FISH ON LINE

A draft guide to learning and teaching ichthyology

using the FishBase information system[1]

 by

Daniel Pauly[2]

Rainer Froese[3]

and

Maria Lourdes Palomares^c

Abstract:

This guide provides a structure and case study material for a computer-based course in ichthyology for upper undergraduate and graduates students in biology or environmental science.

The key resource made accessible through this guide is FishBase, a large database on the biology of fish, available on CD-ROM (for the Windows operating system) and on the Internet (www.fishbase.org/search.cfm).

Following brief introductions to ichthyology and to FishBase, and to the use of the latter to teach the former, the key aspects of ichthyology are presented in five chapters covering Evolution and classification; Morphology and biodiversity; Reproduction; Physiology; and Fishes as part of ecosystems.

For each of these chapters, one or several ‘Exercises’ are presented describing how the relevant topics are covered in FishBase and describing how to access that information. ‘Tasks for the Student’ are provided, along with Internet links to relevant sources other than FishBase.

It is anticipated that this guide will improve as our experience with FishBase as a teaching tool improves. Thus, a final chapter describes how users (both students and teachers) may contribute to the frequent updates that are anticipated for this guide, and to completing the coverage by FishBase of the biology of fishes.

1.     CONTENTS

2.      Introduction

2.1.   What is ichthyology?

2.2.   What is FishBase?

2.3.   Why use one to teach the other?

3.      Evolution and Classification

3.1.   Phylogeny and classification

3.2.   Darwin and natural selection

3.3.   The species concept

3.3.1.      What’s in a name?

3.3.2.      Subspecies vs. populations

3.3.3.      Within-species diversity

3.3.4.      Common names

3.3.5.      Exercise 1

4.      Morphology and Biodiversity

4.1.   Diversity of Indo-Pacific shore fishes

4.2.   Diversity of shapes and sizes

4.2.1.      Exercise 2

4.3.   Diversity of brain sizes

4.3.1.      Exercise 3

4.4.   Diversity of growth and mortality

4.4.1.      Exercise 4

4.5.   Diversity of habitats: inferences from occurrence records

4.5.1.      Exercise 5

4.6.   Diversity of colors and sexual selection

4.6.1.      Exercise 6

4.7.   Diversity of food and feeding habits

4.7.1.      Table 1

4.7.2.      Exercise 7

5.      Reproduction

5.1.   The reproductive load concept

5.2.   Small eggs and no worries

5.2.1.      Exercise 8

5.3.   Large eggs and parental investment

5.3.1.      Exercise 9

5.4.   Variation on the basic themes

5.4.1.      Exercise 10

6.      Physiology

6.1.   Metabolism, gills and size

6.1.1.      Table 2

6.1.2.      Exercise 11

6.2.   Food consumption

6.2.1.      Exercise 12

6.3.   Estimating food consumption from empirical models

6.3.1.      Exercise 13

7.      Fish as Part of Exploited Ecosystems

7.1.   Food webs and trophic levels

7.2.   Trophic levels and sizes of fish

7.3.   Formal description of food webs

7.3.1.      Exercise 14

8.      Contributing to FishBase

9.      Acknowledgements

10.  References

11.  Appendices

11.1.                    Appendix A: Ichthyology resources on the net

11.2.                    Appendix B: fish-related web resources for UBC students

2.     Introduction

2.1.                      What is ichthyology?

Ichthyology, commonly defined as “the study of fish” or “that branch of zoology dealing with fish” has a long documented history, dating thousands of years back to the ancient Egyptians, Indians, Chinese, Greeks and Romans (Cuvier 1828).

This long, sustained interest in fish is due to their double role as highly speciose denizens of a fascinating, yet alien world, and as human food. It has generated, over the centuries, highly heterogeneous information—mainly taxonomic, but also referring to zoogeography, behavior, food, predators, environmental tolerances, etc.

This huge amount of information, embodied in a widely scattered literature, has gradually forced ichthyologists to specialize, and thus accounts on fish are now either global, but highly specialized (e.g. Eschmeyer’s Catalog of fishes (1998) or Pietsch and Grobecker’s Frogfishes of the world (1987) to name two outstanding representatives), or local and deep (e.g. Fryer and Iles’ Cichlid Fishes of the Great Lakes of Africa (1972) or Groot and Margolis’ Pacific Salmon Life Histories (1991).

Thus, with a few exceptions such as the massive Diversity of fishes (Helfman et al. 1997), texts are lacking which bring together, on a global basis, all aspects of ichthyology, such that they can be used for a specialized course, and/or independent learning.

2.2.                      What is FishBase?

FishBase is an information system available in the form of CD-ROMS and on-line, at www.fishbase.org/search.cfm, covering all fishes of the world in a fashion that is both global and deep. FishBase 99, whose accompanying book is available both in English and French, covers over 23,000 species of fish, i.e. most of the 25,000 extant species, and addresses the needs of a vast array of potential users, ranging from fisheries managers to biology teachers. The features of FishBase that enable it to meet such a wide range of needs reside in its architecture, which makes extensive use of modern relational database techniques.

Other features of FishBase are:

·        all information on a given species in the database is accessible through a unique scientific or common name;

·        the wide use of multiple choice field structures standardized qualitative information;

·        numeric fields record quantitative information that has been previously standardized;

·        numerous cross-relationships between data tables enable previously unknown relationships to be discovered; and

·        complementary databases provided by colleagues and linked to FishBase proper, contribute to making the combined package the most comprehensive data source of its kind.

2.3.                      Why use one to teach the other?

For teachers of aquatic biology, or of specialized ichthyology courses, the uses of FishBase will range from practical solutions to theoretical issues:

·        FishBase is directly useable as data source (i.e., as an electronic encyclopedia on fish), thus complementing classical sources of information on fish, e.g., the Zoological Record or Aquatic Science and Fisheries Abstracts, and helping overcome the lack of scientific literature, especially in developing countries;

·        the many pictures in FishBase can be used, just as those in taxonomic books, to provide students with a visual impression of the morphological and color diversity of fish, and/or of specific features of various groups;

·        students will be able to assess the state of knowledge on various groups of fish, and thus obtain some guidance in identifying worthwhile projects; and

·        the synoptical view that FishBase produces by assembling and structuring all available information on one species will help students to obtain material for study (see above) and, perhaps more importantly, to develop a sense of how scattered bits of knowledge can be used to ‘reconstruct’ species, and to show how these fit into their environments, thus encouraging a ‘holistic view’, as now required for most of what we do in the biological sciences.

