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- Herausgeber: John Wiley & Sons
- Kategorie: Fachliteratur
- Sprache: Englisch
Advances in underwater exploration, in situ observation of fish populations, as well as the development of cutting-edge technologies, provide modern insights into behaviors and strategies of fish, whose cognitive abilities have long been underestimated and undervalued. Fish Behavior 1 presents current knowledge about fish biology, ecology and ethology. In light of the most recent scientific work, this book examines the habitats exploited by fish, as well as the strategies and tactics they have adopted regarding the occupation of available territories. It also addresses communication issues between individuals during social interactions. This book is intended for researchers, teachers, master s and doctoral students in biology and biogeography, engineers and technicians responsible for the development and protection of natural environments and public aquariums, in addition to aquaculturists, fishermen, environmentalists and ecologists.
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Table of Contents
Cover
Prefece
Introduction
1 Habitats: Occupation, Protection and Exploitation
1.1. Diverse and unusual habitats
1.2. Food: the use of trophic habitats
1.3. Individual and collective protective habitats
1.4. Breeding habitats (Volume 2, section 2.1)
2 Strategies and Tactics for the Occupation of Available Territories
2.1. Faithfulness to habitat and birth site
2.2. Habitat changes
2.3. The colonization of new territories
3 Communication and Social Life: Behaviors Related to Social Interrelations between Congeners, Parasites and Predators
3.1. Communication between partners
3.2. Neighborly warning
3.3. Groups, shoals, swarms and masses
3.4. Mutualists and parasites
3.5. Cleaners
3.6. Helpers
3.7. Selection of sexual partners
3.8. Sexual conflicts
3.9. Joint provision of parental care
3.10. Competitors
3.11. Sense of family and recognition of familiar congeners
Glossary
Species Index
Summary of Volume 2
End User License Agreement
List of Illustrations
Chapter 1
Figure 1.1. Protected habitat of a squirrel fish, Sargocentron microstoma, with ...
Figure 1.2. Anabantid climbing perch, Anabas sp., able to leave the water and cl...
Figure 1.3. Abyssal fish carrying ventral photophores
Figure 1.4. Diagram of the flight paths of swallows and tigerfish, Hydrocynus vi...
Figure 1.5. Strategy for approaching the Silurus glanis on a river beach of the ...
Figure 1.6. Mediterranean dusky grouper, Epinephelus marginatus, having seized a...
Figure 1.7. Trajectory of the water jet propelled by the archerfish, Toxotes sp....
Figure 1.8. Damselfish in the vicinity of their Acropora sp. coral shelters (sou...
Figure 1.9. Lionfish Pterois sp., protected by its poisonous spines linked to to...
Figure 1.10. Pygmy seahorse, Hippocampus denise, from Australian reefs, hidden i...
Figure 1.11. Camouflage of the eye of a butterfly fish of the Chaetodon genus. A...
Figure 1.12. Camouflage of a flatfish, Solea solea, whose color pattern is homoc...
Figure 1.13. A parrot fish in the shell of deciduous mucus cocoon that provides ...
Chapter 2
Figure 2.1. Juveniles of Atlantic salmon, Salmo salar: “parr” at the top, with a...
Figure 2.2. Marine distribution area of coho salmon, Oncorhynchus kisutch, durin...
Figure 2.3. Life cycle of the European eel, Anguilla anguilla
Figure 2.4. European eel, Anguilla anguilla, in the silvering stage (source: Fou...
Figure 2.5. Eel leptocephalus larvae (top); elver larvae (bottom)
Figure 2.6. Moonfish Mola mola, a large pelagic that makes deep dives
Figure 2.7. A pair of dusky groupers, Epinephelus marginatus, heading towards th...
Figure 2.8. Leafy sea dragon, Phycodurus equus, a syngnathid attached to driftin...
Figure 2.9. Life cycle of the goby or Napoli climber, Sicyopterus stimpsoni, wit...
Figure 2.10. C-start body curvature of a salmonid allowing it to jump over an ob...
Figure 2.11. Golfech fish elevator on the Garonne River (source: Doc.EDF)
Figure 2.12. Particularly fragmented distribution area of the Rhône apron, Zinge...
Figure 2.13. Gas bladder of a European eel, Anguilla anguilla, infested with nem...
Chapter 3
Figure 3.1. Electrical organ of a gymnotiform. For a color version of the figure...
Figure 3.2. Electromotor nervous system, EOD, of a mormyrid
Figure 3.3. Clownfish, Amphiprion sp., protected by the crown tentacles of a sea...
Figure 3.4. Color pattern of the male guppy, Poecilia reticulata, whose red colo...
Figure 3.5. Red-colored pattern of the three-spined stickleback, Gasterosteus ac...
Figure 3.6. Two small male anglerfish, Haplophryne sp., permanently attached to ...
Guide
Cover
Table of Contents
Begin Reading
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Fish Behavior 1
Eco-ethology
Jacques Bruslé
Jean-Pierre Quignard
First published 2020 in Great Britain and the United States by ISTE Ltd and John Wiley & Sons, Inc.
Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under the Copyright, Designs and Patents Act 1988, this publication may only be reproduced, stored or transmitted, in any form or by any means, with the prior permission in writing of the publishers, or in the case of reprographic reproduction in accordance with the terms and licenses issued by the CLA. Enquiries concerning reproduction outside these terms should be sent to the publishers at the undermentioned address:
ISTE Ltd27-37 St George’s RoadLondon SW19 4EUUK
www.iste.co.uk
John Wiley & Sons, Inc.111 River StreetHoboken, NJ 07030USA
www.wiley.com
© ISTE Ltd 2020
The rights of Jacques Bruslé and Jean-Pierre Quignard to be identified as the authors of this work have been asserted by them in accordance with the Copyright, Designs and Patents Act 1988.
Library of Congress Control Number: 2020930372
British Library Cataloguing-in-Publication Data
A CIP record for this book is available from the British Library
ISBN 978-1-78630-536-7
Preface
Fish, our distant cousins, are able to perform a considerable number of daily tasks to survive, having conquered all aquatic environments, in all climates and at all latitudes and depths.
They are the vertebrates most widely used by humans: fisheries exploit stocks of wild fish populations and carry out intensive fish farming, making fish, in number and mass, the most consumed of all vertebrates. They also occupy an important place in aquariology and are used as experimental models in scientific research (second only to mice). However, the general public’s perception remains limited, particularly with regard to their sensitivity, “well-being” and cognitive abilities. Contemporary ichthyologists have a fairly high level of scientific information that can shed new light on the actual behavioral potential of fish.
Observations of animal behavior have long focused on species that are familiar to us and considered worthy of interest, such as birds (parrots, titmice, swallows or wild geese) and, in particular, mammals, especially those to whom we are most closely related (gorillas, chimpanzees, bonobos, etc.) or who live near us (horses) or in our homes (cats and dogs). The enthusiasm they inspire justifies the success of circuses and zoos. Fish, although they arouse a certain curiosity, especially among anglers and aquarists, rarely receive the attention they deserve, being reduced to the unflattering status of “inferior vertebrates”, beings who seem devoid of language, memory and apparent sensitivity. It is an unflattering and erroneous public perception, linked to the fact that we communicate little with them, separated as we are by such distinct natural environments.
