Impact of Tubifex tubifex supplementation on gut microbiota and health in Chinese sturgeon larvae during dietary transition

Recent advancements in the full-cycle artificial breeding of Chinese sturgeon ( Acipenser sinensis ) larvae under recirculating aquaculture systems have underscored the dietary transition period as a critical challenge, characterized by intestinal dysbiosis and bacterial enteritis. A three-month longitudinal metagenomic study was conducted to explore how blended feeding ( Tubifex tubifex + commercial feed) affects gut microbiota dynamics and host health. The results across eight rearing cohorts demonstrated that the mid-transition phase (Month 2) is a key period for microbial restructuring. The blended diet group (experimental group, EG) exhibited higher operational taxonomic unit (OTU) recruitment rates and greater α-diversity compared to the commercial feed-only group (control group, CG). The CG exhibited a predominance of Pseudomonadota at the phylum level, with notable abundances of Aeromonas and Citrobacter at the genus level. These taxa demonstrated an enhanced potential for pathogenicity, supported by functional predictions indicating capabilities associated with biofilm formation, flagellar assembly, and lipopolysaccharide biosynthesis. Although prolonged T. tubifex supplementation enhanced metabolic capacity, it failed to reduce the virulence of opportunistic pathogens. Furthermore, the dietary transition process was associated with a gradual weakening of the "resistance by host-dependent nutrient acquisition" mechanism. Despite observing minimal variations in antibiotic levels and mobile genetic elements (MGEs) across different developmental stages and feeding strategies, the emergence of multi-drug resistance patterns remains a concern. This study provides valuable insights into optimizing feeding strategy for Chinese sturgeon larvae during the dietary transition period and emphasizes the importance of routine non-invasive monitoring of pathogens, contributing to the conservation of this endangered species. • Tubifex +feed elevates gut microbiota α-diversity. • Month 2 is regarded as a crucial time triggering reconfiguration in functions, pathogenicity and drug resistance. • Aeromonas/Citrobacter core functions resist dietary/stage variations. • High-abundance “Multidrug” with “transposase” constitutes a persistent threat across stages.