Benefits of Hatchery Management of BKD Using ELISA-Based Culling

Idaho Department of Fish and Game (IDFG) has managed Renibacterium salmoninarum, the causative agent of bacterial kidney disease (BKD), in hatchery Chinook salmon Oncorhynchus tshawytscha since1969. We have successfully controlled clinical BKD by utilizing the following management strategy since 1993:  (1) intra-peritoneal injection of erythromycin to returning adult salmon; (2) iodophor disinfection of eggs during water hardening; (3) culling the eggs of females with ELISA optical densities greater than 0.25, to reduce the risk of vertical transmission; (4) application of two prophylactic feedings of erythromycin; (5) and when necessary, high BKD segregation groups are released separately from the low/negative BKD rearing groups.   The following benefits in hatchery Chinook have realized: (1) reducing pre-spawning mortality due to BKD (2) reducing mortality from ponding to release in juveniles; (3) improving smolt to adult survival; (4) and increasing the percent of adult females with optical densities less than 0.25. This strategy has reduced the risk of vertical and subsequent horizontal transmission of BKD in all Chinook hatcheries operated by IDFG.  We recommend this management strategy for hatchery reared Chinook salmon.