Fish represent the greatest diversity of all vertebrates , however, understanding their gut microbiota and its significance is lacking compared to terrestrial vertebrates. Loricariidae is a speciose family of fish distributed in freshwater ecosystems of the Neotropics ,. One member of the Loricariidae, Panaque nigrolineatus, has been the focus of study by several groups due to its ability to imbibe large amounts of wood (up to 70% of the GI contents) . This fish uses spoon-shaped teeth and a suckermouth to allow for ingestion of woody material by rasping . Stable isotope studies provide support for the consumption of large amounts of cellulose as part of their diet ,,, which may offer selective advantage when river nutrients are limited during the dry season . The P. nigrolineatus gastrointestinal (GI) tract is approximately 10× its body length, providing a large surface area with many different microenvironments .