White Spot Disease broke out among youngs (total length: 8-10 cm) of the European eel Anguilla anguilla in May 1970. The fishes had been reared in newly constructed ponds near Lake Hamana, Shizuoka Prefecture.
In diseased fishes, covered with numerous white spots all over the body surface, the parasites Ichthyophthirius multifilis were also found situated in the gills and in the wall of the oral cavity.
According to histological observations, swellings, and necrobiosis, were recognized in the cutis at the site of infection. In the gills, the parasites located under the respiratory epithorium in which augmentation was not observable, while, in the oral cavity, the epitherium augmented as in the skin.
Although Ichthyophiriasis, with a heavy mortarity, was once observed among youngs of the Japanese eel Anguilla japonica reared in a pond at the Hamanako Branch, Shizuoka Pref. Fish. Expt. Stn. in April 1969, it is a generally accepted fact that the Japanese eel has a low sensitivity to this parasite.