Thus, a series of lectures on ichthyology may be conceived, based on the following elements:

·        show FishBase pictures through an introductory lecture, to highlight the diversity and colorfulness of fish and similarity of external morphology in related groups (this hopefully would serve to generate interest in the course as a whole, and introduce fish classification);

·        compare the early classification schemes in Cuvier (1828) with a recent one, e.g., that in the Catalog of fishes (Eschmeyer 1998), ‘hosted’ by FishBase and largely identical with the widely used classification in Nelson (1994);

·        introduce the species concept and its requirements (a formal description with figures, a binomen, a holotype, a type locality, etc.) and implications (synonymies, sister species, etc.), using FishBase as source of examples, and its Glossary for definition of terms;

·        define the characteristics (meristics, morphometrics) through which fish species are usually defined and hence identified, and compare identification through keys with computer-based identification using the appropriate FishBase routine (see ‘Quick Identification’);

·        show how museum and other occurrence records, as included in FishBase, can be used to define distribution ranges and habitats, which can then be used for ecological inferences;

·        show how the latitudinal ranges of fish species can be used to test various hypotheses, e.g., on the relationship between fish biodiversity and shelf area (for marine species) or land area (for freshwater species);

·        define and illustrate various life history strategies, and analyze their frequency distribution throughout the world. Show, e.g., that salmon-type anadromy is extremely rare in subtropical or tropical species (it is well documented only in hilsa, Tenualosa ilisha, ranging from Iraq to Myanmar). Show how students can identify the relative frequencies of different strategies and draw inferences from these;

·        let each student select a species, print out the relevant FishBase synopsis and complement it based on a literature review (and send the result to the FishBase Team); and

·        show or let students derive quantitative relationships between different expressions of fish physiology (e.g., respiration, growth) and temperature (and hence latitude) and identify modifying factors (salinity, gill size, food type, etc.).

In the context of higher education, FishBase may also serve as background for Bachelor’s or Master’s theses wherein an area of ichthyology not presently or suitably covered by the tables in the latest version of FishBase would be ‘broken up’ into choice, numeric and text fields, entered and then analyzed on a comparative basis[4].

3.     Evolution and Classification

3.1.                      Phylogeny and Classification

There are different ways in which objects can be classified and the human mind is very good at generating criteria for classification. This is why the following list, assembled by the Argentinean author Jorge Luis Borges, and purportedly extracted from an ancient Chinese encyclopedia (Lakoff 1987), strikes us as funny:

“…it is written that animals are divided into:

·        those that belong to the Emperor;

·        embalmed ones;

·        those that are trained;

·        suckling pigs;

·        mermaids;

·        fabulous ones;

·        stray dogs;

·        those that are included in this classification;

·        those that tremble as if they were mad;

·        innumerable ones;

·        those drawn with a very fine camel’s hair brush;

·        others;

·        those that have just broken a flower vase;

·        those that resemble flies from a distance.”

The two major criteria that are used to classify things (neither met by Borges’ list), are utility or affinity:

·        Utility generates classifications whose objects are easy to find. An example of such a classification would be a dictionary, whose entries are arranged alphabetically;

·        Affinity, on the other hand generates classification wherein adjacent objects s are straightforward to compare (because adjacent entries share important features).

In the European middle ages, animal books (‘Bestiarum’) were usually ordered alphabetically. However, such ordering eventually struck people as odd, especially as people realized, in the course of long debates on ‘universals’ (on whether names are ‘natural’ attributes of things, or not), that names are arbitrary labels.

Thus, authors gradually began seeking for natural classifications, wherein organisms are ordered by affinities, these affinities being initially conceived as reflective of the general rules which god used when creating these organisms.

The work of Linnaeus, whose Systema Naturae, the tenth edition of which in 1758 still marks the beginning of zoological nomenclature, is an example of such attempts to identify the underlying affinities among plants and animals. The resulting ‘natural’ classifications have started to make sense, however, only since Darwin, in The Origin of Species (1859), provided a rationale for affinities, that is, shared ancestry. Darwin not only provided a basis for the affinities between organisms, however. He also provided a mechanism by which new species and higher taxa emerged out of common ancestors. This mechanism he called natural selection.

3.2.                      Darwin and Natural selection

Natural selection is the core of Charles Darwin’s work and is best defined in his own terms: “many of every species are destroyed either in egg or [young or mature (the former state the more common)]. In the course of thousand generations infinitesimally small differences must inevitably tell; when unusually cold winter, or hot or dry summer comes, then out of the whole body of individuals of any species, if there be the smallest differences in their structure, habits, instincts [senses], health, etc., <it> will on an average tell; as conditions change a rather larger proportion will be preserved: so if the chief check to increase falls on seeds or eggs, so will, in the course of 1,000 generations, or ten thousand, those seeds (like one with down to fly) which fly furthest and get scattered most ultimately rear most plants, and such small differences tend to be hereditary like shades of expression in human countenance. (Darwin 1842)

Natural selection, thus, consists of three elements:

·        organisms usually produce far more progeny than their habitat can accommodate;

·        each member of the progeny differs in some inheritable attributes or properties;

·        there is a tendency for those progeny with attributes or properties that are more suitable for the habitat in question to suffer a lower rate of mortality and to reproduce better than their siblings.

These three features jointly cause animals and plants to try to track fluctuation of the environment. In this process, and in conjunction with other mechanisms such as the ‘founder effect’ and the effect of neutral selection, isolated populations can become so different from a mother species that they will not be able to mate if the barrier that once separated them disappears.

3.3.                      The species concept

Species are “groups of actually (or potentially) interbreeding natural populations which are reproductively isolated from other such groups” (Mayr 1942, p. 120).

3.3.1.      What’s in a name?

Since species are the basic rank of biological nomenclature, naming species is very important and we now follow for this a model proposed by Linnaeus, (see above), wherein the species is defined by a so-called binomen consisting of a unique genus name, always starting with a capital letter, and a species epithet , which is never capitalized; both are written in italics font. With regard to the capitalization rule, simply recall that the binomen is the short version of an earlier mode of description wherein a whole paragraph was used to describe, and thereby define, a species. The binomen, thus, was the start of a sentence.

