Abstract
Descriptions are given of two new species of Gyrodactylus collected from the body surface of eel, Anguilla japonica, in greenhouse ponds at Yoshida, Shizuoka Pref. G. egusai sp. nov. differs from most simuilar G. varicorhini ERGENS et IBRAGIMOV, 1976 in considerably smaller hamuli and marginal hook proper. G. joi sp. nov. is distinguished from most related G. anudarini ERGENS et DULMAA, 1968 in the shape of the marginal hook proper.
Long term changes in the occurrence of Gyrodactylus nipponensis on the gill fillaments and G. egusai and G. joi on the body surface were studied during 1980-1985. Gyrodactylus on the body surface was more frequently found than G. nipponensis throughout the study period. Gyrodactylids on both sites were less frequently observed in 1983-1985 than in 1980-1982, and also in summer than in the other seasons. Possible reasons for the seasonal and yearly fluctuations in Gyrodactylus populations are briefly discussed.
