Temporal reconstruction and functional adaptation of intestinal microbiota in Lutjanus argentimaculatus during initial stage of stock enhancement

Lutjanus argentimaculatus is a key species in stock enhancement programs in the South China Sea, yet how its gut microbiota temporally restructures and functionally adapts after release from aquaculture to the natural environment is poorly understood. To investigate these early adaptive changes and to optimize stock enhancement strategies, we collected a total of 24 intestinal samples from cultured and recaptured fish at the 1^st, 5^th, 15^th, and 30^th day post-release (n=3 per time point). High-throughput 16S rDNA sequencing and PICRUSt2 analysis were used to reveal distinct dynamics: the cultured group showed a steady increase in Shannon diversity (1.99 to 3.58), accompanied by a shift in dominant genera from Lawsonia to Photobacterium, suggesting a progression toward multi-genus coexistence under stable rearing conditions. In contrast, the recaptured group exhibited a biphasic "decrease-increase" pattern in microbial diversity, recovering to a higher Shannon index (4.40) by day 30, accompanied by significant enrichment of Burkholderia-Caballeronia-Paraburkholderia and Rhodococcus. Functional prediction indicated that the cultured group's microbiota was enriched in biosynthesis pathways (e.g., energy synthesis and nucleotides), whereas the recaptured group's microbiota showed enhanced catabolic potential for aromatic compounds and complex carbon sources. These findings demonstrate that the gut microbiota of L. argentimaculatus undergoes rapid restructuring and a functional transition from a biosynthesis-oriented profile to an adaptation-oriented one, offering a new way for improving stock enhancement strategies.