An important addition to a species name is the name of the author who first described that species and the date of that description; as in, for example, the Linnaean species Salmo trutta Linnaeus, 1758. At times you will encounter a species, e.g. Oncorhynchus mykiss, with an author’s name and date in brackets, e.g. (Walbaum, 1792). In this case, it means that the species whose epithet is mykiss was originally described as a memeber of another genus, in this case Salmo, and due to better understanding of its relationships with other trouts, was subsequently moved into the genus Oncorhynchus which it is now a member.

Another rule important to animal species names are that the genus part of the name must be unique to the animal kingdom. From the year 2000 on, it must also be unique among all organisms. Thus, when a generic name is coined, the author must verify that this name has never been used by any other zoologist, and, from 2000 on, by any botanist, bacteriologist, etc. The apparently daunting task is not impossible, however, as global catalogues of organism names are now being created; the most important of these is the Species 2000 catalogue (see www.sp2000.org).

3.3.2.      Subspecies vs. populations

Given the mechanism of natural selection, every fish population can be conceived as being a potential new species. All one needs to imagine is that populations become isolated from others long enough for their members to lose the ability to mate with those of other populations. However, as long as some members of each population continue to mate with members of other populations of the same species, a mating barrier will not emerge (only a small gene flow is required to prevent the emergence of a mating barrier). Thus populations, though it might be easy to define them in terms of attributes such as number of scales or spines or body proportions, should not be given full taxonomic status because (contrary to species) they usually do not maintain themselves over a long period. Not having taxonomic status also means they should not have formal names, such as the trinomen that are still frequently used today, e.g. Oreochromis niloticus niloticus. The third part of the trinomen refers to a subspecies, which is, in fact, a population, or, to use a term much used in earlier times, a ‘race’.

3.3.3.      Within-species diversity

Species differ as to the extent of their diversity. Some species consist of a single population of a few individuals — these are often endangered species. Others have wide ranges and a rich structure of populations – the situation which tempted authors to define subspecies as populations at opposite ends of a geographical range often differ in several characters. However, its is usually not objectively defined within-species diversity which has motivated authors to define subspecies, but national or local research traditions, and the resources available for taxonomy. Thus, Berg (1965) established numerous subspecies and even lower taxa for the fishes of adjacent lakes and rivers of the former Soviet Union, while subspecies are rarely proposed by taxonomists working on the many coral reef species of the Indo-Pacific, although their distribution spans thousands of kilometers, and detailed studies may justify this (at least if one believes in subspecies).

3.3.4.      Common names

The common names of fish are what most people know about most fish. Thus, capturing the common names of fish in various languages captures most of what people who speak these languages know about fish. For this reason, FishBase includes over 90,000 names of fish in over 100 languages, ranging from widespread languages such as English or Spanish, to languages spoken by few speakers, such as Haida in Haida Gwaii, British Columbia. Anthropologists, notably Berlin (1965), have established that essentially all ethnic groups in the world spontaneously differentiate a similar number (about 500) of ‘kinds’ of organisms, the kinds roughly corresponding to genera, with important species being named, as well as some of their life history stages.

The sounds in fish names also generate interesting patterns. Thus, small fishes (i.e., fishes with small values of Lmax) tend to have names containing high pitch sound such as ‘i’ or ‘ee’, while large fish tend to have names with lower pitch sounds, such as ‘a’, or ‘aa’ (Berlin 1992; Palomares et al. 1999).

3.3.5.      Exercise 1

4.     Morphology and Biodiversity

The diversity of fish is larger than for any other vertebrate group. Not only are there more species of fish (25,000) than of all other vertebrates together, but also the range of body shapes and sizes of fish is larger than for mammals, birds or reptiles. Consequently, the range of habitat occupied is larger as well.

4.1.                     Diversity of Indo-Pacific shore fishes

The triangle formed by Indonesia, the Philippines and New Guinea, collectively referred to as the ‘East Indies’, form the center of marine fish biodiversity in the Indo-Pacific, with about 2,800 species naturally occurring there. These numbers drop with distance from this center to about 500 species in Hawaii and 120 species in the Easter Islands. The number of endemic species, i.e., fishes that do not occur outside a given area, increases with distance from the center, supporting one hypothesis that species evolved in the outer region and accumulated in the center. Another hypothesis holds that species evolved in the rich and stable habitats of the East Indies and were carried to the periphery by currents. Randall gives 5 explanations for fish biodiversity in the Indo-Pacific:

·        Sea surface temperatures in the East Indies were more stable during the glacial periods and thus extinction rates were lower than in the periphery;

·        Shelf area in the East Indies is much longer than that of the periphery, again making extinctions less likely;

·        Dispersal of shore fishes to remote islands occurs during the planktonic larval phase which lasts from several days to several weeks. However, the larval phase of many species is not long enough for long stretches of open ocean water, thus restricting their distribution;

·        Existing current patterns support dispersal of fish larvae from the area as well as convergence of larvae of species that have evolved in the periphery towards the East Indies;

·        During the last 700,000 years, there have been at least 3 ice age events that reduced the water level in the East Indies and separated populations long enough to become different species.

4.1.1.      Exercise 2

4.2.                     Diversity of shapes and sizes

The shapes of fish are also extremely diverse, and include – besides the torpedo shape perceived as ‘typical’ for fishes and termed ‘fusiform’– shapes ranging from the serpentine (in the Anguilliformes and other orders) to the avian (in ‘flying fishes’), with Latimera chalumnae sporting limbs resembling, but not being used as, those of land-based tetrapods.

Shape and other morphological features are the key characteristics used to date for classifying fishes, and hence understanding their classification requires a basic overview of the basic shapes of fishes, as can be obtained from the outline drawings included, for each of the existing 500 fish families.

Size is the most important attribute of individual organisms; it determines what can be their food, and the extent to which they can be the prey of other organisms. Size also determines how much food an animal requires to eat, how fast it can swim, and to a large extent, where it can live.

The maximum size of fish can range from one centimeter in Philippine gobies, e.g., Pandaka pygmea to 13-15 meters in the Whale shark, Rhincodon typus. This diversity of size allowed widely different environments to be colonized, ranging from temporary puddles to the central gyres of the open ocean. However, colonizing these environments required other adaptations, involving growth and mortality rates, and their various correlates, discussed below.

