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This study evaluated the control of streptococcosis outbreaks in Brazil, isolated from diseased sorubim and identified as Lactococcus garvieae by genetic sequencing. This report determined the potential for lactococcosis control in sorubim Pseudoplatystoma sp. with two vaccines: an aqueous-based, whole-cell inactivated vaccine (bacterin) and an oil-adjuvanted bacterin. Their efficacy was evaluated at 30 days post-vaccination (d.p.v.) by challenge with L. garvieae, and the antibody production response at 15, 30 and 60 d.p.v. and the non-specific immune response were compared amongst treatments. High protection levels (P < 0.05) were achieved with the oil-adjuvanted vaccine with a relative percentage survival value of 81.7% at 30 d.p.v. Additionally, the oil-adjuvanted vaccine increased the immunogenicity of the bacterin as indicated by greater agglutination antibody titres from 15 until 60 d.p.v. This is the first report of a positive effect of vaccine administration on the specific immunity of sorubim, and the study showed that a specific antibody plays an important role in sorubim defence against lactococcosis because the innate immune responses were similar in all of the studied animals. These results demonstrated that oil-adjuvanted vaccine can be an effective alternative for the protection of sorubim from L. garvieae disease.

This study aimed to verify the possible positive effects of feeding the commercial probiotic Bioplus 2BC® [Bacillus subtilis (1.6 × 1010 CFU/g) and Bacillus licheniformis (1.6 × 1010 CFU/g)] to Nile tilapia on its growth performance, nutrient digestibility, gut microbiology, haematology (hematimetric index, erythrocyte, leucocyte and thrombocyte counts) and innate immunology (lysozyme, burst respiratory and phagocyte activities). For this purpose, one in vivo assay was performed following a completely randomized design, with four treatments (0.00%; 0.02%; 0.04%; and 0.08% of probiotic inclusion on ratio) and four replicates. The fish fed with diets containing 0.04% and 0.08% of probiotics presented higher weight gain than the control group, as well as higher thrombocyte counts in the bloodstream. The positive effect of the probiotics on the gut microbiota was illustrated by the higher richness and habitability indexes, soaring genetic variability. On the contrary of control, the groups fed with probiotic had Firmicutes, Fusobacteria and Bacteroidetes phyla, and a lower percentage of Proteobacteria. The inclusion of 0.04% and 0.08% of B. subtilis and B. licherniformis in the fed provides better growth performance and modifies the intestinal microbiota, reducing the class of potential pathogen agent species. The establishment of a beneficial microorganism population may improve host health.