CHAPTER XXX

OPISTHOMI AND ANACANTHINI

=ORDER Opisthomi.=—The order _Opisthomi_ (ὄπισθη, behind; ὤμος, shoulder) is characterized by the general traits of the blennies and other elongate, spiny-rayed fishes, but the shoulder-girdle, as in the Apodes and the _Heteromi_, is inserted on the vertebral column well behind the skull.

The single family, _Mastacembelidæ_, is composed of eel-shaped fishes with a large mouth and projecting lower jaw, inhabiting the waters of India, Africa, and the East Indies. They are small in size and of no economic importance. The dorsal is long, with free spines in front and there are no ventral fins. Were these fins developed, they should in theory be jugular in position. There is no air-duct in _Mastacembelus_ and it seems to be a true spiny-rayed fish, having no special relation to either _Notacanthus_ or to the eels. Except for the separation of the shoulder-girdle from the skull, there seems to be no reason for separating them far from the Blennioid forms, and the resemblance to _Notacanthus_ seems wholly fallacious.

_Mastacembelus armatus_ is a common species of India and China. In _Rhynchobdella_ the nasal appendage or proboscis, conspicuous in _Mastacembelus_, is still more developed. _Rhynchobdella aculeata_ is common in India.

=Order Anacanthini.=—We may separate from the other jugular fishes the great group of codfishes and their allies, retaining the name Anacanthini (ἄνακανθος, without spine) suggested by Johannes Müller. In this group the hypercoracoid is without foramen, the fenestra lying between this bone and the hypocoracoid below it. The tail is isocercal, the vertebræ in a right line and progressively smaller backward, sometimes degenerate or whip-like (leptocercal) at tip. Other characters are shown in the structure of the skull. There are no spines in any of the fins; the ventrals are jugular, the scales generally small, and the coloration dull or brownish. The numerous species live chiefly in the northern seas, some of them descending to great depths. The resemblance of these fishes to some of the Blennioid group is very strongly marked, but these likenesses seem analogical only and not indicative of true affinity. The codfishes probably represent an early offshoot from the ancestors of the spiny-rayed fishes, and their line of evolution is unknown, possibly from Ganoid types. Among recent fishes there is nothing structurally nearer than the _Nototheniidæ_ and _Brotulidæ_, but the line of descent must branch off much farther back than either of these. For the present, therefore, we may regard the codfishes and their allies (_Anacanthini_) as a distinct order.

=The Codfishes: Gadidæ.=—The chief family is that of the _Gadidæ_, or codfishes. These are characterized by a general resemblance to the common codfish, _Gadus callarias_. This is one of the best known of fishes, found everywhere on the shores of the North Atlantic, and the subject of economic fisheries of the greatest importance. Its flesh is white, flaky, rather tasteless, but takes salt readily, and is peculiarly well adapted for drying. The average size of the codfish is about ten pounds, but Captain Nathaniel Atwood of Provincetown records one with the weight of 160 pounds.

According to Dr. Goode:

"In the western Atlantic the species occurs in the winter in considerable abundance as far south as the mouth of the Chesapeake Bay, latitude 37°, and stragglers have been observed about Ocracoke Inlet. The southern limits of the species may be safely considered to be Cape Hatteras, in latitude 35° 10´. Along the coast of New England, the Middle States, and British North America, and upon all the off-shore banks of this region, cod are found usually in great abundance, during part of the year at least. They have been observed also in the Gulf of Bothnia, latitude 70° to 75°, and in the southeastern part of Baffin's Land to the northward of Cumberland Sound, and it is more than probable that they occur in the waters of the Arctic Sea to the north of the American continent, or away around to Bering Strait."

Dr. Gill says:

"The ocean banks of moderate depths are the favorite resorts of the cod, but it is by no means confined to those localities. The fish, indeed, occasionally enters into fresh, or at least brackish, water. According to Canadian authorities, it is found 'well up the estuary of the St. Lawrence, though how far up is not definitely stated, probably not beyond the limits of brackish water.' Even as far south as the Delaware River it has been known to enter the streams. Dr. C. C. Abbott records that in January, 1876, 'a healthy, strong, active codfish, weighing nearly four pounds, was taken in a draw-net in the Delaware River near Trenton, New Jersey; the stomach of the fish showed that it had been in river-water several days. Many of them had been taken about Philadelphia between 1856 and 1869.'

