Effect of Renibacterium salmoninarum levels in the ovarian fluid of spawning chinook salmon on the prevalence of the pathogen in their eggs and progeny.
Chinook salmon, Oncorhynchus tshawytscha, eggs were exposed to ovarian fluid inoculated with various concentrations of Renibacterium salmoninarum (Rs). None of the eggs exposed to 1.7 × 103 or fewer Rs cells ml-1 of ovarian fluid proved to be infected intra-ovum. However, intra-ovum infections occurred in eggs exposed to Rs cells at concentrations of 1.7 × 105 or higher ml-1. Smolts from eggs exposed to Rs cells at concentrations of 1.7 × 103 and higher were Rs-infected. As with eggs, the highest prevalence of infection in smolts occurred in those from eggs exposed to the highest concentration of Rs tested. In addition, smolts from eggs that were not deliberately exposed to Rs, but which were obtained from ovarian fluid naturally infected with as few as 28 to 113 Rs cells ml-1, were also infected. The implications of these findings are discussed.