearly zero by mid-September, when charr have all returned to fresh water (Dempson & Kristofferson 1987). The length of time spent at sea varies depending on individual ﬁsh size and maturational status and the climatic conditions, particularly the timing of spring freshet and fall freeze-up. The ﬁsh’s size is more important than age in determining the time of its ﬁrst seaward migration. In order to handle the change from fresh water to sea water, Arctic charr must be at least 15 cm in length. Those ﬁsh preparing to migrate to the sea go through a transformation called smolting. Compared to other salmonids, this process in Arctic charr is minimal, which is partially why they do not have the capacity to withstand prolonged periods of time in salt water. During smolting, a silvery color appears on the ﬂanks and the ﬁsh loses its parr marks. Size also makes a difference in terms of the length of time ﬁsh spend at sea. Large ﬁsh (over 60 cm fork length) spend the longest time at sea, 60 to 65 days. Arctic charr of smaller size (40 cm fork length) and presumably of younger age spend much less time at sea than the larger charr, while ﬁrst-time smolts may only last 2 or 3 days in the saline environment (see Fig. 2.5) (Gyselman 1984). On average, larger Nauyuk Arctic charr remain in the ocean for 40 to 44 days. In the Vadnes River of northern Norway, the average seawater stay for larger ﬁsh is also 40 days (Johnson 1980).

Resident form Stocks of resident Arctic charr occur sporadically throughout the entire natural range of the species. Within the northern areas of the range, resident Arctic charr usually occur in isolated lakes cut off from the sea by isostatic uplift of the land following glacial retreat. These lakes are usually located within 100 km of coastlines and some of them, for instance Lake Batsvatn in northern Norway (68° N), are over 800 m above sea level. In some High Arctic lake systems with sea access via short rivers, such as Nauyuk Lake and Hazen Lake, both resident and

Fig. 2.5 Relationship between Arctic charr body size and number of days spent at sea. Data source: Johnson 1980.

Wild Arctic Charr: Basic Attributes Important to Culture

25

anadromous forms occur. In regions south of the anadromous Arctic charr range, resident Arctic charr occupy numerous lakes and rivers of western Ireland, Scotland, Wales and northern England, the Orkney and Shetland Islands, Jan Mayen Island, Svalbard, and Iceland. Resident Arctic charr are the most widespread freshwater ﬁsh in Norway next to brown trout (Johnson 1980; Aass 1984; Maitland 1992; Bass 1998). Very isolated natural populations also occur in the European Alps in the headwaters of the Rhine, Rhone, and Danube rivers up to elevations of 3000 m (Schwarzsee). These are relic populations that have been isolated from the rest of their species and cut off by the process of the land lifting up during glacier melt. Many lakes with charr in the Alps have been stocked in recent times and, as mentioned earlier, there is a long history of high alpine lake stocking by the late medieval Tyrolean sovereigns (Pechlaner 1984). In Norway, charr have been stocked into thousands of lakes and rivers throughout the country, more so in the north than the south (Aass 1984). Although they have river access to the sea, all of the charr in the Baltic region of Sweden and Finland are lake/river resident. There are isolated populations of resident charr in the Lena and Angara rivers of Siberia, as well as in some of the rivers draining into Lake Baikal. In Quebec, Canada, there are relic populations of charr known as red trout or l’omble chevalier in lakes, some of which drain into the Gulf of St Lawrence. Farther south in Maine, USA, relic populations of Arctic charr are known as blueback trout, and in New Hampshire as Sunapee charr. Although there are thousands of lakes in the Canadian Shield of mainland northern Canada, no Arctic charr occur much south of the polar basin. These Canadian Shield lakes and rivers are populated with lake charr, brook charr, and in western North America, Dolly Varden charr and bull trout. In Alaska, the only Arctic charr found north of the Arctic Circle are resident forms in landlocked lakes. In the Yukon Territories a few landlocked, pothole lakes in the Yukon River watershed have been stocked with Nauyuk Arctic charr, and a population of Nauyuk charr was inadvertently, through an escape from a hatchery, established in a tributary stream of the Yukon River near Whitehorse in the 1990s.

Morphs Wild populations of resident Arctic charr exhibit a signiﬁcant degree of phenotypic plasticity which means they are often found in several different but co-existing morphs. One of the distinctive differences is size (Jobling & Reinsnes 1987). Researchers have debated whether the variant morphs represent different species or represent one species (Arctic charr) with different morphs (Henricson & Nyman 1976; Klemetsen 1984). Nordeng (1983) cut through many of the arguments by experimentally showing that co-existing forms (anadromous, small resident, and large resident) of Arctic charr belong to the same gene pool, with the ﬁngerlings of each form segregating into all three size morphs. Sympatric or co-existing morphs spawn with each other and produce offspring that can produce all three morphs. Out of a hundred eggs laid and fertilized by one particular morph cross, 33% might become dwarf Arctic charr, 33% normal, and 33% large ones. I have also seen this occur under culture, where any parental cross of various strains will produce young that show distinct size morphs. It is not surprising that researchers have often been overeager to class the different morphs of Arctic charr as new species. The extent and frequency of variations in this species and

26

Arctic Charr Aquaculture

the presence of co-existing morphs are quite remarkable (Johnson 1980). Of the salmonids, Arctic charr exhibit the highest degree of phenotype variability between populations in body shape, in color, and in behavior (Adams et al. 1998). Not only do different forms of Arctic charr show up in the same lake, but the differences can be radical. For example, Arctic charr present in a lake can range from a sexually mature 100 g resident ﬁsh to a sexually mature 1500 g resident ﬁsh. Lionel Johnson (1980) said it best when he stated 20 years ago: ‘This bewildering complexity of morphologically and physiologically differentiated forms in Arctic charr both within and among water bodies, present unique problems for the taxonomist, evolutionist and ecologist to say nothing of the problems associated with the management of such stocks.’ It also presents problems for selecting the best strains for commercial culture. In virtually all populations of resident Arctic charr, at least two basic size morphs occur: larger normal or predatory charr and smaller dwarf charr. Some lake systems support three general size morphs known as dwarf, normal, and large predatory Arctic charr (Eriksson & Wiklund 1989). Regardless of where or how many different morphs occur, they are identiﬁed in terms of a number of traits. Each morph: a different distribution within the lake with respect to water depth and feeding ecol• has ogy; in terms of size and age at maturity; • differs differs in retention or loss of juvenile plumage, notably parr marks at maturity; • has a different time and place of spawning; and • exhibits morphological differences (Johnson 1980). • Typically, the dwarf charr reach sexual maturity at a small size, retain parr marks at sexual maturity, and feed predominantly upon benthic invertebrates. The normal charr reach sexual maturity at a larger size after the loss of parr marks, and feed on larger macroinvertebrates or ﬁsh. Where anadromous forms occur with resident charr, they are signiﬁcantly larger than the resident form, usually have a different coloration, do not show parr marks at maturity, and live longer lives. The most common number of morphs is two: a smaller dwarf resident charr and a larger, more common one. Lake Hazen in Canada is an example of a lake where two distinct morphs – a smaller dwarf and a larger one – are present. The dwarf is slower growing and smaller, while the other has a different color and is larger, with a sudden increase in growth rate that occurs around the age of nine. The presence of the smaller charr morph in the gut of the larger charr morph, and the greater rate of parasitism (from eating ﬁsh) suggests that cannibalism is the proximate explanation for the sudden divergence in size (Reist et al. 1995). The mechanism that triggers this change in diet is still not understood. Still common, but less so, is the presence of three sympatric or co-existing morphs. Loch Rannoch, Scotland, provides an example of this as researchers have deﬁned three forms of resident Arctic charr – based on head morphology, body color, growth rates, and feeding ecology – as planktivorous, piscivorous, and benthivorous morphs. The streamlined, brightly colored, sexually dimorphic (in color) planktivorous morph feed entirely on zooplankton and insects. The other two morphs are cryptically colored (no sexual dimorphism), with the benthivorous morph feeding on benthic macroinvertebrates and the piscivorous morph consuming predominantly ﬁsh and large macroinvertebrates. Head size alone could

Wild Arctic Charr: Basic Attributes Important to Culture

27

distinguish the two cryptic forms from one another, with the piscivorous charr having a more robust jaw, a longer, deeper head, and larger eyes than the benthivorous charr, differences presumably related to the types of food consumed. The benthivorous and planktivorous morphs showed similar patterns of mean length with age, characterized by rapid growth in early years and little growth after age three. The piscivorous morph, much smaller than the other two morphs in their early years, lived longer and attained signiﬁcantly larger sizes (Adams et al. 1998). The co-existence of four morphs is rare, but an example is found in landlocked Thingvallavatn Lake, Iceland. Morphs in this lake differ markedly in life-history characteristics, particularly size and age at maturity. In the wild, the piscivorous morph reaches sexual maturity at an older age (5–10 years) and larger size (2560 cm) than the other three morphs. The small benthivorous morph matured earliest (2–3 years) and at smallest size (7–15 cm), with the other two morphs intermediate in size and age at maturity. When researchers compared the growth rates, size at maturity, and age to maturity of these four morphs, they noted clear differences at an early age in the growth patterns among the progeny of the four groups, which they believed had a strong genetic basis. It was also possible that egg size may have some bearing on the size differences noted. Researchers noted that cultured progeny of the small benthivorous and planktivorous charr matured in their second year (only males) and third year (both sexes), while the large benthivorous and piscivorous charr showed only a few mature males at age three. As juveniles, the large piscivorous and large benthic charr’s growth patterns were similar to those of the smaller charr morphs, but they did not mature as early. The researchers suggested that the genetic segregation of these morphs has its basis in early phenotypic plasticity of a common ancestor stock. As different niches within the lake became more stable, the use of these niches by the different Arctic charr morphs also became more stable and their phenotypic differences more clear and genetically ﬁxed (Skúlason et al. 1996).

Growth, size, and age at maturity Natural populations of anadromous Arctic charr grow in two distinct phases: a rapid increase in weight during the brief northern summer, followed by a slow loss of weight over the long harsh winter season. The rapid summer growth is most evident in anadromous charr and is somewhat analogous in function to the rapid weight gain shown by many other northern animals such as grizzly bears (Ursus arctos) and Arctic ground squirrels (Spermophilus undulatus) in preparation for winter. Since anadromous Arctic charr feed little if at all in fresh water, they must acquire massive stores of energy, not only to sustain basic metabolic functions throughout the winter, but also to accomplish body growth and production of eggs and milt (Jørgensen et al. 1997). Typically, this is done in a feeding period of only 40 to 60 days at sea (Mathisen & Berg 1968; Johnson 1980). During this brief feeding period, growth rates can be extremely high (more than 2% per day), although this may vary considerably over the years (see Table 2.1). It is likely dependent on the food quality and quantity obtained in the open-water season. Upon their return to fresh water, body lipid reserves may have increased ﬁvefold. Given that the summer Arctic seas, even in the shallow waters of bays and river mouths, are rarely above 4 °C, these growth rates of wild Arctic charr are remarkable.

28

Arctic Charr Aquaculture

Table 2.1 Differences in growth rate between summer feeding and winter fasting in anadromous Arctic charr (SGR = speciﬁc growth rate). Source: Johnson 1980. Weight

Summer feeding Maximum Average Minimum Winter fasting Maximum Average Minimum

Length

SGR (%)

Days

2.05 1.55 1.23

37* 44* 45*

– 0.01 – 0.04 – 0.11

320 315 293

Growth (%)

SGR (%)

75 68 74

0.34 0.31 0.25

–4 – 12 0.01

0.02 0.01 0.01

Days 37* 44* 60* 321 315 293

Growth (%) 13 14 15 7 6 3

*Number of days feeding at sea

Even following the best of summers, Arctic charr lose weight over the winter period. Researchers in northern Norway studying wild anadromous charr noted that spawning females lost more than 80% of their lipid reserves between the fall return to fresh water and the next summer’s descent to the sea (Jørgensen et al. 1997). In non-spawning years, weight loss can be as high as 33% and averages 12% over 115 days of winter fasting. Even though they feed for less than 15% of the year, Arctic charr still manage an annual net increase in weight and length. Growth in length occurs rapidly during the summer feeding period and at a slower rate throughout the winter. In some years, growth in length is nearly 20%, with 7% occurring in the long winter period and the rest while at sea in the summer. Growth rate is most rapid when ﬁsh reach a size of 300 g irrespective of age, suggesting growth is more closely related to size than to chronological age (Johnson 1980). Anadromous Arctic charr achieve a substantially larger body weight and length than resident forms (Jørgensen et al. 1997).The anadromous stocks that grow largest occur in the High Arctic of Canada, particularly the Nauyuk Lake and Tree River charr (see Fig. 2.6). These long-lived stocks (10 to 18 years) reach average lengths of over 750 mm and weights of over 5 kg, with some individuals reaching over 12 kg. The mean size of most resident stocks is less than 500 mm, and many only reach sizes of 200–300 mm (see Fig. 2.7). As many as 44% of the resident Arctic charr populations show bimodal or two-sized morph growth patterns, and this pattern persists throughout North America, Iceland, Europe, and Russia. Bimodal growth is also evident in some anadromous populations but is not so pronounced (Johnson 1980). The freshwater growth rate for young Arctic charr (alevin and fry) is not well known and is somewhat confused by the various morphs found in many of the stocks. Growth of young Arctic charr in fresh water commences shortly after hatching and before yolk sac absorption, at a size of about 18–25 mm. In Windermere Lake, resident Arctic charr emerged from gravel redds (nests) in March or April at 20–23 mm, and by the end of August had reached a size of 49 mm (see Fig. 2.8). Yearly growth rates of anadromous Arctic charr prior to going to sea for their ﬁrst time are highly variable, with parr reaching the smolt phase often uniform in size but variable in age. In various Canadian stocks of Arctic charr, the age at ﬁrst migration to sea was 3 to 7 years, at a length of 87–220 mm, corresponding to weights of about 10–100 g. Other anadromous

Wild Arctic Charr: Basic Attributes Important to Culture

29

Fig. 2.6 Size at age for various stocks of anadromous Arctic charr. Data source: Johnson 1980; Dempson 1984; Moshenko et al. 1984.

Fig. 2.7 Size at age for various stocks of resident Arctic charr. Data source: Johnson 1980; Dept. Fish. & Oceans 1983; Fraser & Power 1984; MacCallum & Regier 1984; Nilsen & Klemetsen 1984.

30

Arctic Charr Aquaculture

Fig. 2.8 Growth rates of Arctic charr alevin and fry from Windermere. Data source: Johnson 1980.

stocks remain in fresh water from 2 to 9 years before seaward migration (Johnson 1980; Kristofferson & Sopuck 1983; Fisheries & Oceans 1991). Anadromous and resident Arctic charr also reach sexual maturity at different ages and sizes as shown in Table 2.2. (This is an important point for Arctic charr under cultivation, as they lose ﬂavor, texture, and color and grow more slowly after sexual maturity.) Resident Arctic charr generally mature at a smaller size and younger age (3 to 5 years) than anadromous charr. Dwarfs and resident Arctic charr from landlocked lakes reach maturity at the youngest age (2 years) and smallest size, with some stunted, food-deprived populations maturing at 10–20 g (Eriksson & Wiklund 1989). Females and males of these early maturing populations often retain parr marks into maturity. The age at ﬁrst maturity in anadromous Arctic charr is usually 5+ years, often with the stocks that grow largest, such as those from Nauyuk and Tree River, not reaching maturity until 9 to 11 years (see Table 2.2). Once they reach maturity, ﬁsh can continue reproducing for up to 20 years, with individuals living beyond 30 years of age and in some cases up to the age of 40 (Scott & Crossman 1973). In most anadromous stocks, female Arctic charr do not spawn yearly, often skipping one or a number of years between spawning to allow sufﬁcient recovery of body weight (Johnson 1980). Resident Arctic charr typically spawn every year. A few individual males in many resident stocks reach sexual maturity one year before their female cohort. This is not common in wild anadromous stocks, although mature male anadromous Fraser River charr are found in hatchery populations at age two, a year prior to female maturation.

Wild Arctic Charr: Basic Attributes Important to Culture

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Table 2.2 Age and size at maturity of anadromous and resident Arctic charr. Data source: Johnson 1980; Kristofferson & Sopuck 1983; Moshenko et al. 1984. Stock

Nauyuk Lake, Canada Bafﬁn, Canada Creswell Bay, Canada Tree River, Canada Ellesmere, Canada Sylvia Grinnel, Canada Mackinson Inlet, Canada Cumberland, Canada Olevstatn, Iceland Fraser River, Canada Umboxero, Russia Nettling Lake, Canada Matamek Lake, Canada Bodensee, Germany Blasjon, Sweden Keyhole Lake, Canada Windermere, England Fione Lake, Somerset, Canada Greenlaekur, Iceland

Type

Anadromous Anadromous Anadromous Anadromous Anadromous Anadromous Anadromous Anadromous Anadromous Anadromous Resident Resident Resident Resident Resident Resident Resident Resident Resident

Age at maturity

10 16 13 8 16 14 12 11 5 3 8 3 3 4 7 5

Size at maturation Weight (g)

Length (cm)

3415 2050 2047

620 600 570 500 463 450 447 400

850 1950 925 615

969 395 720 150

330 288 23

262 405 355 299 262 165 156 156 140 130

Matters of fecundity Most Arctic charr spawn in the fall. Stocks in northern Canada usually spawn in late August to late September, while more southerly populations spawn from November to December (Scott & Crossman 1973). In northern Sweden, resident charr of different watersheds and of different morphs spawn from mid-September to late December (Hammar 1984). In Vangsvatnet Lake, Norway, both co-habiting morphs occur together on the fall spawning beds, but peak abundance of the dwarfs was later in the season and deeper in the water than the larger morph. In addition to spawning with dwarf females, male dwarfs sometimes fertilize larger females by sneaking into redds when larger pairs are spawning. A few stocks, such as those of Windermere Lake, contain a fall-spawning and a spring-spawning cohort. Arctic charr spawn on nearshore lake shoals and in streams and rivers in typical salmonid fashion, forming redds in coarse gravel beds normally at water depths of 1 to 3 meters. Morphs of some resident populations in Scandinavia and Europe spawn at depths of 80 to 100 meters. Water temperatures are cold on the spawning grounds, usually in the range of 0.5 to 7 °C. Males in brilliant red dress and white-edged ﬁns defend territories vigorously against other territorial and roving non-territorial males. A territorial male is aggressive and will physically charge and bunt other males in the ﬂanks with its kype, which functions like a battering ram, sometimes knocking them sideways or rolling them onto their sides. When cultured Nauyuk Arctic charr are held in ponds where they naturally spawn, this ﬂank-bunting leaves many males with permanent scarring along the ﬂanks. At other times, a territorial male will grab the ventral or pectoral ﬁns or the tail of an intruder and remain locked with it for many seconds before releasing its hold.

32

Arctic Charr Aquaculture

Females approach these male-held territories and visually inspect the bottom for suitable redd sites. They prepare redds by sweeping debris and ﬁnes away with rapid, vigorous movements of the tail and ﬂanks. Nauyuk females, held in ponds, will defend these prepared redds against other females. Although some researchers suggest that the males must accept the females before courtship begins, my observations of cultured Nauyuk charr indicate the opposite. Females will drive certain males away from the redd and often do not select the dominant male as their partner in the spawning act. A single female may construct and lay eggs in 10 redds over the course of a few hours to 4 days and may spawn with a number of males. The sex ratio of charr in the general adult population is usually 1 to 1, yet on the spawning grounds, in both resident and anadromous forms, females may greatly outnumber the males. At the counting weir on Willow Creek, Nauyuk Lake Arctic charr females outnumbered males in the spawning run by 10 to 1 in one year and 4 to 1 the next. Females from a number of spawning sites on Windermere outnumbered males in ratios up to 7 to 1. Mature anadromous males are not often larger than females, but this does sometimes occur. For example, in Nauyuk Lake, spawning females averaged 622–711 mm, while males were 719–755 mm in length (Johnson 1980). Anadromous males of Tree River are longer and heavier than the female cohort after the age of seven, the year prior to sexual maturity (Moshenko et al. 1984). A sample of male and female anadromous Arctic charr taken from fall upstream migrants in the Sylvia Grinnell River indicated males matured at a larger size than females but also at an older age. When comparing sexual differences of non-spawning Arctic charr from this river, the sizes of males and females were similar (Kristofferson & Sopuck 1983). Resident Arctic charr of both sexes from Char Lake matured at similar size and grew at similar rates (MacCallum & Regier 1984). The absolute number of eggs produced by Arctic charr increases with body size. The larger anadromous females, on average, produce 3000–5000 ova. Resident forms produce only a few hundred to a few thousand eggs per female (see Table 2.3). However the relative number of eggs per kilogram of body weight is generally much higher in resident than anadromous forms. Overall productivity in a resident population is also considerably higher, since resident Table 2.3 Production of eggs in anadromous and resident Arctic charr. Data source: Johnson 1980; Kristofferson & Sopuck 1983; Moshenko et al. 1984.

Anadromous Nauyuk Lake, Canada Tree River, Canada Sylvia Grinnel Lake, Canada Fraser River, Canada Novaya Zemlya, Russia Resident Blasjon, Sweden Bodensee, Germany Windermere, England Keyhole Lake, Canada Matamek Lake, Canada

Absolute

Relative

Eggs/ﬁsh

Eggs/1000 g body weight

4781 4647 3520 4665 3570

1400 1460 1760 2490 1480

451 900 1220 610 1973

3920 9700 4250 1850 2490

Wild Arctic Charr: Basic Attributes Important to Culture

33

females spawn yearly whereas anadromous females skip 1 to 3 years between spawnings. In females near spawning, ovary weight as a percentage of body weight ranges considerably from 20% in Windermere charr to only 10–13% in Nauyuk Lake charr (Johnson 1980). Once eggs are released and fertilized, the female buries the eggs in the gravel to a depth of 100–200 mm. Depending on water temperature, eggs remain in redds for 60 to 230 days. In Char Lake, eggs laid in September hatched in late March or early April after incubating at water temperatures of between 0.75 and 1.5 °C. The time to hatch of fall-spawning Windermere charr, held experimentally, decreased from 97 days at 4 °C to 36 days when incubated at 12 °C. Egg mortality increased above 7–8 °C and was extremely high at 14 °C. Egg mortality of artiﬁcially incubated wild Arctic charr from Grundlsee, Austria, was lowest between temperatures of 3–8 °C, with rapidly increasing mortality at higher temperatures (Nilsson 1992b).

Behavior: aggression, shoaling, and inter-species competition In the wild, Arctic charr alevins and fry are difﬁcult to ﬁnd after leaving the redd. They are rarely seen and never in schools, suggesting that they disperse widely in the rocks and debris of the shallow water areas (Johnson 1980). A few individuals have been observed in shallow littoral waters, sometimes in very open and exposed environments. Resident Arctic charr alevins studied in stream enclosures and aquarium tanks showed an almost total lack of aggressiveness and behavior patterns indicating the defense of territory. They stayed close to the bottom, hiding in gravel and resting on their pectoral ﬁns. Feeding alevins sometimes held station, darting to food then returning, but they often moved about the general feeding area with no indication of territory (Johnson 1980). I have noted that newly hatched anadromous Nauyuk Arctic charr alevins, held at low density in aquariums with gravel bottoms and fed with abundant food, displayed similar behavior: hiding in gravel, then darting at food, then returning to cover. However, once feeding was well established and the ﬁsh had left the gravel substrate, the alevins showed tremendous aggressive behavior to one another, often nipping and chasing others before darting at food. This behavior persisted throughout the fry stage but declined when ﬁsh reached a size of about 30 g. Noakes (1980), working with aquarium-held resident Arctic charr (Batsvatn Lake, Norway), suggested that under natural conditions and at low densities, juvenile Arctic charr (7 cm in length, one year old, 1–2 g) exhibit territorial behavior. He noted essentially linear dominance, with the larger ﬁsh most dominant, holding larger territories at the upstream end of the research tanks nearest to the source of food, and the smaller ﬁsh least dominant. Aggressive interactions were frequent and straightforward, consisting of persistent chasing and attempted nips by the aggressor. Dominance was persistent and unending, with smallest ﬁsh sometimes harassed to death. Access to food resources appeared to be the primary issue. These aggressive interactions were initiated when ﬁsh approached within the personal space (2 to 3 body lengths) of one another and occurred in territorial and non-territorial encounters. Another study showed differences in aggressiveness between hatchery-reared and wild Arctic charr. To study the effects of hatchery rearing on charr destined for sea ranching or restocking, researchers in northern Norway took a group of hatchery-reared ﬁrst generation

34

Arctic Charr Aquaculture

Arctic charr whose wild parents came from Mokkeland Lake, and compared them to a group of wild-caught charr of the same age and parental stock. When reared in their own groups, the wild charr showed evidence of aggressive interactions, caudal ﬁn damage, and considerable mortality. The hatchery-reared ﬁsh displayed little evidence of ﬁn damage and only low mortality. When the two groups were held together, the hatchery-reared charr had the most extensive caudal ﬁn damage and showed weight loss and decreases in condition as well as higher mortality rates (Siikavuopio et al. 1996). A number of incidental accounts suggest that larger juvenile and adult Arctic charr in the wild tend to draw together into shoals and schools. Kerry Finley often noticed schools of similar-sized anadromous Arctic charr cruising in the littoral marine waters of Creswell Bay in the Canadian High Arctic. The capture of many same-sized charr in scientiﬁc gill-nets set in the same location by other researchers supported his observations (Johnson 1980). Researchers working with anadromous Labrador Arctic charr noted that most populations of Arctic charr, migrating both downstream and upstream, show little overlap in the timing of adult and juvenile migration, suggesting each group maintains an independent existence at sea, possibly moving in distinct groups or schools (Dempson & Kristofferson 1987). Alevin and fry resident charr from two lakes in Norway were lone benthic feeders, then switched to open-water pelagic feeding. This shift in feeding behavior from the bottom to the open water column coincided with a shift to a silvery sided body color and a tendency to school. Nauyuk Arctic charr held in ponds tend to loosely shoal rather than tightly school, with ﬁsh of different sizes (0.5–5 kg) interspersed. Interestingly, fry and ﬁngerlings naturally produced in these ponds do not school, remaining camouﬂaged in the littoral zone away from the larger ﬁsh, undoubtedly in response to the cannibalistic nature of larger Arctic charr. Arctic charr start expressing cannibalistic behavior at about 34 cm in length, and it occurs more frequently in those northern lakes where charr are the only ﬁsh present. In lakes such as Hazen Lake, the large morph of charr may depend on smaller charr as a major food resource (Reist et al. 1995). The importance and extent of cannibalism in Arctic charr populations are not well documented, however cannibalism occurs throughout the range of resident Arctic charr (Henricson & Nyman 1976; Johnson 1980; Fraser & Power 1984; Grifﬁths 1994).The incidence of cannibalism in the marine environment during the open-water season is not known. In pond-reared anadromous Nauyuk Arctic charr, I have noticed on numerous occasions larger charr (2–3 kg) in the process of swallowing smaller charr, always head ﬁrst. This behavior was more evident when ﬁsh had been off prepared rations for a number of days. In the extreme northern parts of Arctic charr habitat, they are the only ﬁsh species present in the freshwater environment. As one moves farther south, the number of ﬁsh species occurring with Arctic charr increases dramatically. At Nauyuk Lake and elsewhere along the central Canadian Arctic coast, lake trout, lake whiteﬁsh, Arctic cisco (Coregonus autumnalis), least cisco (Coregonus sardinella), four-horned sculpin (Myoxocephalus quadrincornis), and nine-spined stickleback (Pungitius pungitius) occur together with Arctic charr in fresh water. In Sweden, 10 species of ﬁsh co-occur with resident Arctic charr in lake systems. Next to predators such as burbot (Lota lota) and pike (Esox lucius), brown trout, whiteﬁsh, and lake trout are the most important competitors with Arctic charr in lake environments. Arctic charr and brown trout live in uneasy co-existence in lake systems. In some lakes, brown trout are predators of Arctic charr; in others they are competitors for similar food resources. If Arctic charr and brown trout occupy separate lakes, they are both generalist

Wild Arctic Charr: Basic Attributes Important to Culture

35

feeders in the benthic and pelagic zones. When they occur together, they separate feeding habitats, with brown trout more littoral benthic feeders while Arctic charr feed in the pelagic, open-water zone. A number of researchers suggested that this segregation was detrimental to brown trout by pushing them to lower populations levels than would be found otherwise. In contrast, whiteﬁsh (Coregonus lavaretus), when introduced into Norwegian lakes containing Arctic charr, soon dominate the pelagic feeding zone and either drive Arctic charr to low numbers or eliminate them completely. In both cases, the mechanism is perhaps related to prey size and prey abundance. Fish planktivores can change zooplankton communities in lakes by selectively consuming the largest species of zooplankton to extinction, then moving to the next largest zooplankton, and on down the size chain. Whiteﬁsh are able to feed on smaller zooplankton than Arctic charr, so they can selectively graze zooplankton populations down to levels where Arctic charr can no longer feed efﬁciently. Just the opposite is true with brown trout. Arctic charr are able to feed more efﬁciently on smaller zooplankton than brown trout. In both scenarios, the preferred zooplankton falls below some threshold that cannot support predation by both competing ﬁsh species (Wetzel 1975; Johnson 1980; Hirvonen et al. 2000). Lake trout appear to dominate Arctic charr where they co-exist, and in many lakes that should have Arctic charr, only lake trout occur. In the Nauyuk Lake region, the only lakes that support an abundance of both species are those where anadromous Arctic charr stocks occur, thus giving the charr a feeding habitat not occupied by the lake trout. In the seaward rivers of the Labrador coast, anadromous Arctic charr occur with brook trout and Atlantic salmon. Farther to the west along both coasts of Hudson Bay, Arctic charr overlap in range with brook charr. In both regions, with increased latitude, Arctic charr dominate the river ﬁsh fauna. A similar situation is noted with altitude in rivers of northern Norway, where Atlantic salmon occupy the lower richer reaches, brown trout the middle elevation, and Arctic charr the coldest, most impoverished headwaters. Young Arctic charr, Atlantic salmon, and brown trout occurring sympatrically in northern Norwegian rivers selected different habitats, with Arctic charr occupying areas of lowest water velocity and shallower depth than the other two species (Heggberget 1984).

Food habits Arctic charr feed on a broad range of food types depending on season, food availability, and level of competition with other individuals and other species. They are generalist carnivores, eating all that is available in habitats that often have limited prey diversity and abundance (Johnson 1980). Resident Arctic charr feed throughout the year, primarily on littoral benthic macroinvertebrates, pelagic zooplankton, and terrestrial insects swept into the water or alighting on the surface. Morphs occasionally eat each other or other ﬁsh, and this is affected by the season and by ﬁsh size. Windermere charr feed on chironimid pupae and larvae during the spring and then switch to planktonic foods and crustacea, such as Daphnia spp, during late spring, fall, and early winter. In late winter they eat charr eggs, chironimid larva and pupae. Much the same pattern is found in the resident charr of Canada (Johnson 1980), the Scottish lochs (Maitland et al. 1984), and Scandinavian lakes (Hammar 1984). In all areas where different-sized morphs occur (or where other species of ﬁsh occur sympatrically),

36

Arctic Charr Aquaculture

there is segregation in the use of food resources, with larger Arctic charr consuming larger prey-eating benthic macroinvertebrates and also consuming other species of ﬁsh or, in cannibalistic fashion, their smaller brethren. One of the striking differences between anadromous and resident Arctic charr is the large size attained by anadromous charr in such a short period of feeding. The preferred diet in the sea seems to be invertebrates, particularly amphipods, mysids, and molluscs, but in some regions ﬁsh are more predominant in their diet (Johnson 1980). Large anadromous charr from the Canadian eastern Arctic consumed 34 different invertebrate and vertebrate species, with the most frequent items consisting of amphipods and mysids. They consumed few ﬁsh and virtually no benthic invertebrates. In contrast, the stomachs of Nauyuk Lake charr migrating back to fresh water contained no invertebrates – only capelin (Mallotus villosus), sand lance (Ammodytes spp), and small Greenland and saffron cod. Anadromous Svalbard charr consumed a diet of ﬁsh, notably capelin, sculpins, snailﬁsh (Liparis spp), and various invertebrates. Summing up the food requirements for this species, Scott and Crossman (1973) noted: ‘Arctic charr seem able to utilize for food any smaller creature that appears in their habitat.’ This basic understanding of wild attributes should help in understanding some of the basic rearing requirements discussed in the next chapter. Wild Arctic charr of certain stocks, particularly the anadromous forms, are well suited in body shape, ﬂesh color, and size to be raised as food destined to high-end consumers. They are a ﬁsh of fresh water, and even anadromous forms only tolerate sea water for part of each year. Arctic charr school naturally, a trait of importance in the culture environment, but are highly cannibalistic, so must be sorted by size. They tolerate a wide range of temperatures found in many northern countries, but generally prefer waters with a mean temperature below about 15 °C. They are a rather docile species and are out-competed by other salmonids, so are less likely a threat to wild populations should they escape captivity. Arctic charr consume a wide variety of foods in the wild, which makes them readily adaptable to prepared diets made of a variety of ingredients. They respond to extremes of light and dark and grow best in a rearing environment that reﬂects their northern Arctic wilds.

Chapter 3

The Rearing Environment: Chemical, Physical, and Biological

The rearing environment for Arctic charr is based on the biology of the wild ﬁsh and the habitat conditions found in its northern environment. You cannot take Arctic charr beyond their physiological and biological limits, which are set down in the natural environment. In growing Arctic charr, a ﬁsh culturist’s objective is to maintain optimum ﬁsh health and growth by controlling and monitoring the chemical, physical, and biological quality of the ﬁsh’s rearing environment. concentration of chemicals such as oxygen (O ), ammonia (NH ), and carbon dioxide • The (CO ) must remain within a narrow range in the rearing water or the ﬁsh will perish. Physical include water temperature, ﬁsh density, and changes in daily light • intensity parameters and duration. Water temperature strongly affects Arctic charr growth. During 2

3

2

•

certain phases of their development, Arctic charr will die if the water temperature goes over 10 °C; at other ages they can tolerate a much wider range of temperatures, from 0 to 18 °C. The density of ﬁsh in rearing tanks contributes to the amount of stress they experience, while light cycles affect reproductive development and growth. Complex interactions take place between biological factors such as the ﬁsh’s physiology, disease, disease-causing organisms, and the chemical and physical environment.

Fish culturists must take all elements into account to ensure ﬁsh health and vigour.

Water: the environment of Arctic charr Water is to ﬁsh as air and earth are to humankind. It is both the physical environment and the medium for breathing, communicating, and feeding. In terms of the physical environment for Arctic charr, tank shape, water depth, and current speed are secondary to the ﬂow of water through the ﬁsh-rearing system. A number of water ﬂow systems are used in Arctic charr culture, ranging from single-pass use of water to recirculation of over 90% of the incoming water (see Fig. 3.1). Single-pass use of water is the least complex and easiest to manage as water ﬂows through the tank environment once, then leaves the facility and returns to wild waters. Stocking pothole lakes with low densities of Arctic charr is another simple water ﬂow system used commonly in the Yukon, Sweden,

38

Arctic Charr Aquaculture

Fig. 3.1 The ﬂow of water through an intensive single-pass or recirculation tank system.

and Norway. Recirculation involves pumping water back through the tank system after it has been mechanically and biologically rejuvenated. Water moves in a predictable fashion through a culture facility, ﬂowing from an incoming source, through the rearing environment, then through remediation and back to the wild.

Incoming source water This is the water from the wild. Depending on its source, quantity, and chemical makeup, the incoming water may be suitable for all stages of Arctic charr growth or restricted to supporting only certain aspects of the life cycle. Generally, early rearing and hatchery production require the highest quality fresh water in the form of ground water from springs or wells. Surface waters from creeks or rivers may be suitable for early rearing, but water that wild ﬁsh inhabit poses problems due to the potential transfer of disease-causing organisms. As well, the temperature of surface water is less constant, and temperature ﬂuctuations may be detri-

The Rearing Environment: Chemical, Physical, and Biological

39

mental to the health and growth of the cultured stock. Surface water is ﬁne for on-growing ﬁsh once they are past the ﬁngerling phase of development. Sea water and brackish water are also suitable for on-growing Arctic charr, although there are severe limits to their seawater tolerance, particularly during winter. Each type of incoming water presents unique problems. Ground water is characteristically low in oxygen and high in nitrogen. Surface waters, though usually well oxygenated, may warm to intolerable temperatures during summer. There may be too high a concentration of certain minerals, or pH may be too low. Before using an incoming source of water for culturing charr, you should measure the chemical and physical water quality parameters and make sure they fall within the ranges listed in Table 3.1. If any of the parameters have values outside tolerable limits, then you can either test the source water further, using a sample of Arctic charr under controlled conditions to determine toxicity, or abandon it as a potential incoming water source.

Rearing water Water quality in the rearing tank (tanks, net-pens, or pothole lakes) is affected by: water quality, • incoming the length of time the water stays in the tank (residence time), • feeding regimes, • time of day, and • the biomass or density of charr held. • Water quality in the tank is altered directly by ﬁsh through their consumption of oxygen and their excretion of carbon dioxide, fecal matter, and nitrogenous wastes. It is further altered by the presence of waste feed and dead and dying ﬁsh, the growth of organic matter, and the naturally occurring cyclic changes in tank water temperature. You can maintain chemical parameters within the desired ranges in the tank pens by regulating incoming water ﬂow rates and by rapidly removing ﬁsh wastes and feed. Tank shape and water residence time affect water quality. The longer water remains in an enclosed rearing environment, the greater the level of deterioration, so the tank must be designed to allow rapid passage of all the water through the tank. If inﬂow water is in short supply or requires expensive heating or cooling to meet proper ﬁsh-rearing temperatures, then you can clean rearing water and recirculate it to the tanks. Cleaning involves mechanical ﬁlters that remove solids, biological ﬁlters that break down dissolved wastes, and aerators that re-stabilize oxygen and carbon dioxide levels. Recirculation systems are expensive and require a sophisticated knowledge of operating mechanical ﬁltration equipment and biological ﬁlter systems, but they may be economically viable with Arctic charr. It is important to keep various water quality parameters within Arctic charr tolerance ranges, but this can be a challenge given the high rearing densities used in intensive culture of this ﬁsh. There are times when you can push the parameters into range by various physical, biological, or mechanical techniques – such as aeration to increase oxygen concentration or gas stripping to remove nitrogen. Rarely can you push the ﬁsh to accept conditions outside their biological range without slowing growth or affecting health.

40

Arctic Charr Aquaculture

Table 3.1 Water quality standards for the culture of Arctic charr. Data source: Boyd 1979; Piper et al. 1982; Daily & Economon 1983; Sigma Consultants 1983. Parameter

Standard (mg/L)

Alkalinity (as CaCO3) Aluminum (Al) Ammonia-N (NH3 + NH4) Ammonia (NH3) Arsenic (As) Barium (Ba) Cadmium (Cd) Calcium (Ca) Carbon dioxide (CO2) Chlorine (Cl) Chromium (Cr) Copper (Cu) Fluorine (F) Hardness (as CaCO3) Hydrogen cyanide (HCN) Hydrogen sulﬁde (H2S) Iron (Fe) Lead (Pb) Magnesium (Mg) Manganese (Mn) Mercury (Hg) Nickel (Ni) Nitrate (NO3) Nitrite (NO2) Nitrogen (N2) Oxygen (O2)

20–400 < 0.01 < 2.0 < 0.015 < 0.05 < 5.0 < 0.004 20–160 < 5.0 < 0.003 < 0.03 < 0.006 < 0.5 20–400 < 0.005 < 0.002 < 0.1 < 0.02 < 15.0 < 0.01 < 0.0002 < 0.01 < 1.0 < 0.015 < 103% saturation < 6.5

Ozone (O3) pH Polychlorinated biphenyls (PCB) Potassium (K) Rearing density Salinity

< 0.005 6.5–8.5 < 0.002 < 5.0 40–60 kg ﬁsh/m3 < 7 ppt

Selenium (Se) Silver (Ag) Sodium (Na) Sulfur (S) Sulfate (SO4) Temperature Total dissolved solids (TDS) Total suspended solids (TSS) Uranium (U) Vanadium (V) Zinc (Zn) Zirconium (Z)

< 0.01 < 0.003 < 75.0 < 1.0 < 50.0 < 15 (°C) < 400 < 80 < 0.1 < 0.1 < 0.005 < 0.1

Exceptions to standard

< 0.005 in hard water

< 0.003 in hard water < 10.0 in hard water

< 0.03 in hard water Considered hard water if > 100

< 0.1 in hard water < 107% in larger ﬁsh (> 100 g) Maintain 65% of saturation level. 70% with alevins and fry

130–170 kg/m3 for optimal growth Seawater growing not recommended in winter months

< 15 mg/L above background levels

Outﬂow water Water is a resource that is only borrowed in aquaculture, and outﬂow water from a rearing facility must be returned to the wild in good condition with minimum alteration. Water used for rearing Arctic charr in pothole lakes or net-pens may be of sufﬁcient quality that it can

The Rearing Environment: Chemical, Physical, and Biological

41

be returned to the wild without treatment, but if it has used for rearing Arctic charr under intensive conditions, it will require remediation. It is easy to forget about the quality of water after it leaves the commercial or research facility and returns to the wild. There are too many examples in commercial aquaculture of little thought given to downstream users, which is reﬂected in a growing public opposition to salmonid aquaculture. The grower has an ethical and moral obligation to the wilds and to local communities to manage operations with a high standard of environmental care, particularly regarding the outﬂow water quality. Outﬂow water must support diversity and abundance of life at a level that would occur in the natural system if the facility had not been located there. If meeting this standard of care requires expensive remedial treatment systems to improve water quality, then this should be built into the production costs during the planning stages of the project. Meeting downstream water quality requirements is not an add-on cost after production starts. It is an integral part of the water system. Given the newness of Arctic charr culture, there is an opportunity to avoid the mistakes of other forms of commercial aquaculture and take a more positive approach to outﬂow water quality. It is also possible to enhance the biological productivity of wild systems by adding certain nutrients to outﬂow water that are waste products of aquaculture. However, this approach requires the involvement of the local community and specialists in aquatic ecosystems beforehand. Water quality changes as it ﬂows through the culture system, under different feeding regimes, and at different times of the day and year. Water quality for most parameters remains relatively constant, but depending on the type of culture system employed, temperature, oxygen, ammonia, and pH can change by the hour or day and should be measured at the inﬂow and outﬂow routinely, on a daily or weekly basis.

Chemical parameters of water quality Concentrations of speciﬁc dissolved and suspended chemical compounds, water-saturated gases, and pH must fall within a narrow range imposed by the natural biological requirements of Arctic charr. Failure of any one or a number of parameters to fall within that range may mean poor growth, increased levels of stress, or death to the ﬁsh. For example, if dissolved oxygen levels in rearing water fall below approximately 5 mg/L, then the charr grow poorly and are susceptible to disease; if levels of oxygen fall even lower, then all the ﬁsh die and it will not make a difference that all the other chemical parameters fell within normal range.

Oxygen Dissolved oxygen in water is vital; without a sufﬁcient, continuous supply, ﬁsh die rapidly. Oxygen is absorbed into the blood through simple diffusion as water passes over the gills of the ﬁsh (see Fig. 3.2). The venous blood ﬂows from the heart to the ventral aorta, passing through the gills in the opposite direction to the ﬂow of incoming water. This countercurrent ﬂow of water and blood is crucial. If the blood were ﬂowing in the same direction as the water, there would be no transfer of oxygen since the gradient in oxygen levels (O2 partial pressure gradient) between the water and blood would not be sufﬁciently different to allow for the needed gas exchange. If at some point this oxygen gradient is not steep enough to allow

42

Arctic Charr Aquaculture

Fig. 3.2 Fish gill showing countercurrent ﬂow of blood and oxygenated blood.

passive diffusion, then the ﬁsh is no longer able to meet its metabolic oxygen requirements. Fish culturists must understand how oxygen saturation levels affect the transfer of oxygen from water to ﬁsh when they are determining the ﬂow rates of water needed to meet the oxygen requirements of ﬁsh. The maximum concentration of dissolved oxygen (100% saturation) in the incoming fresh water depends on water temperature and atmospheric pressure. As water temperature rises, dissolved oxygen concentration decreases. Fresh water at 5 °C, saturated with oxygen, contains 12.7 mg/L, while the same water at 10 °C contains only 11.3 mg/L. Oxygen concentration in water decreases as elevation rises (due to decreasing atmospheric pressure). Fresh water saturated with oxygen at sea level contains 12.7 mg/L of water, but at an elevation of 1000 m, with lower atmospheric pressure, the concentration of oxygen in the same water

The Rearing Environment: Chemical, Physical, and Biological

43

decreases to 11.3 mg/L. From this relationship, one can see that at higher altitude and temperature the amount of oxygen available for ﬁsh is considerably less. The relationship between dissolved oxygen concentration and changes in temperature or atmospheric pressure are calculated with the aid of Rawson’s oxygen saturation nomogram (shown in Fig. 3.3). It allows the calculation of dissolved oxygen concentration at saturation for temperatures and atmospheric pressures in mg/L and gives the quantity of dissolved oxygen found at any saturation level. When dissolved oxygen levels in water fall below about 65–70% saturation, Arctic charr experience a loss in oxygen transfer efﬁciency from the water (i.e. the oxygen gradient is not steep enough). At levels much below this, Arctic charr are unable to transfer oxygen from the water to the blood. This means only about 30–35% of the oxygen in the water is available to the ﬁsh for respiration. The useable quantity of oxygen in each litre of water is the difference between its actual concentration and the concentration it would have at 65% saturation. For example, at a ﬁsh farm 1000 m above sea level (ASL), water (10 °C) saturated with oxygen contains 9.9 mg/L. If oxygen levels at the tank outﬂow are maintained at 70% saturation (6.9 mg/L), the ﬁsh have 3 mg of oxygen available to them in each litre of water. At higher temperatures, the amount of oxygen available for respiration in each litre of the same water is reduced (see Table 3.2). In addition to understanding the effects of temperature and saturation on the available dissolved oxygen, different ﬁsh activities affect the amount of oxygen consumed. The rate at which Arctic charr consume oxygen is affected by ﬁsh activity, feed consumption, water temperature, and ﬁsh size. When calculating oxygen requirements of Arctic charr, account for the most extreme effect that these different parameters have on oxygen consumption. For instance, the daily average oxygen consumption rate may be 150 mg/kg h–1, but just after a heavy meal oxygen consumption may increase by 20–25% for a few hours. Fish activity and oxygen consumption Any husbandry activity that increases swimming speed must take into account the increased requirements for oxygen. At complete rest, a condition that rarely occurs with Arctic charr, the basal metabolic rate is about 80 mg O2/kg ﬁsh h–1 (based on 100 g Nauyuk Arctic charr in 15 °C water). This is considerably higher than the 46.4 mg and 57.4 mg /kg h–1 calculated for lake trout and brook trout respectively (Beamish 1980). Once in motion, an Arctic charr’s rate of oxygen consumption increases exponentially, and during high speed or burst swimming it can be 7 to 8 times the basal metabolic rate (see Fig. 3.4). Burst swimming can only be maintained for seconds and is used to avoid a predator (for example, the dip-net thrust into the tank) or to pounce on prey. Depending on ﬁsh size and feeding level, at normal sustained swimming speeds Arctic charr’s oxygen consumption rates are in the order of 110 mg to 180 mg/kg h–1. If you relate this to the available oxygen in water shown in Table 3.2, you can see that a litre of well-oxygenated water does not go far in supplying the needs of even a 1 kg ﬁsh. Food intake and oxygen consumption The rate of oxygen consumption in salmonids increases steeply after food intake, peaking

44 Arctic Charr Aquaculture

Fig. 3.3 Calculation of oxygen concentration by temperature and elevation using Rawson’s nomogram. Reprinted with permission, from Piper et al. 1982.

The Rearing Environment: Chemical, Physical, and Biological

45

Table 3.2 Available oxygen (mg/L) to ﬁsh at different water temperatures and elevations while maintaining 70% saturation. Water temp. (°C)

Oxygen concentration (mg/L) 1000 m ASL

0 5 10 15

Sea level

Incoming water*

Outﬂow water†

Available O2

Incoming water*

Outﬂow water†

Available O2

12.9 11.3 9.9 8.9

9.0 7.9 6.9 6.2

3.9 3.4 3.0 2.7

14.6 12.8 11.3 10.1

10.2 9.0 7.9 7.1

4.4 3.8 3.4 3.0

*100% saturated H2O; †70% saturated H2O

Fig. 3.4

Effect of swimming speed on oxygen consumption by Arctic charr. Modiﬁed from Beamish 1980.

at 2 to 3 times the pre-feeding level. This peak usually occurs a few hours after the end of a meal, and then oxygen consumption gradually declines to pre-feed levels. More oxygen is consumed to accommodate the energy requirements for digestion, absorption of nutrients across the gut wall, storage of nutrients, amino acid breakdown, synthesis of excretory products, biosynthesis of tissue components, protein synthesis, and lipid synthesis (Jobling 1994). Arctic charr show a signiﬁcant positive correlation between oxygen consumption and the size of the daily ration fed (see Fig. 3.5). Oxygen consumption averaged 170 mg/kg h–1 in Hammerfest Arctic charr (30–110 g size) fed continuously (Christiansen et al. 1991b).

46

Arctic Charr Aquaculture

Similarly, Hammerfest Arctic charr of 32–65 g, fed to satiation and deprived of feed the day of measurement, averaged 181.9 mg/kg h–1 (Jørgensen et al. 1991). At low ration levels, O2 consumption ranged from 90 to 120 mg/kg h–1, while at high feed ration levels, consumption rates were almost double. For Arctic charr in the size range of 50–100 g, the relationship between oxygen consumption and meal size is described by the equation: Oxygen consumption = 7.77x + 108.3 where O2 consumption is in mg/kg ﬁsh h–1 and x is daily feed ration in mg/g ﬁsh d–1 (Jørgensen et al. 1993). Water temperature and daily patterns of oxygen consumption Increasing water temperature increases Arctic charr’s metabolic consumption of oxygen (see Fig. 3.6). The oxygen consumption rates of 7–14 g Lake Inari Arctic charr were measured at three temperatures between 11 °C and 18 °C, at different activity levels. The maximum oxygen consumption rates recorded at 11 °C and 17.7 °C were 210 mg and 290 mg/kg h–1 respectively. These charr also showed a rhythmic daily pattern in oxygen consumption that peaked during the daylight hours just after feeding ceased, and declined to lowest levels in the early morning hours. This pattern, which ranged from 37 mg to 45 mg/kg h–1, occurred at all temperatures at which the Lake Inari Arctic charr were held (Lyytikäinen & Jobling 1998). The same researchers noted that when water temperature was increased suddenly, the oxygen consumption rates increased rapidly, then declined to a lower, stable level after 3 to 4

Fig. 3.5 Effect of feed ration size on oxygen consumption by Arctic charr. Reprinted with permission from Elsevier Science: Jørgensen et al. 1993.

The Rearing Environment: Chemical, Physical, and Biological

47

days. This stable level was still higher than the consumption rate at the initial lower temperature (see Fig. 3.7). When water temperature changes rapidly, this temporary overshooting in oxygen demand must be accounted for in the supply of oxygen to the ﬁsh, as well as the longterm oxygen requirements at the higher temperature.

Fig. 3.6 Daily patterns in oxygen consumption of Arctic charr at different temperatures. Modiﬁed with permission from Lyytakäinen & Jobling 1998.

Fig. 3.7 Effect of rapid temperature change on oxygen consumption by Arctic charr. Modiﬁed with permission from Lyytakäinen & Jobling 1998.

48

Arctic Charr Aquaculture

Fish size and oxygen consumption Small Arctic charr consume more oxygenthan larger individuals on a per unit of body weight basis. For example, a tank containing 1000 kg of 100 g charr (10 000 ﬁsh) would require oxygen levels in the order of 170 mg/kg h–1. The same biomass composed of 1000 g ﬁsh (1000 ﬁsh) would require only 144 mg/kg h–1. Oxygen consumption per unit weight declines as ﬁsh weight increases because of changes in metabolic activity and in the relative sizes of different body organs. As a ﬁsh grows, the relative size of metabolically active tissues such as the gut and liver decline in proportion to body weight, and there is evidence that the metabolic activity of the different organs also declines as ﬁsh grow and age (Jobling 1994).

Carbon dioxide The effects of carbon dioxide (CO2) on Arctic charr are not well studied, but they are likely affected in similar fashion to other salmonids. Excessive CO2 affects ﬁsh by lowering blood pH and reducing the O2-binding afﬁnity of hemoglobin (Bohr and Root effects), thus interfering with the blood’s ability to carry oxygen. High CO2 levels can also increase the toxicity of ammonia. Although rainbow trout and Atlantic salmon are capable of tolerating levels over 20 mg/L, there is evidence that Atlantic salmon suffer narcosis in poorly buffered, low pH water when CO2 levels rise above 15 mg/L. In water with higher pH and higher alkalinities (30–60 mg/L), problems with CO2 do not occur until levels of 25 mg/L are reached. Carbon dioxide is present in tank water due to the following reasons: Most CO is the product of ﬁsh respiration. • Occasionally water, particularly from wells and springs, contains high levels of • dissolved CO source . Recirculating water • high CO levels. systems with inadequate degassing columns can also be a source of 2

2

2

The presence of CO2 in the water is not in itself a problem if the water is degassed by exposure to atmospheric air in a degassing/aeration column. Thus spring and well water containing high levels of CO2 do not need to be disqualiﬁed as sources of water for use in charr aquaculture, as it can be removed easily through vigorous degassing/aeration of the water. The design of water recirculation systems must take into account the removal of CO2 from the water before its return to the ﬁsh tank. As well, when you are moving live ﬁsh in sealed containers, be aware that CO2 levels can rapidly climb to over 30 mg/L, which causes a depression in the ﬁsh’s blood oxygen capacity to the point where even concentrated levels of O2 cannot prevent suffocation (Wedemeyer 1996). In Arctic charr culture, recommended levels of CO2 in water are less than10 mg/L at alkalinities lower than 100 mg/L and less than 15 mg/L at higher alkalinities. Calculations can be based on the following formula, which demonstrates the amount of CO2 produced by ﬁsh respiration, based on the amount of O2 consumed. Total CO2 (mg/kg h–1) = 1.238 × oxygen consumption (mg/kg h–1) (Pennell & McLean 1996).

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Total gas pressure and gas supersaturation Total gas pressure is the sum of all the partial pressures of dissolved gases in water. The primary gases are nitrogen (N2) and oxygen (O2). At atmospheric equilibrium (100% saturation), fresh water at sea level contains about 14 mg to 24 mg/L of N2 and 10 mg to 12 mg/L of oxygen, levels amenable to healthy ﬁsh growing well. In the event of air being forced or entrained into water under pressure, or due to heating, the water becomes supersaturated with nitrogen gas; the water now holds more gas in solution than it would normally at atmospheric pressure. Heated water or water from deep wells, artesian wells, and springs are potential sources of supersaturation. Other common sources of supersaturated water are leaky pumps or water lines that allow entry of air, or partially submerged intake lines (Daily & Economon 1983). The ﬁsh breathe in this supersaturated gas mixture, and as the supersaturated gases are re-exposed to atmospheric pressure, whether in the rearing water or internally in the ﬁsh, the excess gas, usually nitrogen, comes out of solution in the form of tiny bubbles. In the ﬁsh, these tiny bubbles lead to gas bubble trauma, a condition not unlike ‘the bends’ that sometimes afﬂict deep-sea divers. Fish suffering from gas bubble trauma may develop bubbles under skin, eyes, gills, in the mouth region, in liver tissue, and in blood vessels. The condition is disﬁguring and often leads to death if exposure is prolonged (Avault 1996). The ugliest brood of Arctic charr I have ever seen had severe symptoms of gas bubble trauma, characterized by protruding pop eyes, swollen jaws, and distorted ﬁns. You can measure the amount of excess gas pressure in water using a saturometer or tensionometer. The percent of supersaturation (TGP%) is calculated by ﬁnding the difference between total gas pressure (TGP) in the water and barometric air pressure (BP). TGP% = [(ΔP + BP)/BP] × 100 where ΔP = TGP – BP (in mmHg) (Pennell & McLean 1996). The safest level for Arctic charr at any age is, of course, no supersaturation, but TGP% of 103% is tolerable, and in water sufﬁciently saturated with O2, ﬁsh can tolerate TGP% levels as high as 107%. Salmonid alevins and fry are the most sensitive to gas bubble trauma, even at TGP levels as low as 103%. Fish in deep water (more than 2 m) are less affected by supersaturated water than ﬁsh in shallow water tanks or near the surface. Aeration of incoming water effectively removes excess gas supersaturation from the water. Aerate water that has been heated before it enters ﬁsh tanks, and inspect any water lines that are under pressure for leaks. Wherever water is leaking from a pressurized line or a gravity feed line, air is entering the water in the line and is a potential source of gas supersaturation.

pH One of the central parameters for the proper functioning of ﬁsh metabolism (such as oxygen uptake, acid–base regulation, and ion regulation) is pH balance. pH is a measure of the number of hydrogen ions (H+) found in solutions and is measured on a logarithmic scale of 1 to 14 based on: pH = – log [H+]

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Water with a pH lower than 7 has many H+ ions and is acidic, whereas water with pH levels between 8 and 14 has fewer H+ ions and is alkaline. A pH measure of 7 is neutral. There is no alkalinity or buffering capacity in water with a pH less than 4.5, and no acidity in water with a pH greater than 8.3. For proper metabolism, a ﬁsh’s blood pH must be within narrow tolerance limits dictated by the pH of the surrounding water. Salmonids will die at pH below 4 or above 11. When the pH levels are low, a condition called acidosis develops. It reduces the blood’s overall capacity to transport oxygen to tissues. On the other end, in waters of high pH, alkalosis threatens the ﬁsh (Willoughby 1999). In addition to the physiological complications posed by extreme pH levels, there are complications involving the toxicity of many substances. At low pH, many trace metals are more soluble in water and thus more toxic. In the case of ammonia (NH3), toxicity increases with high pH, whereas nitrite (NO2) becomes less toxic at high pH. Salmonids in general are sensitive to changes in water pH, but Arctic charr may be less sensitive than other salmonids. Although salmonids can tolerate pH within the range of 5 to 9, maximum productivity occurs at pH ranging from 6.5 to 8.5 (Jobling 1994).

Ammonia-N Ammonia-N, an alkaline compound of nitrogen and hydrogen, is the principal excretory product of ﬁsh. When ammonia-N is excreted by ﬁsh, it dissolves in water and undergoes some reactions to form ammonium ions. Total ammonia in water (ammonia-N) consists of two forms: un-ionized ammonia (NH3) and ionized ammonium (NH4+). In general, ammonia (NH3) is the more toxic form to ﬁsh. The two forms can reach equilibrium in water depending on the pH, temperature, and total amount of ammonia-N present, as demonstrated by the following equation: NH3 + H2O ⇔ NH4+ + OH– Under natural conditions, very little ammonia-N (less than 0.2 mg/L) is present in wild waters. Any amount that does exist is rapidly assimilated by plants or denitriﬁed by bacteria, posing no threat to ﬁsh health. However, in an aquaculture setting with high ﬁsh density, heavy feed rations, and protein-rich diets, ammonia-N and its by-products become a concern to ﬁsh health. The concentration of ammonia-N in rearing water is generally the by-product of biological processes associated with ﬁsh metabolism. When protein is used as an energy source for ﬁsh metabolism, only the carbon chains of the amino acids making up the protein are consumed, leaving the nitrogen fraction of the amino acid as a waste product. Ammonia-N is excreted through the gills, with small amounts also disposed of in urine. Ammonia-N is also produced from the biological degradation of protein in waste feed and ﬁsh feces. Under certain conditions, ammonia (NH3) is toxic to Arctic charr as it readily diffuses back into the ﬁshes’ biological membranes due to its lack of charge and small molecular size. When the concentration of ammonia rises in the rearing water, the diffusion gradient (the difference in ammonia concentration between the water and blood) across the gills decreases, which slows the rate of excretion and elevates blood ammonia levels. Acute toxicity manifests itself as hyperventilation, erratic swimming, convulsions, and ﬁnally death. More commonly,

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chronic long-term exposure to low levels leads to gill hyperplasia, kidney dysfunction, and liver damage (Jobling 1994). Effect of pH and temperature on ammonia toxicity Ammonia-N toxicity is strongly affected by water pH and, to a lesser extent, by temperature, CO2, and salinity. The toxicity of ammonia-N increases dramatically with increasing pH because more is disassociated to ammonia (NH3). For example, at pH 7.0, less than 1% of ammonia-N is NH3, but at pH 8.5, NH3 represents 9% of ammonia-N. Similarly, as temperature rises, the concentration of ammonia produced by Arctic charr also rises (see Fig. 3.8). The rate at which ﬁsh excrete ammonia-N depends on the size of the meal, the protein content of the food, and the water temperature. Arctic charr fed to satiation with commercial salmon feed (44.5% protein) produced signiﬁcantly more ammonia at high temperature (17.7 °C) than at low temperature (see Fig. 3.9). An average of 5.95 mg/kg h–1 of ammonia-N was produced at 11 °C, but the amount varied considerably over the course of the day, peaking 2 to 3 hours after the termination of feeding (Lyytikäinen & Jobling 1998). There is a near linear increase in excretion rates of ammonia-N with the size of ration fed. As a general rule of thumb, 35 g of ammonia-N is excreted per kg of commercial pelleted feed (40% protein) fed per day (Drouin 1999). Safe levels of ammonia We do not know the safe levels of ammonia-N and its two forms for raising Arctic charr speciﬁcally, although Arctic charr are purported to be more tolerant of high ammonia-N levels than other salmonids (Eriksson 1991). At NH3 levels of 0.0015 mg/L and pH of 7.9, Nauyuk Arctic charr (100–200 g) held in 5 °C water at densities of 150 kg/m3 showed normal growth and good health (Ricks 1991). Ammonia is by far more toxic to salmonids than ammonium, but new evidence suggests that in combination both may be toxic, particularly at low pH caused by elevated CO2 levels (Pennell & McLean 1996). In general, salmonid ova, alevins,

Fig. 3.8 The effect of pH and temperature on the concentration of un-ionized ammonia (NH3) and nitrite in rearing water. Reprinted with permission, from Pennell & McLean 1996.

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Arctic Charr Aquaculture

Fig. 3.9 The effect of temperature and time of day on ammonia-N excretion by Arctic charr. Modiﬁed with permission from: Lyytakäinen & Jobling 1998.

and fry are most sensitive to elevated ammonia levels. Lethal levels for Atlantic salmon are in the range of 0.2 to 0.5 mg/L (Willoughby 1999). For optimum Arctic charr health, ammonia levels in fresh water should not exceed 0.015 mg/L and ammonia-N levels should remain below 2.0 mg/L. If Arctic charr are held in sea water, where ammonia toxicity is about 30% less than in fresh water, safe levels can be raised accordingly. The percentage of un-ionized ammonia present in total ammonia-N changes with temperature and pH. When the total ammonia-N concentration is known, Table 3.3 can be used to calculate the amount of NH3 present at different temperatures and pH.

Table 3.3 Percentage of un-ionized ammonia (NH3) in total ammonia-N at various temperatures and pH. Source: Piper et al. 1982. pH

6.0 6.2 6.4 6.6 6.8 7.0 7.2 7.4 7.6 7.8 8.0 8.2 8.4 8.6

Temperature (°C) 2

4

6

8

10

12

14

0.0098 0.0155 0.0245 0.0389 0.0616 0.0977 0.155 0.245 0.388 0.613 0.968 1.53 2.40 3.75

0.0115 0.0183 0.0189 0.0459 0.0727 0.115 0.182 0.289 0.457 0.722 1.14 1.79 2.81 4.39

0.0136 0.0215 0.0340 0.0539 0.0855 0.135 0.214 0.339 0.537 0.848 1.34 2.10 3.29 5.12

0.0159 0.0252 0.0400 0.0633 0.100 0.159 0.252 0.398 0.629 0.994 1.57 2.46 3.84 5.96

0.0186 0.0295 0.0468 0.0741 0.117 0.186 0.294 0.466 0.736 1.16 1.83 2.87 4.47 6.91

0.0218 0.0345 0.0547 0.0866 0.137 0.217 0.344 0.544 0.859 1.36 2.13 3.34 5.19 7.98

0.0254 0.0402 0.0637 0.101 0.160 0.253 0.401 0.633 1.00 1.58 2.48 3.87 5.99 9.18

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Nitrite and nitrate Excreted ammonia-N is oxidized by bacteria in a process called nitriﬁcation. In this twostep process, ammonia-N is converted to nitrite (NO2–) and then nitrite is converted to nitrate (NO3–). Two genera of bacteria, both aerobic chemoautotrophs, are responsible for the speciﬁc steps of the process. Nitrosomas spp. oxidizes ammonia-N to nitrite, while Nitrobacter spp. oxidizes nitrite to nitrate. Both steps require an abundant supply of dissolved oxygen and a substrate surface for bacterial attachment and growth. Nitrobacter are of course dependent on Nitrosomas for a source of nitrite. Nitriﬁcation is one of the primary techniques for removing ammonia-N from a recirculation environment. In a ﬂow-through tank system, little nitriﬁcation takes place in the rearing water. However, the outﬂow water must be treated to reduce nitrite loadings prior to its return to the wild. Nitrite can be toxic to salmonids at relatively low concentrations. It reduces the oxygen transport capabilities of the blood by converting hemoglobin to methemoglobin, which cannot bind oxygen. Under certain circumstances in recirculation systems, particularly at high ammonia-N levels and high pH, which increases the proportion of ammonia (NH3) in solution, ammonia is oxidized to nitrite without moving to the next step. In this case, nitrite may build to toxic levels in tank water even though nitrite toxicity decreases with increasing pH (as shown in Fig. 3.8). Although some believe that Arctic charr can withstand higher levels of nitrite than other salmonids, this has not been assessed quantitatively. Safe levels for other salmonids are below 0.015 mg/L, but ﬁsh may tolerate higher levels (up to 0.10 mg/L) in harder waters (Pennell & McLean 1996).

