Glochidiosis of salmonid fishes. I. Comparative susceptibility to experimental infection with Margaritifera margaritifera (L.) (Pelecypoda: Margaritanidae).

This is the first report on the susceptibility of salmonid fishes to infection with the glochidia of the freshwater mussel Margaritifera margaritifera using known numbers of parasites under controlled conditions. The relative susceptibility of six species of salmonid fish, 20 to 80 mm in total length, to glochidiosis was determined by exposing fish individually to different numbers of parasites and plotting mortalities against these exposure levels at 70 days postexposure and also against the numbers of parasites recovered from fish 48 hr postinfection. The 70-day interpolated LE50 values (exposure concentrations of glochidia that killed 50% of the fish) for kokanee salmon (Oncorhynchus nerka kennerlyi), cutthroat trout (Salmo clarki), Atlantic salmon (S. salar), steelhead trout (S. gairdneri) and coho salmon (O. kisutch) were 17,500, 29,000, 35,000, 57,000, and 105,000, respectively. Chinook salmon (O. tshawytscha) was the most susceptible species. The LE50 values could not be estimated even at the lowest exposure levels because mortalities were too high. On the basis of the LE50 value, coho salmon was the most resistant species.