Scientists, through observations and experiments published in credible international journals and from whom the authors of this book take their inspiration, bear witness to the surprising abilities of fish. Abilities that are not so far removed from those of other vertebrates, and even humans with similar characteristics because they are derived and inherited from these “fish ancestors”.
This book consists of two volumes that provide data of 630 species cited, originating from more than 1,500 bibliographical references. It provides new information on recent achievements in the field of ichthyology. These data reveal that our distant cousins are well endowed with cognitive abilities and a potential for memorization and innovation that explains their remarkable capacity to adapt to often difficult environments.
“Ordinary” fish are capable of doing extraordinary things. Some of them are not only great travelers able to orient themselves using the sun and navigate through terrestrial geomagnetism, but are also capable of adopting sophisticated behaviors. Some are subtle hunters or breeders who call upon collective strategies, clever architects and builders of complex nests designed to protect their eggs, courageous fighters willing to sacrifice their lives to defend their offspring and cooperative beings united with a shared goal or producing descendants. Some are even talented imitators anxious to perhaps deceive their partners or predators, Machiavellian strategists, clever courtiers, flamboyant seducers and great lovers. They also demonstrate memory and calculation skills, and the ability to play, use tools and even indulge in artistic creation. Finally, they can sometimes even be good models that can inspire advances in technology and human health.
Jacques BRUSLÉJean-Pierre QUIGNARDJanuary 2020
Introduction
Those of you who are interested in the natural world and are curious to better understand animal behavior, in all its capacity to surprise and be misunderstood, will probably be satisfied to be able, thanks to this book, to learn what fish really are. They deserve much better than their current, hardly flattering, status as “inferior vertebrates”.
Advancing knowledge in the field of fish ethology requires abundant scientific literature consisting of numerous publications in international journals that constantly provide new data to contribute to enriching our view of the behavior of these “conquerors of the aquatic world”, who are rich in their biodiversity and never cease to amaze us.
The authors of this book, academics who have devoted their careers to icthyological studies, have made extensive use of the most recent data in order to present a broad overview of the knowledge acquired in the field of behavior related to fish feeding, protection, social interrelationships and reproduction. This is based on the most representative and original examples cited among the 30,000 species currently listed, but only a few of them have given rise to field observations and laboratory experiments. Recent technological advances in human penetration of the underwater world (submarines, bathyscaphes, etc.) and in situ observation of fish (video cameras, acoustic markers, satellite telemetry, etc.), as well as laboratory data (samples, video images, etc.), have led to the development of new technologies. Those acquired through the use of advanced technologies applied to fish (radioactive isotopes, magnetic resonance, genetic sequencing, etc.) have greatly contributed to providing a modern perspective on their remarkable strategies and surprising behaviors.
The considerable progress made in the field of neurophysiology, as regards their sensory perception, communication, memory, innovation and so on, suggests that they are so sensitive to stress and pain that they deserve to be treated with more care than they usually are. Their need for “well-being” is as important as ours or that of our cats and dogs.
Acknowledgments
The authors would like to express their sincere thanks to all those who helped them by generously providing the original photos and figures to illustrate this book.
1Habitats: Occupation, Protection and Exploitation
1.1. Diverse and unusual habitats
A species can occupy the same habitat throughout its life, from the larval stage to adulthood (pelagic fish), but most species, after a planktonic larval stage (open water habitat), change habitat to live either near the seabed (benthonectonic and demersal species*1) or in contact with the substrate or even buried in it (benthic species*). In addition, many species, depending on their life stages, choose temporary ecological niches that can be used for protection, feeding and reproduction and where intra- and interspecies competition may be less. Such a choice is often decisive in the survival of individuals and populations.
All aquatic ecosystems, and even some land-based habitats, have been used by fish populations, with few ecological niches deprived of their presence, as evidenced by the examples of fish colonizing many different types of habitats.
1.1.1. Psammophilous* habitats
The catfishPygidianops amphioxus has the distinction of living constantly buried in the sandy substrate of the bed of Amazonian rivers since it has never been seen swimming in open water. More dependent on sediment than flatfish – sole, plaice, etc. – or than weevers, which are rather at the interface between sand and water and move above the seabed, feeding on the prey in this familiar environment: specifically, benthic insect larvae such as chironomids, as well as copepods that they absorb by suction through sedimentary particles. Its feeding activity is essentially nocturnal, like that of other catfish. But how does it reproduce? Is this way of life safe, as though burrowing predators were not able to detect its presence and capture it by digging it up?
Flatfish prefer sandy or gravel substrates of a specifically determined granular size* that provide them with camouflage sites in which to develop their mimicry skills (Volume 1, section 1.3.4). In addition, some species, such as American plaicePseudopleuronectes americanus, use burial in the sediment (3, 6 or 9 cm deep) for the thermal regulation of their body: their internal temperature is higher than that of ambient water in winter and, conversely, lower in summer, with the sediment providing natural air conditioning.
Other nectobenthic species, although less dependent on sandy environments, have an imperative need to use such an environment, either to feed like the red mulletMullus sp., or to reproduce like the Californian grunionLeurestes tenuis, or the Japanese fuguTakifugu sp.
Bibliography: Env.Biol.Fishes, 2014, 97: 59-68 & DOI:10.1007/s10641-013-0123-9, Mar.Ecol.Prog.Ser., 2019, 609: 179-186 & DOI.org/10.3354/meps123354
1.1.2. Reef cavity habitats
Reef corals create complex mineralized structures with an extreme diversity of habitats used by small fish whose size and morphology are perfectly adapted to the geometric structures created. The great diversity of coral structures, constituting a multitude of highly specialized microhabitats, makes it possible to shelter many small fish with highly diverse body shapes that use the structures as anti-predator refuges, food resources and egg spawning sites. On the Australian Great Barrier Reef, blennies such as the Salaria, Glyptoparus and others, all small fish particularly vulnerable to predators, must find safe havens, as species including snappers, groupers and morays are permanent threats. All cavities – holes, crevasses, drop-offs, caves – among Porites corals are therefore sought and occupied according to their diameter, depth and habitability, to within a few millimeters or a few centimeters, and affect all species in accordance with their own morphology, with precise interspecies differences reflecting a very specific division of habitats that promotes their coexistence. Competition for the occupation of the best shelters is generally fierce, and all species sometimes need to defend their personal habitat.
The gobies, Gobiodon histrio, live in close association with the coral reefs of the Red Sea, using microhabitats created by host corals according to the distance between Acropora branches and their own body morphology, in particular, their width, which allows them to creep into interbranchial spaces. Goby species with compressed bodies, laterally flattened, are favored in this interspecies competition and remain particularly faithful to their individual habitat. Described as cryptic*, they shelter in Acropora branches in accordance with their length and the interbranchial space of each branch, with lateral compression of the body and a small size ensuring a certain interspecies segregation. They jointly exploit coral architecture by adapting perfectly to its geometric constraints, with their maneuverability conditioning their protection and movement, and therefore their survival, and justifying their movement from branch to branch as they grow in order to continuously occupy “tailor-made” habitats.
