Monitoring Fish Parasitic Cercaria in the Yodo River Using Experimental Fishes

Cercarial contamination (being suspected as a gasterostome trematode, Bucephalidae: Digenea) in the Yodo River was studied by the water monitoring using experimental fishes. The fishes including Pseudorasbora parva and Squalidus chankaensis subsp. were exposed in the river and the cercariae that penetrated tail fin of the fishes were observed with a stereoscopic microscope. The monitoring was carried out three times from December 2000 to January 2001 in the Yodo River. Over 80% of the fishes were infected by the cercariae (average numbers of metacercariae in an infected fish ranged from 5.2 to 18.1) during 4 to 10 days of the exposure. The numbers of cercariae in the river water were estimated to be 0.12 to 1.72·m-3.