Immersion vaccination of sockeye salmon (Oncorhynchus nerka) with two pathogenic strains of Vibrio anguillarum

Sockeye salmon (Oncorhynchus nerka) were immersion-vaccinated in suspensions containing 5 × 10⁷, 5 × 10⁶, 5 × 10⁵, or 5 × 10⁴ bacteria/mL of bivalent or monovalent, formalin-killedVibrio anguillarum, Types I and II. The fish were split into two lots and held for 54 d. At that time one lot was challenged with living, virulent V. anguillarum, Type I, and one with living, virulent V.anguillarum, Type II. Immunization with bivalent bacterin effectively protected the fish from vibriosis, but monovalent vaccine was effective only against the homologous challenge. Immunization with the highest concentration of Type I monovalent bacterin resulted in 0% Type I and 58% Type II challenge mortality. Immunization with the highest concentration of Type II monovalent bacterin resulted in 41% Type I and 0% Type II challenge mortality. Immunization with the highest concentration of bivalent Type I/Type II bacterin resulted in 2% mortality in both challenges. Protective bacterins were effective at concentrations down to 5 × 10⁵ bacteria/mL.Key words: immersion vaccination, bivalent vaccines, Vibrio anguillarum, vibriosis.