Graded Mulberry Leaf Supplementation Shapes Gut Microbiota, Reprograms Intestinal Metabolism, and Maintains...

Mulberry leaf contains abundant phytochemicals with antioxidant and immunomodulatory activities. However, systematic insight into its dose-dependent regulatory effects on the intestinal health of Amur sturgeon remains limited. In the present study, multi-omics approaches, including 16S rRNA gene sequencing, untargeted metabolomics, transcriptomics, together with RT-qPCR, were applied to investigate graded dietary mulberry leaf supplementation in Acipenser schrenckii. Juvenile sturgeons were fed four experimental diets containing 0%, 2%, 4% and 6% mulberry leaf over a 10-week feeding trial. Dietary mulberry leaf caused no adverse impacts on growth performance or intestinal digestive capacity. Although the overall structure of the intestinal microbiota remained stable, beneficial bacterial taxa were enriched in a dose-dependent manner. Intestinal metabolism underwent hierarchical remodelling: low inclusion levels supported basal nutrient metabolism, medium inclusion strengthened antioxidant capacity, and high inclusion reprogrammed lipid metabolism and immune function. Mulberry leaf reinforced the intestinal chemical barrier by balancing redox homeostasis and reducing mucosal epithelial permeability. Moreover, intestinal immunity was modulated through three sequential phases: initial innate immune priming, B-cell homing, and the establishment of sustained immune tolerance. In conclusion, mulberry leaf maintains intestinal chemical-immune barrier homeostasis in a dosage-tunable manner, supporting its potential application as a functional aquafeed ingredient.