A Comparative Study on Gut Microbiota and Metabolomics in Atlantic Salmon Salmo salar at Different Growth Stages

Atlantic salmon (Salmo salar) represents the primary species in aquaculture. The gut microbiota plays a crucial role in nutrient processing and protection against pathogenic bacteria. Nonetheless, the composition and functionality of the gut microbiota in Salmo salar at different growth stages remain largely unexplored. This study investigated the alterations within the gut microbial communities and their associated metabolites across different growth stages of Salmo salar, specifically when the body weights were 1.0 kg (S1 group), 2.0 kg (S2 group), 4.0 kg (S3 group), and 6.0 kg (S4 group), using microbiome sequencing and liquid chromatographymass spectrometry (LC-MS) technology. Results indicated significant changes in the gut microbiota and metabolite profiles concurrent with fish growth. Notably, the abundance of Firmicutes decreased, and Proteobacteria increased, resulting in a decreased Firmicutes/Bacteroidetes (F/B) ratio. Concurrently, the abundance of potential pathogenic bacteria such as Stenotrophomonas, Vibrio, Aeromonas, Staphylococcaceae, Enterobacteriaceae, Enterococcaceae, and Haemophilus increased, whereas beneficial bacteria like Lactobacillus and Bacilli decreased. The gut microbiota in the S1 group exhibited an increase in the abundance of beneficial bacteria. Conversely, in the S2, S3, and S4 groups, the prevalence of pathogenic bacteria increased. Metabolic profiling revealed significant upregulation of arachidonic acid (ARA) and taurine in the S2 and S3 groups, while citric acid, riboflavin, and pantothenic acid notably increased in the S4 group. Particularly, several amino acids such as threonine, lysine, and serine in the gut microbiota metabolites were significantly reduced in the S2, S3, and S4 groups, correlating positively with the respective essential amino acid concentrations in muscle tissue. The S1 group exhibited a more active gut microbiota associated with amino acid metabolism, resulting in higher muscle amino acid content. This study identified gut microbiota and its metabolic products at different growth stages of Salmo salar, providing a scientific basis for proactive intervention of gut microbiota and improve the quality of aquatic products.