(i) Preamble

The remaining groups of euteleosts are represented by the Protacanthopterygii, Paracanthopterygii, and the Acanthopterygii. The former two consist of about 1500 species (compared to over 13000 in the acanthopterygians), but many are extremely important commercially and represent some of the most interesting biologically.

(ii) Protacanthopterygii

The protacanthopterygians consist of three major lineages (in this case orders): the smelts (Osmeriformes), the pikes and mudminnows (Esociformes), and the salmon trout, graylings, whitefishes, and char (Salmoniformes).

The Osmeriformes: the smelts are marine, freshwater, and diadromous fishes found in north and south temperate areas. Perhaps the best known are the relatively shallow-water smelts, Osmeridae, found throughout the Pacific and Atlantic basins in the northern hemisphere. These are small, silvery fishes that usually possess an adipose fin. Good examples include the eulachon, Thaleichthys pacificus, native to the Pacific coast from northern California to Alaska where it of great traditional importance to aboriginal communities, and the capelin, Mallotus villosus. The capelin is found in both the north Pacific and Atlantic basin where it constitutes and important forage fish for commercially important species such as Atlantic cod.

In the southern hemisphere, the best known smelts are the galaxids and retropinnids that exhibit marine, landlocked freshwater, anadromous and catadromous life histories. Unfortunately, many native galaxids have been extirpated or become extinct owing to introduction of non-native fishes, principally salmonids, through competition and predation.

The Esociformes: these are the pikes, muskellunge, and mudminnows. They are strictly freshwater fish with about 10 species in two families: the Esocidae (pikes and muskies) and the Umbridae (the mudminnows). Both are well recognized by the posterior positioning of the median fins. This body form is usually associated with ambush predatory behaviour which is characteristics of these fishes.

The northern pike, Esox lucius, (shown above) has the distinction of exhibiting the widest distribution of any freshwater fish; it's found throughout the Holarctic (a circumpolar distribution) where it is an important predator in freshwater communities and the focus of intensive sports fisheries.

A nice catch of muskey (Esox masquinongy).

By contrast, many of the mudminnows (Umbridae) are much smaller and have very scattered and unusual distributions. For instance, the Olympic mudminnow (Novumbra hubbsi) is found in a monotypic genus and is endemic to the Olympic Peninsula in Washington State. The Alaskan blackfish, Dallia pectoralis, is restricted to central Alaska, Bering Sea islands, and eastern Siberia. The third genus, Umbra, has three species: two found in eastern north America, and one in the the Danube/Dniester rivers drainages in eastern Europe.

The Salmoniformes: these are the salmon, trout, char, whitefish, and grayling. There are about 70 species of salmoniform fishes. They are characterized by the possession of an adipose fin, no spines in the fins, and a pelvic axillary process (a small triangular flap of skin at the base of the pelvic fins). The Salmoniformes typically consist of three major sublineages (sometimes recognized as three distinct families) in the single family, Salmonidae: (i) the whitefishes and ciscoes, (ii) the graylings, and (iii) the salmon, trout, and char. Nice pics of most of BC's native salmonids can be viewed by clicking HERE.

The salmonids are freshwater and anadromous fishes native to the Northern Hemisphere. They have been introduced worldwide and are incredibly important fish commercially, recreationally, cuturally to humans. They are also fascinating scientifically. Two of the most widely discussed topics in salmon ecology and evolution include the behavioural and physiological aspects of homing and the use of salmonids to study mechanisms of speciation. We'll discuss the latter during the lectures on ecological speciation.

(iii) Paracanthopterygii

The paracanthops (and acanthopterygians) are usually separated from all previous groups by the possession of: (i) ctenoid scales and (ii) an ascending process on the premaxillary bone. The paracanthops themselves are rather poorly defined as a group, but consist of a number of well defined lineages.

These fishes are largely specialists in benthic, marine environments; only about 20 of the 1200 species in total are found in freshwaters.

The Percopsiformes are the "troutperches" (Percopsidae) and the "cavefishes" (Amblyopsidae). As the name implies, the troutperch exhibit a curious blend of ancestral (e.g adipose fin) and derived (e.g., fin spines) teleost features. Most live in eastern North America, but there are two species in western North America. The troutperch, Percopsis omiscomaycus, is native to B.C. in the northeastern portion of the province where it dispersed from the Mississippi-Missouri glacial refugium likely heavily influenced by the extent and lifespan of Lake Aggasiz. By contrast, the Columbia troutperch is much more limited in distribution; it is found only in Columbia/Snake river basins of Washington, Oregon, and Idaho.

