Abstract
Sichuan bream (Sinibrama taeniatu), an endemic small economic fish in the upper Yangtze River, has achieved captive breeding breakthroughs. To advance standardized and large-scale aquaculture, this study investigated intestinal development, enzyme activities, gut microbiota, and its interactions with rearing water microbiota across six developmental stages (G1-G6) from hatching to sexual maturity of Sichuan bream. Results showed its progressive refinement of external morphology and intestinal developing into multiple flexures. Histology examination revealed four foregut layers with continuously increasing villus height. Digestive enzyme analysis revealed significantly higher activity of trypsin compared to that of amylase and lipase (p < 0.05). 16S rRNA sequencing identified Proteobacteria, Firmicutes, Bacteroidota, Actinobacteriota, and Fusobacteria as the dominant phyla in both gut and rearing water microbiota. Gut communities shifted from Proteobacteria-dominance (C(1)-C(5)) to Firmicutes-dominance (C6). The microbial source tracking analysis indicated water contributed to gut microbiota of Sichuan bream, particularly during G3. This study clarified the intestinal development patterns and gut microbiota colonization dynamics of Sichuan bream. The findings provide reference materials for the research on the growth patterns and host-microbe interaction of Sichuan bream. They lay a theoretical foundation for the protection and utilization of Sichuan bream resources, ultimately aiding in their proliferation and release.