INFECTIONS OF DIPHYLLOBOTHRIUM-DENDRITICUM, DIPHYLLOBOTHRIUM-DITREMUM(CESTODA), AND CYSTIDICOLA-FARIONIS (NEMATODA) IN A NORTH NORWEGIAN POPULATION OF ARCTIC CHARR (SALVELINUS-ALPINUS) DURING WINTER

Infections of the parasites Diphyllobothrium dendriticum, Diphylloboth rium ditremum, and Cystidicola farionis in Arctic charr (Salvelinus al pinus) from Takvatn, northern Norway, were followed throughout a 9-mon th overwintering period. The relative density of all three parasite sp ecies increased with the age of the host in response to ontogenetic sh ifts in habitat and food of Arctic charr in the lake. Our results indi cate that some recruitment of the three parasite species, particularly D. ditremum, takes place during the winter. However, winter parasite recruitment was lower than in the ice-free season. In spite of high pa rasite infection in some individuals, no strong indications of parasit e-induced host winter mortality were found for any of the three specie s. Low overwintering mortality of heavily parasitized charr may be con nected with a stock-reduction program in the lake that has improved th e conditions of the fish, and the residual stock is probably less affe cted by parasites.