Salinity, seawater tolerance, and smoltiﬁcation Anadromous Arctic charr are truly amphidromous, migrating from fresh water to the sea as a regular phase of their life cycle – not for breeding, but to feed on the rich food resources available in the marine environment. They do not have to go to sea for any physiological reasons, only to feed and explore new habitats. Moving back and forth between fresh water and salt water requires dramatic physiological adjustments. In fresh water, Arctic charr are living in an aqueous environment that is more dilute than their body ﬂuids. They are hyper-osmotic: water enters the body by osmosis, while ions passively leave through diffusion. To counter this, they excrete large amounts of dilute urine, while their gills actively absorb ions, mostly sodium (Na+) and chloride (Cl–). In contrast, in sea water Arctic charr are in an environment of greater concentration than their body ﬂuids. In this hypo-osmotic condition, they lose water and gain ions. They must compensate by reducing urine ﬂow, drinking sea water, and actively excreting ions through the gills. If they cannot counter the loss of water or the gain of ions, they dehydrate and die, which is the fate of most cultured Arctic charr forced to overwinter in sea water. Arctic charr are amphihaline, which means they have only a seasonal tolerance for sea water; they cannot go back and forth between fresh and saltwater habitats frequently. Like other salmonids, they must prepare for this seawater entry through a process of smoltiﬁcation, involving a number of morphological, physiological, behavioral, and biochemical changes.

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Increased tolerance for sea water (hypo-osmoregulatory ability) in salmonids is associated with a signiﬁcant increase in the number of chloride cells in the gills and in the production of the enzyme Na+,K+-ATPase. This enzyme is needed for the salt extrusion mechanism of the salmonid gill in sea water, and its presence in concentration is a good indicator of successful smoltiﬁcation. In numerous studies, conducted mostly by Norwegians, there is no doubt that hypo-osmoregulatory capacity is established in both cultured and wild anadromous Arctic charr prior to seawater entry, at least in charr held under natural light conditions (Arneson et al. 1992; Staurnes et al. 1992; Nilssen et al. 1997). Changes in daylight (photoperiod) appear to be the cue for initiating smoltiﬁcation in Arctic charr. Fish held under constant 24 hours of light (LDL group) had much poorer tolerance to, and higher mortality in, sea water (35 ppt salinity) than those exposed to normal seasonal light levels (NDL group). Only by acclimating the LDL group by holding it in brackish water (15–17 ppt salinity) for 3 weeks prior to seawater entry could its hypo-osmoregulatory abilities be improved. The LDL group, even though not exposed to natural light, showed an increased tolerance in early spring similar to that of the NDL group prior to the rapid increases in spring light levels, which suggests there may be an underlying endogenous annual rhythm in seawater tolerance, which is synchronized by changes in photoperiod (Arneson et al. 1992; Halvorsen et al. 1994). Changes in spring freshwater temperatures do not act as an important cue for smoltiﬁcation in Arctic charr. In comparing the smoltiﬁcation process of Atlantic salmon with Arctic charr, researchers at the University of Trondheim noted increased water temperature (under a constant 24-h light cycle) was enough to stimulate Atlantic salmon to smolt, but had no effect on Arctic charr, even when they were subjected to a rapid water temperature rise similar to naturally occurring spring conditions in northern Norwegian rivers. In the wild, Arctic charr start moving out to sea during spring break-up in May, when river water is still at 1.8 °C, while Atlantic salmon migrate seaward in June at much higher temperatures (Staurnes et al. 1994). During the fall and winter, cultured Arctic charr have a reduced tolerance for sea water; in a sense, they pass through a desmoltiﬁcation process (Finstad et al. 1989). This comes as no surprise given that all anadromous wild populations of Arctic charr return to fresh water in the fall. Seawater temperature is often cited as the cause of this intolerance, but wild Arctic charr do well in sea water at low and high temperatures (1–8 °C) during the summer months. Anadromous Svalbard Arctic charr, which returned to fresh water in the fall, still exhibited saltwater tolerance after 3 weeks in fresh water, so it is not a physical intolerance to sea water that drives them back to fresh water in the fall. Some researchers speculated that the cue to return to fresh water was light activated. Given that changes in photoperiod initiate seawater tolerance, it only makes sense that Arctic charr undergo desmoltiﬁcation using similar light level cues (Staurnes et al. 1994; Finstad et al. 1989). Body size also affects seawater tolerance in Arctic charr. When Arctic charr of 13–23 cm body length were exposed to sea water, the greatest mortality and lowest physiological adaptation was noted in the smallest ﬁsh. This trend was similar in cultured and wild Arctic charr. First-time migrants to sea water with a body length of 11–20 cm undergo some of the physiological changes associated with smoltiﬁcation, but they were not able to withstand exposure to full-salinity sea water (Arnesen 1994). In the wild, small Arctic charr stay close to river estuaries and may spend only a few days in sea water before returning to fresh water.

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Saltwater tolerance varies between different strains of charr, with the best tolerance of the Norwegian populations shown by anadromous Hammerfest charr (Barnung & Holm 1988). Anadromous charr from northern Norway, exposed to salt water just prior to developing spawning colors, showed impaired seawater tolerance compared to immature ﬁsh (Staurnes & Sigholt 1994). Arctic charr held in sea cages in northern Norway survived well during the summer months, but died by the thousands in the fall and winter (Gjedrem & Gunnes 1978). Resident Arctic charr show a much lower seawater tolerance (high mortality and low Na+,K+ATPase activity) than those from the anadromous populations (Staurnes et al. 1992). During the late spring and summer, both wild and cultured Arctic charr larger than about 150 g grow well in sea water, even at high salinities (Nilssen et al. 1997; Arnesen et al. 1994b). Although abrupt transfer from fresh water to sea water initially suppresses feeding and growth, appetite recovers readily and growth rates improve dramatically. Growth rates of anadromous Arctic charr held in salinities ranging from 10 to 35 ppt were as high as control ﬁsh held in fresh water. In wild anadromous Svalbard and Nauyuk Arctic charr, body growth was above empirical growth model predictions for Arctic charr held in fresh water, suggesting that charr do not suffer from osmotic problems during their seawater stay, at least during the summer months (Nilssen et al. 1997). However, growth rates and gross feed conversion efﬁciency of Arctic charr experimentally held in sea water during the winter months were signiﬁcantly lower than those of ﬁsh held in brackish water or fresh water (Arnesen et al. 1994a). Mortality rates and the percentage of ﬁsh not feeding were very high when Arctic charr have been held in sea water during winter. In summary, Arctic charr are not really a ﬁsh for saltwater culture, as they are not suited for year-round growth in full-strength sea water. Arctic charr under culture do not have to go to sea in the summer. During the summer months, larger Arctic charr can tolerate full-salinity sea water, but they display better gross feed conversion and growth at salinities of less than 15 ppt (Staurnes et al. 1994). Fish smaller than 15 cm or 135 g should not be held in sea water at any time of the year, although they can tolerate salinities up to 7 ppt for short periods of time. Arctic charr brood stock must leave salt water prior to reaching sexual maturity (Staurnes & Sigholt 1994).

Alkalinity and hardness Alkalinity is a measure of the availability of bases – primarily bicarbonates (HCO3), carbonates (CO32–), and hydroxides (OH–) – to neutralize acidity when acids such as carbonic acid (respiratory CO2) are added to water. Alkalinity is a measure of water’s capacity to resist changes in pH. Waters with high alkalinity tend to be more strongly buffered (more able to withstand changes in pH) than waters of low alkalinity. The total concentration of bases in water is expressed as mg/L equivalent calcium carbonate (CaCO3). Total alkalinity of natural waters may range from 5 mg/L to several hundred mg/L. Alkalinity of at least 15–20 mg/L is required to adequately buffer the pH drop resulting from respiratory excretion of carbon dioxide. Alkaline earths such as limestone (calcite) and dolomite are the principal sources of bases in fresh water (Boyd 1979). Total hardness is a measure of the divalent cations (alkaline earth) present in solution. For most waters, this usually represents only calcium (Ca2+) and magnesium (Mg2+) ions. In natural

56

Arctic Charr Aquaculture

waters, hardness levels affect productivity, with waters of about 100 mg/L hardness having better biological productivity than those with lower or higher concentrations (Boyd 1979). From the perspective of salmonid culture, the concentration of calcium ions in the measure of hardness is of most importance. Calcium reduces the deleterious impact of low pH, high nitrite, and metals such as copper and zinc on ﬁsh health. For example, in a number of salmonid hatcheries in British Columbia, ﬁsh held in source waters with a hardness of more than 300 mg/L had no incidence of bacterial kidney disease (BKD), while in facilities with soft water (less than 10 mg/L), BKD was almost endemic. Increasing hardness levels from 18 mg to 90 mg/L reduced the incidence of coagulated yolk disease in steelhead trout alevins, a condition sometimes found in Arctic charr (Pennell & McLean 1996). Waters are classiﬁed as soft to very hard depending on the concentration of bases: mg/L – soft, • 0–60 61–120 – moderately hard, • 121–180mg/L mg/L hard, • over 180 mg/L –– very hard. •

Suspended solids Suspended solids, also referred to as turbidity, occur naturally in source waters usually consisting of ﬁne clays and silts, with concentrations varying from a few mg/L to thousands of mg/L. The level of suspended solids can be particularly high in surface waters during spring run-off or after heavy rains, reaching concentrations of over 100 000 mg/L (Piper et al. 1982). These high levels, if transitory, are of little concern to older Arctic charr, though feeding is impossible until the water clears. Eggs and alevins not yet off the bottom may be smothered as solids settle out. In culture water, suspended solids composed of waste feed and feces are of greater concern than silts and clays. Chronic exposure to low levels of suspended waste feed and feces may irritate gills and can precipitate bacterial gill disease, particularly in ﬁrst-feeding alevins and fry (Pennell & McLean 1996). Although Arctic charr tolerate high levels of natural turbidity, culture water must be clear enough to allow easy food acquisition and inspection of ﬁsh. Take particular care to keep suspended solids levels as low as possible in the rearing tanks containing alevins and fry. Suspended solids from waste feed and feces should not exceed 15 mg/L over the background levels present in inﬂow water.

Physical parameters of water quality Temperature Optimum temperatures for raising Arctic charr vary considerably by life stage, but in general are in the range of 6–15 °C. Optimum growth rates of ﬁngerling and juvenile Arctic charr plateau in the range of 13–18 °C, with an optimum at 14–15 °C (Swift 1965; Jobling et al. 1993; Larsson & Berglund 1998). Larger Arctic charr, when allowed to ﬁnd their own thermal environment in an extremely stratiﬁed seawater net-pen (salinity range 8–27 ppt), chose a

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very narrow range of temperatures over an 8-day period. They selected a mean temperature of 13.4 °C that did not vary with time of day, feeding, or any obvious patterns. Although temperatures ranged from 4 °C at the bottom to 18 °C at the surface of the 8-meter-deep pen, all of the charr remained in water at temperatures between 12 and 15 °C and salinities of 12–20 ppt (Sutterlin & Stevens 1992). The lower temperature limits for feeding are very near zero, with growth noted in cultured charr at 0.3 °C (Brännäs & Wiklund 1992). Indeed, larger wild Arctic charr grow well (more than 1%/day) in sea water at temperatures that hover between 0.5 and 4 °C. The upper temperature limit for feeding and growth is near 21.5 °C; water temperatures above 23 °C are lethal, depending on ﬁsh size and level of temperature acclimatization. Upper lethal limits in temperature are lower for the youngest Arctic charr. Alevins die at temperatures of 19.7 °C, about 2 °C lower than fry (21.8 °C) and 3 °C lower than ﬁngerlings (22.7 °C). At 19 °C growth rate declined markedly to 50% of the rate at 10–13 °C (Thyrel et al. 1999).Southern strains of Arctic charr are no more or less tolerant of high temperature than their more northerly cousins (Thyrel et al. 1999). Cold water in the range of 2–7 °C is a requirement for egg production and incubation of Arctic charr ova. Brood stock will reach maturity in water temperatures of 10–15 °C. However, if they are kept at these higher temperatures during the spawning period, viable egg production is very poor. For example, Nauyuk Arctic charr grow exceptionally well in Yukon pothole lakes at these higher temperature ranges, but at maturity produce very low-quality eggs, most likely because of the warm water during the August–September spawning period. Not far from these pothole lakes, brood stock held at Arctic Ova’s Yukon hatchery produce very good quality eggs in spring water at 4–6 °C. For good hatching success, ova require water temperatures in the range of 1–7 °C from a few weeks before fertilization to a few weeks after ova reach the eyed stage of development. Once ova are eyed, they respond well to water temperatures of 10–12 °C. Although alevins also respond well to temperatures above 10 °C, potential water quality problems with ammonia toxicity and suspended solids during ﬁrst feeding preclude the use of warmer water. Recommended temperatures Considering the high ﬁsh-loading densities used in Arctic charr culture and the profound effect that temperature has on oxygen content of water and on oxygen consumption, there are practical upper limits to production temperatures. Both oxygen consumption and ammonia excretion increase dramatically with temperature (Lyytikäinen & Jobling 1998). Oxygen consumption at 18 °C is more than twice that at 11 °C. In Swedish charr facilities, diseases such as furunculosis, BKD, and fungi show up when Arctic charr are held at temperatures above 15 °C (Glebe & Turner 1993). Similar problems occur with Nauyuk Arctic charr in the Yukon when water temperatures raise much above 15 °C. Culturists must closely monitor oxygen levels, feeding level, water ﬂow rates, and the presence of pathogens when holding charr at temperatures above 15 °C. There is a trade-off between faster growth at higher temperature and the lower risk of catastrophic loss at lower temperatures. Although water temperatures below 12 °C are not optimum for maximum growth, there are fewer water quality concerns and less chance of

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Arctic Charr Aquaculture

losing ﬁsh from diseases or oxygen depletion, particularly when ﬁsh are held at high loading densities. Indeed, food conversion rates are better at lower temperatures. Growth efﬁciency in Arctic charr, that is weight gain for food fed, is a maximum at 9 °C, then decreases linearly with increasing temperature (Uraiwan 1982). The optimum temperatures for growing Arctic charr vary with life stage as follows: (1) (2) (3) (4)

Brood stock – less than 7 °C one month prior to and during spawning. Incubating ova – less than 7 °C until well eyed, then less than 12 °C. Late incubation and ﬁrst feeding – less than 10 °C. Fry, ﬁngerlings, and grow-out charr – between 10 and 15 °C.

Light In the wild, Arctic charr experience great seasonal variation in light levels, from 24 hours of total light during the brief Arctic summer to the total lack of sunlight in the coldest, darkest months of winter. The daily rate of change in light levels during the spring and fall is also very dramatic in the polar regions. Change in photoperiod has a strong effect on smoltiﬁcation, on the timing of return to fresh water, on seasonal growth patterns, and on the initiation of spawning. Despite the importance of light, little rigorous research has been done with Arctic charr, although a great deal is known about photomanipulation of other salmonids (Clarke et al. 1996). The effect of photoperiod and light/dark cycles is one of the most exciting areas of exploration in Arctic charr culture techniques. I have developed some basic guidelines about photoperiod and Arctic charr based on casual observation. Intuitively one might think that since Arctic charr grow well in the long summer days of the north, they should grow well on constant long day length. This is not the case; light levels must change throughout the day to simulate a true northern summer or growth will decline. Even at summer’s peak in the High Arctic there is a daily change in the intensity of light. There is also a marked increase in Arctic charr feeding activity and growth during the rapid increase in spring light levels, and in the fall when light levels rapidly decline. Arctic charr brood stock kept on constant long day length or southern day length do not mature at the same time, as they should, but rather become asynchronous, with individuals spawning from fall to late spring. Arctic charr do perform reasonably well in terms of growth and reproductive potential if kept on a natural photoperiod that mimics light levels found north of the 60th parallel (shown in Fig. 3.10). Tanks or enclosures undergoing light manipulation must be sealed from other sources of light, even at levels of less than 0.05 Lux, as ﬁsh must not be exposed to any other ambient background light. In terms of basic working light levels, Arctic charr, like other salmonids, prefer lower levels in the range of 50–100 Lux. Grow-out ﬁsh in outdoor pens or tanks are subject to sunburn if they are in clear water and full sunlight. It is better if tanks are shaded from full daylight and receive similar light levels over their entire surface. Fish will move to shaded regions of a tank if light levels are not similar in all areas.

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Fig. 3.10 Differences in annual photoperiod between the High Arctic and points farther south.

Rearing densities Rearing density (ﬁsh biomass in kg/m3 of water) is one of the greatest enigmas of charr

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culture. Unlike other salmonids, Arctic charr perform best at very high densities in tanks, or the very low densities found in lake-stocking situations. In all age cohorts, from ﬁrst-feeding alevins to large grow-out ﬁsh, Arctic charr growth rates are better at densities of 40–200 kg/m3 than at lower densities (Jørgensen et al. 1993; Wallace et al. 1988; Christiansen et al. 1992). For example, Arctic charr grown at a density of 44 kg/m3 exhibited signiﬁcantly higher growth rates than ﬁsh grown at low density (8.7 kg/m3) (Wallace & Kolbeinshavn 1988). The average size of these juvenile Arctic charr over a 12-week period was 67% higher in groups of ﬁsh kept at the high density than at the low density. Variation in length and weight is also lower when Arctic charr are reared at high density (Brown et al. 1992). The improvement in overall growth in groups of ﬁsh held at high density is noted in Arctic charr of various ages and various races and appears to be one of the deﬁning differences between Arctic charr and other salmonids when held under culture conditions. Growth rates of Arctic charr are maximized at densities of 130–170 kg/m3, and growth is only slightly less at densities up to 200 kg/m3. Unless one has seen ﬁsh held at these high densities, it is very difﬁcult to visualize, but there is virtually no empty tank space from top to bottom, as shown in Fig. 3.11. Surprisingly, ﬁsh health, body condition, and stress levels appear not to be compromised by high rearing density (Ricks 1991). In low-density tank culture systems, aggressive social interactions among ﬁsh lead to stress-related appetite and growth suppression in many ﬁsh, while at high density aggression seems to be switched off (Brännäs 1998). Researchers have noted that Arctic charr juveniles reared at high densities were less aggressive and spent signiﬁcantly more time shoaling (holding station within a loose aggregation of individuals) than swimming (Brown et al. 1992). Arctic charr, at least those in culture conditions, may be aggressive, not to defend a territory per se, but rather because they perceive other ﬁsh as too close and encroaching on their personal space. At very high density, Arctic charr cannot see many of their nearest neighbours and there is little eye-to-eye contact. The other ﬁsh become a wall of bodies and are no longer seen as ﬁsh – in a sense, it’s a case of not seeing the trees for the forest. The cues for defending personal space may be turned off under these conditions of extreme crowding. If you plan to hold Arctic charr at high density, you must have excellent water quality, dedicated staff, and a well-thought-out backup and alarm system. Water parameters – notably oxygen, ammonia, nitrite, carbon dioxide, and suspended solids – must stay within acceptable limits of concentration or ﬁsh health will be compromised and ﬁsh will die. Maintaining excellent water quality is no easy feat at high rearing density and usually requires very high intake water ﬂows and oxygen injection. High-density stocking also increases the risk of catastrophic loss, as the time to recover from an equipment failure or waterline break is minutes before oxygen falls to lethal levels when holding ﬁsh at 130 kg/m3. For many operators, optimal stocking density that accounts for ﬁsh health, a reasonable proﬁt, and acceptable economic risk may be at much lower densities (40–60 kg/m3) than is biologically possible.

Biological aspects: stress and disease-causing organisms Resistance to disease, both infectious and non-infectious, is affected by physiological stress,

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Fig. 3.11 Arctic charr held at different rearing densities in tanks.

so the ability to control stress is an important factor in successful cultivation of Arctic charr. Stress is the ﬁsh’s response to a negative environmental alteration such as low oxygen, high temperature, or harassment by predators or dip-netters. Stress renders ﬁsh more susceptible to disease, in part by reducing the effectiveness of the immune system. Major stressors of cultured Arctic charr include the following: poor water quality due to low oxygen, high ammonia, or high suspended solids; • inappropriate procedures such as moving ﬁsh during high water temperatures • or handling ﬁshhusbandry many times over a period of days; negative behavioral to the culture environment, such as a negative response to • high temperature or responses to low rearing density in tanks.

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Stress is manifested in the ﬁsh through the action of corticosteroids, a group of steroid hormones that control a variety of cellular processes. One of the corticosteroids, cortisol, is the primary hormone used by animals in mediating their response to stress. It allows a prolonged ﬁght-or-ﬂight response by mobilizing available glucose energy to the brain and muscles, shutting down glucose metabolism in other areas of the body, and shutting down the immune system. Shutting down some metabolic processes and the immune system allows an animal to concentrate all its resources on dealing with the immediate stress. You do not need to heal wounds or ﬁght infections when you are ﬁghting for your life. Shutting down the immune system is a ﬁne and proper response at the time of attack, but not a response you want repeatedly or continuously. Repeated stress or continuous stress may leave the cortisol response turned on, the immune system turned off, and many metabolic functions compromised. An increase in the level of cortisol in blood plasma is a well-documented response in salmonids and other ﬁsh to various types of stressful stimuli. The magnitude and extent of the corticosteroid response usually reﬂect the severity and duration of the stressor. In addition to impairing growth and suppressing physiological processes such as parr-to-smolt transformation, stress-elevated levels of cortisol suppress the immune system, thus increasing the susceptibility to infectious diseases. Researchers in Norway took three groups of Arctic charr and subjected one of them to ‘normal hatchery procedures’, another to ‘excessive stress’, while shielding the third from stress, before all underwent seawater challenge tests. The stressed group had elevated cortisol levels and had the highest mortality rate when exposed to saltwater tests. The stressed group also was affected by a heavy fungal infection. Repeated increases in cortisol levels brought about by stress are known to decrease resistance to fungal infections (Brunsvik et al. 1996). Disease is a relationship or interaction between three factors: the ﬁsh, the ﬁsh’s environment, and a disease-causing agent (see Fig. 3.12). An infectious disease-causing agent such as

Fig. 3.12 Relationship of Arctic charr to environmental conditions, stress, and disease-causing pathogens.

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the bacterium Aeromonas salmonicida may be resident in ﬁsh but will cause no disease if the ﬁsh are under no stress in a healthy aqueous environment. However, should the ﬁsh become stressed from continuous exposure to elevated temperature and low oxygen, then the bacteria are able to overcome the ﬁsh’s immune system, reproduce in large numbers in the organs and muscle, and cause a disease called furunculosis. One way to fend off bacteria is to maintain optimum chemical and physical parameters to avoid causing stress and susceptibility to disease. These parameters have been covered in previous sections of this chapter. The other way is to be aware of biological disease-causing pathogens and the environment in which they could become a problem. The next section introduces pathogens that can affect Arctic charr.

Infectious disease and pathogens Arctic charr appear more tolerant than other salmonids of many common viruses and bacterial agents of disease (Eriksson 1989 [pers. comm.]; Bass 1998). They also appear less susceptible to stress under culture, particularly when kept at high density in tanks (Ricks 1991). This may mean they are able to fend off diseases better than other salmonids. However, they still get disease from pathogens. Like most salmonids, they are susceptible to bacterial infections such as furunculosis and bacterial kidney disease (BKD), and to other diseases if conditions are ripe for infection. One way to prevent infectious disease is to control the spread of pathogens or eliminate them from the culture site. Unfortunately, many if not all of the pathogens that cause infectious disease in cultured salmonids have their origins in the wild and are likely more widespread than we think. In the last few years, researchers have tested and inspected wild ﬁsh and invertebrate populations for the common pathogens of concern to cultured ﬁsh and have found wild species to be carriers both in the freshwater and marine environment. Many pathogens are now virtually cosmopolitan, having been spread through the uncontrolled movement of salmonids before the 1960s. Even today, with mandatory ﬁsh health inspections, strict movement controls placed on live ﬁsh, and mandatory destruction of ﬁsh from grow-out farms and hatcheries infected with pathogens such as infectious salmon anemia (ISA), pathogens and disease still spread from region to region. Pathogens move from one source to another along many long and devious routes. They are horizontally transferred by direct contact from infected wild ﬁsh to cultured ﬁsh or from infected cultured ﬁsh moved to other culture facilities. Some pathogens spread when intermediate hosts shed pathogens into the water. They are transported from site to site by birds or on the hands and boots of wayward hatchery workers. Other pathogens cause infections when cultured ﬁsh eat an intermediate host. In some cases, pathogens are vertically transferred from parent ﬁsh to young, either on the surface of the egg or inside the egg. When the eggs hatch they carry the pathogen to the next generation of younger ﬁsh. Infectious disease in Arctic charr is caused by a number of pathogenic species that belong to the bacteria, virus, fungi, protozoan, metazoan, or crustacean groups. Bacteria, viruses, and fungi constitute the most serious pathogens in cultured Arctic charr, with about six species or groups of concern. Because of their greater complexity in internal structure and larger body size, we make an arbitrary decision and refer to the relationship of protozoan, metazoan, and crustacean

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disease organisms with ﬁsh as a host–parasite interaction. It is really no different than the interaction of viruses or bacteria from the ﬁsh’s perspective, but now the disease organisms are approaching the size where we can almost see them with the naked eye. Protozoan parasites are a diverse lot, with about six groups of concern in salmonid culture. These are in the genera Ichthyobodo, Hexamita, Ceratomyxa, Myxobolus, Kudoa, and an unclassiﬁed myxosporean PKX. Most of the metazoan parasites of importance to charr are ﬂatworms, ﬂukes and tapeworms (Platyhelminthes), roundworms (Aschelminthes), and crustaceans (Arthropoda). With few exceptions, the parasitic fauna of the wild Arctic charr is similar in all the circumpolar regions where it has been reviewed, and it covers a diversity of classes and genera (see Appendix). Farmed Arctic charr stocked in pothole lakes, net-pens, larger lakes, or sea water may have problems with parasites found in wild Arctic charr; however, the three parasitic diseases identiﬁed so far with intensively cultured Arctic charr are all associated with organisms not found in wild charr populations but, rather, in other farmed and wild salmonids. Infectious pancreatic necrosis virus (IPNV) This is a highly virulent viral disease of young salmonids, characterized externally by lethargic corkscrew swimming, a darkening of body color, anemia, swollen abdomen, and possibly trailing fecal casts. Internally, classic symptoms are intestines that become opalescent to white in color, ﬁlled with non-bile-stained mucus; pale-colored liver, spleen, and gills; and often serous ﬂuid in the abdominal cavity (Post 1987; Willoughby 1999). Mortality can reach 100% in young susceptible salmonids and up to 40% in larger ﬁsh. Stress, in many cases induced by poor water quality, handling, or transfer to sea water, appears to be the major factor leading to disease outbreaks (Willoughby 1999). The disease was isolated in domestic Arctic charr fry in Europe during the early 1970s, but little reference has been made to it since. It is present in fresh water and sea water in many species of wild ﬁsh (carp, perch, roach, bream, pike, halibut, turbot, sea bass) and most of the cultured salmons and trout. It has been found in brook trout, which are highly susceptible to the disease; endemically in some wild populations of Dolly Varden charr (referred to as Arctic charr in the reference but now considered Dolly Varden) (Souter et al. 1984); and in domestic Atlantic salmon, particularly in Norway (Willoughby 1999). Brown trout, the Paciﬁc salmons, and rainbow trout are also susceptible to the disease in the wild and under culture. The disease is, unfortunately, ubiquitous and abundant throughout the world except Australasia. IPNV is transferred horizontally from ﬁsh to ﬁsh, with large amounts of the virus shed by the host into the water, or is vertically transmitted in or on the surface of ova (Bruno & Ellis 1996). The virus is resistant to heating (60 °C for 15 minutes) and freezing (5 years at –20 °C), remains active in ﬁsh silage for up to 6 months (Willoughby 1999), and survives well in sea water for weeks and in fresh water for hours. Until recently the best method of control was prevention, by situating hatcheries on pathogen-free water sources, or, if an outbreak occurred, by destroying all ﬁsh followed by facility disinfection. Recently a vaccine has been developed and has gained widespread use in Norway, but its effectiveness with Arctic charr is unknown.

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Infectious hematopoietic necrosis virus (IHNV) This is a hemorrhagic virus that infects the spleen, anterior kidney, and other organs as the disease progresses. The major route of transmission is oral or close contact with other infected ﬁsh, and through vertical transmission from parent to ova, with the virus present in both ovarian ﬂuid and milt. The disease has been found in Atlantic salmon, the Paciﬁc salmons, and rainbow trout cultured in fresh water throughout North America and Japan. Recently it has shown up in isolated outbreaks on rainbow trout farms in Germany, France, and Italy (Bruno & Ellis 1996). Many wild populations of salmonids are carriers of the virus, as are survivors of disease outbreaks occurring in cultured ﬁsh. The disease is more prevalent at water temperatures below 15 °C. Viral hemorrhagic septicemia virus (VHSV) This is an acute to chronic disease mostly conﬁned to European rainbow trout grown in fresh water. Disease signs are loss of appetite and erratic spiral swimming, with some ﬁsh moving away from the shoal and remaining motionless near the surface or edges of tanks. Fish may become dark in color, with distended abdomens and pop eyes from ﬂuids collecting in the tissues. Gills are pale in color, and internally there may be ﬂuid in the abdominal cavity and hemorrhaging of the internal organs and muscles. The kidneys and spleen may be greatly swollen and the liver is pale or yellowish. The virus is transmitted horizontally via the feces and urine of infected ﬁsh, with access to the new host likely through the gill lamella. The evidence for vertical transmission from mother to ova is inconclusive (Bruno & Ellis 1996). Birds that consume infected ﬁsh may act as vectors by transmitting the virus to new locations. In rainbow trout the disease is seasonal, occurring more often in the winter months in colder waters (7–15 °C). Although the disease is mainly of concern for rainbow trout in fresh water, it has been found recently in a seawater rainbow trout farm in Sweden, and in wild Atlantic halibut and turbot, although with a milder variant of the virus (Willoughby 1999). The virus has also been recently isolated from coho and chinook salmon and rainbow trout in North America (Bruno & Ellis 1996). Brook charr have been experimentally infected by contact with virusinfected rainbow trout. Brown trout, coho salmon, and brook trout that had been inoculated intraperitoneally with the virus showed the same course of the disease as did rainbow trout (Post 1987). The disease is currently conﬁned to Europe and North America. Furunculosis This is the most serious bacterial disease in Arctic charr, and in Sweden is considered a major threat to Arctic charr farm development (Eriksson & Wiklund 1989). There are two forms of Aeromonas salmonicida infection: the typical furunculosis ASS, caused by the subspecies A. salmonicida salmonicida, and a more atypical and less virulent form, ASA, from the subspecies A. salmonicida achromogenes. Arctic charr are susceptible to both forms. The disease has few external symptoms other than a darkening of the skin, general lethargy, and general reddening at the base of the ﬁns. Internally there is widespread hemorrhaging of organs and liquefaction of the kidney. Death is via septicemia, likely the result of toxins produced by

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the bacteria shutting down major organ functions (Post 1987). Arctic charr in the early stages of both ASS and ASA infection show ectodermal red spots and point-like bleedings at the base of the ﬁns and along the sides of the belly, anemic gills, and general lethargy with loss of appetite. In the ASS form, these symptoms are followed by the development of furuncles that become open abscesses (Eriksson & Wiklund 1989). Furunculosis is a worldwide phenomenon occurring in many species of cultured and wild ﬁsh, both in fresh water and sea water. It has been found in cultured Arctic charr in North America and Europe, typically when ﬁsh are under stress in conditions of poor water quality at high temperature and low oxygen (Pennell & McLean 1996). Transmission is rapid through horizontal routes, likely entering hosts orally or through injuries to the skin. Large numbers of organisms are shed in the feces of infected individuals and from the bodies of dead ﬁsh. The disease can also be spread by sea lice and possibly via ﬁsh-eating birds such as gulls and cormorants. The bacteria are easily spread from tank to tank by splashing water, and on equipment and clothing that are not disinfected. Transmission can also occur on the surface of eggs that have not been disinfected. This is a difﬁcult disease to treat once an outbreak has taken place. It is easily moved about and likely is endemic to wild ﬁsh populations in most rearing areas where the disease now occurs. Acute outbreaks can be treated by adding oxytetracycline (Terramedic) to feed for 7 to 10 days if the ﬁsh have not lost their appetite. However, some populations of A. salmonicida have become resistant to other antibiotics, and it is only a matter of time until they become resistant to oxytetracycline. With this in mind, it is best to slaughter entire batches of infected ﬁsh and sanitize the rearing unit; however, repeated outbreaks and the recycling of disease agents between groups of ﬁsh are not uncommon (Eriksson & Wiklund 1989). Therefore, the best approach is prevention in the early rearing stages and immunization of older ﬁsh destined for grow-out. This should include other common-sense measures in the grow-out chain: only certiﬁed disease-free eggs to hatcheries that are known to be free of furuncu• Import losis. eggs after water hardening (a process in which water is taken into newly ferti• Disinfect lized eggs to seal them up for protection – see Chapter 6) and before transporting them

• • • •

from one hatchery unit to another. Use clinical tests to ensure that there is no sign of ASS on ﬁshes before they are delivered from a hatchery to rearing units. Transport ﬁngerlings to grow-out sites with a minimum of handling stresses, in wellcleaned containers, during the cool weather of early spring and late autumn. Implement mandatory vaccination of all ﬁsh going to grow-out sites that have a likelihood of containing ASS from feral ﬁsh or other aquatic organisms. Control transmission via birds by limiting bird access to grow-out facilities and by properly disposing of ﬁsh mortalities and ﬁsh-plant offal.

Bacterial kidney disease (BKD) Arctic charr are as susceptible to BKD as any other salmonid. Caused by the pathogen Renibacterium salmoninarum, this is one of the most serious diseases in freshwater and seawater salmonid farms worldwide. Characteristic symptoms include lethargy and partial blindness,

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with individual ﬁsh seeking the slower currents adjacent to tank sides or raceways. Infected ﬁsh may be dark colored with protruding eyes, and they sometimes show slight hemorrhaging at the base of pectoral ﬁns. Internally the kidneys may be swollen, with white or gray-white abscesses in one or more of the visceral organs (Post 1987; Willoughby 1999). Routes of transmission may be oral or through injuries to the skin. Feral or cultured ﬁsh with latent or chronic BKD are likely the source of the disease, spreading it either via feces in water or by release of the organism from skin lesions. The bacterium is well adapted for vertical transmission on the surface of and likely inside the ova (Post 1987; Jónsdóttir et al. 1998). Eggs shipped from Iceland to Ireland in the mid-1990s were BKD positive, as were some eggs shipped from eastern Canada to Ireland. The disease is more prevalent in soft water than hard water conditions. The pathogen causes acute and chronic infections over a wide range of temperatures. All of the salmonids appear to be susceptible to the disease, but not other genera. The disease is widespread in wild and occasionally in cultured populations of Arctic charr in Iceland. The mean prevalence of infection in different Arctic charr populations in Iceland was 46%, with none of the infected ﬁsh showing gross pathological signs of BKD (Bass 1998; Jónsdóttir et al. 1998). There is no effective treatment or vaccine against BKD so, as with furunculosis, prevention is the best approach. In Norway, researchers added an antibiotic, erythromycin, to the water in which newly fertilized eggs were water hardening to control and minimize the vertical transmission of disease organisms. This seemed to work, as no BKD was found in hatched alevins (Barnung & Holm 1988). Vibriosis Vibriosis, caused by the bacterium Vibrio anguillarum, is common in the marine environment and is known to infect cultured Arctic charr. The symptoms of acutely sick ﬁsh are dark, swollen, ulcerating skin lesions; pale gills; and erythema at the base of ﬁns, in the mouth along the grooves of the lower jaw, on the opercles, and around the vent. There may also be boil-like lesions under the skin and in the muscles, which may develop into open sores. Internally, the spleen may be enlarged and the kidney liqueﬁed, with petechial hemorrhages in the kidney, spleen, and liver (Post 1987). In Arctic charr, the most common symptoms are hemorrhages in the head region and on the base of the ﬁns, and a red and swollen anal region. Internally the spleen is enlarged and, occasionally, entirely liqueﬁed (Robbins et al. 1990). The bacterium is ubiquitous worldwide in the marine environment, with many species of marine and freshwater ﬁsh susceptible to the condition. Horizontal transmission likely occurs when bacteria are shed in the feces of infected ﬁsh, with pathogens invading the new host orally, via the gut or through sites of external injury. There is no evidence of vertical transmission from parent to egg. The bacterium can grow at 5 °C, but usually symptoms appear in ﬁsh at temperatures above 10 °C. Stress may be an important contributor to the condition. The disease is of concern with on-growing Arctic charr in sea water or brackish water conditions. Arctic charr destined for grow-out in such water should be vaccinated against vibriosis using interperitoneal injection, which gives protection of about 98%. Dip vaccination is unsatisfactory. During an outbreak of vibriosis, two strains of Arctic charr showed different responses to vaccination. Survival after vaccination was much higher in one strain

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than the other, suggesting there may be genetic differences in response to the vaccination or in disease tolerance (Barnung & Holm 1988). Saprolegniasis Relatively few genera of fungi cause disease in ﬁshes, and only one group of fungi is of concern to Arctic charr culture. Fungi require organic matter for growth and are not capable of synthesizing their own food. They use dead organic matter as a food source (saprobes) or feed on the tissues of living organisms (parasites). Fungi can reproduce vegetatively, which is the main mode of spreading in the host, or sexually through the production of spores. Spores, which are resistant to heat, drying, and many disinfectants, are the main method of transmission to new hosts. Saprolegniasis is a disease common to brood stock and egg incubation rooms. It is also found in all ages of ﬁsh where individuals are under stress or have acquired wounds or abrasions on the body surface. The disease is caused by species in three genera – Saprolegnia, Achlya, and Dictyuchus – and most are saprophytic or facultative parasites (Post 1987). The condition produces dirty-white masses of what looks like cotton wool on the surface of eggs or the skin of ﬁsh. Growth occurs on dead eggs, but the organism rapidly spreads vegetatively to adjacent live eggs. If not treated, the fungus can completely overcome entire trays of eggs, killing the live ova by suffocation. On infected ﬁsh, the initial site is generally an abrasion or wound on the skin’s surface or at a site where the skin’s protective mucous layer has been removed due to rough handling. The fungus grows on the injured site; in stressed individuals it spreads vegetatively to living tissue, which it destroys by releasing digestive enzymes. The spores are present in many but not all water sources worldwide. In three Yukon hatcheries, all on ground water of similar source, only one has persistent problems with saprolegniasis. The zoospores can be carried on the feathers of birds, the fur of animals, and by the wind (Post 1987). The high quantity of organic matter in incubation water may be a factor in saprolegniasis infection of eggs. Dead and heavily infected ﬁsh that are not removed promptly from tanks are a source of zoospores that can contaminate other ﬁsh. The fungal condition is often chronic among spawning Arctic charr, with mature males much more susceptible than females. Losses of male Arctic charr can be quite high, but in many cases the condition clears up when treated with formalin (250–500 mg/L) or sodium chloride (30 ppt) baths, or with time after males are no longer in spawning colors. Maintaining the highest possible water quality, anesthetizing all ﬁsh requiring handling, removing infected ﬁsh, and treating the condition as it appears will reduce the severity of outbreaks (Post 1987; Robbins et al. 1990). Proliferative kidney disease (PKD) This disease, of concern for Arctic charr and other salmonids in North America and Europe, is caused by a ﬂagellated freshwater protozoan, tentatively identiﬁed as a member of the family Sphaerosporidae and known as PKX. The PKX cells are found in the lumen of the kidney tubules, in the spleen, and in the circulating blood of infected hosts. There are few outward signs of the disease in light infections, however advanced PKD symptoms include a darkening in skin color, erratic swimming with individuals gasping at the surface, pale gills, and

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swollen abdomen. Internally, the abdominal ﬂuid may be blood-stained, with the kidneys enlarged, light colored, and containing large white nodules. The spleen may also become enlarged, and the liver may be light in color and mottled. The horizontal mode of transmission is unclear, but ﬁsh placed in the same water source with other infected individuals pick up the PKX protozoan (Post 1987). Vertical transmission is unlikely. The disease occurs more often in the late spring and summer months, when water temperatures are above 16 °C, and is not active in water below 7 °C. Stress from poor water quality or handling appears to increase the severity of infections. Fish surviving an infection appear to be resistant to reinfection (Bruno & Ellis 1996). In Arctic charr, PKD results in lethargic behavior and reduced growth, with mortalities as high as 70% to 90% depending on stress and other factors (Brown et al. 1988). Arctic charr introduced into net-pens in Three Brooks Pond, Newfoundland, suffered very high mortality rates from PKD (Nwﬂd. Aqua. Ind. Assoc. 1998). In response to the serious problems encountered in the net-pens, researchers in Newfoundland compared susceptibility of Arctic charr with that of Atlantic salmon and found that once water temperatures reached 12 °C, the mortality of charr, but not salmon, began to increase, remaining high until temperatures dropped below 12 °C. Onset of mortality increased signiﬁcantly 9 weeks after water temperatures reached 12 °C. In the same experiments, Atlantic salmon indigenous to the region were not diagnosed with PKD, suggesting that the salmon but not the charr had developed an immunity to PKD from exposure to the disease agent in the natural environment. The Arctic charr have no history of exposure from their natal streams of Labrador (Brown et al. 1988). Metazoan parasites – tapeworms and roundworms Tapeworm and roundworm infections are most likely to occur if Arctic charr are feeding on natural foods when stocked into lakes, or where they are supplied with water sourced from lakes or rivers (see Appendix). Arctic charr serve only as accidental hosts for marine parasites acquired during their annual migrations to sea (Due & Curtis 1995), most of which would not be of concern in an intensive farm environment where ﬁsh are fed prepared diets. Parasites acquired by Arctic charr in fresh water are often ingested when ﬁsh eat crustaceans that carry the parasite. Wild populations of Arctic charr from Lake Takvatn, northern Norway, ingest the parasitic roundworm Cystidicola farionis when they feed on freshwater shrimp, Gammarus lacustris. Peaks in infection occur from August to November, while heavily infected ﬁsh die during winter and during spawning when stress levels are high (Giever et al. 1991). Arctic charr become infected with tapeworms, particularly Triaenophorus sp., from eating copepods. The tapeworm incysts on the ﬁsh’s intestines and in the heavy muscles around the spine (Robbins et al. 1990). Heavy infestations prevent the sale of infected ﬁsh for food, and even mild levels of infection limit the marketability of ﬁsh. Consumers are disconcerted when they ﬁnd a cyst in a ﬁsh ﬁllet or steak, even though the cyst is harmless when cooked. When stocking lakes with Arctic charr, you may need to take other parasites into consideration, as that is where charr might pick up certain species of tapeworm (Diphyllobothrium) and roundworm (Anisakis) that can affect human health. The link between Arctic charr, Diphyllobothrium, and human infection is somewhat obscure. Infection is possibly the result of

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eating raw or undercooked ripe roe, or the larval cysts (plerocercoids) adhering to the ﬁsh’s abdominal wall (Bureau & Cho 1998). Anisakis infections in humans, usually associated with eating raw marine ﬁsh such as sockeye salmon (as sushi), have never been linked to the consumption of Arctic charr, which is fortunate as Arctic charr makes the ﬁnest sushi. Gyrodactylid monogenean parasites – ﬂukes Flukes have a worldwide distribution and parasitize most species of freshwater and marine ﬁsh including Arctic charr (see Appendix), usually in a very host-speciﬁc manner (Post 1987). Gyrodactylus salaris is the one species of ﬂuke that is a major pathogen to farmed Atlantic salmon. Unfortunately, it is spread from cultured ﬁsh to wild populations of Atlantic salmon in Norwegian rivers and the White Sea. Signs of excessive infection include frayed ﬁns, damaged gills, and loss of skin epithelium, with mortalities from loss of osmotic control and secondary infections. Horizontal transmission is from close contact via free-swimming larvae. The disease is currently restricted to continental Europe, Scandinavia, and the White Sea. Arctic charr are also susceptible to Gyrodactylus salaris, but at different rates of infection than Atlantic salmon. Some strains of Arctic charr are more susceptible than others. Resident charr from Korssjoen stock, exposed as individuals to heavily infected Atlantic salmon, were considered innately resistant as they lost their infections within 21 days. Individuals of anadromous Hammerfest charr remained infected for up to 150 days, with most infections lasting 30–50 days. The length of the infection on the anadromous charr was highly variable, but in the resident stock of charr, all ﬁsh lost infections in about 30 days (Bakke et al. 1996). The parasite survived and reproduced for up to 280 days in laboratory populations of anadromous charr. Isolated populations of charr, not in contact with new sources of larval ﬂuke, lost infections, suggesting an immune response. Infection in shoaling charr may persist because the immune response of individual ﬁsh eventually forces the ﬂuke to detach, but not die, allowing the ﬂuke to reattach to another ﬁsh. Sea lice Sea lice are parasitic marine crustaceans (subclass Copepoda) that are ubiquitous and abundant at many marine net-pens containing Atlantic salmon. They attach to the outer integument, feeding on mucus, blood, and underlying tissues by rasping through the skin. Light infestations are a minor concern, but as few as ﬁve adults on a smolt may be enough to cause signiﬁcant sickness (Willoughby 1999). They are a serious problem on many marine farm sites but are of no concern in fresh water. Fish farmers on the Bay of Fundy noted that Arctic charr reared with a group of Atlantic salmon in a seawater net-pen were heavily infected with the sea louse Caligus elongatus. In follow-up experiments, researchers at the Huntsman Marine Science Centre placed 2-yearold Atlantic salmon smolts and Arctic charr into a marine net-pen and allowed them to naturally acquire sea lice infestations. They noted the infection rate on charr was signiﬁcantly higher than that of Atlantic salmon (32% vs. 20%) and speculated that charr epidermis is more easily disrupted by feeding sea lice because of osmotic stress from long periods in sea water (Mustafa & MacKinnon 1997).

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Other non-infectious disease agents As well as infectious diseases caused by virulent biological agents such as bacteria and viruses, there are non-infectious diseases caused by poor quality in source water or by deleterious conditions in tank water. Even mild micronutrient deﬁciencies due to poor-quality ingredients in diets, incorrect processing, or feeding rancid or mouldy feeds can induce a wide range of diseases such as cataracts, botulism, and liver cell carcinoma (Post 1987). There is growing evidence that dietary vitamin C and E and fatty acids play a key role in inﬂuencing the immune system of salmonids (Jobling 1993). For example, the incorrect balance of (n-3) (n-9) fatty acids in feed can cause pathological changes such as cardiomyopathy in salmonids. Infectious diseases and some nutritional diseases manifest themselves slowly over the course of days or weeks, with increasing numbers of ﬁsh succumbing to the disease over time. The sudden death of an entire tank of ﬁsh is likely the result of a non-infectious disease caused by poor water quality (i.e. sudden loss of oxygen) or by the addition of a deleterious toxic material or chemical compound to the source water. Toxicity of chemical compounds and construction materials A wide range of synthesized chemical compounds and waste products used in heavy industry and agriculture are potentially toxic to ﬁsh (e.g. pesticides, herbicides, oil-based compounds, industrial chemicals). These products can enter the intake waters of a culture facility as singlepoint sources from an industrial plant discharge, or over a wide area from agricultural surface run-off or groundwater contamination. It is very difﬁcult to protect a facility from this type of disease. You must be aware of what upstream users do in their processes and make them aware of your concerns for good water quality. Monitoring water quality on a regular basis for compounds you may suspect from upstream users can give you lead time in rectifying toxic discharges or at least provide evidence when you notify insurance agents that the ﬁsh loss was preceded by a change in water quality. Another often-overlooked source of toxicity and disease to ﬁsh is the material used in constructing water-supply and ﬁsh-holding systems. Most manufacturers can tell you if their products are safe for ﬁsh. In general, if a product is certiﬁed for use with potable water for human consumption, it will be safe for ﬁsh. Whenever a new system is built, it should be leached, preferably in ﬂowing water, for 24 hours before contact with ﬁsh. Efﬂuent from the leaching process should not contact other ﬁsh in the system nor those downstream. Table 3.4 lists safe and potentially toxic construction materials. If in doubt, consult the manufacturer or conduct a bioassay using Arctic charr and your source water, as pH and water hardness can affect the toxicity of metals. Swim bladder stress syndrome (SBSS) A curious disease found in Arctic charr and a few other ﬁsh species is swim bladder stress syndrome (SBSS) (Jobling et al. 1993). Rem Ricks, who studied SBSS in a commercial Arctic charr facility, described the condition well as ‘characterized internally by an over inﬂation of the swim bladder, sometimes with an accompanying distortion in shape. Behaviorally, the

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Table 3.4 Toxic and non-toxic materials potentially used in construction and operation of ﬁsh culture facilities. Non-toxic materials

Toxic materials

Aluminum Asphalt Concrete Fiberglass Glass Gravel and rock Heavy metal-free paints Iron Nylon Plexiglass Polyethylene Polypropylene Polyvinyl chloride (PVC) type I Rubber Silicon and hot metal adhesives Stainless steel Wood

Cadmium – some plated tools Copper – brass Zinc and copper alloys City water – chlorinated about 0.002 ppm Detergents Heavy metals in paint and coatings Neoprene PVC type II Zinc – galvanization Pool liners impregnated with antifungal agents Oil and grease – gasoline, cutting oil Organic carbon compound – benzene, kerosene, cyclohexane Phenolic compounds – α-cresol, resorcinol Polychlorinated biphenyls

ﬁsh loses its ability to maintain normal positive rheotaxis in the water column. The ﬁsh tends to ﬂoat with the dorsal ﬁn out of the water; the ﬁsh will swim on its side; a vertical posture may be assumed, usually with the anterior end up; ultimately the ﬁsh will ﬂoat in an inverted posture, with a greatly distended abdomen, and become unable to respond even to touch stimulus. While it may take several weeks, the ﬁnal outcome of this condition is death by exhaustion and starvation’ (Ricks 1991). Ricks could not induce the condition by applying repeated stress to ﬁsh held at high densities. He also found no evidence that the condition was pathological, nor was there evidence of bacterial or viral pathogens involved. Ricks suggested that there may be a genetic predisposition to the condition, and his study could not substantiate other studies that suggested stress was the primary cause of the disease.

Summary Although Arctic charr appear to be more tolerant of infectious diseases than other salmonids (Robbins et al. 1990), this may only be a function of the relatively few numbers of charr under culture. The very nature of high-density tank culture of Arctic charr and the potential it creates for a poor aqueous environment set the stage for disease problems. The relative infancy of commercial Arctic charr culture does allow a window of opportunity for managing ﬁsh health through a more proactive approach to anticipating and preventing disease problems than occurred in the earlier days of the Atlantic salmon farming, where heavy reliance was placed on use of chemical treatments after disease occurred. Most diseases in a culture facility can be prevented by adhering to a good ﬁsh health management program (see Chapter 10) that focusses on prevention over therapeutic treatment. The chronic use of drugs and antibiotics is unnecessary and suggests poor husbandry on the culturist’s part. It is better to identify and correct the underlying problem. There may be times when drug therapy is required to manage short-term disease or infection, but this should be a

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last resort and should always be under control of a veterinary service. A proactive approach to ﬁsh health management involves: minimizing stress by maintaining the biological and physical parameters within the toler• ance limits of Arctic charr; developing sh health programs that are woven into the day-to-day routine of ﬁsh main• tenance andﬁwater management; excluding biological from culture facilities by restricting the movement of Arc• tic charr from region pathogens to region, except eyed ova from certiﬁed disease-free facilities; locating hatchery facilities and, where possible, grow-out facilities on source waters free • of wild ﬁsh, or at least in waters where wild ﬁsh are not carriers of disease agents of concern

• • •

to Arctic charr; developing and using vaccines for on-growing Arctic charr in environments exposed to disease agents, particularly furunculosis; reducing stress through proper ﬁsh handling and holding techniques; and feeding nutritionally well-balanced, high-quality diets in adequate amounts.

Chapter 4

Growth, Nutrition, and Feeding

One of the keys to successful Arctic charr culture is understanding the biological and physical requirements for ﬁsh growth, diet, and feeding. Growing Arctic charr to market size in a reasonable amount of time, in a good-quality environment, and at a reasonable cost should be the goal of every operation. In the wild, Nauyuk Arctic charr can take 10 years to reach a weight of about 3 kg. Under intensive culture conditions, by manipulating water temperature and light, and feeding a high-energy diet, you can reduce the time it takes to reach this weight to less than 4 years. This is still considerably longer than it takes to grow Atlantic salmon, but ultimately the time to market will be reduced further when we have a better understanding of growth, nutrition, and feeding practices required for Arctic charr. Arctic charr grow efﬁciently under culture conditions when the nutritional quality of the diet and the techniques used to deliver feed to the ﬁsh support the complex interaction of biological factors that dictate rates of growth. The strains of Arctic charr used in culture are still relatively wild, and culturists should pay attention to their natural feeding behaviors and dietary requirements. These are not necessarily the same as the behaviors and feeding requirements of other cultured salmonids, such as Atlantic salmon and rainbow trout.

Growth in Arctic charr Growth in wild Arctic charr, particularly anadromous forms, is cyclical: long periods of fasting are interspersed with concentrated bouts of heavy feeding. In the Arctic environment, food is only available to Arctic charr for an 8- to 10-week period. All their energy needs for the entire year are met in this short burst of feeding. Throughout the long winter fast they rely on stored internal resources to supply all the energy and nutrients required to maintain metabolic processes and produce any growth. Though many salmonids are feast-and-famine feeders, Arctic charr take it to extremes, and the husbandry practices you use on cultured charr must take into account the biological traits that support this extreme lifestyle. An Arctic charr’s ability to grow in weight and length is limited by the amount of excess food energy and nutrients, above basic metabolic requirements, it ingests. It does not grow steadily; there are starts and stops, with energy sometimes shunted to lipid storage, to the production of eggs or milt, or to nutrient storage for metabolic processes during the long winter fast. Wild Arctic charr may actually lose body mass but still grow in length during the winter if their stored energy resources are large enough.

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Even in cultured Arctic charr offered unlimited feed, growth is not a continuous process. It follows a yearly rhythm that waxes and wanes over the months, and there are deﬁnite periods of increased growth rate and hunger not accounted for by water temperature or body size. These rhythms have evolved in the wild ﬁsh under conditions very different from those found in tanks, and myriad factors directly or indirectly affect the patterns and rates of growth expected under commercial culture conditions: water temperature; • rearing size; • body strain of Arctic charr under culture; • freshwater or seawater environment; • changes in photoperiod, the phase of the moon, and the time of the year; • physiological age, particularly the onset of sexual maturity; • compensatory growth effects; and • feeding and husbandry techniques. • If you plan to grow a tank full of Arctic charr to a large, uniform size, at reasonable cost, you will need to understand these growth factors and their relationship to the time it takes to reach market size and the amount of feed required. Before looking at these factors, however, we need to brieﬂy discuss various measures used to describe growth performance in Arctic charr.

Measuring growth performance The basic information required to monitor growth performance of cultured ﬁsh is a statistical estimate of the mean weight and length of the ﬁsh in each tank, the amount of feed fed, and the tank water temperature. This data, collected at different time intervals, allows the culturist to calculate ﬁsh density and predict ﬁsh size and food requirements at future dates. Knowing the mean ﬁsh weight (and a measure of the size distribution around the mean) and the number of ﬁsh in the tank allows the calculation of feed ration size based on feed tables presented later in this chapter. From this basic information, there are three measures used to determine how well Arctic charr perform: the growth rate (R), or the time taken to reach a certain body size; the body condition (K), or the plumpness achieved; and the food conversion rate (FCR), or the amount of feed used for every kg of weight gain. Growth rate (R) Growth rate is a measure of how fast a ﬁsh increases in size over a speciﬁed period of time. It is sensitive to changes in water temperature, diet, ﬁsh size, and time of year and is usually measured in terms of weight or length of the ﬁsh. In Arctic charr culture, growth rate models are used to predict the time it will take for a ﬁsh to reach a certain size, as a comparative tool to assess growth of one cohort against another held under different conditions (e.g. different feeds or water temperatures), or to predict the size of a ﬁsh after a given period of growth.

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Almost all models of growth assume that ﬁsh are in an active phase of growth, though this assumption is not always valid. A measure of growth seen commonly in the aquaculture literature on Arctic charr is speciﬁc growth rate (SGR), calculated using the following equation: SGR = 100 (ln WT – ln Wt)/(T – t) where SGR is speciﬁc growth rate, WT is ﬁnal weight (in grams) at time T; Wt is initial weight (in grams) at time t and (T – t) is the length of time in days between weighing. SGR is the measure of growth at a speciﬁc instant in time rather than a speciﬁed interval. It is a useful measure for comparing growth rates between experimental treatments – for example, the effects of two different diets on growth, or the growth potential of two different strains of Arctic charr. However, it is not the best tool for predicting growth over the long term or in an environment of changing water temperatures. As body size increases, growth rates decline (as shown in Fig. 4.1). As a comparative tool, SGR is limited by the following factors: conditions, particularly water temperature, must be constant. • Environmental Initial (W ) and ﬁ weights (W ) must be similar between experimental groups. • The time intervalnalbetween must be similar between experimental groups. • Growth of the ﬁsh must be weighing uninterrupted. • t

T

A simple growth model for salmonids developed by Dr George Iwama provides accuracy in predicting and comparing growth of Arctic charr (Iwama 1996). The Iwama model is easy to apply using a calculator and accounts for the effects of temperature and body size on growth. In its basic working form the model equation is: 1

/3

1

/3

WT = Wt + Gs × Time

Fig. 4.1 Effect of increasing body size on speciﬁc growth rate (SGR).

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1

77

1

/3

/3

where WT is the cube root of the ﬁnal weight in grams; Wt is the cube root of the initial weight in grams; Gs is the growth slope [calculated by dividing the mean water temperature in Celsius (T) between weighings by 1000 (T/1000)]; and Time is the number of days between weighing. The Iwama model is based on the following assumptions and calculation rules: 1

/3

cube root of ﬁsh weight (W or √W) increases linearly with time. • The Temperature has a linear effect on growth between 2 and 15 °C. • The model applies to periods of uninterrupted growth. • The cube root is calculated to at least four decimal places. • 3

This basic model is applicable to all salmonids. To adjust the model speciﬁcally for Arctic charr, a correction is introduced into the model. This correction factor, called the growth coefﬁcient (Gc), allows comparisons of actual growth rate observed with a theoretical or predicted growth rate. The growth coefﬁcient is calculated as a ratio: Gc = Gs/Gs1 Gs is the actual growth slope value associated with the weight and temperature data at your / / site and is calculated as Gs = (WT – Wt )/Time, while Gs1, the theoretical growth slope, is the average water temperature (T) divided by 1000 (Gs1 = T/1000). The inclusion of Gc in the basic growth rate equation gives a corrected model suitable for making accurate predictions of any of the three variables important to the ﬁsh culturist. These are: expected ﬁsh weight after a given time period of growth, water temperature required to grow an Arctic charr to a certain size in a given period of time, and time required to grow a ﬁsh to a ﬁnal weight given water temperature and starting weight. Final ﬁsh weight (in grams), given mean water temperature and time period, is calculated with the following equation: 1

1

/3

3

1

3

1

/3

WT = Wt + (T/1000 × Gc) × Time Final weight: WT = (Wt + (T/1000 × Gc) × Time)3 Mean water temperature (in °C), given ﬁsh size and time period, is estimated with this equation: 1

/3

1

/3

Temperature = [(WT – Wt )/Time] × (1000/Gc) And time required for growth (in days) given water temperature and starting weight is calculated with this one: 1

/3

1

/3

Time = (WT – Wt )/T × (1000/Gc)

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Iwama calculated a mean growth coefﬁcient (Gc) of 1.27 for Arctic charr based on ‘normal’ growing ﬁsh from 32 datasets and a value of 1.1 for Nauyuk Arctic charr (Iwama 1996). Condition factor Condition factor (K) is a measure of the plumpness of a ﬁsh and an indirect measure of the ﬁsh’s health and of fat reserves stored in the muscles, bones, viscera, and skeleton. It is a measure of the relationship between body weight and body length (from the tip of the snout to the fork in the tail), expressed as: K = (W/L3) × 100 where W is weight (in grams) and L is total fork length (in cm). The higher the magnitude of the condition factor, the greater the weight in relation to length. A well-fed ﬁsh will have a higher condition factor than a poorly fed one of the same length (Piper et al. 1982). It is a good ﬁeld measure of ﬁsh quality and is also useful to assess if feeding levels are adequate or if ﬁsh are suitably fat and plump for market sale. Arctic charr with higher condition factors receive higher market prices. Well-fed, market-ready cultured Arctic charr have condition factors in the range of about 1.2 to 1.4. Since condition factor is affected by the weight of food in the gut, ﬁsh must be starved to allow the calculation of a standardized K (Boivin & Power 1989; Steffens 1989). Figure 4.2 gives an example of the range in condition factor of an unsorted cohort of ﬁngerling Arctic charr. The poor condition factor of many ﬁsh in this lot suggests they require sorting by ﬁsh size to improve access to feed.

Fig. 4.2 Example of condition factor in sample of ﬁngerling Arctic charr. Data from Arctic Ova hatchery operations [pers. comm.].

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Food conversion ratio (FCR) The food conversion ratio is a measure of how efﬁciently a ﬁsh uses food for the purpose of growth. It indicates how much of the ration fed to ﬁsh converts to body weight, over and above basic metabolic needs and feed wastage. In commercial aquaculture, food conversion is the ultimate measure of operational performance. An Atlantic salmon grower on Canada’s West Coast said, ‘For me, my FCR and my growth rate are close to my heart. In salmon farming, your status, your annual salary, and your bonus depend on a good FCR. FCR, rather than proﬁts, makes a fairer comparison of how advanced one company, or country, is, versus another’ (Nielson 2000). When discussing food conversion efﬁciency we must qualify just what is meant by the term. In the Arctic charr literature there are technical measures of food conversion involving amounts of energy retained, protein retained, or protein efﬁciency ratios, but three simpler measures are more commonly used in commercial aquaculture and practical technical studies (Tabachek 1986). (1)

Feed efﬁciency or gross conversion efﬁciency (GCE) is often used in technical studies of growth and feeding. It is determined by taking the weight gain in body mass of all ﬁsh and dividing it by the total weight of feed consumed, using the following equation: GCE = (WF – WI)/FC

(2)

where WF is the ﬁnal wet weight (in grams) of ﬁsh at the end of the feeding period, WI is the initial wet weight (in grams), and FC is the total food consumed (in grams) during the feeding period. Total food conversion rate (FCR) is the most commonly used measure in practical studies of feeding and on the farm. It is the inverse of GCE and is calculated by dividing the total weight of feed consumed by the weight gain: FCR = FC/(WF – WI)

(3)

FCR in Arctic charr typically falls between values of 1 and 2. In commercial hatchery operations, the reported FCRs ranged from 0.9 to 1.6 kg of feed per kg of ﬁsh produced. FCR rates of juvenile Arctic charr held in net-pens are much higher, ranging from 1.8 to 3.5, which contrasts with land-based tank farms in Sweden that have FCRs of 1.1 to 1.5 kg/kg ﬁsh produced (Glebe & Turner 1993). The high FCR in net-pens may reﬂect feeding methods that must be used to ensure that all the feed is consumed before it falls through the net bottom. In tanks, Arctic charr, particularly the slower growing, less dominant individuals, will take feed off the tank bottom. Economic food conversion rate (EFCR) is the ultimate commercial measure of food use, as it relates the head-on gutted weight (WG) of the ﬁnal product to the total amount of feed fed. EFCR = FC/(WG – WI)

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The beauty of EFCR is that the grower only needs to know the starting weight, the gutted head-on weight, and the total amount of feed fed. EFCR is not yet a widely used measure, but its simplicity of calculation and actual measure of economic cost suggest it should receive greater attention. Ultimately, the price paid to the farmer is based on the gutted headon weight, and input costs should be measured against this benchmark as an economic and industry standard. Maximum growth rate and maximum conversion efﬁciencies are not achieved under the same conditions of feeding, as shown by Fig. 4.3. Food intake for optimum conversion is lower than food intake for maximum growth – for salmonids it is typically about 30% less. Culturists potentially save a lot of money by growing ﬁsh slowly on less feed, but at the expense of more time. A number of other factors affect food conversion efﬁciency in Arctic charr. As salmonids increase in body size, food conversion rates generally decline – that is, more food is required to grow ﬁsh to a certain size. First-feeding and ﬁngerling Arctic charr often show an FCR of less than 1, but this is rarely achieved with larger juvenile ﬁsh. For good food conversion rates, Arctic charr also require a high-energy diet (23 kJ/g) that is high in fat, with at least 1 to 2% of the fat component made up of 18 : 3(n-3) fatty acids combined with an adequate balance of vitamins and minerals (Tabachek 1986; Steffens 1989; Yang & Dick 1993). The condition of the growing environment affects FCR. Arctic charr show better conversion rates in fresh water and brackish water than in sea water (Arnesen 1994). Conversion rates are also higher in well-oxygenated water and are very poor in water at less than 60% oxygen saturation (Steffens 1989). Forcing Arctic charr to swim against a constant moderate current also improves food conversion rates of most individuals in the ﬁsh lot, regardless of size. This may be because it allows less-dominant ﬁsh equal access to feed and lessens the amount of energy dominant ﬁsh must put out to maintain high social standing. Moderately swimming Arctic charr show

Fig. 4.3 Relationship of food intake to optimal conversion efﬁciency and optimal growth. Data source: Jobling 1994.

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much less evidence of agonistic interactions (bite marks) than non-exercised ﬁsh, and oxygen consumption rates of exercised and non-exercised ﬁsh are similar. When forced to swim, Arctic charr show schooling behavior, which may also reduce energy output by providing hydrodynamic improvements in swimming and by making the ﬁsh switch to ram ventilation (water forced past gills by speed of ﬁsh) instead of the rhythmic and active ventilation of the gills employed at slower swimming speeds (Christiansen 1991).

