Latitudinal variations in the occurrence of some cod parasites along the west coast of Norway

Latitudinal variations in the occurrence of four parasite species infecting cod along the west coast of Norway are described, based on data collected at four sampling locations from Øksfjord (Finnmark) in the north to Ålesund (Møre og Romsdal) in the south. The parasites are: the congeneric adult digeneans Hemiurus communis and H. levinseni, metacercariae of the digenean Prosorhynchoides borealis and plerocercoids of the cestode Diphyllobothrium phocarum. The reasons for the latitudinal variations are explained and discussed in terms of the life cycles and endemic areas of the parasites, and we suggest how they may be used as biological tags in population studies of cod and other gadoid fish in Norwegian waters.