Efficiency of monovalent Vibrio alginolyticus formaldehyde-killed vaccine on the immune responses and protection of Asian seabass (Lates calcarifer) juveniles against Vibriosis

Vibrio alginolyticus causes severe health problems in marine fish production each year. Among various therapeutic strategies, vaccination is the most economic, efficient and environmentally-friendly approach against microbial infections. Evaluation of formalin-killed Vibrio alginolyticus vaccine aquired from native isolates was carried out using a total of 200 Asian seabass juveniles (55±6.43 g), which were divided among three groups, including (I) control (non-vaccinated), (II) vaccinated with killed V. alginolyticus and (III) killed vaccine with oral booster. Fish were vaccinated intraperitoneally. Blood samples were taken from fish in each group at three, five, and eight weeks after immunization to assess the antibody levels against V. alginolyticus infection. The efficacy of the killed vaccine was appraised five weeks after the start of the initial vaccination by challenging with twofold LD50 (3.66×108) equivalent of the live suspension of V. alginolyticus through intraperitoneal injection. The results of ELISA showed that there were not any significant differences in antibody response among different groups before vaccination (p>0.05). Also, the mean antibody titer of the group immunized killed-V. alginolyticus with oral booster was significantly higher than the other groups five weeks after the vaccination. The vaccined fish demonstrated higher survival rates than the control with relative percent survival (RPS) of 84.62 and 76.92%, respectively. It is concluded that vaccination could be an effective method to protect farmed Asian sea bass against vibriosis caused by pathogenic V. alginolyticus.