International Journal of Marine Science, 2026, Vol.16, No.1, 14-29 http://www.aquapublisher.com/index.php/ijms 21 products significantly reduced mortality after A. hydrophila challenge, and the probiotic treatments also decreased Aeromonadaceae and Enterobacteriaceae abundance in the intestine, linking disease control to microbial exclusion of potential pathogens (Gao et al., 2024). The disease-resistance effect extends across diverse probiotic taxa and delivery strategies. Autochthonous intestinal bacteria reduced cumulative mortality after A. hydrophila challenge from 80% in controls to 26.67% in the mixed-strain group, showing that consortia can outperform single strains in protection efficiency. Additional lower-ranked but relevant studies support the same pattern: Paenibacillus polymyxa S3 increased survival after A. hydrophila infection while upregulating C3, lysozyme, IgM, TLR-4, and MyD88. Bacillus methylotrophicus XA-8 also reduced A. hydrophila virulence by downregulating aer, act, hylA, lafA, hcp, and luxS, and supplemented fish showed 52.63% infection resistance together with lower intestinal Aeromonas abundance (Figure 2) (Khan et al., 2024). Overall, probiotics strengthen grass carp health by improving innate immunity, antioxidant defense, and pathogen resistance . The evidence across many strains supports probiotics as a practical strategy for reducing disease incidence and lowering dependence on antibiotics in healthy grass carp farming. Figure 2 Mechanisms of probiotic-mediated enhancement of disease resistance in grass carp following pathogen challenge
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