Abstract
This study evaluated the efficacy of an inactivated whole-cell vaccine of Vibrio alginolyticus in preventing hemorrhagic disease in red drum (Sciaenops ocellatus). The V. alginolyticus strain (VA15) was selected from 20 isolates obtained from hemorrhagic diseased cage-cultured fish in coastal areas of Hue City, Vietnam, and was subsequently used for both vaccine preparation and challenge testing in red drum. The vaccine was prepared by formalin inactivation and administered via feed to assess its safety and protective efficacy in experimental fish. The results showed that the vaccine had no adverse effects on growth performance, feed conversion ratio, behavior, or the histological structure of the intestine and liver. Vaccinated fish exhibited enhanced immune responses, with significantly higher antibody titers than those of the control group. Following bacterial challenge, the relative percent survival (RPS) reached 44.2% in the single-dose group and increased to 53.5% in the booster group at a concentration of 10⁶ CFU eq/mL. These findings indicate that the inactivated whole-cell V. alginolyticus vaccine has potential as a safe and effective strategy for preventing hemorrhagic disease in red drum aquaculture.