Microbial Imbalance and Stochastic Assembly Drive Gut Dysbiosis in White-Gill Diseased Larimichthys crocea (Richardson, 1846).

White-gill disease has emerged as one of the major health threats in large yellow croaker Larimichthys crocea (Richardson, 1846) aquaculture, yet its underlying microbial mechanisms remain poorly understood. In this study, we investigated the gut microbiota of healthy and white-gill diseased L. crocea across different growth stages and aquaculture locations using 16S rRNA gene amplicon sequencing and bioinformatics analysis. Across both juvenile and adult fish, as well as multiple sampling locations, diseased individuals consistently exhibited significantly reduced microbial richness and evenness compared to healthy counterparts, along with a clear divergence in community composition. Notably, the relative abundance of Photobacterium damselae subsp. damselae was markedly increased in diseased fish, especially juveniles, accompanied by a decline in beneficial genera such as Bacillus. Co-occurrence network analysis revealed simplified microbial interactions and decreased community stability in gut of diseased fish. Null model analysis further indicated that stochastic processes dominated gut microbial assembly, with a higher contribution in diseased individuals, suggesting weakened host selection pressure and enhanced random colonization under disease conditions. These findings highlight the important role of gut microbiota dysbiosis in the development of white-gill disease and provide new insights into microbiota-based diagnostics and ecological strategies for disease prevention in marine aquaculture.