Vaccination with three inactivated pathogens of cobia (Rachycentron canadum) stimulates protective immunity

Cobia (Rachycentron canadum), a warm water fish recently commercially cultured in Taiwan, has encountered severe mortalities with survival rates often below 20%. The major causative pathogens were Vibrio alginolyticus, Vibrio parahaemolyticus and Photobacterium damselae subsp. piscicida. We prepared a combined three inactivated bacterins antigen preparation and vaccinated cobia. This mixture of bacterins was safe, and the immune response in cobia stimulated specific antibody in 1 week that remained for at least 6 weeks until the end of the aquarium trial. Its efficacy in protecting fish was evaluated in aquarium and field trials. In the aquarium challenge, the vaccine gave a relative percentage survival of 93.8%, 91.1% and 84.7% after challenge with V. alginolyticus, V. parahaemolyticus and P. damselae subsp. piscicida, respectively. In two farm trials using two batches of fish from different hatcheries, one vaccination gave a survival rate of 86–92%. A single vaccination of three combined inactivated bacteria into cobia elicited specific antibodies, and protected fish in both the laboratory aquarium challenge and a farm trial.