256 Isthmus Barriers Separating Fish Faunas 



gion 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 overlap- 

 ping. 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 denned by Fuji 

 Yama and the Bay of Matsushima. It is characterized by the 

 presence of salmon, trout, and sculpins, and northward by stur- 

 geon 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 * and a perch, f 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 dis- 

 tinct, their ancestors must have been estrays from the main- 

 land. 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.J 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 is found in the midway island of Tsushima, between 

 Korea and Japan. 



Faunal Areas of Marine Fishes in Japan. The distribution 

 of the marine fishes of Japan is mainly controlled by the tem- 

 perature of the waters and the motion of the ocean currents. 

 Five faunal areas may be more or less clearly recognized, and 

 these may receive names indicating their scope Kurile, Hok- 

 kaido, Nippon, Kiusiu, Kuro Shiwo, and Riu Kiu. The first or 

 Kurile district is frankly subarctic, containing species charac- 

 teristic of the Ochotsk Sea on the one hand, and of Alaska on 



* Rheopresbe. J Leuciscus hakuensis Gunther. 



t Bryttosus. , Leuciscus jouyi. 



