Bacterial pathogen contagion studies among freshwater bivalves and salmonid fishes.
A part of the conservation efforts of native freshwater bivalves is a relocation program whereby animals are collected and moved to a safe refuge for maintenance and propagation. With the rearing of two different hosts, mussels and fish, on the same facility there is a question of the possibility for contagion of pathogens. The studies presented here are part of a continuing effort to address the concerns of contagion. Freshwater bivalves collected throughout the 1997 season were cultured for fish pathogens. Counts of total bacteria on cytophaga medium ranged between 1.07 × 105 and 4.99 × 1015 cfu/g of mussel soft tissues. The predominate groups of bacteria were motile Aeromonas spp. and Pseudomonas spp., both of which include members that are opportunistic pathogens to salmonid fishes. No primary fish pathogens were cultured; however, cells with correct morphology for Renibacterium salmoninarum, cause of bacterial kidney disease, were detected from mussel soft tissues in all six trials using the direct fluorescent antibody test. Groups of mussels were subjected to 24-h waterborne challenges using bacteria cultured from healthy fish; no mortality occurred to any of the animals. Another group exposed to the fish pathogen Aeromonas salmonicida also showed no effects of the challenge; however, susceptible fish became infected and died after the fish were added to cohabit with this group of mussels.