CHAPTER VIII

SERIES OSTARIOPHYSI

=OSTARIOPHYSI.=—A large group of orders, certainly of common descent, may be brought together under the general name of _Ostariophysi_ (ὀσταρίον, a small bone; θυσός, inflated). These are in many ways allied to the _Isospondyli_, but they have undergone great changes of structure, some of the species being highly specialized, others variously degenerate. A chief character is shared by all the species. The anterior vertebræ are enlarged, interlocked, considerably modified, and through them a series of small bones connect the air-bladder with the ear. The air-bladder thus becomes apparently an organ of hearing through a form of connection which is lost in all the higher fishes.

In all the members of this group excepting perhaps the degraded eel-like forms called _Gymnonoti_, the mesocoracoid arch persists, a trait found in all the living types of Ganoids, as well as in the _Teleost_ order of _Isospondyli_. Other traits of the Ostariophysan fishes are shared by the _Isospondyli_ (herring, salmon) and other soft-rayed fishes. The air-bladder is large, but not cellular. It leads through life by an open duct to the œsophagus. The ventral fins are abdominal in position. The pectorals are inserted low. A mesocoracoid arch is developed on the inner side of the shoulder-girdle. (See Fig. 119.) There are no spines on the fins, except in many cases a single one, a modified soft ray at front of dorsal or pectoral. The scales, if present, are cycloid or replaced by bony plates.

Many of the species have an armature much like that of the sturgeon, but here the resemblance ends, the bony plates in the two cases being without doubt independently evolved. According to Cope, the affinities of the catfishes to the sturgeon are "seen in the absence of symplectic, the rudimentary maxillary bone, and, as observed by Parker, in the interclavicles. There is also a superficial resemblance in the dermal bones." But it is not likely that any real affinity exists.

The sturgeons lack the characteristic auditory ossicles, or "Weberian apparatus," which the catfishes possess in common with the carp family, the _Characins_, and the _Gymnonoti_. These orders must at least have a common origin, although this origin is obscure, and fossil remains give little help to the solution of the problem. Probably the ancestors of the _Ostariophysi_ are to be found among the allies of the _Osteoglossidæ_. Gill has called attention to the resemblance of _Erythrinus_ to _Amia_. In any event, all the _Ostariophysi_ must be considered together, as it is not conceivable that so complex a structure as the Weberian apparatus should have been more than once independently evolved. The branchiostegals, numerous among the _Isospondyli_, are mostly few among the _Ostariophysi_.

To the _Ostariophysi_ belong the vast majority of the fresh-water fishes of the world. Their primitive structure is shown in many ways; among others by the large number of vertebræ instead of the usual twenty-four among the more highly specialized families of fishes. We may group the _Ostariophysi_ under four orders: _Heterognathi_, _Eventognathi_ (_Plectospondyli_), _Nematognathi_, and _Gymnonoti_.

=The Heterognathi.=—Of these the order of _Heterognathi_ seems to be the most primitive, but in some ways the most highly developed, showing fewer traits of degeneration than any of the others. The presence of the adipose fin in this group and in the catfishes seems to indicate some sort of real affinity with the salmon-like forms, although there has been great change in other regards.

The order _Heterognathi_, or _Characini_ (ἕτερος, different; γνάθος, jaw), contains those _Ostariophysi_ which retain the mesocoracoid and are not eel-like, and which have the lower pharyngeals developed as in ordinary fishes. In most cases an adipose fin is present and there are strong teeth in the jaws. There are no pseudobranchiæ, and, as in the _Cyprinidæ_, usually but three branchiostegals. The _Characidæ_ constitute the majority of the fresh-water fishes in those regions which have neither _Cyprinidæ_ nor _Salmonidæ_. Nearly four hundred species are known from the rivers of South America and Africa. A single species, _Tetragonopterus argentatus_, extends its range northward to the Rio Grande in Texas. None are found in Asia, Europe, or, with this single exception, in the United States. Most of them are small fishes with deep bodies and very sharp, serrated, incisor-like teeth. Some are as innocuous as minnows, which they very much resemble, but others are extremely voracious and destructive in the highest degree. Of the caribe, belonging to the genus _Serrasalmo_, known by its serrated belly, Dr. Günther observes:

"Their voracity, fearlessness and number render them a perfect pest in many rivers of tropical America. In all the teeth are strong, short, sharp, sometimes lobed incisors, arranged in one or more series; by means of them they cut off a mouthful of flesh as with a pair of scissors; and any animal falling into the water where these fish abound is immediately attacked and cut to pieces in an incredibly short time. They assail persons entering the water, inflicting dangerous wounds before the victims are able to make their escape. In some localities it is scarcely possible to catch fishes with the hook and line, as the fish hooked is immediately attacked by the 'caribe' (as these fish are called), and torn to pieces before it can be withdrawn from the water. The caribes themselves are rarely hooked, as they snap the hook or cut the line. The smell of blood is said to attract at once thousands of these fishes to the spot."

