A Guide to the Study of Fishes, Volume 1 (of 2)

by David Starr Jordan

Allied to the Scorpænidæ, but confined to the tropical or semi-tropical seas, are the Platycephalidæ, with 27 vertebræ, and the Cephalacanthidæ (flying gurnards), with but 22. In the deeper waters of the tropics are the Peristediidæ, with 33 vertebræ, and extending farther north, belonging as much to the temperate as to the torrid zone, is the large family of the Triglidæ (gurnards) in which the vertebræ range from 25 to 38.

The family of Agonidæ (sea-poachers), with 36 to 40 vertebræ, is still more decidedly northern in its distribution. Wholly confined to northern waters is the great family of the Cottidæ (sculpins), in which the vertebræ ascend from 30 to 50. Entirely polar and often in deep waters are the Liparididæ (sea-snails), an offshoot from the Cottidæ, with soft, limp bodies, and the vertebræ 35 to 65. In these northern forms there are no scales, the spines in the fins have practically disappeared, and only the anatomy shows that they belong to the group of spiny-rayed fishes. In the Cyclopteridæ (lumpfishes), likewise largely arctic, the body becomes short and thick, the back-bone inflexible, and the vertebræ are again reduced to 28. In most cases, as the number of vertebræ increases, the body becomes proportionally elongate. As a result of this, the fishes of arctic waters are, for the most part, long and slender, and not a few of them approach the form of eels. In the tropics, however, while elongate fishes are common enough, most of them (always excepting the eels) have the normal number of vertebræ, the greater length being due to the elongation of their individual vertebræ and not to their increase in number. Thus the very slender goby, Gobionellus oceanicus, has the same number (25) of vertebræ as its thick-set relative Gobius soporator or the chubby Lophogobius cyprinoides. In the great group of blenny-like fishes the facts are equally striking. The arctic species are very slender in form as compared with the tropical blennies, and this fact, caused by a great increase in the number of their vertebræ, has led to the separation of the group into several families. The tropical forms composing the family of Blenniidæ have from 28 to 49 vertebræ, while in the arctic genera the numbers range from 75 to 100.

Of the true Blennidæ, which are all tropical or semi-tropical, Blennius has 28 to 35 vertebræ; Salarias, 35 to 38; Lepisoma, 34; Clinus, 49; Cristiceps, 40. A fresh-water species of Cristiceps found in Australia has 46. Blennioid fishes in the arctic seas are Anarrhichas, with 76 vertebræ; Anarrhichthys, with 100 or more; Lumpenus, 79; Pholis, 85; Lycodes, 112; Gymnelis, 93. Lycodes and Gymnelis have lost all the dorsal spines.

In the cod family (Gadidæ) the number of vertebræ is usually about 50. The number is 51 in the codfish (Gadus callarias), 58 in the Siberian cod (Eleginus navaga), 54 in the haddock (Melanogrammus æglifinus), 54 in the whiting (Merlangus merlangus), 54 in the coalfish (Pollachius virens), 52 in the Alaskan coalfish (Theragra chalcogramma), 51 in the hake (Merluccius merluccius). In the burbot (Lota lota), the only fresh-water codfish, 59; in the deep-water ling (Molva molva), 64; in the rocklings (Gaidropsarus), 47 to 49. Those few species found in the Mediterranean and the Gulf of Mexico have fewer fin-rays and probably fewer vertebræ than the others, but none of the family enter warm water, the southern species living at greater depths.

In the deep-sea allies of the codfishes, the grenadiers or rat-tails (Macrouridæ), the numbers range from 65 to 80.

Fresh-water Fishes.—Of the families confined strictly to the fresh waters the great majority are among the soft-rayed or physostomous fishes, the allies of the salmon, pike, carp, and catfish. In all of these the vertebræ are numerous. A few fresh-water families have their affinities entirely with the more specialized forms of the tropical seas. Of these the Centrarchidæ (comprising the American fresh-water sunfish and black bass) have on the average about 30 vertebræ, the pirate perch 29, and the Percidæ, perch and darters, etc., 35 to 45, while the Serranidæ or sea-bass, the nearest marine relatives of all these, have constantly 24. The marine family of damsel-fishes (Pomacentridæ) have 26 vertebræ, while 30 to 40 vertebræ usually exist in their fresh-water analogues (or possibly descendants), the Cichlidæ, of the rivers of South America and Africa. The sticklebacks (Gasterosteidæ), a family of spiny fishes, confined to the rivers and seas of the north, have from 31 to 41 vertebræ.

Pelagic Fishes.—Among the free-swimming or migratory pelagic fishes, the number of vertebræ is usually greater than among their relatives of local habits. This fact is most evident among the scombriform fishes, the allies of the mackerel and tunny. All of these belong properly to the warm seas, and the reduction of the vertebræ in certain forms has no evident relation to the temperature, though it seems to be related in some degree to the habits of the species. Perhaps the retention of many segments is connected with that strength and swiftness in the water for which the mackerels are preeminent.

The variations in the number of vertebræ in this group led Dr. Günther to divide it into two families, the Carangidæ and Scombridæ.

The Carangidæ or Pampanos are tropical shore fishes, local or migratory to a slight degree. All these have from 24 to 26 vertebræ. In their pelagic relatives, the dolphins (Coryphæna), there are from 30 to 33; in the opah (Lampris), 45; in Brama, 42; while the great mackerel family (Scombridæ), all of whose members are more or less pelagic, have from 31 to 50.

The mackerel (Scomber scombrus) has 31 vertebræ; the chub mackerel (Scomber japonicus), 31; the tunny (Thunnus thynnus), 39; the long-finned albacore (Germo alalonga), 40; the bonito (Sarda sarda), 50; the Spanish mackerel (Scomberomorus maculatus), 45.