Prospection of Autochthonous Lactic Acid Bacteria Displaying Probiotic Potential to Enhance <scp> <i>Colossoma macropomum</i> </scp> Larvae Growth and Immunoprotection Against <scp> <i>Aeromonas hydrophila</i> </scp>

This study assessed the functional potential of autochthonous lactic acid bacteria isolated from the gastrointestinal tract of tambaqui (Colossoma macropomum) as larviculture probiotics. Five strains were selected and identified as belonging to the genus Weissella. In vitro assays revealed high tolerance to acidic pH (2.0-3.0), resistance to bile salts (10%), biofilm formation capacity, hydrophobicity and direct Aeromonas hydrophila inhibition. In in vivo tests, strains M13 and M14 promoted significant increases in tambaqui survival (72.2% and 68.7%; p < 0.05) and growth (standard length and eye diameter), as well as water quality (nitrite reduction), highlighting multiple beneficial effects. Innate immunity was activated, with total protein level (I3 and M14) and agglutinating titre (M13 and M14) increases. Intestinal colonisation was confirmed by bacterial counts, and the observed effects were consistent with adhesive and antimicrobial strain properties. The findings demonstrate a synergistic interaction between probiotics, hosts and pathogens, with integrated health, performance and environmental stability benefits. Strains M13 and M14 are, thus, promising alternatives to the use of antibiotics in intensive aquaculture systems, contributing to sustainable and safe tropical fish production strategies.