Two families of _Heterognathi_ are recognized: the _Erythrinidæ_, which lack the adipose fin, and the _Characidæ_, in which this fin is developed. The _Erythrinidæ_ are large pike-like fishes of the South American rivers, robust and tenacious of life, with large mouths armed with strong unequal teeth. The best-known species is the _Trahira_ (_Hoplias malabaricus_).

Among the _Characidæ_, _Serrasalmo_ has been already noticed. _Citharinus_ in Africa has very few teeth, and _Curimatus_ in South America none at all. _Nannocharax_ in Africa is composed of very diminutive fishes, _Hydrocyon_ exceedingly voracious ones, reaching a length of four feet, with savage teeth. Many of the species are allies of _Tetragonopterus_, small, silvery, bream-like fishes with flat bodies and serrated incisor teeth. Most of these are American. A related genus is _Brycon_, found in the streams about the Isthmus of Panama.

Extinct _Characins_ are very rare. Two species from the Tertiary lignite of São Paulo, Brazil, have been referred to _Tetragonopterus_—_T. avus_ and _T. ligniticus_.

=The Eventognathi.=—The _Eventognathi_ (ἔυ, well; ἔν, within; γνάθος, jaw) are characterized by the absence of teeth in the jaws and by the high degree of specialization of the lower pharyngeals, which are scythe-shaped and in typical forms are armed with a relatively small number of highly specialized teeth of peculiar shape and arranged in one, two, or three rows. In all the species the gill-openings are restricted to the sides; there is no adipose fin, and the broad, flat branchiostegals are but three in number. In all the species the scales, if present, are cycloid, and the ventral fins, of course, abdominal. The modification of the four anterior vertebræ and their connection with the air bladder are essentially as seen in the catfishes.

The name _Plectospondyli_ is often used for this group (πλεκτός, interwoven; σπόνδυλος, vertebra), but that term originally included the _Characins_ as well.

=The Cyprinidæ.=—The chief family of the _Eventognathi_ and the largest of all the families of fishes is that of _Cyprinidæ_, comprising 200 genera and over 2000 species, found throughout the north temperate zone but not extending to the Arctic Circle on the north, nor much beyond the Tropic of Cancer on the south. In this family belong all the fishes known as carp, dace, chub, roach, bleak, minnow, bream, and shiner. The essential character of the family lies in the presence of one, two, or three rows of highly specialized teeth on the lower pharyngeals, the main row containing 4, 5, 6, or 7 teeth, the others 1 to 3. The teeth of the main row differ in form according to the food of the fish. They may be coarse and blunt, molar-like in those which feed on shells; they may be hooked at tip in those which eat smaller fishes; they may be serrated or not; they may have an excavated "grinding surface," which is most developed in the species which feed on mud and have long intestines. In the _Cyprinidæ_, or carp family, the barbels are small or wanting, the head is naked, the caudal fin forked, the mouth is toothless and without sucking lips, and the premaxillaries form its entire margin. With a few exceptions the _Cyprinidæ_ are small and feeble fishes. They form most of the food of the predatory river fishes, and their great abundance in competition with these is due to their fecundity and their insignificance. They spawn profusely and find everywhere an abundance of food. Often they check the increase of predatory fish by the destruction of their eggs.

In many of the genera the breeding color of the males is very brilliant, rendering these little creatures for a time the most beautifully colored of fishes. In spring and early summer the fins, sides, and head in the males are often charged with pigment, the prevailing color of which is rosy, though often satin-white, orange, crimson, yellow, greenish, or jet black. Among American genera _Chrosomus_, _Notropis_, and _Rhinichthys_ are most highly colored. _Rhodeus_, _Rutilus_, and _Zacco_ in the Old World are also often very brilliant.

In very many species, especially in America, the male in the breeding season is often more or less covered with small, grayish tubercles or pearly bodies, outgrowths of the epidermis. These are most numerous on the head and fall off after the breeding season. They are most developed in _Campostoma_.

The _Cyprinidæ_ are little valued as food-fishes. The carp, largely domesticated in small ponds for food, is coarse and tasteless. Most of the others are flavorless and full of small bones. One species, _Opsariichthys uncirostris_, of Japan is an exception in this regard, being a fish of very delicate flavor.