4.3.                     Diversity of brain sizes

The brain size per body weight of adult animals is related to the sensory and behavioral capabilities of the respective species. For example, fishes with well-developed electrosensing capabilities are known to have large brains. The brain is the organ with the highest energy and oxygen demand, and thus, fishes as well as other animals have evolved brain sizes that are neither too small nor too large respective to the niches they occupy in nature.

4.3.1.      Exercise 3

4.4.                      Diversity of growth and mortality

In spite of this wide diversity of fish sizes, clear patterns do emerge: tropical fish tend to be smaller and faster-growing than their cold-water counterparts and their natural mortality tends to be higher. This is due to high temperature elevating the metabolic rates of tropical fish relative to their cold-water counterparts.

Correspondingly, the natural mortalities experienced by fish, which are a function of their sizes, range from values which exterminate an entire cohort in a few months, e.g., the round herring, to 50 and more years in the lake sturgeon and 150 years in the orange roughy. These enormous differences in life span allow fish to respond differently to habitat variations. Small, short-lived fish track such variations, for example, when growing up in temporary puddles and laying desiccation-proof eggs before they dry up, thus being able to live through dry periods or produce a successful cohort every 1-3 years or so (as may happen in such long-lived fish as cod).

4.4.1.      Exercise 4

4.5.                      Diversity of habitats: inferences from occurrence records

Fish inhabit more diverse habitats than any other group of vertebrates, ranging from Himalayan or Andean brooks at 4000 meters to abyssal depth at 10 kilometers, spanning an extremely high range of pressures. The range of temperatures that can be tolerated is also very large, from minus 2^oC as tolerated by the Antarctic fish, Pagothenia borchgrevinki (which sport anti-freeze substances in their blood; see Eastman and Devries 1985); to up to 40^o C for Oreochromis alcalicus, which lives at the edge of a hot spring in Lake Nakuru in Kenya. (This does not consider the temperature tolerance of deep-sea vent fishes, which have not yet been studied in detail).

Because fish occur only in habitats which they can tolerate, and tend to be abundant in those habitats to which they are best adapted, occurrence records kept by museums can be used to reconstruct the habitat preferences of fishes whose ecology is otherwise unknown. Such records have been named bioquads because they refer to biodiversity and consist of four key elements: (a) the name of the organism; (b) the place where it was caught; (c) the source or person who sampled or identified it; and (d) the date. FishBase makes wide use of bioquads for documenting the distribution of fish and this can be emulated by ichthyology students who may assemble bioquads from FishBase and other sources, notably the Internet. (see Appendix A for sources of bioquads).

4.5.1.      Exercise 5

4.6.                      Diversity of color and sexual selection

Fish are beautiful; they have beautiful colors and fascinating body shapes, one of the reasons why people keep them in aquaria. Color patterns in fish have been long misunderstood. Pre-Darwinian authors thought that god had given fish such marvelous colors so that predators would find it easier to see and catch them. We know, since Darwin, that such coloring, if it serves any function at all, must benefit directly the ones who sport it and not their predators as is obvious in the many color patterns that camouflage the owner, or confuse predators, by, e.g., displaying large eyes in the wrong places. Darwin also proposed a reason why non-camouflaging striking coloring should exist, and that is sexual selection.

Essentially, the males entice the females to choose them by displaying nicer colors than other males; they compete in terms of their ‘beauty’, this being related to good genes (remember Darwin did not know of genes and that part of his theory was very hard on him). Recently, the Zahavi’s have complemented Darwin’s version of sexual selection through a new concept, the handicap principle, which takes into account that the colors and other adornments which males use to entice females to choose them are costly to produce (Zahavi and Zahavi 1997). Hence, the color and other adornments represent a handicap and the males capable of displaying these attributes thus must have really good genes for life-supporting traits. We may call this ‘truth in advertisement.’

The idea is that sporting highly symmetrical patterns, as, for example, in Pomacanthus imperator, implies that the fish in question had a harmonious development since development problems, due to genetic problems, parasites or disease (also indicative of ‘bad genes’) would always lead to asymmetries. Also, for colors that do not necessarily camouflage the fish, sporting them indicates that the fish in question has been able to evade predators. Some fish imitate the color patterns of other species to fool prey or predators (mimicry).

4.6.1.      Exercise 6

4.7.                      Diversity of food and feeding habits

Given the diversity of their sizes and habitats it is obvious that fish should also have a wide diversity of food and feeding habits. Thus fish range from feeding on microscopic phyto- and zooplankton to engulfing entire adult fishes, such as is done by Whale sharks or gulpers, respectively. Attempts to link fish to their ecosystems have led to a huge literature on their food and feeding habits. Unfortunately, some of this is useless because it is reported in the wrong units, i.e., frequency of occurrence of certain items in a number of stomachs sampled. Still, there are enough studies in which the proper units have been used (percent contribution in weight, energy or volume to total stomach contents) for a clear idea to emerge of what fish generally eat in their typical habitat. Given knowledge of the average trophic level of their diet items, the trophic level of fish whose stomach content has been studied can thus be computed, which allows evaluation of the position the consumers occupy in the food web.

4.7.1.      Table 1

Hierarchy of food items, simplified from the FishBase table used to compute trophic levels (TL) from diet composition data. Therein, the TL of a consumer is 1 + (mean TL of the prey items).

a)       in FishBase, these food items have distinct trophic levels (and associated standard errors), not presented here.

4.7.2.      Exercise 7

5.     Reproduction

5.1.                      The reproductive load concept

Fish usually reproduce when they have reached about half of the maximum size they are likely to reach (L_max). The size at which maturity is first reached is called L_m and the fraction L_m/L_max, called reproductive load, tends to be higher in small than in large fish. Thus, a goby with L_max=10 cm will have a value of L_m = 7 cm, while in a Basking shark with L_max » 10 m, L_m will be about 4 m. Given that fish of different sizes have different growth rates, their different L_m values imply very different ages at first maturity (t_m).

5.2.                      Small eggs and no worries

Fish differ from most other vertebrates in that for most species, parental care is very limited or non-existent. The typical bony fish produces a large number of small eggs which hatch and become part of the phytoplankton, and which must beware of their parent (or their congeners) if these are zooplankton feeders.

