Streptococcosis and Motile Aeromonad Septicemia (MAS) are important diseases of tilapia (Oreochromis spp.), and causes huge economic losses throughout the world. Streptococcal and aeromonad diseases have proven to be very difficult to control with the use of antibiotics. Hence, the aims of the study were to evaluate the systemic and mucosal immunity of the newly developed feed-based bivalent of killed (Streptococcus iniae and Aeromonas hydrophila) vaccine, and efficacy by intraperitoneal (i.p.) challenges in red tilapia.
A total of 1,050 red tilapia, each 61.23 ± 4.95g were divided into 5 groups with triplicates. Five groups of tilapia were vaccinated orally with bivalent (combined with S. iniae and A. hydrophila) vaccine sprayed on feed (BS group), divalent vaccine incorporated in feed (BF group), monovalent S. iniae and A. hydrophila vaccines incorporated separately in feed as MS group and MA group, respectively, and unvaccinated as a control group. During the experiment, serum, mucus and gut lavage fluid were collected to evaluate the antibody levels via indirect ELISA. The results showed that hybrid red tilapia immunized with bivalent formulate (BF group) achieved a strong and significantly (P<0.05) higher IgM responses in serum, gut and mucus samples than the control group. In this study, a relative percent survival (RPS) of 80.00% (i.p. challenged with S. iniae), 76.67±4.71% (challenged with A. hydrophila) and 76.67?±?4.71% (co-infection) were also observed in bivalent formulate group, which were significantly higher (P?<?0.05) than the other groups. Results show that feed-based bivalent vaccination is an efficacious treatment for the prevention of Streptococcosis and MAS outbreaks throughout the tilapia culture period.