Atypical furunculosis in spotted wolffish (Anarhichas minor O.) juveniles: bath vaccination and challenge

Farmed spotted wolffish (Anarhichas minor O.) is susceptible to infections with atypical Aeromonas salmonicida, and experimental oil-adjuvanted vaccines are previously reported to induce protection against the disease. For prophylactic treatment of juveniles, an immersion vaccine is the preferred alternative, and to test the efficacy of different bath vaccination strategies, a waterborne challenge model has to be established. Exposing the wolffish juveniles to 2×107–108 live bacteria ml−1 for 60–90 min resulted in 70–85% mortality. Bath vaccinating wolffish juveniles (∼25 mm) for 1 h in a bacterin containing 108 inactivated cells ml−1 did not induce specific antibody responses although the bacterial antigens were localised in the muscle, kidney and liver tissues. No protection was established in the bath vaccinated fish after waterborne challenge, nor did a second immersion boost improve the efficacy. For comparison, fish were i.p. vaccinated with an oil-emulsified bacterin and significant protection against the pathogen was induced both after injection and bath challenge. The protection was significantly higher when both the vaccine and the pathogen were administered by injection as compared to i.p. vaccination and challenge by bath.