The high fecundity of bony fish has led many to believe that they can be exploited very strongly, i.e., that there will always be some recruits even if the parental stock is much reduced. This is called the ‘million egg fallacy’ and it has caused untold damage to fisheries, especially cod fisheries. Still, it is useful to know the relationship between numbers of eggs spawned and the weight of the mothers.

5.2.1.      Exercise 8

5.3.                      Large eggs and parental investment

There are many fish which give birth to live young or which construct nests for their eggs, or which practice buccal incubation, e.g., in the Nile tilapia (see also Fish Quiz link in Exercise 7). Some other fish, notably the cartilaginous sharks and rays, give birth to fully-formed pups or produce very large eggs from which fully-formed young are hatched.

5.3.1.      Exercise 9

5.4.                      Variations on the basic theme

As noted by Darwin, fish are extremely labile in their sex determination, i.e., there are lots of fish which change sex, at least, far more than in other vertebrate classes (e.g., wrasses, parrot fishes, groupers). These are called hermaphrodites. In some fishes the different life (and sex) stages differ so much in color and/or form that they were originally described as different species. Fish also give us neat examples of parasitic males, and other aberrant (?) behaviors.

5.4.1.      Exercise 10

6.     Physiology

The basic building blocks of fish bodies are proteins. Proteins have structure at several levels. The primary structure is determined by a sequence of the component amino acids, themselves with a structure determined by their sequence of atoms of carbon, hydrogen, etc. The secondary structure of most protein is a primary coil, similar to a braid.  A third-level structure can emerge when the braids fold onto themselves, with various loops weakly connected by hydrogen bonds. It is this tertiary structure which determines the external shape of a protein, e.g. of an enzyme and hence how it will lock into ‘receptors’, often other molecules on the surface of cells.

6.1.                      Metabolism, gills and size

Thermal noise is ubiquitous above absolute zero (0 Kelvin) and one of its effects is to destroy the tertiary structure of protein, thus rendering it ineffective. As a result, animals must break down such denatured molecules into their constituent parts and re-synthesize them. This is the reason why it costs energy to maintain a living body, even when it ‘does’ nothing, nor grows. In mammals and birds, which maintain more or less constant internal body temperatures, enzyme systems are geared such that the rate of synthesis matches a certain level of thermal noise, i.e. that which occurs at 37 to 38 degrees temperature. In fish, which except for large scombroids and some large sharks, cannot maintain a constant body temperature, different external temperatures thus imply different levels of thermal noise and hence rates of protein denaturation. Thus, metabolic rate must vary with temperature and it does so essentially in function of the need to re-synthesize protein.

However, it must be understood that the oxygen consumed by a fish is not its oxygen demand but the oxygen supplied to it via its gills, i.e., the fish would use more oxygen if it could get it. Hence, the amount of oxygen consumed by a fish is an imperfect measure of its real ‘need’ for oxygen. Gill size grows in proportion to a power of body weight that is less than one, i.e., the bigger fish of a given species become, the smaller the gill area per body weight becomes. Hence, big fish, given a certain level of activity, will tend to run out of oxygen faster than small fish of the same species, other things being equal.

6.1.1.      Table 2

Ten species in FishBase with growth parameters, at least one length-weight relationship and three records each of gill area and oxygen consumption per unit body weight.

6.1.2.      Exercise 11

6.2.                      Food consumption

Like other heterotrophic organisms, fish need food to survive and grow. Within ecosystems, trophic (feeding) relationships and energy flows largely define the function of various species. There are two ways of presenting species-specific consumption:

·        At the individual level, i.e., as the consumption of a particular food type by a fish of a certain size, in the form of a daily ration (R_d); or

·        At the population level, i.e., as the consumption (Q) by an age-structured population of weight (B), in the form of population-weighted consumption per unit biomass (Q/B).

There are a number of methods that can be used to estimate the daily ration of fish: studying the changes in stomach content in the course of a day, direct observation of captive fish, etc. One of these techniques is to infer ration from daily oxygen consumption, which is justified since the oxygen consumed is ultimately combined with the food consumed to generate ATP (adenosine triphosphate, the substance used to fuel internal metabolism). This is illustrated through an example for red piranha, Pygocentrus nattereri, adapted from Pauly (1994):

Data were analyzed using a multiple (log) linear regression which yielded, for prediction of the metabolic rate (C, in mg0₂ · h^-1) in small Pygocentrus nattereri, the model

C = 0.387 · W^0.539· O₂^1.13,                                                                                            … 1)

where W is the live weight of the fish in g, and O₂ is the oxygen content of the water, in mg 1^-1. The overall fit is good (R = 0.950); the standard errors of the exponents are 0.163 and 0.205, respectively, for 4 degrees of freedom. Given the small range of weights considered here, the relatively large standard errors about the estimates, and the low number of degrees of freedom, it would not be appropriate to assume that the slope linking O₂ consumption and body weight is, in P. nattereri, significantly different from that proposed by Winberg (1960) for most fishes larger than guppies, i.e., 0.7 - 0.8. This implies that the equation above can be used only for a small range of weights, here 20 to 160 g.

For a 100 g fish in water with 6 mg O₂1^-1, the equation above predicts an O₂ consumption of 35 mg·h^-1, i.e., 841 mgO₂ ·day^-1. An estimate of daily energy consumption (Q) can be obtained from this using the approach of Wakeman et al. (1979), wherein

R_d = (DW + RESP)/0.75,                                                                                           … 2)

where R_d is the ration, i.e., daily energy consumption in kcal, DW the energy content of the (daily) growth increment, and RESP is the oxygen consumption.

The first derivative (i.e. growth rate) of the von Bertalanffy equation in terms of wet weight is

dw/dt = 3KW ((W_¥/W)^1/b-1)                                                                                       … 3).

