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.
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.
FIG. 124.—White Chub, _Notropis hudsonius_ (Clinton). Kilpatrick Lake, Minn. ]
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.