Microbial community and short chain fatty acid profiles in the gastrointestinal tract of the seaweed-eating New Zealand herbivorous fish Kyphosus sydneyanus

Kyphosus sydneyanus (family Kyphosidae), is a temperate New Zealand marine fish that is exclusively herbivorous as an adult and feeds predominantly on brown seaweed. The objective of this study was to describe the structure of the microbiota communities and the short-chain-fatty-acids (SCFA) as their metabolites, along the gastrointestinal tract of this fish, using 16S rRNA gene sequencing and gas chromatography, respectively to improve our understanding of the contribution the microbiota have to the energy metabolism in herbivorous fishes. A total of 2,354,633 bacterial sequences and 625 operational taxonomic units distributed into 20 phyla and 123 genera were obtained from all samples. Bacteroidetes, Firmicutes, Proteobacteria and Tenericutes were the major phyla in which Firmicutes (64%) was the most dominant group in section III, and Bacteroidetes (69.3%) dominated section V of the gut. At the family level, Ruminococcaceae (22.3%), Lachnospiraceae (21.83%) and Erysipelotrichaceae (10.6%) were the most dominant in section III and Rikenellaceae dominated section V at 69% of which 61.6% was composed of unknown genera . Section IV was distinct in its composition with particular high relative abundance of Tenericutes at 33.2%, and Firmicutes (27.4%) and Bacteroidetes (21.6%) being the two other dominant Phyla. Total SCFA (acetate, propionate and butyrate) concentration was highest in sections IV and V, indicating fermentation activity is highest in these sections. Acetate was highest in sections IV and V . Propionate was highest in section V consistent with high abundance of Bacteroidetes in this section. Formate was produced in sections III and IV but dropped substantially in section V. All these results could offer valuable insights and contribute to future research into herbivorous fish gastrointestinal microbiota and their capability in utilising dietary fiber.