The distribution of various species of damselfish, such as Dascyllus aruanus or Chromis viridis in Red Sea coral reefs, follows well-defined habitat rules reflecting the type of reef, continuous or sparse, and, especially, the specific morphology – size, volume, gill density – of the linked coral species, i.e. seven Acropora species. Similarly, Chrysiptera parasema prefers to use Acropora corals as a habitat-refuge, with 97% of juveniles associated with those corals. The density of its populations is closely correlated with that of the branchy corals of this species, which is particularly favorable to protection against predators. Reefs with wide coral cover support dense populations of these small fish, which are subject to very strong intraspecies competition for the occupation of secure habitats that provide valuable refuges and avoid overly exposed reef areas.
The distribution of butterfly fish, Chætodon sp., in New Caledonia, meets similar requirements for the availability of microhabitats in the coral ecosystem. This kind of individual selection of micro-habitats ensures that each resident is provided with food and, above all, security. The reduction in the coral coverage of more than 90% in some areas of the Great Barrier Reef, following coral bleaching, is seriously affecting populations of the various species of butterfly fish.
Naturally occupying the highly structured coral reef habitats, squirrel fish, Sargocentron microstoma, given their size and morphology and like many reef species, suffer severely from their deterioration and are the first victims of widespread degradation of reef ecosystems, whether caused by climatic phenomena, biological interventions of corallivorous species (starfish, fish) or destruction and pollution of human origin responsible for the loss of irreplaceable refuge habitats.
In contrast, an invasive alien species native to Australia, the serpulid Ficopomatus enigmaticus, a worm that builds serpulid reefs, is currently providing new anti-predatory and egg-laying shelters for the peacock blenny, Salaria pavo, which is encouraging its expansion in Mediterranean lagoons.
Figure 1.1.Protected habitat of a squirrel fish, Sargocentronmicrostoma, with the branches of the Acropora coral adapted to its size and morphology. For a color version of the figures in this book see www.iste.co.uk/bruslé/fish1.zip
Bibliography: Anim.Behav., 2017, 125: 93-100 & DOI:101016/j.anbehav.2017.01.003, Env.Biol.Fish, 2014, 97: 1265-1277 & DOI:10.1007/s10641-013-0212-9, J.Fish Biol., 2003, 66: 966-982 & DOI:10.1111/j.1095-8649.2002.00652.x, 2006, 69: 1269-1280 & DOI:1095-8649.2006.01161.x, Mar.Biol., 2013, 160: 2405-2411 & DOI:10.1007/s00227-013-2235-3, 2014, 161: 521-530 & DOI:10.1007/s00227-013-2354-x, Mar.Ecol.Prog.Ser., 2007, 333: 243-248, 2014, 500: 203-214 & DOI:10.3354/meps10689
1.1.3. Rocky habitats
Interspecies differences in orientation behavior and site memorization are seen between Australian gobies – species not mentioned – in intertidal zones*, with those occupying complex rocky habitats having better capacities for memorizing shelters in case of threat of predation than those of homogeneous sandy habitats, and the learning capacities to locate a shelter in an experimental labyrinth of the former being greater than those of the latter, in relation to many well located landmarks in complex habitats that lack monotonous habitats. Greater spatial information, in a complex familiar environment, results in a sharper neurosensory development that relies, for the marine gobies of rocky habitats, on the memorization of visual topographic cues and the creation of an accurate geometric spatial map of holes, crevices and rock cracks that provide them with stable shelters. The situation is different for sandy habitat gobies, where the location of refuges is more uncertain and unpredictable in the absence of visual physical cues and the physical instability of the substrate due to tidal movements. Their orientation is then based more on extraterrestrial signals such as sunlight – the sun’s position – and UV radiation, and terrestrial signals such as geomagnetism and underwater sounds. Their survival depends mainly on rapid swimming in a zigzag motion and rapid burial in sediment.
Bibliography: Anim.Behav, 2005, 70: 601-607
1.1.4. Plant habitats
The tropical seahorse, Hippocampus, comes from the Pacific, particularly vulnerable to predation because of its low vagility*, seeks protective habitats by successively using, during its growth, macroalgae beds – sargasses – and coral reefs that offer a diversity of protective microhabitats – tree sponges, branchy corals – depending on its size and camouflage capacities: homochromy* and homomorphy*.
Although some adult wrasses, such as Symphodus rostratus, generally occupy rocky habitats on the Mediterranean coast, the juveniles tend to favor underwater meadows of brown algae, Cystoseira sp., rather than other algal habitats and especially bare floors, which provide them, in their three-dimensional canopy*, with shelter from predators and food in the form of epibenthic prey*. These valuable nurseries are often currently in the process of degradation and are sometimes even threatened with extinction, which could seriously affect the recruitment of such labrid populations.
Tree trunks and branches are used as water shelters (Volume 1, section 1.3.1) and pest control refuges in streams in forest regions. A policy to restore some of them is being implemented in Canada and the United States, by depositing tree trunks in the beds of salmon rivers, Onchorhynchus kisutch, with the results proving controversial. On the other hand, an overly high plant density of macrophytes, Eichhornia sp., in Brazilian lakes is not favorable to occupation by various small species that prefer more sparse habitats.
Rhizophora sp. mangroves also provide highly structured complex habitats that form shaded areas rich in shelters that, like those of the Florida Keys, are densely populated with juveniles of many species, including those of the giant grouper, Epinephelus itajara. The hollow trunks of mangrove trees provide habitats for some species (10–20 individuals per trunk) such as the mangrove killfish, Kryptolebias marmoratus.
Bibliography: Can.J.Fish.Aquat.Res., 2014, 71: 1498-1507 & DOI:10.1139/cjfas-2014-0020, Endang.Species Res., 2006, 2: 1-6, J.Fish Biol., 2007, 71: 701-724 & DOI:10.1111/j.1095-8649.2007.01535.x, 2015, DOI:10.1111/s10641-015-0394-4
1.1.5. Zoohabitats
While coral or tube-worm reefs are remarkable sub-rocky complex habitats for many fish, non-calcified isolated organisms can also harbor fish, protect them from predators, feed them or facilitate their feeding and allow them to lay eggs under good conditions. This is the case with some jellyfish, such as Rhyzostoma pulmo and Rhopilema nomadica, which, as welcoming and benevolent hosts, protect, under their umbrella, the juveniles of many pelagic fish, many sea anemones that live in symbiosis* with clownfish of the genus Amphiprion and some holothurians Holothuria tubulosa and Parastichopus regalis that shelter a commensal, the thermometer fish, Carapus acus. Similarly, some ascidians are temporarily occupied to a greater or lesser extent by gobies that lay their eggs in their gill cavity. The snail fish, Coreproctus sp., a liparid from the coast of Georgia, USA, lays its eggs in the peribranchial cavity of the king crab, Lithodes æquispinnis; such commensalism* joins the cases of parasitism as the presence of these eggs affects the respiratory organs of the crustacean.
