DNA Barcode Reference Library and Undetected Diversity of Fish Species in the Yuanjiang River, China

The Yuanjiang River, situated in the upper reaches of the Red River, is a crucial component of a biodiversity hotspot in the mountains of southwestern China, supporting a high diversity of fish species. Nevertheless, systematic research on fish diversity in the Yuanjiang River is scarce, scattered, and outdated. In our study, we produced 764 DNA barcodes belonging to 64 fish morphospecies to evaluate fish diversity in the Yuanjiang River. Barcoding gap analysis and DNA-based delimitation approaches achieved a high identification success rate (>93%), indicating that DNA barcoding is a practical approach for delimiting fish in the Yuanjiang River. However, four species were characterized by high levels of intraspecific divergence, generating multiple clades and/or molecular operational taxonomic units (MOTUs), suggesting that these species might comprise undetected species. Meanwhile, two closely related species within the genus Schistura, i.e., S. callichroma and S. caudofurca, cannot be delimited by the DNA barcoding technique, which is indicative of recent speciation. In summary, this study established a reliable DNA barcode reference library for fish species in the Yuanjiang River and revealed previously unknown fish diversity.