Table Of ContentTHE EEL
THE EEL
Biology and Management of
Anguillid Eels
F.-W. TESCH, Dr. agr.
Bjologjsche Amral! Helgoland, Hamburg
Translated by Jennifer Greenwood
ENGLISH EDITION EDITED BY
P.H. GREENWOOD, D.Se.
Department of Zoowgy,
British Mweum (Natural History)
This first English-language edition of Der Aal by F.-W. Tesch, has
been updated throughout by the author, and physiological sections
have been revised and extended by
I.W. HENDERSON, Ph.D.
Department oj Zoology,
University of Sheffield
LONDON
CHAPMAN AND HALL
A Halsted Press Book
John Wiley & Sons, New York
First published, 1973, by Paul Parey, Hamburg and Berlin
under the title Der Aal, written by F.-W. Tesch
© 1973 Verlag Paul Parey, Hamburg and Berlin
This revised and updated, English-language edition,
a translation approved by F.-W. Tesch,
first published, 1977, by Chapman and Hall Ltd.
ISBN-13: 978-94-009-5763-3 e-ISBN-13: 978-94-009-5761-9
001: 10.1007/978-94-009-5761-9
© 1977 Chapman and Hall Ltd.
Soflcover reprint of the hardcover 1st edition 1977
All rights reserved. No part of this book
may be reprinted, or reproduced or utilized
in any form or by any electronic, mechanical
or other means, now known or hereafter invented,
induding photocopying and recording, or in any
information storage or retrieval system, without
permission in writing from the publisher.
Distribution in the U.S.A. by Halsted Press,
a Division of John Wiley & Sons, Inc., New York
Library of Congress Cataloging in Publication Data
Tesch, Friedrich-Wilhelm.
The eel.
Translation of Der Aal.
"A Halsted Press book."
Bibliography: p.
Includes index.
1. Anguilla (Fish) 2. Eel fisheries. I. Title.
Contents
Foreword page xi
Preface Xlll
Body Structure and Functions
I. [
l.l Skeleton [
I.l.l Skull [
I. 1.2 Pectoral girdle 6
I. 1.3 Vertebral colwnn 6
J.I.4 Fins 8
1.2 Skin and musculature 9
1.2.1 Structure and function of the skin 9
1.2.2 Scales [2
1.2.3 Pigmentation [4
1.2.4 Teeth [9
1.2.5 Muscuiarure 2[
1.3 Respiratory organs and swimbladder 23
l.4 Feeding and organs of digestion 28
1.4.1 The gastrointestinal tract 28
1.4.2 Pancreas 32
1-4-3 Liver and gall bladder 34
1.5 Circulation of the blood 35
1.5. I Cardiovascular system 35
1.5-2 Blood 38
1.6 Urinogenital system 4[
1.6. I The kidneys 4[
1.6.2 The gonads 43
1.7 The endocrine system 58
1.7.1 The pituitary gland 58
v
VI
I.7.2 The thyroid gland 62
1.7.3 The urohypophysis 63
1.7.4 The interrenal tissue (adrenocortical homologue) 64
1.7.5 Ultimobranchial bodies 64
1.7.6 Corpuscles of Stannius 65
I.7.7 Thymus gland 65
I.7.8 The kidney 66
1.8 Nervous system and sense organs 66
1.8.1 The brain 66
1.8.2 Eye 68
1.8.3 Olfaction
73
1.8.4 Hearing and the lateral line sense organs 79
2. Eel Species, their Developmental Stages and
their Distribution 81
2.1 The European and American eels A. anguilla and
A. roslrata 83
2.1.1 Spawning grounds and larval forms 83
2. 1.2 Continental distribution 102
2.2 Indo-Pacific species IIO
2.2. I The south-east African region: A. marmorara,
A. nebulosa iabiala, A. mossambica and
A. hiealor III
2.2.2 The temperate north Pacific zone: The
Japanese eels A.japonica and A. marmorata 114
2.2.3 The south-east Pacific species from the
temperate zone: A. australis and A. dieffenbachi 118
2.2.4 The tropical eels
A. celebesensis, A. megastoma, A. interioris,
A. ancestralis, A. nebulosa, A.m armorata,
A. reinhardti, A.b orneensis, A. biwlor, A. obscura 122
2·3 Zoogeographical relationships 129
3· Post-Larval Ecology and Behaviour 133
3.1 The glass eel and elvers: their migration on the
Continental shelf and into freshwaters 133
3.1.1 Migration in the sea 133
3.1.2 The movement into freshwater 139
3.1.3 Human intervention 150
3.2 Migration of pigmented young eels 154
3.2.1 Dependence on environmental factors 154
3.2.2 Human involvement in the ascent of young eels 162
vii
B The 'Yellow eel' stage to the 'Silver eel' stage 169
3.3.1 Feeding 169
The period of activity and food intake-Seasonal
variations in diet-Choice of food and body
size-Choice of food and head width-The
dependence of diet on food availability-Choice
offood
3.3.2 Age and growth 184
Methodological problems-Differences in growth
between males and females and the age and
length at which migration begins-Head width
and growth-Differences in growth due to
environmental factors-Interspecific differences
in growth-Theoretical pattern of growth-
Length and weight
3.3.3 Location, habitat and behaviour patterns 208
Refuge in tubes and hollows, and contact with
members of the same species-Water depth-
Survival in air-Localization and homing
3·4 Silver eel migration 220
3-4. I Seasonal variation 220
3.4.2 Variations in the time of day, and the influence
of light 224
3.4.3 Correlation with lunar phases 224
3.4.4 Hydrological and meteorological factors 226
Low pressure areas-Water level and currents in
rivers-Tidal currents-Wind and currents-
Temperature and depth-Salinity
3.4.5 In subterranean waters 234
3.4.6 In the sea, with special reference to the Baltic 235
3·4· 7 Behaviour and speed 239
4· Fishing Yields 241
4·1 The development of eel fisheries 241
4·2 Annual and regional fluctuations in yield 244
4.2.1 Variations over the whole North Sea region 244
4.2.2 The effect of differing proportions of males and
females on variations in catch size along the
southern coast of the Baltic and in inland waters 244
4.2.3 The relationship between the west wind and