This, solved for W_¥ = 756 g, K = 0.893/365 = 0.00245 day^-1, and b = 3, gives for a 100 g fish a daily growth increment of 0.706 g, corresponding to 0.706 kcal if the calorific value of fish wet weight is set equal to unity (Brett & Blackburn 1978). The available information on body composition of red piranha flesh (Junk 1976, in Smith 1979) is 8.2 % fat, 15.0 % protein, and 4.4 % ash, not very different from values reported from other fishes (Bykov 1983). Thus, if an oxycaloric equivalent of 0.00325 kcal·mg^-1 O₂ is assumed, as in other fishes (Elliot and Davidson 1975), the above estimate of 841 mg O₂ day^-1 becomes 2.733 kcal day^-1. Thus,

R_d = 0.706 + 2.733/0.75                                                                                             … 4)

or 4.585 kcal day^-1 for a 100 g piranha. Food conversion efficiency (K₁ = (dw/dt)/ R_d ; Ivlev 1966) would then be K₁ = 0.154.

6.2.1.      Exercise 12

6.3.                      Estimating food consumption from empirical models

The method outlined above to deal with the ration of fishes lead to point estimates, pertaining to a single size or age (group). A fish population consists, however, of different size (age) groups, with small sizes and ages being far more abundant than large sizes and ages. Thus, drawing inferences from one (or several) ration estimate(s) pertaining to a given size (range) of fish, to a population containing a multitude of size groups, requires a knowledge of the size (age) structure of the population. An approach for performing this inference is given in FishBase.

A large number of such inferences, from ration to population weighted food consumption estimates (Q/B), have been performed in recent years, notably Palomares and Pauly (1998). These estimates of Q/B can be used in the context of empirical models to predict Q/B from other, easy-to-estimate parameters. One such equation is

log Q/B = 7.964 – 0.204logW_¥ – 1.965T’ + 0.083A + 0.532h + 0.398d                     … 5)

where Q/B is the food consumption, W_¥ is the asymptotic weight in grams, T’= 1000/(°C+273.15), A is the aspect ratio of the caudal fin = h²/s, h=1 and d=0 for herbivores, h=0 and d=1 for detritivores, and h=0 and d=0 for carnivores.

Here, one key input is the aspect ratio of the caudal fin defined as in Figure 1 . Fish with tails with high aspect ratio consume more food than fish with low aspect ratio tails, other things being equal. Needless to say, equation (5) above cannot be used for fish (e.g. eels) which do not use their caudal fin as their main propulsive organ. Other approaches can be used in such cases.

6.3.1.      Figure 1

6.3.2.      Exercise 13

7.     Fish as part of exploited ecosystems

7.1.                      Food webs and trophic levels

Fish populations do not live by themselves. Rather, they are embedded in ecosystems where they perform their roles as consumers and prey of other organisms, including larger fishes.

7.2.                      Trophic levels and sizes of fish

The role of fishes within ecosystems is largely a function of their size: small fish are more likely to have a vast array of predators than very large ones. On the other hand, various anatomical and physiological adaptations may lead to dietary specialization, enabling different fish species to function as herbivores, with a trophic level of 2.0, or as carnivores, with trophic levels typically ranging from 3.0 to about 4.5.

Moreover, trophic levels change during ontogeny of fishes. Larvae, which usually feed on herbivorous zooplankton (TL= 2.0) consequently have a trophic level of about 3.0. Subsequent growth enables the juveniles to consume larger, predatory zooplankton and small fishes or benthic invertebrates; this leads to an increase in trophic level, often culminating in values around 4.5 in purely piscivorous, large fishes.

7.3.                      Formal description of food webs

For formal descriptions of the role of fish in ecosystems and their responses to changes in fishing, and other changes, see the Ecopath modeling tool at www.ecopath.org.

There is a strong link between Ecopath and FishBase, i.e., FishBase has a special routine to assemble and print out information on the fish of a given area or ecosystem, such that ecosystem models can be straightforwardly constructed.

7.3.1.      Exercise 14

8.     Contributing to FishBase

The FishBase project is a large, international, non-profit venture which started in 1989 and whose latest product, FishBase 99 (Froese and Pauly 1999) covers all the fish in the world - at least in terms of nomenclature. In terms of biology and ecology the coverage is, however, rather spotty and it is paradoxically in the well-studied temperate areas that the coverage is most incomplete, at least relative to the available literature. The reason for this is that FishBase was funded by the European Commission to cover countries in Africa, the Caribbean and the Pacific (‘ACP’) that are associated with the European Union.

For FishBase to realize its potential as the integrated, computerized system of fish most useful to the global ichthyological community, it requires input from users, including students. Thus you are encouraged to contribute to FishBase, notably by sending reprints or photocopies of material used for your analyses, as well as other information which you think should be incorporated (with complete sources!). You are also welcome to submit photos or slides whose originals would be returned to you after they have been scanned. See ‘How to become a collaborator and why’ for details on the manners in which such contributions are acknowledged; also note that you retain all rights to any submitted photo).

9.     Acknowledgements

We wish to thank Ms. Donna Shanley, for creating a first workable draft out of a jumble of text notes, references and Internet URLs. Without her dedication and skill, the making of this guide would have continued to be postponed forever.

10.             References

Berg, L.S. 1965. Freshwater fishes of the U.S.S.R. and adjacent countries. In 3 Vol., 4th edition. Israel Program for Scientific Translations Ltd., Jerusalem. [Original Russian version published in 1949].

Berlin, B. 1992. Ethnobiological classification. Princeton Univ. Press, New Jersey. 335 p.

Bykov, V.P. 1983. Marine fishes: chemical composition and processing properties. Amerind Publishing Co., New Delhi. 322 p.

Brett, J.R. & J.M. Blackburn. 1978. Metabolic rate and energy expenditure of the spiny dogfish, Squalus acanthias. J. Fish. Res. Board Can. 35: 816-821.

Cuvier, G. 1828. Historical portrait of the progress of ichthyology, from its origin to our own time. Translated by A.J. Simpson and edited by T.W. Pietsch (1995). The Johns Hopkins University Press, Baltimore. 366 p.

Darwin, C. 1842. The Essay of 1842 p. 1-53 In: F. Darwin (ed.). The Foundation of The Origins of Species: two essays written in 1842 and 1844. Cambridge, 1909. [Vol. 10 of ‘The Works of Charles Darwin’. Pickering & Chatto, London, 199 p.]

Eastman, J.T. and A.L. Devries. 1985. Adaptations for cryopelagic life in the Antarctic notothenioid fish Pagothenia borchgrevinki. Polar Biol. 4:45-52.

