The commercial production of hybrid catfish (Ictalurus punctatus × I. furcatus ) in the United States is continuously increasing, now accounting for nearly 60% of the total catfish production, surpassing the production of channel catfish (I. punctatus) . During this transition , the frequency of disease incidence in hybrid catfish has steadily increased creating cause for concern due to significant economic losses. The utilization of probiotics in aquaculture has been an established practice to improve production yield and animal health in non-ictalurid culture species. However, the use of probiotics has not been commercially adopted in catfish culture due to mixed results related to improved growth and health. Lactococcus lactis MA5 was previously identified as a potential autochthonous probiotic from the intestine of overperforming hybrid catfish reared in experimental earthen ponds. In the present study, three graded levels of L. lactis MA5 (104, 106, 108 CFU/g of feed) were mixed with a commercial diet and used in a comparative feeding trial for hybrid catfish juveniles (16.1±0.1 g initial weight) . In total, 560 fish were equally distributed in 28 tanks and dietary treatments were randomly assigned into each aquarium (36. 6 L, 20 fish/tank), operating as a flow-through system (0.5 L/min) with supplemental aeration . Fish were fed at rations of 3-5% body mass, twice daily, for 56 days. Growth performance, survival rate, water quality, and feeding efficiency were monitored throughout the feeding trial. At the end of the study, the head kidney, anterior intestine, and liver were collected for analysis of inflammatory and anti-inflammatory cytokine gene expression ; serum samples were tested for superoxide dismutase (SOD) and lysozyme activities ; viscerosomatic indices and whole- body proximate composition were also collected. The middle and distal segments of the intestine were sampled for histological examination and analyse s are ongoing . At the end of the feeding trial, fish were fed their respective dietary treatments for an additional week, and digesta samples were collected to evaluate the intestinal microbiota. The DNA samples were extracted, and will be subjected to 16S rRNA gene sequencing targeting the V3-V4 region using Illumina MiSeq. N o significant differences were observed for growth performance, feeding efficiency, or viscerosomatic indices. However, the serum lysozyme and SOD activity were upregulated in a dose dependent manner. Moreover, the gene expression of immune-related cytokines IL-1β, and IL-6 were upregulated in 108 CFU/g, while TNF-α was suppressed. A bacterial catfish pathogen, Aeromonas hydrophila, was used in an experimental challenge (intraperitoneal injection with 5.3×106 CFU/g body mass) to evaluate the disease resistance of the hybrid catfish after the dietary administration of MA5. Notably, the lowest MA5 feeding concentration (104 CFU/g) also demonstrated the highest survival rate (72.45%, p=0.001 ) when compared to the control group (49.5%) 7 days post-challenge. In conclusion , the oral administration of L. lactis, MA5 for 56 days as a probiotic can significantly modulate the non-specific immune responses and cytokine mRNA expression, and increase the survival rate of hybrid catfish after A. hydrophila infection.