Factors affecting patterns and rates of growth Water temperature and its effect on growth Water temperature has a profound effect on the growth rate of Arctic charr (see Fig. 4.4). Given sufﬁcient levels of oxygen and food, Arctic charr show positive growth from about 21 °C down to 0.3 °C. Optimum growth occurs between the temperatures of 12 and 18 °C, declining precipitously at higher temperatures. Below these optimum temperatures, the decline in growth rate is not quite so steep. The absolute optimum temperature for maximizing growth appears to vary either by strain or by age of Arctic charr investigated. In a study using 7 g to 16 g resident Arctic charr from Lake Vattern, Sweden, the highest growth rates occurred at 13–18 °C, with a predicted optimum of 15.1. Immature Hammerfest Arctic charr achieved maximum growth at 14 °C, while in another study based on Arctic charr from Nesjoen, Norway, maximum growth occurred at 11.8 °C (Brännäs & Wiklund 1992; Jobling et al. 1993; Larsson & Berglund 1998). Although Arctic charr are capable of growth at high temperatures, some Arctic charr researchers and commercial growers ﬁnd that a safer temperature range is 10–13 °C. Food conversion rate is better at these lower temperatures, and husbandry is a little simpler, though

Fig. 4.4 Effect of water temperature on growth rates of Arctic charr.

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growth is slower. Higher water temperatures, particularly above 18 °C, cause increased problems with disease, produce an obvious sluggishness in the ﬁsh, and make it harder to maintain adequate dissolved oxygen levels. Fish cannot be moved, sampled, or harvested safely at these higher temperatures without risking stress and disease outbreaks. Arctic charr show considerable growth at low temperatures (less than 5 °C). In the wild, large Arctic charr grow very well at sea in cold water, perhaps due to the presence of abundant feed and increasing summer light levels that stimulate feeding and growth. Under culture conditions, Arctic charr will grow throughout the winter period, but there is little information about the effects of light on growth, feeding regimes, and food composition requirements at these colder winter temperatures. These are areas ripe for research, since many potential growing locations have a long winter season and low water temperatures most of the year (Brännäs & Wiklund 1992). Food conversion rates (FCR) of Arctic charr are better at lower temperatures. At higher temperatures, Arctic charr will grow faster but require more feed to gain weight than at lower temperature (see Fig. 4.5). The feeding conditions for the best FCR are generally at lower temperatures than those of optimum growth (Jobling 1994). This is because Arctic charr have a decreased metabolic rate at lower temperatures, which allows a greater proportion of feed to be used for growth rather than maintenance. In Arctic charr, FCR is about 10% better at 9 °C than at 15 °C, but growth rate is over 50% slower (Johnson & Burns 1984). From a commercial standpoint, the question becomes: is slower growth of that magnitude worth a 10% saving in feed costs? Body size and growth Arctic charr growth rates decrease as the ﬁsh grows larger. In practical terms, this size-related slowing of the growth rate means that it takes longer for a larger ﬁsh to double its weight than it does a smaller ﬁsh. For example, at 14 °C a 10 g Arctic charr could double its weight in about 40 days, but the same ﬁsh would require about ﬁve times longer to double its weight from

Fig. 4.5 Effect of temperature on feed consumption and food conversion rates. Data source: Johnson & Burns 1984; Jobling 1994.

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1000 g to 2000 g (see Fig. 4.6). This is a ﬁxed trait that cannot be readily altered in individual ﬁsh. However, different Arctic charr strains and individuals do have inherent differences for growth rate, so there is the option of ﬁnding or developing a strain of faster-growing ﬁsh (Jobling et al. 1993). This relative decline in growth rate as body size increases holds true for any Arctic charr regardless of water temperature when you are feeding a high-energy diet without restriction before the ﬁsh reaches sexual maturity. Once ﬁsh reach sexual maturity, growth rates in weight and length continue to decline, but at a faster rate than they do for immature ﬁsh, since a proportion of ingested energy is diverted to reproduction on a yearly basis, particularly in females. Size variation, dominance, and growth Food intake and growth rate vary between Arctic charr of the same age, and all races of Arctic charr currently under cultivation show considerable size variation amongst individuals of the same age cohort (Jobling et al. 1989a) (see Fig. 4.7). Some variation may be due to natural genetic variation in size, but much of it is due to dominant ﬁsh in the lot denying subordinate ﬁsh access to food, either by using physical aggression or, more subtly, by using social dominance in the form of psychological aggression. In a study using demand feeders and individually tagged ﬁsh, the Arctic charr sorted out into three size groups: one or two of the largest individuals that self-fed the most and dominated the feeders; a few medium-sized individuals that hit the feeders only occasionally but still grew almost as well as the largest ﬁsh; and a third group of small individuals that never struck the feeder and showed poor growth. These

Fig. 4.6 Relationship of declining growth rates to increased body size and time required to reach market size in Arctic charr. Data from: Jobling et al. 1989b.

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smallest ﬁsh showed clear evidence of physiological stress and subsequent poor growth (Alanärä et al. 1998). A tank containing individuals of varying sizes is difﬁcult to harvest all at once as only a certain number of individuals will have reached market weight. This means multiple harvests over an extended time, which increases stress in the remaining ﬁsh and represents higher harvesting costs. Fish of different sizes require mixed-sized feeds that take more time to prepare and are susceptible to wastage. One husbandry technique commonly used to overcome problems of size variability is routinely sorting ﬁsh by size into different tanks. There are contrasting opinions on the practical effects of size sorting on the growth of Arctic charr. Some quantitative evidence shows that sorting improves gains in biomass, while other evidence indicates that size-sorted Arctic charr suffer a growth disadvantage (Papst & Hopky 1985; Wallace & Kolbeinshavn 1988; Baardvik & Jobling 1990). Jobling and Reinsnes (1987) showed that the small ﬁsh grew better in the absence of larger ﬁsh, but the size sorting led to reduced growth in some of the larger ﬁsh, and overall biomass gain was less than for unsorted groups. Over time, size variation may be reduced by improvements in brood stock. Based on her work done with Nauyuk Arctic charr, Brenda de Marche (1997) concluded that more consistent group size can be obtained if large individuals within families are selected for breeding stock. However, she felt that culture conditions also inﬂuence variation in ﬁsh size. For uniform growth, she suggested that Arctic charr cultured together should be fairly uniform in size and have an initial size variation of less than 25%. Seasonal and daily rhythms in growth In a seasonal environment such as the High Arctic, animals evolve biological clocks that tell them when to anticipate and prepare for changes in seasonal food resources or take advantage of daily rhythms in food abundance. Captive brown trout and Atlantic salmon show daily and

Fig. 4.7 Size distribution in an unsorted lot of Arctic charr of the same age cohort. Data from Arctic Ova hatchery operations [pers. comm.].

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seasonal increases in swimming activity that coincide with the expected time of increased abundance of food items in the wild environment (Eriksson & Alanärä 1990). Biological clocks have evolved in Arctic charr, allowing them to anticipate predictable feeding opportunities in the wild. There are distinct daily and monthly rhythms in Arctic charr feeding behavior, superimposed on seasonal rhythms of feeding and growth. These patterns are evident in cultured Arctic charr, most noticeably in the level of appetite at different times of the day and year whether they are living under controlled artiﬁcial lights or in natural outdoor photoperiod. You must recognize these patterns to understand how charr feed and grow under intensive culture conditions. Seasonal rhythms in growth In the wild, anadromous Arctic charr of all strains show a similar pattern of voracious shortterm feeding and long-term fasting that corresponds to the natural productivity rhythms of the High Arctic seas. These patterns are also evident in well-fed cultured Arctic charr. Regardless of the age, sex, strain, or maturity of the individual ﬁsh, cultured Arctic charr show inherent annual cycles in feeding, growth, and lipid deposition (Näslund & Henricson 1996; Tveiten et al. 1996; Jørgensen et al. 1997). For example, working with Hammerfest Arctic charr held under light equivalent to natural conditions at 70°N latitude and at a constant temperature of 4 °C, researchers found that ﬁsh displayed distinct temporal changes in condition factor and growth rate (shown in Fig. 4.8). From December to April, feed intake and growth rate were low, with only 20% to 60% of individual ﬁsh consuming feed at any one time, leading to declining condition factor. The number of ﬁsh feeding, the amount of food they ate, and their condition factor and growth rate increased dramatically during the late spring and early summer, and then began declining throughout the fall period to winter lows. During the periods of heavy summer feeding, Arctic charr grow in body length and body weight. They also build up signiﬁcant amounts of lipid stores, used in part by mature ﬁsh for

Fig. 4.8 Seasonal changes in growth rates and condition factors in immature Arctic charr. Modiﬁed with permission: Tveiten et al. 1996.

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reproduction during fall, and by all ﬁsh to maintain metabolic functions during the long nonfeeding winter period (Tveiten et al. 1996). At a certain point, wild anadromous Arctic charr reduce their feed intake and eventually turn off their feeding. They become anorexic, relying on body energy and nutrient reserves for all metabolic functions for winter survival or spawning, and return to fresh water for the remainder of the winter. This pattern of cyclic feeding and growth was similar for maturing (ﬁsh spawning for the ﬁrst time that fall) and immature individuals, however mature ﬁsh (ﬁsh that had spawned at least once) stopped eating sooner and at lower speciﬁc growth rates. It is not clear exactly what signals the ﬁsh to stop eating – there are one or more possible factors. The amount of body lipid reserves, one of the measures indicated by condition factor K, may be one of the cues turning appetite and feeding on and off. A number of studies on Arctic char suggest that once ﬁsh reach a certain threshold condition factor K (1.4–1.5), they reduce their feed intake and then stop feeding (see Fig. 4.9). As stores of fat are built up during heavy bouts of summer feeding, condition factor increases; as energy stores are burned during the long winter, or used up during spawning, condition factor decreases. In the spring, low condition factor and the depleted energy stores may well stimulate the onset of the voracious feeding and rapid growth seen during summer months in wild anadromous Arctic charr (Tveiten et al. 1996). The other strong cue for seasonal changes in appetite and feeding is change in photoperiod. At some point, regardless of condition factor, wild anadromous Arctic charr must cease feeding and return from the ocean to fresh water, and changes in light levels are a reliable signal that marks the onset of winter. Perhaps both condition factor and changing light levels are complementary signals in controlling the onset and cessation of seasonal feeding and growth. If a charr reaches a high condition factor and cannot physically pack on any more fat, then it stops feeding regardless of photoperiod cues. On the other hand, once photoperiod declines

Fig. 4.9 Seasonal changes in lipid levels and condition factor in sexually maturing Arctic charr. Modiﬁed with permission: Jørgensen et al. 1997.

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to a certain level, the charr is signaled to stop feeding and return to fresh water, regardless of its condition factor. The need to return to fresh water overrides the need for additional energy stores. This pattern of reduced feeding in winter persists in cultured Arctic charr, although there are always a few ﬁsh that will take some feed during the winter. Mature females return to feeding, as do males once they have lost their spawning colors, but as winter sets in, even ﬁsh in poor condition reduce their feeding. Even when Arctic charr are held under constant light and temperature there seems to be a biological memory of their wild environment, as Jobling (1987) has noted an intrinsic 6-month cycle of growth. Daily and semi-monthly rhythms in growth Superimposed on the seasonal growth rhythms are shorter cycles of growth and feeding behavior oriented to lunar phases and daily changes in light/dark intensity. These cycles are difﬁcult to discern as they are often masked by the larger picture of seasonal growth, but they are real and they have an effect on feeding practices and food consumption. Arctic charr feed throughout the 24-hour day, with at least 20% of the ﬁsh feeding within any 3-hour period regardless of light levels. They show deﬁnite feeding rhythms, with peaks in feed intake occurring roughly at twilight, but varying by season (see Fig. 4.10). Arctic charr held under a 12-hour light/12-hour dark cycle showed two peaks in feeding activity, in the early morning and late afternoon (Brännäs 1998). During fall, winter, and spring, when there is a deﬁnite night and day, Arctic charr feed intake peaked in late afternoon and evening. When held under conditions of 24-hour daylight they increased their feed intake signiﬁcantly at mid-day (Jørgensen & Jobling 1989). Another feeding study showed that there are always individual Arctic charr feeding throughout the entire day based on their social rank. Fish of low rank (slow growers) visited the feeders when few or no larger individuals (fast growers) were present (see Fig. 4.11). Even when the feeders were turned off during the night, certain individual Arctic charr of low rank would visit in hopes of acquiring feed. The large charr that dominate the feeders push submissive charr away from the best feeding sites and best feeding times. Whatever feeding schedule is used, it must accommodate the feeding activity patterns of the competitive as well as the less competitive individuals in the lot (Brännäs 1998). When feeding Arctic charr, mimic the natural twilight zones. Even during the High Arctic summer solstice, there is a perceptible change in the daily intensity of light and a deﬁnite twilight period. There is never a time when Arctic charr in the wild would not experience a daily twilight period, and culturists should remember this when feeding Arctic charr under artiﬁcial light regimes. There are light-intensity controllers available to mimic the twilight zone. Arctic charr show deﬁnite short-term growth cycles that correspond to the moon phases (Dabrowski et al. 1992; Tye 1996). Growth rates wax and wane over a 2-week period, with maximum growth and food consumption occurring midway between the new and full moons, and low growth and food consumption occurring around the full and new moons (see Fig. 4.12). These cycles of growth suggest that the lunar cycle acts as a Zeitgeber (signal or trigger) for synchronization of growth rate rhythms (Farbridge & Leatherland 1987a). In salmonids studied to date (coho and brown trout), growth in body weight is out of phase with growth in length during the semi-lunar cycle. This has been termed growth

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Fig. 4.10 Daily rhythms in Arctic charr feeding during different seasons. Data source: Jobling et al. 1989b.

partitioning. During the period of heavy feeding and rapid growth, ﬁsh convert food resources into lipid stores, which are in turn used for energy during the period of body lengthening that coincides with low food intake (Farbridge & Leatherland 1987b). Although no studies have shown that growth partitioning occurs in Arctic charr, the similarities of their semi-lunar cycles to those of other salmonids strongly suggest a similar mode of growth (Dabrowski et al. 1992). The effect of sexual maturation on growth and market size Early sexual maturation is not a desirable trait in Arctic charr destined for the dinner plate. Sexual maturity leads to poor ﬂesh quality, reduced plumpness, and decreased growth rates. While in spawning colors, the male body shape changes in ways that make it unmarketable.

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Fig. 4.11 Visits to demand feeding sites by Arctic charr of different social rank, exhibiting low, medium, and high patterns of growth. Modiﬁed with permission: Brännäs 1998.

Fig. 4.12 Short-term cycles of growth rate in weight and length of Arctic charr showing lunar periodicity. Modiﬁed from: Farbridge & Leatherland 1987a; Dabrowski et al. 1992.

Similarly, the ﬂesh in both males and females is pale and soft, edible but hardly marketable. There is often increased mortality due to the stress of entering the spawning colors, males damage each other in ﬁghts, and fungus infections proliferate, particularly on males. Although Arctic charr do not die after reaching sexual maturity, they have ﬁnished their rapid immature growth phase. With the onset of sexual maturity, growth in body mass slows

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and energy resources are directed towards sexual activity. Reproduction takes precedence over eating. The ﬁshes’ bodies rely on stored energy supplies, taking away the source of fat, muscle ﬁrmness, and color that gives an Arctic charr ﬁllet its market appeal. In the spring, before Arctic charr reach maturity, there is no signiﬁcant difference in the length or weight of immature or maturing ﬁsh, but by late fall immature ﬁsh are bigger than their maturing cohorts (see Fig. 4.13). Immature Arctic charr grow faster in both length and mass and are plumper than maturing ﬁsh during the last growth period before maturity and will continue to be larger in subsequent years (Jobling & Baardvik 1991). Producing large (approximately 2.5 kg) Arctic charr for market before the onset of sexual maturity, and within a reasonable amount of time, has been a challenge for commercial growers. Many strains of Arctic charr reach sexual maturity at a small size, and others show an undesirable condition known as jacking (a common phenomenon in the salmonids), where some males of a cohort mature a year earlier than other ﬁsh or at a much smaller size. The factors initiating maturity in Arctic charr are not well understood, but as in other salmonids, size may be the most important determinant of whether or not a ﬁsh matures. In the wild, Nauyuk Arctic charr reach sexual maturity at about 60–70 cm, between the ages of 9 and 11 years. When cultivated under the natural photoperiod and water temperatures in the southern Yukon, Nauyuk Arctic charr mature at about the same body size as their wild brethren, particularly males, but in only ﬁve growing seasons, with no evidence of jacking. Using warmer water and manipulated photoperiods, Nauyuk Arctic charr can be grown to satisfactory large market weights in three growing seasons. Methods for preventing or delaying maturity or increasing the size of Arctic charr before they reach sexual maturity are not well understood, but there are a couple of possibilities. Male and female Arctic charr cannot be distinguished until shortly before maturity, and in some strains they appear to grow at about the same rate (Jobling & Baardvik 1991). However,

Fig. 4.13 Effect of sexual maturity on size of Arctic charr. Modiﬁed from: Jobling & Baardvik 1991.

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in other strains, such as Nauyuk, mature males are on average larger than mature females. This fact suggests that growing an all male-population may have merit as a method for increasing the mean market size of a cohort before maturity. There are techniques for producing monosex male populations (through the application of androgens during early development that produce phenotypic males regardless of sexual phenotype) (Donaldson & Devlin 1996). One research group is investigating visual techniques to determine sex in Arctic charr, based on body morphology at the ﬁngerling size. Condition factor (K) appears to be a key factor in determining the onset of maturity (Jobling & Baardvik 1991). Male charr that reached maturity early had higher condition factors in the spring than did ﬁsh that either matured later in the year or remained immature. In the wild, condition factor may also play a role in determining whether Arctic charr spawn. Mature Nauyuk Arctic charr that had spawned the previous fall contained 35 to 46% less energy than immatures and required two years of summer feeding in the Arctic Ocean to recover enough lipid reserves to spawn again (Dutil 1984). Sexual reproduction makes heavy demands on Arctic charr, so the ﬁsh must be a certain weight or length in their last year of immature growth, and then must get through the winter with enough excess energy stores to trigger sexual development in the next growing season. This research suggests that culturists could manipulate condition factor to delay spawning by withholding food late in the winter to decrease body condition. Withholding food may have the added advantage of inducing a compensatory growth response during the next growing season. Compensatory growth When food supplies are increased following a period of restricted feeding or starvation, ﬁsh and other animals display a growth spurt referred to as compensatory growth (Miglavs & Jobling 1989a; Quinton & Blake 1990). When salmonids are kept off food for weeks, or months, they become gluttons when food is again presented to them (Miglavs & Jobling 1989a; Jobling & Miglavs 1993; Nicieza & Metcalfe 1997). This gluttony may be induced in response to low lipid stores in the body. Jobling and Miglaves (1993) found that appetite declines as body lipid reserves accumulate. Food intake in Arctic charr was greatest in the ﬁsh with the lowest lipid stores. When lipid stores are depleted and energy reserves are low, food consumption is large, but as lipids accumulate and energy reserves become replenished, feeding slows. Some form of feedback mechanism leads to a decline in appetite and a reduction in rates of food intake. Anadromous Arctic charr, which fast for most of the year, display an extreme form of compensatory growth, feeding for only 40 to 50 days during the summer and growing more than expected based on water temperature or ﬁsh size. Cultured Arctic charr held on maintenance rations for a few months, then transferred to net-pens and fed to satiation, showed elevated rates of growth (Glebe & Turner 1993). They also show a compensatory growth response when they are repeatedly starved for 1 week and fed for 2 weeks. The true value of the compensatory growth response for commercial aquaculture lies in the feed savings, which can be signiﬁcant in a large grow-out operation. The 1 : 2 feeding cycle (1 week off feed, 2 weeks on) provides optimum savings, as 33% less feed is used while maintaining similar growth rates. The period of food deprivation does appear to increase conversion efﬁciency upon refeeding, as suggested above (Miglavs & Jobling 1989b). Using less

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feed also reduces the size of the waste load in downstream waters, saving on water remediation costs. A compensatory growth response is also evident in Arctic charr and other salmonids exposed to varying water temperatures and under different light regimes, irrespective of ration level. Both Atlantic salmon and Arctic charr show a compensatory growth response when transferred from sub-optimal temperatures to optimal water temperatures; however, the response is not so dramatic as when they are deprived of feed, at least in Atlantic salmon (Mortensen & Damsgård 1993; Nicieza & Metcalfe 1997). Researchers noted that European Arctic charr kept on short day-length (6 hours of light to18 dark), then transferred to long day-length (24 light to 0 dark), increased their growth rates. However the elevated growth rates declined over time under the new light regime. The authors speculated that the short day period may have been recognized by the ﬁsh as a short winter. They suggested that seasonal shifts in growth rate in ﬁsh are under photoperiodic control, while growth rate within a season mainly depends on water temperature (Mortensen & Damsgård 1993).

Nutritional requirements Arctic charr are carnivores, consuming a wide variety of aquatic and terrestrial creatures in the natural environment. Depending on their age, growth form, and size, they may eat anything from small insects, such as chironomid larvae only a few millimeters long, to large Arctic cod and capelin. Proteins and lipids, the main constituents of their wild prey, are burned with oxygen in the cell to supply Arctic charr with the energy needed to push water past the gills, pump blood through the heart, focus the eye, and swim at burst speed to capture prey. Once basic metabolic needs are met, nutrients from food are available for growth, reproduction, and lipid storage. The essential vitamins and minerals supplied by these same foods are required to synthesize the enzymes and hormones needed to carry out metabolism, to assure that milt and ova are produced at the right time, and to mediate the production of tissue and bone. Carbohydrate is not an important constituent in the diets of wild salmonids, but for practical reasons is important in prepared diets. Arctic charr nutritional requirements are divided into two broad groups: macronutrients (proteins, lipids, and carbohydrate) and micronutrients (vitamins, minerals, and carotenoid pigments).

Protein requirements Dietary protein is a major energy source for metabolic functions and is the source of amino acids needed for protein synthesis in ﬁsh (the bonds holding the amino acid carbon skeletons together are used for energy and the amino groups are used for protein synthesis). In carnivorous ﬁsh, optimum growth occurs when protein supplies about 40% to 50% of dietary energy (Jobling 1994). Only a few studies have looked at the dietary protein needs of Arctic charr, and they indicate that requirements range from 37% to 54% depending on age, the strain of ﬁsh studied, and the level of fat in the diet (Tye 1997). Like other salmonids, Arctic charr need less protein as they grow older (Tabachek 1984; de Silva & Anderson 1995). In juvenile Arctic charr, protein requirements appear higher for Nauyuk than other strains, but are similar for

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all other ages regardless of strain (Jobling & Wandsvik 1983b; Tabachek 1986; Gurure et al. 1995). It is important that dietary fat makes up at least 15% of the diet as it maximizes the use of protein for growth rather than as an energy source. Joanne Tabachek investigated the interaction of dietary fat with protein use in juvenile Nauyuk Arctic charr and found that weight gain was maximized in the least amount of time on diets formulated to contain 54% protein with 20% lipid (Tabachek 1986). This sparing effect, in which dietary lipid is used as an energy source instead of dietary protein, occurs in other salmonids as well. She also found that if lowest feed cost is the ultimate criterion, then a 44% protein with 20% lipid diet is less expensive and quite adequate nutritionally, but results in a minor reduction in growth potential. The consensus among commercial growers and some researchers is that Arctic charr require more protein than rainbow trout do at any given age. Their needs are more in keeping with levels fed to Atlantic salmon. The suggested gross dietary protein requirements for different aged charr are set out in Table 4.1. Essential amino acids Arctic charr use the amino acids from food as building blocks for synthesizing the proteins they need for their own growth and body maintenance. Each type of protein is composed of repeating but distinct combinations of 20 different amino acids. Arctic charr and other salmonids can make sufﬁcient quantities of 10 amino acids, but the other 10, known as the essential amino acids, must be present in their diet. The dietary quantities of the amino acids required by Arctic charr are not speciﬁcally known. Of the essential amino acids needed by salmonids, lysine and methionine are usually the most limited in availability. Lysine must make up 2.1–2.4% of total protein in juvenile Labrador Arctic charr diets (Tye 1997), while methionine requirements are 1.8% of dietary protein. Researchers noted that methionine levels of 2.4% prevented cataracts, though feeding these levels of methionine lowered growth rates slightly (Simmons & Moccia 1997). Because blind or partially blind Arctic charr fare poorly in an intensive tank farm environment, often having worn ﬁns and skin abrasions from rubbing against tank walls, it is probably a good idea to set methionine levels at 2.4% of total protein to prevent cataracts in brood stock and for the general well-being of on-growing ﬁsh. Atlantic salmon, rainbow trout, and Arctic charr have similar whole-body tissue levels of amino acid, and the results from a number of nutritional studies indicate that the gross dietary protein requirements of Arctic charr and Atlantic salmon are also similar (Jobling &

Table 4.1 Dietary crude protein requirements (as % of total diet) for various strains of Arctic charr compared to other salmonids. Data source: Jobling & Wandsvik 1983b; Tabachek 1986; Hardy 1991; Gurure et al. 1995. Arctic charr

Alevin/Fry Juvenile Grow-out Brood

Nauyuk

Norwegian

Labrador

50 54 40 45

50 45 40 45

50 42 40 45

Atlantic salmon

Rainbow trout

45–50 40 40 45

45–50 40 35 40

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Wandsvik 1983b; Jobling 1994; Gurure et al. 1995). Arctic charr should perform well on diets with protein levels formulated for Atlantic salmon, with methionine and lysine added to meet the speciﬁc requirements for Arctic charr (see Table 4.2).

Lipids and essential fatty acids Fish use lipids mainly to store energy and as components of cell membranes. Of most interest to ﬁsh nutrition and diet preparation are three groups of lipids: fats, phospholipids, and fatty acids. Fatty acids are the main constituents of fats and phospholipids. The fats are the main long-term energy storage sites in salmonids, ready for mobilization in times of energetic need. They are composed of a glycerol molecule joined, usually, to three fatty acids and are known as triacylglycerols or triglycerides. Phospholipids are structurally similar to fats but have only two fatty acids linked to glycerol, with the third hydroxyl group (an -OH group) joined to a phosphate molecule and other smaller molecules. The tail of the fatty acid is hydrophobic, the phosphate head is hydrophilic, and by lining up they can form cell membranes that repel water. In addition, phospholipids are precursors for eicosanoids, which regulate a wide variety of physiological processes such as ovulation and respiration systems. Lipid as an energy source Dietary lipids are metabolized before being stored in adipose tissue or used as an immediate energy source. They are transported in the bloodstream as lipoproteins, and once within the cells of adipose tissue or skeletal muscle they are either resynthesized into triacylglycerol for storage or oxidized to release energy. When triacylglycerols stored in adipose tissue are required for energy elsewhere in the body, they are hydrolyzed to glycerol and free fatty acids before being transported to other cells (de Silva & Anderson 1995). In Arctic charr, 50% of total body lipid stores are in the skeleton, skin, and head regions, with over 35% of the lipid stores found in the muscle tissue. In mature female Arctic charr, 23% of total lipid stores are in the gonads (Jørgensen et al. 1997).

Table 4.2 Essential amino acid composition of muscle from Arctic charr, Atlantic salmon and rainbow trout. Data source: Jobling et al. 1993, Jobling 1994. Values in parentheses are calculated dietary requirements. All values as % of total protein.

Arginine Histidine Isoleucine Leucine Lysine Methionine Phenylalanine Threonine Tryptophan Valine

Arctic charr

Atlantic salmon

Rainbow trout

4.6 2.2 4.6 8.3 8.7 (2.1–2.4) 3.0 (2.4) 3.6 5.3 Unknown 6.3

6.6 3.0 4.4 7.7 9.3 1.8 4.4 5.0 0.9 5.1

6.4 (3.5) 3.0 (1.6) 4.4 (2.4) 7.6 (4.4) 8.5 (5.3) 2.9 (1.8) 4.4 (3.1) 4.8 (3.4) 0.9 (0.5) 5.1 (3.1)

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Arctic charr require at least 15 to 20% dietary fat for good growth, combined with at least 37% protein. Levels of 10% fat are inadequate for good nutrition (Tabachek 1986). Growth rates are very good at dietary fat levels of 24%, however the ﬂesh and particularly the belly skin are noticeably oily, imparting a rich ﬂavor but unsatisfactory to some consumers. Essential fatty acids From a nutritional perspective, there are two classes of fatty acids that vary in structural properties because of differences in the length of the carbon chain and in the number and location of double bonds. Saturated fatty acids have no double bonds and are found typically in mammal fats such as butter, beef fat, and pig lard. Most are not suitable as an energy source for coldwater salmonids, as they congeal into solids at low temperatures. Unsaturated fatty acids have one or more double bonds that ‘kink’ the molecule, preventing it from packing closely together, which makes these fatty acids liquid even at temperatures below 0 °C. Unsaturated fatty acids with two to four double bonds are termed polyunsaturated fatty acids (PUFAs). Almost all of the prey fed upon by wild Arctic charr, such as amphipods and copapods, aquatic and terrestrial insects, and freshwater and marine ﬁsh, contains a very high proportion of PUFAs. A few of the fatty acids must be included in manufactured food as they are essential fatty acids (EFAs). Fish are unable to synthesize PUFAs of the (n-3) and (n-6) series, notably α-linolenic acid (18 : 3 (n-3)) and linoleic acid (18 : 2 (n-6)). Arctic charr need these PUFAs to form highly unsaturated fatty acids (HUFAs). The HUFAs are incorporated into the phospholipids that become components of cell membranes and that are precursors of eicosanoids (Jobling et al. 1993). About 1 to 2% of total diet, or 20 to 40% of total dietary lipid, should be made up of α-linolenic acid. The linoleic acid requirement is not so clear, but there is evidence that small amounts (less than 0.7% of total diet) are beneﬁcial, or at least not detrimental to growth in Arctic charr (Yang et al. 1994). Higher levels of 18 : 2 (n-6) inhibit growth once the requirements for α-linolenic acid have been met (Yang & Dick 1994b). Arctic charr show typical EFA deﬁciency signs such as fatty liver, elevated water content in whole body tissues, poor feed efﬁciency, and poor growth when deprived of (n-3) PUFAs (Yang et al. 1994). The type and amount of fatty acids in Arctic charr diet are important to culturists because the composition, texture, and taste of Arctic charr ﬂesh are strongly affected by what the ﬁsh eats. Over time, the fatty acid composition of muscle reﬂects the contents of the ﬁsh’s diet, and this can make it more or less appealing to the consumer. Fatty acid composition of cultured Arctic charr fed prepared diets is different from that of wild Arctic charr (see the comparison in Table 4.3) and can impart differences in taste. For example, a diet containing 10% or more fatty acids sourced from plant meals or oils can give off-ﬂavors to the cooked ﬂesh (Bjerkeng et al. 1997b). The source of dietary fatty acids is also important from a human nutritional standpoint. One of the positive marketing considerations for Arctic charr is that they are a source of nutritionally beneﬁcial (n-3) unsaturated fats. These are the omega-3 fats that nutritionists around the world exhort us to consume on a weekly basis. If cultured Arctic charr are fed diets made up primarily of plant oils and terrestrial animal fats, then the muscle is dominated by 18 : 2 (n-6) fatty acids, monoenes, and saturated fatty acids, which are undesirable from a

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Table 4.3 Fatty acid composition as percent of total muscle lipids in cultured and wild Arctic charr compared to Atlantic salmon and rainbow trout. Data source: Yang & Dick 1994a. Commercial diet§

Wild diet

Fatty acid

Rainbow trout

Arctic charr†

Arctic charr‡

Atlantic salmon

12 : 0 14 : 0 16 : 0 16 : 1 n-9 16 : 1 n-7 18 : 0 18 : 1 n-9 18 : 1 n-7 18 : 1 n-5 18 : 2 n-6 18 : 3 n-6 18 : 3 n-3 18 : 4 n-3 20 : 1 n-9 20 : 2 n-9 20 : 2 n-6 20 : 3 n-9 20 : 3 n-6 20 : 4 n-6 20 : 3 n-3 20 : 4 n-3 20 : 5 n-3 22 : 1 n-9 22 : 4 n-6 22 : 5 n-6 22 : 5 n-3 22 : 6 n-3 24 : 1 n-9 Σ saturates Σ monoenes Σ PUFA Σ (n-9) Σ (n-6) Σ (n-3)

0.1 3.0 15.0 0.1 6.5 3.4 7.4 3.2 0.3 5.1 0.2 0.5 0.6 0.8 0.1 0.4 0 0.3 0.5 0.1 0.5 4.2 0.4 < 0.1 0.2 1.1 15.8 0.6 22.2 37.6 30.1 0.2 7.0 23.0

0.1 3.4 14.4 0.1 7.7 2.7 16.4 3.2 0.3 5.9 0.2 0.6 0.8 3.8 0.1 0.3 0.2 0.3 0.5 0.1 0.6 5.3 1.1 0.1 0.1 1.1 13.5 0.6 21.3 44.7 30.4 0.4 7.8 22.3

ND 1.0 15.9 0.4 3.7 5.5 11.3 3.9 ND 6.8 < 0.1 1.8 0.4 0.5 ND 0.5 ND 0.7 8.3 0.2 0.5 8.0 0.1 0.7 1.1 3.3 18.3 0.8 23.36 22.3 50.2 ND 18.1 32.1

* 1.5 14.2 5.5 * 5.3 12.6 * * 3.1 * 2.2 8 0.8 * * * * 8.0 * * 4.6 * 1.3 2.0 3.3 15.4 * 24.4 26.5 45.3 * 15.8 27.2

*Included in other fatty acids or not reported; †Cultured Nauyuk Arctic charr (2–16 g size); ‡From Saguagjuac, Nunavuut (480–705 g size); §Trout pellets containing 52% protein, 15% lipid, 2.5% ﬁber; ND = not detectable

human health perspective. On the other hand, if cultured Arctic charr are fed diets formulated with marine ﬁsh oils as the major lipid source, then ﬁllets will taste better and should contain relatively high levels of nutritionally beneﬁcial (n-3) types of fatty acids. Thus from both a ﬂavor perspective and a human nutritional perspective, it is important to minimize plant and terrestrial animal fats in prepared diets, and there are few arguments for replacing marine ﬁsh oils with any plant oils or terrestrial animal fats (Jobling et al. 1993; Jobling 1994; Bjerkeng et al. 1997b).

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Dietary carbohydrate Carbohydrates are organic molecules composed of hydrogen, carbon, and oxygen. They range in size from simple monosaccharide sugars such as glucose to the large polysaccharide storage macromolecules of starch and glycogen. As well as storing energy, carbohydrates have important structural functions as cellulose in plants and chitin in the exoskeleton of invertebrates. Arctic charr, like other salmonids, have no known dietary requirements for carbohydrate other than as a metabolic energy source. However, they may use carbohydrate to form the amino sugars that are components of glycoproteins such as collagen, and they may use it in building the carbon skeleton for fatty acid synthesis. As an energy source in prepared diets, carbohydrate is cheaper than protein and is acceptable to Arctic charr depending on the percent composition in the feed. Arctic charr may be more sensitive than other salmonids to levels of carbohydrate higher than 15% of total diet by weight (Eriksson 1991). Increasing levels of carbohydrate in ﬁsh diets can decrease the use of all feed, possibly by physically obstructing digestive enzymes. Salmonids digest and metabolize the simple sugars easily, but they digest and absorb large polysaccharides, like cellulose and starch, poorly. Raw starch becomes more digestible, however, if it is gelatinized by heating during feed manufacture (Jobling 1994). Carbohydrates from the seeds of soybean, canola, wheat, and maize are used as binding agents in manufactured feeds and therefore make up much higher dietary levels (10 to 20%) than they do in wild food sources (0 to 10%). These sources of carbohydrates also contain good levels of protein and some fat, but each has a downside as a feed additive, and you should view their inclusion in Arctic charr feeds with caution, as illustrated by Table 4.4.

Vitamin requirements Vitamins are organic compounds that are required by all animals in very small amounts relative to other nutrients in the diet. They are intimately involved in the regulation of many metabolic processes as constituents of enzymes and co-enzymes, and as structural components of

Table 4.4

Suitability of various carbohydrate-containing plants as Arctic charr feed ingredients.

Plant

Value as feed ingredient

Problem

Solution

Soybean

Excellent protein/lipid proﬁle

Controlled heat treatment to reduce trypsin inhibitor

Canola

Good protein source

Cottonseed meal

Good amino acid proﬁle

Corn gluten meal Wheat gluten meal

Good protein source Excellent protein source

Trypsin inhibitor reduces protein digestibility. Phytic acid negatively impacts reproduction, binds minerals Poor palatability. Phytic acid impacts reproduction, binds minerals Contains alkaloids and cyclopropene fatty acids, causing liver necrosis Adds ﬁber, colors ﬁsh yellow Too expensive

Dephytinize canola oil

Use at low dietary levels

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cell membranes, but they have no value as a source of energy. Most are supplied in the natural diet, but some can be synthesized in the body or by microbes in the gut. Of the 15 vitamins required by salmonids, 11 are water soluble and 4 lipid soluble. The lipid-soluble vitamins A, D, E, and K are required in feed in very small amounts. They are absorbed with lipids across the gut mucosa and are stored primarily in the liver. Eight of the water-soluble vitamins are B-complex members involved with co-enzyme functions and are needed in small quantities. The other three water-soluble vitamins – choline, inositol, and ascorbic acid – are generally required in larger doses than the B-complex vitamins. The water-soluble vitamins are stored in small amounts in the liver, so there is a regular requirement for these vitamins either through diet or through synthesis. Vitamin requirements for most of the salmonids are in the same order of magnitude, so one would expect the requirements of Arctic charr to be similar. There is no evidence in the literature or anecdotally from producers or researchers suggesting that Arctic charr suffer any vitamin deﬁciencies when fed commercial diets prepared for Atlantic salmon. On a practical level, the guidelines suggested for salmonids by Malcolm Jobling (1994), set out in Table 4.5, are the best approach until more is known about speciﬁc Arctic charr requirements. There is evidence that some vitamin requirements increase with the age of the ﬁsh, reproductive status, or with the amount of protein in the diet (vitamin B6). Joanne Tabachek suggested adding 1000 mg/kg vitamin C and 600 mg/kg vitamin E to Arctic charr brood stock diets (Krieger 1991). When feed is heated during manufacture, the quality of some vitamins is degraded, so they must either be included in greater levels than actually needed or added afterwards as a pre-mix to compensate for their loss in potency. Vitamins are generally not toxic in modest excess, although some of the fat-soluble vitamins can be stored to toxic levels if fed in too high a concentration. This is not likely to be a concern with commercially produced feeds used in the salmon industry. Table 4.5 Dietary vitamin requirements for Arctic charr based on data from other salmonids. Data source: Jobling 1994; Avault 1996; Halver 1996. Vitamin (mg/kg dry diet) Water soluble Thiamine (B1) Riboﬂavin (B2) Pyridoxine (B6) Pantothenic acid Niacin Folic acid Cyanocobalamin (B12) Myo-inositol Choline Biotin Ascorbic acid C Lipid soluble Vitamin A* Vitamin D† Vitamin E Vitamin K

Brook charr 10–12 20–30 10–15 40–50 120–150 6–10 R R R 1–1.2 R R R R R

Lake charr

Atlantic salmon

5

0.1 50

35 0.5–1.0

Rainbow trout

Paciﬁc salmon

Salmonids

1–10 2.7–15 2 20 10 1.0 R 250–500 1000 0.08 40

10–15 7–25 6–15 17–50 150–200 2–10 0.02 300–400 600–800

15 30 20 50 200 10 0.02 400 3000 1.5 200

0.75 0.04–0.06 30–100 ?

R NR 30–50 R

50

R = required; NR= not required; *1 IU = 0.30 μg all trans-etinol; †1 IU = 0.025 μg cholecalciferol

0.75 0.06 50 10

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A common complaint of small-scale producers ordering feed from commercial feed companies involves shelf life. The marine oils in feed are susceptible to oxidative degradation or rancidity, which is prevented by the addition of vitamins C and E as anti-oxidant agents. Vitamin supplements in ﬁsh feed remain stable after manufacturing for a period of months at some farms, but they are also subject to oxidative degradation over time when stored under normal temperatures (at feed moisture levels in pelleted and extruded feeds). Different forms of vitamins have different shelf lives. For example, two forms of vitamin C used in salmon feeds, known as ascorbyl 2-sulfate and ascorbyl 2-polyphosphate (C3-P), were compared for vitamin C stability and availability. The ascorbyl 2-sulfate was much more stable, retaining close to 100% stability when stored at 23 °C for 3 months (Maugle 1993). To assure the maximum shelf life of feeds, culturists should insist that each feed order is of recent production and uses antioxidant agents that give long shelf life to the feed.

Minerals and other trace elements Minerals are inorganic, naturally occurring compounds or elements required in small amounts by salmonids. Like vitamins, they are associated with the production of enzymes required in many metabolic functions. For example, iron is a critical part of cellular respiration in binding oxygen to hemoglobin. Magnesium is essential to intermediary metabolic reactions in cell construction and in respiration. Calcium and phosphorus are both required by salmonids in relatively large amounts for the formation of bone and cartilage. Most of the dietary requirements for minerals are met through ingestion, but salmonids can absorb some of the minerals they require through the gills – particularly Na+, K+, Ca2+, and Mg2+. The availability of these ions in the water affects dietary requirements. Calcium is not required in the diet in most fresh waters because it is readily available and easily absorbed. Zinc is an essential element in low concentrations, but when present in elevated concentrations in surrounding waters it can inhibit respiration. Selenium is required at 0.5 mg/kg in fresh water, but if supplied at 1–2 mg/kg prior to smolting, survival rates of rainbow trout, coho, and Atlantic salmon improve (Halver 1996). The dietary mineral requirements for ﬁsh are poorly deﬁned in general and are unknown for Arctic charr. However, there is no evidence that Arctic charr suffer deﬁciency symptoms when fed commercially produced salmon feeds. They have whole body levels of similar magnitude to other salmonids, and the dietary levels suggested by Jobling for salmonids in general, and those suggested for rainbow trout by Halver, are currently the best idea we have for Arctic charr mineral requirements. They are set out in Table 4.6.

Carotenoid pigments Carotenoid pigments belong to a family of diverse plant-synthesized products called isoprenoids, which include steroids, carotenoids, turpentines, and rubber. They are hydrocarbon compounds in pigment shades of red, yellow, and orange that protect the chlorophylls in plants from photo-oxidation and expand the bandwidth of light available for photosynthesis. They can ﬂuoresce when excited by light. The two groups of carotenoid pigments, carotenes and xanthophylls, have general properties similar to lipids (Jobling 1983).

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Table 4.6 Mineral requirements for Arctic charr based on those of other salmonids. Data source: Huet 1972; Yurkowski 1986; Jobling 1994; Halver 1996. Mineral

Calcium (Ca) Cobalt (Co) Copper (Cu) Iodine (I) Iron (Fe) Magnesium (Mg) Manganese (Mn) Phosphorus (P) Potassium (K) Selenium (Se) Sodium (Na) Zinc (Zn)

Whole body levels (mg/kg)

Dietary requirements (mg/kg dry diet)

Arctic charr

Atlantic salmon

Rainbow trout

Salmonids

6467 NR 3.4 NR 41 980 2.6 14 133 12 167 1.04 2517 54.1

NR NR

NR NR

3000 5–10 ~5 ~ 0.3 30–60 500 ~ 20 6000 NR ~ 0.3 NR 30–100

6 R 73 NR 20 13 000 NR R NR NR

3 1.1 60 500 13 6000 700 0.5 6000 30

NR = not reported; R = required but levels uncertain

Although there are over 80 different carotenoid pigments, only two – astaxanthin and canthaxanthin – are important to salmonids. Arctic charr, like other ﬁsh and animals (except protozoa), must obtain carotenoid pigments from dietary sources. Natural sources of astaxanthin available to salmonids in the wild include many species of invertebrates such as shrimp, copepods, and insects. There are few natural sources of canthaxanthin, and only astaxanthin and its metabolite idoxanthin are found in wild Arctic charr (Aas et al. 1997). Either astaxanthin or canthaxanthin or a mixture of both are added to pelleted feed. These two pigments are synthetically produced, with astaxanthin (produced only by Hoffman-La Roche as Carophyll Pink©) having the greatest use in salmonid aquaculture. The yeast Phafﬁa rhodozyma is a natural source of astaxanthin, but its use as a pigment source for salmonid aquaculture is in its infancy (Nickell & Bromage 1997). There are marketing and nutritional reasons to add carotenoid pigment to Arctic charr diets. Flesh color in salmonids is an important measure of market acceptability by the consumer, and the orange-red ﬂesh of a ﬁllet is the result of ingested carotenoid pigments contained in wild invertebrate foods or added to prepared diets. The overall appearance of salmonid ﬂesh is produced by an interaction of many factors, only one of which is the chemical state and concentration of carotenoid pigment. However, without ingesting pigment, the ﬂesh of salmonids is dull and pale. Arctic charr marketed in Canada has a tradition of red or orangered ﬂesh, and this is what the consumer wants and expects. This is also the color preferred by many European and Asian consumers in their premium salmon products (Nickell & Bromage 1997; Olsen & Mortensen 1997; Hatlen et al. 1998). Arctic charr also appear to grow better and resist disease when fed relatively high levels of astaxanthin or canthaxanthin. Researchers at the University of Guelph noted that when Arctic charr were not fed any pigment, they exhibited signs of a nutritional muscle degeneration (Swatland et al. 1998). Astaxanthin may play an important role in protecting lipid tissue from peroxidation and may enhance immunity or the immune response (Christiansen et al. 1995). There is some evidence it increases resistance to Aeromonas infections in Atlantic salmon, as the mortality rate was much lower in parr receiving astaxanthin than in the control group fed none. There is also some evidence that hatching success and survival of Arctic charr and

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Atlantic salmon alevins were improved when brood stocks were fed diets containing carotenoids, perhaps acting as a vitamin A precursor (Torrissen 1984; Metusalach et al. 1996b). Researchers from Bergen noted that the growth of Atlantic salmon parr was signiﬁcantly improved when fed diets containing astaxanthin at 60 mg/kg for 10.5 months (Christiansen et al. 1995; Swatland et al. 1998). Astaxanthin is absorbed through the intestinal wall and is packaged into discrete particles of lipoprotein, which enables its transport through the blood. The pigment is deposited in muscle tissue, with the level of deposition dependent on the binding properties of the pigment-carrying lipoprotein. The absence of certain pigment-carrying lipoproteins may explain the wide variation of muscle pigment levels in salmonids of different ages and in different strains of Arctic charr (Nickell & Bromage 1997). Dietary carotenoids are highly sensitive to oxidative degradation, so diet formulation affects the ability of salmonids to use them. For example, the presence of vitamin E may reduce the oxidative degradation of carotenoids in the intestine, and an increase in dietary lipid levels may increase the efﬁciency of astaxanthin retention in the ﬂesh. Absorption of carotenoids is also affected by age, reproductive status, size, water temperature, and genetics (Christiansen & Wallace 1988). In general, smaller juvenile Arctic charr deposit pigments less evenly than older ﬁsh, with lesser amounts in the muscle and more in the skin. Research involving immature Hammerfest charr revealed that the smaller, younger charr (1 year of age, 31 g) deposited less than half as much canthaxanthin, predominantly in the caudal region, while the larger, older char (2+ years, 203 g) deposited pigment evenly between the caudal and dorsal regions. The larger char had twice as much pigment in the ﬂesh as the small charr, but there was considerable variation between individuals, ranging from slightly pink to very red (Christiansen & Wallace 1988). Researchers from Tromsø, Norway, found that idoxanthin, a metabolite of astaxanthin, was the predominant pigment in the ﬂesh of Arctic charr, irrespective of age. However, the younger, smaller ﬁsh had relatively higher levels of idoxanthin than the older ﬁsh, which may explain why other researchers have found low levels of astaxanthin in younger ﬁsh. The younger ﬁsh are metabolizing the astaxanthin as part of their natural development. As they get older, more of the pigment remains as astaxanthin (Aas et al. 1997). When charr reached the size of 900–1200 g, they showed no difference in color or in carotenoid concentration in ﬂesh between the sexes of immature and non-spawning mature Arctic charr (Hatlen et al. 1998). Sexually mature female charr mobilize carotenoids to the maturing ova, while they move to the skin in sexually mature males, making the ﬂesh of both mature sexes considerably paler during the spawning period. The considerable differences in ﬂesh color of various races of charr, both in the wild and under culture, suggest a strong genetic component to pigment uptake. Wild Arctic charr from northern Bafﬁn Island are much redder than the orange-red Arctic charr from Nauyuk Lake. Labrador Arctic charr vary in color from ivory to pale red and even show variation in different locations in the muscle, giving a mottled coloration to the ﬂesh. Nauyuk Arctic charr take up pigment more evenly throughout the muscle mass. The evenness and darkness of Arctic charr ﬂesh affect the price to the producer, just as they do with other salmonids. Chinook salmon also show a considerable variation in the ability to deposit pigment in the ﬂesh, with some races very red-ﬂeshed and others with ﬂesh the color of ivory. On Canada’s West Coast, a red-ﬂeshed chinook salmon is known as a ‘smiley,’ as it commands about twice the price of an ivory-ﬂeshed ﬁsh.

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Levels of pigment required Salmonids retain pigment from pelleted feeds more poorly than they do from a wild diet, at rates of only 2% to 10% of dietary intake. In some races of Arctic charr, retention is at the lower end of this range. In general, culturists must add at least 4 mg of pigment per kg of muscle (and preferably more) to meet consumer preference (Jobling et al. 1993). This means adding signiﬁcantly more pigment into prepared feeds to get this level of uptake in the muscle tissues. Olsen and Mortensen (1997), using cultured Arctic char from northern Norway, established a dose response relationship between the amount of dietary astaxanthin and the degree of redness in the ﬂesh of Arctic charr (see Fig. 4.14). As dietary carotenoid levels rose to 70 mg/kg, they noted a clear tendency towards increased pigment retention in Arctic charr muscle, giving a redness of 7 to 9 that they felt was satisfactory for the marketplace. (A redness of 8 to 10 would be similar to the darkest red achieved in Atlantic salmon, but not as red as sockeye salmon.) At higher levels of dietary pigment, muscle deposition and redness appeared to level off. In general, larger ﬁsh have higher levels of muscle pigment than smaller ﬁsh, but older ﬁsh also had higher levels of pigment and it is not clear which factor – age or size – is the crucial factor in pigment retention. Since carotenoid pigments are important to aspects of reproductive maturity, reproductive age and not size may be the important factor (Metusalach et al. 1996a). Researchers noted that redness of muscle was always higher in Arctic charr grown at 8 °C than at 12 °C and suggested that this may be because food is held longer in the gut at colder temperatures, thus allowing increased absorption of astaxanthin. They were unable to achieve a minimal level for astaxanthin of 6 mg/kg in the ﬂesh of pan-sized Arctic charr (350 g) even after 18 weeks on pigmented feed (Olsen & Mortensen 1997). In none of

Fig. 4.14 Relationship of visual redness to muscle pigment concentration in Arctic charr. Source: Olsen & Mortensen 1997.

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the studies, which used strains of Arctic charr from Norway, Svalbard, and Labrador, did the ﬂesh attain pigment content that could be considered of high market appeal. At best it would be considered only satisfactory. Nauyuk Arctic charr larger than 500 g take up pigment in the muscles, giving a very consistent orange-red coloration similar to Atlantic salmon. Astaxanthin, astaxanthin–canxanthin mixtures, and canxanthin on its own gave about the same levels of pigmentation (Tabachek 1993). The entire issue of pigmentation in Arctic charr is rather confused. Carotenoid pigments are required for good nutrition and health in all stages of life and should be included in all feeds, but the levels required for good marketability are not clearly understood. Genetic origin, the size and age of the ﬁsh, and feeding conditions all affect ﬁllet color in Arctic charr, independent of carotenoid concentration in the muscle. In some strains, particularly European and Labrador charr, it may not be possible to pigment ﬁllets to an acceptable orange-red color. Nauyuk Arctic charr give very good, even, orange-red color throughout the muscle mass, and they should be the standard to measure color against instead of attempting comparisons with Atlantic salmon and rainbow trout. Nonetheless, there are some guidelines with respect to pigment usage that will help to improve Arctic charr health and marketability: muscle pigmentation occurs in larger Arctic charr, over 500 g; do not attempt to color• Best up pan-size Arctic charr. is required at levels of 70 mg/kg feed for at least 15 weeks to gain sufﬁcient • Astaxanthin pigment deposition in ﬂesh. Pigmentation is better in water at 8 °C than 12 °C. • Arctic charr should always, throughout their lives, be given pigmented feed. • Feed high-fat, high-energy to maximize pigment deposition. • Nauyuk Arctic charr have adiets darker orange-red ﬂesh color and more consistent color than • other strains, so raise them.

Prepared diets and manufactured feeds In the wild, Arctic charr use a variety of foodstuffs, all of them from live animal sources, to meet their nutrient requirements for minerals, vitamins, lipids, proteins, and energy. These wild food sources are not usually available in sufﬁcient or economic quantities for use in prepared diets for intensive culture. Under intensive culture, all of the nutrients and energy required for body maintenance, growth, good health, and reproduction must come from prepared diets. The prepared diets must also supply an acceptable level of lipid and pigment to the ﬁnished ﬁllet. Slight alterations in diet formulations may contribute to subtle changes in the ﬂesh color, texture, and taste, all of which are important criteria when a ﬁsh consumer makes purchasing decisions. It is not an easy task to prepare a diet that supplies all of the gross macronutrients and complex micronutrients required by Arctic charr, encapsulated in a compact feed pellet. The diet must adhere as a pellet during transportation and feeding, be palatable to the ﬁsh at low moisture levels, and remain stable under varying storage conditions without losing its nutritional qualities. This single-source diet in a pellet is one of the most important factors

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inﬂuencing the ability of a cultured ﬁsh to attain good growth, reproduction, and consumer appeal. It must meet a number of criteria, including: ll the nutritional and metabolic requirements for good health and body maintenance; • fulﬁ rapid growth in body length and muscle mass; • impart be highly and digestible, particularly to ﬁrst-feeding Arctic charr alevins; • maximizepalatable reproductive capabilities in brood stock and enhance survival of eggs and pre• feeding alevins; good ﬂesh color, texture, and taste to ﬁnished ﬁllets; • promote minimize production of waste products by being highly digestible. •

Investigations of Arctic charr diets The earliest investigations into diets suitable for rearing Arctic charr were conducted in Austria, Norway, and Canada during the late 1970s and early 1980s. Steiner, working at the University of Innsbruck, compared a variety of start-feeding diets (diets for newly hatched ﬁsh) including live plankton, commercial trout and salmon food, and specialty diets composed of curd, blood powder, and dried marine crustaceans. He concluded that the optimum diet for start-feeding Arctic charr alevins was natural crustacean and plankton, which gave higher growth rates and lower mortality rates than freeze-dried plankton or commercial dry feeds (Steiner 1984). Other researchers from the University of Innsbruck, at a much later date, were able to come up with a more practical diet formulation that did not contain live or frozen zooplankton. Using resident charr from Plansee, Austria, they compared various startfeeding diets and concluded that diets with high protein levels (66–67% of diet content) and fat (13–17%) were best. Mortality was low on these high-protein diets when they were composed of ﬁshmeal. However, in diets containing lower levels of protein, particularly those formulated with soybeans (which contain trypsin inhibitor), growth rates were lower and the mortality rates were many times higher. Small changes in diet formulation – for example, the use of lower grade ﬁshmeal or the addition of non-ﬁsh protein sources such as soybeans or blood meal – may lead to dramatic declines in food acceptance and growth, and to increased mortality in alevins (Dabrowski et al. 1992). There is some debate whether Arctic charr need a diet different from other salmonids. Jobling and Wandsvik (1983b) compared the growth of juvenile Norwegian Arctic charr fed diets of different protein levels, and they suggested that Arctic charr protein requirements were almost identical to those of rainbow trout and that no special diet formulations were required. Tabachek (1984), working at the Freshwater Institute in Winnipeg, showed that juvenile Arctic charr diets were a bit more complicated than that. She evaluated a series of ﬁve commercial trout and salmon formulations and a control diet to determine suitable commercial diets for raising various strains of Arctic charr. The control diet worked well with both Labrador and Sunndalsora strains, but they each differed in their growth response to the other diets. Neither strain of Arctic charr grew as well as did the rainbow trout. These differences between the strains were attributed to either variations in nutritional requirements, nutritional tolerance of dietary ingredients, or digestibility of certain ingredients. The basic nutritional requirements for Arctic charr are similar to those of other salmonids, although charr differ in a number of ways:

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alevins require a semi-moist, highly palatable, high-quality protein diet. • Start-feeding All ages appear sensitive to carbohydrate levels above 15% of the diet. • Charr require higher levels of the 18 : 3 (n-3) fatty levels than other salmonids, and they • may require 18 : 2 (n-6) essential fatty acids. require higher-quality protein than do rainbow trout. • They They higher levels of carotenoid pigment than do salmon or trout. • Variousrequire strains and ages show marked differences in their responses to the same levels of • carotenoid pigments. • Various strains and ages show slight differences in their responses to the same diet. Digestibility is a measure of the difference between the gross energy or nutrient value of an ingredient and the amount actually absorbed across the gut wall by the ﬁsh. In the best of feeds, about 90–95% of the energy available in the raw diet is used by the ﬁsh. Digestibility varies between feed ingredients and ﬁsh species. Arctic charr’s ability to digest common ingredients used in commercial feed was investigated by Gurure et al. (1996). The researchers compared six feed ingredients – herring ﬁshmeal, menhaden ﬁshmeal, South American ﬁshmeal, wheat middlings, corn gluten meal, and soybean meal – to a reference diet and calculated apparent digestibility coefﬁcients (the amount actually digested) for dry matter, crude protein, fat and gross energy, and apparent amino acid availabilities. The results are shown in Table 4.7. Overall, digestibility was highest and very similar for herring meal and Table 4.7 Apparent digestibility of different feed ingredients for Arctic charr. Data source: Gurure et al. 1996. Component

Apparent digestibility coefﬁcients Herring meal

Dry matter Crude protein Fat Gross energy

89 97 97 95

Menhaden meal 87 95 93 92

Corn gluten meal

Wheat middlings

Soybean meal

S. American ﬁshmeal

80 93 89 87

53 104* 89 58

81 103* 85 83

70 85 90 78

100.7 93.0 81.9 84.7 90.1 94.6 92.7 93.4 94.9 82.5 80.9 90.6 85.1 90.8 90.0 78

87.1 85.1 89.0 66.1 78.0 95.1 80.1 84.0 89.7 67.1 67.1 75.9 67.9 87.9 75.0 97

Apparent amino acid availability Alanine Arginine Asparagine Glutamic acid Histidine Isoleucine Leucine Lysine Methionine Phenylalanine Proline Serine Threonine Tyrosine Valine Rank

102.1 97.9 98.6 96.7 96.8 99.5 97.3 98.2 98.9 94.7 96.0 95.9 94.2 99.0 98.2 28.5

103.3 98.5 96.5 100.1 97.6 99.1 97.9 97.9 98.9 93.4 96.6 97.8 95.7 98.9 98.9 29.5

*Artifact of prolonged retention in gut

99.7 94.5 97.4 90.6 92.4 99.9 93.8 94.8 95.8 88.1 86.5 95.7 79.7 95.8 90.7 54

94.7 87.5 98.2 66.0 81.0 94.0 85.4 88.0 90.6 73.3 71.6 81.3 76.0 83.9 74.4 89

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Arctic Charr Aquaculture

menhaden meal, followed closely by corn gluten meal. These values are similar to those reported for other salmonids. The overall amino acid availability was highest for herring meal and menhaden meal. Corn gluten meal was similarly high in all amino acids except threonine and lysine. Soybean meal was by far the most deﬁcient in amino acid availability.

The ideal Arctic charr diet Given the basic nutritional requirements for Arctic charr, Table 4.8 presents the composition of four diets for ﬁrst-feeding alevins and fry, juveniles, ﬁnal grow-outs, and brood stock. These reﬂect the charr’s need for a diet similar to, but subtly different from, that fed other salmonids. All four diets assume that the feed is manufactured from the highest-quality ﬁshmeals and ﬁsh oils available. There is always a trade-off between feed ingredient quality and cost, but in many cases the cheapest feeds have not met with success (de Silva & Anderson 1995). Fishmeal is the preferred constituent of protein, followed by corn gluten and wheat middlings. Corn gluten meal contains xanthophylls, which have the unfortunate attribute of making the skin along the ﬂanks and ﬁns of Arctic charr yellow (the addition of astaxanthin in the feed will mask the yellow). Protein sourced from a high proportion of soybeans, blood Table 4.8

Recommended diets for Arctic charr.

Dietary component (% dry weight)

Starter

Grower

Finish

Brood

Crude protein Total lipid Carbohydrate Fiber Ash

60 20 8 1 11

54 20 13 4 9

52 22 13 4 9

50 28 13 1 8

% As-fed weight of diet

Starter

Grower

Finish

Brood

Crude protein Crude fat Moisture Carotenoid pigment (mg/kg) Linolenic acid 18 : 3 (n-3) Methionine (% of total protein)

48 16 20 40 10–16 2.7

49 18 10 20 10–16 2.7

47 20 10 70 10–16 2.7

45 25 10 60 10–16 2.7

Vitamins (mg/kg dry diet)

All diets

Minerals (mg/kg dry diet)

All diets

Thiamine (B1) Riboﬂavin (B2) Pyridoxine (B6) Pantothenic acid Niacine Folic acid Cyanocobalamin (B12) Myo-inositol Choline Biotin Ascorbic acid (C) Vitamin A Vitamin D Vitamin E Vitamin K

15 30 20 50 200 10 121 400 1000 1.5 400 7000 IU 3000 IU 350 350

Calcium (Ca) Cobalt Co) Copper (Cu) Iodine (I) Iron (Fe) Magnesium (Mg) Manganese (Mn) Phosphorus (P) Potassium (K) Selenium (Se) Sodium (Na) Zinc (Zn)

3000 5–10 5 0.3 40 500 15 6000 700 0.3 6000 30

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meal, or feather meal is less effective in terms of ﬁsh growth and may lead to higher mortality in Arctic charr. The quality and type of the fatty acids in the feed are also very important both from a nutritional perspective and in terms of consumer pleasure in the product. Ultimately, the composition of fatty acids in the charr ﬁllet, which is a big part of the taste and texture experience for the consumer, is dictated by the feed, particularly the lipids. Arctic charr require lipids high in PUFAs, particularly 18 : 3 (n-3), for both good health and good ﬁllet taste. Whenever possible, to enhance ﬂavor, lipids should be high in unsaturated fatty acids sourced from marine ﬁsh oils rather than other animal and plant oils. The higher fat levels in the ﬁnishing diet impart a richer taste and preferred texture to the ﬁllet. Although not a nutritional requirement, an attractant such as krill makes the diet for ﬁrstfeeding alevins highly palatable. Astaxanthin is added to all four diets for its nutritional contribution throughout the life cycle of Arctic charr. In the ﬁnishing diet, higher pigment levels redden the ﬂesh, enhancing consumer appeal. Depending on the strain of Arctic charr under cultivation, higher levels than suggested in this diet may be required to achieve acceptable orange-red ﬂesh. Manufactured feeds for Arctic charr A few feed companies in North America and Europe produce specialty feed rations for Arctic charr. One company is producing about 500 tonnes/year, mostly for freshwater farmers in Sweden, Germany, and Denmark. In North America the feed mills producing Arctic charr feed do not maintain inventory, as the existing market is too small to warrant production except upon order. In both markets, the special nature of the demand for charr feed dictates a slight to moderate premium over the cost of salmon feeds. Until the production of farmed Arctic charr really takes off, manufacture upon order (and resulting delays in producing feeds) and premiums on price will be the norm. The needed research to develop the ingredients for a range of feeds to cover each age group will also lag. Luckily, Arctic charr grow fairly well on existing salmonid diets available from most of the feed manufacturers. Some of the technical and company promotional literature suggests that Arctic charr grow well on commercial diets produced for rainbow trout; however, they perform much better on diets developed for Atlantic salmon. The newer Atlantic salmon feeds are highenergy diets formulated with an optimal balance of nutrients provided by highly digestible ingredients. They are high in fat with reduced protein and carbohydrate levels. The fat increases the energy content, thus sparing the protein for body growth. High-energy salmonid diets contain about 45% protein, 20% fat, and 17.4 mJ/kg of diet (or more) of digestible energy, while lowenergy diets are in the range of 38% protein, 12% fat, and 14.6 mJ/kg of diet. High-energy diets give superior feed conversion, faster growth rate, better use of protein, and lower waste production than low-energy diets when used with Atlantic salmon and rainbow trout, but not with chinook salmon (Gavine et al. 1995; Heinen et al. 1996; Rees 1997). Some feed manufacturers are producing salmon diets containing over 35% fat, but this level is untested with Arctic charr. When selecting a feed for Arctic charr, compare the composition with the guideline diets presented in Table 4.8. Of course the closer the ration is to these suggested formulations, the better it should perform. Ask the manufacturer about the ingredient levels of soya meal, carbohydrates, methionine, and linolenic acid, as these are often not stated in promotional

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Table 4.9 Nutritional composition of manufactured salmonid feeds. A Bio-Oregon – Bio-Diet; B Biomar – Eco-Life; C Zeigler – Arctic Charr; D Skrettling – Elite. Diet composition

Commercial diets

% Dry weight of diet

Starter A

Grower B

Grower C

Crude protein Total lipid Carbohydrate (NFE) Fiber Ash

59.1 20.8 6.3 2.5 11.3

53.2 26.3 12.8 2.7 12.4

47.7 20.5 19.0 2.3 10.2

47.0 16.5 20.5 3374 NS NS R

48.5 24.0 8.9 4542 1.4 NS R

42.0 18.0 12.0 3900 NS NS

Grower D 48.9 17.4 22.3 2.7 8.7

% Weight as feed Crude protein Crude fat Moisture Metabolizable energy (kcal/kg) Methionine Linolenic acid Recommendation

45.0 16.0 8.0 14.2* NS NS

*MJ/kg; NS = not signiﬁcant; R = required but level uncertain

literature or on the feedbag label. You may need to adjust levels of carotenoid pigment in the feed. Table 4.9 compares a number of manufactured diets produced for salmonids and speciﬁcally for Arctic charr. A semi-moist starter diet such as Bio-Diet works very well with Arctic charr. Ration formulations for three grower Arctic charr diets show a wide range of carbohydrate and fat levels in the formulations compared to the suggested levels in Table 4.8. Of the three formulations, I would be comfortable using Biomar’s Eco-Life 10 given the good ratio of protein to lipid and the high energy and low carbohydrate content, although the level of methionine is lower than recommended. In general, trout broodstock diets are well outside requirements for brood charr, but salmon brood diets are ﬁne. I have used both these diets with Arctic charr brood, and the salmon brood diet was far superior to the trout diet. When using commercial feeds prepared for Atlantic salmon, keep in mind that the manufacturer’s recommended feed sizes, feeding tables, and expected food conversion rates do not apply to Arctic charr. The differences in charr feeding behavior, growth rates, responses to photoperiod, and other factors profoundly affect their response to feed and their ability to use it well. These differences are discussed in more detail in the following section of this chapter.

