Sub-chronic ammonia nitrogen exposure disrupts gut microbiota and intestinal structure in hybrid sturgeon

Ammonia nitrogen is a common pollutant in aquaculture, and its sub-chronic toxicological mechanisms on hybrid sturgeon remain unclear. This study conducted a 60-day experiment (4 replicates per group) to explore the effects of 0, 1, 2, and 4 mg/L TAN on hybrid sturgeon (Huso dauricus♀ × Acipenser schrenckii♂). Results showed: Low concentration (1 mg/L) significantly increased Fusobacteriota (+49.5 %) and Cetobacterium abundance, decreased Proteobacteria (-46.8 %), caused the most significant decline in α-diversity (p < 0.05), and reduced intestinal villus/muscular layer ratio to 3.86 ± 0.44; Medium concentration (2 mg/L) induced mild microbial changes with partial recovery, nonlinear diversity response, and intestinal structure repair in some individuals (ratio 9.89 ± 1.09) but large intra-group differences; High concentration (4 mg/L) led to continuous increase in Fusobacteriota (+39.7 %) and Firmicutes, decrease in Bacteroidota, elevated F/B ratio, re-impaired intestinal structure (ratio 5.33 ± 0.79), and aggravated metabolic disorders. Low concentration maintained homeostasis via liver-intestine-gill crosstalk; medium concentration triggered inconsistent compensatory responses; high concentration exceeded the host's compensatory capacity. This study provides references for differentiated ammonia nitrogen regulation in sturgeon aquaculture.