eDNA reveals extraordinary fish diversity in the Urauchi River, Iriomote Island, Japan, a UNESCO World Heritage Site

A groundbreaking study using environmental DNA (eDNA) metabarcoding has uncovered extraordinary fish diversity in the Urauchi River, Iriomote Island, Japan—a UNESCO World Heritage Site. The research identified 254 fish species across 10–11 sampling sites along an 18.8 km stretch, with species richness peaking in mangrove zones of the mid-to-lower estuary. Notably, eDNA detected 16 conservation-priority taxa listed on Japan's Red List and six IUCN Red List species, including critically endangered Anguilla japonica and Cheilinus undulatus. The study also revealed unexpected detections of deep-sea taxa, likely due to tidal transport or diel migrations. Using high-throughput sequencing and advanced biodiversity analyses, the research demonstrated that fish biodiversity in this system remains incompletely characterized, underscoring the importance of integrating eDNA with conventional surveys for comprehensive assessments. This first molecular baseline provides a practical early warning system for detecting ecological shifts and guiding targeted conservation efforts in this globally significant watershed.

Pananganan, B. G. S., Juliano, M. G., Isowa, Y., Artigas Ramirez, M. D., Motomura, H., & Kajita, T. (2026). eDNA reveals extraordinary fish diversity in the Urauchi River, Iriomote Island, Japan, a UNESCO World Heritage Site. PeerJ, 14, e21399. Portico. https://doi.org/10.7717/peerj.21399