Catch of Coho Salmon (Oncorhynchus kisutch) Infected with the Freshwater Parasite Salvelinema walkeri (Nematoda: Cystidicolidae) in the Gulf of Alaska in the Early Winter

Abstract

The cystidicolid nematode Salvelinema walkeri (Ekbaum, 1935) is a swim bladder parasite of freshwater salmonids in western North America, ranging from northern California to southern British Columbia. This parasite was found from two age-2.0, juvenile coho salmon Oncorhynchus kisutch (Walbaum, 1792) caught in the southern central Gulf of Alaska in December 1992. This represents the first record of S. walkeri from salmonids caught in offshore waters of the North Pacific Ocean. The two coho salmon harbored as many as 1053 and 278 nematodes, respectively, but there was no significant difference in the condition factor between infected and uninfected fish. The recovered nematodes are highly likely to have been alive in the host swim bladder when the fish were caught because their bodies were in good condition. Based on the observations in this and other papers, S. walkeri is inferred to survive throughout marine residence of salmonids after these fish are infected in streams and enter the sea. While the usefulness of S. walkeri as a stock discrimination tool is less than that of current methods employed for a similar purpose, the potential use of this freshwater parasite as a biological tag is also discussed for studying the ecology of ocean-migrating salmonids.