Feeding Arctic charr In a commercial setting, the objective of feeding is to achieve optimal growth of an entire tank of ﬁsh, each growing at a slightly different rate. This means feeding to maximize uniformity in size, minimize food conversion rates, and maximize growth rates of the entire group of ﬁsh. The feed pellet size, ration size, and feeding techniques must accommodate the various ﬁsh sizes, water temperatures, and feeding patterns speciﬁc to each lot of ﬁsh. Feeding dynamics are changed by factors within the tank environment such as ﬁsh density, water currents

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and temperature, ration amount, feed type and pellet size, and the natural rhythms of growth. Finally, behavior patterns among ﬁsh dictate how often and when an individual ﬁsh gets access to food. Culturists must keep the following points in mind: the context of the natural rhythms of growth: take into account daily patterns • ofFeedfeedwithin intake, seasonal variations in appetite, and monthly variations in growth alloca-

• •

tion. Feed so that no waste feed is produced. All feed should pass through the ﬁsh. Feed to give the best combination of food conversion rate and mean growth for the ﬁsh lot.

Setting daily ration levels Since there is a close, positive relationship between ﬁsh growth rates and food consumption, all of the factors discussed in the section on growth rates come into play when setting daily rations over the long term (Jobling et al. 1989a). If the ﬁsh are in an active growth phase, then the two primary factors controlling daily food intake by Arctic charr are body size and water temperature. This relationship between Arctic charr body size, water temperature, and food intake was modeled by Jobling et al. (1989a; 1993), based on a number of studies on feeding rates of Arctic charr (Jørgensen et al. 1991). The relationship of food intake (FI, as mg/ﬁsh d–1) to temperature (T, in °C) and body weight (W, in grams) for Arctic charr in the active growth phase is calculated from the equation: FI = [1.15 (1.671 + 3.319 T)] W0.651 The model gives a relatively good picture of daily food intake for Arctic charr in an active growth phase when fed commercial dry feed with energy content of at least 23 mJ/kg. Arctic charr will not compensate for the low energy content of feed by eating more feed of lower nutrient value. The ﬁsh given the high-energy food just grow faster (Alanärä & Kiessling 1996). Although the above equations allow you to calculate appropriate daily rations based on different temperatures and body size (see Fig. 4.15), clearly the amount eaten on any given day will vary tremendously due to other factors affecting growth and feed intake, like the changing seasonal and monthly rhythms of growth (Alanärä & Kiessling 1996). For example, Arctic charr held in water at 2 °C in December, under a natural winter photoperiod in Whitehorse, Yukon, consume only about one-tenth the daily feed ration calculated from the above equation. However, at the same temperature in late April, when the daylight is increasing and Arctic charr enter an active growth phase, they easily consume food rations set at the calculated level. Changing photoperiod has a powerful effect on food intake in Arctic charr. In general, increasing photoperiod stimulates growth and feeding, while decreasing photoperiod reduces growth and feeding – regardless of water temperature. Feed tables prepared by feed manufacturers or by using these equations are only guidelines for setting daily feeding levels and for long-term planning of required feed rations. They must be adjusted to accommodate the real feeding conditions observed in the tank on a day-

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Fig. 4.15 Effect of water temperature and ﬁsh size on daily ration allocation for Arctic charr. Data source: Jørgensen et al. 1991.

to-day basis. The ultimate arbitrator of ration levels consumed are the ﬁsh, and ingestion rates are subject to many factors discussed in previous sections. Actual rations consumed will vary according to the time of month and season in accord• ance with natural growth cycles, particularly in response to photoperiod. Stocking density and swimming speed affect food conversion rates and growth. • Husbandry activities (sorting, weighing, tank cleaning, etc.) and the prevailing environ• mental conditions in the tank water (O , NH , etc.) will affect how much the ﬁsh eat. Method of feed presentation and time of day also affect consumption. • 2

3

Feed sizes Food pellet characteristics, particularly pellet size, shape, and texture, affect food acceptance and thus growth and conversion rates in Arctic charr. Artiﬁcial food must attract attention, stimulate an attack response, and be of a size easy for charr to handle and swallow without difﬁculty (Jobling 1993). In the wild, Arctic charr are adapted to consume smaller prey species than other salmonids, including most other members of the Salvelinus, but they do show a general salmonid characteristic of taking larger prey sizes with increasing body size (Tabachek 1988; Linér & Brännäs 1994). Under culture conditions, Arctic charr prefer pellets of a slightly smaller size than those preferred by rainbow trout, Atlantic salmon or Paciﬁc salmon (Tabachek 1988; Jobling 1993; Pennell & McLean 1996). If offered different-sized pellets that are both within their ability to handle and swallow, Arctic charr invariably select the larger pellet. At any given body length, there is an optimum food pellet size that gives the best performance in terms of growth and food conversion. Signiﬁcant differences in growth rates occur as food particle size becomes more optimal. For example, 3 g Nauyuk charr increased growth rates from 1.42% to 1.99% body weight/day and feed efﬁciency from 48% to 78%, while 21 g charr improved growth rates from 1.03% to 1.68%/day and feed efﬁciency from 57% to 98% when offered feed of a more optimum size (Tabachek 1993). Optimum food size depends on mouth width and throat size; however, there is a simpler relationship where food size is

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related to body length. In small Arctic charr (about 100 mm length), growth is best when food pellet size is in the range of 1.5% to 1.8% of body length. For slightly larger fry, a pellet size of 2.3% to 2.5% of body length promotes the best growth (Tabachek 1988). Arctic charr of larger sizes grow well on pellets of about 2% to 3% of body length. Brännäs found that pellets within a size range of 1.75% to 3% of fork length gave reasonably good handling time and minimal food losses. She also noted that Arctic charr quickly learned which feeder dispensed the optimally sized pellets and used that feeder. If the location of feeders offering differentsized pellets was changed, in a matter of 1–2 weeks the ﬁsh learned which feeder offered the preferred feed size, which offers culturists a technique for determining speciﬁc food size preferences (Linér & Brännäs 1994). Wild prey of Arctic charr and other salmonids is generally more elongate than round. Artiﬁcial food that mimics this characteristic is more accepted than long and thin or round particles. Under culture conditions the shape and size of feed pellets also affect the amount of time taken to attack and consume food. Linér and Brännäs (1994) found that when Arctic charr were fed pellets of a size equalling approximately 2% of body length, they took the shortest consumption time (sum of attack and handling times) and missed the fewest pellets. Although there was no indication this represented the most efﬁcient use of food in terms of SGR or FCR, it does indicate a food size that minimizes food wastage and handling time by the ﬁsh. From this work, Brännäs suggested a compromise pellet – a long pellet that is not of optimum size but is more attractive to a greater size range of ﬁsh than a round pellet (see Table 4.10). This compromise pellet may be advantageous in Arctic charr culture, where often there is a wide variation in ﬁsh sizes.

Feeding strategies Feeding ﬁsh is a collective process. How you feed Arctic charr will determine just how well each ﬁsh grows and how efﬁciently they use feed. Under commercial culture conditions, the object is to get an entire tank of ﬁsh, containing individuals with different feeding strategies, to grow well and uniformly. Some will be subordinate night feeders; others will be aggressive feeders, always ﬁrst to feed; and there will be another group somewhere in the middle. Feeding strategies also inﬂuence the range in sizes found within each lot of ﬁsh. Some feeding practices tend to exacerbate differences in ﬁsh size, an undesirable condition in ﬁsh produced for market. The process of feeding ﬁsh involves making decisions about how to maximize growth at a reasonable cost in feed and time. There are four areas to consider: feeding or restricted rations; • satiation optimum times to feed in terms of daily, monthly, and yearly growth rhythms; • spatial distribution and feeding frequency of the daily feed ration; • delivery method, whether by hand, automatic feeder, or demand feeder. • Satiation, restricted, or compensatory feeding One of the controversies in feeding Arctic charr and other salmonids centers on what level of appetite to feed to. They can be fed to satiation – that is, to the point where their appetite tells them to stop feeding – or they can be placed on restricted rations so they remain hungry at

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Table 4.10 Optimum feed pellet size for Arctic charr, based on body length. Data source: Tabachek 1993; Linér & Brännäs 1994. Fish size (mm)

Optimum pellet size

Compromise pellet size (length × diameter, mm)

50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250 260 270 280 290 300 310 320 330 340 350 360 370 380 390 400 410 420 430 440 450 460 470 480 490 500 510 520 530 540

0.9 1.1 1.2 1.4 1.6 1.8 1.9 2.1 2.3 2.5 2.6 2.8 3.0 3.2 3.3 3.5 3.7 3.9 4.0 4.2 4.4 4.6 4.7 4.9 5.1 5.3 5.4 5.6 5.8 6.0 6.2 6.4 6.5 6.7 6.8 7.0 7.2 7.4 7.5 7.7 7.9 8.1 8.2 8.4 8.6 8.8 8.9 9.1 9.3 9.5

1.4 × 1.1 1.7 × 1.4 1.9 × 1.6 2.2 × 1.8 2.5 × 2.0 2.8 × 2.3 3.0 × 2.5 3.3 × 2.7 3.6 × 2.9 3.9 × 3.2 4.1 × 3.4 4.4 × 3.6 4.7 × 3.8 5.0 × 4.1 5.2 × 4.3 5.5 × 4.5 5.8 × 4.7 6.1 × 5.0 6.3 × 5.2 6.6 × 5.4 6.9 × 5.6 7.2 × 5.9 7.4 × 6.1 7.7 × 6.3 8.0 × 6.5 8.3 × 6.8 8.5 × 7.0 8.8 × 7.2 9.1 × 7.4 9.4 × 7.7 9.7 × 7.9 10.0 × 8.2 10.2 × 8.4 10.5 × 8.6 10.7 × 8.8 11.0 × 9.0 11.3 × 9.2 11.6 × 9.5 11.8 × 9.7 12.1 × 9.9 12.1 × 9.9 12.1 × 9.9 12.1 × 9.9 12.1 × 9.9 12.1 × 9.9 12.1 × 9.9 12.1 × 9.9 12.1 × 9.9 12.1 × 9.9 12.1 × 9.9

all times. Both types of feeding have merits and drawbacks. There is also a third possibility: combining both techniques for a compensatory feeding approach.

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Satiation feeding assumes that the entire lot of ﬁsh has its maximum amount of ration for the day. The ﬁsh end the day full or satiated, not overfed, but at the point where their appetite is satisﬁed and they are growing at maximum rates. The daily ration allocation for Arctic charr of different size and at different water temperatures presented in Fig. 4.15 are examples of feeding levels required for satiation feeding. Feeding Arctic charr to satiation will reduce competition for food, thus leading to more uniform growth and less individual size variability between ﬁsh of the same lot. The ﬁsh reach desired market weight sooner, but at poorer conversion rates. In theory, the savings in time from faster growth should offset the increased cost of feed. However, depending on many factors such as the cost of feed and the amount of feed wasted, the savings in time may not offset the increased feed costs. Satiation feeding also leads to ﬁsh acting sluggish when presented with feed, which requires you to feed carefully to minimize waste. Increased feed wastage means there are excess nutrients in outﬂow waters, which is undesirable in an intensive recirculation system or where wildlife in downstream waters is sensitive to high waste discharges. The drawbacks to satiation feeding point up some obvious advantages to feeding restricted daily rations. The amount of feed required to reach market weight is substantially less because food conversion efﬁciencies are better. The volume of fecal material and dissolved solids in wastewater are substantially reduced, taking pressure off biological ﬁlters, perhaps by as much as 25% to 30%. However, it is difﬁcult to control uniformity in growth when ﬁsh are on restricted rations, and a greater proportion of ﬁsh will show stunted or small morph growth characteristics. Competition for food often leads to less dominant ﬁsh not receiving sufﬁcient ration and growing poorly (Brännäs & Alanärä 1994). If feed is released from one source, dominant Arctic charr will control access to the site sometimes long after they have reached satiation. Some ﬁsh receive enough food to reach a very high condition factor while others remain thin and unattractive to the market. A possible compromise solution is to combine the principle of compensatory growth with the techniques of feeding to satiation. Arctic charr are natural feast-and-famine feeders in the wild, and after a period of starvation they will undergo catch-up growth that converts nutrients to growth very efﬁciently. Under culture conditions, short feast/famine cycles result in periods of compensatory growth. The ﬁsh grow as well as satiated Arctic charr in the same amount of time, but on about 20% to 25% less feed. There are two possible types of compensatory feeding: short-term feast/famine cycles of a few weeks’ duration, and long-term seasonal feast/famine cycles. The short-term method involves repeatedly mimicking a cycle of feast-or-famine conditions to induce the compensatory growth response. During a period of abundant food rations, the ﬁsh are fed to satiation each day; during the famine they are not fed. The famine period need only last long enough to induce a compensatory response, which in Arctic charr appears to be reached after about a week of starvation. The process is enhanced by manipulating water temperatures, as Arctic charr appetite increases when water temperature is increased even a few degrees. Long-term compensatory growth involves manipulating Arctic charr’s natural seasonal feast-and-famine growth rhythms. This seasonal growth cycle lasts for a period of 6 months, which means that two feast/famine cycles could be created in each year by manipulating light regimes and feeding schedules. In theory, using this method one could produce market Arctic charr in half the time it takes when they are kept on a natural year-long cycle.

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In a high-density culture facility, shortening the time to market using either long-term or short-term compensatory growth makes great sense given the high ﬁxed costs of operating this type of facility. Compensatory growth feeding would also improve the water quality of outﬂow waters, reduce the amount of waste feed, and decrease size variability in each ﬁsh lot. Optimum feeding times Though ﬁsh will learn to feed at prescribed times during the 9-to-5 working day, they will not grow or convert feed as efﬁciently as they do if fed to their natural daily, monthly, and seasonal rhythms. They will grow well, but not to predicted rates. The natural feeding rhythm likely causes physiological changes in ﬁsh that prepare them to ingest and digest feed. At other times they are not prepared to feed or not interested in feeding, and it does not make sense to feed them at these times. The natural feeding rhythms caused by the moon phase and changing seasons can also have profound effects on ﬁsh appetite from day to day. When held under natural light, there are seasonal shifts in the time of day most Arctic charr prefer to feed, and seasonal shifts in the volume of feed consumed, regardless of water temperature. In winter, for example, feed consumption can drop to about 10% of summer levels, even when the ﬁsh are held at similar water temperatures. Arctic charr prefer to feed in the twilight hours surrounding dawn and dusk. As spring changes to summer, more ﬁsh will feed in the daylight hours, though twilight feeding is still important. Even on the longest days of summer, there are still dawn and dusk changes in light intensity, though culturists often forget this when feeding charr under artiﬁcial 24-hour lights. Although the greatest amount of food should be offered during dawn and dusk, there are many ﬁsh taking feed at other times of the day. The daily ration allocation must accommodate the feeding behaviors of all the ﬁsh within the tank and these natural shifts in appetite to maximize uniform growth. Spatial distribution and feeding frequency The way food is distributed within each tank must take into account the effect dominance hierarchies have on the feeding behaviors of individual Arctic charr and the slow feeding response of Arctic charr in general. If you supply feed at a point source, then the most dominant Arctic charr will monopolize the feeding station until they are satiated. They may also defend the area around the feeder from other ﬁsh even when they are satiated, which further increases the disparity in feed distribution to smaller ﬁsh. Off-bottom feeding and night feeding displayed by some groups of Arctic charr are responses to dominant ﬁsh excluding submissive ﬁsh from the prime feed sources. Some researchers found that Arctic charr may take a signiﬁcant portion of their feed off the bottom, and if they are not allowed access to bottom feeding, mean growth of the entire ﬁsh lot will be inhibited (Jobling et al. 1989b). However, off-bottom feeding is not practical in commercial tank operations or in net-pens. One way to minimize the effects of social dominance on feeding behavior is to distribute the pellets during each feeding session over as wide a surface area as possible. This prevents dominant Arctic charr from controlling access to all of the feed, as they cannot be everywhere at once. Another effective means of reducing social tension and improving the allocation of

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feed is to force ﬁsh to swim against a current of about 1 to 2 body lengths/second. These two techniques appear to curtail the social dominants’ ability to bully lesser individuals away from feed. Wide distribution of feed is also necessary when Arctic charr are held at high density, as ﬁsh are unable to push their way to point sources of feed in a heavily crowded tank. Arctic charr are much slower at catching feed pellets in the water column than rainbow trout or Atlantic salmon. They are also more inclined to take feed from within the water column than on the surface, so avoid the use of ﬂoating ﬁsh feeds. For optimum feeding, release slow-sinking pellets in small portions over many feeding sessions. In other words, have enough feeding sessions to deliver the daily ration in portions that give each ﬁsh access to 2 to 5 pellets, or about 1% of its daily diet at a time. If too many pellets are offered during a feeding session, ﬁsh cannot sight, approach, and ingest all of the feed in a given time period. This can decrease feeding efﬁciency by as much as 35% to 55% (Tabachek 1988; Brännäs & Alanärä 1994). Of course, the depth of the tank and the sinking speed of the feed will inﬂuence the amount of time pellets remain available in the water column. Larger pellets drop through the water column faster than small pellets, so fewer large pellets should be presented at each feeding session (Tabachek 1988). It may seem ludicrous to calculate the number of pellets and sinking rates of feed, but it does make a difference in growth, feed wastage, and feeding economies. The number of pellets per gram and sinking rates of various sized pellets are available from feed manufacturers for their individual feed types. Feed delivery methods There are three ways to deliver feed to a tank of ﬁsh: by hand, by automatic feeders on timers, and by demand feeders triggered by the ﬁsh themselves (see Fig. 4.16). Each method must effectively accommodate the delivery of many different meals of various amounts and pellet sizes. Each method has its merits and constraints, and the use of one over the other is determined by the size of the facility, the ability to afford different types of feeding systems, and the nature of the operation. Whatever the feeding system employed, it must be ﬂexible enough to accommodate the changing feeding rhythms, pellet sizes, and volumes of feed required by each lot of ﬁsh. In general, it should: deliver an adequate daily ration to each ﬁsh in the tank; • shut rapidly if waste feed reaches unacceptable levels; • deliverdown sufﬁ feed in each interval to allow each ﬁsh a feeding opportunity; • spread feed cient over a wide surface area of the tank; • trigger many feeding of varying lengths throughout the 24-h day; • deliver feed of differentsessions sizes and types; and • control the feed ration size and number of feedings/day. • Of course there is only one feeder that meets all of these criteria: the human hand. Handfeeding allows you to match each day’s rations to the hunger levels of ﬁsh in each individual tank. Good hand-feeding relies on dedication to the task and operator skill to determine hunger levels. Initially there is a tendency to feed faster than Arctic charr can handle food, to feed in too few sessions, or to overfeed. If daily rations and feeding intervals are calculated from

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Fig. 4.16 Different types of feeders used for feeding Arctic charr.

tables, then hand-feeding is relatively easy, as the calculated ration gives a sense of what the ration should be for that particular lot of ﬁsh. Hand-feeding also forces regular scrutiny of each ﬁsh lot, which goes a long way to assure good ﬁsh management. The capital cost of hand-feeding is also very low, though the cost of labor may make hand-feeding prohibitively expensive, particularly on larger operations. It is also difﬁcult to feed Arctic charr at times most optimum for them without incurring overtime labor costs. Some commercially available automatic feeders are well suited to meet the food-delivery criteria listed above. Most operate on low-voltage current or compressed air and can be adjusted to accommodate different-sized pellets. They have sophisticated programmable controllers to accommodate a variable number of feeding intervals, delivering a variable amount of feed per interval throughout the day. They are expensive to purchase but have very low

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operating costs, particularly in large operations, and deliver feed at the times when Arctic charr prefer feeding. However, they are automatic and they just keep running, regardless of whether ﬁsh are eating, so staff must monitor ﬁsh appetite and adjust feeding rates accordingly. Alternatively, the controllers can be connected to a waste feed monitoring system that shuts them down automatically when a predetermined amount of waste feed is detected. Demand feeders, activated by ﬁsh within the tank, work well with Arctic charr. The principle is simple and clearly shows that Arctic charr are as sharp as laboratory rats. A trigger mechanism mounted on a thin wire is located in the water below a feed hopper. The ﬁsh knock or bite the trigger, which is connected to the feeder, and a supply of feed drops from the feed hopper into the tank. Arctic charr learn to strike the trigger mechanism for a feed reward in a matter of hours. In a commercial setting, the trigger toggles an electronic switch, which then activates an automatic feeder that broadcasts a predetermined amount of feed over the tank’s surface. Thus a few ﬁsh activating the trigger feed all of the ﬁsh in the tank. The amount of food released upon each trigger activation is adjusted periodically to the number and size of ﬁsh in the tank and the size of feed pellets (Brännäs & Alanärä 1994). For example, researchers determined the best reward for Arctic charr in the size range of 100–300 g is about 0.1 g feed/kg ﬁsh per trigger actuation. They noted that food conversion efﬁciencies were very good, in a range of 0.7–0.8 kg of feed to 1 kg of mass increase (Alanärä & Kiessling 1996). Only 5–15% of the most dominant ﬁsh monopolize the triggers, so you are relying on these few ﬁsh to feed the rest. In experiments with demand feeders that delivered feed to one place in the tank, Arctic charr showed three feeding behaviors. Those few feeding during the day that triggered at the highest rate showed the best growth, followed by moderate growth rates for most of those Arctic charr that triggered at lower rates. A third group, which ate only food missed by their more aggressive cohorts, had growth rates of less than half of the other two groups (Alanärä & Brännäs 1997). To avoid this disparity in feeding opportunities and growth rates, it is important that the ration levels and feeding intervals are set to accommodate all individuals in the tank and that feeders broadcast the feed over the tank’s surface (Alanärä & Brännäs 1996).

Feed monitoring All of the feeding methods discussed above beneﬁt greatly when combined with a system for monitoring waste feed. Such a system detects the presence of waste feed pellets in the tank water or in the outﬂow of the tank, allows quick correction of an overfeeding problem, and can also help cut feed costs. When salmonids are small, the relative cost of feed compared to other operating expenses is small (roughly 10%). However, in grow-out operations the relative cost of feed can be 40% to 60% of total cost (Costello et al. 1996). Minimizing the amount of wasted feed is one of the easiest ways to control feed costs. For example, in a study conducted at Atlantic salmon growout farms in Ireland, the food conversion rates were much higher than predicted by the feed manufacturers. The researchers concluded that farmers were not responding rapidly enough to changing water temperatures at the onset of winter and were overfeeding ﬁsh. They suggested that calculating FCR on a regular basis and closely monitoring food consumption

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by using feed collectors placed under the cages would reduce overfeeding (Costello et al. 1996). Setting ﬁxed feed rations based on estimated growth rates results in overfeeding or underfeeding if not monitored closely. On many farms, ﬁsh are traditionally fed based on their surface feeding behavior; that is, feeding ends when ﬁsh stop responding to feed near the surface, where they can be seen by staff. Researchers studied the differences in determining the feeding endpoints (after which point feed is wasted) when staff used either surface water visual cues or underwater cameras to feed Atlantic and chinook salmon. The researchers found that when using surface water visual cues, feeding endpoint was underestimated over 74% of the time with Atlantic salmon. In contrast chinook salmon were overfed 80% of the time. In both cases, the use of underwater cameras to monitor feeding behavior deep in the pen corrected the feed delivery problem (Ang et al. 1996). A local Atlantic salmon farm manager told me that they have recently started using underwater cameras to monitor feeding activity and that the feed savings have been substantial. These underwater camera systems should also work well with Arctic charr. There are other systems that can monitor waste feed passing out of tanks. These are as simple as placing a screen over the tank outﬂow pipe to collect uneaten feed. There are commercial systems using an ultrasound probe placed in the efﬂuent pipe that detects uneaten food without confusing it with ﬁsh feces. The probe is connected to a controller that automatically turns off feeders after a predetermined amount of uneaten feed has passed the sensor (Timmons et al. 1998). This type of system should be integral to any type of automatic or demand feeding system with Arctic charr. Whatever system is used for feeding Arctic charr, keep the following points in mind: Adjust daily ration size and pellet size on a regular basis, based on ﬁsh weight and the • number of ﬁsh in the lot. Feed Arctic charr often throughout the day and night. • Broadcast feed over the entire area of the tank. • Pay close attention • accordingly. to the natural feeding rhythms of Arctic charr and adjust feeding levels

Section II

Husbandry

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Arctic Charr Aquaculture

Raising Arctic charr begins when you select the best strains as brood ﬁsh and ends with either processed ﬁsh for sale to the consumer or ﬁngerlings released to enhance wild populations. In commercial operations the rearing process falls into three discrete areas, each requiring a degree of specialization and each with a different outcome: 1. 2. 3.

Brood stock and incubation hatcheries produce eyed ova for sale to other hatcheries or direct to grow-out operations. Hatchery operations produce ﬁngerlings for sale to grow-outs or for release to the wild. Grow-out operations produce market ﬁsh processed for sale to consumers.

Although a facility can incorporate all levels of ﬁsh-rearing, most commercial operations specialize in one of the categories (see Fig. II.1). A facility that incorporates more than one level could have all the operations located in one site or spread out over a number of sites. As well as commercial operations there are research facilities run by private and government agencies. They address applied and theoretical problems of Arctic charr biology and aquaculture. Because Arctic charr aquaculture is so new, with many unknowns, the interaction between commercial operations and scientiﬁc research facilities is vital in the develop-

Fig. II.1 The Arctic charr production cycle under culture conditions.

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ment of new husbandry techniques, prepared diets, and genetic improvements in strains under culture. Research facilities have traditionally concentrated on brood stock development and early rearing, but some are now addressing issues at the grow-out stage of the commercial production process. In all stages of production and research, raising healthy and contented ﬁsh requires technical knowledge – like knowing how to handle them without injury – but also demands a dedication and a sixth sense that anticipates their needs. This sixth sense is similar to what gardeners call a green thumb. Eunice Lamb, who co-ordinates the aquaculture program at Malaspina College in Nanaimo, British Columbia, refers to it as a slimy thumb. You can watch men and women working with the brood ﬁsh or young ﬁsh in a hatchery and soon know who has the slimy thumb. They are the people who anticipate a ﬁsh health problem before it happens. They see ﬁsh acting strangely and know to turn the water ﬂow up a notch or adjust the feeding level up or down. They move about the hatchery calmly and can catch ﬁsh without causing injury. They look in an outdoor brood tank and can tell that spawning is soon to commence or will be a little late or early. Some people have this knack and some never get it. When you are working with Arctic charr, having a slimy thumb is especially important. Unlike farmed Atlantic salmon or rainbow trout, only a few strains of Arctic charr have been domesticated for more than three or four generations, so you are working with ﬁsh that still respond as wild animals. Many of the husbandry requirements for Arctic charr are based on data from research studies that do not consider practical issues of culturing ﬁsh. This means culturists must think like a ﬁsh, like an Arctic charr that has been forced into an unfamiliar environment with a new food source and a light regime that may be very different from the one found north of the 60th parallel. The ﬁsh’s genetic cues are all a little messed up, and the culturist must learn how to mimic the familiar environment as closely as possible, or trick the ﬁsh into accepting the new one. Over time culturists can select for brood stock those ﬁsh that do better in the artiﬁcial environment, creating a domesticated ﬁsh. On the other hand, they may want to raise charr that are as close as possible to the natural wild manifestation. In the next three chapters we examine the best strains of Arctic charr for commercial rearing and the practical aspects of Arctic charr husbandry. The techniques for rearing brood ﬁsh, taking eggs, and early rearing procedures in the hatchery are discussed in detail. Although the focus is on raising ﬁngerling Arctic charr for commercial grow-outs, many of the techniques are also applicable to early rearing of Arctic charr destined for reintroduction to wild populations. The actual process of growing-out ﬁsh for the consumer is deferred to the last section of the book, as grow-out operations are best viewed in the context of growing Arctic charr as a business.

Chapter 5

The Standard Arctic Charr

Arctic charr do not have a long history of selective domesticity or cultivation in hatcheries for enhancement of wild stocks. Not all stocks of Arctic charr are suited for culture, and there was minimal effort at the national or international level to ﬁnd the best stocks for the development of commercial strains. Many countries simply worked with the national stocks they had, regardless of their suitability for intensive culture or their market appeal. Even today there are research groups in various countries attempting to develop commercial strains out of Arctic charr stocks entirely unsuited for culture (Rioux & Noris 1997). In this chapter I explore the attributes displayed by the various strains currently under culture, outlining the traits needed for a viable commercial Arctic charr and the existing attributes that lend themselves to selective breeding. I propose a ‘standard’ Arctic charr based on the best strain available and incorporate ideas for improvement through accepted animal breeding techniques.

The attributes for culture There are three main methods of rearing Arctic charr, each requiring different levels of domesticity in brood stock: or augmenting local wild populations; • rehabilitating extensive low-density culture in pothole lakes; and • intensive high-densitynatural tank culture. • Arctic charr raised for rehabilitating or enhancing wild stocks require no domesticity; the wide range and variability of types seen in the local wild stock must remain in these ﬁsh. The very act of raising ﬁsh under culture conditions subtly changes their wild nature, so the less time they remain under culture the better for the recovering stock. Arctic charr destined for the commercial market but raised under natural conditions in pothole lakes require market traits acceptable to the consumer, but they must retain wild survivor traits that enable them to avoid predators and acquire food in an uncontrolled environment. A docile, slow-to-respond Arctic charr ﬁngerling will not long survive the depredations of a wily mink or fast-diving kingﬁsher in a pothole lake.

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On the other hand, ﬁsh destined for rearing in tanks are selected because they show good growth in a crowded, highly artiﬁcial environment. They must remain calm when held at high density under the day-to-day husbandry practices of an intensive tank operation. From the ﬁsh’s perspective, the sudden appearance of humans hovering above a tank and dipping nets into the water is not unlike the attentions of a predator. Those ﬁsh least disturbed under these conditions are the brood candidates for a domestic strain of Arctic charr. Two strains of Arctic charr are needed to meet the two latter methods of commercial culture. Both strains will show similar traits during early rearing in the hatchery, but will exhibit slightly different growing qualities thereafter. Arctic charr destined for market, whether grown organically in pothole lakes or under tank culture on pelleted diets, must display the following attributes for consumer acceptance and a good market price for the producer: orange-red ﬂesh coloration without marbling; • consistent a body conformation thick, well-proportioned ﬁllets and steaks; • head-on gutted weightgiving of 2–3 kg; • good taste and texture; • resistance to stress and diseases and a low mortality rate under culture; • ability to reach market weight in a reasonable amount of time (24–30 months) without • reaching sexual maturity. Some of the Arctic charr studied to date in research facilities, in the wild, and in commercial farms have shown these desired attributes, but different subspecies and stocks have also exhibited the following negative characteristics: grow-out period to reach market weight of 2–3 kg; • long sexual maturity before reaching market weight; • reach great size in same-age cohorts; • inconsistentvariability ﬂ esh coloration. • For example, in Sweden the strains used are said by commercial growers to have the following poor qualities (Eriksson 1991): difﬁculties; • start-feeding to bottom-feeding and slow-feeding tactics; • tendency sensitivity temperatures above 15 °C; • sensitivity toto diseases such as furunculosis, viruses, BKD, and fungal infections; • variable growth performance; • variable success of brood stock; • poor quality ova. • Some of these problems may be the result of poor husbandry and poor growing conditions, but they are also due to the fact that the Swedish ﬁsh, like most strains of Arctic charr, are not suitable for cultivation because their age or size at maturity, growth characteristics, and ﬂesh color are inappropriate.

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Other necessary attributes for culture appear to be present in all strains – the ability to grow well under high density and at low water temperatures, for example – and a few strains of Arctic charr have almost all of the positive traits even though they are not long from the wild. Because growth characteristics are so different between the various stocks of Arctic charr, it is clear that selecting the right strains for development is important in commercial culture (Näslund & Henricson 1996).

Attributes of existing strains used for commercial culture There are about six strains of Arctic charr that have been used for commercial culture with varying levels of success. All of them have originated from collections of ova and milt taken from wild stocks by scientiﬁc research institutions in various northern countries. The stocks collected from the wild and used commercially in Canada, Iceland, and Norway are from anadromous populations, while those used in Sweden and Finland originated from lakeresident populations. Brood stocks collected from lake-resident stocks in Britain (Loch Rannoch, Windermere), and a number of sites in the alpine regions of central Europe are of little interest to commercial growers because of their small size (Jobling et al. 1993). An evaluation of the various strains used for commercial culture is based on the following points: Egg size: Large eggs (greater than 4.5 mm) produce young with lower mortality rate, • increased growth rate, and decreased size variability. Late sexual Arctic charr is not marketable at sexual maturity because it loses • ﬂavor, texture,maturity: and color. If the ﬁsh matures at a young age (one to three years) it will be

• • •

difﬁcult, if not impossible, to reach the marketable size of 2–3 kg. Flesh color: Flesh color should be consistent and measure between 6 and 9 on the Roche scale (a standardized color chart used to measure ﬁsh color). Size at harvest: The market does not want small Arctic charr. There are fewer production costs with large Arctic charr and the market is willing to pay a higher price. The ideal market size is 2–3 kg. Size variation: The less variation in size of each age cohort, the lower the production costs.

The Norwegian Hammerfest and Svalbard strains Much of the Norwegian research conducted on practical aspects of Arctic charr culture over the past 25 years is based on the responses of the Hammerfest strain, which is the main one used by commercial growers in Norway. The strain’s parental stocks were collected in the early and mid-1970s from anadromous Arctic charr that migrate to and from Lake Storvannet, near the town of Hammerfest, northern Norway. From a commercial perspective, the Hammerfest strain is not ideal. reaches sexual maturity at an early age and a small body size, with some males (jacks) • Itmaturing as early as age one, and most males and some females reaching sexually maturity at two years of age (Damsgård et al. 1999).

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slaughter weights are less than 1.5 kg and usually much smaller. • Practical It has poor and uneven coloration of ﬂesh at slaughter. • There is great size variation within cohorts of the same age. • It produces small • lison 1991). eggs (3 mm) and alevins that have difﬁculty at ﬁrst-feeding (Hall & ColResearchers at Fiskerifoskning, Tromsø, are excited by the Svalbard strain from Lake Vårﬂusjøen, Svalbard, which has better growth characteristics than the Hammerfest strain. It grows to a larger size before reaching maturity. A comparison of Hammerfest charr with Svalbard charr indicated no difference in weight, feed intake, and growth in the ﬁrst year, but by 19 months the Svalbard charr were 25% larger than the Hammerfest charr and none had reached maturity. By age two, only 5% of the Svalbard strain was mature, compared to 78% of the Hammerfest ﬁsh (Damsgård et al. 1999). Despite the advantages Svalbard has over the Hammerfest strain, it still does not reach the favored market weight.

The Swedish Hornavan strain Sweden has no populations of anadromous Arctic charr, so it is developing a commercial strain based on large lake-resident stocks from Hornavan Lake, a large deep lake located in northern Sweden. The founding stock of this strain was collected in 1979 from an effective population of 12 to 14 ﬁsh (Nilsson 1992a). The Hornavan strain is the best native stock available and is the most commonly used strain for commercial farming in Sweden. Much of our knowledge about the heritabilities of various traits is based on work conducted with this strain of Arctic charr. The Hornavan strain showed less variability in size, had the highest ﬁnal weight, and had lower early juvenile mortality when compared to four other lake-resident stocks from various lakes in Sweden (Näslund & Henricson 1996). Although the Arctic charr from Hornavan Lake grow to a relatively large size for a lake-resident morph, they are still small for the market. Other traits also make them less than ideal: About 19% of males mature at age one at less than 200 g, and most are sexually mature at • age three at a size of less than 650 g. Commercial market weights less than 1.5 kg dressed, head-on. • Fish of less than 300–400 g have a pale ﬂesh color. • Small egg and alevin size. • Appear sensitive to furunculosis, and BKD. • Variable growth performance andvibriosis, variable body trait quality (Eriksson 1991; Näslund & • Henricson 1996).

The Icelandic Grenlækur and Ölvesvatn strains There are two strains of Arctic charr used commercially in Iceland: an anadromous strain, Grenlækur, and a lake-resident strain known as Ölvesvatn. Both are under development within the Icelandic Arctic charr breeding program, with a third strain under assessment. These two strains show more promise than other strains:

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growth rate and maturation rate are similar for both strains, with some males maturing • The at age one. There are generally fewer than 5% mature after two years and 50–80% mature

• • •

at age three. Jack males reach maturity at 100 g and females at 200 g. The ﬂesh color, measured in immature ﬁsh of 500–1000 g size, averaged 5 on the Roche scale for both strains, although commercial farmers usually feel that the ﬂesh color of Grenlækur is darker than that of Ölvesvatn. This strain has produced good-quality ﬁsh in the 1–2 kg size and some in the 2–3 kg size. Their early maturation age continues to be of concern in the production of larger ﬁsh (Svarvarsson [pers. comm.] 2000), but since they have produced some ﬁsh in the 2–3 kg size it might be possible to increase the average size through genetic selection.

The Canadian Fraser strain This is also known as the Labrador strain, as it originates from the Fraser River in Labrador. The founding stocks were collected in 1980, 1981, and 1984, and genetic material collectively represented about 50 family groups (Delabbio 1991). A very good breeding program with known pedigrees of all ﬁsh was developed at the Department of Fisheries and Oceans Canada (DFO) Rockwood hatchery, and much Canadian research concerning Arctic charr husbandry requirements, feeding, nutrition, and genetics involved this strain. However, the research material is now lost after many sales and foreclosures on the Rockwood facility. Despite the tremendous research efforts in developing this strain and its wide dissemination to Canadian ﬁsh producers across Canada, it was the wrong strain for commercial production. Its faults are many and positive attributes few: growth in the ﬁrst year, and plateaus at about 20 months of age (Picard 1997). • Rapid Frequent early maturation. • Pale and inconsistent coloration in ﬂesh (Robinson et al. 1995). • Variable growth performance, with great size variation in same-aged cohorts. • Signiﬁcant percentage (20–30%) do not reach harvest size desired by marketplace. • Spawning window of four to ﬁve months duration instead of the usual two to three weeks • (Srivastava et al. 1991). size 4–5 mm. • Egg are less than 1.5 kg and generally smaller, pan-sized. • Fish Market price for wild Fraser stock is about half the price commanded by Nauyuk stocks • (Kim 1993).

The Canadian Nauyuk strain The Nauyuk strain comes from an anadromous population spawning in the Nauyuk Lake system of the Kent Peninsula, Nunavut, and was based on the collection of eggs and milt from a few individuals (two to four families) in the fall of 1978 by Lionel Johnson, the guru of Arctic charr biology in Canada (de March 1993). The fertilized eggs were incubated using heated water at the DFO Rockwood hatchery and gave rise to a brood stock of 139 individuals, which commenced spawning in 1982 (Papst & Hopky 1984). Progeny from the second

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generation were transferred to commercial growers and government institutions in the Yukon, Ontario, and the three Prairie provinces (Papst & Hopky 1984). Of all the strains now under commercial culture, this is by far the most ideal for growth to large market size. sexual maturity at a late age (ﬁve years) and large size (2–3 kg) under culture • Reaches conditions. ﬂesh coloration (5 to 6 on Roche scale) and consistent pigmentation. • Good Grows to 2–3 kg slaughter weight in 24–30 months (Purves et al. 1997). • Large egg size (5 mm) and large alevin size at ﬁrst-feeding. • No precocious/early maturing males (jacks). • Moderate size variation in same-aged cohorts. • Although there are no quantitative studies comparing the commercial attributes of all these strains under similar growth conditions, various researchers have recorded well-known attributes of the Norwegian, Swedish, Icelandic, and Canadian strains. Table 5.1, which compares the attributes of various strains of Arctic charr, is based on these studies, as well as the incidental observations of researchers and the experiences of commercial growers (Ringø 1987; Nilsson 1993; Skúlason et al. 1996; de March 1997; Damsgård et al. 1999). The Nauyuk strain, the only one developed from the subspecies S. a. erythrinus, is notably different from the others in that it grows to large market size before reaching maturity, has good coloration at slaughter, shows no incidence of precocious males, and has a large egg size. For these reasons it is the preferred commercial strain in Canada and in other countries where it has been introduced to commercial growers (Picard 1997; de March 1997). Other strains were used because they were available as captive stocks under the control of each country’s research institutions, and because of a misunderstanding of the requirements and economic forces in the marketplace. In Canada, federal government researchers promoted the Fraser River strain to commercial growers in an attempt to justify research budgets, as it was the only certiﬁed strain available at the time. Unfortunately, its poor commercial abilities set back Arctic charr culture in Canada by decades. In retrospect, this is surprising given that the Nauyuk strain was already known in the mid-1980s to be a better performer than Fraser, Hammerfest, or the Hornavan strains. Researchers believed either they could bend the marketplace into accepting smaller, pale-ﬂeshed ﬁsh, or they thought they could manipulate these strains through husbandry techniques and genetic selection to eventually ﬁt the market. The marketplace said no to a small Arctic charr, and researchers never really carried through in any concerted way to develop a standard commercial Arctic charr from these inferior strains.

Potential for improving attributes of existing strains There are two steps in the process of improving Arctic charr for commercial growth. In the short term, improvements are possible through better husbandry methods and by better management of the physical grow-out environment, feeding methods, and diet preparation. Longterm improvements require a selective breeding program with the intent of improving culture attributes of the best strains currently in use. This need not involve high-technology, invasive,

Table 5.1

Comparison of growth attributes and body traits in Arctic charr strains used for commercial production. Hammerfest

Svalbard

Hornavan

Grenlækur

Ölvesvatn

Fraser

Nauyuk

Age at maturity Early maturation of males Flesh coloration at slaughter Slaughter weight 2–3 kg Egg size (mm) Presence of size morphs Subspecies Form

2+ Yes Poor No 3–4 Moderate S. a. alpinus Anadromous

3+ Yes Poor No 3–4 Moderate S. a. alpinus Anadromous

3+ Yes Poor No 3–4 High S. a. alpinus Resident

3+ Yes Good Some 3.9–4.1 High S. a. alpinus Anadromous

3+ Yes Good Some 4.1–4.3 High S. a. alpinus Resident

3+ Yes Poor No 4–5 High S. a. alpinus Anadromous

5+ No Good Yes 4.9–5.1 Moderate S. a. erythrinus Anadromous

The Standard Arctic Charr

Attribute

129

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genetic modiﬁcation (GM) aimed at producing a super-ﬁsh with duplicate copies of growthhormone-activating genes. A simple, traditional, farm animal breeding program based on quantitative genetics, selecting the highest-ranking individuals as parents for the next generation, will improve the quality of market ﬁsh without the controversial label of a GM product. Salmonids are particularly well suited for selective breeding programs as they produce a great many progeny from external fertilization which show a lot of variation, allowing for easily controlled one-on-one mating. They also exhibit many heritable, quantitative traits of economic importance, which show relatively normal distributions (Gjerde 1993). In other words, measurable traits such as length, size, ﬂesh color, and rate of growth can be improved by selecting an above-average parent stock. The value of ﬁrst testing strains and selecting the best strain for culture may be equivalent to several generations of selective breeding within a less desirable strain (Gjerde 1993). A selective breeding program would concentrate on improving traits of economic importance – for example, improved growth traits – that lower the cost of production and/or improve market traits that govern sale price to the consumer. The primary objectives of an Arctic charr breeding program are to: consistent slaughter weight (2–3 kg) in a reasonable amount of time before reaching • reach sexual maturity; consistent, uniform orange-red ﬂesh color (Roche 6 to 9) with minimal addition • achieve of pigment; and • decrease size variation and/or eliminate the presence of morphs within cohorts. Genetic selection may also improve the consistency of body traits such as condition factor, belly thickness, and fat content of meat.

Heritability of growth-related traits Genetic selection makes it possible to improve the size traits (length, weight, and condition factor) of Arctic charr before ﬁsh reach sexual maturity. The heritability (h2) – that is the degree that the expression of a trait in the offspring is controlled by genetic contribution from the parents – of size-related traits is moderately high for strains of charr studied to date (Elvingson & Nilsson 1994; Skúlason et al. 1996; de March 1997). Heritabilities of weight estimated from parental stocks of the Hornavan strain ranged from 0.25 to 0.62, but varied with age. Heritability of weight increased with age of the offspring, and at larger slaughter weights was higher in the paternal component than the maternal. That means that large males will contribute more to improving the size at slaughter than females, although both parents’ genes contribute to improving the trait. Genetic dominance and epistatic effects (interactions of two or more different genes) are small or absent on growth-related traits and diminish with age. A similar pattern is evident in the heritability estimates of length and condition factor (see Table 5.2). Early maturation is not a major concern with the Nauyuk strain, but appears to some extent in all other strains of commercially raised Arctic charr. Some strains show a proportion of males and females spawning earlier than others in their cohorts, while other strains have only

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Table 5.2 Heritability estimates of growth-related traits in Arctic charr. Attribute

Body weight age 2.0 age 2.5 age 3.0 Body length age 2.0 age 2.5 age 3.0 Condition factor age 2.0 age 2.5 age 3.0 Early sexual maturity Speciﬁc growth (age 2–2.5) Round weight Gutted weight Visceral weight Fat content ﬁllet Flesh color

Arctic charr h2

Atlantic salmon h2

Paternal

Maternal

Both

Both

0.34 0.39 0.52

0.65 0.38 0.38

0.45 – –

– – –

0.25 0.29 0.38

0.65 0.44 0.42

0.29 – –

– – 0.32

0.49 0.42 0.59 0.45 0.37 – – – – –

0.32 0.16 0.17 0.12 0.12 – – – – –

0.29 – – – – 0.45 0.43 0.25 0.06 0.27

– – 0.37 0.15 – – 0.36 – 0.21 0.09

males spawning earlier. The concern with Nauyuk charr is that slaughter weights of 2–3 kg sometimes occur just before maturity, so selective breeding aimed at increasing the mean slaughter weights must not push forward the time of maturity. Although the additive genetic correlation between size and early maturity incidence is low in Arctic charr, additive genetic correlations are moderately high for weight and condition factor (Nilsson 1992a). This means if you are selecting for large body weight, then condition factor will likely increase. A high condition factor is a good market attribute, but the signal to mature this year or next appears to be related to condition factor. Fish that spawned ﬁrst in a given cohort had higher condition factors than those that did not. Improving a trait such as weight, which can increase condition factor, might also lower the mean age of sexual maturation. This potential conundrum highlights the importance of understanding interactions between genetic traits and hidden environmental effects. Improving one trait, such as body size, may require changes in husbandry practices to reduce the effect of another trait, such as condition factor, on the timing of maturity.

Heritability of other traits The heritabilities of other traits related to body composition and early mortality are relatively low, as shown in Table 5.2. There is a positive genetic correlation between growth traits and fat content, suggesting that selection for increased weight will lead to higher fat content; however the additive genetic variation in fat content suggests the realized changes would be small (Elvingson & Nilsson 1994). No additive genetic effects on mortality to age 18 months were discerned in Hornavan Arctic charr, which agrees with results from other studies of salmonids (Nilsson 1994). Although mortality rates in Arctic charr are often high from

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ﬁrst-feeding until ﬁsh are two months of age, changes in environmental conditions and feeding techniques generally address the problem efﬁciently. The heritability of pigment deposition in the ﬂesh from one level of pigment added to feed (60 mg/kg) has been investigated. Results from Hornavan Arctic charr suggest that the level of pigment deposited in the ﬂesh is under genetic control, with a heritability of astaxanthin deposition in the muscle of 0.26–0.28. There was a positive genetic correlation between body size and pigment uptake, with low levels of pigment noted in the ﬂesh of charr of less than 600 g gutted weight, even when they were fed astaxanthin at a rate of 60 mg/kg feed. This conﬁrms a problem recognized by commercial growers: small Arctic charr of all strains deposit little pigment in the ﬂesh, as is reﬂected in the pale color of pan-size ﬁsh.

Breeding strategies for improving commercial stocks A breeding program strategy involves improving the mean value of a trait in the offspring to an average above that of its parents’ generation. The difference is known as genetic gain. Some of the expected genetic gains in traits important to commercial Arctic charr culture are presented in Table 5.3. Breeding programs typically involve inbreeding, crossbreeding, or purebreeding. Inbreeding, the mating of closely related individuals, generally reduces performance in salmonids, particularly with traits connected to reproductive capacity and viability (Gjerde 1993). Inbreeding may become a concern with existing strains, given the small number of animals used as founding stock from the wild. There has been research into this issue, and brief examination by de March and Tabachek of Fraser strain individuals held at some facilities raised concerns about potential inbreeding effects (Tabachek & de March 1991). Crossbreeding between different strains, stocks, or inbred lines sometimes leads to hybrid vigour or heterosis. Heterosis is the tendency of a crossbred individual to show qualities superior to those of both parents. It does not occur in Arctic charr. The genetic diversity among Arctic charr stocks was initially thought to be a useful source for broodstock enhancement from crossbreeding. In Sweden, researchers crossed three strains of Arctic charr from different stocks from northern Sweden, hoping for heterosis in body weight and sexual maturation in the ﬁrst generation (F1) progeny. No useful heterosis was found in the strain crosses. Offspring in the crosses resembled the male parent strain more than the female parent strain with respect to growth and male maturation pattern. The male parent strain had a pronounced effect on the frequency of maturation in males and on the size of mature males. This paternal effect has been

Table 5.3 Genetic gain in growth-related traits and body traits important in commercial Arctic charr culture. Data from Elvingson and Nilsson (1994).

Ungutted weight (g) Astaxanthin deposition (mg/kg) Condition factor

x

SD

h2

i

L

Per year ΔG

% ΔG

ΔG

% ΔG

609 1.3 1.8

230 0.6 0.2

0.45 0.28 0.24

3.37 3.37 3.37

5 5 5

69.76 0.113 0.03

11.5 10 1.8

348.8 0.57 0.16

57.2 43.8 9

i intensity of selection; L generation time in years; G

genetic gain

Per generation

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noted in other salmonids, guppies, and catﬁsh and is referred to as ‘paternal predominance’ (Purdom 1993). Dominance effects are also observed in crosses between normal and dwarf Arctic charr, with F1 offspring showing dominance of the dwarf form over the normal form. This may explain the persistence of a bimodal size distribution seen in many charr populations. A similar lack of heterosis was evident in crosses between Nauyuk, Fraser, and Hammerfest Arctic charr. None of the researchers recommended crossbreeding as a useful tool to improve growth performance (Eriksson et al. 1993; Nilsson 1993; de March 1997). Most researchers suggest that selective breeding of the pure strain, or purebreeding, is the best method for long-term improvement of growth and body composition traits in Arctic charr (Eriksson et al. 1993; Gjerde 1993). Research to date suggests culture traits that show improvement through additive genetic selection in Atlantic salmon or rainbow trout are also amenable to improvement in Arctic charr. In Sweden, performance was initially improved by 20% in each generation in the Hornavan strain for growth-related traits using family selection and mass selection techniques (Eriksson 1991). To summarize, growth traits have relatively high heritabilities, and it is best to select brood stock from those ﬁsh reaching harvest weights most quickly, before the onset of sexual maturity. Size variation is also heritable but is often overshadowed by environmental effects, making a selection program difﬁcult. De March suggested that the best approach is to select large individuals from within families that have the narrowest range of size variation (de March 1997). Flesh color is also amenable to improvement through genetic selection, with brood selection taking place at the time when harvest weight is reached. This involves choosing families rather than speciﬁc ﬁsh, as individuals must be killed to determine ﬂesh color. Further research is required to determine degree of genetic control over evenness of ﬂesh color throughout the ﬁllet and pigment levels required in feed to achieve acceptable color.

The standard Arctic charr One of the problems in developing better strains of Arctic charr for commercial culture is the lack of a standard for measuring performance. Jobling devised a growth model based on the Hammerfest strain that is widely used for comparing growth rates amongst various strains. However, a broader model based on growth traits, body traits, and other measures of performance having relevance to both the consumer and the producer is required. The Nauyuk strain of Arctic charr grows proﬁtably under intensive culture conditions while meeting the large size and dark ﬂesh color demanded by the consumer. This strain should be the standard of performance and the starting point for producing a strain with superior attributes for intensive culture. Table 5.4 shows performance benchmarks developed for eight traits important to the consumer and the producer, calculated for a standard Arctic charr using the Nauyuk strain and two hypothetical standards improved by husbandry techniques and genetic gain in the existing Nauyuk strain. In all three models, an alevin ﬁrst-feeding weight of 0.06 g is assumed. Improvements in ﬂesh color, measured using the Roche color card for salmonids, are only possible through genetic gain that increases ﬁshes’ ability to absorb astaxanthin. Improvements of food conversion rates are based on improved feeding techniques. Head-on slaughter weights are standard for all three models and cover processing losses (blood, viscera, drip) into the shipping box.

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Table 5.4 Characteristics of a standard Arctic charr for intensive culture. Attribute

Months to harvest weight Harvest weight (kg) Growth constant (kg) Head-on slaughter weight (kg) Condition factor Flesh color (Roche scale) Economic food conversion Expected mortality (%) Expected cull rate (%)

Standard

Target 1

Target 2

Nauyuk

Nauyuk improved

Nauyuk superior

40 2.5 1.1 2.1 1.3 5–6 1.6 10 20

30 3.0 0.8 2.6 1.3 6–7 1.4 5 10

24 3.0 0.6 2.6 1.3 7–8 1.0 5 5

The growth model, based upon the time required to reach a market weight of 2.5 kg, uses a standardized water temperature proﬁle that mimics optimum growth conditions for Arctic charr (see Fig. 5.1). In the ﬁrst months of life the water temperature rises from 8 °C at ﬁrstfeeding to 14 °C at the fry stage. Thereafter, water temperatures remain at optimum except for a winter period ﬁtted around the natural winter solstice. This yearly cycle repeats until ﬁsh reach market weight. Growth, estimated from the Iwama model, uses a speciﬁc growth constant (GC) of 1.1 calculated for Nauyuk Arctic charr which also coincides with farm data (Iwama 1996). Improvements in the time to harvest weight, and increases in harvest weight of the two hypothetical strains (improved and superior), are based on genetic improvements reﬂected in the model by a declining growth constant. The time required to reach a market weight of 2.5 kg in the standard Arctic charr is attainable with existing Nauyuk stocks under good husbandry conditions, but the size variation within cohorts is still relatively wide compared to rainbow trout and Atlantic salmon. Condition factor at harvest will likely increase with increasing weights but is also affected by the level of starvation applied before slaughter. The standard Arctic charr, based on the Nauyuk strain, is the ﬁrst step towards the creation of a domesticated Arctic charr for harvest as a food ﬁsh. It is the transition from the biology of

Fig. 5.1 Growth rate and water temperature proﬁle for the standard Arctic charr.

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wild Arctic charr, their environmental requirements and nutritional needs, to actually rearing domestic Arctic charr under culture. The standard I present here can be achieved by using good husbandry techniques and is a good mark to measure performance against. In the following chapters I discuss the methods needed to raise brood stock, look after eyed eggs, and bring alevins through the hatchery phase of early rearing. Reaching harvest weight is ultimately what it is all about in commercially rearing Arctic charr, and the Nauyuk strain should allow achievement of harvest size in a commercial facility.

Chapter 6

Brood Operations: Keeping Brood, Egg Collection, and Incubation

Brood operations, whether commercial or for research, cover three areas of management that require a high degree of technical skill and knowledge: stock management involves raising and maintaining a mixed-sex population of • Brood Arctic charr for the production of eyed eggs. Spawning management involves selecting ripe ﬁsh as parents, artiﬁcial removal of ova • and milt from ripe ﬁsh, and fertilization of ova. Incubation involves placing fertilized eggs into hatching trays, managing the incubation • process, and controlling hatching. Depending on the structure of the commercial venture or the type of research facility, the care of brood stock, the spawning process, and incubation may occur under the same roof. Some facilities may specialize in keeping brood stock for the production of eyed eggs (eggs that are only a few weeks from hatch) for sale to commercial or research hatcheries and grow-out facilities. The ultimate goal of a brood stock program is the production of viable ova that hatch into high-quality offspring. There are two measures for quality. One is the physical health of the offspring, expressed in terms of good growth and body conformation, disease tolerance, and robust, vigorous character. The other is how consistently offspring exhibit traits suitable for on-growing in tanks at high density or in low-density lakes, either for the commercial market or for reintroduction programs that re-establish or enhance wild ﬁsh populations. Some of these qualities are the result of genetic selection in the brood stock program while others are the product of a well-managed egg-take program. The phenotypic traits needed in an Arctic charr used for commercial culture, discussed in Chapter 5, are not the same as those of a ﬁsh destined to enhance a wild stock, and these two ends cannot be achieved with the same brood stock program. In an aquaculture program destined to enhance wild stocks, culturists make every attempt to retain wild traits and genetic diversity by avoiding genetic selection for speciﬁc traits. The wider the genetic pool or number of randomly selected parents, the better the chance a wild population of ﬁsh will survive to maturity in an uncontrolled wild environment. Of course, the very nature of artiﬁcial propagation will subtly inﬂuence the gene pool. There are natural forces affecting behavioral responses that bring various ﬁsh together to mate in the wild that cannot be duplicated when eggs and sperm are stripped from random individuals and united

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through artiﬁcial fertilization. Similarly, the artiﬁcial nature of egg incubation and early rearing in no way mimics the wild conditions found in the spawning redds of wild Arctic charr. At best, you can try to minimize hatchery effects on ﬁsh destined for the wild environment by following these guidelines designed for salmonids in general: one-on-one crosses of parents randomly selected from all sizes and shapes of • Perform mature ﬁsh. parents throughout the entire spawning period, including early and late ripening • Select individuals. Select brood stock from progeny that have returned from the wild to spawn – • that is,replacement ﬁsh that have not been raised to adulthood in an artiﬁcial environment. Select individual brood stock from the local wild stock that is being enhanced or from the • nearest wild population that contains similar size morphs and uses a similar habitat type. When enhancing stocks, the cultured ﬁsh should not swamp the numbers of spawn• ing ﬁsh. Althoughwild it is difﬁcult to estimate, the cultured ﬁsh should not exceed 50% of the

• •

total spawning population. Release all progeny reared and do not cull small ﬁsh. Release young ﬁsh to wild waters as soon as possible, minimizing their time under artiﬁcial culture conditions (Pepper & Crim 1996).

In contrast, a captive brood stock used for intensive/extensive culture requires traits that improve ﬁsh health and marketability. Breeding for market growth rates, color of ﬂesh, condition factor, etc., takes cultured ﬁsh in a completely different direction than ﬁsh destined for reintroduction to wild waters. This brood stock is selected for traits that enhance growth in the highly artiﬁcial tank environment. They are still creatures on their ﬁrst steps toward domestication, so the offspring of each generation of brood stock selected for commercial traits should be easier to grow under cultivation and more proﬁtable without sacriﬁcing the attributes that make Arctic charr a unique eating pleasure. Developing better brood stocks is the primary concern of a number of specialty egg producers in both the commercial sector and research facilities in North America and Europe, but sourcing good-quality seed stock will continue to be a concern for commercial growers of Arctic charr for the foreseeable future. For these reasons, a facility may want to develop its own brood stock program to assure itself a continuous supply of quality eggs. The development and management of brood stock requires different sets of husbandry skills and management skills than those needed for ongrowing ﬁsh to market. You have to keep enough genetic lines, and they must be kept separate until they are large enough to individually mark, all of which requires a lot of incubation and early rearing space, which is separate from the on-growing tanks. Maintaining a viable brood stock program also takes a great deal of time and expense, but is a worthy enterprise. You should familiarize yourself with the related considerations and constraints before choosing to develop your own brood stock. The foundation stock should start with a large amount of genetic variability. This can be • achieved by purchasing eyed ova from a number of suppliers. It takes ﬁ ve years for the best strains to reach sexual maturity under natural light condi• tions found north of the 60th parallel. If raised south of this latitude, you will need to have

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• •

•

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artiﬁcial light that mimics northern light/dark cycles. You can advance the time of sexual maturity by manipulating light, water temperature, and food, but it may compromise egg quality and brood stock health. There must be enough ﬁsh in the brood stock program to prevent inbreeding and allow an ongoing selection process to improve culture traits and consumer acceptance traits in carcass quality. You must take into account adult ﬁsh losses incurred in the yearly dead sampling that is required to test the ﬁsh for pathogens to maintain a certiﬁed disease-free brood stock. The number of ﬁshes sampled each year depends on the requirements of the certifying agency. For example, in Canada a four-year development of brood stock containing 2500 ﬁsh would require the dead sampling of 120 ﬁsh per year, accounting for almost 20% of the population (Fisheries & Oceans). There has to be a continuous supply of new brood stock to replace mortalities associated with the egg-take and losses incurred during ﬁsh health sampling. This can be combined with a selection program that brings on line new brood ﬁsh that have superior attributes. The selection process for many traits is made at market size, which means keeping potential brood stock for 24–36 months before selecting individuals. This places additional pressure on rearing space and ﬁnancial resources. Select as brood stock those ﬁsh that reach harvest weight in the most efﬁcient manner in terms of feed and time. Note that the fastest-growing ﬁsh will not necessarily be the ones reaching market weight. For example, the fastest-growing Fraser strain appear to be jack males, and you deﬁnitely do not want them in a commercial facility. Often the best-performing individuals are from the same families, so to prevent brother– sister mating, a sophisticated marking system is required to identify family groups or, preferably, individual ﬁsh. This assures outbreeding and enables the best crosses based on parental and progeny performance. Although costly, the passive integrated transponder (PIT) tag system is the best method of individually marking brood ﬁsh. A small electronic tag, about the size of a rice grain, is inserted surgically in the body cavity, from where it transmits a unique identiﬁcation code to the observer when activated by a handheld receiver. The tags are inert and can be inserted into Arctic charr smaller than 10 g size (Brännäs et al. 1994). PIT tags have few side effects and are functional for the life of the ﬁsh. They can also be reused. External tagging systems have drawbacks of one form or another. The most serious problem with external tags such as Floy tags or disc tags is secondary infection, particularly fungal infection at the site of attachment. Visual implant tags, which are inserted under the skin, have a very high loss rate when used on Arctic charr.

Brood ﬁsh can be kept in tanks under the same conditions used for rearing other Arctic charr. If the brood stock is being developed for raising Arctic charr at high density in tanks, then potential brood ﬁsh should be subjected to those conditions, at least until they reach harvest weight. Arctic charr brood used for low-density pothole lake stocking are best kept in ponds subject to natural conditions. In both cases, the brood ﬁsh that reach harvest weight in the least amount of time should be selected and individually tagged as the future brood. Water temperature becomes critical in the last summer of development, and water must be kept cool, particularly as spawning approaches. Speciﬁc water temperatures, light conditions, and

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special handling techniques for brood ﬁsh are discussed in the following sections on spawning Arctic charr.

Spawning The spawning window Arctic charr have a long natural spawning window lasting up to 10 weeks. This varies in duration depending on the charr strain under cultivation and environmental conditions (Robbins et al. 1990). Depending on the strain, the spawning period can begin anywhere from mid-July to January (see Table 6.1). The time of spawning is relatively consistent in each age cohort from year to year. Within each cohort, males are ripe for a prolonged period of 4–10 weeks, whereas females have a much narrower peak period, lasting, at most, a week. The time of peak ripeness for individual females in a cohort might differ by many weeks (Eriksson & Wiklund 1989), and if they spawn early or late one year, they usually spawn at the same relative time in subsequent years. Culturists can inﬂuence spawning time by using drugs and photomanipulation. Drugs such as Ovaprim shorten the spawning window in salmonids by inducing ovulation, but they will not induce spawning in Arctic charr that have not reached sexual maturity, regardless of how large they are. In experimental work done by Prince Edward Island Veterinary College, Arctic charr that were induced to ovulate using Ovaprim had egg survival rates to ﬁrst-feeding of 75% (Krieger 1991). Photomanipulation has been used successfully to produce off-season Arctic charr ova in the spring instead of the normal fall spawning. In one Canadian hatchery I visited there were a number of races of Arctic charr producing eggs in almost every month of the year, a condition that may have merit, but put hatchery staff and brood ﬁsh under tremendous pressure. This constant ovulation was induced by a bizarre, unplanned light regime that allowed random light into the hatchery at all hours of the day and night. Once a light regime is set, it is very important that no other light is allowed entry into the area. For normal fall spawning, it is important to keep brood stock under a photoperiod that mimics light conditions found north of the 60th parallel. Although changes in photoperiod appear to be the primary initiator of ovulation and spawning, water temperature also inﬂuences the timing of spawning (Eriksson & Wiklund 1989; Jobling et al. 1993). Ovulation may be delayed if brood stock are held in water temperatures over 8 °C for prolonged periods, and it may be completely inhibited at temperatures over 11 °C. Table 6.1 Variation in natural spawning window of different Arctic charr stocks. Data source: Johnson 1980; Krieger 1991. Stock/Strain

Natural spawning window

Latitude

Country

Nauyuk Lake (wild) Nauyuk Lake (domestic) Fraser River Storvatn

15 Sept–7 Oct 21 Aug–25 Sept 1 Oct–early Jan 21 Sept–31 Oct

68°15´N 61°00´N 56°39´N 61°37´N

Canada Canada Canada Norway

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Water temperature appears to be the most important variable in terms of the quality and viability of Arctic charr ova. When water temperatures are held above 5 °C for several weeks prior to and during spawning, the quality of the collected eggs may be poor (Gillet 1991). High water temperatures tend to accelerate the aging processes, resulting in over-ripeness in eggs. At water temperatures above 5 °C the effects of over-ripening become more severe, and egg mortality in the eyed stage increases rapidly after three days from the time of ovulation. In both Lake Geneva and Nauyuk races of Arctic charr, researchers have noted that egg viability is higher if brood ﬁsh are held in water temperatures below 6 °C for a few weeks prior to spawning. Prior to this period, higher temperatures are conducive to the formation of larger ova. Females kept in 5 °C water prior to spawning had smaller ova than ﬁsh kept at 8 °C (Gillet 1991). The effective spawning window also becomes narrower as temperature increases above 5 °C. In essence, Arctic charr brood require warmer water during the summer, when eggs are developing in the ovaries, and cooler water just prior to ovulation and spawning. Keeping the water temperature of the brood stock holding tank below 5 °C prior to and during egg-take makes it cold for the hatchery staff handling ﬁsh, but it is the best temperature for maximizing egg quality. The ambient air temperature in the area of the egg-take must also be kept as low as possible to prevent eggs from warming up.

