HUMORAL ANTIBODY-RESPONSE OF BROWN TROUT SALMO-TRUTTA VACCINATED AGAINST FURUNCULOSIS

Two year old brown trout Salmo trutta L. in a freshwater farm with a h istory of enzootic Aeromonas salmonicida infections were vaccinated wi th a commercial vaccine against furunculosis by intraperitoneal inject ion either with or without a booster. Antibody levels to 3 cellular an tigen preparations from A. salmonicida, i.e. whole cells of A. salmoni cida, A-layer protein, and lipopolysaccharide (LPS) isolated from the bacterium, were measured using an ELISA technique. Antibodies to whole cell A. salmonicida and LPS were demonstrated in both vaccinated and non-vaccinated fish. Antibodies to A-layer protein were only detected in very low quantities in non-vaccinated fish, In vaccinated fish, the levels of these antibodies were significantly higher in boosted fish than in fish vaccinated only once. Western blot analyses of fish serum also revealed antibodies to LPS and A-layer protein. Antibody activit ies to extracellular products from A. salmonicida were mainly against a 70 kDa component and LPS. Prior to a challenge test in which furuncu losis was induced by increasing the water temperature, all fish were b led and individually marked. Only boosted fish showed significant prot ection in this challenge, and no mortalities were recorded in this gro up. The groups of fish which had received only 1 immunization were not protected against furunculosis. In these groups, pre-challenge antibo dy levels to cell membrane antigens, as measured by ELISA, did not dif fer between survivors and non-survivors. This indicates that high leve ls of specific antibodies to cellular antigens do not correlate with s urvival of the individual fish.