Co-Encapsulated Probiotic Bacillus aryabhattai CKNJH11 With Algae-Derived Polysaccharides on Growth Performance and Immunity in Asian Seabass (Lates calcarifer).

Antimicrobial resistance and environmental impacts have driven the search for effective nonantibiotic strategies in aquaculture. In this study, Bacillus aryabhattai strain CKNJH11 was isolated from shrimp pond sediment and systematically evaluated its suitability as a probiotic both in vitro and in vivo experiments. The results revealed that CKNJH11 spores formed with 95.7% efficiency, survived extreme gastric (pH 2.0, 64.9% viability) and bile salt (5%, 78.1% viability) conditions, and inhibited biofilm formation by Pseudomonas aeruginosa and Vibrio parahaemolyticus by 58.3% and 59.9%, respectively. Hemolysis tests and antibiotic-susceptibility profiling confirmed the strain's safety. To assess its performance in fish, 120 Asian seabass juveniles (initial weight 13.50 ± 0.35 g) were randomly assigned to four diets (1 × 106 CFU/g) as a no-probiotic control, unformulated spores, alginate-encapsulated spores, and spores co-encapsulated with Gracilaria fisheri polysaccharides. After 8 weeks, the co-encapsulated group exhibited the greatest improvements in growth (60.7 ± 1.98 g weight gain (WG) vs. 38.6 ± 1.34 g in controls; p < 0.05), feed conversion ratio (FCR, 5.67 ± 0.18 vs. 8.13 ± 0.37), and immune indices (elevated leukocyte counts and hemoglobin levels). Gut microbiota analysis confirmed successful colonization by B. aryabhattai (3.75-3.93 log CFU/g) and a 60%-75% decline in Vibrio counts (p < 0.05). The enhanced stability and activity afforded by alginate protection combined with prebiotic polysaccharides underscores the potential of this formulation as a sustainable biocontrol agent in aquaculture health management.