Ovulation and spermatogenesis Ovulation is the release of mature eggs or ova from the ovaries into the body cavity, where they are lubricated with ovarian ﬂuid and made ready for release from the vent. In Arctic charr, all the ova develop in unison, leading to one massive spawning event. Maturation of the eggs within the ovary and the release of eggs during ovulation are induced by the hormone GtH (pituitary gonadotropin). The pituitary is cued to release this hormone by a complex chain of events that converts environmental stimuli (i.e. changing photoperiod and water temperature) into a signal from the brain (Redding & Patiño 1993). Once ovulation has occurred, the eggs should be removed from each female as soon as possible. Correct timing of the egg collection is one of the most important variables in ensuring good-quality eyed ova. Removing eggs prior to complete ovulation is not recommended, as the eggs are not free in the body cavity and it requires considerable pressure to squeeze them out, at high risk of damage to the female. On the other hand, eggs taken too long after ovulation will be of low quality and fertility. The optimum period for taking Arctic charr eggs is in the ﬁrst four days after ovulation. Declines in fertility (expressed as a percentage of eggs that survive to the eyed or hatched stage) remain low 7 days after ovulation, but by day 11 there is a rapid decline in egg survival (Collison 1991; Gillet 1991). There is some evidence that the quality of eggs varies depending on the relative time females ovulate during the spawning season. Eggs produced during the middle of the spawning window had a higher biochemical nutrient composition, which correlated to greater growth and survival of alevins and fry than for eggs collected early or late in the season. Alevins from mid-spawning females were signiﬁcantly heavier and longer than those from early and late spawners. Fingerlings from mid-spawners also showed larger size and weight one month after ﬁrst-feeding (Srivastava et al. 1991). Although survival of eggs from early and latespawning females was lower than that of mid-spawners, the difference was less than 10%. This may be related more to egg size than the timing of ovulation per se.

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Arctic charr males mature prior to females. I have never found ripe females without at least a few ripe males already present. Fish sperm are typically immotile and inactive when they are still in the testes. Motility is initiated after sperm are released from the body and activated by the presence of water or ovarian ﬂuid (Redding & Patiño 1993). Once motile, sperm have only minutes to fertilize an egg before they run out of energy. However, unlike ova, they can remain healthy and viable in the testes for weeks. It is the female’s sexuality that is of primary concern during spawning, and the identiﬁcation of ovulation is the most critical factor.

Methods for sexing and assessing ripeness In both maturing males and females, the onset of spawning is preceded by obvious physiological changes. Weeks prior to spawning, most males will take on the bright red or orange spawning colors, and some females will also show brighter hues along the ﬂanks and belly. Both sexes show a loss of the silvery or white belly walls. Overall, the sexually mature female has a brighter hue than an immature ﬁsh, with ﬂanks and belly varying in color from bronze to orange-red. The leading edges of ﬁns are white, backed with pale orangered. Mature male charr are remarkably bright, with some Nauyuk males almost ﬂuorescent orange, and other strains showing bright red hues along the belly and ﬂanks. Males are generally brighter than females, especially in the underbelly, which may become yellow or orange if pigmented feed is used. The bodies of mature males are laterally compressed and much deeper through the ﬂanks than females. Females become rounder and fuller in the belly, though they may not have the protruding genital papillae that are seen in fully ripe Atlantic salmon (Delabbio 1991). The snouts of males become more pointed, turn light brown when viewed from the top, and develop a hooked kype, many with bulbous tips, though the kype is not so pronounced as it is with Atlantic salmon. Females may also develop a slight kype. Many of these characteristics fade rapidly after spawning is completed, which is another reason to tag all of your brood stock. Tagging each brood ﬁsh makes the sorting process much easier in future years. Before any females ovulate, most of the male Arctic charr destined to reach sexual maturity in any given cohort will have done so. Once males become ripe, they are sexually viable for weeks, often for the entire spawning period. Males that show secondary sexual development (bright colors and kype) but are not producing milt should be checked regularly throughout the spawning period. If they do not produce milt by year-end, remove them from the brood stock program as they are unlikely to produce milt in following years. Within each cohort there will be a residual group of non-spawners/immatures, which are difﬁcult to sex. They show some coloration, even kypes, but they do not ﬁt either sex category. They are large – usually some of the largest ﬁsh in a given cohort – and silvery, with just a touch of color. Upon dissection, they are mostly males with small undeveloped testes or females with small ovaries. Generally, male and female charr slow their feeding or go off feed entirely as they approach spawning time. In some races of charr the ﬁrst manifestations of reproductive interest are changes in swimming behavior, such as milling about the water intakes or swimming in the opposite direction to incoming water ﬂow.

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Sorting brood ﬁsh prior to spawning Sorting prior to spawning involves, ﬁrst, determining the sex of each ﬁsh and then the degree of ripeness. Distinguishing males from females has its own challenges, as the sexes can be difﬁcult to distinguish early in the year prior to spawning, though many males do develop rudimentary kypes, at least in the Nauyuk strain. The development of secondary sexual characteristics is highly variable in Arctic charr, and there are some males and females that show very little skin brightness or intensity of spawning colors. Before separating the females from males, they should be exposed to each other, as it is likely that females release a pheromone which induces milt production in males (Vermeirssen et al. 1997). This does not need to be an extra step, as the brood stock can be kept in the same tank together up until they are sorted for spawning. This sort should take place about two weeks after the ﬁrst males have colored up or shown signs of a kype. There is a normal distribution in the time of spawning among Arctic charr, with a few early spawners, a mid-peak in numbers, and ﬁnally a tailing off of late spawners (Ingram 1985). To minimize stress for the brood ﬁsh, it is a good idea to sort them into groups based on their closeness to ripeness (see Fig. 6.1). By doing this, you need only spawn-check those that are very close to spawning; the others can wait a week or two.

Fig. 6.1 Sorting brood ﬁsh prior to spawning.

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Males should be checked on a weekly basis and classed as ripe (expressing milt with slight hand pressure), unripe (bright spawning colors and kype), and eunuchs (little color, no kype). It is more difﬁcult to determine the degree of ripeness in female Arctic charr, but with experience (or a slimy thumb) you can pick up a female and have a good sense of her ripeness. Unripe females usually have white, hard, unswollen bellies. They may be late-spawners or non-spawners. Nearly ripe females have soft bellies, slightly protruding in many cases, with dark mottled ﬂanks and slightly swollen genital papilla, but express no eggs under hand pressure. In some females that are nearly ripe, the egg mass will fall forward in the abdominal cavity if the ﬁsh is gently lifted by the tail with her snout pointed downward (Delabbio 1991). As ovulation approaches, the genital papilla becomes more protruded and enlarged. Ripe females have distended, soft, dark bellies, and gentle hand pressure from the belly towards the vent will release eggs (Eriksson & Wiklund 1989). In most ripe females the papilla are enlarged, slightly red or pink, and protruding, while the belly is dark brown or ﬂecked with bronze. The occasional female will show little spawning color or be small with a ﬂat belly, while still producing many ova. Keep ripe females and ripe males in separate tanks and spawn the females immediately (within one to ﬁve days of ovulation). Nearly ripe females and unripe males can be placed in the same tank, while unripe females should be kept in their own tank and checked only every other week. As ﬁsh ripen, move them into the appropriate tank. Good-quality males can be kept in the ripe tank and reused in subsequent egg-takes. Having enough ripe males is often a problem, particularly with Nauyuk Arctic charr. If there is a shortage of mature males, cross the largest males with multiple females. One of the secrets for maximizing the quality of Arctic charr ova is frequent sorting of female brood. Females classed as nearly ripe should be spawn-checked at least once a week (Eriksson & Wiklund 1989). If the water temperature of the brood stock holding tank is above 6 °C, then nearly ripe females should be spawn-checked twice weekly. When sorting brood stock and checking for ripeness, use a gentle hand. At this point, you are simply trying to assess the stock’s ripeness, and gentle pressure will determine this as a ripe female will expel eggs at the lightest pressure. Eggs that are expelled in sorting are wasted, so the expulsion of one egg is all that is needed to determine ripeness. A heavy hand can express hundreds of eggs in a second and cause damage to many other ova if water ﬂows back into the vent. Sometimes a female will have all the characteristics of ripeness but will not express eggs. This may mean that eggshell from last year’s ova has formed a plug in the vent that prevents the release of ova. Gentle hand pressure applied near the vent will expel the plug, allowing the free ﬂow of eggs. Handling Arctic charr during spawn-check and egg-take is a stressful activity for both brood ﬁsh and hatchery staff. Charr are more susceptible to fungal infections and other pathogens and have the highest mortality rates among salmonids during spawning. Sorting must be done with gentleness and with a minimum of fuss. I prefer not to anesthetize ﬁsh during sorting. It greatly lengthens the time needed to sort ﬁsh and, as stated in the section on anesthetic below, ﬁsh should not be anesthetized more than once a week. However, if you are not comfortable with assessing stages of ripeness in charr,

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it is best to put the ﬁsh under. This allows handlers to give their full attention to determining ripeness, without worrying about a struggling ﬁsh. Male Arctic charr are particularly difﬁcult to hold; they are strong and can slither out of your hands like a snake. Dropping a ripe female to the ﬂoor can rupture her internal organs and ripe ova, leading to serious egg losses and death of a valuable ﬁsh.

Careful handling of spawning ﬁsh Be careful when handling spawning ﬁsh. Arctic charr brood stock are the most valuable ﬁsh at any facility. They are repeat spawners that will last 5 to 10 years if carefully handled. Vigorous handling during spawning increases the risk of injury to brood stock. Egg stripping is particularly hard on them, and improper handling is the greatest reason for internal organ damage. Often injuries are not fatal, but become evident when the ﬁsh shows poor weight recovery after spawning or poor egg production the following season. Place only one or two ﬁsh at a time in a dip-net, as too many ﬁsh in a net puts excessive pressure on ﬁsh in the lower portion of the net. Fish should never be dropped, tossed, or thrown. Move each ﬁsh gently, and place it into a holding container large enough that the ﬁsh does not become bent or twisted. Lower the net into the water and let the ﬁsh swim out. Never hold brood ﬁsh only by the tail, as this can lead to severe bruising in the muscle. When handling brood ﬁsh, always support the ﬁsh belly-up with two hands – one hand clasped around the back behind the head, and the other clasped around the peduncle region of the tail, as shown in Fig. 6.2. Working with brood charr can be extremely cold work, with water temperatures in the 6 °C range and ambient air temperatures, at least in theYukon, to –20 °C. Wearing gloves can improve handling success, but I ﬁnd bare hands are better for determining ripeness during the ﬁrst sort.

Fig. 6.2 Correct method for holding brood ﬁsh.

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Fish can be spawned indoors as long as the cold water temperature is maintained, and this may make it more comfortable for workers, which lowers the chances of injury. If you are getting bloody reproductive ﬂuids from males or females during the stripping process, you are squeezing too hard. Warm up your hands or reassess your technique (Munkittrick).

Egg collection Timing and attention to detail are crucial in developing a good-quality egg harvest and a successful hatching. Sloppy procedures such as dripping water into egg bowls, poorly rinsing anesthetized ﬁsh, or bumping eggs when they are sensitive to shock can cause damage or dead eggs – and it will take many hours of labor to remove them from hatching trays. A delay of a few minutes when adding milt to ova, or waiting just a few days longer to collect eggs, can drastically decrease the quality of fertilized eggs and the subsequent alevins. You must be sure of each step in the spawning cycle to ensure maximum production of eyed eggs. Although the process of collecting eggs from Arctic charr is similar to that used for any other salmonids, there are subtle differences in the development of secondary sexual characteristics, fecundity of females, color and size of eggs, and, most important, the optimum water temperature for egg fertilization and incubation. These differences, like other aspects of Arctic charr husbandry, have led to difﬁculties for culturists experienced with other salmonids, who treat spawning charr like salmon or trout. Julie Delabbio (1991), who has worked with trout, charr, and Atlantic salmon, has said, ‘The spawning of Arctic charr brood ﬁsh should be approached without the expectations associated with Atlantic salmon and trout.’ Her observations are worth noting: (1)

(2)

(3)

(4)

Secondary sexual characteristics do not clearly indicate the state of gonadal development in Arctic charr. Some Arctic charr, particularly females, show very low intensity and fulsomeness of spawning colors, even when they are ripe. Males and females that do show vivid spawning colors are usually ripe or will be soon. Female charr may or may not show protruding genital papillae and they may develop a small kype. Male Arctic charr develop an obvious kype, but it is often not so developed as in rainbow trout or Atlantic salmon. The skin mucous layer on male and female Arctic charr is thicker than that of rainbow trout and Atlantic salmon. When towelling dry the charr’s skin surface (to remove anesthetic) prior to stripping milt or eggs, it is common to remove too much mucus under the assumption that the thick layer of mucus is water. Excessive drying of the skin can lead to serious post-spawning fungal infections, particularly in males. The technique used to assess ripeness in female Atlantic salmon – that is, looking for a pucker around the genital opening while the ﬁsh is held head down – is not reliable in Arctic charr. Many female charr show no pucker when fully ripe. In general, Arctic charr produce more eggs per kilogram of body weight than Atlantic salmon do, and charr eggs are smaller and paler in color. Incubation equipment designed for Atlantic salmon may require modiﬁcation to ensure charr eggs are adequately held and newly hatched alevins cannot escape. Equipment designed for rainbow trout incubation is adequate for most Arctic charr strains.

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The standard Arctic charr takes up to ﬁve years to reach sexual maturity, which is a tremendous investment in tank space, husbandry effort, and time. However, the upside to Arctic charr is that they are repeat spawners. Although there has been a trend with farmers of Atlantic salmon brood stock (also repeat spawners) to kill the female ﬁsh and surgically remove eggs (Willoughby 1999),this is not a good approach with Arctic charr. The ﬁrst spawn of eggs from a female of a given age cohort is generally lower than what she will produce in her second, third, and fourth year of production. Generally, the older the female, the better the quality and quantity of eggs produced (see Table 6.2). This is somewhat related to increased body and increased egg size, but some other factors of quality seem to be in play also. A ﬁnal good reason for keeping brood stock for at least four production years is that the appearance of good grow-out traits in the progeny may not manifest itself for 24–36 months. By marking individual brood ﬁsh and following their progeny through the grow-out process, it is possible to reproduce ﬁsh from that speciﬁc line much sooner than it would be if you had to wait for the progeny to reproduce.

Management and organization of the egg-take The egg-take must be well managed to ensure that ova and milt are collected with minimal stress to the ﬁsh, in a manner assuring quality eggs of highest viability. The area for collecting eggs should be clean and dry, preferably close to holding tanks, and under cover for protection from direct sunlight and rain. Sunlight, infra-red, and possibly ﬂuorescent lights are detrimental and can kill eggs after only a few minutes of exposure (Brännäs et al. 1994; Munkittrick). The ambient air temperature should be cool, preferably in the 4–6 °C range. The physical set-up for spawning should be designed to follow a natural ﬂow of ﬁsh from the holding tank to the fertilization table and back to the recovery tank with as little effort as possible (see Fig. 6.3). It is difﬁcult to assess the amount of time required to spawn Arctic charr, as it depends on the efﬁciency, size, and experience of the spawning crew, as well as the quantity of charr spawned. Preparation for egg and milt removal takes about 3–4 minutes per ﬁsh and includes catching the ﬁsh, transferring them to small tubs, and sedating them with clove oil in the tub water. Removing the eggs from one female and the milt from one male Arctic charr takes another 3–4 minutes, after which the two are returned to holding tanks. Then it takes a couple of minutes to fertilize and weigh the eggs. In total this comes to about 8–10 minutes for each bowl of eggs.

Table 6.2 Relationship of egg production to ﬁsh size and successive spawning in Arctic charr. Data source: Eriksson & Wiklund 1989. Year

Fish size (g)

1st year spawner 2nd year spawner 3rd year spawner

500–1000 1000–2500 2000–3000

Egg production No. of eggs/ﬁsh

No. of eggs/kg*

% increase in eggs/ﬁsh

1950 3300 3900

2600 1885 1560

NA 169 200

*Based on midpoint ﬁsh weight 750, 1750, and 2500 g

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Fig. 6.3 Organization of the Arctic charr egg-take.

It is important to identify each parent and collect data on the physical conditions of the eggs, the number of eggs per female, their quality, and other attributes. This data allows you to control egg inventory and assures eggs are loaded into the correct incubators. It also forms the basis of a quality assurance program by allowing you to track progeny performance criteria back to parent stock and conditions of the egg-take. Good data collection is important if you are selecting for attributes in grow-out ﬁsh that may not be evident for many months or years – long after you have forgotten who was mated with whom. As well, you can determine your ﬁsh handlers’ success rate. For example, if all the eggs die every time one person spawns a ﬁsh, you might want to move that person to another job in your operation.

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Preparation of equipment for egg-take and incubation Prior to the ﬁrst egg-take, you should disinfect and check all of the equipment needed to make sure it is in good working condition and that you have sufﬁcient quantities of supplies. There is nothing worse than running out of oxygen or paper towels when you are in the middle of a large egg-take. A take of a million eggs can last the better part of a day and requires efﬁcient ﬁsh handling. The equipment should be laid out in advance and in the order required, as listed below: quantities of anesthetic to prepare new anesthetic baths after 20 to 30 ﬁsh have • Measured been anesthetized and solution is weakened by contaminants. able to hold 100–200 L of water for anesthetic bath, rinsing bath, and recovery • Containers bath. equipment to oxygenate anesthetic and recovery baths. • Aeration Stainless bowls for collecting eggs; beakers for collecting milt. • A table forsteel holding bowls and other equipment. • Paper towels or softspawning to wipe down ﬁsh prior to spawning. • Flowing fresh water cloths to rinse eggs. • Weigh scales. • Microscope to check sperm viability. • Paper for recording data, pencils, and waterproof markers. • Wet-weather gear, insulated rubber gloves, and warm clothing for the spawning crew. • The incubation room also needs to be prepared for receiving eggs. Vertical incubation cabinets that hold stacks of egg trays, shown in Fig. 6.4, work well for Arctic charr. Water ﬂows down through the cabinet and wells up into each tray before cascading down to the next. The stacks take up minimal space, and the tray design allows efﬁcient egg picking as they can be readily removed from the stack without disturbing other groups of eggs. The combi-tank system, which combines a hatchery/ﬁrst-feeding tank with a screened insert upon which eggs are placed, also works well for incubating masses of eggs, particularly eyed eggs. As the eggs hatch, the alevins can move down into the ﬁrst-feeding tank, so this system eliminates the need for moving alevins from egg trays to tanks. Mass incubation jars or upwelling incubators also work well with Arctic charr eggs and require very little space. Water ﬂows into the bottom of the cylinder and wells up through the eggs and out a spout at the top of the container. The upwelling incubator can be placed into a ponding tank, and when the alevins hatch, they will exit the top of the incubator and ﬂow into the ponding tank. Inspect supply and wastewater systems and all the egg trays to make sure they are in serviceable condition, and then wash, disinfect, and rinse the trays. Turn on the water system and allow it to ﬂow through the trays for 24–48 hours prior to the ﬁrst egg-take. Just before the egg-take, set and adjust appropriate water ﬂow rates. The egg room should be considered separate from other zones within the hatchery, with boot baths and hand-washing protocols that workers must follow before entry and exit. Use only red lights in the egg room.

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Fig. 6.4 Egg incubators suitable for rearing Arctic charr eggs.

Anesthetizing Arctic charr brood Although some facilities do not use anesthetic during the spawning process, sedating Arctic charr greatly improves the quality of eggs taken and assures low mortality and rapid recovery of brood stock. Sedated charr are very malleable and this allows handlers to focus their attention on the process of collecting eggs and milt instead of on controling a lively squirming ﬁsh that is desperately seeking to escape from their hands to the hard concrete ﬂoor. There are a number of chemical agents that can be used to sedate and anesthetize Arctic charr brood (see Table 6.3), including benzocain, chlorobutanol, 2-phenoxyethanol, carbon dioxide, and tricaine methane sulfonate, which are used on a wide range of salmonids (Munkittrick; Piper et al. 1982; Ingram 1985). Researchers at the University of Guelph and at some commercial facilities have used clove oil as a sedative for Arctic charr and rainbow trout, with good results (Peterson et al. 2000). It is non-toxic for humans, low-toxic for ﬁsh, inexpensive, approved as food safe, and works quickly to sedate ﬁsh (Keene et al. 1998). Another good alternative is a proprietary product based on clove oil called Aqui-S™, produced by a company from New Zealand, which is currently being certiﬁed for use in North America and Europe.

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Table 6.3

Chemical agents used to sedate Arctic charr.

Drug

Dose

Comments

Tricain methanesulfonate (MS-222) 2-Phenoxyethanol Chlorobutanol Metomidate (Marinol™) Clove oil Benzocaine

0.5 g/10 L H2O 1 : 1000 H2O 10 mL/10 L H2O 4 mg/L H2O 30 ppm 40 ppm

Works well, lowers pH of water Also mild fungicide, possible carcinogen Dissolve in ethanol Dissolve in ethanol Dissolve in ethanol Dissolve in acetone

The amount of anesthetic required to fully sedate Arctic charr depends on the drug used, ﬁsh size, water quality, and water temperature. When an anesthetic is used for the ﬁrst time at a facility, or used on different sizes of ﬁsh, it is a good idea to test the manufacturer’s protocol on a small number of ﬁsh to determine suitable concentrations. Whatever you discover to be the ‘best’ concentration should become the facility’s standard. When it starts taking longer to anesthetize the ﬁsh, or if the water becomes frothy or contaminated with ﬁsh mucus and suspended solids, it is time to change the bath (Munkittrick). Keep the anesthetic bath water well aerated with oxygen and minimize the time each ﬁsh remains in the bath. The person moving charr to the anesthetic baths must control the ﬂow of ﬁsh to the ova/milt strippers so that each ﬁsh is exposed to the anesthetic for the shortest period. Like other salmonids, Arctic charr pass through three stages of deepening anesthesia over a period of two to ﬁve minutes: (1) (2) (3)

Light sedation with a slight loss of reaction to external visual and tactile stimulation. Partial loss of equilibrium, turning on their sides, reaction only to strong tactile stimulus, increased gill cover movement. Total loss of equilibrium, with ﬁsh ﬂoating or lying belly up, the operculum rate very slow, and virtually no response to tactile stimulation – they do not respond when they are grabbed around the tail.

The ﬁsh should remain in the anesthetic bath until they reach stage 3. Using tricaine methane sulfonate (MS-222), Arctic charr brood held in 5 °C water are fully sedated in 5 minutes and are safe from death for up to 15 minutes but no longer. If left in the dip for more than about 20 minutes, the ﬁsh will stop moving water over their gills and die (Ricks 1991). Although Arctic charr will recover from MS-222 within a few minutes when placed back into fresh water, it takes at least six hours for blood plasma levels of MS-222 to return to normal, and the drug’s residual effects on ﬁsh can exist for up to a week. Anesthesia with MS-222 may reduce the oxygen-carrying capacity of blood during sedation and for several days after recovery, so be sure to maintain high oxygen levels in anesthetic baths, recovery baths, and holding tanks. Fish should not be re-anesthetized until completely recovered, and should be put under as few times as possible – ideally not more than once a week (Munkittrick). Clove oil is preferable to MS-222 as large brood ﬁsh can remain under sedation for 30–40 minutes without any ill-effects. The time to recovery is however longer for clove oil than MS-222.

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Techniques for taking eggs Two people can manage a small egg-take of only a few females. One person moves ﬁsh in manageable groups from the holding tanks to the anesthetic bath for sedation, then rinses them in clean water, towels them dry, and passes them to the other person, who removes ova/milt. This division of labor helps keep the eggs and milt uncontaminated by water and anesthetic. Anesthetic on the surface of eggs or in the ovarian ﬂuid will slow sperm motility, leading to poor fertilization. As little as 19 parts per million of MS-222 can reduce sperm motility (Piper et al. 1982). The rinse bath should be supplied with a continuous ﬂow of water or changed often to prevent contamination with anesthetic. After they are immersed in the rinse bath, lightly towel each charr dry. This helps prevent water dripping into the egg and milt collection bowls. Note that Arctic charr have a thicker dermal mucous layer than other salmonids. When they are towelled dry, they should not be over-dried as the mucous layer is important in protecting them from fungal infections (Delabbio 1991). In a large egg-take the process is best handled in a production line, with a crew of four to ﬁve divided into wet and dry crews (see Fig. 6.3). One wet-crew member moves ﬁsh from the holding tanks to the anesthetic bath and returns spawned ﬁsh to recovery tanks. The other member of the wet crew moves ﬁsh from the anesthetic water to rinse water, dries them, and passes the ﬁsh to the dry crew. One or two people of the dry crew remove the eggs/milt and fertilize the eggs, while another rinses and moves fertilized eggs to the incubation room. The dry fertilization method of egg taking In dry fertilization, ova and milt are collected into separate bowls and no water is allowed in contact with them until ready for fertilization. Water activates both eggs and sperm. Once in contact with water or ovarian ﬂuid, sperm become motile and begin to actively seek out an ovum for about 60 seconds before they run out of energy. When in contact with water, unfertilized ova will absorb water through the eggshell or chorion into the perivitelline space (see Fig. 6.5). This process is known as water-hardening, and as it proceeds, the micropyle, which is the doorway for sperm entry, closes up. Once the door closes there is no chance of fertilization. If freshly removed eggs and ovarian ﬂuid are kept cool, protected from light, and not exposed to water, the eggs remain viable for up to 8 hours (Ingram 1985). Salmonid milt will retain its viability for 24 hours if held under the same conditions (Munkittrick). Removing eggs The eggs of each ovulated female charr are removed by hand into 2-litre stainless steel bowls, preferably at 5 °C ambient air temperature. Keep the ﬁsh belly-up with the head elevated and the vent slightly above and close to the edge of the bowl (see Fig. 6.6). The hand holding the base of the tail supports the ﬁsh, while the other hand slips over the ventral surface, thumb on one side of the ﬂanks, ﬁngers on the other side. With gentle pressure slide the hand from the pectoral ﬁns towards the vent. With two to four gentle strokes of the hand, the eggs, along

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Fig. 6.5 Structure of an Arctic charr ovum and spermatozoon.

with clear ovarian ﬂuid, should ﬂow into the bowl in a continuous golden stream. Once she is clear of eggs, place the female gently in a recovery bath until the anesthetic has worn off. Inspect the eggs for contaminants. Occasionally they will contain blood, mucus, broken eggs, or feces. Review the stripping process if these contaminants are found on a regular basis, as this may indicate rough handling or poor technique during either the spawn-check or spawning. Small amounts of blood and feces can be removed with the tip of a paper towel or drained off the egg batch when the eggs are rinsed. If it is heavily contaminated, the entire batch should be discarded, as fertilization may be as low as 25% (Munkittrick). Fecal contamination can be minimized by taking brood stock off feed at least a week prior to spawning. Broken eggs or overripe eggs can cause a problem as they may release albumen into the egg mass, clogging the micropyle of viable eggs (Piper et al. 1982). Broken eggs can also inhibit the motility of sperm, so be sure to remove the stringy white albumen with the tip of a paper towel. Again, if the batch is badly contaminated, discard it (Munkittrick). You should also examine the eggs for quality. Prime Arctic charr eggs are a solid pale yellow to golden color. They are round, 4–5 mm in diameter, with no concave or dimpled surfaces, and they should be in a mass with eggs touching but in moderate amounts of clear

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Fig. 6.6 Correct method for holding ﬁsh while spawning.

ovarian ﬂuid. If more than 5% of the eggs are moon-eyed, of irregular shape, or ﬂoating in milky colored or excessive amounts of ovarian ﬂuid, they should be discarded. Set aside eggs of satisfactory quality for fertilization. Cover them with a towel so they are not contaminated by water spray – the egg-take process always seems to involve water and other ﬂuids going everywhere. Removing milt The process of stripping males of milt is similar to that described for females. Light hand pressure along the posterior ﬂanks will force out a stream of milt if the ﬁsh is ripe. The ﬁrst little stream of milt is best discarded to ensure it is not contaminated with urine, feces, water, or anesthetic. Then with two or three strokes, strip the male of his milt, using a half-litre stainless steel bowl or beaker. The stream of milt should arc from the cloaca to the bowl and not ﬂow down the skin of the male and drip into the bowl. Strip the milt from each male into separate bowls and inspect it for contaminants and quality. Good-quality milt is the color and consistency of whole milk. If the milt is contaminated with feces or mucus, or is watery like skim milk or very thick like cream, it should be discarded. Check sperm motility by placing a drop of milt on a microscope slide, positioning it under 40× magniﬁcation, and adding a drop of water. If the sperm are healthy, they will become frisky within seconds, wriggling about in a mass of exuberant energy (be quick, as they stop moving in 30–60 seconds after water activation!). If activated sperm move slowly, or if only a few are actively moving about the slide, discard the batch of milt from which this sample was drawn. This male should be placed under watch or taken out of the breeding program. Generally, if a male Arctic charr produces good-quality sperm, he will continue to do so throughout the spawning season. Once you have found good sperm-producing males, use

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them regularly throughout the spawning period, keeping in mind that they should not be subjected to anesthesia more than once per week.

Fertilizing eggs When a batch of eggs is ready for fertilization, pour the milt over the eggs and allow nature to take its course. There is no need to add water as the ovarian ﬂuid is an excellent stimulator for sperm motility. It has the additional beneﬁt of prolonging the viability of sperm for up to two minutes, which, when fertilizing large batches of eggs with small quantities of milt, is an added assurance that all eggs will meet a spermatozoon (Munkittrick). To ensure good mixing of the milt with eggs, gently stir the milt and sperm with a clean hand for 5–10 seconds or until the ovarian ﬂuid in the bowl has turned a uniform milky white. Some people mix with a feather, but mixing gently with a clean hand is more efﬁcient and ensures better distribution of milt among the eggs in the spawning bowl. One minute after fertilization has commenced, add 250 mL of water to the bowl. Allow the eggs to stand for two minutes, stirring occasionally to prevent the eggs from sticking to one another, as water absorbed through the porous eggshell makes them slightly adhesive. Unless you require speciﬁc one-on-one crosses of selected females and males for a brood stock program, mixing eggs and milt from multiple ﬁsh is the most efﬁcient way to fertilize and incubate eggs. A batch of 10 000–15 000 eggs is a manageable number to fertilize and rinse in one bowl. Depending on the age, race, and size of females, this could be the output of three to ﬁve females. Generally about 1–2 mL of milt (the output of one to seven males) per batch of eggs is sufﬁcient to ensure maximum fertilization in Arctic charr. In some commercial operations, to ensure high fertilization, staff strip four females into separate bowls, pool the milt of seven males, and distribute it evenly to the four bowls of eggs (Krieger 1991). Another method is to place all the eggs from the females into one stainless steel bowl, pool the milt from all the males into one beaker, then add the milt to the eggs. A technique used in other salmonids to improve the chances of each individual male fertilizing some eggs, is letting the mixed pool of milt stand in a cool dry place for an hour before use. For unknown reasons, this equalizes the chances of each male contributing to fertilization of the eggs (Pepper & Crim 1996). Rinse the fertilized eggs by gently ﬂowing water down the side of the bowl and decanting milt, ovarian ﬂuid, and broken eggshell over the edge until the rinse water has lost its milky appearance and runs clear. After rinsing, ﬂood the batches of eggs with fresh water and set them aside or move them directly to incubators to water-harden for 2–4 hours. In this egg-activation or water-hardening process, extracellular water is drawn into the perivitelline space and increases the volume of the egg by 30–40% (Eriksson & Wiklund 1989). The outermost layer of the egg is shed and replaced by a harder polymerized protein coat that protects the embryo from physical injury and from pathogens, as it also has bactericidal properties. During this phase the sperm and egg unite to form a diploid zygote nucleus or embryo (Redding & Patiño 1993).

Loading incubation trays There are two schools of thought concerning the advisability of moving salmonid eggs during

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the water-hardening process. One school believes that eggs should be set aside after fertilization for 3–4 hours without disturbance, then placed into incubators (Willoughby 1999). This supposes that once the water-hardening process is complete, the eggs are resilient to shock and can be handled, moved, or disinfected during the next 48 hours before they again become sensitive to mechanical shock (Olsen 1990). The other school maintains that eggs should be moved to their permanent incubation trays within an hour of the addition of water during the early stages of water-hardening (Ingram 1985; Munkittrick). With Arctic charr I am inclined to move eggs into incubation trays as soon as possible for two reasons. In the wild, most salmonids cover their eggs with gravel immediately after spawning (Scott & Crossman 1973), suggesting that the eggs are not sensitive to mechanical shock at this time. I have not experienced high mortality in eggs moved within that ﬁrst hour. On the other hand, on a number of occasions I have moved Arctic charr eggs after the water-hardening process, and there were high mortality rates. Perhaps the most important criterion is that you treat the eggs gently when moving them at any time. Do not abruptly set the bowls of eggs down. Pour them from a low height into the egg trays, and gently slide the egg trays into position. As eggs are loaded into trays, remove any remaining contaminants, broken eggshells, or dead eggs, which are white or partially white. The most important aspect of loading trays with eggs is not to overload them and it is also a good practice to estimate the number of eggs placed into each incubation tray. Place Arctic charr ova one layer thick, as this maximizes oxygen gas exchange, minimizes fungal problems, and allows for easy removal of dead eggs. Measure eggs into batches for placement in incubation trays or baskets. Weigh the eggs by ﬁrst calculating a mean egg weight from a sample of water-hardened eggs drained of residual water. Then drain the entire batch in a preweighed ﬁne-meshed strainer, weigh batch and strainer, and calculate the number of eggs by dividing the total weight of the batch by the mean egg weight. Alternatively, eggs can be measured volumetrically based on the number of eggs per litre (see Table 6.4). The eggs should be surface-disinfected with a buffered iodine solution before they are moved into incubation trays, or immediately after they are placed into the trays. If you are disinfecting eggs in vertical incubators, load trays from the top down so that water from newly disinfected trays does not ﬂow into trays of treated eggs. Use a buffered iodine solution such as Buffodine® or Ovadine at 100 ppm for 10 minutes to surface-disinfect eggs (Eriksson & Wiklund 1989; Willoughby 1999). Using a buffered solution is especially important in lowpH water. Table 6.4 Ova volume, diameter, and weight of different strains of Arctic charr. Data source: Scott & Crossman 1973; Bass 1998. Type

Nauyuk Fraser Icelandic Swedish N Irish Kindrum NR = not reported

Form

Anadromous Anadromous Resident Resident Resident

Origin

Canada, NWT Canada, Labrador Iceland, Hololax Sweden, Kalarne Ireland

Ova No. (per litre)

Weight (g)

Diameter (mm)

10 000 11 000 11 700 10 700 15 300

0.05–0.06 NR NR NR NR

5.1 4.5 NR 3.5 NR

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A buffered iodine egg disinfection is recommended to prevent the transmission of viral and bacterial pathogens that may be present on the surface of eggs. It is effective in greatly reducing, though not entirely eliminating, infectious pancreatic necrosis virus (IPNV), viral hemorrhagic septicemia virus (VHS), and infectious hematopoietic necrosis virus (IHNV) on the egg surface. A 5-minute exposure to iodine at 80–110 mg/L eliminated 90% and 99.9% of IPNV and VHS respectively from salmonid eggs. When rainbow trout eggs were experimentally treated with IHNV, then exposed to an iodine of 100 mg/L water for 60 minutes, at least 99.9% of the virus was destroyed (Goldes & Mead 1995).

After spawning The spawning period is a demanding time for ﬁsh, and the egg-take process is particularly stressful, especially on male Arctic charr. After spawning, ﬁsh are susceptible to disease, particularly fungal infections. In order to help ﬁsh recover, place them in their own recovery tanks, separate from the spawning chaos. They may also need prophylactic treatment for fungal infections. All females should have their eggs removed one last time before their post-spawning recovery period, as up to 10% of eggs can remain in a female either because the person doing the spawning was inexperienced or because the ﬁrst removal of eggs was done too soon, before ovulation was completed. If any mature females are not spawned, they also need to have their eggs removed. This should be done as soon as possible after spawning is complete (Krieger 1991). Unremoved eggs are gradually reabsorbed, but eggshells will remain and form a plug in the anterior portion of the oviduct. It is difﬁcult to remove this plug in the next season, and it can lead to injured ﬁsh, broken eggs, or overripe eggs (Tabachek 1990). Both males and females usually start to eat again shortly after they have had their eggs removed or when males lose their spawning colors. Researchers suggest that this is induced by low condition factors and depleted energy reserves. Feeding will help the ﬁsh recover body condition, and you will likely notice positive growth and improved condition factor that increases over the next few months.

Egg incubation Egg incubation is a quiet time in the hatchery. Aside from checking fertilization rates of each egg lot, assuring good water ﬂow, and monitoring ova for fungus, things are dull in the egg room until the eyed phase. Much like other salmonids, Arctic charr ova pass through three distinct phases of development in the egg room, each of which demands its own husbandry techniques (Huet 1972): (1) (2) (3)

Early egg stage: 5–6 weeks, from fertilization to the eyed-egg stage. Eyed-egg stage: 7–8 weeks, from the appearance of eyes to hatching. Early alevin stage: 6–7 weeks, from hatching until the alevin yolk sac is absorbed.

Hatchery staff can easily discern the distinct embryonic development at each of these three stages. At a certain point in cell division, the developing embryo is clearly visible under low-

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power magniﬁcation (3× to 4×) when held in full spectrum light. This usually occurs at the four- to eight-cell division point (see Fig. 6.7), which takes place anywhere from 24 to 72 hours after fertilization, depending on water temperature. It is a good idea to do fertilization checks of a sample of eggs from each egg lot in the ﬁrst three days after fertilization. Examining 10 to 20 eggs randomly selected from each lot will give you a good indication of the percentage of eggs that have been successfully fertilized. At the eyed-egg stage, the embryo’s two black eyes are clearly visible near the egg surface. Any dead eggs will appear light yellow to white and will not have eyes present. This is the time when eggs are ‘shocked,’ dropped into a bucket of water, which ruptures the egg wall on any dead eggs. These eggs are then removed from the egg trays in a process known as egg picking. The early alevin stage begins when the ﬁrst embryonic alevins hatch and ends when the alevins are moved to tanks for ﬁrst-feeding – a process known as ponding.

Fig. 6.7 Early cell development and the timing of a fertilization check.

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Many farmers have been disappointed by the low survivability of Arctic charr eggs to the eyed stage and beyond. Because Arctic charr are not yet domesticated, their needs under commercial farm conditions are still poorly understood, so one can expect 30–75% initial egg loss. Fortunately much of this loss can be attributed to husbandry techniques, so with experience, mortality rates can be reduced signiﬁcantly so they are more in line with mortality levels found in Atlantic salmon (10–15%) (Stickney 1991). The husbandry techniques discussed below should improve egg viability.

Effect of temperature on embryo development and mortality The rate of development and the survival of an Arctic charr embryo is strongly inﬂuenced by water temperature (see Table 6.5). Embryo development can be expressed in terms of accumulated days since fertilization or as accumulated temperature units (ATU). An ATU is determined by multiplying the daily average water temperature in degrees Celsius by the time that has passed since fertilization (e.g. 10 days @ 5 °C = 50 ATU). At any given water temperature, the number of ATU required for an embryo to hatch is relatively constant. However, if the temperature is higher, the hatch will occur sooner, and if the temperature is lower it will occur later. For example, Arctic charr hatch at 171 ATU when held at 1 °C but 440 ATU at 5 °C. The time required to reach each phase of development also varies among races of Arctic charr. For example, Hammerfest Arctic charr require about 440 ATU to hatch, while the Sunndalsora strain takes about 515 ATU when held at 7–8 °C. Under natural conditions, Arctic charr typically lay their eggs in areas of upwelling spring water, which ensures a relatively constant temperature throughout the ice-covered period. Arctic charr eggs develop best when held at constant water temperatures in the hatchery. Most researchers and commercial operators agree that mortality rates are low when Arctic charr ova are incubated in water temperatures between 3 and 7 °C (Robbins et al. 1990). Some Table 6.5 Effect of water temperature on egg development and time of hatch in Arctic charr. Data source: Robbins et al. 1990; Stickney 1991. Temp. (°C)

1 2 3 4 5 6 7 8 9 10 11 12 14 16

Days

ATU

Fertilization to eyed stage

Fertilization to hatch

Hatch to swim-up

Fertilization to eyed stage

Fertilization to hatch

% mortality to hatch

90 70 56 46 37 34 28 23 21 20 19 19 — —

171 139 115 100 88 73 63 56 50 45 40 40 31 27

— — 66 59 — 45 — 39 — 36 35 35 — —

90 140 168 184 185 204 196 184 189 200 209 209 — —

171 278 345 400 440 438 441 448 450 450 480 480 434 432

10–15 10–15 10–15 10–15 10–15 10–15 20 25 45 70 95 95 99 99

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strains such as Hammerfest or Nauyuk even do well at temperatures of 1 °C. Above 7 °C the mortality rates increase rapidly for most charr strains, with expected losses approaching 70% when held at 10 °C, and 95% at 12 °C (see Table 6.5). Research done with Fraser and Nauyuk strains suggests that temperature-related mortality occurs prior to the eyed stage, as eggs from both races had low mortality rates when held in 12 °C water after eyeing. Aside from the effect of temperature, some higher mortality rates may be a result of poor fertilization rates, sloppy egg-taking practices, or other unknown factors related to husbandry techniques or water quality. It is good practice to record details of each egg-take and relate this information to the results of the fertilization checks, as this can help pinpoint causes of poor survival. The degree of fertilization in each egg lot can be related back to spawning conditions, or to those who participated in the spawning, or to conditions incidentally recorded about the egg-take.

Husbandry techniques in the egg room During incubation, egg-room husbandry revolves around controlling fungal growth and monitoring water ﬂows, oxygen levels, and rates of egg development. During the early egg stage there is little to do other than perform fertilization checks, monitor water temperatures and fungal growth, and treat fungus. The eyed stage requires more attention and labor, as you need to remove dead eggs and alevins. This will raise the activity level, particularly if eggs are from a poor-quality egg-take. Early alevin stage activities include monitoring the hatch, removing dead alevins and eggshells, and assessing time to ponding. As mentioned previously, it is important to treat the egg room as a separate work area, with its own equipment, boot baths, and hand-washing procedures. Keep light levels low, and red light is preferred. Eggs are best kept in total darkness, at least until they hatch. Prior to ponding, light levels can be increased in order to adjust alevins to hatchery light regimes. Oxygen levels in the outﬂow water should be at 8 ppm. There should be enough of a water ﬂow to meet this requirement, but watch for too much ﬂow. The eggs should not be unduly disturbed by turbulence, which might cause damage from physical abrasion. As eggs approach hatching time, oxygen requirements increase, so you may have to adjust water ﬂows accordingly.

Monitoring egg development and inventory control It is important to be able to follow each lot of eggs (the egg inventory) through the incubation process and beyond, to the hatchery. This is a basic requirement of a quality assurance program. It enables you to assess parental performance, select husbandry techniques best suited to spawning, and assess the effects of environmental conditions on egg survival. Keeping data on incubating ova is important for two other reasons. By keeping track of the ATUs or number of days from fertilization, you can calculate with precision the time when eggs will require shocking, picking, or ponding. This allows you to plan the labor required for these husbandry activities and to estimate the number of alevins expected to hatch and the starter feed rations they will need. To assist in keeping track of the egg inventory, assign each lot of eggs a unique number, which is kept on ﬁle along with the corresponding basic information about parental stock,

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time of fertilization, and spawning conditions. Keep data sheets in the egg room so that as dead eggs and alevins are removed, they can be subtracted from the balance to give accurate estimates of egg inventory. You can also keep track of chemical treatments applied to each lot, or speciﬁc activities or traumas that could affect the outcome or quality of the eggs from each lot. It takes a few minutes to record this type of data, and a few hours each month to permanently record it in a computerized or manual data ﬁle, but it is well worth it.

Monitoring and controlling fungal growth Saprolegnia is a group of aquatic fungi that feed on dead matter and thrive at the low temperatures ideal for incubation of Arctic charr ova. The fungus is present in the water supplies of many hatcheries and spreads via spores in the water, which settle on eggs or other organic matter and feed on dead matter. Dead eggs, eggshell, and blood in egg trays are excellent media for its growth. If not treated promptly, the fungus spreads in a thick mat over adjacent live eggs, smothering them and producing a putrid mess. It can wipe out a tray’s entire batch of eggs. The fungus is difﬁcult to prevent but can be controlled by the following methods: dead/blank eggs by assuring maximum fertilization from good spawning tech• Minimize niques. blood, feces, and eggshell prior to placing eggs into egg trays. • Remove Remove all dead eggs during the ﬁrst 12 hours after fertilization. • Filter incubation water to minimize organic load, which acts as a growth • mediumincoming for fungus. eggs and, at the ﬁrst sign of fungus, treat them with chemicals until the eyed • Monitor stage. • Once eggs have eyed up, inspect and pick dead eggs regularly until hatch. Fungal control often comes down to a combination of mechanical picking of dead eggs and chemical control of fungal growth. Since most of the fungus problem occurs during the sensitive pre-eyed stage, when the eggs should not be handled, it is best to treat them with a chemical agent. However, if you are extremely gentle you can pick dead eggs throughout the entire incubation process. This method has proved successful in my own hatchery, but egg losses due to handling sometimes occur. You can easily control fungus in Arctic charr eggs with treatments of formalin or malachite green. The downside of these chemicals is they are nasty substances for hatchery staff, as they are potentially carcinogenic. In fact, malachite green is banned in many countries. Table 6.6 lists a number of other treatments that generally work with salmonids and should be ﬁne for Arctic charr. Any chemical treatment should be tested on a small batch of eggs ﬁrst to ensure its suitability under the environmental conditions of your hatchery. Stop antifungal treatments once the eggs reach the eyed stage.

Egg shocking and picking techniques When charr eggs reach the eyed stage, they become resilient to mechanical shock. They are

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Table 6.6 Chemical treatments for controlling fungal infections in Arctic charr ova. Chemical

Concentration

Duration of treatment (h)

Repeat every (days)

Efﬁcacy on charr ova

Formalin Sodium chloride Hydrogen peroxide Malachite green Quaternary ammonium

200–250 mg/L 3% 250–500 mg/L 5 mg/L 2 ppm

1 ½ ¼ ¾ 1

5 2 5 5 4

Good Unknown Unknown Good Unknown

quite tough, and if you accidentally drop one on the ﬂoor, you might see it bounce back and wiggle its eyes at you. The fertility checks done at the beginning of incubation will give you a good idea which batches of eggs will require a lot of egg picking – the lower the fertilization rate, the higher the number of dead eggs to pick. Depending on the fertilization rate and mortality during early incubation, batches may contain many eggs that are not clearly dead but nonetheless should be removed. To pick out these dead or infertile eggs, you can ‘shock’ batches of eggs by gently releasing them from a height of about 100 cm into a bucket of water. Shells of the eggs that are unfertilized or contain dead embryos will be easily ruptured by this mechanical shock, and the water entering through the ruptured shell coagulates the yolk, turning the egg white. Pick out these dead eggs for disposal and return viable eggs to their trays immediately after shocking to ensure that oxygen levels are not depleted. Carry out the shocking and picking under dim or red light to prevent damage to the eyed embryos. There are a number of mechanical pickers on the market that use photocell technology to separate dead from live eggs. They tend to be expensive and rather ﬁnicky to operate. Unless you are dealing with more than a million eggs, chances are it is more economical to pick eggs by hand. Forceps or tweezers with small wire loops or cut-outs that grip one egg at a time are effective. Another useful tool is a siphon and bulb (like a turkey baster) or a siphon egg picker. The siphon picker is efﬁcient but requires a high level of operator skill to remove only dead eggs (Piper et al. 1982). Egg picking is a job well suited for students – they can turn their music up loud and pick away. A good egg picker listening to their current favorite at high volume can remove 1000–1500 dead eggs per hour. After shocking and picking, the eyed eggs should be inspected and dead eggs picked on a weekly basis until hatch commences.

Hatching Within each lot of eggs, hatching is spread out, usually taking 15–20 days from ﬁrst hatch to last. Alevins, as the young hatched ﬁsh are called, depend on their yolk sacs for nutrition and can remain in the egg trays for many weeks. For the ﬁrst two or three weeks they will rest on the bottom. At this stage it is important not to handle or stress them. Minimizing stress allows them to use their energy stores for growth instead of for an escape response (Eriksson & Wiklund 1989). When about 70% of the yolk sac reserves have been metabolized, the alevins will actively start searching for food. At this point you can initiate ponding, moving the alevins from

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hatching trays to tanks for ﬁrst-feeding. Depending on the water temperature, ponding occurs 40–45 days after hatch (Jobling et al. 1993). As hatching approaches, be sure that alevins cannot escape the incubation trays. They will move downcurrent, going with the system’s water ﬂow, and can ﬁnd their way out the smallest hole or gap in an outlet screen. Keep the outlet screen free of leftover eggshells, as they clog the screen and prevent adequate water ﬂow. Small amounts of eggshell will break down rapidly and may not be of concern. It is best to remove dead and disﬁgured alevins just before you transfer alevins from the egg trays to ponding tanks. If there are large numbers of dead alevins, remove them as soon as possible, but in general, the less disturbance to the newly hatched alevins, the better.

Methods for receiving and transporting eyed ova In most commercial grow-out operations, it is more efﬁcient to purchase eyed eggs from specialty egg suppliers than to keep your own brood stock. If you are buying eyed eggs, negotiate payment requirements, information on rearing requirements, and quality assurance that eggs meet certain expectations with the seller. When importing eggs, be sure the ﬁsh health inspection certiﬁcate and importation documents are completed well before the date of delivery. The receiver of eyed eggs will need a permit for importation and a declaration of the disease-free status of the hatchery from which the eggs originated. This declaration needs to be sent from the ﬁsh health ofﬁcer of the exporting country to his or her counterpart in the importing country. Standards for ﬁsh health vary greatly from country to country. Although they are being reviewed by the Ofﬁce Internationale Epizootistique, world standards are not yet in place. For the well-being of your facility, it is important to know the reputation of the company selling eggs. Ask for references from other clients and demand that the hatchery either disclose its history of diseases or prove that it is regularly inspected for disease by an independent agency. In the recent past, Ireland imported Arctic charr eggs from hatcheries in Iceland and eastern Canada that apparently had been screened as disease-free but were found to contain BKD (Bass 1998). In terms of packing and shipping procedures: eyed eggs ship very well. If packed properly, they can survive shipping times of 60–70 hours. However, it is best to minimize transport time to 24 –48 hours (Eriksson & Wiklund 1989). This should be sufﬁcient time for an airfreighted shipment of eggs to reach anywhere on the globe. Eggs for transport can be packed into Styrofoam boxes specially designed to hold eggs in trays that are kept moist through high humidity or dripping ice water. Or they can be placed into sealed plastic bags partially ﬁlled with water and oxygen. Both methods work, but I have found that plastic bags are far superior to boxes. The boxes are large with respect to the number of eggs shipped, and unless heavily iced they do not keep cool. If they are overturned, which seems to happen often, the eggs lump together into masses, and mortality can be high. For transport in plastic bags, about 5000 eggs and water should half ﬁll a seamless 1- to 2-litre plastic bag. Suck the air out of the bag and replace it with pure oxygen, then seal the bag, preferably with electrical tape. Place it and other bags of eggs inside a Styrofoam ﬁsh box

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containing crushed ice, with an outer cardboard layer to protect the eggs. For safe transport, the water temperature should remain below 5 °C, preferably cooled to 3 °C. Upon arrival at their destination, unpack the eggs in a cool, dimly lit room. Leave them in the sealed bag until the water temperature in the bag has been acclimated to the water temperature in the receiving hatchery. Once equilibrated, gently cut open the plastic shipping bags and release the eggs into incubators or directly into rearing troughs with bio-mats, as the eggs will soon hatch. If they have not started to hatch, eggs should be surface disinfected with an iodophor and, if possible, held in quarantine until hatched fry can be inspected for disease by a ﬁsh health ofﬁcer or biological laboratory. Arctic charr commonly begin the next phase of their development from the delivery of eyed eggs from a specialty egg producer to a commercial grow-out. In this case, the eggs may only require holding space for a few weeks or even days until the alevins hatch and start their free-swimming existence in a hatchery setting.

Chapter 7

Raising Alevin, Fry, and Fingerlings

The life of a young Arctic charr in the hatchery is one of extremes. It moves from an environment of complete dark in the incubation trays to the full light of day. Body weight increases 200-fold as the ﬁsh develops from a larval alevin to a ﬁngerling ready for transfer into the grow-out world. The greatest change occurs in its source and method of nutrition, from endogenous dependence on its own yolk sac to exogenous free feeding in the water column. Crossing this divide from embryonic life to free feeding is the most signiﬁcant and trying moment in the life of a hatchery-reared Arctic charr. During their stay in the hatchery, Arctic charr pass through two relatively distinct husbandry phases: (1)

(2)

Phase 1: Stage I: Alevins are ponded and begin free feeding (35–45 days). Stage II: Charr, now called fry, consolidate their free-feeding ability until they are large enough for grading at 1–1.5 g size (45–60 days). Phase 2: Fingerlings grow in a rapid, efﬁcient manner for about 170–300 days until they are ready for transfer to grow-out operations or release to the wild.

The length of time Arctic charr remain in each phase is inversely related to the intensity of husbandry skills required, illustrated in Fig. 7.1. Establishing ﬁrst-feeding in Stage I takes only a few weeks but is a difﬁcult and demanding husbandry task. Fry of about 0.1 g in Stage II are less sensitive than alevins to the hatchery environment, but they still demand close attention to their water quality in the way of tank sanitation and careful feeding. They also require a lot of mothering. By Phase 2, 1–1.5 g ﬁngerling Arctic charr are relatively tough, can be handled for grading or moving to larger tanks, and are more resilient, so they do not need as much intense care. How long Arctic charr remain in the hatchery depends on the intended grow-out environment, the distance and mode of transportation to the grow-out site, and the time of year for moving. In few hatcheries is it practical or necessary to hold Arctic charr much beyond the spring of the year following their hatch. By the fall of their ﬁrst year, ﬁngerlings will be 50–100 g in weight. If they are kept in warm water, they will grow to 300 g by the following spring.

From larval alevin to free-swimming fry Life in the hatchery starts with the transfer of alevins from the egg room to small ponding tanks.

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Fig. 7.1 Stages of development of Arctic charr in the hatchery environment. Data source: Wandsvic & Jobling 1982; Jobling et al. 1993; Tabachek 1993.

Ponding is the term used to describe the process in which the larval alevins, weighing about 0.06 g and entirely dependent on yolk to this point in their lives, must venture off the bottom substrate and begin actively searching and ingesting food – free swimming and free feeding. It is a rapid transition period, and if the charr alevins are not successful, they exhaust their yolk reserves and die. Inducing Arctic charr to ﬁrst-feed is one of the most difﬁcult aspects of hatchery rearing, and it demands a great deal of care and attention to ﬁsh behavior, tank sanitation, and feeding. Determining the best time to pond and ﬁrst-feed Arctic charr is not an exact science, but is vital to assure good growth and survival. If ponded too early, without an artiﬁcial substrate to hide in, mortality can be high. Similarly, ponding too late, after yolk reserves have been depleted, leads to high mortality and great variation in the size of surviving fry. Bio-mats are a helpful tool for improving the ponding environment for Arctic charr alevins. These plastic or rubber mats act as an artiﬁcial substrate. They are about 40 by 40 cm, 2–3 cm high, with hundreds of thin plastic ﬁngers or projections spaced about 1 cm apart. The mats are placed with the ﬁngers resting on the bottom of the ponding trays, giving the alevins a threedimensional forest-like structure in which to hide and rest. This is probably the closest we can get to reproducing the gravel substrate where alevins would naturally live during the process of learning to feed in an open-water environment. On the top side of the mats there are rows of slits that allow alevins and water to move through the top of the mats (see Fig. 7.4). The alevins venture out the sides and through the slits in the top of the mats at their own volition. Slowerdeveloping alevins can remain in a protected environment that gives them physical support and cover from the open water environment. Use one bio-mat for each 10 000 alevins ponded, and place them evenly about the tank bottom with open spaces between mats. It is important that water ﬂows evenly through and over the mats, which is best accomplished in a circular tank. Few studies have looked speciﬁcally at techniques to determine the optimum time to pond Arctic charr, and every hatchery seems to have a slightly different solution. Often it comes down to hatchery-speciﬁc environmental conditions, particularly temperature, the skills of

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hatchery staff, and the strain of Arctic charr under cultivation. After hatching, alevins slowly absorb their yolk sac as fuel for basic metabolic functions and for growth. The yolk is converted to tissue, and mean alevin wet weight (MAWW) increases to a maximum value near the end of yolk absorption. The charr require some yolk sac reserves to carry them through the difﬁcult process of learning to feed. In other salmonids, lowest rearing mortality and maximum biomass are achieved when ﬁrst-feeding occurs just prior to MAWW, and the pattern for Arctic charr is likely similar (Pennell & McLean 1996). Under practical hatchery conditions, determining MAWW is not easy. In my opinion it is best to move alevins into start-feeding tanks equipped with bio-mats when they still have about 30% of their yolk sac reserves, which means a substantial amount of yolk sac is visible (see Fig. 7.2). Once they are into ponding tanks, nestled down in the bio-mats, the point at which they should be given

Fig. 7.2 Body development from alevin stage to ﬁngerling.

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feed can be determined by the number which are swimming up into the water column. Swimup occurs as the alevins leave the substrate and begin hovering in the water column as freeswimming ﬁsh. The normal course of swim-up goes something like this: At ﬁrst just a few individuals are present in the water column, and they will dart back to the substrate if disturbed by movements or shadows. Over the course of days, more and more individuals appear, then hundreds and thousands until all are up and swimming. The transition to free swimming in the water column is not immediate, and the ﬁsh move between the two modes of life for a short while. It can take as long as 10–15 days from the time you observe the ﬁrst individuals in the water column to 100% emergence from the substrate. Depending on water temperature and race, 50% of alevins will swim up at 30–60 days after hatch (see Fig. 7.3) (Gjedrem & Gunnes 1978; Eriksson & Wiklund 1989).Almost all Arctic charr will start to take feed when they are free swimming in the water column, but culturists and researchers have noticed that charr alevins will dart off the bottom, take food, and return to the substrate prior to swim-up.

Preparing the ponding environment Alevins must receive the best water quality and husbandry attention of any ﬁsh in the entire facility, particularly at ponding. Careful preparation of the physical environment – the ponding tanks, water ﬂows, light levels, and water temperature – helps to eliminate many stressors in the life of alevins. Small round tanks with centre-drain standpipes are preferable to troughs or raceways for ponding Arctic charr (see Fig. 7.4). Water circulation is much better in round tanks than troughs, and it is easier to remove waste feed and feces. Troughs require frequent sweeping or siphoning of wastes, as water velocity is not high enough to carry them to the drain. Steep oxygen gradients can develop as water ﬂows the length of the trough, and most of the alevins will gather near the water intake at the top end of the trough, where oxygen levels are highest.

Fig. 7.3 Length of time from hatch to swim-up at different temperatures.

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Fig. 7.4 Ponding tank conﬁguration for ﬁrst-feeding alevin Arctic charr.

Round tanks require little cleaning, especially if you install horizontal spray bars that direct water ﬂow across the radius of the tank. The spray bars allow an even distribution of alevins once they reach swim-up, as water velocity is more evenly distributed across the tank. Spray bars also make it easy to adjust water velocity (the speed water moves around the tank) independent of ﬂow (the amount of water passing through the tank). When more water ﬂow is required, turn the spray bars downwards to reduce velocity. You need water ﬂows high enough to maintain oxygen at sufﬁcient levels for the alevins, while water velocity must be high enough to move waste feed and ﬁsh waste to the drain, but slow enough to allow alevins to hold position in the water column or under bio-mats. If water velocity is too high, alevins are pushed against the outﬂow screen or whirl about the tank, heads to the current but moving backwards. Too weak a velocity can create problems with accumulation of waste products on the tank bottom, which degrades water quality. Arctic charr alevins always seem to want to travel downstream if given the chance. Assure that the exit holes in the outer standpipes are covered with ﬁne screening that prevents escape of small alevins but allows water and waste to leave the tank. Window screening works well. As the alevins grow, you can adjust the size of the screening to accommodate the increasing size of waste feed and feces. Also note that, because of the higher water ﬂows required for Arctic charr kept at high density, you will need larger standpipes and drain lines or the tanks will overﬂow. Older Arctic charr alevins and fry are kept at high density (40–125 kg/m3) to conserve tank space, improve food utilization, and accustom ﬁsh to the densities they will experience

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in tank-based grow-out farms. It is safe to assume that when fry do well at high density in the start-feed tanks, they will also do well under high-density grow-out conditions. Rearing Arctic charr at high density requires good water quality, particularly during ponding and ﬁrstfeeding. Bacterial gill infections are a real concern at this stage, so tank water should be high in oxygen and low in suspended solids, carbon dioxide, and ammonia-N. The alevins should have ﬁrst use of the water in a reuse water system, and they should not be kept in recirculated water, at least until they are well on feed. Water quality guidelines for ponding, ﬁrst-feeding, and actively feeding fry are listed in Table 7.1. Use these guidelines for setting water temperatures, ﬂow, and velocity rates based on tank volume and ﬁsh size or density. Actual ﬁsh density at ponding is not critical (Wandsvik & Jobling 1982), but it should be kept in the range of 40–125 kg/m3 by the time fry reach the 1 g size. Small tanks in the range of 100–300 L of water volume are best for ﬁrst-feeding and can accommodate up to 30 000 alevins per tank. For example, three bio-mats, with 10 000 alevins/mat, will ﬁt into a 300-L tank. That would give an initial loading density of 6 kg/m3 ((30 000 alevins × 0.06g/alevin)/1000/0.300) with a ﬁnal loading density of 100 kg/m3 when the alevins reach a size of 1 g. With alevins on ﬁrst-feed, suspended solids from the ﬁne start-feeds are a critical water quality concern. The very ﬁne feed, if fed in excess, will clog gills and degrade water quality with ammonia. As a rule, the ratio of daily food input (in grams) to water ﬂow (litre/minute) should be less than 9 g/L min–1 (Pennell & McLean 1996). For example, ponding 10 000 charr alevins weighing 0.06 g, fed at a rate of 4% body weight/day, would require inﬂow water at a rate of 2.7 L/min (10 000 × 0.06 × 4%/9). Basing water ﬂows on this formula will give ﬁrst-feeding alevins a better margin of safety, as it is well above the ﬂow requirements for maintaining oxygen at acceptable levels. Suspended solids, oxygen, carbon dioxide, and ammonia-N concentrations should be monitored on a regular basis at the tank outlet to ensure good water conditions are maintained. Keep light levels low, at less than 50 Lux in the area of the ponding tanks. That is just light enough to discriminate between colors. Alevins in the wild would be in gravel and under a thick layer of ice prior to ﬁrst-feeding. They do not know the hatchery is a predator-free Table 7.1 Water quality guidelines for rearing Arctic charr alevins and fry. Activity

Ponding

First feeding

Free feeding

0.05–0.06 6–8 125 0.89 <1 10

0.06–0.10 8–10 125 0.57 1 10

0.10–1.50 10–14 60 0.66 1.5 30–100

< 0.010 < 0.013 < 15 < 15 9.5

< 0.010 < 0.013 < 15 < 15 9.5

< 0.012 < 0.015 < 20 < 20 8.5

Fish and physical parameters Fish weight (g) Water temp. (°C) Fish density (kg/m3) Fish loading (kg/L/min) Water velocity (body length cm/sec) Water depth (cm) Chemical parameters (mg/L) Ammonia-N Nitrite Suspended solids CO2 O2

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environment, so they need a sense of protection from predators, and it is easier to hide in a darkened environment than in a bright open hatchery tank. For this reason, the background of tanks should be dark green or blue to further reduce the exposure of the alevins to a backlit environment. The tank standpipes and screens should be a lighter color to dissuade alevins from aggregating where they can be sucked up against the outlet screens. The water temperature in the ponding tank is initially set at the same temperature as the incubation water from which the alevins are being transferred. Optimally this should be 5–6 °C. Water temperature can remain static for the ﬁrst few days, but gradually increase it to 8–10 °C once you see the ﬁrst few alevins swimming in the water column. Increasing the water temperature stimulates swim-up and initial feeding (Tabachek 1993). Once feeding is well established in all the alevins of a particular tank, increase the water temperature to 10–12 °C for the remainder of the ﬁrst-feeding stage. At no time should the water temperature exceed 12 °C, as there is evidence that growth rates decline and mortality increases – at least in the initial ﬁrstfeeding stage (Eriksson & Wiklund 1989; Bebak & Hankins 1999 [pers. comm.]). The risk of health-related problems from bacteria and fungal infections increases with temperature. Arctic charr do just as well in cooler water (3–6 °C), with fewer health-related problems, but their growth rates are much reduced. Before you actually move the alevins to the ponding tanks, run the ponding system under operating conditions for at least 24 hours. This removes any leachate from new equipment, pipe glue, or residual disinfection compounds. As well, you should inspect and adjust water ﬂows, water temperatures, and the structural integrity of the tanks, valves, alarm and backup system, and standpipe screens.

