Incidence of Renibacterium salmoninarum infections in juvenile hatchery spring chinook salmon in the Columbia and Snake Rivers

From 1988 through 1992, we assessed the prevalence (frequency of occurrence) and severity (degree of infection) of Renibacterium salmoninarum (RS) among fish in marked groups of Columbia River basin and Snake River basin hatchery spring chinook salmon Oncorhynchus tshawytscha before release and during their seaward migration. During the study, prevalence of RS infection decreased (from >90% to 90%) than in the hatchery (mean