In America 225 species of _Cyprinidæ_ are known. One hundred of these are now usually held to form the single genus _Notropis_. This includes the smaller and weaker species, from two to seven inches in length, characterized by the loss, mostly through degeneration, of special peculiarities of mouth, fins, and teeth. These have no barbels and never more than four teeth in the main row. Few, if any, Asiatic species have so small a number, and in most of these the maxillary still retains its rudimentary barbel. But one American genus (_Orthodon_) has more than five teeth in the main row and none have more than two rows or more than two teeth in the lower row. By these and other peculiarities it would seem that the American species are at once less primitive and less complex than the Old World forms. There is some evidence that the group is derived from Asia through western America, the Pacific Coast forms being much nearer the Old World types than the forms inhabiting the Mississippi Valley. Not many _Cyprinidæ_ are found in Mexico, none in Cuba, South America, Australia, Africa, or the islands to the eastward of Borneo. Many species are very widely distributed, many others extremely local. In the genus _Notropis_, each river basin in the Southern States has its series of different and mostly highly colored species. The presence of _Notropis niveus_ in the Neuse, _Notropis pyrrhomelas_ in the Santee, _Notropis zonistius_ in the Chattahoochee, _Notropis callistius_, _trichroistius_, and _stigmaturus_ in the Alabama, _Notropis whipplei_ in the Mississippi, _Notropis galacturus_ in the Tennessee, and _Notropis cercostigma_ in the Sabine forms an instructive series in this regard. These fishes and the darters (_Etheostominæ_) are, among American fishes, the groups best suited for the study of local problems in distribution.

=Species of Dace and Shiner.=—Noteworthy species in other genera are the following:

Largest and best known of the species of _Notropis_ is the familiar shiner or redfin, _Notropis cornutus_, found in almost every brook throughout the region east of the Missouri River.

_Campostoma anomalum_, the stone-roller, has the very long intestines six times the length of its body, arranged in fifteen coils around the air-bladder. This species feeds on mud and spawns in little brooks, swarming in early spring throughout the Mississippi Valley, and is notable for its nuptial tubercles and the black and orange fins.

In the negro-chub, _Exoglossum maxillingua_ of the Pennsylvanian district, the rami of the lower jaw are united for their whole length, looking like a projecting tongue.

The fallfish, _Semotilus corporalis_, is the largest chub of the Eastern rivers, 18 inches long, living in swift, clear rivers. It is a soft fish, and according to Thoreau "it tastes like brown paper salted" when it is cooked. Close to this is the horned dace, _Semotilus atromaculatus_, and the horny head, _Hybopsis kentuckiensis_, both among the most widely distributed of our river fishes. These are all allied to the gudgeon (_Gobio gobio_), a common boys' fish of the rivers of Europe, and much sought by anglers who can get nothing better. The bream, _Abramis_, represented by numerous species in Europe, has a deep compressed body and a very long anal fin. It is also well represented in America, the golden shiner, common in Eastern and Southern streams, being _Abramis chrysoleucus_. The bleak of Europe (_Alburnus alburnus_) is a "shiner" close to some of our species of _Notropis_, while the minnow of Europe, _Phoxinus phoxinus_, resembles our gorgeously colored _Chrosomus erythrogaster_. Other European forms are the roach (_Rutilus rutilus_), the chub (_Leuciscus cephalus_), the dace (_Leuciscus leuciscus_), the id (_Idus idus_), the redeye (_Scardinius erythropthalmus_), and the tench (_Tinca tinca_). The tench is the largest of the European species, and its virtues with those of its more or less insignificant allies are set forth in the pages of Izaak Walton. All of these receive more attention from anglers in England than their relatives receive in America. All the American _Cyprinidæ_ are ranked as "boys' fish," and those who seek the trout or black bass or even the perch or crappie will not notice them. Thoreau speaks of the boy who treasures the yellow perch as a real fish: "So many unquestionable fish he counts, then so many chubs which he counts, then throws away."

=Chubs of the Pacific Slope.=—In the Western waters are numerous genera, some of the species reaching a large size. The species of squawfish (_Ptychocheilus lucius_ in the Colorado, _Ptychocheilus grandis_ in the Sacramento, and _Ptychocheilus oregonensis_ in the Columbia) reach a length of 4 or 5 feet or even more. These fishes are long and slender, with large toothless mouths and the aspect of a pike.

