The Effect of Depuration on Transmission ofAeromonas salmonicidabetween the Freshwater BivalveAmblema plicataand Arctic Char

A model system was used to study bacterial fish pathogen transmission between the freshwater bivalve Amblema plicata and two strains (Nauyuk and Labrador) of Arctic char Salvelinus alpinus. Aeromonas salmonicida, the cause of fish furunculosis, was readily transmitted from Arctic char to A. plicata and vice versa via simple cohabitation. Clinical furunculosis was artificially established in Nauyuk Arctic char via horizontal exposure to Labrador Arctic char that received intraperitoneal injections of A. salmonicida. After the Nauyuk Arctic char began to die, A. plicata were placed in the tank with the fish. After 33 d of cohabitation, a group of 10 A. plicata was cultured, and A. salmonicida was isolated from all 10. The remaining A. plicata were transferred to other tanks being supplied with specific-pathogen-free water. At 1, 5, 15, and 30 d after transfer, 60 uninfected Labrador Arctic char were cohabitated with the A. plicata. Transmission of A. salmonicida from A. plicata to the Arctic char was evaluated via fish mortality and bacterial culture after 3–4 weeks of exposure. Mortality to A. salmonicida occurred in groups exposed to A. plicata after 1 and 5 d of depuration but not in groups exposed after 15 and 30 d. The bacterium was not isolated from either the A. plicata or the Arctic char in the 15- and 30-d groups. Results indicate that the current minimum 30-d quarantine of freshwater bivalves destined for relocation to prevent spread of zebra mussels Dreissena polymorpha is sufficient to allow depuration of a fish pathogen and, thus, to prevent the spread of disease.