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.
[Illustration:
FIG. 119.—Inner view of shoulder-girdle of the Buffalo-fish. _Ictiobus
bubalus_ Rafinesque, showing the mesocoracoid (59). (After Starks.)
]
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_.
[Illustration:
FIG. 120.—Weberian apparatus and air-bladder of Carp. (From Günther,
after Weber.)
]
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_).
[Illustration:
FIG. 121.—_Brycon dentex_ Günther. Family _Characidæ_. Nicaragua.
]
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.
[Illustration:
FIG. 122.—Pharyngeal bones and teeth of European Chub, _Leuciscus
cephalus_ (Linnæus). (After Seelye.)
]
=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.
[Illustration:
FIG. 123.—Black-nosed Dace, _Rhinichthys dulcis_ Girard. Yellowstone
River.
]
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.
[Illustration:
FIG. 124.—White Chub, _Notropis hudsonius_ (Clinton). Kilpatrick Lake,
Minn.
]
[Illustration:
FIG. 125.—Silver-jaw Minnow, _Ericymba buccata_ Cope. Defiance, Ohio.
]
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.
[Illustration:
FIG. 126.—Silverfin, _Notropis whipplei_ (Girard). White River,
Indiana. Family _Cyprinidæ_.
]
=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.
[Illustration:
FIG. 127.—Stone-roller, _Campostoma anomalum_ (Rafinesque). Family
_Cyprinidæ_. Showing nuptial tubercles and intestines coiled about
the air-bladder.
]
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.
[Illustration:
FIG. 128.—Head of Day-chub, _Exoglossum maxillingua_ (Le Sueur).
Shenandoah River.
]
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."
[Illustration:
FIG. 129.—Horned Dace, _Semotilus atromaculatus_ (Mitchill). Aux
Plaines River, Ill. Family _Cyprinidæ_.
]
[Illustration:
FIG. 130.—Shiner, _Abramis chrysoleucus_ (Mitchill). Hackensack River,
N. J.
]
[Illustration:
FIG. 131.—The Squawfish, _Ptychocheilus grandis_ Agassiz. (Photograph
by Cloudsley Rutter.)
]
=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.
[Illustration:
FIG. 132.—Chub of the Great Basin, _Leuciscus lineatus_ (Girard).
Heart Lake, Yellowstone Park. Family _Cyprinidæ_.
]
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.
[Illustration:
FIG. 133.—Lower pharyngeal of _Placopharynx duquesnii_ (Le Sueur).
]
=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.
[Illustration:
FIG. 134.—Creekfish or Chub-sucker, _Erimyzon sucetta_ (Lacépède).
Nipisink Lake, Illinois. Family _Catostomidæ_.
]
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.
[Illustration:
FIG. 135.—Buffalo-fish, _Ictiobus cyprinella_ (Cuv. & Val.). Normal,
Ill.
]
[Illustration:
FIG. 136.—Carp-sucker, _Carpiodes cyprinus_ (Le Sueur). Havre de
Grace.
]
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_.
[Illustration:
FIG. 137.—Common Sucker, _Catostomus commersoni_ (Le Sueur). Ecorse,
Mich.
]
[Illustration:
FIG. 138.—California Sucker, _Catostomus occidentalis_ Agassiz.
(Photograph by Cloudsley Rutter.)
]
=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_.
[Illustration:
FIG. 139.—Pharyngeal teeth of Oregon Sucker, _Catostomus
macrocheilus_.
]
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.
[Illustration:
FIG. 140.—Razor-back Sucker, _Xyrauchen cypho_ (Lockington). Green
River, Utah.
]
=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.