Isolation and characterization of Lactococcus lactis from Anabas testudineus (Bloch, 1792) as a potential probiotic for sustainable Aquaculture.

The present investigation provides the first report of Lactococcus lactis isolated from the intestinal tract of Anabas testudineus (Bloch, 1792), emphasizing its probiotic attributes and biosafety for aquaculture applications. From 100 bacterial isolates, three strains (GUNA, GUN-1, GUN-2) were identified as L. lactis via 16 S rRNA sequencing. These isolates displayed pronounced antagonism against Aeromonas hydrophila and A. jandaei, along with marked tolerance to gastrointestinal stressors, including low pH (71-80% survival at pH 2.0-3.0), bile salts (69-78% at 0.3-0.5% oxgall), and phenol (66-91% at 0.2-0.4%). Functional traits such as auto-aggregation (21-35%), co-aggregation (15-24%), and hydrophobicity (18-29%) indicated strong adhesion potential. All isolates were non-hemolytic, gelatinase-negative, and devoid of biogenic amine production, confirming their safety. Antibiotic profiling revealed resistance to streptomycin, tetracycline, and ciprofloxacin, but sensitivity to ampicillin. In vivo assays with Labeo rohita and Cirrhinus mrigala confirmed 100% survival without adverse effects. Collectively, these findings highlight L. lactis from A. testudineus as a safe, potent probiotic and a promising bio-alternative to antibiotics in aquaculture.