"The cod ranks among the most voracious of ordinary fishes, and almost everything that is eatable, and some that is not, may find its way into its capacious maw. Years ago, before naturalists had the facilities that the dredge now affords, cods' stomachs were the favorite resort for rare shells, and some species had never been obtained otherwise than through such a medium, while many filled the cabinet that would not otherwise have been represented. In the words of Mr. Goode, 'codfish swallow bivalve fish of the largest size, like the great sea-clams, which are a favorite article of food on certain portions of the coast'; further, 'these shells are nested, the smaller inside of the larger, sometimes six or seven in a set, having been packed together in this compact manner in the stomachs of the codfish after the soft parts have been digested out. Some of them had shreds of the muscles remaining in them and were quite fresh, having evidently been but recently ejected by the fish.' Even banks of dead shells have been found in various regions, which are supposed to be the remains of mollusks taken by the cod. Shell-fishes, however, form probably but the smaller portion of its diet, and fishes of its own class contribute materially to its food,— such as the herring family, the capelin, etc.

"The codfish in its mode of reproduction exhibits some interesting peculiarities. It does not come on the coast to spawn, as was once supposed, but its eggs are deposited in mid-sea and float to the surface, although it does really, in many cases, approach the land to do so. Prof. C. O. Sars, who has discovered its peculiarities, 'found cod at a distance of twenty to thirty Norwegian miles from the shore and at a depth of from one hundred to one hundred and fifty fathoms.' The eggs thus confided to the mercy of the waves are very numerous; as many as 9,100,000 have been calculated in a seventy-five-pound fish. 'When the eggs are first seen in the fish they are so small as to be hardly distinguishable; but they continue to increase in size until maturity, and after impregnation have a diameter depending upon the size of the parent, varying from one-nineteenth to one-seventeenth of an inch. A five- to eight-pound fish has eggs of the smaller size, while a twenty-five-pound one has them between an eighteenth and a seventeenth.' There are about 190,000 eggs of the smaller size to a pound avoirdupois. They are matured and ejected from September to November."

Unlike most fishes, the cod spawns in cooling water, a trait also found in the salmon family.

The liver of the cod yields an easily digested oil of great value in the medical treatment of diseases causing emaciation.

The Alaska cod, _Gadus macrocephalus_, is equally abundant with the Atlantic species, from which it differs very slightly, the air-bladder or sounds being smaller, according to the fishermen, and the head being somewhat larger. This species is found from Cape Flattery to Hakodate in Japan, and is very abundant about the Aleutian Islands and especially in the Okhotsk Sea. With equal markets it would be as important commercially as the Atlantic cod. In the codfish (_Gadus_) and related genera there are three dorsal and two anal fins. In the codfish the lateral line is pale and the lower jaw shorter than the upper.

The haddock (_Melanogrammus æglifinus_) closely resembles the cod and is of similar quality as food. It is known at sight by the black lateral line. It is found on both shores of the Atlantic and when smoked is the "finnan haddie" of commerce.

The pollack, coalfish, or green cod (_Pollachius carbonarius_) is also common on both shores of the north Atlantic. It is darker than the cod and more lustrous, and the lower jaw is longer, with a smaller barbel at tip. It is especially excellent when fresh.

The whiting (_Merlangus merlangus_) is a pollack-like fish common on the British coasts, but not reaching the American shores. It is found in large schools in sandy bays. The Alaska pollack (_Theragra chalcogramma_) is a large fish with projecting lower jaw, widely diffused in the north Pacific and useful as a food-fish to the Aleutian peoples. It furnishes a large part of the food of the fur-seal (_Callorhinus alascanus_ and _C. ursinus_) during its migrations. The fur-seal rarely catches the true codfish, which swims near the bottom. The wall-eyed pollack (_Theragra fucensis_) is found about Puget Sound. Smaller codfishes of this type are the wachna cod (_Eleginus navaga_) of Siberia and the Arctic codling (_Boreogadus saida_), both common about Kamchatka, the latter crossing to Greenland.

Several dwarf codfishes having, like the true cod, three dorsal fins and a barbel at the chin are also recorded. Among these are the tomcod, or frostfish, of the Atlantic (_Microgadus tomcod_), the California tomcod (_Microgadus proximus_), and _Micromesistius poutassou_ of the Mediterranean. These little cods are valued as pan fishes, but the flesh is soft and without much flavor.

Other cod-like fishes have but two dorsals and one anal fin. Many of these occur in deep water. Among those living near shore, and therefore having economic value, we may mention a few of the more prominent. The codlings (_Urophycis_) are represented by numerous species on both shores of the Atlantic. _Urophycis blennoides_ is common in the Mediterranean. _Urophycis regius_, on our South Atlantic coast, is said to exhibit electric powers in life, a statement that needs verification. In the Gulf of Mexico _Urophycis floridanus_ is common. Farther north are the more important species _Urophycis tenuis_, called the white hake, and _Urophycis chuss_, the squirrel-hake. The ling (_Molva molva_) is found in deep water about the North Sea.