Moving alevins to ponding tanks The entire move from the egg room to ponding tank is done under low light conditions and as calmly as possible. It is best to move alevins ﬁrst thing in the morning, as this gives staff all day to monitor their well-being and to adjust water ﬂows for best tank performance. Before moving the alevins from the egg room to ponding tanks, inspect each lot and remove as many deformed alevins (gimps, crinkle-backs, and Siamese twins) as possible as it is much harder to remove poor-quality alevins once they are ponded. Once the deformed alevins are removed, gently pour the alevins from the egg trays into a water-ﬁlled bucket in lots of about 10 000. Then pour each lot gently and slowly into the ponding tank, adjacent to an empty bio-mat. The alevins will naturally dart under the closest mat. Once each tank has received its allotment of alevins, cover it to exclude light for at least 48 hours, then gradually increase light levels over the next few days to acclimate the alevins to a lighted environment. During the ﬁrst few hours after ponding, monitor outﬂow oxygen levels until you are satisﬁed with water ﬂows. If alevins are drifting out from underneath the bio-mats, water velocity is probably too high and should be adjusted accordingly. A few weak and deformed alevins will be pushed out during the ﬁrst few days of ponding and usually end up near the tank outﬂow, where you can remove them.

First-feeding techniques Arctic charr are much smaller than rainbow trout and Atlantic salmon at ﬁrst-feeding

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(0.06 g vs. 0.25 g), and this small size mean charr alevins require the smallest available feed sizes produced for salmonids (Eriksson & Wiklund 1989; Eriksson 1991). Like other salmonids, Arctic charr alevins will aggressively attack and mouth any small item that is in their feeding zone (within one or two body lengths). Whether they are offered natural food or prepared food, as long as particles are moving and are small enough to ingest, alevin charr will feed (Jensen et al. 1989). There is good evidence that it is natural and advantageous for alevins to start feeding before they have completely absorbed their yolk sacs. Arctic charr, Atlantic salmon, and brown trout have all been found with food in their guts well before all their yolk sac has been absorbed, even though they remained down in the gravel or on the substrate of tanks (Jensen et al. 1989; Nilsson 1993; Tabachek 1993). In one study, charr alevins that received ﬁrst-feeding when they still retained 96% yolk sac showed growth rates signiﬁcantly higher than alevins ﬁrst fed when they retained only 1.5% of their yolk sac (Eriksson & Wiklund 1989). Given that Arctic charr take feed before swim-up, it is important to start the initial feeding process at the ﬁrst signs of swim-up or even a few days before you expect swim-up to take place. I have had no problem getting Arctic charr onto ﬁrst-feed using very ﬁne (0.3 mm) semi-moist and live diets as long as food was offered when the ﬁrst individuals swam up. Water temperature strongly affects the time from hatch to 50% ﬁrst-feeding. Table 7.2 gives estimated times from hatch to ﬁrst-feeding for a range of temperatures. The time from observing about 10% of alevins in the water column to 90% free swimming is 5–7 days (Jensen et al. 1989). Once they are free swimming, charr alevins distribute themselves fairly evenly from the tank bottom to the surface and remain throughout the water column unless under predator stress (Tabachek 1993). A shallow water depth seems to improve the transition to ﬁrst-feeding, so maintain a water level of 10–15 cm in the ponding tanks until alevins are all free swimming. At that point the depth can be raised to full tank levels. Types and sizes of starter diets There are a wide range of prepared starter diets available for salmonids that are suitable for Arctic charr. Both dry and semi-moist feeds have been used for start-feeding charr; however, semi-moist diets are superior for ﬁrst-feeding (Piper et al. 1982). A semi-moist extruded feed called BioDiet®, produced by Bio-Oregon Inc., has proven itself with charr growers in North America, giving higher growth rates and lower mortality compared to alevins and fry fed dry diets (Krieger 1991). This is not to say that dry diets will not work. Moore-Clark produces a Table 7.2 Time to ﬁrst-feeding and start-feeding tables for Arctic charr alevins. Data source: Bebak & Hankins 1999 [pers. comm.]; Bio-Oregon Inc. 1999. Feeding rate (% body weight per day) Alevin/Fry size

Temperature (°C)

Weight (g)

Length (mm)

Feed size (mm)

2

4

6

8

10

12

0.05–0.29 0.3–0.59 0.6–1.0

16–33 34–42 43–75

0.3–0.59 0.6–1.5 0.86–1.4

2.5 2.3 2.1

3.0 2.8 2.6

3.5 3.3 3.1

4.0 3.8 3.6

4.5 4.3 4.1

5.0 4.8 4.6

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starter diet called Nutra that has proven effective with charr. Live food, particularly mosquito and blackﬂy (Simulidea) larvae, is an excellent starter diet for Arctic charr. Newly hatched mosquito larvae are just the right size to start-feed Nauyuk charr, and in Canada there is no shortage of this food resource. The size of the feed particles is critical to getting Arctic charr onto feed (Eriksson 1991). Arctic charr alevins are small (0.06 g) and must be presented with the ﬁnest size of feeds, with the ﬁrst feed in the particle size range of 0.25–0.35 mm. As the alevins grow in size and weight, feed size is increased accordingly. Table 7.2 presents the feed particle size required for ﬁrst-feeding, along with feeding rates by temperature. As with all feeding tables, it is only a guide to feed size and feeding rates. By observing charr response to feed, you can discern if the feed size is in the right range. If some alevins are repeatedly grabbing food particles and spitting them out, then feed size is likely too large. Individual size variation in Arctic charr starts at the alevin stage, so it is important that the starter feed is sized to the smallest ﬁsh in each lot. Charr will always take feed particles of a less than optimum size, so if in doubt about the ability of smaller alevins or fry to take a larger-sized feed, leave the entire lot on the smaller feed size. To assure an adequate range of particle sizes, feeds of the next size up can be mixed with smaller feed. Some starter feeds like Moore-Clark’s Nutra and Bio-Oregon’s BioDiet® have good overlapping feed particle sizes within the same bag of feed. Starter feeds for Arctic charr must comprise at least 90% premium quality ﬁshmeal supplemented with vitamins and micronutrients (see Table 7.3). Use only recently manufactured feeds, not leftover feed from the previous year. It is well worth the extra cost to purchase the highest quality starter feeds, as they help to avoid problems of poor growth and high mortality. Very little feed is required per ﬁsh at this stage of life, so even if starter feeds are three times the cost of grow-out feed, the relative cost they represent is less than 0.1% of the total feed required to raise a 2.5 kg market ﬁsh. All starter diets, either semi-moist or dry, are sensitive to biological degradation, so store them in a cool, dry, dark place prior to use. Keep semi-moist diets refrigerated or frozen once the bags are opened. Methods for delivering starter diets Feed the alevins often during daylight hours, at least every 10 minutes, for a minimum of 10 hours per day (Eriksson & Wiklund 1989). The ration at each feeding should deliver an equal amount of the daily food ration. Over the two-week period of ﬁrst-feeding, increase Table 7.3 Feed composition of hatchery diets for Arctic charr. Feed composition

Range (%)

Comments

Protein Fat Carbohydrate Fiber Ash Moisture Vitamin C Metabolizable energy

47–55 15–22 < 10 <2 < 14 7–21 250 mg/kg 3300–3800 kcal/kg

90% premium quality ﬁshmeal As marine oils

Semi-moist starter diet and dry ﬁngerling diet

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day-length slowly from 10 to 14 hours. Long day-length, or at least increasing day-length over the start-feeding time, will mimic the natural photoperiod charr alevins would be exposed to in the wild. My best advice is to feed early, use the feeding guidelines in Table 7.2, and spend a lot of time watching newly ponded alevins’ response to small offerings of feed. Hand-feed the alevins until at least 50% of them are in the water column. Frequent hand-feeding forces you to observe ﬁrst-feeding behavior and helps you control the amount of feed delivered. Spend a lot of time watching alevins take feed, particularly as the ﬁrst individuals swim up. Try dropping small amounts of feed near them and note their response. Normal active alevins in the water column dart at feed particles that come close to them; those on the bottom under the bio-mats will dart out and grab feed drifting down. A sure sign that alevins are feeding well is the presence of feces trailing from their vents and feces on the tank bottom. You can also see feed in the gut as a dark mass. Expect a lot of waste feed to pass through the tanks. At this phase of growth the objective is to get the alevins to initiate feeding; optimizing feed usage should not be an issue. Once alevins are well onto feed, it is much more efﬁcient, and less stressful on the ﬁsh, to use automatic feeders. Unless done in slow motion, hand-feeding induces a ‘predator response’ in charr fry. Automatic feeders do not elicit this response, and they free up staff for endless other hatchery tasks. Continue hand-feeding for a few meals daily to ﬁne-tune ration levels for minimum feed wastage and to monitor ﬁsh health and behavior. Adjust daily rations using Table 7.2 for guidance. Reset feed rations weekly, based on the number and size of alevins, expected food conversion rates, and water temperature. Develop your own feeding tables based on locally available feeds and hatchery conditions. Rotating disk feeders, such as the Ewos 505, or belt feeders can deliver continuous amounts of feed throughout the daylight hours. Position feeders to deliver feed to all areas of the tank rapidly. In small round tanks, the circular ﬂow of water swirls the food around to all areas, but in troughs it is difﬁcult to get even distribution of feed. Some ﬁrst-feeding charr will take feed off the bottom, but most prefer feeding from the surface or in the water column. Mount the feeders as close to the water surface as possible to ensure that feed ﬂoats on the surface for as long as possible.

Ponding tank maintenance: good health or mortality It is labour-intensive and tiresome to keep water quality high by scrupulously cleaning ponding tank bottoms, outlet screens, and feeders while monitoring feed usage, but this is a critical job at this stage of charr development. Feed is fed in excess and is poorly consumed by alevins. Water quality degraded by decomposing feed (increased ammonia-N) and high amounts of suspended solids (mostly the very ﬁne feed particles that clog gills) are both conditions that cause physiological stress, leading to slower growth, fungal and bacterial gill disease, and higher mortalities (Eriksson 1991). Semi-moist diets mould rapidly, so any waste feed or unfed ration left on the feeders must be removed daily. Bio-mats can act like sponges in their ability to accumulate waste feed and feces. The mats need to be swept clear of feed daily. You can gently lift them up for inspection and cleaning. Keep them in the tanks until 50% of the alevins are feeding or until it is too difﬁcult to keep them clean. Once they have been removed, circular tanks are usually self-cleaning, though

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screens on the standpipes clog easily and must be cleaned and monitored daily or as often as required to keep them clear of organic material. Keeping outlet screens clear of debris while preventing the escape of tiny ﬁrst-feeding alevins can be frustrating. Generally, alevins found about the screens are smaller, weaker, or deformed ﬁsh that cannot make it in the main ﬁsh school. They can be discarded and added to the daily tally of mortalities. If there are hundreds of healthy-looking fry about the screen, it may indicate that water ﬂow is too high or that the lighting and shading environment places the outﬂow screen in shadow. Keep the standpipe area brighter than other areas of the tank, or construct it of light-colored material. It is a good husbandry practice to monitor the daily and accumulated mortalities separately for each lot of alevins, as well as to keep cumulative mortalities for all lots. Mortality rates can vary signiﬁcantly between ﬁsh lots. In Sweden, a good result is 50% of fertilized eggs surviving the initial feeding stage, but much of this mortality occurs prior to hatch (Eriksson & Wiklund 1989). Given good-quality eyed eggs combined with good technique, over 80% of hatched charr should make it to the ﬁngerling size. Most mortality can be attributed to poorquality eggs or poor husbandry during the ﬁrst-feeding period. Picking out a few dead alevins per tank per day at ﬁrst-feeding is not unusual, but if daily mortality rates approach 1%, it is cause for alarm. Mortalities generally will peak around the end of ﬁrst-feeding, then decline rapidly. To assure healthy alevins and fry, good growth, and low mortalities, follow these guidelines: water temperatures below 10 °C until alevins are well onto feed. • Keep Monitor water quality on a regular basis and adjust water ﬂows when required. • Spend time • behavior. with your alevins and fry and do some hand-feeding each day to monitor not use recirculated water until fry average 0.5–1 g. • Do Maintain high standards of sanitation in ponding tank environment. • Use only high-quality starter diets and select appropriate feed size. •

Into larger tanks: rearing ﬁngerlings Once beyond the alevin stage, the fry become increasingly less sensitive to the hatchery environment, but you must still pay close attention to water quality, through-tank sanitation, and feeding. Charr over 1.5 are known as ﬁngerlings. They are less subject to water quality problems and food-related stresses, are well adapted to the open water environment, and feed well on less expensive, dry diets. Fingerlings are robust enough to handle mechanical grading and a move to a larger tank. To rear ﬁngerling Arctic charr successfully, the hatchery tank system must be designed to meet the high-density loading requirements (40–150 kg/m3) of this species. Loading densities over 75 kg/m3 generally require oxygen injection and high water ﬂows, so the tank intake and outﬂow are designed around these two requirements. Be prepared for catastrophic failures of water and oxygen delivery systems by having secure alarm and backup systems in place (see Chapter 10). During the ﬁrst cycle of Arctic charr in a new hatchery, keep ﬁsh

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densities between 40 kg/m3 and 60 kg/m3 until the equipment and hatchery personnel have shown they can handle working with these high densities. In Europe, most if not all hatchery-reared Arctic charr are held in circular tanks similar to the tanks used for Atlantic salmon (Robbins et al. 1990). North Americans have used raceways and troughs for charr in the past, but most surviving facilities have switched to round tanks. The perfect tank-rearing environment for Arctic charr has yet to be designed, but we do know some of the basic characteristics to look for in ﬁngerling tanks. They must have: and wastewater systems designed to support high ﬁsh-loading rates (125 kg/m ); • anfreshwater inﬂ ow water system designed to deliver sufﬁcient oxygen and maintain water quality • at maximum water temperatures at maximum ﬁsh-loading rates; systems that rapidly ﬂush waste from tank water; • water depth in the range m (Eriksson & Wiklund 1989); • tank depth to tank width ofin 0.75–1 the ratio of 1 : 3 or 1 : 3.5, with a diameter of 2–3 m; and • a standby emergency system designed to deliver sufﬁcient oxygen at extreme maximum • water temperature and maximum ﬁsh loading. 3

Fibreglass or polyethylene tanks that contain about 2–4 m3 of water are a good size for rearing ﬁngerling Arctic charr. They are small enough to allow you to access all areas with a hand net, and shallow enough to permit removal of dead ﬁsh or debris from the drain area. Tanks with cylindrical, central outﬂow screens that extend up to the water surface, with or without interior standpipes, are safer for rearing Arctic charr than tanks with ﬂat bottom screens (see Fig. 7.4). When Arctic charr ﬁngerlings are newly placed in a tank or startled by bright light or sudden overt movement, they will often crowd to the bottom and plug ﬂat screen outlets, causing the tank to overﬂow. Cylindrical screens that are perforated along the length of the pipe allow better water circulation and less crushing when ﬁsh crowd to the bottom of the tank. They are also easier to clean and can be pulled out. If equipped with an interior standpipe, cylindrical screens can be exchanged for larger screens as the ﬁsh grow without your having to drain the tank. Whatever type of tank is used, be sure that it meets the rapid cleaning requirements for high-density rearing. High ﬁsh loading means large concentrations of feed ﬁnes and waste particles in the water column, and these must be cleared from the tank in an efﬁcient manner. Some of the newer tanks remove waste in a side stream, which should work well, but they rely on a ﬂat-screen technology that carries some risk during emergencies, as described above. There are no rigorous studies that conﬁrm what color tank charr prefer. Atlantic salmon raised in light gray or blue tanks under high light intensity grew better than those in dark green tanks under normal indoor light levels (Willoughby 1999). Arctic charr ﬁngerlings appear to do well in dark blue or green tanks.

Light levels and photoperiod control Many aspects of photomanipulation of Arctic charr are not yet understood, so I believe it is best to mimic light conditions found in the wild. In their natural northern habitat, Nauyuk Arctic charr experience rapidly increasing light levels until a 24-hour day is reached in late

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May, lasting until late July. Then light levels rapidly decrease in mid-August (see Fig. 3.10). This brief summer is the most important feeding period for wild Arctic charr, so it makes sense to place hatchery charr on the same photoperiod. Arctic charr ﬁngerlings grow well under long day-length. When they reach a weight of 1.5 g, increase photoperiod from 14 hours to 24 hours over a two-week period. Once on a 24-hourlight regime, the lights should be dimmed to twilight levels (50 Lux) at least four hours during the night to simulate a twilight effect they would experience in the High Arctic. They can be kept on long day-length for their entire stay in the hatchery, but before they leave the facility for grow-out, adjust light levels to correspond to the light regime at the on-growing site. If charr ﬁngerlings are kept in the hatchery over winter, I believe there is merit in giving the ﬁsh a short winter period of long night, followed by a rapid increase in day-length. Light intensity in the hatchery and in the vicinity of the tanks can be increased to about 10 000 Lux during the day (at water’s surface), which is good working light (Willoughby 1999). It is best to use halogen lights as they produce a light spectrum in the blue-green range preferred by ﬁsh. Light controllers that gradually turn lights on and off to mimic dawn and dusk stimulate feeding and also decrease the shock experienced by ﬁsh when exposed to sudden light or dark. If dawn/dusk controllers are not available, turn hatchery lights on and off in stages.

Feeding ﬁngerling Arctic charr When feeding ﬁngerling Arctic charr, follow the general guidelines discussed in Chapter 4. The best types of feeds for ﬁngerling Arctic charr, the best method of presentation, and the quantities needed for good growth are still being researched. Since these variables are affected by the strain of Arctic charr under cultivation, water temperature, and site-speciﬁc conditions at each hatchery, you should monitor feeding behavior closely and keep good track of ﬁsh performance to build a feeding model suitable for Arctic charr at your facility. The following are important points to keep in mind when feeding charr. ﬁngerling charr below satiation; do not overfeed the daily ration. • Feed Adjust daily rations weekly, according to ﬁsh growth. • Feed throughout hours with peaks at dawn and dusk. • Adjust feed size totheﬁshdaylight size. • Deliver sufﬁcient food pellets at each feeding to give each ﬁsh in the tank a portion of • ration. good-quality feed. • Provide Keep records amount of feed fed, weight gain, and mortality by ﬁsh lot. • Develop a senseof the of the ﬁshes’ appetite and feed accordingly. • Fingerling Arctic charr are voracious feeders, particularly during increases in water temperature and day-length. Because Arctic charr are kept at high densities, it is important to monitor feeding levels. The ﬁsh should never be fed to satiation. Rather, keep an edge on their hunger. Overfeeding can cause water quality problems and can also decrease food conversion rates. Overfeeding high-energy dry diets will lead to obesity and impaired liver and kidney function (Post 1987).Although researchers have shown that Arctic charr take a signiﬁcant amount

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of feed off the bottom, this type of feeding is to be discouraged as tanks are designed to remove waste off the bottom rapidly. Good tank design that rapidly clears ﬁsh waste will just as rapidly remove feed particles from the substrate, increasing the downstream pollution load. If you feed rations of the right size and quantity at suitable intervals, you will achieve good results without bottom feeding. If you observe feed on tank ﬂoors or exiting the drain lines from tanks, it indicates there is a problem with the feeding regime being used. I do not know of any companies that produce pelleted feeds speciﬁcally for ﬁngerling Arctic charr. Most pelleted dry diets formulated for Atlantic salmon ﬁngerlings are acceptable to Arctic charr, though some manufactured trout and salmon diets produced in the US and Canada gave poor growth performance in Arctic charr (Tabachek 1984). Formulated diets in the protein/lipid range suggested in Table 4.8, containing high-quality ﬁshmeal and marine oils from reputable manufacturers, will sufﬁce until we have a better grasp of charr dietary needs. Table 7.4 presents feeding tables for ﬁngerling Arctic charr. Often Arctic charr will show considerable variation in appetite from day to day and throughout the day, so the tables act only as a guideline. Most charr will feed during daylight hours, with peaks in feeding during ﬁrst light and a secondary peak around lights off (Alanärä & Brännäs 1997) which is the classic dawn–dusk feeding behavior of many salmonids. You can mimic this by delivering rations throughout the day, with more rations in the early morning and evening. Fingerling Arctic charr are best fed using mechanical feeders. They require many feedings throughout the day and a lot of feed when held at high density. Feeders should be adjustable to allow the delivery of different-sized feeds, from 0.5 mm to 4 mm pellets, over many short feeding bouts throughout the day. Feeders that can deliver feed over a wide area are helpful in assuring that all individuals have access to feed. Even in high-density, crowded tanks, dominant Arctic charr will set up stations adjacent to feeders, preventing shyer charr from feeding. Maintaining a water current of 1.1 to 2.3 body lengths per second helps minimize this type of aggressive feeding behavior (Christiansen et al. 1989).

Table 7.4

Feeding tables and feed size for ﬁngerling Arctic charr. Feeding rate (% body weight/day)*

Fish size

Temperature (°C)

Weight (g)

Length (cm)

Feed size (mm)

2

4

6

8

10

12

14

1 5 10 15 20 30 40 50 60 70 80 90 100

4.8 7.9 9.8 11.1 12.1 13.7 15.0 16.1 17.0 17.9 18.6 19.3 19.9

0.9 1.2 1.5 2.5 2.8 3.2 3.5 3.7 3.9 4.1 4.3 4.4 4.6

1.07 0.64 0.52 1.17 0.43 0.37 0.35 0.32 0.30 0.29 0.29 0.27 0.26

1.99 1.19 0.98 0.85 0.80 0.70 0.66 0.61 0.57 0.54 0.54 0.51 0.50

2.92 1.74 1.43 1.24 1.17 1.02 0.96 0.89 0.83 0.79 0.78 0.75 0.72

3.85 2.30 1.89 1.64 1.55 1.34 1.26 1.17 1.10 1.04 1.03 0.99 0.96

4.77 2.85 2.34 2.03 1.92 1.66 1.57 1.45 1.36 1.29 1.28 1.23 1.19

5.70 5.65 2.79 2.42 2.29 1.99 1.88 1.73 1.63 1.54 1.53 1.47 1.42

6.62 3.96 3.25 2.82 2.66 2.31 2.18 2.02 1.89 1.79 1.78 1.71 1.65

*assume food conversion rate of 1.1 : 1

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Size-grading, sorting, and splitting Arctic charr lots By the time they reach 1–1.5 g, Arctic charr are tough enough to survive sorting and grading. As ﬁngerling charr grow, each lot must be split up, with some ﬁsh moved into other tanks to maintain biomass densities at safe levels. This is an opportunity to grade the ﬁsh based on body size or weight. Fish are then allocated to new tanks in groups of similar size. A physical inventory can also be done at this time. The process of splitting, counting, and size-grading is stressful for ﬁsh. It puts them off their feed for a few days, usually causes a few deaths, and requires a great deal of time. However the beneﬁts in terms of better feed allocation in sizegraded groups and better inventory control outweigh these concerns. All of the strains of Arctic charr currently under commercial cultivation show considerable size variation among individuals of the same age cohort at an early stage. A typical group of ungraded Nauyuk Arctic charr ﬁngerlings with a mean weight of 3.5 g, for example, will contain individuals as small as 1 g and as large as 6.5 g (see Fig. 7.5). Although current research suggests that total biomass gain is not affected when ﬁsh are held in mixed-size groups, variation in size does create husbandry problems. In ungraded groups of charr, feeds of different sizes must be mixed together, food conversion rates are poor with mixed-size feeds, and tank outlet screens sized to prevent the escape of the smallest ﬁsh become plugged with feces from the largest ﬁsh. Size variation and associated husbandry problems increase as the ﬁsh grow. Another important reason for size-grading ﬁngerling Arctic charr is to pull out the runts. The charr strains currently available for commercial cultivation, all of which are essentially wild stocks, contain a portion of ﬁsh that never grow well; they are runts in a hatchery and remain runts in a grow-out environment (see Fig. 7.6). This trait varies with race. In my experience with Nauyuk and Fraser Arctic charr, most of the smallest (bottom 10–20% of the cohort) individuals in ungraded groups grow poorly throughout their lives if kept under intensive culture. They do well if stocked at low density in pothole lakes, but not in tanks at high density. Until Arctic charr become more domesticated, this will remain a fact of life for Arctic charr growers. There is evidence that large eggs produce larger alevins with better

Fig. 7.5 Size distribution in an unsorted ﬁngerling cohort of Arctic charr.

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Fig. 7.6 Variation in body shape of ﬁngerling Arctic charr.

growth rates and lower mortality rates than do smaller eggs. One egg producer is investigating the feasibility of size-grading eggs for sale to producers. Arctic charr should ﬁrst be graded when each lot reaches a mean weight of 1–1.5 g and then again at about 10–15 g. The ﬁrst grading is done to remove the runts and slow growers, that is the bottom 10–30% of each group. These ﬁsh are held separately and are either stocked at low density in lakes or ponds, or are killed. Whether the larger ﬁsh are graded into one or two groups at this time is a matter of judgment and available tank space. In the next grading they can be split into groups based on ﬁsh size. Generally, Arctic charr ﬁngerlings grade nicely into small, medium, and large groups, with the size boundaries based on available tank space and feed size considerations. Another grading may be required depending on the size variation observed in the various lots as they grow. Grading techniques As with any husbandry activity involving ﬁsh handling, the tools and equipment for grading and splitting Arctic charr lots are best set up and tested well before the operation is under way. There are ﬁve steps to grading ﬁngerling Arctic charr: (1) (2)

Sample each lot of ﬁsh to determine existing size distributions and determine required biomass allocations for new tanks. Determine size boundaries for dividing ﬁsh into different-sized lots.

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(3) (4) (5)

Arctic Charr Aquaculture

Adjust the ﬁsh grader for the required size distributions of each new lot. Grade ﬁsh and count them as they are returned to new tanks. Sample new size-graded lots to re-establish mean weights and size distributions.

Proper grading can only be done if the ﬁsh have been randomly sampled using a large sample size. This will give a true estimate of the ﬁsh lot’s variation in size. Use the information on size distribution from the sample, combined with the estimated number of ﬁsh in the lot, to determine at which size the ﬁsh should be divided. You always need to do some juggling based on the number of ﬁsh, the available tank space, the number of ﬁsh grades, and feed sizes to determine the best size at which ﬁsh should be split into new lots. Grader boxes designed for rainbow trout or Atlantic salmon work well with Arctic charr if the bar spacing is adjustable. No manufacturer has a ﬁxed-width grader that is designed for the peculiarities of Arctic charr body width to ﬁsh weight. Belt graders, such as those produced by FischTech, allow you to adjust the width at which each group falls out and work well for larger ﬁngerlings (see Fig. 7.7). There are a number of ﬁsh counters that can be used with graders to greatly simplify inventory control of graded ﬁsh. Adjust the grader bars for size categories, using a few sample ﬁsh from the lots to be sorted. Arctic charr are tough, but they should still be handled in numbers and in a manner that does not push the grading equipment beyond its limits. Bear in mind that few systems handle as many ﬁsh as the manufacturer claims. Pushing the charr through the grading routine too fast gives poor size grade performance and leads to higher mortality levels during and after sorting. Fish should not be sedated during the grading process. Prior to grading and sorting, take Arctic charr off their feed for two days and keep water temperatures as low as possible. Never grade when water temperatures are above 10 °C, and keep holding-tank water well oxygenated. It is best to have supplemental oxygen going into hatchery tanks through air stones placed at the bottom of the tank, since stressed-out

Fig. 7.7 Belt grader for size-sorting Arctic charr.

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ﬁngerling Arctic charr sink to the bottom and can have high respiration rates. Arctic charr do not lose scales during grading, and they survive the grading process well at very high numbers.

From the hatchery to grow-out facilities Generally, the sooner Arctic charr are moved out of the hatchery, the better. Maintaining ﬁsh in a heated, indoor facility is expensive compared to on-growing in larger outdoor tanks or in natural lakes and ponds. Move ﬁngerlings to open water or tank farms in the fall and spring, when ambient air and water temperatures are cool and predators few. For saltwater grow-out, move ﬁngerlings to sea in the spring. They must weight at least 125 g. There is an advantage to moving ﬁngerlings during natural shifts in photoperiod that they would respond to in the wild. Although I have only incidental observation rather than data to support this theory, charr seem to pick up their feeding and growth when moved to new habitat during increasing or decreasing light regimes such as occur in the spring or fall. Of course, tank availability and market factors may outweigh the best biological times for moving ﬁngerlings. The principles of transporting Arctic charr ﬁngerlings from the hatchery to on-growing facilities are similar to those employed for other salmonids. A large mass of ﬁsh moved in a small mass of water require a life-support system and husbandry protocols that keep them in good health for the duration of the move. There are two basic methods for moving ﬁsh: (1) (2)

In open tanks (with lids but open to the atmosphere to allow carbon dioxide removal) when moving short distances by truck or boat. In sealed bags for shipping long distances by aircraft.

Regardless of the transport method used, the life-support system must allow infusion of adequate amounts of oxygen into the water and must remove carbon dioxide from the water. As with any intrusive ﬁsh-handling operation, success in large part will depend on attention to detail. The charr must be handled gently, with minimum time out of the water in a wellplanned process. When moving ﬁsh in open containers, the most important points are to: that the transportation tank water is cooled and well-aerated prior to loading the • insure ﬁsh. Respiration rates of excited ﬁngerling charr can double normal oxygen consumption

• • • •

rates; insure transport water is aerated with oxygen and remains above 80% saturation with carbon dioxide levels remaining below 10 mg/L; keep the transport water cool (2–3 °C) throughout the trip. It should never be above 10 °C; take Arctic charr off feed 2–3 days (48–72 hours) prior to the move to ensure empty digestive tracts and low ammonia production; and lower hatchery light levels when loading ﬁsh, and keep outside activities (loading, transporting, and delivery) in the shade, preferably moving ﬁsh during the dusk to dawn period (Eriksson & Wiklund 1989; Wedemeyer 1996).

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If the move is going to take longer than a few hours, add 1% NaCl to the water to minimize the effects of osmotic stress. It is feasible to move small Arctic charr long distances by air in sealed plastic bags. The secret is to use very cold water, supersaturated with oxygen, and to hold ﬁsh off feed for at least 72 hours. Fill 10-litre food-grade plastic bags or semi-rigid potable water containers with 3–4 L of chilled water, well oxygenated, before adding ﬁsh. After you have placed the ﬁsh in the container, compress it to remove all air and replace with pure oxygen, then seal. If charr are to be transported longer than 6 hours, add 1% NaCl and an ion exchanger such as zeolite or other commercially available products (e.g. Ammo Lock or clinoptilolite) to absorb ammonia (Wedemeyer 1996). Place the containers in insulated ﬁsh-shipping boxes with ice packs to keep the water cool throughout the journey. The density at which charr can be loaded depends on a myriad of interacting factors – water temperature, size of ﬁsh, length of trip, physiological state of the ﬁsh, and the physical parameters of the transportation system. You will have to experiment to determine the best system for your facility. As a general rule, the larger the ﬁsh, the higher the allowable loading rates (but the fewer ﬁsh per container – shipping small ﬁsh is of course more economical). Small ﬁngerling salmonids can be transported at loading rates of 240 g/L of water, and larger parr at rates of 360 g/L of water (Wedemeyer 1996). In Sweden, Arctic charr ﬁngerlings (50 g size) are transported by truck in 400- to 250-litre tanks at loading rates of 100 kg/m3 of water (0.1 kg/L of water), and larger ﬁsh at 150 kg/m3 (Eriksson & Wiklund 1989). Table 7.5 gives guidelines for allowable loading densities when transporting Arctic charr in open tanks and sealed bags. Arctic charr are susceptible to fungal infections from handling during loading and unloading, and there are a number of products available that may help with this concern. A polymer formulation (polyvinylpyrrolidone) used in the tropical ﬁsh trade greatly reduces the level of Saprolegnia infections in transported tropical ﬁsh. It temporarily bonds to exposed tissues that have been damaged or had their protective slime layer removed, preventing attack by pathogens such as Saprolegnia. A product with the trade name Polyaqua has been used successfully at a concentration of 100 ppm in the shipping water to decrease the incidence of fungal infections in other salmonids, and this should also work with Arctic charr (Wedemeyer 1996). Whenever you are transferring ﬁsh between the hatchery and grow-out facilities, you should take the following precautions: Table 7.5 Guidelines for shipping Arctic charr ﬁngerlings. Data source: Avault 1996; Wedemeyer 1996; Bodvin et al. 1996. Mode of transport

Open tank Open tank Open tank Sealed bags Sealed bags Sealed bags

Fish size

Fish loading density (g/L of water)

Weight (g)

Length (cm)

Shipping time (h) 1–6

6–12

12–24

24–48

1–25 26–75 76–150 1–25 26–75 76–150

4.7–13.0 13.1–18.0 18.1–23.5 4.7–13.0 13.1–18.0 18.1–23.5

260 390 440 150 220 250

200 290 330 120 170 190

130 190 220 80 120 130

70 100 110 40 60 60

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Always surface-disinfect transportation equipment arriving at your facility. • To minimize movement of pathogens, do not dump transportation water into receiving • facility water when transferring ﬁsh. Keep transport water cool and be sure that ice is made from dechlorinated water. • Estimate how long transportation will take from the time loading commences to complete • unloading, and assess what this means in terms of oxygen requirements and ammonia

•

production. Also allow for adverse temperature ﬂuctuations and weather conditions. Minimize transportation stress by thorough planning prior to loading. Ensure the entire process is done calmly and efﬁciently.

For me, the transportation of ﬁsh from the hatchery to the grow-out site is the beginning of the serious business of growing Arctic charr commercially for sale as food. In the next section the husbandry techniques for growing larger Arctic charr are discussed in the context of culture economics and of marketing Arctic charr to the consumer. Although growing-out larger charr is technically less challenging than rearing brood ﬁsh and ﬁngerlings, it is very challenging in terms of making a proﬁt.

Section III

The Business of Production

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Arctic Charr Aquaculture

Growing Arctic charr commercially requires you to change your focus from growing ﬁsh to producing food products. You must make enough proﬁt selling your product to sustain the business and pay a reasonable return to the investors who supplied the working capital. Although brood stock rearing and hatcheries are part of this equation, it is at the grow-out stage where production of ﬁsh for the consumer takes place. Supplying eggs and ﬁngerlings is just an input cost to the grow-out, similar to feed and ﬁsh processing supplies. By the turn of the twentieth century, the business of growing salmon in containment, particularly Atlantic salmon and rainbow trout, had proven to be proﬁtable, but it was not an easy road. During the early days of salmonid culture there were many booms and busts as the biological and technological aspects of holding, managing, and feeding ﬁsh were developed, tested, and found wanting. Many bankruptcies were attributed to poor marketing, as the entrepreneurs who dominated new aquaculture species did not always have the knowledge or skills to get new product to the market in the proper form, at the right time, or at a good price. In some cases, bad timing dropped prices below the cost of production, as when the Japanese emperor died, driving down the demand for salmon as gifts just as many growers on the West Coast of Canada brought their ﬁsh to market. Greed killed some farms in the early shake-outs as the expectations of investors exceeded the reality of corporate farms they had invested in. Unlike Atlantic salmon culture, Arctic charr aquaculture is still in its infancy, but it has the advantage of learning from the mistakes that other salmonid cultures have gone through on their way from new species status to mature status. And Arctic charr has distinct advantages over other salmonids – unique marketing image, a ﬁne ﬂavor, and the ability to grow at high density in land-based tank farms – that will make it proﬁtable for the producer and friendlier to the environment.

Chapter 8

Production of Arctic Charr for the Consumer

The commercial production of Arctic charr for the consumer begins with the on-growing process. It is simple enough: small ﬁngerlings are placed into tanks, fed a good-quality diet, harvested a few years later when they reach market size, slaughtered, and processed, ready for delivery to the consumer. The goals of the producer of cultured Arctic charr are: sell high-quality ﬁsh products to the high-end consumer; • toto produce sh with a high nutritive value and distinctive taste and texture; • to grow ﬁshﬁunder conditions that meet high standards for the well-being of the ﬁsh, work• ers, and the downstream environment; to produce high-quality ﬁ sh while striving for least cost of production. • Growing ﬁsh is a business. Sometimes producers fall into a trap where on-growing the ﬁsh becomes an end in itself. They forget that the ultimate goal is a dead ﬁsh to be sold to a discerning customer. There is no point in on-growing ﬁsh of poor quality and low market value, or in producing more ﬁsh than could possibly be sold into a limited, undeveloped market. This may seem self-evident, but many times I have talked with Arctic charr farmers who could not see beyond the process or perhaps just the joy of growing the ﬁsh. For example, I once did a management audit of a failing Arctic charr farm where tens of thousands of excess ﬁngerling charr, mostly of the inferior Fraser strain, piled up in the hatchery while the managers built their tank farm. They spent their limited resources adding temporary tank space in the hatchery to house the growing ﬁsh. They had three age cohorts crammed into tanks of all shapes and sizes that were everywhere, propped up in the aisles and even out in the storage sheds. Management focussed almost entirely on keeping every ﬁsh alive, adding tank space and plumbing new waterlines, but forgetting about the real goal of producing quality market ﬁsh and getting the tank farm built. The solution was very simple: terminate the low-quality Fraser strain and all but one age cohort of the Nauyuk strain and concentrate their resources on growing fewer ﬁsh to larger size. But they could not bring themselves to kill any of their ﬁsh, and they are now out of business.

Different production strategies for on-growing A production strategy is the plan for rearing ﬁsh from the time they are delivered to the on-growing facility as ﬁngerlings to the time they reach market size. To determine this

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Arctic Charr Aquaculture

strategy for your facility, you need to know the expected yearly volume of ﬁsh sold and the size of the ﬁsh at slaughter. The production strategy is also determined by site-speciﬁc conditions, such as the volume of water available, the proximity to markets, the cost of transportation, and the availability of services and supplies. There is always an interplay between the number of ﬁsh that can be sold, the type of on-growing site available, and the number of ﬁsh that can be economically grown at the site. Once you have decided the volume and harvest strategy (e.g. one massive harvest or many small harvests) of ﬁsh grown at a speciﬁc grow-out site, you can determine the volume and type of holding space you will need.

Holding structures Two holding methods have proven most effective for on-growing Arctic charr: low-density lake stocking and high-density intensive culture in land-based tanks. Pothole lake stocking, in which ﬁngerling Arctic charr are released into isolated lakes, is an effective and cheap method for on-growing Arctic charr to large market size. Commercial growers in the Yukon have successfully raised Arctic charr in pothole lakes that contain no other ﬁsh species, while stocking lakes of larger size has worked reasonably well in Sweden, Norway, and Finland. The success depends primarily on a plentiful supply of isolated lakes rich in invertebrates, particularly freshwater shrimp (chieﬂy gammarids). At the other end of the spectrum in capital cost and ﬁsh density is intensive culture in tanks. Arctic charr grow well at high density given sufﬁcient oxygen, proper husbandry, and rapid clearing of ﬁsh waste. The high ﬁsh density, low mortality rates, and good food conversion rates of Arctic charr held in tanks make this an effective method to on-grow high-value ﬁsh, though it requires considerable expertise, heavy capital outlay for tank construction, and considerable carrying costs for feed, electricity (if water is pumped through the system), and oxygen. It is not for the faint of heart as success is measured by an operator’s ability to prevent catastrophic loss from mechanical system failures, over and above the usual considerations of achieving good food conversion rates, low mortality, and rapid growth. Land-based tank farms have proven successful in Canada and Iceland, but there have been a number of spectacular failures in the past when ﬁsh were lost due to a misunderstanding of Arctic charr husbandry requirements and use of the wrong strains of charr. A variant on land-based tanks are bag-pens. These bags, constructed of a tough PVC material, ﬂoat in the water, with the top of the bag only a few centimeters higher than the surrounding water. The water level in the bag is higher than the surrounding lake, which allows gravity ﬂow of water through the bag, much like in a land-based tank. Intake water is pumped into each bag via a low head pump, and the efﬂuent water exits the bag via a special valve structure located at the bottom of the bag (Brenton-Davie & Groot 1997). Waste feed and feces can be removed after they leave the bag. Essentially, bag-pens are ﬂoating tank farms that have the advantage over net-pens of allowing oxygen injection, high water ﬂows, and protection from predators. They are being used with some success for growing Arctic charr in northern Canada. Two other methods have been tried for on-growing Arctic charr: net-pens and duo-culture with other salmonids. Net-pens have been used in both fresh water and salt water in North America and Europe with limited success. They make it more difﬁcult to keep Arctic charr rearing densities high enough to achieve good ﬁsh health and low food conversion rates while

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maintaining adequate water quality. In fresh water, culturists have had trouble keeping water temperatures within tolerable levels in the summer and dealing with ice cover in the winter. The low ﬁsh densities required to maintain acceptable oxygen levels in lake net-pens that have no tidal or current ﬂow lead to behavioral problems, which then cause poor growth, feed wastage, and poorer food conversion rates. Freshwater net-pens in Newfoundland failed because of disease, likely exacerbated by stress from low density. In sea water, Arctic charr do poorly during the winter, almost always showing unacceptable mortality rates and poor feed conversion (Jobling et al. 1993). One technique to get around the seawater intolerance problem is to create freshwater lenses in the closed sea pens. Fresh water ﬂoats on sea water, so ﬁsh can move away from the saline waters without being transferred from the pens. However, there are few places where sea water is in proximity to suitable sources of fresh water in the winter months (Heggberget et al. 1994). Another method used in Sweden and Iceland is to on-grow ﬁsh in freshwater tanks until they reach a weight of 300 g, then transfer them to sea cages in June and July for additional growth to a target weight of 1.5 kg (Jobling et al. 1993). An exciting concept for growing Arctic charr is duo-culture with other salmonids. Researchers and commercial culturists have tried growing Arctic charr with Atlantic salmon a number of times, with positive effects on salmon growth and normal growth of Arctic charr (Nortvedt & Holm 1988). Salmon held with Arctic charr all showed greater gain in weight and condition factor than control groups held at similar densities in mono-culture. The shading effect from the other species masks the presence of charr (and vice versa), which dampens the tendency of intraspecies aggression. In another case, a group of Kokanee (Oncorhynchus nerka) of about 20 g, held in a tank at low density, started to die even though conditions seemed ideal for growth. The ﬁsh looked healthy and had no disease, but they died at a rate of more than 1% per day. When the survivors were moved to a tank containing Arctic charr of equal size and held at about 75 kg/m3, the Kokanee death rate dropped off rapidly and growth resumed, even though they were packed shoulder to shoulder with charr. Stocking density for growing Arctic charr in lakes In pothole lake stocking, ﬁsh density is measured as kg/ha of lake surface. The number of Arctic charr you can stock depends on the size of the lake, the productivity of natural feed, economic considerations concerning the cost of harvesting, and market conditions. Before you even think of stocking a lake, however, it must meet the following criteria: It must contain no predatory ﬁsh that might consume young Arctic charr or compete with • Arctic charr for food. It must be large enough (more than 100 ha) to afford some economies of scale in harvest• ing. be deep enough that ﬁsh are not winter-killed due to lack of oxygen. • ItIt must should have many shallow shoals with rich emergent and submergent plant zones. • It must have • relicta. an abundance of large invertebrates such as Gammarus lacustris or Mysis should have a long fetch to the prevailing winds to assure good mixing of oxygen-rich • Itsurface waters with deeper waters.

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Arctic Charr Aquaculture

It must be accessible for harvest by plane or vehicle, but not so accessible that poaching • becomes an issue. When stocking a lake for commercial production, it is important to keep the ﬁsh numbers within the carrying capacity of the lake. The carrying capacity in simple terms is the ability of the lake to supply enough preferred foods to keep the Arctic charr population growing rapidly. Arctic charr will selectively graze on preferred foods ﬁrst, and over time they can remove prey faster than it is naturally replaced. As Arctic charr switch to less suitable prey items, growth rates will decline, and if too many ﬁsh are present, food resources are removed at such a rate that the entire Arctic charr population will become stunted and unmarketable. Determining the carrying capacity, or the number of ﬁngerlings to stock, is difﬁcult and depends on site-speciﬁc factors discussed above. A couple of examples give a general sense of what yields of Arctic charr are possible in northern lakes. In a Norwegian lake created by a hydro dam, the estimated total yield of Arctic charr was 10 kg/ha y–1 (Aass 1984). Arctic charr yields in Icelandic lakes average 10–15 kg/ha y–1, with the most productive lakes yielding 45 kg/year (Kristjánsson & Adalsteinsson 1984). These estimates are from natural lake systems that contain other ﬁsh predators such as brown trout. Based on these yields and practical experience gathered from stocking pothole lakes in the Yukon, a recovery of 20–25 kg/ha is reasonable for a lake stocked with Arctic charr and not containing any other predatory ﬁsh (lake trout, northern pike, brown trout, whiteﬁsh, grayling, etc.). Recovery yields are also affected by the level of predation from birds and mammals such as mink and otters (Mustela). Assuming that the recovery yield of marketable ﬁsh is about 25–50% of ﬁsh initially stocked, and given a recovery weight for Nauyuk Arctic charr averaging 2 kg, then the number of ﬁsh needed for stocking is 20–40 ﬁngerlings for each hectare of lake surface (see Table 8.1). Stocking density when growing Arctic charr in tanks In intensive culture systems, ﬁsh density in each tank is measured as the weight of ﬁsh per cubic meter of water and is known as ﬁsh-loading density or standing biomass. As ﬁsh grow within the tank, the biomass increases while the number of ﬁsh remains constant or decreases Table 8.1

Stocking and recovery rates for Arctic charr grown in pothole lakes. Stocking rate 20 kg/ha

Stocking rate 25 kg/ha

25% recovery

50% recovery

25% recovery

50% recovery

40 10 20

20 10 20

50 12.5 25

25 12.5 25

20 000 5 000

10 000 5 000

25 000 6 250

12 500 6 250

10 000

10 000

12 500

12 500

Per ha lake area Fingerling stocked No. of ﬁsh harvested Total round weight harvested (2 kg/ﬁsh) 500 ha lake Fingerling stocked No. of ﬁsh harvested (2 kg/ﬁsh) Total yield round weight (kg)

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due to mortality. Although Arctic charr grow well at the low densities of pothole lake stocking, they grow poorly under intensive culture conditions when held at densities much lower than 40 kg/m3. Fish density can rise to 100–125 kg/m3 without harm if water quality remains within tolerance levels as discussed in Chapter 3. These high ﬁsh densities make tank culture economic for Arctic charr, but they create management and husbandry concerns that must be addressed at the planning stage of a grow-out operation. The tanks must be designed to accommodate the high water ﬂows and high oxygen requirements of Arctic charr held at high density. Arctic charr are normally held at densities two to three times higher than used for Atlantic salmon or rainbow trout, so tank designs developed for these ﬁsh will not work well with Arctic charr. An oxygenation system is integral to high-density on-growing, as oxygen must be added to the supply water at concentrations higher than saturation. The water ﬂow through the tank must rapidly remove metabolic waste products while still distributing the water in a uniform manner throughout the tank at velocities that are manageable by the ﬁsh. L-shaped spray bars are an effective way to create high ﬂow rates while controling water velocity (see Fig. 8.1).

Fig. 8.1 Grow-out tank for intensive culture of Arctic charr.

192

Arctic Charr Aquaculture

Water velocity is important to Arctic charr growth, and you should work into tank design an ability to bring water into the tank at different velocities to take advantage of the beneﬁts this imparts to ﬁsh growth and well-being. charr grow better if they are forced to swim against a moderate current (1 to 2 body • Arctic lengths/second) (Jobling et al. 1993). in the size of Arctic charr is decreased dramatically when they are held in moving • Variation water. Arctic charr do not consume more food than unexercised charr, but their speciﬁc • Exercised growth rates are higher, implying a better use of ingested food. When designing the holding system, think about the maximum ﬁsh biomass predicted for each tank. This maximum may only be reached for a few months prior to harvest, but the system must be able to accommodate even temporary spikes in ﬁsh density. The tank design must also accommodate the maximum oxygen consumption rates needed by ﬁsh during periods of heavy feeding in warm water conditions. Arctic charr oxygen consumption rises rapidly during feeding periods, and water’s capacity to carry oxygen diminishes with increased temperature. The size of the tanks is also important to economic success. They must not be too large in terms of volume, width, and depth. The failure of many large land-based tank farms in Iceland and Canada was in part due to using over-large tanks (500–6000 m3) (Willoughby 1999). It is difﬁcult to manage water quality, ﬁsh biomass, feeding, and practical aspects of moving, grading, and harvesting the ﬁsh in tanks of 500 m3, let alone a tank containing 6000 m3 of water. Tanks big enough to hold 20 tonnes of Arctic charr at maximum loadings of 125 kg/m3 are large enough to meet some economies of scale while small enough to allow easy handling. When designing on-growing tanks, consider the following points: you visually assess ﬁsh throughout the tank? • Can Can easily remove mortalities without entering the tank? • Will you you • ment? be able to crowd up ﬁsh for harvest and sorting without needing heavy equipmanagement and ﬂow dynamics be best at this tank size? • IsWillthewater system to remove metabolic waste products rapidly? • Can you supplydesigned enough to keep water quality high? • Will it be easy to handle water ﬁsh during sorting, feeding, and harvesting? • Bear in mind that there is less risk of catastrophic loss or disease when fewer ﬁsh are contained in each tank. You may want to request assistance from specialists in Arctic charr culture and engineers with expertise in aquaculture water system design when you are designing water supply and water drain systems.

Production cycles For many grow-out operations, the most efﬁcient way to obtain seed stock to begin the

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193

production cycle is to purchase enough eyed ova from specialty egg producers each year to meet their farm’s needs. (This assumes the farm has a hatchery facility to hatch eggs and rear ﬁngerlings.) Typically a grow-out operation requires about one eyed egg for every kilogram of Arctic charr produced (harvest weight of 2.5 kg) under intensive culture, and about four eyed eggs to support the same level of production from pothole lakes. There are hatcheries that also specialize in the production of ﬁngerlings for sale to grow-out operations. It is better to pay a higher price for quality eyed ova (or ﬁngerlings) than to accept cheaper ova that produce ﬁsh unacceptable for the market. Only eyed ova, certiﬁed disease-free by an ongoing ﬁsh health protection program, are allowed into the receiving facility in most countries. For reasons related to the health security of ﬁsh, some countries may limit the importation of eyed ova to government aquaculture facilities or to a limited number of private facilities. They may also impose quarantine conditions on a facility receiving foreign eyed ova until progeny are tested for certiﬁable pathogenic diseases. Importation can suddenly cease at any time due to changes in disease proﬁles within the country shipping eggs or for reasons related to protective trade barriers or national or international politics. The production cycle, or the amount of time required to grow ﬁsh from ﬁngerling to market weight, is determined by many different variables. Although it takes about 36 months under standard conditions (see Chapter 5), the length of the cycle for a given cohort of Arctic charr is site-speciﬁc and is difﬁcult to predict without real data. Often it is not clearly deﬁned until the ﬁrst batch of ﬁsh is on-grown to market weight. There is a general pattern in all production cycles, with Arctic charr entering the cycle as live ﬁngerlings (5–70 g) and leaving as large dead ﬁsh (1–3 kg) 24–36 months later. The type of holding method used, the size at which ﬁngerlings enter the grow-out, the ﬁsh size required at market, the strain of Arctic charr under culture, the amount of feed available, water temperature, latitude of the culture site (which affects light/dark periods), and husbandry practices all interact to determine how long the cycle takes. For example, the production cycle for growing a 2.5 kg Nauyuk Arctic charr from a 10 g ﬁngerling in Yukon pothole lakes is about three summers of growth. Under the same conditions, a Fraser Arctic charr may only grow to half this size, as it reaches sexual maturity in its second year of growth. If the lake is overstocked with Arctic charr and food is scarce, it may take twice as long to grow ﬁsh to market size. In Iceland, Arctic charr grown in freshwater tanks at 7–12 °C reach 300 g in two years (including time in hatchery) and then are transferred to sea cages in June and July to grow to a target weight of 1.5 kg. Arctic charr grown in Sweden are transferred to freshwater net-pens at 30–40 g in the spring, reaching 200–300 g in the ﬁrst year and 700–800 g at harvest in fall of the second year (Robbins et al. 1990). In the cold of 60° North it takes about 36 months to grow an Arctic charr to 2.5 kg in an outdoor tank system. When the same strain is grown in tanks where water temperature and light are controlled, the grow-out time is reduced to about 24 months, at least under experimental conditions (Bass 1998). Arctic charr do not need to pass through a smoltiﬁcation process, so they can be transferred from the hatchery to on-growing operations when it is most suitable for the culturist. From a biological perspective, however, it is best to make this transfer in the early spring or late fall. Early spring coincides with a natural burst in growth rates related to increased day-length and is the preferred time for entry into tank farms. In the Yukon, the most efﬁcient time for pothole lake stocking is in the fall, just before freeze-up. Most bird predators such as loons

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Arctic Charr Aquaculture

(Gaviidae), gulls (Laridae), and mergansers (Merginae) have ﬂown south, and the cool daytime temperatures are easier on the ﬁngerlings as they are transported from the hatchery to the lake. The long winter also gives the hatchery-reared ﬁsh time to adapt to the wild ways of nature under the safe cover of ice and snow (Johnston 1999). One other important aspect of the production cycle, which determines the amount of grow-out space required, is steady-state production. Since the grow-out cycle is longer than one year, the on-growing operation must have more than one cohort of ﬁsh to assure that market ﬁsh are available each year. For example, in a pothole lake operation that requires three years of growth for ﬁsh to reach market size, the grower must have at least three different ponds stocked with cohorts of different ages to ensure that one cohort is reaching market weight each year. (The different cohorts cannot reside in the same lake because this creates harvesting problems, and because Arctic charr are cannibalistic.) In addition, each lake is left fallow after harvest for at least one year. This allows invertebrate populations to recover from Arctic charr feeding pressure (Eriksson & Wiklund 1989) and helps to break the chain of any parasitic infections involving an intermediate host and Arctic charr. Thus, in our example of a three-year grow-out, four different lakes are needed: one fallow, one ready for harvest, one in its second year of growth, and one newly stocked. In a tank farm there is a similar need to hold different-aged cohorts separately. There is also the need to grade each cohort by size into different tanks to assure better growth and food conversion rates. A tank farm operation becomes a juggling act of different-aged cohorts and different-sized grades of ﬁsh. The amount of holding space (expressed as m3 of water) required can be predicted based on maximum standing biomass of all ﬁsh, the expected number of size grades in each age cohort, and the type of harvesting strategy. As a general rule, an on-growing operation that holds ﬁsh for one or two harvests per year will require about 1.5 times as much holding space as the expected yearly volume of sales. If you were harvesting ﬁsh on a monthly basis, you would require only enough space to hold 0.6 times the annual harvest. For example, if you were selling 200 tonnes in one or two large harvests per year, the grow-out would require tank space for holding about 300 tonnes of ﬁsh. Selling the same amount of ﬁsh on a monthly basis would reduce that to enough tank space for holding about 130 tonnes. The production cycle is an important planning and managing tool, but is difﬁcult to discuss generally, given its site-speciﬁc and multi-variable nature. It affects many things, including: amount of tank space required to hold ﬁsh until they reach market weight; • the amount of initial capital required for constructing the on-growing facility; • the the of working capital required to carry the ﬁsh inventory until it is sold; and • the amount amount of ﬁsh available to the consumer on a month-by-month basis. • The production cycle of a 200 tonnes/year Arctic charr grow-out is modeled in Table 8.2 and is based on a continuous harvest of ﬁsh on a monthly basis. Basic assumptions are that each Nauyuk Arctic charr cohort is stocked into the facility at 50 g size and harvested at 2.4 kg, after a maximum grow-out period of 24 months. The fastest-growing ﬁsh of the ﬁrst cohort stocked would reach harvest size in 14 months. New cohorts are added at six-month intervals, and the grow-out reaches steady-state production in year three, at which point it will contain ﬁve different cohorts of Arctic charr, with monthly average harvest volumes ﬂuctuating from 13 to 28 tonnes.

Table 8.2 Production model for a 200 tonnes/annum Arctic charr grow-out. Production variables: ﬁngerling start weight 50 g; cohort no. 50 000; cohort start 6-monthly; mortality 0.4%/month; water temperature 8–14°C. Data source: Bass 1998. (Continued.) Biomass per cohort (tonnes) Month

Cohort 1

1

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

3 4 6 8 10 13 17 21 26 31 36 42 50 59 69 74 79 76

2

Cohort 2

3 4 6 8 10 13 17 21 26 31 36 42

Cohort 3

3 4 6 8 10 13

Cohort 4

Cohort 5

Cohort 6

Cohort 1

5 6 12

Cohort 2

Cohort 3

All current cohorts (tonnes) Cohort 4

Biomass

Harvest

3 4 6 8 10 14 20 25 32 39 46 55 70 84 101 113 125 131

5 6 12

Production of Arctic Charr for the Consumer

Year

Harvest per cohort (tonnes)

195

196

(Continued.) Biomass per cohort (tonnes)

Year

3

Harvest per cohort (tonnes)

Month

Cohort 1

Cohort 2

Cohort 3

Cohort 4

19 20 21 22 23 24

65 42 23 11 5

50 59 69 74 79 76

17 21 26 31 36 42

3 4 6 8 10 13

65 42 23 11 5

50 59 69 74 79 76 65 42 23 11 5

17 21 26 31 36 42 50 59 69 74 79 76

25 26 27 28 29 30 31 32 33 34 35 36

Cohort 5

Cohort 6

Cohort 1 19 28 19 12 6 5

3 4 6 8 10 13 17 21 26 31 36 42

Cohort 2

Cohort 4

5 6 12 19 28 19 12 6 5

3 4 6 8 10 13

Cohort 3

All current cohorts (tonnes)

5 6 12 19 28 19 12 6 5

5 6 12

Biomass

Harvest

135 19 126 28 124 19 124 17 130 12 131 17 Total annual harvest 135 134 19 125 28 123 19 124 17 130 12 132 17 135 19 126 28 123 19 124 17 130 12 131 17 Total annual harvest 224

Arctic Charr Aquaculture

Table 8.2

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197

Of course this is a best-case model that is feasible, but may not be obtainable, particularly in terms of meeting production goals during the start-up phase. There are always problems in a start-up operation that cause delays in meeting production targets. For instance, it may be difﬁcult to access two cohorts of Arctic charr per year, as there are few hatcheries producing off-season eyed ova. Most brood hatcheries only produce eyed ova in the fall of each year. Water temperatures may not reach the desired levels, or design problems may slow the production process, pushing harvest times back by months. It may take four or ﬁve years to reach steady-state. This is not a serious problem as long as you have adequate working capital to see you through the initial start-up phase to full production. Be sure to warn investors and bankers of the potential for such delays, and work this possibility into the ﬁnancing agreement. To grow 200 tonnes/annum, a commercial operation would need a number of differentsized tanks to hold the various cohorts and sizes of Arctic charr. The tanks are sized to the ﬁsh, with ﬁngerlings in smaller tanks and on-growers in larger tanks. They are normally arranged in banks of similar-sized tanks in a layout, illustrated in Fig. 8.2, that makes it easy and less stressful to move the ﬁsh from tank to tank as they grow larger and approach harvest weight. A number of smaller harvest tanks are used for starving ﬁsh prior to slaughter.

Fig. 8.2 Layout of a land-based tank farm for a 200 tonnes/annum Arctic charr grow-out. Reprinted with permission: Bass 1988.

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Arctic Charr Aquaculture

Light manipulation and growth As discussed elsewhere, Arctic charr come from the High Arctic, where there is an extreme contrast between the light and dark cycles of winter and summer (refer to Fig. 3.10). Light duration and light intensity affect time of spawning, saltwater tolerance, and growth rates. If you can control light levels, there is merit in placing cultured charr on a daylight cycle that mimics their natural photoperiod. It also makes sense to create a shorter winter period, which will result in more growth cycles than naturally occur in a year. Arctic charr have an intrinsic six-month growth cycle that you should take advantage of in the grow-out routine, potentially reducing the time to market substantially. Whether you manipulate light levels or not, keep the following points in mind: Arctic charr in tanks in northern climates should be sheltered from direct light to prevent • sunburn and exposure stress. Mimic the northern light/dark cycle whenever possible. • Arctic charrnatural do not well to constant 24-hour light. Create daily dusk and dawn • periods of dim lightrespond when mimicking summer light conditions. Even in the high north

• •

there is a daily change in light intensity. Arctic charr grow most rapidly when day-length is rapidly increasing or decreasing, as occurs in northern climates. Their response to day-length may override their response to water temperature. If you are using artiﬁcial light/dark cycles, charr will react to lights being turned off or on abruptly by crowding to the bottom of tanks, possibly blocking drain screens and causing oxygen depletion. You can prevent this by staggering the on/off period, adjusting a few lights at a time to create a prolonged dawn/dusk, which they would experience in the wild. There are light controllers on the market that can mimic the dawn/dusk conditions and natural photoperiod for any latitude.

Feeding strategies The cost of feed represents about 45–55% of the direct costs in a grow-out operation. Controlling the amount of feed required to produce a quality Arctic charr is one of the most important aspects of the on-growing process. Chapter 4 discusses growth, nutrition, and feeding for all ages of Arctic charr, while this section describes methods for controlling the amount of feed fed and feed delivery techniques for Arctic charr larger than about 50 g. There are four main areas to consider: the ration size to approximate hunger levels; • Calculating Delivering the ration in the most efﬁcient manner; • Monitoring thedaily delivery of food to maximize growth and minimize food waste; • Monitoring condition factor, growth rate, and ﬁsh quality. •

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Ration size The hunger levels of the ﬁsh in each tank dictate the amount of feed consumed on a daily basis, and when the ﬁsh are in an active growth phase, water temperature and ﬁsh size are the two most important variables determining hunger. Table 8.3 presents an approximation of daily ration size as a percentage of body weight (%DR) for ﬁsh from 50 g to 2500 g, in water temperatures up to 14 °C. You can calculate the amount of feed needed by multiplying the daily ration size by the mean individual ﬁsh weight, and multiplying that amount by the number of ﬁsh in the tank. During an active growth phase, the ration level could be increased daily, but it is more practical to calculate new ration levels on a weekly basis. A simple calculation that incorporates initial ﬁsh size at the beginning of the week, ﬁnal ﬁsh size at the end of the week, the number of ﬁsh in the tank, and %DR can be used to update the daily ration level. The estimated ﬁsh size for setting each week’s daily ration is approximated using Iwama’s growth formula discussed in Chapter 4. Table 8.4 presents an example of the amount of feed for two tanks of ﬁsh with starting weights of 50 g and 1500 g. Table 8.3 Daily feed ration size for grow-out Arctic charr. Daily ration as % of ﬁsh body weight Fish weight (g) Water temperature (°C)

50 60 70 80 90 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000 2100 2200 2300 2400 2500

2

3

4

5

6

7

8

9

10

11

12

13

14

0.24 0.23 0.22 0.21 0.20 0.19 0.15 0.13 0.12 0.11 0.10 0.10 0.09 0.09 0.09 0.08 0.08 0.08 0.08 0.07 0.07 0.07 0.07 0.07 0.07 0.07 0.07 0.06 0.06 0.06

0.34 0.32 0.30 0.29 0.28 0.27 0.21 0.18 0.17 0.15 0.14 0.14 0.13 0.12 0.12 0.12 0.11 0.11 0.11 0.10 0.10 0.10 0.10 0.10 0.09 0.09 0.09 0.09 0.09 0.09

0.44 0.41 0.39 0.37 0.36 0.34 0.27 0.23 0.21 0.20 0.18 0.17 0.17 0.16 0.l5 0.15 0.14 0.14 0.14 0.13 0.13 0.13 0.13 0.12 0.12 0.12 0.12 0.12 0.11 0.11

0.54 0.50 0.48 0.46 0.44 0.42 0.33 0.29 0.26 0.24 0.23 0.21 0.20 0.20 0.19 0.18 0.18 0.17 0.17 0.16 0.16 0.16 0.15 0.15 0.15 0.15 0.14 0.14 0.14 0.14

0.63 0.59 0.56 0.54 0.52 0.50 0.39 0.34 0.31 0.28 0.27 0.25 0.24 0.23 0.22 0.22 0.21 0.20 0.20 0.19 0.19 0.19 0.18 0.18 0.17 0.17 0.17 0.17 0.16 0.16

0.73 0.69 0.65 0.62 0.60 0.57 0.45 0.39 0.35 0.33 0.31 0.29 0.28 0.27 0.26 0.25 0.24 0.23 0.23 0.22 0.22 0.21 0.21 0.21 0.20 0.20 0.20 0.19 0.19 0.19

0.83 0.78 0.74 0.70 0.67 0.65 0.51 0.44 0.40 0.37 0.35 0.33 0.31 0.30 0.29 0.28 0.27 0.27 0.26 0.25 0.25 0.24 0.24 0.23 0.23 0.22 0.22 0.22 0.21 0.21

0.93 0.87 0.82 0.79 0.75 0.73 0.57 0.50 0.45 0.41 0.39 0.37 0.35 0.34 0.33 0.31 0.31 0.30 0.29 0.28 0.28 0.27 0.27 0.26 0.26 0.25 0.25 0.24 0.24 0.24

1.02 0.96 0.91 0.87 0.83 0.80 0.63 0.55 0.50 0.46 0.43 0.41 0.39 0.37 0.36 0.35 0.34 0.33 0.32 0.31 0.31 0.30 0.29 0.29 0.28 0.28 0.27 0.27 0.27 0.26

1.12 1.05 1.00 0.95 0.91 0.88 0.69 0.60 0.54 0.50 0.47 0.45 0.43 0.41 0.39 0.38 0.37 0.36 0.35 0.34 0.33 0.33 0.32 0.31 0.31 0.30 0.30 0.29 0.29 0.29

1.22 1.14 1.08 1.03 0.99 0.96 0.75 0.65 0.59 0.55 0.51 0.49 0.46 0.44 0.43 0.41 0.40 0.39 0.38 0.37 0.36 0.36 0.35 0.34 0.34 0.33 0.33 0.32 0.32 0.31

1.32 1.23 1.17 1.12 1.07 1.03 0.81 0.70 0.64 0.59 0.55 0.52 0.50 0.48 0.46 0.45 0.43 0.42 0.41 0.40 0.39 0.38 0.38 0.37 0.36 0.36 0.35 0.35 0.34 0.34

1.41 1.33 1.26 1.20 1.15 1.11 0.87 0.76 0.68 0.63 0.59 0.56 0.54 0.52 0.50 0.48 0.47 0.45 0.44 0.43 0.42 0.41 0.40 0.40 0.39 0.38 0.38 0.37 0.37 0.36

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Table 8.4 Example of daily feed ration calculation for two lots of actively growing Arctic charr.

