Toshifumi OYAMADA
Takashi YOSHIKAWA
Department of Veterinary Pthology, School of Medicine and Animal Sciences, Kitasato University, Towada-shi, Aomori 034, Japan.

Haruo KAMIYA
Department of Parasitology, Hirosaki University School of Medicine, Hirosaki-shi, Aomori 036, Jpan.

Abstract
From July 1992 to September 1995, to clarify the exact source of human gnathostomiasis nipponica occurred in northern part of Honshu, a total of 1427 freshwater fishes consisting two species was caught in an endemic area of Gnathostoma nipponicum in Aomori Prefecture, and was examined for this larvae. Eight of 291 (2.75%) Onchorhynchus masou (Salmonidae) and 2 of 1136 (0.18%) Tribolodon hakonensis (Cyprinidae) were infected with gnathostome larvae, 12 larvae were recovered from 10 fishes. Taxonomically, all the larvae were identified as the advanced third-stage larvae of G. nipponicum. From these results, it would seem that Salmonidae and Cyprinidae freshwater fishes, including P. masou and T. hakonensis, may be important as the source of human gnathostomiasis nipponica in conjunction with custom of eating raw fresh fishes among the inhabitants at northern Honshu. In addition, it also confirmed newly that two freshwater fish species, which could serve as the second intermediate and/or paratenic hosts of this nematode in nature. This is the first record of naturally-infected O. masou and T. hakonensis with G. nipponicum larvae in Japan.