Abstract
Between January and April 2000, the cyprinid fishes Zacco platypus and Squalidus chankaensis in Uji River, Kyoto Prefecture showed inactive swimming and hemorrhages on the fins, skin and eyes. No bacterial or viral agents seemed involved in the disease outbreak; however, numerous metacercariae of unidentified trematodes of the family Bucephalidae were found encysted in the fins, skin, musculature and eyes of diseased fish, suggesting these parasitic infections were the etiological agents. The metacercariae comprised two species, designated here as Metacercaria A and Metacercaria B. It is assumed that the infection started with an accidental introduction of infected first intermediate hosts, the freshwater mussel, Limnoperna fortunei, into Uji River, and that Z. platypus and S. chankaensis served as the second intermediate hosts, and the sheatfish Silurus biwaensis as the final host to complete their life cycles. This is the first case of bucephalid infections of freshwater fishes in Japan. The Yodo River system, including Uji River, is the only area in Japan where the bucephalid infections have so far been confirmed. Comments are made on the possible danger of translocation of even a single infected first, second or final host from Uji River to Lake Biwa or other water systems.
