Infection by the cestodes Triaenophorus crassus and Diphyllobothrium spp. in a polymorphic whitefish population

Abstract

The whitefish (Coregonus lavaretus s.l.), stock in Lake Femunden, Norway, includes three morphs: D-, R-and S-whitefish. Infections by Diphyllobothrium spp. and Triaenophorus crassus in the morphs were monitored during 1988-2005. In all three morphs T. crassus prevalence increased significantly, but at a varying rate, with age. In juvenile fish, prevalence was lowest in D-whitefish and highest in Swhitefish. As the rate of increase was lower in R-and S-whitefish than in D-whitefish, prevalence was more equal in older fish. The relative differences in parasite load of T. crassus among the three whitefish morphs appear mainly to be in line with the morph differences in habitat use, and associated with the habitat use of the final host of the parasite (pike, Esox lucius).Almost all individuals of D-, R-and S-whitefish were infected by Diphyllobothrium spp., with prevalence higher than 75% from age 2. In all three whitefish morphs, mean abundance of Diphyllobothrium spp. increased with the age of the fish, with the most rapid increase in young age groups. The development of infection with age was almost identical in S-and D-whitefish, whereas Rwhitefish was at a higher level from an early age. The high prevalence of Diphyllobothrium spp in all three whitefish morphs probably reflects the distribution of parasite eggs over all lake habitats by the avian final hosts. The differences in the mean abundance of Diphyllobothrium spp. with age, with a heavier parasite load in R-whitefish than the nearly identical levels in D-and S-whitefish, is not easily explained by differences in habitat use or diet among the whitefish morphs.