PARASITE COMMUNITIES IN 2 SYMPATRIC MORPHS OF ARCTIC CHARR, SALVELINUS-ALPINUS (L.), IN NORTHERN NORWAY

In this study from Fjellfrosvatn, an oligotrophic lake in northern Nor way, the parasite communities in two sympatric Arctic charr population s were compared. The dwarf morph, which inhabits the profundal zone, e xhibited the lowest parasite diversity, seven species, and 72% of thes e charr harboured only one or two parasite species. In contrast, 10 pa rasite species were encountered in the larger normal charr, and betwee n 5 and 8 species were present in 73% of these fish, which also utilis ed a broader food and habitat niche. Proteocephalus sp. was by far the most abundant species in the dwarf charr, probably because this morph fed intensively upon the benthic copepod Acanthocyclops gigas. On the other hand, parasites that are transmitted with littoral benthic prey (i.e., Phyllodistomum umblae, Cyathocephalus truncatus, Cystidicola f arionis, and Crepidostomum spp.) were almost absent in the dwarf charr , though they were common in the normal morph. Also, Diphyllobothrium spp. were more prevalent in the normal charr, and this was attributed to their feeding upon limnetic copepods in the pelagic zone. The only recorded parasite with a direct life cycle, the copepod Salmincola edw ardsii, had relatively similar abundances in the two morphs. The consi derable differences in parasite community structure and abundance betw een the two charr populations were closely related to differences in t he width and composition of the habitat and food niches between the mo rphs.