Cavefishes are another relatively small family of freshwater fishes rendemic to eastern North America. They are typically small (< 20 cm) with no scales, eyes, or skin pigmentation. These traits are considered as highly specialized adaptations for life in caves. Many are endangered, such as the Ozark cavefish (see below).

The Ozark cavefish (Amblyopsis rosae). Note the lack of pigmentation and reduced eyes.

The Batrachoidiformes are the toadfishes. They consist of a single family of benthic, nearshore marine fishes. They show "typical" adaptations to such a benthic mode of life (eyes on dorsal surface of head, dorso-ventrally flattened, large "upturned" mouths). Most are restricted to North, Central, and South America and many can produced sounds through muscular contraction of muscles around the swimbladder (click HERE for more on "singing" toadfish). A well known local species is the plainfin midshipman (Porichthys notatus) well recognized by the 600-800 lateral photophores which are usually found in ore deepwater fish. Other sound-making (soniferous) fishes can be explored HERE.

The Lophiformes are the frogfishes, goosefishes and relatives (all often called anglerfishes).

They are a fairly diverse group (almost 300 species) that again, show specializations for a benthic existence. They rely heavily on camouflage as a prey capture technique and possess the illicium ("fishing rod") and esca ("lure") as modified dorsal spines to lure prey to near their mouths. They have reduced gill openings and pelvic and pectoral fins that are highly modfied. Some great pics can be seen by clicking HERE. As well as their unusual appearence, a particular group of deep sea anglerfishes display sexual parasitism. Males are typically much smaller than females and when they encounter one another (pretty rare in the deep sea??), the male attaches itself to the urogenital area of the female and becomes parasitically dependent on her for nutrition. The internal organs of the male degenerate except for the testes.

The Gadiformes are the cods, hakes, grenadiers, pollocks, and related fishes. They are clearly one of the most important commercial species. If in doubt, read "Cod: a biography of the fish that changed the world" by Mark Kurlansky (Penquin Books). A great read about the rise (and fall) of the east coast Atlantic cod (Gadus morhua) fishery. More info on the one take on the history and biology of the cod fishery collapse can be viewed by clicking HERE.

These fish are typically recognized by the presence of chin barbels and an elongate dorsal fin that may be subdivided into 2-3 dorsal fins. They are marine fish usually of the benthic or epibenthic habitats in mid- to deep-water areas (about 480 species) with a single exception, the lingcod (or just "ling"), Lota lota,

which is found throughout the Holarctic in freshwaters. Unfortunately, the lingcod has also been subject to overexploitation throughout most of its range.

(iv) The Acanthopterygii

This is the final major group of fish (the "spiny-rayed" teleosts) that we will discuss in our survey. The acanthops consist of the majority of all fishes, about 250 families and 13,500 species. They are incredibly diverse morphologically, behaviourally, and in terms of life style. For example, recall from our trip to Bamfield, that 24/29 (83%) of the species that we caught (using trawl and seines) were acanthopterygians. We can't hope to cover all the major families so, I will simply outline the two major sublineages and develop some trend in acanthopterygian evolution.

The group consists of two major superorders: the Atherinomorpha and the Percomorpha. Both groups possess the highest development of advanced teleost traits that we have been discussing (jaw protrusion, pharyngeal jaw development, ctenoid scales, fin placement, spines in the fins, etc).

The Atherinomorpha (silversides) are a relatively small group (about 1300 species) of freshwater, estuarine, and marine fishes that show many specializations as predominantly surface-dwelling fishes (upturned mouths, eyes located near the top of the head, fins placed far back on the body or modified as "wings"). This morphological specialization for surface dwelling can be seen in the outlines of the various families shown below.

These fish include the guppies (Poecilidae, well known to aquarists), flying fish (Exocoetidae), needlefishes (Belonidae), and various cyprinodontiform fishes (guppies, killifishes, pupfishes). They alkso display a bizzare degree of behavioural and life history variation. Some guppies are unisexual, that is there are "all female" species that reproduced either by hybridogenesis (genetic material from a male of a related species is integrated and expressed in the offspring, but the paternal genome is discarded during gametogenesis) or gynogenesis (male sperm is needed only to initiate embryogenesis and is NOT incorporated or expressed in the offspring). Others (the rivulins) may be hermaphroditic, and many (especially the Poecilidae) are livebearers.

Of course, the Exocoetidae (flyingfishes) are some of the most bizzare, using heterocercal caudal fins and elongate pectoral fins to glide through the air to (some suspect) escape predators. The cyprinodontids include the pupfishes (Cyprinodon) which consist of about 20 or so desert-adapted fishes endemic to the southwest United States.