Lot 1 Starting weight (g) Total no. of ﬁsh Total ﬁsh weight (kg) Water temperature (°C) Daily feeding rate (%) Daily ration size (kg) Lot 2 Starting weight (g) Total no. of ﬁsh Total ﬁsh weight (kg) Water temperature (°C) Daily feeding rate (%) Daily ration size (kg)

Week 1

Week 2

Week 3

Week 4

50.0 10 000 500 14 1.41 7.05

54.3 10 000 543 14 1.41 7.66

59.1 10 000 634 14 1.41 8.94

64.1 10 000 684 14 1.41 9.64

1500.0 10 000 15 000 14 0.43 64.5

1532.8 10 000 15 328 14 0.43 65.9

1576.2 10 000 15 371 14 0.43 66.1

1620.4 10 000 15 415 14 0.43 66.3

In addition to ration size, you need to monitor the feed pellet size as the ﬁsh grow. At any given ﬁsh size there is an optimum pellet size that gives the best performance in terms of handling time, growth, and food conversion (Table 4.10). The feed pellet size must be appropriate for the smallest ﬁsh in the tank, or different feed sizes may be mixed together to accommodate the different-sized ﬁsh. It does no harm to keep ﬁsh on a smaller pellet size, but it means you must increase the number of meals to assure the larger ﬁsh get the increased number of pellets they need to meet their daily needs. It is not unusual for Arctic charr to spit out a larger-size feed pellet the ﬁrst time they get one. When ﬁsh are ready for a larger feed size, it is best to mix the new feed in with the smaller feed pellets for a few days until they have adapted to the larger feed. An alternative method is to starve the ﬁsh for a day or two before presenting an entirely new ration of the larger size. Hungry Arctic charr are less inclined to reject a new food.

Feed delivery Arctic charr show pronounced daily and yearly feeding patterns that must be accommodated in the daily feeding regime. On-growing Arctic charr appear to grow more uniformly and show better conversion rates if fed many meals throughout the day, but with most of the meals taken at dawn and dusk (Jobling & Wandsvik 1983a). Each meal should present the entire tank of ﬁsh with an opportunity to receive about 1–2% of the daily ration, as Arctic charr are rather slow feeders. This means between 50 and 100 meals a day, so in an 18-hour day the ﬁsh should be fed about every 10 minutes. The many meals required by on-growing Arctic charr make the use of automatic or demand feeders a preferred method of feeding, although hand-feeding works well if labor costs are low. The feeders must be able to deliver feed over the entire tank area and should be adjustable so you can vary the number of meals delivered at different times of day and the size of the meal delivered. Many commercial feeders and feed controllers meet these criteria. Feeding levels and feed delivery must match the natural cycle of Arctic charr feeding rhythms. A feed-monitoring system that assesses how much feed the ﬁsh are consuming will greatly assist in matching hunger level to feed fed throughout the day. Some monitoring sys-

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tems use an underwater sensor that monitors uneaten food and then regulates food delivery via computer-controlled feeding systems. Other sensors mounted in the wastewater system of each tank work in a similar fashion, with both systems able to discriminate feed from feces. Field trials done with Atlantic salmon in net-pens showed a 10–15% increase in growth, 5% improvement in food conversion, and less variation in size at harvest when feed monitors were used (Novotny & Pennell 1996). Where hand-feeding is used, underwater video cameras monitored by the ﬁsh feeder are effective for visually monitoring ration consumption. When ﬁsh pellets start passing the ﬁsh by, hand-feeding stops.

Diet The types of diets used for on-growing Arctic charr are discussed in Chapter 4, and Table 4.8 suggests a suitable diet. If specialty Arctic charr feeds are unavailable or are too costly, you can on-grow Arctic charr using Atlantic salmon diets. Rainbow trout diets are not recommended, particularly in the last six months before harvest. To a large extent, the taste and texture of Arctic charr are determined by its diet. Salmon diets, with their higher fat content, give Arctic charr a better taste and may affect texture as well. Arctic charr require higher pigment levels in the feed than other salmonids to attain a ﬂesh color acceptable to the consumer, so you should supply pigmented feed throughout the on-growing phase. Charr may have a dietary requirement for carotenoid pigments, such as astaxanthin, as well. They do lose color if taken off pigment for more than a month or two, which suggests they are metabolizing or excreting it from muscle/fat stores. Pigment is expensive, so use as little as possible. Astaxanthin may account for 15–20% of the total feed cost, though only 15% of ingested astaxanthin, at most, may be recovered in the muscle depending on dose and species of ﬁsh (Bjerkeng et al. 1997a). Increasing the level of dietary carotenoids in feed increases the concentration of pigment in the ﬂesh up to a point, but above 50 mg/kg the relative amount deposited in the ﬂesh decreases. In the last two months before harvest, you may need to increase pigment levels to 80 mg or 100 mg/kg of feed as a ﬁnishing diet to get acceptable color. Nutreco has come up with a new feed called VIC (for ‘visually improved color’) that enhances color by two points on the Roche scale (see below) after six to eight weeks of feeding if ﬁsh already have some minimum level of astaxanthin in their ﬂesh (Anon. 1999). (Note that it has not yet been tested with Arctic charr.) Monitor the amount of pigment in the ﬂesh to determine the value of adding more pigment to the feed. Fish lose a minimal amount of pigment when they are starved for a short period, but they should not be off pigment prior to starving for harvest (Nickell & Bromage 1997). It is important to monitor fat content, visual color, and chemical color before ﬁsh reach market weight. Testing these parameters requires destructive sampling of 5 to 10 ﬁsh per sample and must be carried out in a private laboratory specializing in food quality analysis. A sample known as the Norwegian Quality Cut (NQC), shown in Fig. 8.3, is taken from the same area of the midsection of each ﬁsh. Color and fat content vary at different places in the ﬁsh, so using the NQC allows a standard for comparison between different ﬁsh lots regardless of their origin. Visual color is measured by comparing a ﬁllet cut from the NQC area to a standardized color chart (the Roche scale), which deﬁnes a range of color by number from very pale orange

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Fig. 8.3 The Norwegian Quality Cut, sampling point for color and fat content.

(1) to dark red (8). The ﬁllet or steak is examined using a standardized color box (created by the International Standards Organization) containing a lighting source equivalent to natural bright daylight. Chemical color, which refers to the relationship between ﬂesh color and carotenoid pigment in the muscle, is measured by extracting pigment from a muscle sample, passing it through a high-performance liquid chromatograph, and using an ultraviolet spectrophotometer to calculate the pigment content (Willoughby 1999). It is expressed as milligrams of carotenoid pigment in the muscle per kilogram of ﬁsh. Fat levels are calculated by grinding up a sample of ﬂesh, chemically extracting fat, then measuring it as a percentage of body weight. You should start doing fat and color quality tests about six months prior to expected harvest, or at a standardized weight in each lot of ﬁsh, so that you have time to make changes in diet if color or fat levels need to be improved. Repeat the sampling three months later to determine if corrective action has brought fat and color levels to acceptable levels. Test the color and fat content of each batch of ﬁsh again at harvest and include it as marketing information for prospective buyers. In order to control feed cost, it is also important to monitor the relationship between feed fed and ﬁsh growth. Each lot of ﬁsh should be sampled on a regular basis, monthly or bimonthly, to assess actual length and body weight of the ﬁsh lot. Collect information on the amount of feed fed, the feeding method used, and the type of feed for the time period between weight samplings. With this data you can determine growth rate, variation in ﬁsh sizes, condition factor, and food conversion rates. Over time you will build up a picture that shows you the best feeding methods and feed types that work on your speciﬁc grow-out operation.

Sorting and other ﬁsh husbandry practices Arctic charr ﬁngerlings should arrive at the grow-out unit sorted into lots of similar-sized ﬁsh, but they may still require sorting a couple of times during the on-growing process. The best times to sort ﬁsh are in the early spring and late fall when water temperatures are low and growth rates are minimal. When the variation in ﬁsh size gets to the point where more than one feed pellet size is required, the ﬁsh should be sorted and split into two or three groups of similar size so that variation is minimized within each tank. Fish lots will also need to be split

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into new tanks as the ﬁsh density rises above acceptable levels. Depending on the harvest technique, you may need to sort Arctic charr near harvest to select ﬁsh suitable for market. Handling stresses ﬁsh and depresses feeding and growth for a number of days. When you must handle ﬁsh, take the following precautions to minimize the effects on ﬁsh growth and well-being: Arctic charr off feed for at least 24 hours before handling begins. • Take Pre-plan to minimize the length of time ﬁsh are handled. If equipment and work crews are • well prepared and organized, handling and sorting should ﬂow smoothly. Handle ﬁ sh with Work with slow, deliberate motions and scoop ﬁsh gently from the • water. Do not drop,care.throw, or heave ﬁsh about. Reduce light levels in the handling area or work in the early hours of morning or • evening. Do not handle ﬁsh in hot weather or when water temperature is above 10 °C. • Use • supplemental oxygen in areas where ﬁsh are crowded or in holding tanks. You will need various pieces of heavy machinery to move large ﬁsh in a grow-out operation (see Fig. 8.4). Brail nets, used for moving large numbers of ﬁsh from the tank and moving totes full of water, are extremely heavy and require an automated crane. When moving totes of ﬁsh to distant tanks or onto trucks for shipment to processing plants, you will need mechanical forklifts, able to lift tonnes. A wheeled tractor equipped with a jibe-boom and a set of forks is ideal for moving ﬁsh about the farm. More versatile is a rubber-tired backhoe with a frontend bucket, since it is easily modiﬁed to do all the heavy lifting of ﬁsh and digging, snow removal, etc., required on a grow-out operation. For the actual sorting you need large mechanical ﬁsh graders that can be adjusted to sort ﬁsh into at least three size grades. A number of North American and European manufacturers sell good-quality graders, either bar graders or belt graders. Bar graders are constructed of long parallel bars (2–4 m long) that get progressively farther apart at one end. The grader is on an incline, and the ﬁsh are loaded at the high end, where the bars are close together. They wiggle down the parallel bars until they fall through into a collecting bin mounted underneath the grader. There are no moving parts – gravity and a spray of water move the ﬁsh along. A belt grader has two parallel motorized belts that are spaced progressively further apart. The belts gently move the ﬁsh along until they fall between the belts into collecting bins. In both types of graders, the width of the collecting bins is adjustable, with movable cross boards that allow collection of ﬁsh of similar size. The individual bins have chutes that allow ﬁsh to be dumped into totes or pipelined directly into different tanks. The belt graders are more efﬁcient, grading ﬁsh rapidly, and they require less space as they are more compact, but they also need a power source to operate and demand more maintenance than the bar graders. Both types of graders require heavy equipment to move them about the tank farm, or alternatively, ﬁsh can be moved to them. The success of a ﬁsh sort depends on good organization and a well-set-out routine for moving ﬁsh from the tanks, through the grader, and back to the tanks. The ﬁsh are starved for 24–48 hours to minimize stress. You should weight-sample the ﬁsh lots a day before the sort to determine the new size grades required and to estimate the numbers of ﬁsh that will be in each new grade. This allows the allocation of tank space. It is most efﬁcient to grade all the

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Fig. 8.4 Types of equipment used for crowding and moving ﬁsh about a tank farm.

ﬁsh lots at the same time, with the new size grades made up of ﬁsh of similar size from each of the original lots. Combining ﬁsh lots this way re-sorts the ﬁsh into similar-sized ﬁsh and simpliﬁes tank allocations. The downside of mixing lots is potential disease transmission and a loss of information on which ﬁsh is from which parental stock. When ﬁsh are ready to be graded and moved, you need to crowd them together either by lowering the water level in the tank or by herding the ﬁsh into a small section of the tank using nets or movable ﬁsh crowders. A custom-built round purse seine net that ﬁts the outer diameter of the tank is an effective method for crowding, but only works in a tank without an

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internal standpipe. In-tank rigid crowders made of two connected, movable panels are also an effective way of crowding. Each panel is half the diameter of the tank and is hinged to the other, allowing the panels to be folded together with the crowded ﬁsh between them. The panels are constructed of light aluminum pipe spaced closely together. (You can also use crowders of this design to separate market-size ﬁsh from smaller ﬁsh when you are harvesting on a continuous basis. The aluminum pipes are spaced so as to allow all but market-sized ﬁsh to pass through.) Position the crowder in the tank in such a way that ﬁsh want to move through the crowder to a source of food or away from a bright light source. Once ﬁsh are crowded up, brail them from the tank or pump them out using a ﬁsh pump. The method of passing ﬁsh through the grader is similar to that described in Chapter 7 for grading hatchery ﬁsh. Again, it is important to move ﬁsh through the grading process slowly and calmly to maximize the grading efﬁciency and minimize stress and damage to the ﬁsh. The graded ﬁsh are moved and counted into their new tanks as rapidly as possible. Once the grading procedure is complete, each new grade of ﬁsh is weight-sampled to establish new mean weights and size distributions. This allows you to calculate the proper size of feed and ration size for each tank of ﬁsh.

Harvesting and processing Harvesting begins the live ﬁsh/dead ﬁsh divide, when your ﬁsh becomes a food product, a steak or a ﬁllet, something good to eat, but not a living creature anymore. This is the great paradox of on-growing ﬁsh: you work so hard to nurture the ﬁsh, to keep them alive and growing well, only to pass them on to death. Nevertheless, that death is as much a part of ongrowing as any other step in the commercial production of ﬁsh. The harvesting and processing of ﬁsh products require a different knowledge than that needed for growing ﬁsh and is tightly controlled to maintain quality, food safety, and a long shelf life. Each ﬁsh is handled many times, processed, graded, passed into the distribution chain, and moved to the consumer as fast as possible to maximize its inherent quality as food. It is important that the on-growing group understand that harvesting and often primary processing are their responsibility. They must get the ﬁsh into the distribution chain in quality condition, at the right size, taste, and texture. Never forget that the live Arctic charr grown in commercial operations become saleable, high-quality, premium-priced ﬁsh products.

Harvesting There are two basic approaches to harvesting Arctic charr. The one you use depends on the nature of the market being served. On one hand, all the ﬁsh can be harvested when they are, on average, at market weight (1.5–3 kg). Regardless of their individual size, they are harvested and sold into size categories all at once, thus freeing up an entire tank or lake at once. This technique is well-suited to ﬁsh destined for value-added products like smoked Arctic charr, where the raw product – in this case head-on, gutted Arctic charr – can be frozen and stored in bulk, then reprocessed later. The downside is that the smaller ﬁsh will fetch lower prices, and frozen ﬁsh may also receive a lower price than fresh.

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Alternatively, the largest ﬁsh are harvested on a weekly or monthly basis that meets the ongoing requirements of the customer. The market for this type of harvesting is a retailer or a restaurant that resells fresh Arctic charr. The method used for on-growing also inﬂuences the method of harvesting and the timing of the harvest. Arctic charr grown in lakes are best taken in a few large harvests because moving ﬁsh to and from the lakes is logistically difﬁcult and expensive. Aircraft or small trucks are often required to move equipment in and ﬁsh out, so the more ﬁsh hauled out in one trip, the lower the overall cost of harvesting. Weather, ice conditions, and access problems can all disrupt a harvesting schedule in a pothole lake, which also encourages making one harvest trip rather than several. Lake stocking is more suited to servicing a market that does not rely on a constant weekly supply of fresh ﬁsh. Fish in pothole lakes are harvested by net, and everything caught is processed as it is usually dead in the nets. It is difﬁcult to control the number of ﬁsh caught and the size of the catch. It is also harder to control the quality of ﬁsh from a pothole lake, so when quality is good, the tendency is to remove all the ﬁsh to maximize the overall quality. For example, Arctic charr harvested in late winter are generally softer, in poorer condition, and lower in fat than fall-harvested Arctic charr and will not command as high a price. The same ﬁsh in the fall will have a higher condition factor, higher fat content, ﬁrm ﬂesh, and a richer taste. In that case, you would want to take all the ﬁsh in the fall, even though some may not have reached the same peak as others. On the other hand, in some pothole lakes Arctic charr develop a slightly muddy ﬂavor by eating freshwater shrimp containing a chemical called geosmin, which is produced by a blue-green algae that is a problem in the summer and fall. Fish are not saleable in this condition, but by early winter, once they have been off feed for a few months, the charr will lose the muddy taste. There are many more harvest options when Arctic charr are reared in tanks, as the environment is controlled, the ﬁsh can be sorted to size without killing them, and the tank farm is usually located closer to services and the transportation infrastructure. What is required on a tank farm is careful design of the tank layout to accommodate different types of harvests. If ﬁsh are sold into the market on a continuous basis, you need a series of harvesting tanks separate from on-growing tanks (see Fig. 8.2). This allows for pre-harvest starving and minimizes the number of sorts required in the production tanks to remove Arctic charr of market size. Pre-harvest preparation Before you actually commence the harvest, two conditions must be met. One, the ﬁsh have been sampled and meet market expectations in ﬂesh quality, ﬁsh size, and the number of ﬁsh available. Two, there is a reasonable expectation of a sale at a price that is acceptable to the buyer and the seller. Once these conditions are met, the harvest can begin, following these steps: the number and size of ﬁsh needed and the timing of the harvest with the process• Discuss ing plant and the buyer. • Starve the ﬁsh for 7–14 days to clear food from the gut and ﬁrm up ﬂesh.

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harvesting equipment is in place and supplies such as ice and salt are stockpiled. • Ensure Arrange the logistics of transporting the harvest from the tank farm or pothole lake. Make • sure all participants understand the harvesting routine and timing of ﬁsh transport, that aircraft or trucks are in place, and that the processing plant is ready to receive ﬁsh. Harvesting ﬁsh from pothole lakes requires a lot of co-ordination as there are usually many trips with small loads of ﬁsh. Harvesting methods Gill-nets are the most efﬁcient and cheapest method of harvesting Arctic charr from lakes, though their efﬁciency depends on mesh size and location in the lake. For any given ﬁsh length over 28 cm and condition factor of 1.35, there is a mesh size most efﬁcient for capture (Donaldson & Devlin 1996). The mesh sizes suggested by Jensen are the best estimate for capturing Arctic charr (see Fig. 8.5). He noted that gill-nets used for brown trout, whiteﬁsh, and Arctic charr are comparable and that as condition factor increases at any given length, the optimum mesh size for capture also increases. By varying the mesh size, it is possible to do some selection of ﬁsh by weight and to allow ﬁsh too small for market to escape. The most efﬁcient harvesting may involve a series of different-sized nets that accommodate the different sizes of ﬁsh found in each lake. The location of gill-net sets will determine the number of Arctic charr captured. Charr generally shoal or school in lakes when actively feeding, and they may distribute themselves in different habitats, such as the shoreline, the deeper benthos area at the bottom of the lake, or in the open water zone. Often this distribution is affected by water depth and water temperature. Arctic charr will move away from warm surface waters above 16 °C on the long calm days of summer, and in the winter they may remain stationary for long periods of time (Aass 1984). Arctic charr often move parallel to shorelines, so prominent points are obvious places to locate nets. Fishing in the near bottom zone is also a proﬁtable way to catch Arctic charr.

Fig. 8.5 Best gill-net mesh size for selective capture of different-sized Arctic charr.

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All of the ﬁsh may be concentrated in a very narrow band at a certain depth because of a temperature or food gradient. Electronic ﬁsh ﬁnders and, over time, experience make it easier to ﬁnd ﬁsh. The longer ﬁsh are left trapped in a gill-net, the more their quality will deteriorate, so recover them from the nets as soon as possible. Leaving ﬁsh struggling in nets too long leads to unsightly net marks on the skin, which often bruise the underlying ﬂesh and will decrease the price you receive for the ﬁsh as the buyer will expect to be compensated for the reduced quality. Belly burn, where the digestive juices in the stomach start to break through the belly wall and dissolve the muscle, also increases as ﬁsh remain in the net. Ideally you want to remove the blood from the ﬁsh when the heart is still beating, as this allows proper bleeding out of the ﬁsh, so for best quality the ﬁsh should be removed from the net while still alive. This requires very short net sets of no longer than a couple of hours. Funnel traps constructed of netting over a light frame have a number of advantages over gill-nets. They catch ﬁsh alive, allowing you to selectively harvest ﬁsh by size. They make it possible for you to properly bleed stunned ﬁsh, and the overall condition of the ﬁsh is higher than that of net-caught Arctic charr. You can also catch and hold ﬁsh until you have enough to make a full load for transportation. The traps are very effective in Yukon pothole lakes even when not baited. The downside is that you may need 10–20 traps to efﬁciently harvest a lake, and they are difﬁcult to use during the winter when lakes are ice-covered.

Reaching sexual maturity before harvest In both intensive and lake on-growing operations, it is preferable to harvest ﬁsh before they reach sexual maturity. Maturation is accompanied by a slowing growth rate and increased mortality (particularly in males). Sexually mature ﬁsh are not marketable, as ﬂesh quality deteriorates, becoming softer and paler as fats and pigments are mobilized to the skin surface or incorporated into ova. Using late-maturing strains of Arctic charr, such as Nauyuk, is the easiest way to deal with the maturation problem, although under certain light conditions and feeding regimes they can mature at a smaller-than-preferred market size. One of the factors that induces sexual maturity is condition factor in the spring prior to spawning, so one method of preventing maturity is to take near-harvest-weight ﬁsh off feed in late winter and reduce body condition to less than 1. They can be placed back onto feed later in the spring. If ﬁsh do reach sexual maturity, take them completely off feed during the spawning period to reduce stress. They will not spawn if kept crowded in tanks, and they will naturally recover body shape and coloration once their sexual proclivities have passed. To speed up the recovery process, cover their tank to exclude all light for 10 days. It is hard to believe that a male Arctic charr – with its bulbous hooked kype, deep red color, and very thin body – will regain its round, fat, marketable shape, but it does. There is some debate over whether to hand-strip eggs out of mature females or leave them to be naturally reabsorbed. Hand-stripping is stressful for the ﬁsh, but removing the eggs reduces the time it takes the females to recover. Offer the ﬁsh plentiful feed once they have ﬁnished with spawning. It may take three months of feeding for matured ﬁsh to recover body condition to a level suitable for sale. At that point they should be sold as soon as possible, since their growth rates will never be as high as those of immature ﬁsh.

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Processing Fish are highly perishable and must be carefully handled, processed, and chilled as soon after capture as possible, as there is a continual and irreversible deterioration in quality as soon as they are taken. Rough handling will bruise ﬂesh, so never grab ﬁsh by the tail or throw them. The harvest and primary processing must take place quickly at low temperature. Above 4 °C, muscle tissue spoils rapidly. Increasing the body temperature of ﬁsh from zero to 5 °C doubles the rate of spoilage. Use lots of ice to keep ﬁsh temperature near zero. Processing a catch of ﬁsh in the hot afternoon sun may be enough to downgrade the entire lot of ﬁsh due to spoilage problems that lead to: of muscle tissue leading to texture loss; • softening off-ﬂ avor and off-odors in ﬂesh due to bacterial decomposition; • decomposition wall and separation of ﬂesh from the rib cage; • bacterial growthofonbelly skin leading to off-odors; and • a drastic shortening of shelf life in fresh and frozen products. • The best way to bleed a live ﬁsh is to stun it with a blow to the head, then cut a gill arch and place the ﬁsh into a tote of ice water to bleed out. Bleeding out is only effective if the ﬁsh is still alive, as the heart pumps the blood out of the muscle mass. Dead ﬁsh will not bleed out so they should be gutted immediately to slow down bacterial spoilage as much as possible. After they are bled, gut the ﬁsh and remove their gills, leaving the head on. Use a spoon to completely remove the dark red kidney, which lies along the backbone. Carefully wash the ﬁsh to remove traces of blood, gills, and viscera from the belly cavity and the skin surface. Once they are processed, transport the ﬁsh in insulated totes, in tubs full of slush ice, or individually packed in ﬂake ice. If you are using ﬂake ice, place each gutted ﬁsh on its side (this allows melting ice water to drain away from the ﬁsh), with ice packed into the belly cavity and between layers of ﬁsh. The transportation containers must be waterproof and insulated, but there should be a plugged outlet for draining melt water. When the ﬁsh arrive at a registered ﬁsh-processing plant, they are graded for size and quality, cleaned up, then repackaged for delivery to the next step in the distribution chain. Although the harvest and processing of Arctic charr may be the end of the grow-out process, the marketing of ﬁsh, the economics of raising ﬁsh, and the business of managing the grow-out are a big part of the picture. These are covered in the next two chapters.

Chapter 9

Marketing and Market Economics

Marketing Arctic charr Wild Arctic charr has always been marketed as an exclusive product, even back in the days of the Windermere potted charr craze. Cultured Arctic charr must also enter the market as an exclusive product. Within the established distribution chain for ﬁsh products, however, it is easy to categorize charr as just another salmon, positioned with Atlantic salmon and rainbow trout. Producers must take care to market Arctic charr outside the salmon and trout channels, with other exclusive food products like trufﬂes and organically grown spring lamb. Up until about 12 years ago, Atlantic salmon was the top ﬁsh in terms of quality and uniqueness, only served in the ﬁnest restaurants. With production volumes now approaching a million tonnes a year, though, it has become a commodity and is now sold on the basis of price alone, like other commodity products such as grain and cattle. Rainbow trout never had the exclusive stamp of Atlantic salmon and was always priced lower. One of the dangers of selling small, poorly pigmented Arctic charr is that this inferior ﬁsh will cause all charr to be deﬁned as just another trout product, unable to sustain a price higher than trout, which like salmon is sold on a commodity basis, where price is more important than quality. People in Scandinavia and Canada, where Arctic charr is more familiar, rate the ﬂavor and texture superior to Atlantic salmon. Charr tastes smoother and milder and has a lower fat content than farmed Atlantic salmon. In professional taste tests and consumer surveys from restaurants, Arctic charr scores higher than salmon (Richardsen 1991). Consumer surveys performed in Canada indicate that Arctic charr is not seen as a replacement product for rainbow trout and is only a minor substitute product for salmon. Most respondents consider Arctic charr to occupy a special niche, separate from salmon or trout (Smith 1989). Arctic charr must be marketed as a proﬁtable entrée for the white-tablecloth establishments. Many chefs worldwide already perceive Arctic charr as a delicacy enjoyed by connoisseurs of salmon, as a high-quality ﬁsh from the cold clean waters of the High Arctic. This is the image that must be cultivated, but to be an exclusive product, Arctic charr must have characteristics that distinguish it as such: in appearance, freshness, and taste; • quality high price; • deliberate and purposeful marketing strategy; • specialized distribution channels (Richardsen 1991). •

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Quality in Arctic charr products A Norwegian marketing expert said that quality is, and will be, the key word in marketing Arctic charr products. Quality is a difﬁcult concept to measure or deﬁne because it is subjective and covers a range of characteristics. When you buy a salmon in a store, you measure quality in terms of appearance, freshness, and, after purchase, by the taste, texture, and ultimately the enjoyment of the meal. Quality is also measured by the price paid and the image that the product projects in the buyer’s mind. The experience of a ﬁne meal of Arctic charr is enhanced by images of eating a ﬁsh from the Arctic, grown in a pristine environment. Over 80% of consumers name freshness and taste as the main criteria in judging ﬁsh quality (Richardsen 1991). These characteristics are affected by the action of bacteria as the ﬁsh ages. Depending on how warm the ﬁsh gets, and how well it is processed and handled, a fresh ﬁsh may lose its freshness and taste quality in a few days, as illustrated in Fig. 9.1. This is why careful, efﬁcient processing and storage at the right temperature is so important when the end product is fresh ﬁsh. Freshness and taste in Arctic charr can be judged in three ways. Its inherent quality, which is the best quality the product will have, occurs just after it has been harvested and has left rigor. If the live ﬁsh is stressed, in poor condition, low in fat, or not starved properly before harvest, then nothing you do in later handling of the product will disguise that fact. The ﬁsh will never be in better quality – from this time onwards, freshness and taste of ﬁsh products only deteriorates. Processed quality refers to the condition of the ﬁsh after it has been cleaned, graded, and boxed in the processing plant. At this point quality is affected by: well the ﬁsh is starved, bled, cleaned, and washed; • how whether was processed in a timely manner on a ﬁrst-in, ﬁrst-processed basis; • how wellittemperature is controlled through icing and chilling the ﬁsh; • how well the ﬁsh is graded quality; and • how well it is packaged andforstored. •

Fig. 9.1 The effect of temperature on ﬁsh quality after processing.

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Arctic Charr Aquaculture

The ﬁnal measure of quality is presentation quality, which refers to how fresh the ﬁsh appears and tastes when the consumer eats it. Perhaps the most important measure, this is in the hands of the chef preparing the meal or of the manufacturer of value-added products, but the ﬁnal level of quality experienced by the consumer will only be as good as the product received from the producer. The producer must supply the highest-quality products to ensure the consumer receives the same. There is a set of measurable criteria that allow ﬁsh to be graded into groups of similar standards. These standards are based on the size of the dressed ﬁsh with head on, the ﬁsh freshness, and body attributes after primary processing. There are no grading standards set speciﬁcally for Arctic charr, so in Table 9.1 I have adapted standards for farmed Atlantic and Paciﬁc salmon. The size standards of Arctic charr are presented in increments of pounds (in the North American marketplace, ﬁsh are grown in kilograms but sold in pounds) and closely follow those size ranges used for sockeye salmon, a ﬁsh of similar size and quality.

Product forms best suited for Arctic charr The primary product form supplied by the producer is fresh, whole, head-on, gutted ﬁsh. The producer ships this on ice to the ﬁrst receiver, usually in standard-sized Styrofoam boxes. At this point the ﬁsh may continue down the distribution chain to the consumer as a whole ﬁsh, or it may become value-added products, such as ﬁllets, portions, steaks, or sliced, smoked, cured, or pickled Arctic charr. The slightly lower fat content of charr compared to Atlantic salmon, and the ﬁne grain of its ﬂesh, make Arctic charr suitable for all known methods of preparation used for salmon or trout (Heggberget et al. 1994), and value-added Arctic charr products have always received good consumer response. For example, large and mediumsized Arctic charr can be cold-smoked or hot-smoked. Hot-smoked charr and gravid lax sell well in Sweden, but there is not a tradition for cold smoke there. In North America, coldsmoked wild Arctic charr is popular in major eastern cites like New York, Montreal, Toronto, and Boston. The raw material is purchased frozen and locally smoked. The preferred market size for selling whole or producing value-added products is 4–6 pounds (1.8–2.7 kg), a medium-sized ﬁsh, as this offers the greatest range of use. It is large enough for cooking whole, for the production of smoked sides, or for smaller, portion-sized ﬁllets and steaks. Small Arctic charr (2–4 pounds; 0.9–1.8 kg) are saleable but less versatile. The market for charr under 2 pounds (known as pan-sized) is limited, and end-users often confuse charr of this size with trout. In the eyes of ﬁsh buyers, Arctic charr must be at least 2 pounds before it is considered a salmon and receives the price it deserves. In all sizes of Arctic charr, the end-user prefers a darker ﬂeshed ﬁsh colored orange-red or red. Pan-sized Arctic charr have paler ﬂesh than larger ﬁsh, which further reinforces the view that they are just another trout. One of the major challenges in marketing fresh Arctic charr is the problem of skin slime. Fresh Arctic charr displayed whole on ice in ﬁsh shops and at grocery store counters have not been a top seller because of excess slime on the skin, which discolors rapidly, giving the outer body the appearance of a tired old ﬁsh even though it is fresh inside. Slime-removal methods that have worked on other species do not work with Arctic charr. Saltwater immersion actually tends to increase the production of slime, while vinegar baths merely turn the slime opaque, further complicating the problem. The only method that has worked to date is

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Table 9.1 Quality standards for processed Arctic charr. Format source: B.C. Salmon Growers. Characteristics

Grades Premium

Standard

Utility

Some dulling of color. Traces of red on sides, dark bronze on belly may be present Slight scale loss acceptable (< 15%), but must be uniformly distributed Too fat bellies acceptable 1.2 > K > 1.0 Damaged, abraded, or naked ﬁn rays without soft tissue acceptable Clear

Obvious signs of maturation including orange dark belly and red sides

External surfaces Color/sexual maturity White belly, silver sides, or light bronze sides, to dark dorsal surface Scale loss

No scale loss or scarring

Body contour Fins

No signs of sexual maturity. K > 1.2 No damaged ﬁns accepted

Slime

Clear

Eyes

Convex eye; black pupil and clear (not clouded) cornea External surface Firm and elastic – ﬁnger does not leave impression when depressed Cuts, scars, punctures None permitted

Clear eyes but slight damage accepted Finger’s impression recovers slowly when ﬂesh depressed Minimal clean knife cuts or small bites and scrapes acceptable

Moderate to extensive, but skin is intact. Obvious scarring Deformities or ‘pinheads’ acceptable. K < 1.0 Extensive damage to ﬁns acceptable Can be somewhat dull or cloudy Sunken, concave eye and extensive damage accepted May be soft; ﬁnger impressions retained longer Limited number of clean cuts, punctures and scars permitted

Belly cavity Bled

Flesh color

Well-bled ﬁsh although small pin veins may not be completely drained Orange/red coloring obtained with no bleaching and uniformly distributed. > 5 on Roche scale

Gut condition

No belly burn, no blush, lining intact, no knife cuts or tears

Bruising and hemorrhage

No bruises permitted

Cleaning

Thorough; no traces of blood or kidney Fresh, no abnormal odor

Odor Flesh texture

May be incompletely bled, May be incompletely bled with traces of full blood vessels in belly cavity Basic level of pink-red coloring obtained, although may be varying in intensity. < 5 on Roche scale No belly burn but some blushing acceptable; clean cuts and tears up to 2.5 cm; no protruding ribs < 3 small bruises/ hemorrhages permitted in body cavity wall Thorough; no traces of blood or kidney Fresh, no abnormal odor

Firm and resilient; no separation in belly

Impression may remain when ﬂesh depressed; no ﬂesh separation

Large Medium Small Pan-size

6+ lb 4–6 lb 2–4 lb < 2 lb

Color weaker than normal, bleaching or whitened ﬂesh allowed Up to moderate belly burn allowed; up to 25% of lining may be broken; clean cuts and tears up to 5 cm; some ribs protruding > 3 bruises are permitted

Thorough; no traces of blood or kidney May be slightly oily or yeasty, but no strong off-odors May be soft, with limited ﬂesh separation

Size grades (head-on gutted)

2.7+ kg 1.8–2.7 kg 0.9–1.8 kg < 0.9 kg

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layering the ﬁsh in ﬂake ice overnight after slaughter, then removing the slime with a soft brush designed for washing cars (one that has water pouring out of the brush bristles) before packaging. Until this problem can be resolved, the best approach is customer education: Buyers need to know that slime production is a biological process that only stops when the ﬁsh is past its prime, and a slimy ﬁsh has perfectly fresh ﬂesh on the inside. In any grow-out operation, no matter how focussed on shipping quality fresh ﬁsh, there will be excess ﬁsh that do not meet the high quality expectations of the marketplace. These lower-quality or undersized ﬁsh can be processed in one of two ways. You can send them, fresh, into an alternative market at a lower price. This should not affect the high-priced superior product as it is differentiated by a lower quality and lower price. Alternatively, you can blast-freeze excess ﬁsh, although this process adds additional cost to the freezing and packaging process and will likely never be earned back from the buyer. The name of the game in most salmonid markets is fresh, and, traditionally, frozen wild Arctic charr has the appearance of a commodity product offered at gourmet prices – it does not sell well, has variable ﬂesh color, and in some markets sells for 20% below fresh prices (Eriksson 1991). Arctic charr are similar in size and quality to sockeye salmon, which are currently used in high-end smoked products, so this may be a market for frozen Arctic charr, particularly in Japan. Arctic charr grown in pothole lakes can be harvested in large batches, then frozen for the production of this type of value-added product. Great care must be taken that Arctic charr are frozen rapidly and under controlled conditions to maximize quality. Another promising format is well-trimmed, blast-frozen, vacuum-packaged ﬁllets, ﬁllet portions, or steaks, attractively presented and ready for the gourmet retail shelf or the food service trade. These give Arctic charr a presentation that traditional freezing does not. Average head-on (Hd/on) yields are 88% of whole ﬁsh weight, and average yield after ﬁlleting is 60% of the Hd/on weight. Arctic charr lends itself to machine ﬁlleting due to its body form and skin texture (Eriksson 1991). In addition, freezing in this manner affords a slightly longer shelf life (weeks instead of days) and gives the producer the opportunity to brand name the product. Afﬁxing a label (branding) with ingredients, food serving suggestions, and the producer’s name is an effective way to create a brand identity in the hotel, restaurant and institutional (HRI) market and to receive a premium price for a product that is perceived to have premium quality.

Price of Arctic charr products Arctic charr over 2 pounds (900 g), either farmed or wild, usually command a higher price than other salmonids. The farm gate price (the price paid by the ﬁrst receiver) for Arctic charr in North America is two to four times the price of Atlantic salmon, and over the past 10 years the wholesale price of Arctic charr has remained high in Europe and North America, despite a decline in the price of Atlantic salmon and trout (see Table 9.2). Some traditional ﬁsh traders view this high price as a deterrent to greater sales of Arctic charr, but for the consumer it may well signal high quality, as the high price suggests that Arctic charr is near the top among the exclusive food items. Arctic charr is best targeted at the upper end of the HRI segment of the market, particularly the white-tablecloth restaurant trade, where price sensitivity is lower than in other segments of the market. A representative of a major grocery chain in Canada suggested that any new

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Table 9.2 Wholesale prices of cultured Arctic charr. Data source: Robbins et al. 1990. Strain

Year

Wholesale price (US$/kg)

Fish weight (g)

Price (US$/kg)

European

1994 1995 1996 1997 2001 2001

9.99 9.75 9.89 12.22 9.00 8.90

200–400 400–700 700–1000 1000–2000 2000+

4.41 8.87 9.07 9.51 9.86

Norwegian Canadian

seafood product must ﬁrst make its name in the food service sector before it becomes proﬁtable for the retail sector to carry it (Hall & Collison 1991). In Canada and the United States, 75–80% of the Arctic charr sold goes to upper end restaurants, with the remainder sold in specialty ﬁsh stores and gourmet retail outlets. The size of Arctic charr entering the market affects the image of quality and thus the price that can be attained. In Sweden, prices for all charr have fallen when large volumes of pansize Arctic charr were in the market (Heggberget et al. 1994). The market will absorb a certain volume of pan-size charr at a high price, but a high price is unsustainable at anything but small volumes. Arctic charr producers must stop producing pan-size ﬁsh if they are to maintain the quality image and high price Arctic charr has earned on the world market. Pan-size Arctic charr are expensive to produce (see the section below on market economics) and command a lower price than larger ﬁsh (as indicated in Table 9.2), so it makes more sense to grow larger Arctic charr such as the Nauyuk strain. Another primary marketing requirement when selling Arctic charr at a high price is the color of the ﬂesh. Chefs consider color one of the most important criteria for distinguishing salmon from trout. Consumer panels view farmed salmon that lack salmon color as little more than trout, and the perception is no different for Arctic charr (Metusalach et al. 1996b). It is difﬁcult, if not impossible, to pigment Arctic charr smaller than about 500 g, and some strains of Arctic charr color poorly at any size. Again, using strains that have an orange-red ﬂesh color will alleviate this concern. In recent years consumers have become concerned about foods that contain chemical and antibiotic residues. They perceive products with no additives and no medicines to be of superior quality. A certain segment of the market also attributes quality to products that are grown organically, and they are willing to pay a premium price for these products. It is feasible to produce organic Arctic charr given the ability of these ﬁsh to grow well at low density in lakes and under intensive culture conditions without the use of antibiotics. There are a few organically certiﬁed producers of Arctic charr in Europe, and they are doing well both ﬁnancially and biologically. Arctic charr raised under organic conditions in hatcheries without antibiotics, then grown-out in pothole lakes on natural feeds could exceed the standards of agencies certifying organic products.

Marketing strategies Arctic charr is just beginning to be known in North America and Europe and is virtually unknown in the rest of the world. The Canadian government traditionally serves Arctic charr to visiting heads of state and royalty, and many of the ﬁner restaurants in the major cities list

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Arctic charr on their menus. Despite its appeal in Canada, however, there is no comprehensive, unifying marketing strategy to help ensure or promote the position of Arctic charr as a Canadian specialty item. This is also the case in other countries growing Arctic charr. Arctic charr is best marketed by bringing attention to its quality attributes and not by positioning it as part of the salmon/trout complex. Arctic charr is a niche species and should be aimed at the very top end of the market, complementing and competing with caviar, roe-onkelp, and rarer ﬁsh such as orange roughy and fresh tuna. The Norwegians have said it best: ‘Charr must have an exclusive proﬁle, exclusive presentation and marketing. The packaging, brand names, and advertising signal and emphasize exclusivity’ (Heggberget et al. 1994). Raising the proﬁle of Arctic charr will require building upon the good reputation the ﬁsh already enjoys. Educating chefs who manage the white-tablecloth restaurants and the ﬁner catering services is an obvious way to position Arctic charr as an exclusive, superior product worth placing on their menu. If these people are convinced of the proﬁtability and desirability of Arctic charr, slow and steady growth in sales volume will follow. Coupled with brand identiﬁcation, this is an effective way of developing a reliable market for the product. Promotional emphasis should be placed on the following points: is the new, exclusive salmonid, something different but not too different. • This Arctic charr is an exclusive food from the cold waters of the High Arctic. • It is a premium product at premium prices. • To fulﬁll the promise made in the promotion, producers should make every effort to: sell large, orange-red-ﬂeshed Arctic charr; • sell smaller Arctic charr to existing niche markets that want small ﬁsh, but without expand• ing the volume of this ﬁsh size too much for fear that Arctic charr will become confused

• •

with trout; target the high-end hotel, restaurant, and catering segment of the market; and focus marketing effort on end-users (chefs, food buyers) and their customers by attending food shows open to the public.

Promotion is expensive, and it may be cost-effective for growers to form trading associations or co-operatives so they can afford the level of promotion required to bring Arctic charr to the attention of consumers. A co-ordinated market approach involving all Arctic char producers within a marketing region would help produce the materials and proﬁle needed to educate people about Arctic charr. A professional association of this kind could also assist in controlling ﬂuctuations in supply and quality of ﬁsh and providing growers with support and professional development. An international organization made up of regional and national growers associations could act as an overall co-ordination group for setting standards, creating a common product proﬁle, monitoring production, and assisting in the dissemination of growing and marketing techniques for Arctic charr.

Distribution channels In the normal food distribution channels, the producer sells whole ﬁsh to the primary proces-

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sor, who then sells to either the value-added processor or the wholesaler. The product is then either reprocessed into a value-added product or is sold as it is to the regional distributor, who delivers it to four types of establishments in the HRI trade for presentation and sale to the end-user (see Fig. 9.2). The ﬁrst step in the distribution of fresh Arctic charr can be sale to a primary processor or can take the form of ‘custom processing.’ In the ﬁrst case the grower loses control of his product as it is purchased by a second party. The grower accepts the price the processor offers, and the processor, in turn, sells the ﬁsh and makes a proﬁt. In custom processing, the grower does not lose ownership of the product and is responsible for selling his or her own product. The grower pays the processing plant for the services of dressing and boxing the ﬁsh. If your objective is to do your own marketing, but capital is short for the construction of your own processing facility, custom processing is the way to proceed. The next stage is the wholesaler or secondary processing stage. This is when the ﬁsh is held for distribution or delivered to ﬁsh-processing plants for value-added processing. It is a good idea at this stage to have the product branded with the producer’s logo. A quality product reinforced by a distinctive label will catch the eye of the buyer and will return the investment in the form of orders. In a soft market it is usually the high-quality branded producers who get the business before the price falls. The ﬁnal stage of the distribution channel is the end-user. This includes the chef as well as his customer in the restaurant. Both must be satisﬁed if the product is to be successful. Arctic charr is best marketed and sold through selected distributors that supply the top-end

Fig. 9.2 Market distribution channels for Arctic charr.

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restaurant, hotel, and catering segment of the market with high-quality products. These distributors must understand quality ﬁsh products, but more importantly, they must understand they are selling Arctic charr, a unique, exclusive product originating from the High Arctic that happens to be a ﬁsh. At the same time, producers must understand their product is aimed at a food service sector that demands: supply in volume and time, • aa reliable stable price, • consistent product quality and consistent sizes, and • year-round availability of fresh product (Hall & Collison 1991). • Upscale restaurants, for example, have expensively printed menus and they do not want to reprint them frequently, which means that reliability of supply and stability in price are important in their product-buying decisions (Smith 1989). It is difﬁcult for a single producer to meet market expectations unless they develop a production model and marketing plan that can predict when and in what quantities Arctic charr will be available from the operation. Even then, the ﬁsh may not reach market weights at preferred times because of weatherrelated changes or some other problem that delays growth or decreases production levels. This is a concern to ﬁsh buyers, particularly those dealing with the HRI, which requires fresh ﬁsh on a regular basis. One way to alleviate concerns about continuity of supply is to work as part of a cooperative or growers’ group that can collectively meet commitments for fresh ﬁsh in the right sizes and at the right time. A number of Arctic charr buyers have cited the uncertainty of a constant supply when dealing with just one producer as a reason for not buying Arctic charr products. Producers may be able to sell their Arctic charr directly to local niche markets in whitetablecloth restaurants and specialty ﬁsh shops. One Arctic charr producer in the Yukon is selling all of its production as vacuum-packed smoked product to local buyers and through an internet website. However, as production increases on a regional level, trade customers, such as wholesalers and value-added processors, will be required to handle marketing and distribution of Arctic charr. Another Yukon producer is already selling to larger ﬁsh distributors that have contacts with the HRI trade in southern Canada and the United States. Often producers think they have lost control of their product when it is sold to the distributor, but there are steps you can take to insure that your product is represented the way you want in the market. Taking time to visit the end-user with a sales representative of the distribution ﬁrm is a good way to get an idea of how the product is represented. Sales representatives of distribution companies are only too glad to have an expert along with them while they are making their sales calls. Participating in food shows with a regional distributor is another way of getting the brand known, as well as obtaining valuable information from the end-user of your product. If you are working with a distributor, do not succumb to a chef’s requests to sell direct. Delivering directly to restaurants is a poor strategy as it will limit sales and isolate an important customer, the distributor. They are in a competitive industry and can deliver your product far less expensively than you can. Leave them to their business of distribution and concentrate on producing a high-quality product.

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In summary, the success of the Arctic charr producer is in large part dictated by meeting the needs of the consumer. At no time should the producer forget that the marketplace and, ultimately, the end-user are the starting points for commercial success. The entire grow-out operation must therefore be geared to the market needs of the consumer. work from the market back to production. A marketing plan combined with a • Always production plan must be in place before growing starts. This means having a reasonable

• • •

picture of what you can sell before placing ﬁsh in the water. Always schedule harvesting and delivery of Arctic charr products for the convenience of the customer. This may be as simple as letting customers know well in advance when ﬁsh are scheduled for harvest. Produce the sizes, color, and texture of Arctic charr wanted by the consumer. Do not surprise customers with a different product and expect them to take it. Maintain quality control of your ﬁsh through to the consumer, even when selling to a primary processor. The processed quality of your Arctic charr upon delivery to the enduser is your reputation in the Arctic charr marketplace.

Market economics of raising Arctic charr There are economic variables involved in growing Arctic charr that inﬂuence both proﬁtability and market acceptance. For example, the harvest size of Arctic charr has a profound effect on cost of production and on acceptance by the consumer. Grow-out density also affects proﬁtability. Although market prices are set by forces beyond the direct control of the producer, you can make your operation more or less proﬁtable by understanding the economic factors of raising Arctic charr. In this section I use an economic model to illustrate the effect different variables have on proﬁtability. This model is based on the sale price of processed Arctic charr, the capital costs associated with building, managing, and overseeing a landbased tank farm, and the variable costs associated with growing the ﬁsh, all costs as at year 2000.

Capital costs Capital costs include all the costs associated with construction and equipment purchase for containing the ﬁsh (tanks, bag-pens, or net-pens), for supplying and monitoring water ﬂows (pumps, pipelines, valves, alarms, backup systems, etc.), for supplying and monitoring oxygen, for remediation of water quality after it passes through the tanks, and for all the ancillary equipment needed to move and manage live ﬁsh inventory (ﬁsh graders, ﬁsh pumps, weighing equipment, feed storage, etc.). The costs of constructing ofﬁce space and on-site employee housing are also signiﬁcant capital costs associated with an on-growing operation. Costs for capital construction of ﬁsh holding space vary considerably depending on the type of facility built (see Table 9.3). An Arctic charr tank farm constructed on land in Canada costs about $1000 to $1200/m3 of holding space (exclusive of land cost). Contained bag-pens that ﬂoat in the water cost about $185/m3, and a standard salmon net-pen about $41/m3. Based on these costs, the capital required to build a 2000 m3 Arctic charr grow-out facility would

220

Table 9.3

Arctic Charr Aquaculture

Relative capital cost of constructing different types of grow-out facilities for Arctic charr, year 2000.

3

Holding space (m ) Capital cost ($/m2) Total cost ($1000/2000 m3) Fish density (kg/m3) Fish standing biomass (kg × 103)

Land-based tanks

Floating bag pens

Conventional net pens

2000 1200 2400 90 180

2000 185 370 90 180

2000 41 82 30 60

vary from $42 000 for a net-pen to $2 400 000 for a land-based tank farm. The capital cost for a land-based facility is very high, but as you will see later, the return on capital is very good because of the high loading densities possible with Arctic charr. The cost of a conventional net-pen is presented only as a comparison, as using net-pens for Arctic charr is unrealistic for reasons previously discussed.

Fixed operating costs Fixed operating costs are annually recurring expenses that are not directly attributable to the cost of growing ﬁsh. These general and administrative costs do not change appreciably regardless of how many ﬁsh are grown, and include such items as permits and licenses, general insurance, legal and accounting, and ofﬁce overhead. The costs of monitoring and testing water quality, preparing annual reports for various government licensing/regulatory agencies, and analyzing ﬁsh and feed quality are other types of common ﬁxed operating costs associated with an Arctic charr grow-out operation. Fixed operating costs also include some labor costs, speciﬁcally the personnel required to manage the general operation of the business that is not directly related to care and management of the ﬁsh.

Variable operating costs Costs directly associated with the production of one unit of ﬁsh are variable costs. That means these costs vary proportionately as the volume of ﬁsh produced increases. If production of ﬁsh were to double, then the total variable costs would also double. Variable costs represent the greatest proportion of the total annual operating costs. In all grow-out operations, the three major categories of variable costs are: cost of acquiring ﬁngerlings or smolts; • the the of feed; and • the cost cost of labor for feeding and managing ﬁsh. • The ﬁrst two are directly related to the number of ﬁsh produced. If you increase the number of ﬁsh grown by any amount, the total cost of acquiring ﬁngerlings and feed will increase proportionately. Labor is a step variable cost. For example, an employee can only manage the care of so many ﬁsh – say 40 tonnes – before another employee is needed, and a third employee is not needed until production exceeds another 40-tonne threshold. Depending on the type of grow-out operation, there will be other variable costs associated with pumping water, oxygenating water, running ﬁltration systems, and, in certain operations, ﬁsh stock

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insurance. These other costs may be signiﬁcant, but will still be less than any of the major costs for ﬁngerlings, feed, and labor and are not included in the basic discussion of variable costs. Feed is the major contributor to total production costs in salmonid grow-out operations, averaging 58% for Atlantic salmon and 64% for Arctic charr (see Table 9.4). Labor and ﬁngerling purchase costs are similar to one another in Arctic charr production, but the contribution of smolt purchase is higher than labor in Atlantic salmon culture. The three components that affect the feed cost are the cost of purchasing the feed, transportation, and the conversion rate of feed to ﬂesh. In the ﬁnal analysis, the feed cost per kg of processed Arctic charr is the economic conversion rate (total feed bill/total kg of charr produced). As the conversion rate goes up, the feed component of the average cost rises signiﬁcantly, as shown in Fig. 9.3. Fingerling contribution to the cost of production is affected by three variables – the purchase cost of the ﬁngerlings from a hatchery, the percentage of ﬁngerlings that survive to harvest (the recovery), and the size at which the ﬁsh are harvested. The cost of ﬁngerlings per kg of harvested ﬁsh is calculated using this equation: (Fingerling purchase price/% recovery)/average harvest weight Arctic charr ﬁngerlings cost less to purchase than Atlantic salmon smolts because they do not have to wait for smolting and can therefore be placed in grow-out tanks at a smaller size. However, the strains of Arctic charr currently available for commercial production require Table 9.4 Relative contribution of feed, ﬁngerlings, and labor to the cost of production in Arctic charr and Atlantic salmon, year 2000. Variable costs

Fingerling or smolt purchase Feed cost Labor cost

Arctic charr

Atlantic salmon

Cost ($/kg of ﬁsh produced)

% of total

Cost ($/kg of ﬁsh produced)

% of total

0.19 0.71 0.19

18 64 18

0.26 0.59 0.18

25 58 17

Fig. 9.3 Effect of food conversion rates on the relative cost of feed.

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Arctic Charr Aquaculture

culling the smallest ﬁsh, often representing a recovery of only 70–80% of the ﬁngerlings initially stocked. The mean size of ﬁsh at harvest has a dramatic effect on the cost of ﬁngerlings, and Fig. 9.4 makes it clear why harvesting ﬁsh at a small size is so expensive. Although labor has many of the attributes of a ﬁxed cost, it is represented on the ﬁnancial statements as a variable cost because it increases when production levels exceed a certain threshold. People are also hired during speciﬁc activities, such as grading and harvesting, on a short-term basis. Although its value is difﬁcult to quantify, a well-motivated, well-trained work force that understands the principle of productivity is fundamental to a well-run growout operation.

Proﬁtability and contribution margin Over the past 15 years there has been a raging debate about the proﬁtability of raising salmonids in contained systems (tanks or ﬂoating bag-pens). Proﬁtability has been marginal for Atlantic salmon and large rainbow trout when grown in contained systems (Willoughby 1999), but Arctic charr have one biological attribute that makes them well-suited for intensive culture in tanks: they grow best at stocking densities much higher than imaginable with other salmonids. In order to show the effect of stocking density (ﬁsh/m3)and other variables on proﬁtability, it is useful to view it from a marginal contribution perspective. Simply put, the contribution margin indicates proﬁtability on a per unit basis. It is the net revenue of ﬁsh sold, minus the variable costs of production per kg of ﬁsh sold. It does not consider the ﬁxed costs of a growout; instead it concentrates on the costs that vary per kg of ﬁsh sold. Proﬁt is expressed in terms of dollars per m3 of grow-out space, and return on capital as a percentage of the capital value (on a per m3 basis). Both relate back to the central theme of maximizing proﬁt on capital invested. To calculate projected proﬁts, you need to start with a standard production model, like the one shown in Table 9.5. To estimate proﬁtability, you insert estimated values for the various parameters within the model. The primary variable costs of production are feed price, ﬁngerling cost, labor, as well as size at harvest, food conversion rates, recovery rates, growing

Fig. 9.4 Fingerling cost relative to Arctic charr harvest weight.

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Table 9.5

223

Standard production model for growing Arctic charr in tanks.

Primary variables Feed price ($/kg) Size at harvest (kg) Conversion rate (kg feed/kg ﬁsh) Grow-out recovery (%) Variable labor ($/kg) Fingerling purchase cost ($) Market price ($/kg) Fish density (kg/m3) Production statistics Grow-out space (m3 of water) Annual production (kg) Ex-plant weight (kg) Labor cost ($) Capital cost ($/m3 space) Capital invested ($) Contribution statement Sales ($)* Fingerling cost ($) Feed cost ($) Labor cost ($) Total variable cost ($) Contribution margin ($) Financial statistics Return on invested capital (%) Proﬁt ($/m3 space) Payback (years) Proﬁt margin (%) Proﬁt margin ($/kg)

Arctic charr

Atlantic salmon

Tanks

Tanks

Net pens

1.20 2.5 1.3 95 0.42 0.85 12.10 90

1.20 2.5 1.3 95 0.42 0.85 7.70 30

1.20 2.5 1.3 95 0.42 0.85 7.70 15

2000 171 000 153 900 71 478 1200 2 400 000

2000 57 000 51 300 23 826 1200 2 400 000

2000 28 500 25 650 11 913 41 82 000

1 709 998 72 000 266 760 71 478 410 238 1 299 760

344 279 24 000 88 920 23 826 136 746 207 533

172 140 12 000 44 460 11 913 68 373 103 767

54 650 1.85 76 7.60

9 104 11.56 60 3.64

127 52 0.79 60 3.64

*Sales are minus processing and packaging costs.

density, and market price. The production statistics indicate the size of the grow-out, the ﬁxed labor costs, and the amount of capital invested. Together, the results of all these variables will be an estimate of the contribution margin (or proﬁt without ﬁxed costs) for the given set of parameters. It is management’s responsibility to insure that these estimates are met or exceeded when the operation is in production. The major parameters are inﬂuenced by forces outside and inside the grow-out operation. Variables such as the price of feed and ﬁngerlings, and the market price received for processed ﬁsh are largely outside the control of the producer. Improvements in husbandry practices will not likely affect the cost of these variables. Other variables such as grow-out density, food conversion rate, grow-out recovery rate, and size at harvest are under the control of the growout operator and are inﬂuenced by each operator’s ability to make good husbandry decisions at speciﬁc grow-out sites. Production is measured by ﬁsh density per cubic area of growing space, and proﬁtability is best viewed on a similar basis, as a return/m3 of growing space. This is different from the wild capture ﬁshery, where proﬁtability is based on a return per kg. Arctic charr grow-out

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operations are more akin to farming, where a grain farmer calculates his return in terms of growing space – for example, bushels/acre. The standard model in Table 9.5 is based on an Arctic charr grow-out containing 2000 m3 of tank space with ﬁsh growing at a density of 90 kg/m3 and a capital investment of $1200/m3 of tank space. This model shows the profound effect density has on proﬁtability. The return per m3 of tank space when growing Arctic charr at 90 kg/m3 is six times greater than that of growing Atlantic salmon in a net-pen. If you told a grain farmer he could increase production per acre by a factor of six times, he would be ecstatic. Figure 9.5 shows the effects on proﬁtability of growing Arctic charr at different densities within the ranges at which they grow well. Doubling the stocking density from about 40 kg/m3 to 80 kg/m3 is the greatest kick available to the grow-out operator for improving proﬁtability. At densities much beyond 90 kg/m3, however, the marginal gains in proﬁtability are not worth the risk of catastrophic losses.

Harvest size and proﬁtability Harvest size has the most marked effect on proﬁtability of all the variables. Growing pan-size Arctic charr reduces the return on capital to less than 3%, while growing larger ﬁsh improves proﬁtability to 48% at constant market prices. From this analysis, it does not make sense to harvest Arctic charr before it reaches 1 kg per ﬁsh, since proﬁtability per kg increases as harvest size increases (see Fig. 9.6). This is because the cost of ﬁngerlings makes up a larger proportion of the cost of production for a small ﬁsh. At 250 g the ﬁngerling costs over $5 per kg of ﬁsh produced, while at a market size of 2.5 kg, the ﬁngerling cost is only about $0.80/kg. This assumes that small ﬁsh receive the same price as large ﬁsh in the marketplace, which is not the case in real life. In Sweden, medium-sized ﬁsh fetch more than twice the price of pan-size Arctic charr.

Market price and proﬁtability Market price is another variable that greatly affects the proﬁtability of a grow-out, and some in the ﬁsh business have said that price is your most important cost. Increasing the market price by about 20% increases the proﬁtability by 10%. Of course a decline in market price

Fig. 9.5 Effect of ﬁsh density on proﬁtability.

Marketing and Market Economics

225

has a similar but opposite effect (see Fig. 9.7). This variable seems to be out of the control of independent growers, particularly small-volume growers who are often ‘price takers’, which means they must accept the market price whether it is going up or down. There are some ways to exert a measure of control over price: the image of exclusivity. • Maintain Grow ﬁ sh and large size. • Keep supplyto medium less than demand by expanding the market – do not ﬂood your existing cus• tomers, but ﬁnd new customers to take up increased production. As mentioned earlier in the chapter, it may help to form marketing groups to facilitate increase in demand or to arrange voluntary reductions in production volumes if prices are soft. The alternative, one that happened with salmon farming on the west coast of Canada, is the collapse of prices and bankruptcies. A consolidation period of adjustment follows, with one or

Fig. 9.6 Effect of harvest weight on proﬁtability.

Fig. 9.7 Effect of market price on proﬁtability.

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Arctic Charr Aquaculture

Fig. 9.8 Effect of harvest recovery on proﬁtability.

two large organizations gaining control of production. These companies can remove product from the market in order to ﬁrm-up prices or prevent a price decline. Sometimes the mere perception of stability in production volumes caused by a consolidation will prove beneﬁcial in stopping a downward pressure on prices. Needless to say, this is not an ideal solution.

Other variables Recovery refers to the number of ﬁsh that make it to harvest. It is affected by normal mortality throughout the grow-out cycle (about 5%) or by a catastrophic loss of ﬁsh (due to system failure or disease) that can be one of the most demoralizing events on a grow-out operation. Catastrophic loss of more than 20% of the ﬁsh, particularly when they are nearing harvest size, has a serious effect on proﬁtability (see Fig. 9.8). Insuring inventory against the more common types of losses is expensive, but depending on site-speciﬁc risks it may be worth the cost. Normal losses, even if they account for 10% of the ﬁsh, have little impact on proﬁtability. The price of feed has only a slight effect on proﬁtability – even when feed prices double, proﬁtability only falls by 10% in our model. Given the increase of salmonid aquaculture and shrimp culture, the price of feed is likely to rise over time. Although this is outside the control of the producer, improving food conversion rates by practicing better husbandry and using better quality feeds may offset higher feed costs. In summary, marketing Arctic charr must be done in the context of its niche position as a specialty food product. Arctic charr is unique and worthy of high price – it should not be marketed as part of the salmon and trout commodity complex. This requires the production of high-quality products of the size and ﬂesh color in demand by the end-user. Arctic charr marketing should target the chefs who prepare ﬁsh for the upper-end HRI sector. The three areas where contribution margin analysis suggests grow-out operators can improve proﬁtability are: produce ﬁsh in the 2–3 kg size range and do not grow pan-size products. • Size: Density: grow Arctic charr at high density in tanks. • Price: maintain image of exclusivity and control supply into market. •

Chapter 10

Managing Culture Facilities

Management is the art of making all the systems in an aquaculture facility work together to meet the objectives of the operation. Good grow-out managers must balance the business skills of selling ﬁsh products for a proﬁt, the husbandry skills for growing live ﬁsh of high quality, the technical skills necessitated by the infrastructure, and the entrepreneurial skills demanded by the high-risk business of ﬁsh culture. They must be more like a farmer than a factory manager producing inanimate widgets. They must have an intuitive feel for their live inventory, and because they are working with a species new to culture, they must be adaptable and innovative in their approach to raising ﬁsh. The skills required to manage a grow-out operation are not often all found in the same person. Managers can be deﬁcient in some areas as long as they recognize their limitations and hire people who can look after the areas outside their expertise. As a general rule, it is better to have the operational skills required to grow ﬁsh and hire business expertise than it is to have business expertise but no skills in raising ﬁsh, though all managers should combine their set of specialized skills with common sense and a working knowledge of basic management concepts. In large operations (greater than a few hundred tonnes per annum), management will likely involve a team of people with expertise in the different areas. In small, familyrun operations, one or two people will need to have the skills required for all areas. Fish husbandry and infrastructure are the two components of operational management – the hands-on part of culturing ﬁsh. They both involve day-to-day operation of the culture facility: calculating feeding rations and maintaining pumps and other vital equipment. In many farms, particularly small operations, the operations manager is directly involved in feeding ﬁsh, moving them about, and repairing equipment. It is a difﬁcult position, as this manager must have hands-on husbandry skills, good ﬁsh sense, and the communication skills to deal with the business management side of the operation. Proﬁtability depends on management being clear about what is possible from an operational point of view and what is required from a business management perspective in terms of ﬁnance, marketing, and ofﬁce operations.