Elliott, J.M. and W. Davidson. 1975. Energy equivalents of oxygen consumption in animal energetics. Oecologia 19: 195-201.

Eschmeyer, W.N. (Editor). 1998. Catalog of fishes. California Academy of Sciences, San Francisco. 3 vols. 2905 p.

Fryer, G. and T.D. Iles. 1972. Cichlid Fishes of the Great Lakes of Africa. Oliver & Boyd, Edinburg, UK.

Froese, R. and D. Pauly (Editors). N. Bailly and M.L.D. Palomares (Translators). 1999. FishBase 99: Concepts, structure, et sources des données. ICLARM, Manila, Philippines. 324 p.

Groot, G. and L. Margolis. Editors. 1991. Pacific Salmon Life Histories. University of British Columbia, Vancouver, Canada. 564 p.

G.S. Helfman, B.B. Collette and D.E. Facey. 1997. The diversity of fishes. Blackwell Science, MA. 512 p.

Ivlev, V.S. 1966. The biological productivity of waters. [translated by W.E. Ricker]. J. Fish. Res. Board Can. 23: 1717-1759.

Junk, W.J. 1976. Biologia de água doce e pesca interior, p. 105. In: Relatorio Anual de INPA, Instituto Nacional de Pesquisas da Amazonia, Manaus.

Linnaeus, C. 1758. Systema Naturae per Regna Tria Naturae secundum Classes, Ordinus, Genera, Species cum Characteribus, Differentiis Synonymis, Locis. 10th ed., Vol. 1. Holmiae Salvii. 824 p.

Lakoff, G. 1987. Women, fire and dangerous things: what categories reveal about the mind. University of Chicago Press, Chicago, 614 p.

Linnaeus, C. 1758. Systema naturae per regna tria naturae secundum classes, ordinus, genera, species cum characteribus, differentiis synonymis, locis. 10^th ed. Vol. 1. Holmiae Salvii. 824 p.

Mayr, E. 1942. Systematics and origin of species. Columbia University Press, New York. 334 p.

Nelson, J.S. 1994. Fishes of the world. 3rd edition. John Wiley and Sons, New York. 600 p.

Palomares, M.L.D. and D. Pauly. 1998. Predicting food consumption of fish populations as functions of mortality, food type, morphometrics, temperature and salinity. Mar. Freshw. Res. 49:447-453.

Palomares, M.L.D., C.V. Garilao and D. Pauly. 1999. On the biological information content of common names: a quantitative case study of Philippine fishes, p. 861-866. In: B. Séret & H,-Y. Sire (eds.) Proc. 5^th Indo-Pac. Fish Conf., Nouméa, 1997.

Pauly, D. 1994. Quantitative analysis of published data on the growth, metabolism, food consumption, and related features of the red-bellied piranha, Serrasalmus nattereri (Characidae). Environ. Biol. Fish. 41:423-437.

Pietsch, T.W. and D.B. Grobecker. 1987. Frogfishes of the world. Stanford University Press, Stanford, California. 420 p.

Randall, J.E. 1998. Zoogeography of shore fishes of the Indo-Pacific region. Zoological Studies 37(4):227-268.

Smith, N. 1979. A pesca no rio Amazonas. Instituto Nacional de Pesquisa da Amazonia, Manaus.

Wakeman, J.M., C.R. Arnold, D.E. Wohlschlag and S.C. Rabalais. 1979. Oxygen consumption, energy expenditure and growth of the red snapper (Lutjanus campecheanus). Trans. Amer. Fish. Soc. 108: 288-292.

Walbaum, J. J. 1792. Petri Artedi Sueci Genera piscium. In quibus systema totum ichthyologiae proponitur cum classibus, ordinibus, generum characteribus, specierum differentiis, observationibus plurimis. Redactis speciebus 242 ad genera 52. Ichthyologiae, pars iii. Artedi Piscium 1-723.

Winberg, G.G. 1960. Rate of metabolism and food requirements of fishes. Fish. Res. Board Can. Transl. Ser. (194). 239 pp.

Zahavi, A. and A. Zahavi. 1997. The handicap principle: a missing piece of Darwin's puzzle.  Oxford University Press. 304 p.

11.              Appendix A: Web sites of institutions/organizations with ichthyological collections and/or associated links

This site includes a page with links to Museums and Collections world-wide: www.biology.ualberta.ca/jackson.hp/iwr/iwr.html (click on museums)

Albany Museum - (Freshwater Ichthyology): www.ru.ac.za/departments/am/

American Museum of Natural History: www.amnh.org/ (no link to Department of Herpetology & Ichthyology, however link to Center for Biodiversity Conservation available at http://research.amnh.org/biodiversity)

Aquatic animals mailing lists maintained by individuals from various institutions www.actwin.com/fish/lists.html

Australian Museum – Ichthyology: www.austmus.gov.au/fish/

BBCWS - Biodiversity and Biological Collections Web Server: www.keil.ukans.edu

Bernice P. Bishop Museum - Ichthyology Department: www.bishop.hawaii.org/bishop/fish/fish.html

Burke Museum, University of Washington, Seattle www.washington.edu/burkemuseum/

California Academy of Sciences - Ichthyology Department: http://web.calacademy.org/research/ichthyology/

Canadian Museum of Nature - Research and Collections - Recherche et collections: www.nature.ca/english/collect.htm or  www.nature.ca/francais/collect.htm

Carnegie Museum of Natural History, Pittsburgh: www.clpgh.org/cmnh/

Chicago Academy of Sciences Nature Museum: www.chias.org/index.html

Coleccion Nacional de Peces (Mexico): www.ibiologia.unam.mx/cnp/acervo.html

FishGopher - The FishGopher Project: www.as.ua.edu/biology/uaic/fishgopher.html

Florida Museum of Natural History - Ichthyology Page: www.flmnh.ufl.edu/fish/

Grice Marine Laboratory, University of Charleston, SC: www.cofc.edu/~grice/

Humboldt State University Fish Collection: http://sorrel.humboldt.edu/~raf1/fish.htm

Illinois Natural History Survey - Fish Collection: www.inhs.uiuc.edu/cbd/collections/fish.html

Instituto Nacional de Pesquisas da Amazônia - Neodat page: http://curupira.inpa.gov.br/colecoes/bdados/neodat/Index.htm

