Isolation and characterization of a marine strain: Bacillus inaquosorum, and its feeding effects on Sebastes schlegelii as feed additive

The intensive development of industrial-scale aquaculture has led to overreliance on antimicrobial agents, raising global concerns about residual contamination and the proliferation of antimicrobial resistance. Marine-derived Bacillus spp., due to their proven probiotic effects, have emerged as a promising alternative to traditional antibiotics in aquaculture systems. A marine-derived Bacillus inaquosorum strain M1 demonstrating potent Vibrio-inhibitory activity was isolated from coastal sediment samples. Comprehensive assessments demonstrated that M1 exhibited excellent environmental adaptability and stability while maintaining sensitivity to commonly used antibiotics. To explore the potential applications of M1 in aquaculture, animal trials were conducted to evaluate its effects on Sebastes schlegelii, including growth performance, activity of digestive enzymes, intestinal health, and response of the immune system. The results revealed that oral M1 significantly enhanced the growth rate, feed efficiency, and intestinal digestive enzyme activities in S. schlegelii (p < 0.05). Furthermore, improvements in intestinal structure and increased activities of immune and antioxidant enzymes were observed. Notably, levels of IL-2 and IFN-γ in various organs of S. schlegelii were significantly elevated following dietary supplementation of M1 (p < 0.05). Conversely, levels of IL-1β, TNF-α, and IL-10 were reduced (p < 0.05). Additionally, the fish exhibited enhanced resistance to V. harveyi infections, with a protection rate of up to 73.33 %. These findings suggested that B. inaquosorum M1 can modulate the immune function of S. schlegelii, thereby improving their growth performance and overall health status. Consequently, B. inaquosorum M1 is posited as a potential candidate for application as an aquaculture feed additive and a promising alternative to antibiotics.