In South America and the Caribbean, aquaculture has grown above the global average in recent years (2000-2022), with rates of 7.7 and 5.0%, respectively, and Nile tilapia is the most important species. In Brazil, this species is produced intensively, mainly in net cages, in rivers and reservoirs where there is no control whatsoever over the limnological parameters of the water and health problems, mainly caused by bacteria, are frequent and cause many morbidities and mortalities. To confront these challenges, producers use commercial vaccines and autogenous vaccines. However, autogenous vaccines still require scientific studies to prove their effectiveness. Thus, the objective of this study was to evaluate the effectiveness of an autogenous trivalent vaccine against Streptococcus agalactiae serotype Ib, one of the main agents causing mortality, poor performance and discarding of tilapia in slaughterhouses. The experiment was conducted at the Laboratory of Microbiology and Parasitology of Aquatic Organisms of CAUNESP, Jaboticabal, SP, Brazil, from March to July 2024. The design was completely randomized with four treatments and three replicates: Group 1 (G1) unvaccinated and challenged with S. agalactiae serotype Ib, G2 vaccinated with an inactivated trivalent autogenous vaccine (S. agalactiae serotype Ib, Aeromonas hydrophila and Edwardsiella tarda with oily adjuvant), challenged with the same agent, G3 unchallenged physiological control and G4 PBS control. After the 56-day acclimatization period (23.20 ± 6.30 g), the fish in each group were vaccinated (intraperitoneally) with the autogenous vaccine or not and returned to 300-liter tanks with independent water inlet and outlet. Groups G1 and G2 were challenged with S. agalactiae (the same strain used in vaccine production) at a dose established at LD50% with a concentration of 2.42 x 106 CFU/mL-1 30 days after vaccination. The clinical signs and daily mortalities were recorded. Dead fish were collected, and the bacteria reisolated until mortality stabilized (between days 15-18 post-challenge). The water quality parameters (temperature, pH, and conductivity) remained within the levels required by the species, except for oxygen, which frequently remained below (1.1 – 4.4 mg/L-1), influenced by temperature. This stressful condition may have compromised the fish’s immune system, partially reducing the vaccine’s effectiveness. Despite this, the average survival rate of the vaccinated group (41.67%) was 4.2 times higher than that of the unvaccinated group (Table 1).
The autogenous trivalent vaccine was effective to provide protection against S. agalactiae serotype Ib (p =0.01).