James Ford Bell Museum of Natural History - Fish Collection: www.gen.umn.edu/faculty_staff/hatch/fishes/index.html (database still under construction)

J. L. B. Smith Institute of Ichthyology: www.ru.ac.za/affiliates/jlb/

Massachusetts Museum of Natural History - Fish collection: http://snapper.bio.umass.edu/vmmnh/fishcoll.html

Milwaukee Public Museum - Vertebrate Zoology Section: www.mpm.edu/collect/vert.html

Museu de Ciências e Tecnologia PUCRS - Laboratório de Ictiologia: http://ultra.pucrs.br/museu/ictio/

Museu Nacional, Universidade Federal do Rio de Janeiro - Setor de Ictiologia: http://acd.ufrj.br/museu/home.html

Muséum d'histoire naturelle de la Ville de Genève - Catalogue des types: http://www.ville-ge.ch/musinfo/mhng/erpi/cat2.html

Muséum National D'Histoire Naturelle, Paris – Search: www.mnhn.fr/base/gicim.html

Museum of Comparative Zoology, Harvard University - Fish Page: www.mcz.harvard.edu/fish/

Museum of Southwestern Biology, University of New Mexico - Division of Fishes http://biology.unm.edu/~fishes/fishes.htm

National Museum of Natural History, Smithsonian Institution - Division of Fishes www.nmnh.si.edu/vert/fish.html

Natural History Museum (London) – collections: www.nhm.ac.uk/info/collections.html

Natural History Museum of Los Angeles County: http://www.nhm.org/sitemap/ (click on Ichthyology; note that collection database still not available)

Naturhistorisches Museum der Burgergemeinde Bern - (Vertebrate animals - collections): http://nmbe0.unibe.ch/abtwt/abtwt_coll.html (under E.A. Göldi collection, click on Gopher, then on Search Pisces collections; note that this is a downloaded file and may take more than 5 minutes)

Naturhistoriska Riksmuseet (Swedish Museum of Natural History) – Collections, Ichthyology Section, Department of Vertebrate Zoology: www.nrm.se/ve/pisces/collpage.shtml.en

Nova Scotia Museum   www.ednet.ns.ca/educ/museum/mnh/index.htm (click Backstage, then Collections, note that data computerization is incomplete and the collection is not yet searchable)

NEODAT - Neotropical Biodiversity Database: www.keil.ukans.edu/~neodat/

Oklahoma Museum of Natural History - Collections and Research: www.snomnh.ou.edu/collections/index.shtml (Division of Ichthyology is not on line)

Ohio State University’s Museum of Biological Diversity: http://www.biosci.ohio-state.edu/~herb/museum/musehome.htm (internal link to Museum of Zoology currently not available)

Philadelphia Academy of Natural Sciences: www.acnatsci.org/biodiv/

Provincial Museum of Alberta - Ichthyology Program – Holdings: www.pma.edmonton.ab.ca/natural/fishes/collects/collects.htm

Royal British Columbia Museum - Ichthyology and Herpetology Collection: http://rbcm1.rbcm.gov.bc.ca/research-collectionsdept/nat-hist/section/herpcol.html

Royal Ontario Museum - Centre for Biodiversity and Conservation Biology: www.rom.on.ca/biodiversity/cbcb/

Santa Barbara Museum of Natural History: www.sbnature.org/vertzoo.htm

Scripps Institute of Oceanography - Marine Vertebrates Search: http://www-sioadm.ucsd.edu/siofish/

Staatliches Museum fur Naturkunde, Stuttgart, Germany: http://ourworld.compuserve.com:80/homepages/naturkundemuseum/home-e.htm

Texas Natural History Collection (Austin) - Ichthyology Division: www.utexas.edu/depts/tnhc/.www/fish/

The Field Museum of Natural History, Chicago, Illinois - Fish collection: www.fmnh.org/research_collections/zoology/divisions_fishes.htm

Tulane University Museum of Natural History – Fishes: www.museum.tulane.edu/museum/fishes.html

University of Alabama Ichthyological Collections: www.as.ua.edu/biology/uaic/index.html

University of Alaska Museum, Fairbanks - Aquatics collection: http://zorba.uafadm.alaska.edu/museum/aqua/index.html

University of Alberta Laboratory for Vertebrate Paleontology: www.biology.ualberta.ca/wilson.hp/UALVP.html

University of Alberta Museum of Zoology – Collections: www.biology.ualberta.ca/uamz.hp/collections.html

University of Arizona Zoological Collections - Fish Collection: http://eebweb.arizona.edu/collections/fishcoll.htm

University of Arkansas Museum, Fayetteville: www.uark.edu/campus-resources/museinfo/public_html/

University of California Museum of Paleontology - Vertebrate Collection: www.ucmp.berkeley.edu/collections/vertebrate.html

University of Georgia Museum of Natural History: http://museum.nhm.uga.edu/mnhrep.html (Icthyology collection not online).

University of Kansas Natural History Museum - Division of Ichthyology: www.nhm.ukans.edu/~fishes/ (click on Collections)

University of Michigan Museum of Zoology - Division of Fishes: http://ummz1.ummz.lsa.umich.edu/fishdiv/

University of Nebraska State Museum - Division of Zoology www.museum.unl.edu/research/zoology/zoology.html

University of Washington Fish Collection  http://artedi.fish.washington.edu/

Virginia Institute of Marine Science - Ichthyology Collection www.vims.edu/ich_coll.html

Western Australia Museum - Aquatic Zoology www.museum.wa.gov.au/nat_sci/aq_zool/aq_zool.htm

Yale University Peabody Museum of Natural History - Ichthyology Collection www.peabody.yale.edu/collections/ich/

Zoological Museum, University of Copenhagen - Ichthyological Section www.aki.ku.dk/zmuc/ver/ichthylo.htm

Zoologisches Museum, Universität Hamburg - Ichthyological Collection www.rrz.uni-hamburg.de/ichthyo/welcome.htm

12.             Appendix B:

University of Alberta Ichthyology Web Resources: http://www.biology.ualberta.ca/jackson.hp/iwr/museums.html

The University of British Columbia Library: www.library.ubc.ca

Aquatic Sciences and Fisheries Abstracts: http://www.silverplatter.com/catalog/asfa.htm