Allied to these are the "hard tails" (_Gila elegans_ and _Gila robusta_) of the Colorado Basin, strange-looking fishes scarcely eatable, with lean bodies, flat heads, and expanded tails. The split-tail, _Pogonichthys macrolepidotus_, is found in the Sacramento.

In the chisel-mouth, _Acrocheilus alutaceus_, of the Columbia the lips have a hard cutting edge. In _Meda_, very small fishes of the Colorado Basin, the dorsal has a compound spine of peculiar structure. Many of the species of Western waters belong to the genus _Leuciscus_, which includes also many species of Asia and Europe. The common Japanese dace (_Leuciscus hakuensis_) is often found out in the sea, but, in general, _Cyprinidæ_ are only found in fresh waters. The genus of barbels (_Barbus_) contains many large species in Europe and Asia. In these the barbel is better developed than in most other genera, a character which seems to indicate a primitive organization. _Barbus mosal_ of the mountains of India is said to reach a length of more than six feet and to have "scales as large as the palm of the hand."

=The Carp and Goldfish.=—In the American and European _Cyprinidæ_ the dorsal fin is few-rayed, but in many Asiatic species it is longer, having 15 to 20 rays and is often preceded by a serrated spine like that of a catfish. Of the species with long dorsal the one most celebrated is the carp (_Cyprinus carpio_). This fish is a native of the rivers of China, where it has been domesticated for centuries. Nearly three hundred years ago it was brought to northern Europe, where it has multiplied in domestication and become naturalized in many streams and ponds. Of late years the cultivation of the carp has attracted much attention in America. It has been generally satisfactory where the nature of the fish is understood and where expectations have not been too high.

The carp is a dull and sluggish fish, preferring shaded, tranquil, and weedy waters with muddy bottoms. Its food consists of water insects and other small animals, and vegetable matter, such as the leaves of aquatic plants. They can be fed on much the same things as pigs and chickens, and they bear much the same relation to trout and bass that pigs and chickens do to wild game and game-birds. The carp is a very hardy fish, grows rapidly, and has immense fecundity, 700,000 eggs having been found in the ovaries of a single individual. It reaches sometimes a weight of 30 to 40 pounds. As a food-fish the carp cannot be said to hold a high place. It is tolerated in the absence of better fish.

The carp, either native or in domestication, has many enemies. In America, catfish, sunfish, and pike prey upon its eggs or its young, as well as water-snakes, turtles, kingfishes, crayfishes, and many other creatures which live about our ponds and in sluggish streams. In domestication numerous varieties of carp have been formed, the "leather-carp" (Lederkarpfen) being scaleless, others, "mirror-carp" (Spiegelkarpfen), having rows of large scales only along the lateral line or the bases of the fins.

Closely allied to the carp is the goldfish (_Carassius auratus_). This is also a common Chinese fish introduced in domestication into Europe and America. The golden-yellow color is found only in domesticated specimens, and is retained by artificial selection. The native goldfish is olivaceous in color, and where the species has become naturalized (as in the Potomac River, where it has escaped from fountains in Washington) it reverts to its natural greenish hue. The same change occurs in the rivers of Japan. The goldfish is valued solely for its bright colors as an ornamental fish. It has no beauty of form nor any interesting habits, and many of our native fishes (_Percidæ_, _Cyprinidæ_) far excel it in attractiveness as aquarium fishes. Unfortunately they are less hardy. Many varieties and monstrosities of the goldfish have been produced by domestication.

=The Catostomidæ.=—The suckers, or _Catostomidæ_, are an offshoot from the _Cyprinidæ_, differing chiefly in the structure of the mouth and of the lower pharyngeal bones. The border of the mouth above is formed mesially by the small premaxillaries and laterally by the maxillaries. The teeth of the lower pharyngeals are small and very numerous, arranged in one series like the teeth of a comb. The lips are usually thick and fleshy, and the dorsal fin is more or less elongate (its rays eleven to fifty in number), characters which distinguish the suckers from the American _Cyprinidæ_ generally, but not from those of the Old World.

About sixty species of suckers are known, all of them found in the rivers of North America except two, which have been recorded on rather uncertain authority from Siberia and China. Only two or three of the species extend their range south of the Tropic of Cancer into Mexico or Central America, and none occur in Cuba nor in any of the neighboring islands. The majority of the genera are restricted to the region east of the Rocky Mountains, although species of _Catostomus_, _Chasmistes_, _Deltistes_, _Xyrauchen_, and _Pantosteus_ are found in abundance in the Great Basin and the Pacific slope.

