Early-life Bacillus circulans L38 intervention enhances growth and intestinal health in large yellow croaker (Larimichthys crocea) larvae

Abstract

The early life stage is often regarded as a “window of opportunity” for microbial colonization. Targeted intervening with probiotics during this period may be a beneficial approach to foster the healthy development of larvae. Consequently, the aim of this study was to evaluate the impact of supplemental Bacillus circulans L38 (BC) on survival, growth performance, and intestinal health of large yellow croaker larvae. The larvae were fed diets containing different concentrations of BC (0 CFU/g, 10⁶ CFU/g, 10⁷ CFU/g, and 10⁸ CFU/g) for 30 days. Results demonstrated that larvae fed the diet with 10⁸ CFU/g BC significantly enhanced growth performance (P < 0.05). Concurrently, larvae fed the diet containing 10⁸ CFU/g BC significantly promoted intestinal development by increasing intestinal fold height, enhancing expression of markers related to intestinal epithelial cell proliferation and apical junction complex, and boosting brush border enzyme activity (P < 0.05). Furthermore, larvae fed a diet containing 10⁸ CFU/g BC exhibited a significant enhancement in both the activity and expression levels of digestive and absorption-related enzymes and genes (P < 0.05). Supplementation with 10⁸ CFU/g BC further enhanced the larval antioxidant capacity, likely by modulating both the activity and expression of antioxidant connected to enzymes and genes (P < 0.05). Additionally, supplementation with 10⁷–10⁸ CFU/g BC can alter the activity of enzymes connected to innate immunity and modulate the expression levels of genes involved in inflammatory response, thereby enhancing the immunity of larvae (P < 0.05). Meanwhile, larvae fed a diet containing 10⁸ CFU/g BC maintained healthy intestinal microecology by regulating microbial diversity and boosting the proportion of health-promoting bacteria (P < 0.05). In conclusion, supplementation with 10⁸ CFU/g BC could improve the growth performance and intestinal health of large yellow croaker larvae. This improvement are attributed to the promotion of intestinal development, improvement of digestive and absorptive capacity, augmentation of antioxidant capacity, bolstering of immune function, and optimization of the gut microbiota diversity and composition.