Parasites and Diet of Trout-Perch (Percopsis omiscomaycus) from Northwest Territories, Canada, with Comments on the Range of Crepidostomum percopsisi Nelson, Choudhury and Dick 1997

The trout-perch, Percopsis omiscomaycus (Wal- baum), is a widely distributed species in North America. Despite several compound community surveys, the north- ernmost survey of trout-perch parasites is from southern Manitoba, Canada. A total of 42 parasite species have been reported from trout-perch, with 2 species being strictly host specific. During limnological surveys of Sid and Blitzen lakes, Northwest Territories, Canada, 4 parasite taxa were recovered from trout-perch: Protozoan cysts, Diplostomum sp., Proteocephalus sp., and Crepidostomum percopsisi. The present study area is approximately 1,547 km northwest of Dauphin Lake, which is the northernmost documented range for C. percopsisi. These data provide further support for Halvorsen's ''constant fauna'' as a general rule for north temperate fish parasite communities. Comparisons with other trout-perch surveys from more southern portions of the biogeographic range suggest that parasite composition, at least in small, nutrient- and species-poor lakes at northern latitudes have decreased richness, despite trout-perch having a diverse diet compared with more southern surveys. The intermediate host of C. percopsisi is unknown. Other Crepidostomum spp. are transmitted through Ephemerop- tera, which occur in the diet of the trout-perch from Blitzen and Sid lakes. However, the high prevalence of cladocerans in this study, similar to other published reports, might implicate cladocerans as a potential intermediate host for C. percopsisi.