Analysis of protective mechanisms in cultured ayu, Plecoglossus altivelis Temminck and Schlegel, administered Vibrio vaccine by the immersion method

Abstract. The protective effect of Vibrio angnillarum immunization administered by the direct immersion technique in ayu, Plecoglossus altivelis Temminck and Schlegel, was investigated. The activities of phagoeytic cells were suppressed at the time of vaccination by previous bath exposures to a cyclophosphamide solution containing a concentration of 500 mg/kg/ml on days 2 and 3 before vaccination. An artificial challenge was carried out 3 weeks after vaccination by bath exposure. The survival rate of the vaccine group pretreated with cyclophosphamide was 96%. In the group given traditional vaccine only, 73% survived; and in the non-vaccine control group, 10% survived. These results suggest that protective immunity of ayu vaccinated by the direct immersion technique may not implicate the early activities of phagoeytic cells.