At present about 900 species of fishes are known from the four great islands which constitute Japan proper--Hondo, Hokkaido, Kiusiu, and Shikoku. About 200 others are known from the volcanic islands to the north and south. Of these 1100 species, about fifty belong to the fresh waters. These are all closely allied to forms found on the mainland of Asia, from which region all of them were probably derived. In general the same genera appear in China and with a larger range of species. =Fresh-water Faunas of Japan.=--Two faunal areas of fresh waters may be fairly distinguished, although broadly overlapping. The northern region includes the island of Hokkaido and the middle and northern part of the great island of Hondo. In a rough way, its southern boundary may be defined by Fuji Yama, and the Bay of Matsushima. It is characterized by the presence of salmon, trout, and sculpins, and northward by sturgeon and brook lampreys. The southern area loses by degrees the trout and other northern fishes, while in its clear waters abound various minnows, gobies, and the famous ayu, or Japanese dwarf salmon, one of the most delicate of food fishes. Sculpins and lampreys give place to minnows, loaches, and chubs. Two genera, a sculpin[37] and a perch,[38] besides certain minnows and catfishes, are confined to this region and seem to have originated in it, but, like the other species, from Chinese stock. =Origin of Japanese Fresh-water Fishes.=--The question of the origin of the Japanese river fauna seems very simple. All the types are Asiatic. While most of the Japanese species are distinct, their ancestors must have been estrays from the mainland. To what extent river fishes may be carried from place to place by currents of salt water has never been ascertained. One of the most widely distributed of Japanese river fishes is the large hakone dace or chub.[39] This has been repeatedly taken by us in the sea at a distance from any stream. It would evidently survive a long journey in salt water. An allied species[40] is found in the midway island of Tsushima, between Korea and Japan.