Fish: An Enthusiast's Guide - Softcover

Moyle, Peter B.

Softcover

ISBN 10: 0520201655 ISBN 13: 9780520201651

Publisher: University of California Press, 1995

Synopsis

Engagingly written, with both learning and humor, Fish bridges the gap between purely pictorial books and scholarly texts, and provides a succinct summary of fish biology and conservation for students and fish enthusiasts.

About this title

About the Author

Peter B. Moyle is coauthor of Fishes: An Introduction to Ichthyology (1988). He is Professor of Fisheries Biology at the University of California, Davis. Chris Mari van Dyck, who trained as a fish biologist, is a professional illustrator living in McAllen, Texas.

From the Back Cover

In this book, Peter Moyle successfully illustrates the joys of the study of living fishes, revealing why those of us who have spent a lifetime studying fish as a profession consider ourselves to be so fortunate. We are constantly rewarded by discovering new and unexpected things that fish will do.

Excerpt. © Reprinted by permission. All rights reserved.

Fish: An Enthusiast's Guide

By Peter B. Moyle

University of California Press

Copyright 1995 Peter B. Moyle
All right reserved.
ISBN: 0520201655
Chapter I
Introduction

In a cool curving world he lies
And ripples with dark ecstasies.
Rupert Brooke, "The Fish"

The basic shape of a fish is simple; it can be drawn with a single sweep of a pencil. This elegant design is a reflection of how superbly adapted fish are to the "cool curving" world of water. To understand the ways of fish, the nature of their environment must be understood, as in many ways it is alien to us terrestrial creatures.

Because water is nearly eight hundred times more dense than air it is easy for fish to live suspended effortlessly in it, simply by balancing the heavy mass of bone and muscle with an internal float full of gas or lightweight oil. This means that their muscles can be devoted to producing the power it takes to push forward through the water, resulting in the streamlined shape that means "fish." A powerful, streamlined body is also necessary, however, because water resists movement much more than airas any swimmer can attest. An extremely high proportion of each fish's body is devoted to swimming muscles. This is very convenient for those of us who eat fish, because these muscles make up the fillets that can be so easily removed with a few slices of a knife.

When pushing their way through the water, fish cause the water to swirl about them. The eddies created by the movement persist for some time after a fish creates them. Eddies are also created by the movement of the water itself, most noticeably as ocean currents, waves, and flowing streams. Thus the turbulence of water is a major environmental feature, much like wind over land. Fish have a special sensory system to detect this turbulence, which has no counterpart in mammals, birds, and reptiles. This lateral line system can provide many clues as to the

Figure 1-1
Large males (top ) of bluechin parrotfish usually result from a female ( bottom ) changing sex
when a previously dominant male dies.

nearness of predators, prey, or school mates or to the presence of favorable or unfavorable environmental conditions. It is usually most visible as one or more narrow lines running down the side of a fish. In some fishes, the lateral line system has been partially converted into another sensory system that is equally alien to our experience: an electrical sensory system . This system takes advantage of the fact that water is a good conductor of electricity. In sharks, the electrical sense is used to detect the slight electrical fields generated by the muscles of their prey, whereas in some freshwater fishes it is used to monitor a special electrical field the fish set up about themselves. Objects and prey are identified by their differing abilities to conduct electricity and by how much they distort the electrical field around the fish producing it.

Other senses of fish are less alien to our experience, although water does put special constraints on them. Vision, for example, is quite important for most fishes, but its usefulness is often limited by lack of water clarity and by the way water acts as a selective filter of the spectral colors. Red light is excluded by the surface layers of water, whereas blue light penetrates the farthest. Thus the brilliant red fish frequently found in the ocean depths are nearly invisible in their natural habitat! Some fishes reduce their dependency on external light by producing their own light in photophores , whereas others, like catfish, rely on their sense of smell or taste to find their way about, following odor trails in the water or tasting and touching the bottom with sensitive whisker-like appendages (barbels ).

Although water is a barrier to light, it is an excellent carrier of sound waves. In fact sound travels over three times faster in water than in air and carries much farther. Not surprisingly, most fish have an excellent sense of hearing, a fact we often do not appreciate because fish lack the external ears so characteristic of land vertebrates. They do not need external ears because the density of fish flesh is so close to the density of water that it carries sound waves with little distortion. The fish consequently need only an internal organ that is either more dense or less dense than water to intercept the sound waves and transmit the message to the inner ear. Usually this is done either by the air-filled swimbladder or by special earstones (otoliths ). Many fish also produce sounds important for communicating with their fellows, especially when courting. The song of a courting toadfish may approach the hundred-decibel level! We rarely hear such sounds because sound waves do not move easily between water and air.

