Gyrodactylus Infestations of Cultured Eels (Anguilla japonica and A.anguilla) in Japan

Abstract

An examination of Gyrodactylus infestations of cultured eels in Japan has revealed that Gyrodactylus nipponensis OGAWA et EGUSA, 1978 was parasitic on the Japanese eel, Anguilla japonica at 19 culture ponds in Chiba, Shizuoka, Tokushima and Miyazaki Prefectures and on the European eel, A. anguilla at 3 ponds in Tokushima Pref., while G. anguillae ERGENS, 1960 was found on A. anguilla at 2 ponds in Shizuoka Pref. There seems no difference in intensity of infestation of G. nipponensis between the two species of eels. The intensity attained to 20, 000 parasites/fish in A. japoinca of 45 cm in body length. The infestation of G. anguillae is the first record in Japan; G. anguillae is redescribed here. It is natural to consider that G. nipponensis was formerly the only gyrodactylid of A. japonica in Japan, since the eel has been found infested with G. nipponensis only. According to our opinion, G. anguillae was introduced with the host fish, A. anguilla from France, while G. nipponensis was, in some cases, parasitic on A. anguilla after the introduction of A. anguilla into Japan. No evidence was obtained that G. anguillae had settled at A. japonica-culturing ponds in Japan. The authors disagree with GOLOVIN (1977) on that G. anguillae was introduced into U.S.S.R. from Japan with the host fish, A. japonica.