Ethologists now consider that certain large fish, such as sharks and tuna, constitute, alone and individually, and because of the hydrodynamic and trophic environment they create, a real habitat from which the suction cup fish, Echeneis remora, Remora sp., and pilot fish, Naucrates doctor, benefit. This is therefore a modern extension of the concept of an ecosystem as the shark alone constitutes a real ecosystem*.
Bibliography: J. Mar. Biol. Ass. UK, 2000, 80: 379-380
1.1.6. Intertidal* habitats
On the coast, in the tidal swing zone exposed to strong water agitation from currents and waves, mechanical erosion forces small fish with limited swimming ability to either take refuge in crevasses to protect themselves, cling to the bedrock or bury themselves in loose sediment if it exists. Gobiids and gobiesocids, such as Gobiesox maeandricus, achieve such anchorage through a ventral suction cup producing a suction force. They cling to all kinds of substrates of varying roughness, with the rocks rarely bare and generally covered with a slippery mat – a bacterial and algal biofilm that acts as a lubricant – that modifies the conditions of fixation, thereby reducing the friction forces between the suction cup and the rock and making it difficult for this small fish (1.5–15 g) to adhere to it mechanically and to attach to a support. Tests on substrates of various sizes show that it is more difficult for it to stick to smooth surfaces than to rough surfaces. Small discs of 13 mm in diameter cannot adhere to substrates with a grain size greater than 270 μm, while larger discs of 34 mm in diameter attach firmly to coarser supports with a grain size of 2–4 mm. Choosing suitable granularity from the substrate and having a lot of tenacity allow the fish to stay well attached.
Juvenile Australian gobies, Bathygobius cocosensis, living in pools of intertidal water have differential cognitive skills depending on the type of habitat they have frequented during their ontogeny: those in structured habitats (rocks, oyster substrates) have a greater ability to adapt to new habitats than those from simple habitats (sand, gravel), demonstrating the importance of early development in complex habitats.
Bibliography: Animal.Cogn., 2019, 22: 89-98, J.Exp.Biol., 2014, 217: 2431-2432 & DOI:10.1242/jeb.110361, 2458-2554 & DOI:10.1242/jeb.100149
1.1.7. Karst* habitats
In order to cope with the periods of low surface water levels, some species inhabiting karst* systems, such as the cyprinidDelminichthys adspersus of the limestone mountains of Croatia and Bosnia, find refuge during the summer in groundwater where they spend several months migrating to deep locations in accordance with the hydraulic inputs from the various temporary sources feeding the complex networks of karst. The result is a fragmentation of populations and a high dispersion of sub-populations concerned with ensuring their survival during a very difficult period. The so-called cave populations (Volume 1, section 1.1.16.2), which temporarily or permanently occupy hypogeous environments*, such as caves, underground rivers and phreatic waters, are very interesting models that illustrate the phenotypic plasticity of fish able to “adapt to anything”.
The world’s greatest biodiversity of cavern fish is found in the western Balkans with about 400 described species. A new species of loche of the Barbatula genus has recently been discovered in southern Germany, in the 250 km2 karst system of the Danube–Aach system. It is clearly distinguished from the epigeal* Danube species by small eyes, more developed barbels, a shorter lateral line and pale body coloring, characteristics considered adaptations to underground life. Its microsatellite genetic characteristics* confirm its recent genetic isolation from surface populations and its low genetic diversity – lower heterozygosity*, higher inbreeding coefficient – characteristics that have been linked to recent glaciations from −20,000 to −16,000 years and the retreat of alpine glaciers, proof of a relatively recent conquest of certain habitats.
Bibliography: Curr.Biol., 2017, 27: R243-R258 & DOI:10.1016/j.cub.2017.02.048, Mol.Ecol., 2012, 21: 1658-1671 & DOI:10.1111/j.1365-294X.2012.05507.x
1.1.8. Intermittent habitats
Species living in the African savannah are subject to strong hydrological variations characterized by a period of pond desiccation during the dry season. The survival of species depends on physiological resistance in response to the intermittent nature of the availability of water in their environment. Adult killifish, Notobranchus furzeri, have a short life of a few months during the wet season and early sexual maturation: females are sexually mature at 18 days of age. They die at the beginning of the dry season after several egg-laying cycles, and their eggs only survive at the bottom of the dried ponds, with their embryonic development being physiologically stopped during a period of dormancy or diapause lasting a few months. The resumption of embryo development is chronologically programmed and anticipates the return of rainfall, so as to allow rapid hatching as soon as the ponds return to water, with their life cycle properly programmed according to seasonal cyclical variations.
Bibliography: Curr.Biol., 2015, 25: R741-R742
1.1.9. Habitats modified by other animals
In some rivers in the United States, the small cyprinidae, Lepidomeda copei, benefit from the structured and complex habitats resulting from beaver activity, particularly through the creation of deeper pools and warmer, macrophyte-rich waters upstream of dams built by these rodents. The recent ecological reintroduction of beavers is proving beneficial for fish.
Bibliography: Ecol.Freshwat.Fish, 2018, 27: 606-616 & DOI:10.1111/eff.12374
1.1.10. Manmade habitats
Many marine fish have benefited greatly from the development of oil and gas platforms, with more than 7,500 of these metal structures worldwide, located in the coastal zone or on the high seas offshore, making them ideal habitats. The submerged structures of derricks constitute complex habitats that serve both as shelters and food storage, taking into account the development of an algal flora and a fixed fauna made up of sponges, corals – epibionts and vagile forms* – worms, mollusks and crustaceans. A number of fish with platforms located at depths of −85 to −175 m and aged 16–22 years have been studied in Queensland, Australia, using submarines. The ichthyic populations, i.e. 31 species belonging to 14 families, are made up of both in transit pelagic* – yellowtail, Seriola dumerili, jacks, Caranx melanpygus, whale sharks, Rhincodon typus – and large sedentary predators – snappers, Lutjanus argentimaculatus and groupers, Epinephelus multinotatus. This case is an example of ecological conversion and an interesting example of sustainable development. However, such structures, when obsolete, can become dangerous vectors for the spread of their fauna and associated flora over long distances. For example, platforms towed by sea from the Gulf of Mexico to the Adriatic Sea have introduced fish from that Gulf.
Other marine developments are accompanied by an increase in the structural complexity of the environment, which is favorable to the artificial creation of new microhabitats such as shellfish beds, floating and/or submerged fish cages, marinas, artificial reefs, groynes and dikes protecting beaches from erosion.
Aquaculture farm cages, artificial reefs and FAD (Fish Aggregating Devices) (Volume 1, section 2.3) play an identical role as artificial habitats. The Marennes–Oleron intertidal zone, exploited by the shellfish industry, is subject to significant biodeposition (600 t/km2/d) made of lamellibranch mollusk feces and a diatomaceous biofilm, with these ex-polysaccharides organized in colloids*. Inside, soles, Solea solea, often have to withstand the hypoxic conditions of this muddy substrate.
