THE islands of Japan are remarkable for their richness of animal life. The variety in climatic and other conditions, the nearness to the great continent of Asia and to the chief center of marine life—the East Indian Islands—its relation to the warm Black Current or Kuro Shiwo—the Gulf Stream of the Orient—and to the cold current from Bering Sea, all tend to give variety to the fauna of its seas. Especially numerous and varied are the fishes of Japan.
About nine hundred species of fishes are known, from the four great main islands of Japan, and about two hundred more from the volcanic islands (Kuriles and Liu Kiu) to the north and south. Of the eleven hundred, about fifty are fresh water. All these are derived from the mainland of Asia. Two faunal districts, the north and the south, may be recognized among the fresh-water fishes. The mountain region and the region lying to the north of Fuji abound in trout, with salmon, sturgeon, lamprey and other northern fishes. In the southern district these are absent and the chief fresh-water fishes are ayu, or dwarf salmon, chubs, minnows, cat-fishes and loaches.
The marine fishes are far more varied, their distribution being mainly controlled by temperature and currents. Among these, five districts may be recognized, their range sufficiently indicated by the names, Kurile, Hokkaido, Nippon, Kiusiu, Kuro Shiwo and Liu Kiu. Of these, the Kurile Fauna is subarctic, similar to that of the Aleutian Islands, that of the Liu Kiu islands is tropical, that of the promontories, which strike out into the Kuro Shiwo, is Polynesian. The central region (Nippon) contains the forms essentially Japanese. Kiusiu lias much in common with China, and Hokkaido with Siberia and Manchuria. Each of these districts overlaps, by a broad fringe, on the others.
It has been noted that the fish fauna of Japan bears a striking resemblance to that of the Mediterranean, and Dr. Günther has suggested that this can be accounted for by supposing that in recent times a continuous coast line and sea-passage extended from one region to the other, the Isthmus of Suez not existing.