Renibacterium salmoninarum in spring-summer chinook salmon smolts at dams on the Columbia and Snake Rivers.
R. salmoninarum infection was evaluated in smolts of hatchery and wild spring-summer chinook salmon (Oncorhynchus tshawytscha) sampled during most of the out-migration at Little Goose (1988) and Lower Granite dams (1988-1991) on the Snake River and at Priest Rapids and McNary dams on the Columbia River (1988-1990) in the Pacific Northwest USA. 860-2178 fish per dam were sampled each year. Homogenates of kidney-spleen tissue from all fish were tested for the presence of R. salmoninarum antigens by ELISA, and homogenates from 10% of the fish were examined by the fluorescent antibody technique (FAT). Although only 1-11% of fish sampled at a given dam during any 1 year exhibited lesions characteristic of bacterial kidney disease, 86-100% of the fish tested positive for R. salmoninarum antigen by ELISA, whereas 4-17% of the fish tested positive by the FAT. During most years, the majority (68-87%) of fish testing positive by the ELISA had low R. salmoninarum antigen levels, but in 1989, 53% of positive fish from Lower Granite Dam and 52% from McNary Dam showed medium-to-high antigen levels. For most years, the highest mean antigen levels were measured in fish sampled after 75% of the total out-migrants had passed a given dam. When the largest numbers of fish were being collected for bypass or downriver transportation, mean antigen levels were relatively low.