They inhabit some of the most extreme environments for fish, e.g. temperatures ranging from near zero to 44 C and salinities from freshwater to 3-4X that of seawater (140 ppt)!! In addition, the Devil's Hole pupfish (Cyprinodon diabolis) is known from a single spring basin (18 sq m) that is thought to be the smallest distribution of any vertebrate.

The Percomorphs: this is the single largest superorder of fishes with about 12,000 species and 240 families. The are represented in all major aquatic habitats, but tend to dominate the nearshore, benthic marine environment. Notwithstanding such diversity, there are a set of characters that appear to be integral to their success:

(1) pelvic fins in thoracic or jugular position

(2) pectoral fins, when present, high up on lateral portion of body wall

(3) fin spines present

(4) highly protusible pre-maxilla

(5) upper and lower sets of pharyngeal jaws

(6) ctenoid scales

(7) large eyes

(8) swim bladder either absent or, if present, with no direct connection to the esophagous (known as the "physoclistic" condition (contrasted with a direct connection = "physostomous" condition)

(9) the widespread tendency to NOT display the characters listed above! Usually, this stems from the secondary loss of these features as specialized adaptations to particular life styles (see below for examples).

Below is a "classic" percomorph, one of the rockfishes, genus Sebastes, which are abundant members of the marine fish fauna of the North Pacific (less abundant in the Atlantic) where they constitute a "species flock" of about 100 species (see Johns and Avise, 1998).

These features probably contributed to the evolutionary success (at least in terms of diversity) by percomorphs by making them so good at dealing with ecological and evolutionary problems in:

(1) Predator avoidence: the presense of spines where probably a major innovation that reeuced the need for heavy armour and consequently increased mobility of percomorphs - so important in the complex habitats (intertidal areas, coral reefs) that they tend to dominate. Spines as a defense mechanism probably also facilitated morphological changes that could focus on feeding specializations rather than escape from predators. For instance, many of the body form specializations of percomorphs come at a cost of reduced swimming speed and highlight maneuverability.

(2) Feeding specialization: clearly extensive jaw protrusion and the development of pharyngeal jaws increased the "degrees of freedom" of feeding parts in these fishes. This, as we'll see in the next lecture, opened up a whole new world of feeding opportunities/ecological niches which probably directly promoted lineage diversification.

(3) Behaviour: Percomorphs display some of the most remarkable diversity in behaviour and life history. I'll discuss some specific examples below, but the diversity of behaviour/life history was likely an important factor that increased the number of ecological "roles" that these fishes could play and, hence, promoted lineage diversity.

All this is well and good, but despite these apparent commonalities, what is truly impressive about the percomorphs is their apparent "willingness" to abandon particular traits or features (e.g. spines, fins, swim bladders) as specializations to particular niches. This "flexability" undoubtably also promoted diversification within the group.

For example, the following three figures illustrate some of the tremendous morphological diversity in percomorphs - many are vastly different from the Sebastes above.

First, body form of some "classic" percomorph families

Now for something(s) completely different: In particular, note the various flatfish (left column), and puffers (Tetraodontidae), boxfish (Ostraciidae - name remind you of anything???), and ocean sunfishes (Molidae) right column)

Finally, some more curious shapes: Note the lack of all paired fins in the Synbranchidae (swamp "eels", second from bottom right) and the tubular-shaped mouths in most of the gasterostiform fishes in the left column. The leafy sea dragon ( a relative of seahorses) takes the cake for bizzare morphology.

Composition of the Percomorpha:

There are 10 orders and 240 families in the percomorphs. Less than 10% of these families are completely freshwater fish, most are marine or anadromous. I'll just introduce you to some of the more notable orders ones to illustrate the range of variation.

The single largest order is the Perciformes with about 9200 species. The order includes the gobies (Gobiidae) which constitute the single largest family of marine fish (and includes the smallest-sized fishes maturing at less than 10 mm!). These fishes are usually characterized by having the pelvic fins "united" which they use to "perch" on the substrate or, in some species, as a suctoral disc. Gotta' be one of the neatest fish: the mudskippers - a group of gobies that live OUT of water most of the time. They have developed many adaptations to a semi-terrestrial existence. If you click HERE, you'll see that many are very enthusiastic about mudskippers!

The Scombridae are the mackerals and tunas which represent, in many ways, the opposite extreme to gobies. These fish are often very large (> 500 kg in the bluefin tuna) and are built for speed.

They have lunate caudal fins, streamlined bodies, small finlets posterior to the dorsal and anal fins (to reduce drag?), and efficient "counter-current" heat exchangers to facilitate endothermy (up to 15 C above ambient) which increase the efficiency of muscle contraction.

