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_.