A Slimy Business: the Future of Fish Skin Microbiome Studies.

Fish skin contains a mucosal microbiome for the largest and oldest group of vertebrates, a location ideal for microbial community ecology and practical applications in agriculture and veterinary medicine. These selective microbiomes are dominated by Proteobacteria, with compositions different from the surrounding water. Core taxa are a small percentage of those present and are currently functionally uncharacterized. Methods for skin sampling, DNA extraction and amplification, and sequence data processing are highly varied across the field, and reanalysis of recent studies using a consistent pipeline revealed that some conclusions did change in statistical significance. Further, the 16S gene sequencing approaches lack quantitation of microbes and copy number adjustment. Thus, consistency in the field is a serious limitation in comparing across studies. The most significant area for future study, requiring metagenomic and metabolomics data, is the biochemical pathways and functions within the microbiome community, the interactions between members, and the resulting effects on fish host health being linked to specific nutrients and microbial species. Genes linked to skin colonization, such as those for attachment or mucin degradation, need to be uncovered and explored. Skin immunity factors need to be directly linked to microbiome composition and individual taxa. The basic foundation has been laid, and many exciting future discoveries remain.