Regional variation in the gut microbiota of olive flounder (Paralichthys olivaceus) farmed in Korea

The gut microbiota composition is closely linked to fish health. Understanding this composition may help develop strategies to enhance the productivity and sustainability of aquaculture. In this study, we investigated the gut microbiota of olive flounder (Paralichthys olivaceus) based on aquaculture regions in Korea. Similar-sized flounders were collected from farms in Gyeongsangbuk-do (A group), Gyeongsangnam-do (B group), Jeollanam-do (C group), and Jeju Island (D group). The intestines of 10 flounders per group were aseptically collected and analyzed for microbiota composition. Alpha diversity analysis revealed regional differences in the richness and diversity of the gut microbiota. Similarly, beta diversity analysis indicated distinct clustering patterns between groups, and individuals within the same group were relatively close in microbial composition. Proteobacteria was the most abundant microbial phylum. However, the proportion varied among individuals, and in some cases, Firmicutes was the dominant phylum. At the genus level, the analysis results showed that there were also differences between individuals within groups. Linear discriminant analysis effect size (LEfSe) analysis identified distinct group-specific enrichments: Group A was enriched with Vibrio, Lactobacillus, and Leuconostoc; Group B with Edwardsiella; Group C with Photobacterium; and Group D with Sphingomonas. Our results indicate that the composition of the gut microbiota in olive flounder varies depending on the aquaculture region, with variations observed among individuals within the same region. These findings suggest that the gut microbiota composition of farmed flounder is influenced by both individual characteristics and environmental factors specific to the farming region.