Infection of whitefish (Coregonus lavaretus L. s.l.) by Triaenophorus crassus Forel (Cestoda: Pseudophyllidea): a case study in parasite control

A case study of Triaenophorus crassus control in two sympatric whitefish populations was carried out in Stuorajavri, northern Norway. The densities of whitefish and pike were markedly reduced by an intensive fishing programme and during the 6 years of investigation, a dramatic decline in T. crassus infection of whitefish was observed. The mechanisms involved in parasite control were elucidated by studying the differences in infestation over time between T. crassus and a related cestode, Diphyllobothrium ditremum, in the two whitefish populations. Reduction in population density of the final host, pike, is suggested as being the key factor in control of T. crassus. Exploitation and reduction of whitefish population density contributed to decreased infection in one of the whitefish populations by influencing its acquisition of parasites via a change in its food selection.