DNA barcoding reveals low-level species substitution, threatened species and cross-border sales in South China seafood products

Seafood products provide significant nutritional and economic benefits to humans. However, profit motives can lead to species substitution, resulting in food fraud that may impact both the economy and species conservation. Therefore, the development of accurate and convenient methods for seafood identification is essential. DNA barcoding is a reliable tool for precise species identification. This study investigated species substitution, mislabeling, and the sustainability of seafood products in the seafood markets of South China. Cytochrome c oxidase subunit I (COI) gene amplification was performed on 478 samples collected from 11 cities across three provinces (Guangxi, Guangdong, and Hainan), identifying 156 fish species across 105 genera and 60 families. A combination of morphological and DNA barcoding methods produced an atlas guide for these 156 economically important fish species. Molecular identification revealed that 9.6 % (15/156) of fish species were mislabeled, with commercial fraud detected in three processed species: Hilsa kelee , Chelidonichthys kumu , and Argyrosomus japonicus . Some substitutions may have been unintentional. Furthermore, 3.8 % (6/156) of species identified were classified as threatened by the International Union for Conservation of Nature. The study also uncovered an example of cross-border sales of fish products. These findings provide a technical reference for effective fish species identification and offer valuable insights into seafood market monitoring. • An assessment was conducted on 478 fish samples spanning 11 cities across three provinces in Southern China. • An atlas guide of 156 seafood fish species (105 genera and 60 families) was created to serve as a reference for consumers and merchants. • Seafood fish species were documented to have mislabeling rates of 9.6 % (15/156). • 3.8 % (6/156) of fish species listed as threatened on the IUCN Red List were sold alongside local and sustainable species. • One case of cross-border sales was documented.