Figure 1-2
Water acts as a selective filter of light. Red light waves penetrate the shortest distance,
so a red fish that appears brilliantly colored when brought to the surface is in fact nearly
invisible when below the level that red light penetrates.

Water carries sound waves so well because it is virtually incompressible. This same feature is used by many fishes to great advantage when they feed, because it causes water to rush into any new space, without any expansion. This is unlike air, whose gasses expand to fill empty space and compress easily as well. Most fishes are capable of rapidly increasing the size of the mouth cavity, forcing water to flow in rapidly through the small mouth opening, like sucking water through a straw. Fish that feed on insects and other small organisms can thus literally suck their prey into their mouths. The water taken in is expelled through the gills by closing the mouth and compressing the mouth cavity. The food is retained by the gill rakers . These projections from the supporting arches of the gills function much like the bars of a cage. The smaller the prey, the closer together the gill rakers. This expandable mouth cavity is also very handy for breathing (respiration) because it allows large volumes of water to move continuously across the gills, even when the fish is not feeding.

Having gills that are efficient at extracting oxygen from the water is important because water typically contains less than 8 milliliters of oxygen per liter of water, compared to 210 milliliters in a liter of air. Furthermore, the capacity of water to hold oxygen decreases as temperature increases, while at the same time the fish's demand for oxygen is increasing. The decay of organic matter, either natural or man-made, also removes oxygen from the water. Thus the activities of fish often may be limited by the shortage of oxygen in the water, even though the gills may be extracting most of the oxygen available. The efficiency of the gills depends on having a vast surface area in the gill filaments and a multitude of blood vessels into which the oxygen can be taken from the passing water. The fish take advantage of proximity of the blood to water by using the gills to eliminate waste carbon dioxide, ammonia, and heat at the same time that they take up oxygen. This exchange system also creates some problems, however, because it makes fish very vulnerable to other substances dissolved in the water, especially pollutants such as mercury or pesticides which can kill the fish after being taken up through the gills. The thin membranes that separate the blood from water can act as selective filters to some compounds, however, especially salts. Few fish can live in both fresh and salt water. Marine fishes need to filter out excess salt. Freshwater fishes have the opposite problem of needing to retain salt, because there is so little salt in fresh water.

Figure 1-3
An evolutionary tree for fish and agnathans.

Evolution and Classification of Fishes

The history of fishes through time is fascinating not only because it helps to explain the development of their many exquisite adaptations but because the early history of fishes is that of all vertebrates, including ourselves. Fish made their first appearance in the fossil record nearly 500 million years ago. These early vertebrates, called ostracoderms, were small, heavily armored forms that seem to have lived by sucking algae, small invertebrates, and ooze from the bottoms of seas and lakes. They lacked both the jaws and paired fins that are characteristic of "higher" fishes. Their closest relatives alive today are lampreys (order Petromyzontiformes) and hagfishes (order Myxiniformes), strange eel-like creatures that also lack jaws and paired fins. Hagfishes are so peculiar looking that early taxonomists classified them as worms! Despite their ancient affinities, both hagfishes and lampreys are quite abundant today, in part because they can prey on more "advanced" fishes.

The first fishes with jaws and paired fins to appear as fossils, some 440 million years ago, were the acanthodians, small minnow-like creatures. These fishes had a whole row of fins on each side of the body, unlike more modern fishes that have only two sets of paired fins (the equivalent of legs on land vertebrates). The relationship of the acanthodians to modern fishes is a subject for debate, as is the relationship of their contemporaries, the placoderms (class Placodermi). This bizarre collection of armored fishes greatly overshadows the acanthodians in the fossil record. The placoderms were mostly bottom-dwellers; some were fearsome predators 10 or more meters in length. They dominated the oceans for about 100 million years but were replaced completely by the two groups that dominate the waters of the world today, the class Chondrichthyes (cartilaginous fishes, such as sharks and skates) and the class Osteichthyes (bony fishes). The sharks and skates have had almost their entire evolutionary history in salt water, in contrast to the bony fishes which seem to have developed initially in fresh water and invaded salt water fairly late in their evolution. As a consequence of their independent evolutionary histories, the two groups have developed rather different solutions to the problems of living successfully in water. The sharks, for example, store lightweight oils in their livers to make themselves buoyant, whereas bony fishes use gas bladders. Other differences are discussed in chapter 5.

