Prevalence of Renibacterium salmoninarumamong DownstreamMigrating Salmonids in the Columbia River

Bacterial kidney disease (BKD) is an important contributor to mortality of salmonids in hatcheries in the Columbia River basin. However, the impact of BKD on the survival of downstream migrants is difficult to determine because there is little information on the disease-related mortality among these fish. In this study, the impact of BKD on juvenile salmonids was examined by determining the percentage of downriver migrants infected with Renibacterium salmoninarum(the causative agent of BKD) and evaluating the effects of salt water on the progress of the disease. During the 2 years of this study, approximately 20% of the three species of migrating hatchery and wild salmonids (Oncorhynchusspp.) collected were infected with R. salmoninarum. Mortality caused by BKD increased when fish were held in salt water.