Seasonality of Clinostomum complanatum Cercariae in the Snail Host Radix auricularia japonica and Drug Treatment of the Parasite in Goldfish Carassius auratus

― Clear peaks of trematode Clinostomum complanatum cercariae detection rate in snails Radix auricularia japonica were observed around July in a goldfish Carassius auratus farm in Aichi Prefecture. Effects of Trichlorfon and praziquantel were examined against C. complanatum in artificially infected goldfish. Both were effective in the early phase of infection in goldfish cohabitating with infected snails. Trichlorfon was effective in a 300 mg/t bath treatment for 13 d and praziquantel was effective with 3 d of oral administration at 138 mg/kg body weight. Tratements with trichlorfon or praziquantel around July may reduce infection of C. complanatum without serious damage to fish caused by the excystation induced by the drug treatment in ornamental fish farms.