Artificial reefs offer cavities and alveolar structures of various sizes from which fish can benefit. Wrecks of warships and commercial vessels are also rich habitats that have been successfully colonized by morays, conger eels, groupers and many sparids. It has been shown that marinas in north-western Italy and along the rocky coasts of France are favorable to sparid juveniles, such as the four species of sars, Diplodus sp., which find protective shelters in areas sheltered by boulders and artificial wavebreakers, thereby increasing their recruitment success*.
Bibliography: J.Fish Biol., 2005, 66: 865-870, 2008, 73: 186-195 & DOI:10.1111/j.1095-48649.2008.01924.x, J.Mar.Biol.Ass.UK, 2006, 86: 847-852, Mar.Ecol.Prog.Ser., 2007, 331: 219-231, 2016, 547: 193-209 & DOI:10.3354/meps11641, Scientia.Mar., 2014, 78: 505-510
1.1.11. Ecological niches not frequented by other species
Being assured of a lack of interspecies competition may mean occupying sites that are not frequented by others. Some species do not mind occupying extreme habitats, even if they are considered dangerous owing to their toxicity. Some populations succeed in colonizing them, following remarkable adaptive resistance. As a result, sources rich in hydrogen sulfide, H2S, a gas toxic to most animals, which results from the decomposition of organic matter, are inhabited in Mexico by small endemic livebearers, Poecilia sulphuraria and Gambusiaeurystoma which have developed physiological resistance mechanisms in these microhabitats particularly low in oxygen and rich in hydrogen sulfide, H2S, which is detoxified into thiosulfate by their liver mitochondria*. Species subject to anthropogenic pollution from tanneries, pulp mills and other sources, and especially those whose natural habitats are deep hydrothermal springs (Volume 1, section 1.1.17.2), have homeostasis* saving mechanisms that make them “extremophilic” fish.
Bibliography: Ecol.Lett., 2014, 17: 65-71 & DOI:10.1111/ele.12209, J.Fish Biol., 2008, 72: 523-533 & DOI:10.1111/j.1095-8649.2007.01716.x
1.1.12. Seemingly unlimited pelagic habitats
Open water species such as tuna and whale sharks apparently have no physical limits to their mobility, except for gradients in temperature (thermocline), salinity (halocline) and oxygen concentration (oxycline), which constitute hydrological and ecological barriers that can only be crossed with thermal, halin, respiratory and osmoregulation stress, which are always costly in terms of energy. In addition, current dynamics can lead to the creation of sanctuaries or corridors with a certain autonomy and hydrological originality that affect their frequency. Their freedom to maneuver, within the masses of oceanic or lacustrine waters, is therefore not as considerable as could be imagined, with some ocean courses sometimes presenting constraining limits.
1.1.13. Temporal fluctuations in habitat occupancy
The occupation of space by a species varies over time in accordance not only with the local hydrological fluctuations in its habitat during floods, low water levels, etc., but also the presence or absence of predators. Consequently, in an English river, during the winter, Thymallus thymallus graylings show large variations in distribution in their home range*. This increases 5–20 times in relation to the higher density of avian predators, such as Phalacrocorax carbo cormorants. A greater activity would correspond to behaviors to avoid predators rather than to the search for refuge habitats that other salmonid species, such as trout, preferentially exhibit.
1.1.14. Ontogenic and/or physiological fluctuations
A distribution of species according to depth – bathymetry* – concerns the different stages of development by an optimal occupation of the water layers according to their own hydrological characteristics, as well as their richness in planktonic prey. Separate ecological distributions can also result from parasitic infestation, such as in Gadus morhuacod on the Norwegian coast where individuals infested with the parasitic trematode Cryptocotyle lingua are found at a greater depth than healthy fish. Is this so as not to transmit their black spot disease to their fellow fish?
Habitat changes occur episodically in migratory species (Volume 1, section 2.2.1), between their feeding and breeding habitats and vice versa, and more randomly, but generally caused by thermal preferences and food requirements in nomadic species and, in particular, frequent travelers (Volume 1, section 2.2.3).
1.1.15. An amphibious existence
1.1.15.1. Freeing oneself from the aquatic environment, a climax for a fish to achieve
A successful transition from the aquatic to the terrestrial environment is an important step in the evolution of vertebrates, with an exit from the water followed by a gradual conquest of continental habitats. The physical conditions in the aquatic environment and those in the terrestrial environment are quite different, with the former containing only 3% of oxygen, O2, compared to 78% in the latter. Such a continental “conquest” is considered advantageous because it is accompanied by the possibility to exploit new energy resources.
1.1.15.2. A new way of breathing
Such a change of environment can only be successfully achieved if the fish has the ability to capture atmospheric oxygen, with an aquatic respiration mode based on the gills through which normal respiratory gas exchanges occur, an almost universal mode of aquatic respiration.
About 450 fish species do not use only dissolved oxygen in the water, as most of the other 30,000 fish species do. Why do they have such a physiological peculiarity? It is a response to difficult periodic environmental conditions: water loss (low water levels in rivers, seasonal drying of lakes and lagoons, low tide, etc.) or to a drastic decrease in the concentration of oxygen (hypoxia*). These aerial fish generally have a double respiratory system, namely, gills and a complementary system that promotes gaseous exchanges between their blood and the atmosphere: either their skin, or oral, pharyngeal or intestinal diverticulae consisting of cavities irrigated by networks of blood vessels, with the transport of oxygen, O2, ensured by the hemoglobin contained in red blood cells (erythrocytes) and the elimination of CO2 ensured by the skin or gills.
This use of respiration is necessary for marine species (more than 70 intertidal species* belonging to 12 families) that are subjected to alternating periods of flooding* and immersion in relation to the rhythm of the tides, high and low.
In the pantodon, Pantodon buchholzi, which has to breathe air, the respiratory organ is its very large and vascularized swim bladder. It is related to the anterior part of the digestive tract through the pneumatic channel, which allows this African freshwater fish to breathe air at the surface and out in the water during the gliding flights that earned it the name “butterfly fish”. It swallows air every 2 or 3 minutes at rest if the water concentration is 5 mg O2/l. Its air swallowing activity increases or decreases with the saturation rate of the water, but the breathing of air always dominates breathing through the gills. The Japanese bluespotted mudhopper, Boleophthalmus pectinirostris, which digs a burrow in the coastal mudflat area and remains partially confined within it, has a unique air storage method: when its burrow is submerged, it continues to breathe the air stored in it (up to more than 400 ml) and which provides it with the additional oxygen necessary for its survival in this confined environment.
Other species optionally breathe atmospheric air by “swallowing” it at the surface. This breathing pattern is a useful adaptation to ensure the survival of these fish in swamps where hypoxic conditions* often prevail, following an increase in temperature or fermentation phenomena (decomposition of organic matter). This is the case of the endemic Brevimyrus nigermormyrid in African tropical fresh waters, which breathes on the surface when it reaches 26°C, generating a deficit in dissolved oxygen. Similarly, some African anabantid animals, such as Ctenopoma muirei from Lake Victoria, are able to use alternately aquatic gill breathing and air breathing depending on the level of dissolved oxygen in the water. Airborne breathing, made possible by a vascularized suprabranchial chamber, supplements a risk of hypoxia* in the lacustrine aquatic environment (0.49 mg of O2/l in the morning), as fish come to the surface to absorb atmospheric air.