A related genus, _Lota_, the burbot, called also ling and, in America, the lawyer, is found in fresh waters. This genus contains the only fresh-water members of the group of _Anacanthini_.

The European burbot, _Lota lota_, is common in the streams and lakes of northern Europe and Siberia. It is a bottom fish, coarse in flesh and rather tasteless, eaten sometimes when boiled and soaked in vinegar or made into salad. It is dark olive in color, thickly marbled with blackish.

The American burbot, or lawyer (_Lota maculosa_), is very much like the European species. It is found from New England throughout the Great Lakes to the Yukon. It reaches a length of usually two or three feet and is little valued as food in the United States, but rises much in esteem farther north. The liver and roe are said to be delicious. In Siberia its skin is used instead of glass for windows. In Alaska, according to Dr. Dall, it reaches a length of six feet and a weight of sixty pounds.

The rocklings (_Gaidropsarus_ and _Enchelyopus_) have the first dorsal composed of a band of fringes preceded by a single ray. The species are small and slender, abounding chiefly in the Mediterranean and the North Atlantic. The young have been called "mackerel-midges." Our commonest species is _Enchelyopus cimbrius_, found also in Great Britain.

The cusk, or torsk, _Brosme brosme_, has a single dorsal fin only. It is a large fish found on both shores of the North Atlantic, but rather rare on our coasts.

Fossil codfishes are not numerous. Fragments thought to belong to this family are found in English Eocene rocks.

_Nemopteryx troscheli_, from the Oligocene of Glarus, has three dorsal fins and a lunate caudal fin. Other forms have been referred with more or less doubt to _Gadus_, _Brosmius_, _Strinsia_, and _Melanogrammus_.

Gill separates the "three-forked hake" (_Raniceps trifurcus_) of northern Europe as a distinct family, _Ranicipitidæ_. In this species the head is very large, broad and depressed, differing in this regard from the codlings and hakes, which have also two dorsal fins. The deep-water genus, _Bathyonus_, is also regarded as a distinct family, _Bathyonidæ_.

=The Hakes: Merluciidæ.=—Better defined than these families is the family of hakes, _Merluciidæ_. These pike-like codfishes have the skull peculiarly formed, the frontal bones being paired, excavated above, with diverging crests continuous forward from the forked occipital crest. The species are large fishes, very voracious, without barbels, with the skeleton papery and the flesh generally soft. The various species are all very much alike, large, ill-favored fishes with strong teeth and a ragged appearance, the flesh of fair quality. _Merluccius merluccius_, the hake or stock-fish, is common in Europe; _Merluccius bilinearis_, the silver hake, is common in New England, _Merluccius productus_ in California, and _Merluccius gayi_ in Chile.

=The Grenadiers: Macrouridæ.=—The large family of grenadiers, or rat-tails, _Macrouridæ_, is confined entirely to the oceanic depths, especially of the north Atlantic and Pacific. The head is formed much as in the codfishes, with usually a barbel at the chin. There are two dorsals, the second like the anal being low, but the leptocercal tail is very long and tapering, ending in a filament without caudal fin. The scales are usually rough and spinous. The species are usually large in size, and dull gray or black in color.

The best-known genus is _Macrourus_. _Macrourus berglax_ is found on both shores of the north Atlantic. _Macrourus bairdi_ is abundant in off-shore dredgings from Cape Cod to Cuba. _Macrourus cinereus_, the pop-eye grenadier, outnumbers all other fishes in the depths of Bering Sea. _Cœlorhynchus japonicus_ is often taken by fishermen in Japan. _Coryphænoides rupestris_ is common in the north Atlantic. _Bogoslovius clarki_ and _Albatrossia pectoralis_ were dredged by the _Albatross_ about the volcanic island of Bogoslof. _Trachyrhynchus trachyrhynchus_ is characteristic of the Mediterranean. _Nematonurus goodei_ is common in the Gulf Stream, and _Dolloa longifilis_ is found off Japan. Other prominent genera are _Bathygadus_, _Gadomus_, _Regania_, and _Steindachnerella_.

The _Murænolepidæ_ are deep-sea fishes, with minute eel-like scales, and no caudal fin. The ventrals are five-rayed and there are 10 pterygials.