Immunization of Brook Trout (Salvelinus fontinalis) against Aeromonas salmonicida: Immunogenicity of Virulent and Avirulent Isolates and Protective Ability of Different Antigens

Brook trout (Salvelinus fontinalis) passively immunized with antisera from rainbow trout (Salmo gairdneri) prepared against virulent or avirulent cultures of Aeromonas salmonicida were equally protected from challenges with concentrated suspensions (10 9 cells/mL) of A. salmonicida. Brook trout immunized with washed or unwashed formalin-killed virulent cells of A. salmonicida had mean humoral agglutinating antibody titers of 14 (washed cells) and 205 (unwashed cells) after 21 d. However, fish so immunized were not protected when exposed to a virulent challenge. Trout inoculated with crude extracellular material extracted from culture supernatants had a mean agglutinin titer of 122, and fish so immunized were resistant to challenge.