<![CDATA[Graphical Abstract Highlight Research 1. Aeromonas hydrophila PTF3 was identified and analysed as a causative agent of a previously identified hemorrhagic syndrome in Tor tambroides. 2. Lactococcus garvieae JAL37 supplementation in feed can enhance the growth of Tor tambroides fingerlings. 3. Lactococcus garvieae JAL37 can increase the resistance of Tor tambroides fingerlings to Aeromonas hydrophilla PTF3. 4. Relative mRNA levels of ghrelin, GH, and I-FABP genes were increased after 90 days of tor cultivation with Lactococcus garvieae JAL37 supplementation. Abstract Mahseer, or tor fish, an indigenous Asian fish of great socio-economic value, is gaining attention as it faces threats to its survival. However, slow growth rates and disease outbreaks, particularly hemorrhagic septicemia caused by Aeromonas hydrophila, significantly reduce survival rates and productivity in Tor tambroides aquaculture systems in Indonesia. A diet supplemented with probiotic Lactococcus garvieae JAL37 (1.0 × 10⁸ CFU/g feed) was administered twice weekly for 90 days to evaluate its effects on growth performance, intestinal morphology, gene expression, and disease resistance compared with a non-supplemented control. Triplicate groups of T. tambroides fingerlings (average weight 1.86 ± 0.09 g) were cultivated for 90 days. On day 90 posttreatment, mahseer were orally challenged with A. hydrophila at 5.0 × 105 CFU g⁻¹ fish body weight to assess survival rates and mRNA expression levels of pro-inflammatory cytokine-related genes (TNF-α and IL-1β). Weight gain, specific growth rate, and villus length in T. tambroides fingerlings treated with probiotics showed significant increases (p < 0.05). Real-time PCR results indicated upregulated mRNA expression of ghrelin, I-FABP, and GH genes in the probiotic group, whereas IGF-1 gene expression was similar to that in the control group. Probiotic treatment significantly improves the survival rate of T. tambroides after A. hydrophila challenge, while suppressing mRNA expression of TNF-α and IL-1β genes post-challenge. These findings demonstrate that L. garvieae JAL37 supplementation promotes growth and was associated with improved survival following challenge in T. tambroides fingerlings.]]>
