a1 Department of Aquatic Ecology, University of Amsterdam, Kruislaan 320,1098 SM Amsterdam, Netherlands
The natural infection of tench by Asymphylodora tincae in a lake was studied during one summer season. The incidence of infection was 57%, the mean intensity about 50. The distribution of the digencans along the host's intestine showed a maximum in the second half; this could be modified by the presence of other helminth species. Tench caught in early spring and kept in the laboratory retained their natural infection throughout the summer. Starvation of hosts during two months caused disappearance of the infection. Experiments showed that metaecrcariae, introduced into the intestine of tench, can excyst within one hour. In vitro, cysts in contact with tench bile opened within 15 seconds. Bile of several other cyprinid fisli species caused excystment within 60 seconds. Asymphylodora eggs appeared in tench faeces 7 to 10 days after infection. Progenetic specimens of A. tincae probably disintegrate in the intestine of the tench and their eggs arc passed out with the faeces.
(Accepted February 04 1981)