Background Important changes in microbiome composition related to sexual maturation have been already reported in the gut of several vertebrates including mammals, amphibians and fish. Such changes in fish are linked to reproduction and growth during developmental stages, diet transitions and critical life events. We used amplicon (16S rRNA) high-throughput sequencing to characterize the skin and gill bacterial microbiomes of farmed seabass and seabream belonging to three different developmental age groups: early and late juveniles and mature adults. We also assessed the impact of the surrounding estuarine water microbiome in shaping the fish skin and gill microbiomes.
Results Microbiome diversity, composition and potential metabolic functions varied across fish maturity stages. Alpha-diversity in the seabass microbiome varied significantly between age groups and was higher in older fish. Conversely, in the seabream, no significant differences were found in alpha diversity between age groups, although it was higher in the skin of juveniles. Microbiome structure varied significantly across age groups. Different bacterial metabolic pathways were predicted to be enriched in the microbiomes of both species. Finally, we found that the water microbiome is significantly distinct from all the fish microbiomes across the studied age groups, although a high percentage of ASVs is shared with the skin and gill microbiomes.
Conclusions We report important microbial differences in composition and potential functionality across the different ages of farmed seabass and seabream. These differences may be related to somatic growth and the onset of sexual maturation. Importantly, some of the inferred metabolic pathways could enhance the host coping mechanisms during stressful conditions. Our results provide new evidence suggesting that growth and sexual maturation have an important role in shaping the external mucosa microbiomes of fish and highlight the importance of considering different life stages in microbiome studies.