Bibliography: J.Fish Biol., 2005, 67: 292-298 & DOI:10.1111/j.1095-8649.2005.00725.x, 2007, 71: 279-283 & DOI:10.1111/j.1095-8649.2007.01473.x, 2014, 84: 577-602 & DOI:10.1111/jfb.12270, 774-793 & DOI:10.1111/jfb.12324, Zeit. für vergl. Physiol., 1969, 65: 324-339
1.1.15.3. Mangrove visitors
The Florida mangrove cyprinodont, Kryptolebias (ex Rivulus) marmoratus, has developed the ability to emerge from the water and travel on land in order to feed (capture insects such as termites and locusts), although it does not have morphological adaptations that favor land movement. Its movements on wet ground were analyzed from videos that show body oscillations consisting of the body swaying, “snake-like” ripples (lateral curvature of the vertebral spine), “rolling” movements and jumps (pectoral fin thrust). Would such “non-tetrapod terrestrial” vertebrate behavior constitute an evolutionary step towards a historic exit from water for these fish? Irrespective, it does not move away from its natural environment and the prey it captures in the air is immediately taken and consumed underwater. However, it is likely to live long enough out of the water (more than 30 days on wet leaves) due to its ability to breathe through the skin. This is proof that fish can exploit terrestrial habitats and consume aerial prey by leaving their natural environment in a more or less sustainable way. This fish lives most often in holes dug by crabs, which are a poor oxygen environment that it willingly leaves during periods of emergence. Its ability to remain out of water for a long time is related to the development of a rich vascularization (angiogenesis) of its skin, mouth and bucco-opercular chamber which are permanently moistened and to the activation of oxygen transport through an increase in the number and density (hematocrit*) of red blood cells and an increase in the affinity of its hemoglobin, Hb, for oxygen (HbO2). It regularly swallows air, with its ventilation rate being approximately one “breath of air” every 12 minutes. Such a successful adaptation to aerial life would be similar to the one likely to have been experienced by the primitive tetrapods who left to conquer the Permian and Carboniferous continents. The removal of water from this mangrove killfish would also allow it to cool down on land by causing the moisture from its body surface to evaporate when the temperature of the mangrove water reaches high temperatures (sometimes as high as 38°C).
In tropical coastal areas, when leaving the water at low tide, periophthalms, Periophthalmus argentilineatus, also use the abundant food resources (copepods, amphipods, polychaeta worms, crabs, etc.) of mangroves that are not accessible to most marine species. Some marine blennies do the same.
Bibliography: J.Exp.Biol., 2013, 216: 3988-3995 & DOI:10.1242/jeb.089961, 2014, 217: 3988-3995 & DOI:10.1242/jeb.110601
1.1.15.4. Fish in the trees
Are fish unable to “get up high”? Didn’t Albert Einstein once write: “if you judge a fish by its ability to climb a tree, it will live its whole life believing that it is stupid”. Yet, this great thinker did not know that other fish species, quite different from goldfish, were actually able to climb trees. Indeed, climbing perch of the Anabas and Ctenopoma genera are anabantidae from Southeast Asia that are able to leave their lacustrine and marshy living environment to crawl on the ground, from hole to hole, and thereby reach the low branches of trees. Anabas testudineus is the best known of these perches. Originally from China and India, it tends to colonize Indonesian and Australian waters and is even considered invasive in Australia. Equipped with the capacity to breathe air (possession of a suprabranchial cavity) that renders it able to spend 6 hours of its life out of the water and an ability to crawl on the ground using its pectoral fins used as crutches, it hides in the foliage of trees where it captures flying insects (flies, wasps), which even act as food. Its feeding strategy is unique as it does not swallow the ingested prey but stores this material in its mouth. Its consumption of prey therefore takes place at a site other than that of their capture. Such climbing fish would have astonished Albert Einstein.
Figure 1.2.Anabantid climbing perch, Anabas sp., able to leave the water and climb trees
Bibliography: J. Fish Biol., 2008, 73: 1053-1057 & DOI:10.1111/d.1095-8649, 2008.01987.x
1.1.15.5. Surviving the dry season
Lungfish, which are the best known of the “aerial respirators”, are becoming more sustainable in the aquatic environment. The Australian lungfish, Neoceratodus forsteri, is able to survive, in dry season and in a subtropical climate, a total flooding, enclosed in a cocoon of soil and mucus buried in the soil of the dried Australian marshes. However, it cannot escape the aquatic environment during reproduction, which occurs in the wet season (August–December) by depositing its eggs in inert waters in shallow (<20–40 cm) flooded areas on the banks of rivers, which are covered with submerged or aquatic terrestrial plants (macrophytes) (Eichhornia water hyacinths). This spawning is threatened by extreme thermal variations (approximately 20°C, with maximum values of 32°C), a decline in oxygen concentration (<1–2 mg O2/l), changes in water level, poisoning due to the decomposition of plant material, the development of filamentous algae and desiccation when water levels fall. For these reasons, the long duration of egg incubation (23–30 days) and larval development (21 days) compromises the survival of embryos and larvae. Such mortality risks, combined with low fertility (maximum 500 eggs), explain why this fish is considered an endangered species. Protopterusdolloi, which also grazes during the dry season (5–6 months) in a mucus cocoon that protects it from water loss, has a significant reduction in its metabolic activities, which allows it to avoid weight loss, energy decline or the melting of its muscle proteins, with its muscle and liver glycogen reserves preserved following low enzymatic glycolysis* activity. On the other hand, its production of ammonia, NH3, a very toxic waste, is replaced by an increase in the synthesis and accumulation of urea in its tissues, linked to an activity of the liver enzymes* of the “ornithine urea cycle”. Such metabolic progress in waste disposal is quite comparable to that of mammals. The neighboring species Protopterus annectens moves on the ground using its pelvic fins, with a “walk” (claudicant) involving only two muscles (a retractor and a protractor) whose morphology is simple compared to that of the muscles that rotate the pelvic joints of the tetrapods, which can be considered a first “historic” attempt to “walk on the Earth”.
Such respiratory capacity to use atmospheric oxygen, sometimes surprising in the case of air breathing through the vascularized digestive tract, as in several species of catfish, such as loricariidae such as Hypostomus pardalis and Pterygoplichthys sp., which can live up to 30 days out of the water, callichthydae such as Coridoras sp. and the weatherfish, Misgurnus fossilis, is interesting to consider in an attempt to explain the anatomo-physiological evolution of vertebrates during their conquest of the terrestrial world.