Early in their evolutionary history, the cartilaginous fishes split into

two independent lines: the sharks, skates, and rays (subclass Elasmobranchi) and the ratfishes (subclass Holocephali). The sharks, skates, and rays only number about seven hundred species but they are quite successful and widely distributed as top predators. Some species even feed largely on mammals and birds and a few others have invaded fresh water. The ratfishes are a rather peculiar group of about thirty bottom-dwelling species, named for their long, rat-like tails. They have changed little since they first appeared in the fossil record, being specialized for crunching clams and other invertebrates in the ocean's depths.

Like the cartilaginous fishes, the bony fishes split into different evolutionary lines early in their history. One line, the ray-finned fishes (subclass Actinopterygii), gave rise to the bony fishes that dominate the waters today. The three other lines resulted in small, rather obscure groups that all possess lobed (limb-like) fins. These obscure fishes are of considerable interest, however, because one of the lines gave rise to the terrestrial vertebrates (tetrapods). One of the more prominent living groups, the lungfishes (subclass Dipneusti), even breathe air. Another group, the coelacanths (subclass Crossopterygii), are most famous because they were thought to be extinct for nearly 10 million years until a fisherman pulled one from the depths of the ocean off the coast of Africa. It is perhaps the only fish that has made newspaper headlines all over the world.

Although the cartilaginous and lobe-finned fishes are of great interest, their role in this book is minor compared with that of the ray-finned fishes. The rayfins, with over 21,000 species, dominate both fresh and salt water in both number of species and number of individuals. The first fossils appear in freshwater deposits over 400 million years old. By about 340 million years ago they had assumed their dominant position in fresh water and were moving into the seas, eventually to displace the placoderms. The earliest ray-finned fishes were the chondrosteans (infraclass Chondrostei), represented in the modern fauna only by about twenty-five species of sturgeon and two species of paddlefish (order Acipenseriformes). They were gradually replaced by various groups of more "modern" fishes (infraclass Neopterygii), represented today by the gars (order Lepisosteiformes, nine species) and the bowfin (order Amiiformes, one species). The gars, bowfins, and their relatives dominated the seas and fresh waters in the age of dinosaurs but were replaced in their turn by the dominant modern fishes, the teleosts (subdivision Teleostei). The teleosts have diversified in many directions, producing forms adapted for living in most of the aquatic habitats of the world.

Figure 1-4
Some traits of a successful teleost, as illustrated by a small, nearly transparent
tetra that is commonly kept in aquaria.

The many evolutionary directions are represented by the twenty-five to thirty teleost orders (the number depends on who is doing the classifying), the hundreds of families, and thousands of species that have been described.

Why have the teleosts been so successful? Their success is due to a set of adaptations that together have made this group superbly adapted for living in water. The tail is symmetrical and provides even, powerful thrust for swimming. The scales are thin but strong, providing protection without weighing down the fish with armor. The skeleton is mostly bone, with strong but light construction. The skull is complex in structure and has been modified for many specialized types of feeding, especially suction feeding. The gas bladder is used to create neutral buoyancy and its volume can be finely controlled, making it possible to move through the depths. The fins are highly maneuverable and give each fish fine control over its movements. The body shape shows tremendous variability (see chapter 2) so the fishes can occupy many unusual habitats (especially the many small species).

Habitats of Fishes

The amazing array of fish body shapes and sizes reflects the equally amazing array of habitats in which they can be found. There are fish in mountain lakes above 4,000 meters and fish in the deep ocean, at depths of at least 8,300 meters. In the outflows of hot springs fish can be found living at temperatures of around 42 C, whereas in the Antarctic, fish can be found resting on chunks of ice surrounded by water that is within

a fraction of a degree of freezing solid. The salinities of the water in which fish are known to live range from the purest water of granitic mountain basins to water over four times saltier than sea water. The oxygen content of the water can be at saturation, as in cold mountain streams, or at essentially zero, as in tropical swamps (where most fishes breathe air). Even light does not seem to be necessary for fish life. Some of the most peculiar-looking fishes are those inhabiting the lightless depths of the ocean or deep underground aquifers. Socially, fish can be found in densely populated coral reefs where hundreds of individuals representing dozens of species can be found in areas only a few meters square, or they can be found singly, sparsely scattered in mountain lakes or the waters of the open ocean.

