Abstract
The lethal toxicity and immunogenicity of salmolysin purified from the culture supernatant of Aeromonas salmonicida were investigated. Median lethal doses of salmolysin to juvenile white-spotted char, Salvelinus leucomaenis by intramuscular or intraperitoneal injection were estimated as 196 and more than 556 μg/kg body weight, respectively. The toxin was detoxified by either heating at 100°C for 10 min, or incubated at 37°C for a week with 0.4% formalin. No lethalities were found when the treated salmolysins were injected intramuscularly into juvenile white-spotted char. Antigenicity of each detoxified toxin was detected by immunodiffusion analysis as these formed a precipitating line against rabbit anti-salmolysin serum. Immunogenicity of heated, formalinized or native salmolysin to adult white-spotted char were found. Agglutinating antibody titers of the fishes immunized with the detoxified or native toxin were about 16 to 64 at three to five weeks after. These results suggest that the detoxified salmolysin may be an effective toxoid to protect the fish from furunculosis.