Business management of commercial culture facilities The business end of an aquaculture facility is not much different from that of any other agricultural business. It is more closely related to growing crops than catching wild ﬁsh, as

228

Arctic Charr Aquaculture

happens in the commercial ﬁshery. It demands ﬁnancial control of assets, liabilities, and inventory; a good marketing plan; skilled personnel; and solid ofﬁce management skills. The bills must be paid on time and the receivables collected. A myriad government regulations must be observed, and reports and forms processed correctly. It is different from other businesses because of the living, breathing nature of the inventory and the relative newness of Arctic charr culture and marketing. This is a business that requires individuals with lots of entrepreneurial skills and a willingness to take risks. It is also a business that requires very good planning and ﬁnancial control from construction of the facility right through to the day-to-day management at full operation. Developing a 200 tonne per annum grow-out operation follows a cycle that goes from conceptual to construction, ramping the system up, and reaching full-scale production. At each level there are predictable types of problems that require planning and ﬁnancial control to overcome. For example, constructing a grow-out will often cost more than initially budgeted. Simple things like bad weather delaying and increasing the cost of construction, or soil conditions requiring different techniques in tank construction, or higher costs for materials, can lead to serious cost overruns. Complicated issues like who pays for design changes on ﬁxed bid contracts or what happens when a contractor installs defective materials that must be replaced after the contractor has been paid out can also add substantially to construction costs. Sometimes simple things like not planning enough room between tanks for the heavy equipment needed to move ﬁsh can lead to expensive solutions that push the cost well beyond the budget. Another common problem in running a new grow-out system up is that it often takes longer to reach full-scale production than anticipated. Construction delays may set back the time at which ﬁngerlings are placed into tanks to the point that you miss the period of rapid summer growth, which then pushes back growth and the date of ﬁrst harvest. Growth rates in your facility may not be as high as anticipated because of unusually low water temperatures in the ﬁrst year of operation. Your inexperience with equipment may lead to improper feeding or losses of large numbers of ﬁsh. Any of these problems will lead to poor cash ﬂow when it is most needed. Once operational levels of production have been met, it is often difﬁcult to match supply with demand. This happens when ﬁsh growth has been delayed by a slow ramp-up to full production or when management has not been able to correctly model growth under the conditions at their facility. It leads to a loss of conﬁdence and low sales to ﬁsh buyers. These types of problems will lead to a shortage of cash. This is a major killer of new aquaculture facilities and leads to problems with investors, who see massive cost overruns and delays in meeting production targets in a very different light than entrepreneurs excited about starting a new venture. Depending on their nature and the rapport you have with them, investors may be supportive as you resolve the issues, or they may terminate further ﬁnancing. Out of desperation they may try to resolve the issues themselves, even though they have less experience than you do. I am aware of one operation where ﬁnanciers thought the solution to cost overruns in a tank farm expansion was to stop feeding the ﬁsh for a few months to save money and place pressure on management to mend its overspending ways. This solution was not a success for the investors or the ﬁsh. Bad-luck stories and problems can be minimized by good pre-planning, good management, and sound ﬁnancial resources. As an Arctic charr entrepreneur, the vision and concept can be yours, but at an early stage you should consult with experts who have a sound knowl-

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229

edge of Arctic charr culture, expertise in tank farm design, and a thorough understanding of aquaculture ﬁnance requirements. Recognizing your business or operational limitations and hiring skilled managers is often the best way to see an operation through to proﬁtability. A sound business plan, well researched, is a basic requirement in starting and operating an Arctic charr culture operation. It serves as the blueprint or guide for the lifetime of the operation and is the tool that keeps the entire process of ﬁnancing, constructing, and operating a culture facility on track. The business plan is a benchmark against which you can measure progress, but at the same time it is a ﬂuid document that can be adjusted and added to as the operation matures. It is also the basic tool for seeking ﬁnancing from investors; a welldeveloped plan will go a long way to address the issues discussed above. The business plan is made up of three types of information – organizational, marketing, and ﬁnancial – arranged into four sections. (1)

(2)

(3)

(4)

A statement of purpose or a mission statement outlines what the goals and objectives of the operation are. It gives a brief summary of the organization, marketing objectives, ﬁnancing required, and payback schedules, and a timeline for reaching full-scale production volumes. An organizational plan details the corporate structure of the grow-out, types and volumes of ﬁsh to be produced, the management and personnel required to run the operation, and back-up and contingency plans for critical points in the grow-out process. A marketing plan identiﬁes target markets, pricing, distribution methods, timing of market entry, market locations, and competition. Marketing is the starting point of an Arctic charr venture, not the end point. It is an area that is often overlooked by those new to aquaculture. Growing the ﬁsh is relatively easy; selling them at a proﬁt is the difﬁcult part. A well-researched marketing plan is the ﬁrst requirement when you decide to raise Arctic charr. A ﬁnancial plan details cash ﬂows, income projections, break-even analysis, balance sheets, and proﬁt-and-loss statements. Much of this information on a new grow-out operation will be in the form of proforma documents built around information discussed in Table 9.5, the standard production model. New operations require ﬁnancial contingency plans to deal with worst-case scenarios of construction and ramp-up to full production.

There is also an issue of business ethics that is as important to successful operations as making a reasonable proﬁt. Other salmonid operations have caused great public outcry because of their poor environmental practices and detrimental impact on surrounding waters and wildlife. The industry has been slow to react and has a difﬁcult time facing up to its problems. With Arctic charr we have an opportunity to do things right, to change the negative public perception of aquaculture to one that is at least benign. I have always believed that Arctic charr grown at high density in tanks met the criteria of many environmental and public policy groups for culturing ﬁsh in a sustainable fashion with minimal impact to the environment, at the same time taking pressure off wild stocks. When I think of growing Arctic charr, I have a mental image of the sustainability that I saw at Creswell Bay in the High Arctic, where people were ﬁshing for wild Arctic charr, catching enough to see them through the winter, but knowing they were leaving enough for the resource to go on forever. We all have a responsibility

230

Arctic Charr Aquaculture

to operate our businesses in a sustainable manner that minimizes their negative effect, both on the terrestrial and aquatic environment and on the local community. Arctic charr grow-out operations are in a good position to do this. tank farms allow you to remove waste from the efﬂuent before returning it • toLand-based the wilds. The water going out as efﬂuent should not dilute the downstream water qual-

• • •

ity. You can add oxygen to tank water in a controlled manner, keeping ﬁsh happy and healthy even at high-density growing conditions. High-density growing of Arctic charr makes a smaller footprint than other salmonids, as land-based tanks hold many more ﬁsh. You can grow 170 tonnes of Arctic charr in 2000 m3 of water, but only 30 tonnes of Atlantic salmon. Arctic charr are not stressed at high culture densities, showing little or no ﬁn abrasion or lost scales, so they are better suited to conﬁnement in tanks than other salmonids and should require less intervention with antibiotics and other chemical treatments.

Operations management Operational management is the soul of a culture facility. No matter how well the business side of an operation is run, unless the ﬁsh grow well, convert feed at a good rate, and reach market in top shape, the business will fail. Operational managers make the ﬁsh grow. The operational management of a culture facility focusses on a number of interrelated systems and areas of concern that support the well-being and growth of the live ﬁsh inventory: health of the live ﬁsh inventory, the downstream water community, and ﬁsh • environmental culture employees; systems that support the live ﬁsh inventory and downstream waters (including • mechanical water pumps, pipelines, oxygenation equipment, and water ﬁltration equipment); alarm and back-up systems that monitor critical points for keeping ﬁsh alive and protect• ing the facility from intrusion and ﬁre; inventory that monitors and controls the growth of the live ﬁsh, plans the • grading andmanagement sorting of ﬁsh, and predicts the harvest times of market-sized ﬁsh.

Environmental monitoring In all aspects of environmental health monitoring, it is better to emphasize preventive measures, which reduce the occurrence of disease or poor downstream water quality, than it is to try to get a handle on disasters or problems after they occur. The International Standards Organization (ISO) has developed a set of standards, the ISO 14000, to help industry monitor and regulate its environmental impacts. It is a practical method of monitoring environmental health, recognized in more than 100 countries, and is an important tool for avoiding problems before they start and addressing problems when they happen. The ISO 14000 is also a useful set of guidelines for ﬁsh culture facilities to use when they formalize environmental manage-

Managing Culture Facilities

231

ment systems (EMS) for recognizing, monitoring, and responding to environmental impacts. An EMS requires ﬁve key steps (Hatt 1998): (1)

(2)

(3) (4) (5)

Establish an environmental policy by identifying activities at the facility that may have environmental impacts: for example, incoming water quality, impact of water withdrawal on the groundwater table, impact of feral disease organisms, impact of ﬁsh food on downstream water quality, noise pollution from pumps and discharge lines, etc. Undertake a planning phase in which you rate the signiﬁcance of different impacts on a scale of severity and frequency. In this phase you can develop action plans and operational targets to reduce or eliminate the environmental impact. Implement and operate the EMS at the facility. The plan’s effectiveness will depend on how well management and workers buy into its importance. Assure that the EMS meets the objectives, and correct or tweak the plan if required. Periodically review the overall EMS.

You do not have to have a formal ISO 14000 certiﬁcation, but every facility should have a working EMS that addresses ﬁsh health and downstream water quality.

Fish health management A ﬁsh health management plan is an important part of an EMS and is designed to prevent disease-causing organisms from infecting cultured ﬁsh. Many of these organisms are ubiquitous and abundant; you cannot eliminate them, but good husbandry practices and good waterquality management, which minimize stress on Arctic charr, reduce and prevent disease outbreaks. This is a case where good management will prevent potential hazards. Other disease-causing agents are not present in the normal background environment but are transmitted to cultured ﬁsh by other ﬁsh or ﬁsh eggs, by contaminated humans or equipment, or by wild animals gaining entry to the facility. A management program can prevent contaminants from entering the facility in the ﬁrst place. One of the basic tenets of a ﬁsh health protection program is to understand the proﬁle of potential disease-causing agents in your watershed area. Some of the common salmonid pathogens of concern to Arctic charr are discussed in Chapter 3, but there may be others in your area. Testing wild ﬁsh for the common salmonid pathogens is a ﬁrst step in understanding what diseases occur in your area. It is also important to know the disease proﬁle of any other culture facilities operating on your watershed, though this information is often kept secret. This attitude of secrecy needs to change, as sharing this information will allow all operators to manage for existing disease-causing organisms. With this information in hand, you can develop an integrated ﬁsh health protection program around a number of themes: ﬁsh against disease-causing organisms that are known to occur in your water• Immunize shed area. There are vaccines available to prevent a wide variety of common salmonid

•

viral diseases that affect Arctic charr. Develop contingency plans to deal with disease outbreaks. This involves identifying the source of the disease, breaking the connection between the source of the disease and the

232

• • •

Arctic Charr Aquaculture

susceptible ﬁsh, and reducing the susceptibility of exposed ﬁsh by applying a therapeutic agent or destroying diseased ﬁsh stock. Minimize environmental stress to cultured ﬁsh through good husbandry practices and contingency plans. Monitor ﬁsh health with regular inspections and necropsies of dead ﬁsh. Make sure disease-causing organisms do not establish a foothold in your facility.

You should monitor the live ﬁsh inventory daily and develop a plan to control critical points where disease-causing organisms could potentially enter the facility. This plan should include the following: A visual inspection of ﬁsh in each tank throughout the day to assess their general well• being: Are they exhibiting symptoms of stress? Are they agitated or too docile? Have they

• • • •

stopped feeding? Inspect each tank each morning and remove dead and dying ﬁsh (morts), placing them in mort pails. Record ﬁsh removals on inventory sheets. Take suspect ﬁsh to the laboratory for necropsy. At the end of the day, remove morts from mort pails, freeze or dispose of them, and disinfect the mort pails. Record the number of morts and the suspected or known cause of death on daily mortality sheets for each tank. Disease conditions may be indicated by a gradual increase in mortality, a dramatic increase, or just low-level chronic morts in one tank that stands out from others.

It is difﬁcult to prevent the entry of disease-causing organism into a facility. You cannot see disease organisms, which makes it hard to believe in their existence, but you have to believe they are everywhere. It is best to treat the entire operational area of the culture facility as an area under quarantine, with entry controlled at critical points. The culture facility should be fenced to prevent entry by people and animals (small mam• mals, birds, bears, mink, etc.) except at a few controlled points. Entry to the grow-out should be restricted to as few people as possible, with particular care • taken when people have been visiting other culture facilities. Everyone entering the facility should change into outerwear and boots assigned to the unit, • wash hands thoroughly, and pass through a boot bath. Wash disinfect all equipment before it enters the unit. It is best to have equipment • remainandin the unit at all times. Each tank should have its own net and pail for collecting morts. All nets must be disinfected • between uses. String nets over the entire grow-out to prevent the entry of birds, which all too efﬁciently • transmit viruses from one facility to another. Birds should also be scared off intake ponds

•

or header ponds. Color-code equipment to prevent cross-contamination. For example, mortality pails and nets could be red; live ﬁsh pails and nets, blue; cleaning pails, yellow; feeding pails, green.

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233

Water-quality monitoring One of the particular concerns when culturing Arctic charr is the effect of high stocking density on water quality. Arctic charr can only be grown at high density if the water quality remains within limits that sustain and promote good growth in the ﬁsh (see Chapter 3). This is why a water-quality monitoring program, which assesses changes in the quality of incoming water, tank water, and discharge water, is a requirement in any culture facility. Water should be sampled at critical points in the water system on a regular basis (see Table 10.1). Some critical points are monitored continuously, while others are monitored on a daily, weekly, or monthly basis. The monitoring program should also include methods for correcting situations where water quality falls outside acceptable limits. Temperature and oxygen levels in tank water have such a profound effect on ﬁsh health that they should be monitored on a continual basis. Fish show behavioral cues when starved of oxygen, and you should watch for these as well. When only slightly stressed, they will go off their food and swim slowly, just fast enough to keep moving and upright, but not at all vigorously. As they become more stressed from lack of oxygen, they will gather near the surface with their backs out of the water, and as oxygen levels continue to drop, they will group tightly about the intake if any new water is still entering the tank. Not long after this stage a few individuals will turn belly up, and over the course of the next few minutes hundreds, then thousands, will go white belly up. It is not yet a complete loss, but many will die even if recovery starts immediately. If the oxygen alarm has not sounded by now, the entire tank of ﬁsh will soon be dead, with perhaps a few (less than 1%) barely alive. Oxygen failures in ﬁsh culture facilities are often accompanied by a profound silence. I have walked into a silent hatchery, the water ﬂow gone and the alarms not ringing, to stare at hundreds of thousands of dead Arctic charr. It is shocking to see so much death in so many tanks. In order to prevent similar situations from occurring, you must be aware of oxygen levels at all times. Water ﬂows, temperature, and ﬁsh-rearing density all affect oxygen levels and should be monitored closely. Summer is an especially dangerous time, as water temperature rises with the air temperature. When temperature rises, oxygen availability decreases. Suspend feeding if water temperature rises above 18 °C in warm summer weather. Watch ﬁsh Table 10.1 Water-quality monitoring at critical points. C = continuously; D = daily; W = weekly; M = monthly. Critical point

Water ﬂow Temperature Oxygen Ammonia-N Nitrite

Nitrate

Carbon Total pH dioxide solids

Main incoming water Fish tank inlet Fish tank outlet Main outﬂow line Before biological ﬁltration After biological ﬁltration Downstream

C

M

C

C

M

M

M

M

M

C

C

W M

W M

W M

W M

W M

C

C

W

D

D

W

W

C

W

W

D

D

W

W

M

M

M

M

M

M

C

W

M

M

M

M

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Arctic Charr Aquaculture

loading in the summer months and calculate how much oxygen will be required at the higher temperatures, and beware of warming surface waters during the summer heatwaves of July and August. Steps you can take to prevent oxygen depletion include the following: Install a standby oxygen system to kick in if the main system breaks down, to accom• modate incidental dips in oxygen, or for prolonged periods of supplementation during

•

• •

warm spells or low ﬂow periods. Install an oxygen alarm system with a sensor in each tank and ensure that personnel will respond to it rapidly. Do not count on an automatic back-up system to work. Always respond to an alarm. A night watchman at one tank farm facility ignored a pump alarm because he thought the other pump would cut in. It did not, the entire crop of salmon was lost, and the company went out of business. Monitor water ﬂows into each tank on a daily basis and adjust as required. There must be personnel on site or on standby 24 hours per day, 7 days a week, to monitor all recirculation systems and to respond to emergencies.

Managing downstream water Maintaining high-quality outﬂow or downstream water is a fundamental requirement when operating an aquaculture facility. Water is only borrowed for aquaculture, and the ultimate goal of management should be to return the water to nature in the same state as when it entered the facility, despite the production process (Bodvin et al. 1996). The ideal is to have water clean and healthy enough to reuse in your own facility. Those designing new Arctic charr tank grow-outs should meet this target, while managers at existing facilities should keep this goal in mind. Public policy has in many countries led ﬁsh farm regulations in this direction anyway, so this is an opportunity for culturists working with a new species to show sensitivity to the public’s concern about the environmental impacts of ﬁsh farming. A company that demonstrates it has low environmental impact and practices good wastewater management, or can show that it is considering such issues openly, may well be able to command a higher price for its products or reach markets otherwise not available (Kelly et al. 1997). Waste from a culture facility comprises by-products from feeding, from dead ﬁsh, and from chemicals used in the ﬁsh production process. Most of the waste is composed of uneaten feed and ﬁsh feces as suspended solids, and nitrogen and phosphorus in solution. Suspended solids not removed from the efﬂuent can smother benthic organisms and act as a source of excessive nutrients for fungus, bacteria, and plant growth. Phosphorus and nitrogen can also act as nutrient sources for downstream plant growth to such an extent that when the plants die and are decomposed by bacteria, they place a high oxygen demand on the water. If the oxygen depletion is severe enough, this condition will kill higher invertebrates and vertebrates in the receiving water. There are three fundamental strategies for reducing waste from ﬁsh culture facilities: improve feed formulation, minimize food consumption, and remove the waste stream from the water. For example, you can signiﬁcantly reduce total phosphorus and total suspended solids in outﬂow waters by using high-quality, high-energy diets low in phosphorus (Sugiura et al. 1998). Such diets may include low-ash ﬁshmeal (feed ingredients of animal origin contain

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the highest concentration of phosphorus). Good husbandry, such as better feeding practices and using more palatable feeds, will improve the food conversion rate, which in turn reduces the environmental phosphate loadings by limiting feed wastage. Freshwater Atlantic salmon net farms in Scotland have improved their overall phosphorus discharge in part by reducing the food conversion rate and thus decreasing the amount of waste feed and feces entering the water (Gavine et al. 1995). Wastewater from aquaculture is unique in that the ﬂow rate of water is high and the concentration of potential pollutants is low when compared to other industrial and domestic wastewaters. Although the efﬂuent from a tank farm contains a dilute amount of waste, its long-term, cumulative effect on the environment is a critical problem, so it is vital that you remove the waste stream from discharge water in order to prevent negative impacts on downstream waters. The ability to ﬁlter farm wastewater is a considerable advantage of land-based tank farms (Kelly et al. 1997), and the equipment required to meet high standards of waste removal is available. You need only install the best materials given the design and layout of your facility. The ﬂow rate of water through the system, the expected feeding rates, and loading rates of ﬁsh are variables you must consider when designing a wastewater treatment system. Mechanical ﬁltration removes the suspended solids (feed and feces), while biological ﬁltration uses bacteria to break down ammonia and other organic compounds. Mechanical ﬁltration can take the form of gravity sand ﬁlters, separation ﬁlters, hydro-cyclones, rapid sand ﬁlters, and micro-screens. Screens are the most efﬁcient method, removing the most waste while requiring low maintenance. Rotating micro-screen drum ﬁlters work very well and are more efﬁcient to operate than sand ﬁlters (White & Townsend 1996). A ﬁve-panel ﬁlter screen of 60 microns (μm) removed 100% of particles larger than 33 μm, while a ﬁvepanel screen of 9 μm removed all particles larger than 13.3 μm. Using ﬁner screens removes a greater size range of waste, but at the expense of efﬁciency and cost. A ﬁlter of 60 μm will process eight times as much water as a 9-μm screen, and if it is placed close to ﬁsh tanks, where waste particles are still relatively large, it will remove a substantial portion of the waste. As a compromise between efﬁciency of operation and waste removal, it is best to use screens of 60–100 μm. Be sure the ﬁlter system is designed to process the highest expected water ﬂow rate. In newer, two-drain tanks this will occur during and after feeding, while in older singleoutlet tanks it will be during tank cleaning. New tanks are designed to rapidly remove waste before it breaks up into ﬁne particles, which makes it easier to remove waste from ﬁltration screens. If you stabilize and purify the collected sludge with lime, which eliminates odors, it may be suitable (depending on local regulation) for application onto agricultural lands as fertilizer (Bergheim & Cripps 1998). Once the solids are removed, there may still be a requirement to remove dissolved organic compounds (NH4, P, etc.) from the outﬂow water. This is best done through biological ﬁltration by bacteria that use ammonia and other organics as a nutrient source. In recirculation systems the biological ﬁlter is integral to reusing the water, while in single-pass grow-outs they are needed if outﬂow water cannot meet water quality standards for wild waters. In both cases the design of bioﬁltration systems requires technical assistance from specialists in their design and operation. Biological ﬁlters are living systems that require as much care as the ﬁsh in the tanks. The cold water temperatures used with Arctic charr present some problems for biological

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ﬁltration systems, as the reproduction time and respiration rates of bacteria are slower than they are at higher temperatures. A larger bioﬁltration area may be required for Arctic charr tank grow-outs (Drouin 1999). Settling ponds do not adequately remove nutrients from ﬁltered wastewater, but created wetlands planted with different types of aquatic grasses, sedges, and rushes have effectively lowered the concentration from aquaculture systems. Under experimental conditions they remove over 80% of total nitrogen, phosphorus, and dissolved phosphates (Summerfelt et al. 1999). The wetland must be carefully designed and correctly sized to hold wastewater as long as necessary to remove excess nutrients, and it does not work as well during the winter months when plants are not in an active respiration and growth phase. If chemo-therapeutants such as fungicides, and antibiotics must be used in Arctic charr facilities, they should not enter the downstream environment as studies show they have a bad effect on non-target organisms. Malachite green, for example, is an effective fungicide but is also carcinogenic; formalin and pesticides used for lice treatment are toxic to aquatic invertebrates. The indiscriminate use of antibiotics has led to antibiotic resistance in pathogens of shrimp and salmon. Dilution in the outﬂow water will not deal with these products (Bergheim & Åsgård 1994; Weston et al. 1996). If you need to use them, there are methods of administration that can minimize their entry into discharge waters. For example, ﬁsh can be moved to treatment baths rather than adding treatment to tank water. The water from the baths can be disposed of in ﬁltration beds on land or can be treated to make it inert. Antibiotic treatment can be administered via injection rather than in the feed. A contingency plan that details techniques for delivering therapeutants in a manner that is safe for the ﬁsh, the environment, and the workers should be part of the EMS. Bear in mind that the best method of controlling disease transmission is to manage the ﬁsh well and prevent pathogen entry into the facility in the ﬁrst place. Besides waste and disease causing downstream effects, ﬁsh can also escape from farms to the wild. Installing and maintaining high-quality screens on all tank outlets and on main outﬂow lines are the minimum prerequisite for preventing ﬁsh escape. The main line screens must be ﬁne enough to block the escape of the smallest ﬁsh in the grow-out and should be removable for cleaning. Double screens are required so that while cleaning one screen, there is still a screen in place to prevent ﬁsh escape. The screened area should be easily accessible and allow for inspection and capture of escaped ﬁsh. Despite the presence of screens, ﬁsh do escape most facilities at one time or another. A company is developing an electrical grid that would kill any ﬁsh swimming out the wastewater outlet, but until these are available, you will need to set up a contingency plan for recapturing escaped ﬁsh. Cripps and Kelly (1994) summarized the aquaculture wastewater situation well in a book entitled Aquaculture and Water Resource Management. It should be required reading for managers of Arctic charr culture facilities. They note the following: wastewaters are difﬁcult to treat because ﬂow rates are high and waste con• Aquaculture centrations are low. However, they must be treated because the cumulative load of waste

•

products is high. Treatment technology is aimed at reducing the concentration of suspended solids, phosphorus, and nitrogen compounds and producing associated reductions in organic concentration and biological oxygen demand (BOD).

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characteristics of aquaculture wastewaters vary greatly with time, location, and site • The management. Their treatment is site speciﬁc. nutrients in aquaculture wastes are partially associated with the large particle fraction • The (waste feed and feces), so treatment methods that separate particles from the efﬂuent are

•

common in the industry. Rotating axial and radial ﬂow screens are currently the most suitable group of methods commercially available for treating efﬂuents from intensive land-based aquaculture facilities. As demands for these devices and for efﬁciency increase, unsuitable designs will disappear.

Importance of good mechanical systems management Unlike in net-pen operations, mechanical systems that support ﬁsh are extremely important in Arctic charr tank farms. The ﬁsh rely on water lines, valves, and often pumps and ﬁlters to assure them a supply of quality water. In the high-density tanks used with Arctic charr, the ﬁsh are particularly reliant on oxygenation systems. Alarm systems and back-up equipment take on a critical role as there are many points to monitor and maintain, and when systems fail, they fail rapidly and often in catastrophic ways. Managing a high-density Arctic charr tank farm is a 24-hour-a-day, seven-day-a-week operation. It cannot be left alone for long, and is more similar to a dairy operation than a prairie wheat farm. Dairy farms are 24/7 operations, while grain farms have periods of intense activity followed by periods of little or no intervention in the production process. The mechanical systems and equipment in a tank farm must be designed to manage the high loading rates used for charr grow-out. Tanks must be designed for high ﬂow and rapid solids removal, and feeding systems for the special requirements of Arctic charr discussed in Chapter 4. If you are converting a system that has been used to rear salmon, you will need to reﬁt it to accommodate the increased water ﬂow required for the higher loading rates. It is well worth the expense to employ specialists familiar with Arctic charr to assist in the design process for both new systems and redesigned existing operations. A simple ﬂow-through tank farm will consist of ﬁve mechanical systems. They interact to support the ﬁsh but can be viewed as discrete systems: (1)

(2)

A water system brings intake water from wells or a header pond down a main line to an aeration tower. From there water is carried to main feed lines that supply banks of tanks, and then to secondary lines that supply individual tanks. Drain lines remove water from the tank to a main discharge line that leads to a ﬁltration system before exiting to the wild or a wetland remediation. The system can be complex, with bypass lines and ﬂow-control valves, but even simple operations involve a maze of water lines, cross lines, valves, and inline equipment not easily understood at a glance. Your water system should come with a large schematic that details critical points and method of operation. An oxygenation system adds oxygen to the incoming tank water to meet the increased demand for oxygen when Arctic charr are held at high density. This is a critical piece of equipment and there are a number of designs and installation arrangements on the

238

(3)

(4)

(5)

Arctic Charr Aquaculture

market. Be sure you understand how each system works, as well as its beneﬁts and drawbacks, and choose the one that is most suitable for your site and needs. Pure oxygen from a pressurized tank or from an onsite oxygen generator passes through the delivery system that adds the gas to tank water. The system can be integrated with a controller that automatically increases the oxygen ﬂow rates to a tank if dissolved oxygen falls below a certain level. Mechanical and biological ﬁltration systems for removing waste were covered in the previous section. In recirculation systems, the bioﬁltration system is integral, as it refurbishes water so it can be reused. There are companies and individuals that specialize in producing the cold-water bioﬁltration systems necessary for Arctic charr (Drouin 1999). A feeding system should be designed to allow the specialized feeding regimes needed by Arctic charr. These systems can be manually operated or managed by automatic controllers that deliver different allocations of feed to different tanks (see Chapters 4 and 8). Alarm systems alert workers when equipment fails, while back-up systems of standby equipment carry out the function of equipment that has failed or requires repair. The core piece of equipment in a back-up system is a stand-alone oxygen supply that can deliver oxygen to all the tanks for several hours.

In new facilities, all the mechanical systems should be of high quality, purchased from suppliers that can assure continuity of service and rapid delivery of parts for items needing repair or replacement. There is no sense in purchasing a used main water pump from a supplier in Norway for a facility in the Yukon. Also remember that mechanical systems will operate more reliably and last longer if quality is not sacriﬁced to low price. It is not worth buying cheap water pumps that require constant repair and burn out in a year, but spending twice as much on a high-quality pump that lasts ten years is a good investment as it will end up saving you money every year it is in operation, and it also decreases the possibility of a catastrophic loss due to pump failure. The mechanical systems manager makes sure the systems operate smoothly and are maintained on a regular basis. The manager must be able to bring systems back to full operation after sudden failures. It is much easier to recover from a sudden failure if standby equipment is ready to replace the disabled system and personnel know how to diagnose and repair the problem. Mechanical systems management is easier if the manager takes a few steps to prepare an operational manual. This should include: point assessment of each system to identify potential failure points or hazards; • aa critical schematic of the system that identiﬁes all the critical points and names all the compo• nents; action plan for dealing with all known failures that can occur at critical points in the • ansystem. The plan should identify the critical condition, suggest solutions for preventing

• •

critical point failure, and suggest methods for repairing failures; a monitoring plan that schedules inspection and preventive maintenance for each critical point; and a log of all system failures to update critical points and methods for dealing with them.

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Emergency preparedness: alarms and back-up systems Alarm systems alert workers when ﬁsh support systems have failed or are about to fail. They consist of probes or sensors that measure the parameter of interest – such as oxygen level in a ﬁsh tank – and are connected to a controller/monitor (see Fig. 10.1). Using the example of an oxygen monitor, if the concentration of dissolved oxygen in a tank falls below a certain level, the controller activates an alarm. The alarm system usually consists of very loud horns or sirens located at strategic locations about the facility. It may also be connected to a telephone callback that dials a series of telephone numbers monitored by real people dedicated to responding to the alarm. On critical systems like oxygen, the controller can also send a signal to a standby oxygenation system to automatically activate an emergency supply of oxygen to the tank. Back-up or standby systems are used to keep the ﬁsh alive until the regular equipment is functioning again. This equipment is not used often, but when required it must work properly. Too often back-up systems are neglected or set aside and are not ready when the emergency arrives. Many facilities have lost ﬁsh because back-up systems were not connected, had broken down, or lacked fuel in the case of generators. The operations manager must test alarms and back-up systems on a regular basis and keep back-up equipment in good repair. A program of emergency drills that take all staff through different emergency scenarios requiring the use of back-up equipment is one of the easiest ways of insuring the integrity of the facility’s emergency procedures. In a high-density Arctic charr tank farm, where thousands of ﬁsh can die in a matter of minutes, the importance of alarm systems and emergency preparedness of personnel cannot be overemphasized. I have lost a few ﬁsh to disease, but the catastrophic losses I have experienced and heard about from others have been caused by human error or equipment

Fig. 10.1 Schematic of oxygen alarm and standby system.

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failure. Human error is difﬁcult to eliminate, and equipment will always fail, so alarms are important. They will identify the condition and allow operators to recover the system before catastrophic losses occur. When you are installing an alarm system, keep the following points in mind: The alarm system is the ﬁrst line of defense against catastrophic loss. • Alarm critical pieces of equipment or situations, such as loss of dissolved oxygen • in tanks,thelossmostof water ﬂow to tanks, loss of power, or high water temperature on ﬁsh intake

• • •

lines. Critical alarms should be connected to automatic back-up systems (e.g. emergency generators to return electrical power, oxygenation to restore dissolved oxygen, sprinklers in case of ﬁre). Sirens should be loud enough to instantly awaken even the deepest-sleeping night duty person. Make sure you have an alarm system that will go off if the alarm itself, or an individual sensor, becomes faulty. I have lost ﬁsh when an alarm system failed to notify that a sensor was no longer sending the controller an accurate signal.

Emergency preparedness involves knowing the operations and knowing where all the critical points are, while understanding how to repair or correct any situation that may go wrong. Everyone working in a tank farm must understand the normal operating procedures of the facility; they must be able to operate all of the equipment correctly and monitor equipment and systems as they work with them. This understanding helps to prevent emergency situations from happening and gives each worker the knowledge to correct problem situations. For example, workers must know how to redirect water from one feed line to another, but must also know which feed line to use, even when it is 4 a.m., the power is off, the oxygen cylinder is empty, and the ﬁsh are dying. The following are important parts of an emergency preparedness system: an emergency procedures manual that details all the critical points, their possible • Have causes of failure, and corrective action needed to restore them. Keep this manual in a three-

• • • • •

ring binder to allow easy updating. Update the emergency manual whenever a new critical point is added or a repair procedure is altered or improved. Be sure all personnel understand the emergency procedures and have the conﬁdence and training to respond in a successful way to an emergency. Run emergency drills on different types of critical point emergencies with everyone involved in the facility, talk about potential problems and how they could be corrected, and give your employees a sense of conﬁdence in their ability to operate the facility through an emergency. Always respond to an alarm or an emergency as calmly as possible by ﬁrst stabilizing the ﬁsh, then identifying the source of the problem (failed water line, broken pump, etc.), and then correcting the problem. A daily log book gives continuity to the operation. It is a place to notify the next shift of the status of different pieces of equipment or to record observations on particular ﬁsh tanks that may help other workers assess their well-being.

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Production management Production management involves keeping track of the ﬁsh inventory. You can do this with a production model, which is built around an inventory management module, a predictive module, and a data collection module. The inventory module is a database that keeps track of the number of ﬁsh in each ﬁsh lot, their location in the grow-out, their estimated weight and biomass, and other information about amounts and type of feed fed and origins of the stock. The predictive module takes inventory information and calculates the amount of feed required for the next day or week, predicts when the ﬁsh will reach a certain biomass within each tank, or predicts the time to harvest based on water temperature and feed fed. The predictive module bases its calculations on equations such as the Iwama growth model that are only estimates of the real world. To make those estimates as accurate as possible, you must regularly add real data to the model using the data collection module. This involves recording and entering into the inventory on a daily basis the number of mortalities, the amount of feed consumed, and the water temperature. To correct for actual weight gain, sample the ﬁsh lots on a monthly basis, using standard statistical techniques for weight and length determination. This involves taking a random sample representing about 1% of the total ﬁsh in the tank. Starve the ﬁsh for 24 hours prior to sampling to remove food from the gut. To take a random sample, net ﬁsh from the tank without selection to ensure the sample includes ﬁsh of all sizes. Dipping out many small samples from different locations in the tank is preferable to scooping out the entire sample in one place with one or two scoops of the net. Anesthetize the ﬁsh, lightly towel off the excess water, then weigh and measure each individually. This data is used to calculate the true size and distribution of ﬁsh in each lot using a scientiﬁc hand calculator or packaged statistical programs available with most computer spreadsheets. Tracking production information allows you to assess a ﬁsh lot all the way through the grow-out process. You can follow each ﬁsh lot from the time they are alevins and will have a record of all the information pertinent to quality control such as the ﬁsh lot’s origin, feed, antibiotic treatments, type and amount of pigment added to the feed, and ﬁnal fat content, ﬂesh color, and condition factor (see Fig. 10.2). Because Arctic charr are relatively new to culture, much of this hard data is not available for culturists, and keeping track of what husbandry practices worked, or what brood stock produced the best offspring, is a valuable way to improve later crops of ﬁsh. There are custom-built software programs to monitor and manage ﬁsh inventory through the production process (Karreman 1997). They are expensive, but for those who have not built predictive or inventory models or worked with database systems or spreadsheets, they are the best way of acquiring a production management system. If you plan to build your own, be sure to include the following capabilities and information: You should be able to follow each lot of ﬁsh through the grow-out process by assigning • each lot a unique code. This code becomes the identiﬁer for that lot, regardless of its location in the grow-out. When lots are moved to new tanks or to the processing plant, the identiﬁer moves with them. When ﬁsh lots are sorted by size, the new lots are given a new identiﬁer, but the inventory module must be able to relate the new lot number back to the original pre-sort information.

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Fig. 10.2 Inventory management model displaying ﬁnal harvest information. Reprinted with permission from Superior Systems.

lot of ﬁsh has its own inventory sheet that contains all information needed for inven• Each tory control, including the origin of the ﬁsh, starting weights and numbers, feed types

•

used, water temperature, ﬁsh health information, all of the sampling data, and summaries of condition factors and growth rates. The inventory sheet would also record the results of ﬂesh color and fat content analysis. This inventory sheet is updated on a daily, weekly, and monthly basis with information collected from the real world. Every day record the number of mortalities, tank water temperature, and amount and type of ration consumed for each lot and enter it into the inventory module. Information on

Managing Culture Facilities

•

243

ﬁsh well-being or records of medications or general observations can be collected in a comments section of the data entry program. The data collection program feeds into the predictive module so that it automatically updates inventory, feed, and size information for each lot of ﬁsh. The predictive module is designed to output summaries of statistics that allow managers to predict time to market or implement changes in feed or changes in the level of pigment added to feed. It is the basic tool for controlling and managing the growth and health of each lot. The predictive module uses inventory information to update feed ration size, the estimated size of the ﬁsh, the mortality rates, and the food conversion rates of each ﬁsh lot. Real sampling data is entered into the model on a monthly basis so ‘estimated’ information can be corrected or ‘truthed’. The real ﬁsh sizes based on the sampling data are then entered into the inventory. The predictive module can also generate graphs that show how closely predicted information reﬂects real growth rates. Over time you can adjust the predictive model so it closely mimics the real picture in the grow-out operation.

The operations manual One more tool that managers can use in any type of culture operation is an operations manual. All facets of environmental, mechanical, inventory, and alarm/back-up systems should be brought together in a detailed manual that is accessible to and understood by all. This manual is an important tool for training new employees in the intricacies of the operation, as well as being the operations bible for all those involved in the facility. It contains the information, instructions, and solutions needed to get you through the hard times and to maintain consistency when, inevitably, key people move on. An operations manual brings all the systems together under one cover by: stating the objectives of the operation and the philosophy of the organization; • giving and management the expected standards of behavior in treating each • other, theemployees ﬁsh, the environment and the local community; including for every activity required in the day-to-day functioning of the facil• ity such asinstructions methods used for sampling ﬁsh, grading ﬁsh, and feeding; schematics of all the operating systems with critical control points clearly • showing marked; containing the emergency procedures manual and a quick reference emergency sheet that • details the most common types of emergencies, their solutions, and likely causes; and containing the environmental management plan. • The operations manual is arranged so that any operational requirement can be found easily. Use cross-referencing and color codes, and keep it in a three-ring binder to allow periodic updating as new systems are brought online or different solutions or procedures are developed. Growing Arctic charr is a new venture and the wise manager should review operations on a regular basis. The operations manual is the place to keep on top of the operation as it matures.

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A ﬁnal word A successful Arctic charr grow-out facility depends on well-trained and motivated management and workers. They must believe in the ﬁsh and see them as more than just another salmon or trout. Culturists switching to Arctic charr from growing other salmonids such as Atlantic salmon or rainbow trout have to change their husbandry practices to accommodate the special needs of this species. Arctic charr must be crowded at high density in tank grow-outs, but they still need a pristine water environment. This requires changes in tank design, oxygenation of the water, and different feeding regimes than used with other salmonids. Managers and workers moving from net-pen operations to tank farms must completely rethink their approach to ﬁsh management when working with Arctic charr. The high loading densities used with this species means the grow-out is a 24-hour, 7-day-a-week operation. Growing Arctic charr in tanks is an ongoing, critical situation. It can never be left alone. Despite all I have said about the problems of growing this ﬁsh, its newness to aquaculture, and the short distance of brood stock from the wild, it is still the most exciting and proﬁtable salmonid for culture. Its long history of use as a food ﬁsh and exotic High Arctic background give it a mystique that is easily carried into the marketplace. Its newness to aquaculture offers opportunities for many to start operations based on land-based tank farm technology. The high densities allowable in tanks and the good market prices paid for Arctic charr mean that operations need not be big to be economic; the ecological footprint on the land can be quite small. Given the right strains, and good husbandry practices, this ﬁsh by any name – Arctic charr, irkalukvik, or l’omble chevalier – is just ﬁne for culture.

Appendix

Protozoan and Metazoan Parasites of Wild and Cultured Arctic Charr

Adapted from Dick 1984; Kolasa & Curtis 1995; Due & Curtis 1995; Galbreath et al. 1994. * parasite reported only from cultured Arctic charr ** presence in wild and cultured Arctic charr

Protozoa Chloromyxum coregoni Dermocystidium salmonis Haemogregarina irkalukpiki Henneguya zschokkei Leptotheca krogiusi Myobolus neurobius Myxidium oviforme Myxidium salvelini PKX* Trichodina nigra kamchatika Trichophyra piscium Zschokkella orientalis

Monogenea – Trematodes Discocotyle sagittata Gyrodactylus birami Gyrodactylus salaris** Tetraonchus alaskensis

Digenea – Trematodes Brachyphallus crenatus Bunodera luciopercae

246

Appendix

Crepidostomum cooperi Crepidostomum farionis Crepidostomum transmarinum Derogenes varicus Diplostomum spathaceum Lecithaster gibbosus Neascus sp. Phyllodistomum conostomum Phyllodistomum sp. Prosorhynchus squamatus Prosorhyncoides ozakii

Cestoda – Tapeworms Bothrimonus sturionis Cyathocephalus truncatus Dibothrium fasteni Diphyllobothrium dendriticum Diphyllobothrium ditremum Diphyllobothrium norvegicum Diplocotyle olrikii Eubothrium crassum Eubothrium salvelini Nybelina surmenicola Pelichnibothrium caudatum Pelichnibothrium speciosum Proteocephalus articus Proteocephalus exiguus Proteocephalus longicollis Proteocephalus salmonidicola Proteocephalus tumidocollus Scolex pleuronectis Triaenophorus sp.

Nematoda Anisakis laevis Anisakis simplex Bulbodacnitis alpinus Capillaria salvelini Contracaecum aduncum Contracaecum osculatum Cucullanus truttae

Protozoan and Metazoan Parasites of Wild and Cultured Arctic Charr

Cystidicola cristivomeri Cystidicola farionis Cystidicola stigmatura Cystidicoloides tenuissima Dacnitis laevis Hysterothylacium aduncum Metrabronema salvelini Philonema agubernaculum Philonema oncorhynchi Philonema salvelini Phocanema decipiens Phyllodistomum umblae Pseudocapillaria salvelini Pseudoterranova decipiens Rhabdochona denudata Rhaphidascaris acus Thynnascaris adunca Truttaedacnitis truttae

Acanthocephala Acanthobdella livanowi Acanthobdella peledina Bolbosoma caenoforme Corynosoma strumosum Echinorhynchus gadi Echinorhynchus lateralis Metechinorhynchus lateralis Metechinorhynchus salmonis Metechinorhynchus truttae Neoechinorhynchus rutili Pomphorhynchus laevis

Crustacea Caligus elongatus* Lepeophtheirus salmonis Salmincola biaculiculata Salmincola carpionis Salmincola edwardsii Salmincola salmonea Salmincola thymalli

247

248

Appendix

Mollusca Anodonta yukonensis

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Index

acid-base balance, 49 aggression, 60, 81, 83 feeding frequency, 81, 83 alarm systems, 60, 237–40 alevin, 161–2, 164 ammonia sensitivity, 51, 169 ATU, 158, 167 behavior, 60, 161, 167 diets, 93, 101, 104, 171–2 emergence, 165 ﬁrst feeding, 165, 166, 167, 170–73, 174 hatching, 161 oxygen requirement, 169 ponding, 164–7, 170 swim-up, 165, 167 yolk sac, 161, 171 alkalinity, 48, 55–6 amino acids, 93–4, 105 ammonia, 40, 50–52, 181 carbon dioxide, 51 pH, 51 ration size, 51 temperature, 51 toxicity, 51–52 un-ionized, 52, 149 anesthetics, 148, 149–50 anesthetizing, 143, 147, 148, 149–50 antibiotics (see chemotherapeutants) aquaculture development, 10–13, 14 Arctic charr anadromous forms, 21–4, 36, 53, 55, 91, 129 anatomy, 20 association with humans, 3, 4–6 behavior, 33–5

commercial exploitation, 6–10 distribution, 3, 16, 17 morphology, 19 morphs, 25–27 resident forms, 24–5, 36, 55, 129 sexing, 141 standard Arctic charr, 133–5, 223 taxonomy, 17, 19 wild ﬁshery, 6–10 astaxanthin, 99–103, 132 ATPase, Na ,K, 53, 54 ATU, 158, 159, 167 backup systems, 239–40 behavior, see feeding bio-ﬁltration, 235, 236–7 bio-mats, 165, 168 bleeding ﬁsh, 208, 209 blood, 48, 41–2, 50, 53, 62, 94 Bohr effect, 48 breeding programs, 128–30, 137; see also brood stock handling, brood stock maturation age at maturity, 31, 125 anesthetic chemicals, 143, 149–50 attributes for culture, 123–5, 129 crossbreeding, 132, 133 diet, 106 disease, 68, 67 domestication, 123 egg quality, 125, 140 family selection, 133 fecundity, 32, 146 feeding, 93, 98, 101, 138, 141, 156 ﬂesh pigmentation, 125, 129, 132

266

Index

foundation population, 137 fungus, 68 genetic gain, 132 genetic variation, 132 growth rates, 83 heritability, 130–32 heterosis, 132 hybridization, 132, 138 inbreeding, 132, 138 mass selection, 154 mating programs, 138 maturation, 88, 90, 125, 129, 142–4 monitoring systems, 147 nutrition, 98, 101, 106 pure breeding,132 quality of eggs, 125, 136 rearing conditions, 138 salinity tolerance, 55 saprolegnia, see disease selection goals, 124–5, 128–30, 138 sexual maturation, 91, 90, 125, 129, 141 size variation, 125, 129, 133 spawning time, 139 standard Arctic charr, 133–5 stocking density, 138 strain selection, 125–8, 138 stress, 68 survivability, 138 temperature regime, 57 weight, 132 wild strain evaluation, 125–30, 137 brood stock handling, 68, 143–5 brood stock maturation, 91, 129, 139, 141, 142–4, 149 altering photoperiod, 58 egg quality, 138, 140, 146, 147 spawning times, 31, 139 brood stock nutrition, 93, 98, 138, 141, 156 brood stock programs, see breeding programs business management, see management business plan, 229 canthaxanthin, 100, 101, 103 cage culture, see rearing containers carbohydrates, 96, 97, 106 carbon dioxide, 40, 48 carotenoid pigments, 99–103, 106, 201–202 carrying capacity, 190

catastrophic failures, 9, 12, 174, 233, 186, 239–40 chemotherapeutants; see also disease antibiotics, 66, 67, 72, 156 bacterial resistance, 66 controlling fungal infections, 155, 160, 161 formalin, 160, 161 fungicides, 155, 161, 182 hydrogen peroxide, 161 iodine solutions, 155, 156 malachite green, 160, 161 sodium chloride, 68, 161 toxicity to downstream biota, 236 circulating tanks, see rearing containers clove oil, 149, 150 compensatory growth, see growth, feeding condition factor (K), see growth Coregoninae, 35 cortisol, 62; see also physiological stress density, 12, 13, 15, 61 current velocity, 168 effects on growth, 169 optimum density, 168, 169, 174, 190, 191 desmoltiﬁcation, 54 diet, 103–108 carbohydrate, 92, 96, 97 carotenoid pigments, 102–103, 106, 201–202 feeding behavior, see feeding formulation, 96, 106 lipids, 92, 93, 95, 96, 106 minerals, 99, 100, 106 protein, 92, 93, 106 vitamins, 97–9, 106 dietary efﬁciency, 71 digestibility, 105 disease, see Chapter 3 Aeromonas salmonicida, 62, 63, 65–6 bacterial gill disease, 169 bacterial kidney disease (BKD), 66–7, 162 Caligus spp., 70 certiﬁcation, 66, 138 Cestoda, 70, 246 control, 72–3, 159, 231 density effects on, 60, 61 Digenea, 245 disease-free stock, 66, 162

Index

egg diseases, 68 ﬂukes, 70 fungal diseases, 62, 68, 143 furunculosis, 62, 65–6 Gyrodactylus salaris, 70 health management, 72–3, 148, 159, 231–3 horizontal transfer, 66, 67, 68, 69, 70, infectious haematopoietic necrosis (IHN), 65, 156 infectious pancreatic necrosis (IPN), 64, 156 metazoan parasites, 64, 69–70, 245 Nematoda, 64, 69–70, 246 pancreatic necrosis, 64 parasites, 64 PKX organism, 68 proliferative kidney disease (PKD), 68–9 protozoan parasites, 64, 68, 245 Saprolegnia spp., 68, 143, 155, 160, 182 sea lice, 66 stress, see physiological stress swim bladder stress syndrome (SBSS), 71 tolerance to, 68, 72 toxic chemical compounds, 71, 72 toxic construction materials, 71, 72 Trematodes, 69–70, 245 vaccination, 231 vaccines, 64, 67 vertical disease transfer, 67, 69 Vibrio anguillarum, 67 vibriosis, 67 viral haemorrhagic necrosis (VHS), 65, 156 dissolved oxygen, see oxygen disinfectants, 66, 68, 148, 155, 156 Dolly Varden, 17, 19 domestication, see breeding programs economics, see market economics eggs, see also fecundity, fertilization, gamete removal assessing ripeness, 141 egg shipment, 66, 67, 162–3, 193 egg size, 140, 152 eyed eggs, 156, 157, 158 ovulation, 140–41 quality, 143, 152, 153, 158 saprolegniasis, 68, 155, 160 survival, 140, 146 egg collection, 145–8

267

egg incubators, 149 egg trays, 149, 154 fertilizing, 154 loading trays, 154–6 management of, 146–8 removing eggs, 151–3 egg development, 139, 156 activation, 154 ATU, 158, 159 development rates, 156, 158 models for, 158 oxygen levels, 159 temperature, 57, 58, 158 water-hardening, 151, 155 egg incubation, see incubation egg shocking, 157, 160–1 egg picking, 161 egg take, 136, 146–8, 151–3 embryology, 158, 159 emergency preparedness, 239–40 environmental impacts, 41, 229–30, 230–31 essential fatty acids, 94–6 linoleic acid (n-6), 95, 96 linolenic acid (C18:3-n-3), 95, 96, 106 n-3 fatty acids, 95, 96 polyunsaturated (PUFAs), 95, 96 exercise, 192; see also rearing container velocity eyed ova, see eggs fasting, see compensatory growth fat-soluble vitamins, see vitamins fecundity, 31–3 feeding aggression, 33, 83, 87, 114 appetite, 113, 17, 176, 200 automatic feeders, 115, 116, 173, 177, 200 behavior, 34, 200 biological clocks, 85 cannibalism, 34 compensatory feeding, 111–12 conversion efﬁciency, 79–81 cycles, 84–5, 86, 87, 200 demand feeders, 83, 117, 116, 200 diurnal feeding patterns, 84, 87–8, 114 feed cost, 82, 91, 113, 172, 198, 202, 226 feed delivery, 115–17, 173, 177, 200–201 feed distribution, 111, 113–15, 117, 173, 177

268

Index

feed energy content, 80, 172 feed palatability, 105, 106, 171, 172 feed shape, 111, 112, 172, 177 feed size, 110–11, 112, 171, 172, 177, 200, 205 feed storage, 99, 173 feed tables, 109, 171, 172, 177, 199 feeding behavior, 84, 87, 173 feeding frequency, 114–15, 172, 173, 176, 200 feeding rhythms, 84–5, 87, 114 feeding strategies, 111–17, 172–3, 176 feeding systems, 238 ﬁrst feeding, 165, 166, 167, 170–73 hand feeding, 173, 201 in nature, 34–6, 84, 85, 86, 189 monitoring, 200–201, 235 pigments, see carotenoid pigments prey size, 35 ration level, 109–10, 117, 171, 177, 199–200, 205 restricted feeding, 111–12, 176 satiation feeding, 91, 111–12 seasonal feeding patterns, 84, 87 size variance, 83, 84 strategies, 87, 172–3, 198–202, 235 temperature, 56, 171, 199 feeds, 107–108, 171, 172, 201 pellet density, 115 types of, 106, 107, 108, 171, 172, 201 fertilization, 154 activation of eggs, 154 activation of the spermatozoa, 141 dry method, 151 fertility check, 157 micropyle, 152 milt pooling, 154 milt to egg ratio, 154 motility, 141, 153 spermatozoa, 141, 151 techniques, 151–4 water-hardening, 151, 155 ﬁngerlings, 12, 66, 165, 166, 174, 175, 179, 181–3, 169, 222 ﬁsh density, see density, rearing density ﬁsh health management, 72–3, 231–3 ﬁsh products, see marketing folic acid, see vitamins

fry, 10, 165, 166, 169, 174, 175 fungus, 68, 143, 158, 160, 182 gamete quality, see fertilization gamete removal, 140; see also egg collection broken eggs, 145 egg plug, 143 egg removal, 151–3 expression, 153 sperm removal, 153 gas bladder, 20, 71–2 gas bubble trauma, 49 gas supersaturation, see total gas pressure genetic traits, see breeding programs gills, 41, 42, 81 gill nets, 7, 8, 9, 207; see also harvesting grading, 84, 165, 174, 178–81, 194, 202–205; see also feeding, sorting ﬁsh grow outs, see production growth, 74–92; see also breeding programs body size, 82–3 compensatory growth, 86, 91–2 condition factor (K), 78, 85, 86, 91, 113, 131, 134, 179 controlling factors, 75, 86, 87 conversion efﬁciency, 79–81, 82, 91, 110, 117 daily growth, 87–8 density, 60; see also rearing exercise, 80, 115, 192 feed quality, 80 feeding strategy, 27, 111–17 ﬂuctuating temperatures, 113 food conversion ratio (FCR), 79; see also feeding growth acceleration, 113–14 growth formulae, 76, 77 growth models, 29, 75–8, 134 growth partitioning, 87–8 heritability, 29, 130–31, 133 Iwama growth model, 76–8, 134 length-weight relationship, 28, 29, 78, 85, 87, 90 light intensity, 58 limiting factors, 80, 87, 88 lipid levels, 28, 93, 108, 106 lunar cycles, 87–8, 114 natural growth, 27, 74 photoperiod, 58, 82, 86, 92

Index

polyculture, 189 protein requirements, 92, 93–4, 106, 108 optimum growth, 80 ration, 108, 109–10 salinity, 55, 80 seasonal growth rate, 84–7, 113 sexual maturity, 30, 31, 88–91 size variation, 83–4, 113, 178 speciﬁc growth rate, 27, 28, 75–6, 85 standard growth model, 133–5 starvation, 91–2 strain differences, 29 stress, 83, 89 temperature, 27, 75, 76, 77, 81–82, 92 handling ﬁsh, 144, 145, 146–7, 153, 170, 174, 179–80, 181–3 hardness, 40, 55–6 harvesting, 4, 6, 7, 8, 84 194, 197, 205–208, 209 hatcheries, 137, 138, 148, 156, 159, 167–8, 175 brood, 138 hatching, 161–2 health management, see ﬁsh health management heritability, see genetics historical developments, 10–13, 128, 186, 244 homing, 22, 23 immune system, 61–2 incubation, 156–8 ATU, 158–9 dissolved oxygen, 159 egg hatching, 161–2 egg picking, 161 egg shocking, 160–61 fungus control, 160 incubators, 148, 149, 162 inventory control, 157, 159–60 loading trays, 154–5 mechanical shock, 157 monitoring, 159–60 water quality, 158, 159 International Standards Association (ISO), 230–31 inventory, 159–60, 178, 194, 196–7, 241–3 jacking, 90 land-based culture, 169, 194–7, 219, 220, 230

269

lake stocking, see pothole lakes light, 58–9, 86, 87 feeding, 58, 86–7, 109, 113 light/dark cycles, 58, 88, 176, 198 light levels, 58, 87, 159, 169, 170, 176, 181, 198 manipulation, 87, 113, 173, 175, 198 photoperiod, 58, 59, 86–7, 90, 139, 173, 175–6, 198 lipids, 86, 91, 92, 94–6, 105, 106 management, 187, 228–30 attributes for, 12–13, 227 construction, 228 critical points, 232, 239 ﬁnancing, 228 ﬁsh health, 231–3 live ﬁsh operations, 227, 228, 230–43 mechanical systems 237–41 production systems, 241–3 water quality, 233–7 market economics, 219–226 marketing principles, see Chapter 9 associations, 216, 218 branded products, 214 generic advertising, 216, 225 organic products, 215 packaged products, 214 pricing, 214–15, 224–5 product competition, 210, 216, 226 product distribution, 210, 216–19 product quality, 95, 100, 102, 103, 201, 206, 208, 209, 211–13 product shelf life, 209, 211, 214 product yields, 214 production planning, see production products, 3, 7, 8, 14, 201, 205, 212–14, 216, 226 public perception, 212, 214, 215, 216, 229 quality control systems, 210–212 quality standards, 211–13, 218 selling, 206, 216, 218 strategies, 215–16, 225, 226 types of products, 205, 206, 218 value added products, 212, 213 vertical integration, 217 maturation; see also brood stock determination of, 90, 91, 141

270

Index

harvesting, effects on, 90, 208 in the wild, 31 mechanical systems, 148–9, 161, 167, 170, 174–6, 179–80, 188, 191. 237 metabolic rate, see oxygen consumption ﬁsh size, 48 stress, 180; see also physiological stress swimming activity, 45 temperature, 46–7 migration, 21–4 homing to natal rivers, 21 ocean, 21, 23–4 milt, see spermatozoa minerals (dietary), 99, 100 models, 23, 38, 44, 46, 48, 49, 53, 76–8, 79, 109, 133–5, 158, 182 morphs, 25–7, 35 mortality, 100, 143, 158, 159, 162, 170, 171, 174, 226 niacin, see vitamins nitrate, 40, 53 nitrogenous wastes, 40, 50–53 ammonia, 40 ammonia toxicity, 51–2 nutrition, 92–103 on-growing, see production operations manual, 238, 243 operculum, 20 organic growing, 215; see also pothole lakes organs, 20 osmotic regulation, see salinity ovulation, see eggs oxygen, 41–8 aeration devices, 168, 180 concentration, 42, 44, 167 emergency life support, 180 injection, 174, 191 metabolism, 43 Rawson’s nomogram, 144 requirements, 40, 159, 169, 191 saturation, 42 oxygen consumption, 41–8, 180 atmospheric pressure, 43, 44 counter-current ﬂow, 41–2 ﬁsh size, 48, 169 food intake, 43–6

swimming speed, 43 temperature, 42, 43, 44, 46–7 pan size ﬁsh, 14, 214, 215, 224–5, 226 pantothenic acid, see vitamins parasites, 64 sea lice, 66 particulate waste, see waste loadings pH, 40, 49–50, 55 phosphorus, see waste photoperiod, see light physiological stress, 60–63, 65, 67, 83, 84, 89, 180, 232 pigment, see carotenoid pigments ponding, 164–71 ATU, 165 MAWW, 166 preparing for, 167–70 water ﬂow, 167, 168, 169 pothole lakes, 37, 69, 189–90, 193, 205, 206 precocious males, 90 predictive models (rearing), 75–8, 133–5, 165, 194–7, 223 processing, 205, 209, 217 production, 120; see also models, predictive models costs, 220–26, 219 cycles, 192–7 management, 241–3 monitoring, 201–202, 195–6, 239, 241 stocking density, 188–92 strategies, 187–8, 192–7, 205–206, 219, 223, 226 types of grow-outs, 188–9 production volumes, 194, 196–7 historical, 6–10, 13, 14 world, 13–15 products, see marketing proﬁtability, see market economics protein, dietary, 92–94; see also growth amino acid digestibility, 105 digestibility, 105 feedstuff components, 95, 104, 106 protein requirement, 92–4 psychological aggression, 83 quality, 211–12, 213 rearing

Index

densities, 59–60, 169, 174, 175, 188–92 environment, 232, 235; see also Chapter 3 water ﬂow, 37, 169, 175 rearing containers alarm systems, 174, 237, 238, 239–40 bag pens, 188, 219 cages, 55, 91, 117, 118, 219 color, 170 costs, 219–20, 223 diameter–depth ratios, 169, 175 duo culture, 189 ﬂow-through tanks, 168, 175, 237 grow-out tanks, 188, 189, 190–92, 194, 197, 206, 237 inﬂow design, 167–8 maintenance, 170, 173, 240 materials, 168, 175 net-pens, 55, 91, 219 outﬂow design, 168, 235 oxygen injection, 174, 197, 237, 239 ponding tanks, 165, 166, 167, 170, 173 pothole lakes, 69 self-cleaning, 173, 175, 235 troughs, 167 velocity, 168, 175, 177, 192 recirculation, 235 redd, 33 reproduction, see spawning, fertilization, breeding programs respiration see also metabolic rate, oxygen consumption riboﬂavin, see vitamins Roche color card, 133, 134, 213 salinity, 23–4, 53–5, 70 Salmonidae Atlantic salmon, 10, 14, 16, 35, 48, 52, 54, 65, 70, 84, 92, 93, 96, 98, 100, 107, 117, 118, 121, 145, 146, 171, 186, 191, 210, 221, 223, 224 brook charr, 19, 25, 35, 64, 65, 98 brown trout, 34, 35, 65, 84, 93, 171 Chinook salmon, 65, 101, 118 Dolly Varden charr, 19, 64 Lake charr, 34, 35, 96, 98 rainbow trout, 14, 16, 48, 65, 93, 100, 107, 121, 145, 186, 191, 210 sockeye salmon, 70, 189, 212, 214

271

whiteﬁsh, 35 Salmoninae, 17 sea water tolerance, see salinity settling ponds, 236 size grading, see grading size variation, see growth, feeding, brood stock slimy thumb, 121 smolting, 23 ATPase, Na, K, 53, 54 environmental cues, 54 ﬂuctuating water temperature, 54 photoperiod, 54 physiological changes, 53 silvering, 24 size, 24 transfers, 55, 193 sorting ﬁsh, 84, 178–81, 202–205; see also grading spawning, 139–43 behavior, 31, 141 equipment for, 148–9 monitoring egg quality, 147 non-spawners, 141 preparation, 148 redds, 31 sorting, 142–3 spawning window, 139–40 time required, 146 timing, 31, 139–40, 141, 143 sperm, see spermatozoa, fertilization spermatozoa, 141, 151, 152, 153 standard Arctic charr, 133–5, 223 strains, 125–8 Fraser (Labrador), 12, 30, 69, 93, 101, 103, 127, 128, 129, 178, 187 Grenlaeker, 126–7, 129 Hammerfest, 45, 55, 81, 85, 101, 103, 125–6, 128, 129, 133, 159 Hornnavan, 126, 128, 129, 130 Nauyuk, 12, 13, 19, 20, 21, 22, 24, 25, 28, 30, 31, 32, 43, 51, 55, 57, 84, 90, 91, 101, 103, 127–8, 129, 130, 131, 133, 134–5, 142, 159, 178, 193, 194 Olesvatn, 126–7, 129 Svalbard, 20, 54, 55, 125, 126, 129 stress, see physiological stress suspended solids, 56, 169 swim bladder stress syndrome (SBSS), 71–2

272

Index

swimming, see exercise systems management, 237–41 tanks, see rearing containers temperature, 56–8, 158 lethal, 57 limiting, 57 metabolic rate, 42, 43, 44 optimum, 40, 56, 57, 81–2, 158, 163, 180, 209 total gas pressure (TGP), 40, 49 transport systems, 66, 209 aeration, 181, 182 carbon dioxide, 48, 181, 182 fertilized eggs, 162–3 iced ﬁsh, 209 juvenile ﬁsh, 181–3 loading densities, 182 plastic bags, 181, 182, 183 processed ﬁsh, 216–17 traps, 208 vaccination, 65, 67, 231 viral disease, see disease vitamins, 97–9, 101 waste loadings, see also environmental impacts, cage culture bio-ﬁltration, 235, 236–7 collection of solid wastes, 235 current velocity, 177 diet composition, 107 dissolved waste, 237 feeding, 92, 117, 113, 118, 177, 234 phosphate, 234, 235, 236 phosphorus, 234, 236 post-farm aeration screening, 235, 236 settlement, 235

sludge, 235 suspended solids, 56, 234, 235 water, see Chapter 3 aeration, 38, 48, 49, 168 alkalinity, 40, 55–6 ammonia, 40, 53, 169, 181 BOD, 236 CO2 level, 40, 48 criteria for rearing, 37, 139, 169, 173 ﬂow, 169, 192, 237 gas bubble trauma, 49 guidelines for rearing, 168, 173, 192 incoming, 38–9, 167, 168 incubation, 139, 140 loading rate, 169 minimum DO, 40 models, 37 nitrite, 40, 53 outﬂow, 40, 41, 168 oxygen, 40, 45, 169 rearing, 39, 167, 169, 173, 191 residence time, 39 single-pass systems, 37 suspended solids, 40, 56, 169, 173, 234, 235 systems, 37–41, 237, temperature, 40, 139, 140, 169 total gas pressure (TGP), 40, 49 un-ionized ammonia, 40 wild water, 38, 40–41, 236 water hardening, 151, 155 water quality guidelines, 39, 40–41, 169, 229, 233–7 water re-use, 39, 236 ammonia, 53, 181 water system 37–41, 148–9, 237 water use impacts of, 41, 92, 229 wild ﬁshery, 6–10

Clupeiformes (order)

Salmonidae (family) Coregoninae

Thymallinae

Salmoninae (sub-family) (Trout, Charr, and Salmon)

Grayling

Salmo

Whiteﬁsh

Oncorhynchus

Atlantic Salmon

Brown Trout

Pink Salmon

Chum Salmon

Coho Salmon

Sockeye Salmon

Chinock Salmon

Rainbow Trout

Cutthroat Trout

Salvelinus (genus) fontinalus

namaycush

malma

conﬂuentus

Brook Trout

Lake Trout

Dolly Varden

Bull Trout

alpinus (species)

taranetzi

erythrinus

alpinus

Plate 1 The taxonomic relationship of Arctic charr to other salmonids.

oquassa (subspecies)

Plate 2 Nauyuk Arctic charr showing sea-run (top), mature female, and mature male colors.

Recirculating Aquaculture

Aquaculture Science

Aquaculture Engineering

Ecological Aquaculture

Ecological Aquaculture

Arctic Gold

Arctic Floor

Arctic Chill

Arctic Gold

Arctic Drift

Arctic Rising

Arctic Drift

Arctic Revolution

Arctic Winds

Arctic Drift

Arctic Drift

Arctic Chill

Arctic Drift

Arctic Drift

Arctic Dragon

Arctic Shift

Arctic Fire

Arctic Enemy

Arctic Drift

Arctic Drift

Arctic Trucker

Arctic Drift

Arctic Chill

Arctic Fire

Arctic Gold

Arctic Charr Aquaculture

Recirculating Aquaculture

Aquaculture Science

Aquaculture Engineering

Ecological Aquaculture

Ecological Aquaculture

Arctic Gold

Arctic Floor

Arctic Chill

Arctic Gold

Arctic Drift

Arctic Rising

Arctic Drift

Arctic Revolution

Arctic Winds

Arctic Drift

Arctic Drift

Arctic Chill

Arctic Drift

Arctic Drift

Arctic Dragon

Arctic Shift

Arctic Fire

Arctic Enemy

Arctic Drift

Arctic Drift

Arctic Trucker

Arctic Drift

Arctic Chill

Arctic Fire

Arctic Gold

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