In size the suckers range from six inches in length to about three feet. As food-fishes they are held in low esteem, the flesh of all being flavorless and excessively full of small bones. Most of them are sluggish fishes; they inhabit all sorts of streams, lakes, and ponds, but even when in mountain brooks they gather in the eddies and places of greatest depth and least current. They feed on insects and small aquatic animals, and also on mud, taking in their food by suction. They are not very tenacious of life. Most of the species swarm in the spring in shallow waters. In the spawning season they migrate up smaller streams than those otherwise inhabited by them. The large species move from the large rivers into smaller ones; the small brook species go into smaller brooks. In some cases the males in spring develop black or red pigment on the body or fins, and in many cases tubercles similar to those found in the _Cyprinidæ_ appear on the head, body, and anal and caudal fins.

The buffalo-fishes and carp-suckers, constituting the genera _Ictiobus_ and _Carpiodes_, are the largest of the _Catostomidæ_, and bear a considerable resemblance to the carp. They have the dorsal fin many rayed and the scales large and coarse. They abound in the large rivers and lakes between the Rocky Mountains and the Alleghanies, one species being found in Central America and a species of a closely related genus (_Myxocyprinus asiaticus_) being reported from eastern Asia. They rarely ascend the smaller rivers except for the purpose of spawning. Although so abundant in the Mississippi Valley as to be of importance commercially, they are very inferior as food-fishes, being coarse and bony. The genus _Cycleptu_s contains the black-horse, or Missouri sucker, a peculiar species with a small head, elongate body, and jet-black coloration, which comes up the smaller rivers tributary to the Mississippi and Ohio in large numbers in the spring. Most of the other suckers belong to the genera _Catostomus_ and _Moxostoma_, the latter with the large-toothed _Placopharynx_ being known, from the red color of the fins, as red-horse, the former as sucker. Some of the species are very widely distributed, two of them (_Catostomus commersoni_, _Erimyzon sucetta_) being found in almost every stream east of the Rocky Mountains and _Catostomus catostomus_ throughout Canada to the Arctic Sea. The most peculiar of the suckers in appearance is the harelip sucker (_Quassilabia lacera_) of the Western rivers. Very singular in form is the humpback or razor-back sucker of the Colorado, _Xyrauchen cypho_.

=Fossil Cyprinidæ.=—Fossil _Cyprinidæ_, closely related to existing forms, are found in abundance in fresh-water deposits of the Tertiary, but rarely if ever earlier than the Miocene. _Cyprinus_ _priscus_ occurs in the Miocene of Germany, perhaps showing that Germany was the original home of the so-called "German carp," afterwards actually imported to Germany from China. Some specimens referred to _Barbus_, _Tinca_, _Rhodeus_, _Aspius_, and _Gobio_ are found in regions now inhabited by these genera, and many species are referred to the great genus _Leuciscus_, _Leuciscus œningensis_ from the Miocene of Germany being perhaps the best known. Several species of _Leuciscus_ or related genera are found in the Rocky Mountain region. Among these is the recently described _Leuciscus turneri_.

Fossil _Catostomidæ_ are very few and chiefly referred to the genus _Amyzon_, supposed to be allied to _Erimyzon_, but with a longer dorsal. _Amyzon commune_ and other species are found in the Rocky Mountains, especially in the Miocene of the South Park in Colorado and the Eocene of Wyoming. Two or three species of _Catostomus_, known by their skulls, are found in the Pliocene of Idaho.

=The Loaches.=—The _Cobitidæ_, or loaches, are small fishes, all less than a foot in length, inhabiting streams and ponds of Europe and Asia. In structure they are not very different from minnows, but they are rather eel-like in form, and the numerous long barbels about the mouth strongly suggest affinity with the catfishes. The scales are small, the pharyngeal teeth few, and the air-bladder, as in most small catfishes, enclosed in a capsule. The loaches are all bottom fishes of dark colors, tenacious of life, feeding on insects and worms. The species often bury themselves in mud and sand. They lie quiet on the bottom and move very quickly when disturbed much after the manner of darters and gobies. Species of _Cobitis_ and _Misgurnus_ are widely distributed from England to Japan. _Nemachilus barbatulus_ is the commonest European species. _Cobitis tænia_ is found, almost unchanged, from England to the streams of Japan.

Remains of fossil loaches, mostly indistinguishable from _Cobitis_, occur in the Miocene and more recent rocks.

From ancestors of loaches or other degraded _Cyprinidæ_ we may trace the descent of the catfishes.

The _Homalopteridæ_ are small loaches in the mountain streams of the East Indies. They have no air-bladder and the number of pharyngeal teeth (10 to 16) is greater than in the loaches, carp, or minnows.