Gut-Derived Lactic Acid Bacteria, Pediococcus pentosaceus, Enhances Growth Performance and Resistance to Pathogenic Vibrio harveyi of Hatchery-Bred Milkfish (Chanos chanos) in Nursery Culture.

Hatchery-bred milkfish (Chanos chanos) fry continue to face stocking challenges due to inferior growth performance and reduced resilience compared with wild-caught fry. Recent metagenomic studies have shown that wild fry harbor a higher relative abundance of bacterial taxa belonging to the phylum Bacillota. These include lactic acid bacteria (LAB), which are widely recognized for their probiotic potential in aquaculture. Building on this metagenomic insight, the present study adopted a targeted approach to isolate LAB with anti-Vibrio activity and evaluate its probiotic potential in hatchery-bred C. chanos nursery culture. Screening identified Pediococcus pentosaceus HLAB22 as a promising LAB candidate, which was subsequently assessed through in vivo probiotic trials. Probiotic supplementation significantly improved growth performance, survival, and reduced the incidence of opercular deformities in early juveniles. The most pronounced effects observed at 106 CFU, followed by 103 CFU g-1 feed compared with the control group. Gut colonization experiment demonstrated that dietary supplementation with P. pentosaceus HLAB22 at 106 CFU g-1 feed enabled intestinal colonization within 12 days. This also resulted in near-complete suppression of Vibrio populations, supporting the significant decrease in water and C. chanos gut Vibrio load during the feeding trial. Furthermore, during immersion challenge with pathogenic V. harveyi, the in vitro anti-Vibrio activity of P. pentosaceus HLAB22 was translated into enhanced in vivo protection, yielding a survival rate of 83.33% in treated fish compared with 33.33% in the control group. Collectively, these findings indicate that oral application of P. pentosaceus HLAB22 at 106 CFU g-1 feed is an effective strategy for promoting growth and enhancing resilience in C. chanos nursery culture. This study supports the use of targeted, host-associated probiotics to improve the performance of hatchery-bred milkfish fry and mitigate key challenges in nursery production systems.