Despite their enormous ability to adapt to a wide range of aquatic environments, fish are far from being uniformly distributed in the waters of the globe. Thus 41 percent of all fish species are found exclusively in fresh water, even though fresh water covers only about 1 percent of the earth's surface and comprises less than .01 percent of the earth's water by volume. The reason for this is that fresh water is a highly diverse and fragmented habitat, so that fish populations frequently become isolated from one another, an important condition for the evolution of species to take place. Isolation is also promoted by the instability of the earth's crust and climates, as mountain ranges rise and fall and glaciers advance and retreat. The oceans, of course, are major barriers to the movements of freshwater fishes; only 1 percent of fish species move freely between the two environments. Perhaps because so few species are capable of this feat, the species that do move between the environments are often very abundant: salmon, shad, eels, striped bass.

Although 97 percent of the earth's water is in the oceans (the 3 percent remaining consists of 1 percent in fresh water and 2 percent in glaciers and the atmosphere), most of this water is open at best to species highly specialized to live under great pressure and food scarcity. The mean depth of the ocean is around 4,000 meters and 98 percent of its water is below 100 meters, the maximum depth at which enough light can penetrate to allow plants to grow. Seventy-five percent is below 1,000 meters, the usual total limit to light penetration. What all these numbers mean is that most marine fishes live in about 2 percent of the available water, although the deep ocean is so voluminous that about 12 percent of all known species are found there. Even the 2 percent figure for prime fish habitat, however, is deceptive, because much of that

Figure 1-5
The importance of fish to humans is well illustrated by this
design from an ancient Mimbres bowl from arid central
New Mexico. Mimbres people traveled long distances and
recorded not only local fish but fishes from the reefs in the
Gulf of California.

water is in the vast surface reaches of the open ocean, which are turbulent, featureless, and generally unproductive. They support as a consequence only about 1 percent of the fish species. This leaves only the narrow strip of shallow water along the continents, above the continental shelves, and the reefs around oceanic islands to support 44 percent of all fish species and the majority of individual fish as well. The size of our marine fisheries is an indication of the richness of these areas: 70 million metric tons of fish are taken from the sea each year, mostly close to the continents in temperate areas. Even more remarkably, over 30 percent of all known fish species are found in direct association with tropical reefs, which occupy just a tiny portion of the marine environment. This book can only sample the diversity of fishes and aquatic environments, but it should be viewed as an invitation to the reader to explore them further, preferably by getting wet.

Value of Fish

Humans are increasingly dependent upon fish for protein. If we assume a world population of 5 billion people (headed for 10) and, conserva-

tively, an annual catch of fish from all sources (including fish farming) of 100 million metric tons, roughly 20 kilograms (44 pounds) of fish are caught and consumed per person each year. The actual amount is probably somewhat higher. The monetary value of world fisheries is hard to estimate because there are so many poorly recorded fisheries. However, an indication of the value is given by the fact that the United States alone imports about $3 billion worth of fish products each year, and American anglers spend over $8 billion each year on their hobby. Even the trade in aquarium fishes has become a major worldwide industry, valued at hundreds of millions of dollars per year. The value of the aquarium trade is indicative of the increasing awareness of the aesthetic value of fish. This is seen also in the increasing numbers of people taking up scuba diving and snorkeling as hobbies and, of course, in the increasing number of intelligent people reading books like this one.

Fish Conservation

The ever-increasing popularity of fish has its down side: commercial fish stocks are being depleted everywhere, from the once phenomenally abundant herring and cod to the rare and delicate species sought by the aquarium trade. Equally alarming is the decline of fish diversity as we divert and pollute the fresh waters of the world or dump our wastes into productive coastal waters. In regions of the world with Mediterranean climates, where humans love to live but fresh water is scarce (such as California, South Africa, Chile, or Spain), 60 to 70 percent of the native freshwater fishes are well on their way to extinction. Some species are already gone. In tropical areas, fishes are being lost faster than they can be described by ichthyologistsprobably two hundred species of cichlids have been lost from Africa's Lake Victoria alone (see chapter 15). Thus one of the goals of this book is to create a greater appreciation for what we are losing in hope that greater awareness can at least slow down the rate of loss of our beautiful, irreplaceable fishes.

Continues...

Excerpted from Fish: An Enthusiast's Guide by Peter B. Moyle Copyright 1995 by Peter B. Moyle. Excerpted by permission.
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Edition details

• Publisher: University of California Press
• Publication date: 1995
• Language: English
• ISBN 10: 0520201655
• ISBN 13: 9780520201651
• Binding: Paperback
• Illustrator: Van Dyck Chris Mari
• Number of pages: 292