Immersion and injection vaccination of salmonids against furunculosis with an avirulent strain of Aeromonas salmonicida

Replicate groups of brook trout (Salvelinus fontinalis) immunized by intraperitoneal injection of graded dilutions of an avirulent strain of Aeromonas salmonicida were protected from a virulent challenge. Mean mortality after challenge was 88% in control trout, 66% in trout immunized with 3 × 10⁶ or 3 × 10⁵ cells, and 39% in trout immunized with 3 × 10⁴ to 3 × 10¹ cells. In brook trout challenged after immersion for 60 s in a culture containing 2.3 × 10⁹ avirulent cells of A. salmonicida per milliliter, mortality was 44%, compared with 94% in controls. In Atlantic salmon (Salmo salar), similarly vaccinated by immersion, mortality was 12.5% after challenge compared with 87.5% in controls. In additional studies, mean mortality of Atlantic salmon vaccinated by immersion was 14%, whereas that of control salmon was 92%.