| Summary: | One of the main factors limiting tilapia’s production is the occurrence of infections caused by <i>Aeromonas</i> and <i>Streptococcus</i> species. This work intended to evaluate a bivalent vaccine against <i>A. hydrophila</i> and <i>S. agalactiae</i> by intraperitoneal (i.p) administration in Nile tilapia (<i>Oreochromis niloticus</i>) in Brazil. The study was carried out in two phases: one in the laboratory, on a small scale, and from the results obtained, the study was expanded to a large scale in a production system in cages. The vaccine proved to be safe and effective in laboratory tests, with a vaccine efficacy (VE) of 93.66%. However, in large-scale tests with 12,000 tilapias, the VE was 59.14%, with a better food conversion ratio (1.54 kg) in the vaccinated group compared to the control group (1.27 kg). These results corroborate the efficiency of this tested vaccine; however, they indicate the need for field tests to attest to real protection.
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