Efficacy of Vibrio anguillarum antigen administered by intraperitoneal injection route in Japanese flounder, Paralichthys olivaceus (Temminck et Schlegel)

Japanese flounder, Paralichthys olivaceus (Temminck et Schlegel), were immunized by the intraperitoneal (i. p.) injection route with formalin-killed whole cells of Vibrio anguillarum that originated from a diseased fish. Fifty days later, a booster vaccination was given by the same route. Control fish were similarly treated with sterile phosphate-buffered saline. The efficacy of vaccination was evaluated based on protection against two bacterial challenges and immune responses (both specific and non-specific). The challenges were performed by i. p. injection with V. anguillarum or V. parahaemolyticus. The results indicated that the vaccinated fish showed higher non-specific immune activity than the unvaccinated fish. The effects of vaccinations on the phagocytic activity of phagocyte, bactericidal and lysozyme activities were notable, especially on bactericidal activity. Determined by ELISA, antiserum of vaccinated fish displayed high antibody titres. The vaccination conferred protection against V. anguillarum challenge (81.25-93.75% relative percentage survival (RPS)). The RPS was 46.15-53.85% against V. parahaemolyticus challenge, indicating some degree of cross-protective immunity.