Fig. 242.—The Aspron, Aspro asper (Linnæus). Rhone River. Family Percidæ. (After Seelye.)
The pike-perch, or zander, of central Europe, Centropomus (or Sandrus) lucioperca, is an excellent game-fish, similar to the sauger, but larger, characterized technically by having the ventral fins closer together. Another species, Centropomus volgensis, in Russia, looks more like a perch than the other species do. Sandroserrus, a fossil pike-perch, occurs in the Pliocene. Another European fish related to the perch is the river ruff, or pope, Acerina cernua, which is a small fish with the form of a perch and with conspicuous mucous cavities in the skull. It is common throughout the north of Europe and especially abundant at the confluence of rivers. Gymnocephalus schrætzer of the Danube has the head still more cavernous. Percarina demidoffi of southern Russia is another dainty little fish of the general type of the perch. A fossil genus of this type called Smerdis is numerously represented in the Miocene and later rocks. The aspron, Aspro asper, is a species like a darter found lying on the bottoms of swift rivers, especially the Rhone. The body is elongate, with the paired fins highly developed. Zingel zingel is found in the Danube, as is also a third species called Aspro streber. In form and coloration these species greatly resemble the American darters, and the genus Zingel is, perhaps, the ancestor of the entire group. Zingel differs from Percina mainly in having seven instead of six branchiostegals and the pseudobranchiæ better developed. The differences in these and other regards which distinguish the darters are features of degradation, and they are also no doubt of relatively recent acquisition. To this fact we may ascribe the difficulty in finding good generic characters within the group. Sharply defined genera occur where the intervening types are lost. The darter is one of the very latest products in the evolution of fishes.
Fig. 243.—The Zingel, Zingel zingel (Linnæus). Danube River. (After Seelye.)
The Darters: Etheostominæ.—Of the darters, or etheostomine perches, over fifty species are known, all confined to the streams of the region bounded by Quebec, Assiniboia, Colorado, and Nuevo Leon. All are small fishes and some of them minute, and some are the most brilliantly colored of all fresh-water fishes of any region, the most ornate belonging to the large genus called Etheostoma. The largest species, the most primitive because most like the perch, belong to the genus Percina.
First among the darters because largest in size, most perch-like in structure, and least degenerate, we place the king darter, Percina rex of the Roanoke River in Virginia. This species reaches a length of six inches, is handsomely colored, and looks like a young wall-eye.
Fig. 244.—Log-perch, Percina caprodes (Rafinesque). Licking Co., Ohio.
The log-perch, Percina caprodes, is near to this, but a little smaller, with the body surrounded by black rings alternately large and small. In this widely distributed species, large enough to take the hook, the air-bladder is present although small. In the smaller species it vanishes by degrees, and in proportion as in their habits they cling to the bottom of the stream. The air-bladder is least developed in those species which cling closest to the bottom of the stream.
