LONG-TERM CHANGES IN PARASITES OF SOCKEYE-SALMON (ONCORHYNCHUS-NERKA)SMOLTS

Parasites were examined in 41 annual samples of sockeye salmon (Oncorh ynchus nerka) juveniles originating from lakes in British Columbia: Ch ilko and Shuswap. Nine species of parasitic helminths and two species of parasitic Crustacea were recovered from various organs. The number of species ranged from three to nine per year. Most (94%) parasites be longed to three tapeworm species, identified as core to the parasite c ommunity because they also infected the most hosts. Two of these cesto de species are probably maintained by resident freshwater hosts in the lakes. Positive numerical associations were observed between four par asite species pairs. Parasite communities in both lakes were composed of similar species, with the exception of three rare Chilko Lake speci es that were never recovered from Shuswap Lake. Parasites were often a s variable within stock (temporally) as between stocks (geographically ), except for the prevalence of Eubothrium sp. and Neoechinorhynchus s p. and mean annual intensity of Proteocephalus sp. and encysted digene tic metacercariae, which were greater at Chilko Lake than at Shuswap L ake. Discrimination between the two lakes based on their parasite comm unity is possible only in extreme cases of infection and thus is of li mited use to fisheries officers attempting to distinguish between thes e stocks.