Three of the most notable freshwater familes include the Percidae (perches), Centrarchidae (sunfishes) and the Cichlidae (cichlids). The percids are largely of North American distribution (150/160 species), all east of the Rocky Mountains. The perches include the walleye (Stizostedion vitreum), of great importance as a sport and commercial fish and the yellow perch (Perca flavescens). The darters are the most abundant (145 species) and are small, often colourful, benthic fishes that dominate the streams of the eastern USA and southern Canada.

The Johnny darter (Etheostoma nigrum)

Thge gilt darter (Percina evides)

The sunfishes are the dominant predators in most lakes in eastern North America and include the large- and smallmouth basses, sunfishes, and rock bass. The basses are also very important sport fish and display well known "nesting" behaviour in shallow waters on lakeshores in the spring.

Finally, we have the cichlids. These fishes have fascinated aquarists and evolutionary biologists for decades owing to their often bright colours, interesting behaviour (e.g., mouthbrooding), penchant for morphological specialization to different diets (see figure below), and the presence of "species flocks" of several hundred species that are endemic to several of the Great Rift Lakes of central Africa. How so many species could evolve apparently within single lake basins over, in some cases, short time periods (<15,000 years) have made cichlids the focus of much current research in speciation.

Some of the morphological differences among Lake Malawi cichlids and their feeding modes.

The other major orders in terms of diversity are the Scorpaeniformes (rockfishes, greenlings, sculpins, poachers and related fishes) with about 1300 species, the Pleuronectiformes (flatfishes, soles) with about 500 species, and the Tetraodonitiformes (puffers, boxfishes, triggerfishes, ocean sunfishes) with about 350 species, some of them pretty bizzare. In particular, the flatfish and tetraodontiforms are good examples of the "abandonment" of the "typical" higher teleost body plan to reflect specialization to particular habitats. The flatfish start out as larvae as bilateraaly symmetric and pelagic, but metamorphose such that one of the eyes migrates to the opposite side and the fish settles to a benthic existence resting on its "blind" side. A truly bizzare way that teleosts have exploited a benthic existence.

The Tetraodontiformes represent, in many ways, the apex of teleost evolution. They are highly specialized morphologically, including fusion or loss of many bones in the head, fusion of the hyomandibular to broad areas of the skull and of the maxillary to the premaxillary bone (hence reducing flexability) which may reflect the rather specialized feeding habits of many of the species (e.g., hard corals, sea urchins, jellyfish). As another example of bizzare deviations from the general trends in teleosts, many of the puffers and boxfishes have re-invented the concept of body armour. The ostraciid boxfishes, for instance, have the entire body encased in a bony box. Only the fins protrude and remain flexible allowing precise movements around coral reefs (leading to a specialized, caudal fin-based swimming mode - Ostraciform swimming - where undulatory propulsive waves are passed aong the fin margin).

Yellow Boxfish (Ostracion cubicus). They have even designed a new car after the boxfish which, apparently, is sleeker than it looks!

Finally, the ocean sunfishes (Molidae) represent some bizzare specializations. They lack a true tail, instead having a "pseudocaudal" tail made up mostly of modified dorsal and anal rays! Much of their skeleton in the skull and fins is cartilaginous. They can exceed 1000-kg (see pic) and are open water, jellyfish-feeding specialists.

Therein lies a likely secret of teleost success - the most "advanced" group of fishes have "re-invented" traits (cartilaginous skeletal features) found in the most "primative" groups (e.g., lampreys, sharks, chondrostean "bony" fishes)! A good example of why "primative" and "advanced" are tricky terms when dealing with fish!

This survey of the major groups of fishes may leave you a bit bewildered by the massive amount of diversity. As an aid to dealing with such diversity, and as we now look at some key mechanisms that probably promoted its evolution, perhaps the words of French philosopher Rene Descartes (1596 - 1650) are soothing:

References:

Avise,JC,Trexler,JC,Travis,J,Nelson,WS,1991. Poecilia mexicana is the recent female parent of the unisexual fish P. formosa. Evolution,45,1530,1533.

Greenwood, PH, Rosen, DE, Weitzman, SH, and Myers, GS. 1966. Phyletic classification of teleostean fishes, with a provisional classification of living forms. Bull. Amer. Mus. Nat. Hist. 131:339-456.

Johns,GC,Avise,JC,1998. Tests for ancient species flocks based on molecular phylogenetic appraisals of Sebastes rockfishes and other marine fishes. Evolution,52,1135,1146.

Rosen,DE,1982. Teleostean interrelationships, morphological function and evolutionary inference. Amer. Zool.,22,261,273.

Rosen,DE,1985.An essay on euteleostean classification. American Museum Novitates,Number 2827,1,57.

Vrijenhoek,RC,1994
Unisexual fish: model systems for studying ecology and evolution. Ann. Rev. Ecol. Syst.,25,71,96.