Cobia (Rachycentron canadum) is one of the most common marine fish cultured species in Vietnam. Cobia often infected by Vibrio spp., including three species of Vibrio alginolyticus, V. parahaemolyticus and V. harveyi with mortalities of up to 80 percent in the grow-out phase. Vaccine is a suitable preventive measure for bacterial diseases in cultured copia. However, in order to produce vaccine, a part from having high virulent pathogengic bacteria, it is important to have high antigenic bacteria strain. The bacteria strains included: AlOCO2 (collected in Khanh Hoa), AO4CO1 and AO4CO2 (collected in Hai Phong), AO9TO6 (collected in Quang Ninh) of V. alginolyticus, PO5CO1 (collected in Hai Phong), P10TO4 and P10TO5 (collected in Quang Ninh) of V. parahaemolyticus and H10CO2, H10CO5 (collected in Hai Phong) and H10CO7 (collected in Khanh Hoa) of V. harveyi inactivated by formalin 1 percent (with or without oil adjuvant) were intrapetonealy injected to cobia. Serium were collected at 7, 14 and 21 day post vaccinated by bacterins
10 and 20 day post vaccinated by bacterins with oil adjuvant. ELISA method was used to evaluate specific antibodies induced by the bacteria. The results showed that the inactivated bacterial strains with or without oil adjuvant elicited immune responses in cobia. However, the bacterins, without oil adjuvant, induced strong immune response at 7 days, but then tended to decrease at 14 and 21 days post vaccination. Meanwhile the combination of bacterin and oil adjuvant induced immune response increasing dbring time (10 days and 21 days post injection to cobia). The bacteria strain AO4CO1, H10CO2, H10CO7, PO5CO1, P10TO4 given better immune response compared to the other tested strains.