glass eel invasions 246
4.2.4 The influence of seasonal temperature levels 248
viii
4.2.5 Catch variations in Canada 248
4·3 Variation in catch size throughout the year 249
4·4 Population density and catch sizes from an economic
and ecological viewpoint 252
4.4. I Regional differences 252
4.4.2 The eel in competition with other fishes and
with crustaceans 256
4-4.3 Improving yields by stocking 265
4.4.4 Summary of yield and stocking success 270
5· Fishing Methods 272
5.1 Eel traps 273
5. I. I Eel baskets 273
5.1.2 Fyke nets 277
5.1.3 Pound nets 281
5-2 Stow nets 285
5.2.1 Staked stow nets 286
5.2.2 Anchored stow nets 286
5.2.3 Onerboard stow net 288
5-3 Permanent eel traps 292
5.3.1 Eel weirs in rivers 292
5.3.2 Eel traps in streams and rivers 297
5·4 Seines and trawls 300
5·5 Angling and line fishing 304
5·6 Lift nets, spears and other equipment 315
5·7 The use of electricity 318
5.8 Combination with light 322
6. Eel Culture and Live Storage 328
6.1 Eel farming in Japan 329
6.1.1 The importance of eel farming 329
6. 1.2 Pond systems and yields 330
6. 1.3 Rearing techniques 332
6.1.4 Feeding 333
6. 1.5 Profit and expenditure 335
6.2 Experiments on eel farming in Europe 335
6·3 Live storage 340
7· Diseases, Parasites and Injuries 342
7-I Virus and bacterial diseases 342
7. I. I Cauliflower disease 343
ix
7.1.2 Fresh- and saltwater eel diseases
Freshwater eel disease-Saltwater eel disease 346
7·2 Infestation by fungi, protozoa and metazoa 351
7·3 Teratological and other defects 356
8. Trade and Processing 363
8.1 International trade 363
8.2 Prices 364
8·3 Quality 367
References 371
Index 423
Foreword
by Dr P. H. Greenwood
British Museum (Natural History), London
Dr Tesch's wide ranging account of anguillid eels impinges on the
interests of many biologists; it is not simply a specialized tome narrowly
aimed at ichthyologists and fishery scientists, rather it provides a
source of primary reference and a comprehensive sununary of informa
tion that is not likely to be superseded for a long time. It is significant
that the bibliography includes references to learned journals concerned
with physiology, pharmacology, taxonomy, genetics, zoology, endo
crinology, botany, ecology and environmental interactions. Such is the
breadth of interest in the Anguillidae.
Few fish species have been subjected to as detailed review as Dr Tesch
gives for the (wo Atlantic species of Anguilla. An equally comprehensive
resume of research into the fourteen, rather less well-studied Indo
Pacific species gives balance and reciprocal illumination to several
biological problems posed by these similar but quite distinctive species.
The German language edition of Dr Tesch's book was well received
and much consulted. The present English edition should greatly increase
its readership, and more especially since the author has revised and
updated the entire text. Those sections concerned with facets of eel
physiology have been expanded and revised in collaboration with
Dr Ian W. Henderson himself actively engaged in investigations into
certain aspects of anguillid physiology. The sections on hormonal
physiology of the eel have received considerable attention, as it is in this
sphere that great progress has been made in recent years. Indeed, studies
of eel systems have contributed greatly to furthering knowledge of fish
physiology generally. The final product is in my opinion an even more
useful and comprehensive volume that was its predecessor, Der Aal.
xi
Preface
A little more than sixty years ago, the life cycle and transoceanic
migrations of the Atlantic eels were first revealed through the work of
the Danish scientist, J. Schmidt. These studies and the way in which
they were conducted are still held in high regard, and Schmidt's work
is recounted in almost every scientific and popular book on eels.
Less widely known, however, are the results of research into the
biology of related eel species from the Pacific and Indian oceans. In this
book data relating to all species of the genus Anguilla have been brought
together for the first time, so that interspecific comparisons can now be
made more readily.
Although research into eels' spawning grounds may once have
appeared the most spectacular contribution to OUf knowledge of these
animals, the eel's anatomical and morphological characteristics are of
equal interest. A creature with such a variety of unusual ecological
characteristics is bound to show a corresponding variety of physical
features, and the number of scientists studying the morphology and
physiology of the eel thus continues to increase. This is the case not
only in Europe and Japan, where the eel is one of the more widely
distributed species of fish, but also in North America, where it has a
much more restricted distribution. A detailed description of the eel's
physical characteristics, its behaviour patterns, and its relationship
with the environment seems urgently required. The eel should not be
used as an experimental animal without an awareness of the special
features in its ontogeny and growth. For example, after a lecture on
respiratory physiology at an international symposium, a member of the
audience asked if the experimental animals were 'yellow' or 'silver'
eels. The lecturer replied that neither of these varieties had been avail
able, only species of Anguilla anguilla had been used!
Xl1l
