Functional evaluation of Lacticaseibacillus paracasei AAHM-LP2301 on immunity, growth, antioxidant defense, and resistance to Edwardsiella tarda infection in tilapia

Tilapia aquaculture faces escalating disease losses under intensive farming, motivating safe antibiotic alternatives. We evaluated the probiotic potential of Lacticaseibacillus paracasei AAHM-LP2301, a strain isolated from healthy tilapia during a disease outbreak. Whole-genome sequencing confirmed species identity and safety indicators (3.12 Mb; GC 46.4 %; 2892 CDS). Red tilapia were fed for 30 days with cells, cell-free supernatant (Cfs), or both, then maintained 30 days on a basal diet. Growth performance and brain, muscle, and liver growth hormone ( gh ) expression were unaffected at Day 30 and Day 60 ( P > 0.05). In contrast, antioxidant capacity improved broadly. During feeding, catalase (CAT), superoxide dismutase (SOD), and glutathione (GSH) increased across multiple tissues compared with controls ( P < 0.05), with a CAT-centered carry-over at Day 60. Lipid peroxidation decreased by Day 60, malondialdehyde levels rebounded in controls but remained significantly lower in probiotic groups ( P < 0.05). Intestinal barrier and immune readiness were enhanced, with marked upregulation of tight-junction genes muc , zo1 , ocln , cldn , and immune genes nfκb , il1b , il6 , il8 , ifng , tnfa , hamp , lyz, ctl , c3 at both time points ( P < 0.05). Humoral responses increased, including lysozyme activity, bactericidal activity, and serum IgM. Challenge with Edwardsiella tarda demonstrated functional protection: survival rates were 70 % in Cell (relative percent survival 53.8 %) and 65 % in Cfs and Cell+Cfs (RPS 46.2 %), exceeding controls (35 % and 45 %; P < 0.05). Principal component and correlation analyses supported coordinated antioxidant and immune profiles distinguishing probiotic groups from controls. Overall, L. paracasei AAHM-LP2301 is a safe, multifunctional probiotic that strengthens mucosal barriers, enhances antioxidant defenses, and increases disease resistance without compromising growth, supporting resilience-focused tilapia aquaculture. • Genome sequencing verified the identity and biosafety of Lacticaseibacillus paracasei AAHM-LP2301. • Probiotic supplementation enhanced antioxidant defenses, lowering oxidative stress in tilapia tissues. • Tight junction integrity and immune-related gene expression were significantly upregulated. • Humoral immunity was strengthened, with elevated lysozyme activity, bactericidal capacity, and IgM levels. • Dietary supplementation improved tilapia survival following Edwardsiella tarda challenge.