Bibliography: J.Exp.Biol., 2014, 217: 3474-3482 & DOI:10.1242/jeb.105262, J.Fish Biol, 2008, 73: 608-622 & DOI:10.1111/j.1095-8649.2008.01955.x, 2014, 84: 163-177 & DOI:10.1111/jfb.12264, 547-553 & DOI:10.1111/jfb.12349, 554-576 & DOI:10.1111/jfb.12323, 603-638 & DOI:10.1111/jfb.12279
1.1.15.6. Ground and air spawning
Australian species such as Galaxias truttaceus, a small galaxid in the southern hemisphere, lay their eggs upstream of estuaries or in streams along seasonally submerged forests, in shoreline vegetation, among plant roots. Eggs develop out of water, but in a humid atmosphere, with their hatching dependent on a seasonal rise in water levels in the floodplain. This spawn may not be submerged when the embryos have exhausted their energy reserves, but, generally, the arrival of high water in the wet season not only promotes their hatching (after some mechanical agitation), but also ensures the downstream transport of larvae to the sea and their dispersion, with the high turbidity of the water reducing the risk of predation. These “aerophilic” spawners are waiting for the water to rise to save their lives.
This is also the case for the California grunion, Leuresthes tenuis, which lays eggs at low tide in wet beach sediments and whose eggs hatch only when they are covered with water during the high tides of the next tidal cycle*. Similarly, the eggs of the splash tetra, Copella arnoldi, develop in the open air, glued to the underside of the leaves of plants on the banks of the Amazon, with their humidification ensured by water projections (tailbeats) made by the male.
Bibliography: Fish Fish. 2006; 7: 153-164
1.1.16. An underground life
1.1.16.1. Living in burrows
Some fish have an affinity for life underground, at least during a phase of their life cycle, such as the goby-loteZosterisessor ophiocephalus, which digs burrows to lay eggs, as well as to pass the winter. Some other gobies also live in burrows, along with shrimp that have dug them. Typhlogobius californiensis, a blind and depigmented fish at the adult stage, lives in pairs at the bottom of a vast burrow dug by a pair of Callianassaaffinis shrimp. Another goby, Cryptocentris sp. (Vanderorschia sp.), a fish with good eyesight, lives at the entrance of the burrow dug by the shrimp Alpheus djiboutensis, which has poor eyesight. Such cases of “shrimp-fish” associations within a burrow occur often in warm seas and are examples of “mutualism*” (Volume 1, section 3.4).
1.1.16.2. Living in caves
Other species complete their entire life cycle in caves. Living conditions “underground”, in the absence of light, are necessarily more difficult than those in light environments and require specific adaptations to cope with them. Fish living in light environments use their vision to orient themselves in space and navigate within their habitats. But what is it that forms living in underground environments, known as “troglomorphs” or “troglobies”, do in total darkness in a difficult environment, poor in nutrients*, and when they have undergone a reduction in eye size, or even an evolutionary regression of their visual functions, a situation comparable to that of life in the deep?
The underground populations of the Mexican tetra, Astyanax mexicanus, are blind. The question arose about their use of geometric spatial landmarks. In the absence of light signals that are picked up in conspicuous epigenetic* surface shapes, these hypogenetic shapes use hydrostatic pressure measurement signals, both with their gas bladder (pressure along a vertical axis, which varies with depth) and with the neuromasts* of their lateral line* (horizontal axis). They are able, thanks to their mechano-receptors, the hair-cells of their lateral line, to perceive the slightest change in their immediate environment, to detect obstacles encountered as a function of the distortion of water flows at their level and to obtain a “three-dimensional map” of their environment.
A sensory system such as the lateral line is present in all fish, but it is hyper-developed here to meet the ecological needs for adaptation to life in dark caves and in groundwater, in the manner of a “supplemental radar”. Their superficial neuromasts* are more numerous than those of their counterparts living in light environments. In the absence of visual signals, these sensory cells, particularly those in the orbit and in the suborbital position, which are twice the size of those of surface fish, receive messages produced by hydraulic flows generated by fish swimming and reflected by obstacles, as well as by prey, allowing them to feed “blind”.
The study of their swimming trajectories was carried out during tests in labyrinths integrating various horizontal and vertical components, with this fish showing its ability to use all spatial information, memorize it and adapt to the cognitive data characterizing its environment. It detects the position of stationary obstacles thanks to signals produced by the hydraulic movements of its own swimming, with its lateral line* capturing the disturbances of fluids generated (reflected waves) by the presence of obstacles whose distance it can measure. It therefore navigates using a combination of signals that constitute a system reminiscent of bat echolocation*. Memorizing certain spatial landmarks and the topography of the site (a GPS-type geometric map!) then facilitates its movement in a familiar environment in accordance with a precise geometric representation of its spatial environment.
The production of oral suction movements also generates a hydrodynamic flow that varies according to pressure gradients according to the distance of the obstacles, which facilitates the detection of obstacles through the lateral line using an echolocation method. It thereby manages to find its way with its mouth.
Their need to group together in schools for anti-predatory purposes is less than in enlightened environments due to the absence or rarity of predators, and populations of cave species tend to live in a more dispersed manner, with reduced social cohesion. They seem to lead a quiet life, far from the frenzied world of light environments.
Amblyopsis spelæa is also a blind and depigmented cavern fish. It was discovered by biospeleologists in a Kentucky cave in 2002. Its characteristics, in particular, the absence of colored pigment, are reminiscent of those of the famous axolotl Ambystoma mexicanum, a Mexican newt. The colonization of such environments does not appear to have been accidental and could be explained by their quality as climatic refuges during ice ages and as secure habitats, given the scarcity of predators (except bats, Noctilio leporinus).
Many of these species found in caves, karsts* and groundwater are still largely unknown. Periodically, new species are discovered and described, such as Triplophysa sp., a blind loach, in China in 2002.
Bibliography: Anim.Behav., 2004, 68: 291-295 & DOI:10.1016/j.anbehav.2003.11.009, 2005, 70: 405409 & DOI:10.1016/j.anbehav.2004.11.007, 2013, 86: 1077-1083 & DOI:10.1016/j.anbehav.2013.09.014, Curr. Biol., 2013, 23: 1874-1883 & DOI:10.1016/j.cub.2013.07.056, J.Exp.Biol., 2014, 217: 886-895 & DOI:10.1242/jeb.064599, 1955-1962 & DOI:10.1242/jeb.098384, J.Fish Biol., 2005, 67: 3-32 & DOI:10.1111/j.1095-8649.2005.00776.x1.1.16.3. Regressive evolution or proof of plasticity?
Biospeleologists have been interested in these cave forms, which are considered unique in comparison with those of the epigeal* conspecific populations from which they seem to derive, sometimes leading, due to a loss of pigmentation and the disappearance of the eyes, to the idea of the existence of a “regressive evolution” that is both anatomo-morpho-physiological and behavioral. However, the hypothesis of the accidental colonization of hypogeal* waters does not seem to be accredited and has given way, on the contrary, to the concept of a biological evolution based on a remarkable organic plasticity aimed at exploiting “underground niches” as “new” niches, which are both under-exploited by other species and lacking predators. These cave fish are said to be pioneers rather than refugees.
The evidence would be provided by comparative genetic examinations of the epi- and hypogeal* populations of the Mexican characin, Astyanax fasciatus, whose “divergence”, said to have occurred between −525,000 and −700,000 years ago, predates the most recent glaciations (see Amblyopsis spelæa). These fish can serve as models for studying the plasticity of organisms, demonstrating that “phenotype = genotype + environment”.
