Gut microbiota of Japanese eel (Anguilla japonica) larvae originates from particulate organic matter (POM) in the open ocean
The Japanese eel (*Anguilla japonica*) has a catadromous life cycle in which leptocephalus larvae drift across the western North Pacific before recruiting to coastal habitats. However, little is known about the microbial communities associated with early larval development. This study investigated the origins and potential nutritional roles of gut microbiota by comparing bacterial communities in larval gut contents and surrounding particulate organic matter (POM) using 16S rRNA gene sequencing, bacterial isolation, and stable isotope analyses. Gut bacterial communities differed from those in POM but shared several taxa, including *Tenacibaculum* and *Thalassomonas*. Isotope results suggest larvae assimilate nutrients processed by associated bacteria, highlighting the ecological importance of microbially mediated nutrient pathways in eel larval development.