The infection of Eurasian perch Perca fluviatilis L. with Triaenophorus nodulosus (Pallas) plerocercoids in lake Constance (Germany)

Eurasian porch (Perca fluviatilis L.) were sampled in 1997/98 at six sites in Lake Constance (Germany) and examined for Triaenophorus nodulosus pleroc ercoid infestation. Prevalence was low in age-0 perch (8.7%), while more th an 80% of perch from age classes 1 and older were infected. Intensity of in fection ranged from 1 to 3 in age class 0, while older perch harboured up t o 15 plerocercoids in their livers. Liver weight (plerocercoid cysts includ ed) could only be used in age-0 fish to quantify pathological effects, but severe lesions of liver tissue were always observed in infected fish. A pre valence of more than 80% is the highest value ever recorded in Lake Constan ce, but the reasons for this recent increase remain unknown.