Bibliography: J. Fish Biol., 2005, 67: 3-32 & DOI:10.1111/d.1095-8649.2005.00776.x
1.1.16.3. The advantages of an underground life
Living in environments deprived of light and, as a result, of resources related to photosynthesis, seems, apriori, difficult, and hypogeal* populations appear to have to endure physiological handicaps and are therefore “to be pitied”. Yet, these environments offer a number of eco-physiological advantages: an almost constant temperature and a scarcity of predators, which are usually of major concern to species in light environments. As for nutrient* poverty, this is sometimes compensated for by a high food detection capacity. For example, all catfish have barbels, but those of hypogeal species such as the blind catfish, Trogloglanispattersoni, present in Texas groundwater, are hyper-developed and very rich in chemosensory cells. Taking advantage of their “colonizing spirit”, these fish have had access to a vast and complex underground domain and a rich network of underground interconnections, most of which are still ignored.
These environments are known to be particularly soothing, to the point that their inhabitants are almost completely unaware of competition, combativeness and competition, sexual harassment and all other factors of agitation in enlightened environments.
Bibliography: Behav., 2008, 145: 73-98, 931-947
1.1.16.4. Opaque environments
Weakly electric gymnotiform fish use the distortions of the electrical signals (electrical waves) produced by their electrical organ, EOD*, and reflected back to their electrical receptors, forming a 3D “electrical image” of moving or immobile bodies in their environment. Such electro-localization constitutes a “sixth sense” (Volume 1, section 3.1) that allows them to navigate in opaque tropical waters, as well as at night. Spawners among Petromyzon marinussea lampreys do not use any visual signals to migrate to their continental spawning grounds at night, although they have, in addition to eyes, epiphyseal* (pineal gland*) and dermal photoreceptors in the tail that function as effective “radar” if they cannot navigate by sight.
1.1.17. Living in the abyss
1.1.17.1. A difficult world
Life in the depths of the oceans is particularly difficult because of the “extreme” conditions prevailing in this cold environment (0–4°C), which is deprived of light −in fact, there is weak light in the mesopelagic zone* between −150 m and −1,000 m and an almost totally aphotic environment* above −1,000 m (although bioluminescence is not insignificant) – characterized by very high pressures, a low oxygen concentration and often a high poverty of food resources, although the bodies of large pelagic fish and, in particular, those of marine mammals (whales, killer whales, dolphins) constitute significant nutrient inputs. The corpse of a whale is a blessing for an entire sector of the abyssal ecosystem.
The number of species that have managed to adapt to such an “extreme” environment is limited by this relative scarcity of food, to the point that it has long been accepted (Forbes 1844) that these deep waters were deprived of life and are azoic* from more than −550 meter deep. This is not the case, as demonstrated by the expedition of the Challenger (1876). Some groups of fish, generally endemic* ones, have successfully colonized these deep waters with varying degrees of success: hagfish (Volume 1, section 1.2.1.8) down to −2,750 meter deep, cartilaginous fish up to −3,000 m and chimeras (holocephalic) up to −8,300 m, with the depth record for Abyssobrotula galatheae (ophiidae) at −8,370 m. These species are considered “extremophilic”.
Anoxic attacks* have occurred on various occasions since the dawn of the fish (Devonian: −400 MA, sometimes referred to as the “fish age”) and current fauna result from the recolonization of surface species, which is believed to have occurred since the Cretaceous period (−94 MA). Specialized invasive families (ophidiids, liparids, ceratoids) are dominant at depths greater than −6,000 m.
Fish adapted to the ambient conditions of the deep waters mentioned above often, but not exclusively, have elongated morphologies and practice an “anguilliform” mode of locomotion, with the degree of elongation increasing with depth between −300 and −2,030 m in the northwest Atlantic. The Coryphænoides rupestris (macrouridae) grenadier dominates in these oceanic areas, with sharks and rays rare and flatfish completely absent. In depths greater than −1,000 m in the western Mediterranean, Coryphænoides mediterraneus grenadiers and other deep-sea species feed at daily rates that correspond to the temporary availability of pelagic prey* that migrate vertically, unlike their counterparts who, consuming permanent benthic* prey, do not show any feeding pattern. A certain lack of knowledge of these species comes from the fact that they are difficult to access and victims of the sudden decompressions suffered during their surface rise during deep fishing operations that cause the formation of gas bubbles in the blood, internal bleeding, exophthalmia* and gastric extroversion that are followed by death. The use of hyperbaric* chambers to bring back caught samples alive, effective in shallower fish (redfish, Sebastes sp., caught from −100 to −150 m), is rarely sufficient for more abyssal species.
Particular attention was paid to the visual devices used in bathypelagic* and bathybenthic* species (tubular or bidirectional eyes, large pupil, reflective mirrors). In deep water, where the absence of light is compensated for by the production of biological light (bioluminescence) (Volume 1, section 1.1.17.2), vision is provided by anatomical–physiological eye structures that are generally very complex and often associated with specialized bacteria.
While it was generally accepted that color vision did not exist in the dark depths of the abyss (“where all cats are gray”!) due to the single opsin in their retinal* sticks that is responsible monochrome vision, it has just been demonstrated that certain abyssal species such as the silver spinyfin, Diretmus silvery, are endowed with the ability to perceive certain colors, in this case certain shades of blue, thanks to the cones and rods of their retinas of 14 genes encoding several rhodopsins that are sensitive to several portions of the blue light spectrum. This fish can thereby capture residual sunlight and, above all, discern congeners, prey and predators, particularly those that produce blue bioluminescence.
Bibliography: Biol.Rev.2004, 79: 671-712 & DOI:10.1017/S1464793103006420, J.Fish Biol., 2007, 70: 867-878 & DOI:10.1111.1095-8649.2007, 01347.x, 2013, 83: 1528-1550 & DOI:10.1111/jfb.2013.83, 1576-1591 & DOI:10.1111/jfb.12266, Proc.Roy.Soc.B, 2014, 281: 20133223 & DOI:10.1098/rspb.2013.3223, Science, 2019, 364, 6440: 588-592 & DOI:10.1126/science.aav4632
1.1.17.2. One exception: hydrothermal springs
A special and original case concerns the ichthyofauna (Hydrolagus sp., Epigonus sp., Mora sp., etc.) of the deep hydrothermal springs of the Atlantic Rift (−3,200 m) which are distinguished by their high chemosynthetic productivity, low O2 concentration, high hydrogen sulfide, H2S, content and high metal content, particularly methyl mercury, with high muscle and liver contamination (1.9 and 1.7 μg Hg/g respectively) due to bioconcentration* caused by their situation as “top predators” (biomagnification*). These hydrothermal springs with naturally hypertoxic waters are nevertheless considered “islands of productivity” on the ocean floor, compared to a particularly poor bathyal* environment. At least 40 species of bathyal fish* have been inventoried (bottom longlines) on this mid-Atlantic ridge at depths ranging from −900 to −1,760 m. They are all endemic* and feed, like the rabbit fish, Hydrolagus pallidus
