Bacterial pathogen contagion studies among freshwater bivalves and salmonid fishes

A part of the conservation efforts of native freshwater bivalves is a reloc ation program whereby animals are collected and moved to a safe refuge for maintenance and propagation. With the rearing of two different hosts, musse ls and fish, on the same facility there is a question of the possibility fo r contagion of pathogens. The studies presented here are part of a continui ng effort to address the concerns of contagion. Freshwater bivalves collect ed throughout the 1997 season were cultured for fish pathogens. Counts of t otal bacteria on cytophaga medium ranged between 1.07 x 10(5) and 4.99 x 10 (5) cfu/g of mussel soft tissues. The predominate groups of bacteria were m otile Aeromonas spp. and Pseudomonas spp., both of which include members th at are opportunistic pathogens to salmonid fishes. No primary fish pathogen s were cultured; however, cells with correct morphology for Renibacterium s almoninarum, cause of bacterial kidney disease, were detected from mussel s oft tissues in all six trials using the direct fluorescent antibody test. G roups of mussels were subjected to 24-h waterborne challenges using bacteri a cultured from healthy fish. no mortality occurred to any of the animals. Another group exposed to the fish pathogen Aeromonas salmonicida also showe d no effects of the challenge; however, susceptible fish became infected an d died after the fish were added to cohabit with this group of mussels.