DNA barcoding species identification unveils mislabeling of processed flatfish products in southern Italy markets

•Forty flatfish fillets were processed by COI DNA barcode for species identification.•Fillets labeled as European plaice were found to include 3 species.•Fillets labeled as Common sole were found include two species.•The percentages of mislabeled products was higher than those previous detected. The frozen seafood market in southern Italy is susceptible to fraudulent species substitution of fresh and frozen flatfish fillets, but as yet this has been poorly tested. Forty fresh and frozen fillet samples labeled as European plaice (Pleuronectes platessa) and common sole (Solea solea) were randomly purchased at several supermarkets in Sicily and Calabria. A 660bp of COI barcode sequence was obtained from the fillets and compared with the sequences of a COI barcode reference library previously constructed using 20 samples of morphologically validated Pleuronectiformes species and 43 additional COI flatfish sequences from GenBank. The screening allowed us to detect mislabeled products both for European plaice (35% of the cases) and common sole (41% of the cases). P. platessa was replaced by Platichthys flesus, Limanda limanda and Pangasius hypophtalmus; S. solea was replaced by Arnoglossus laterna. The results of our investigation adds further concern regarding the trade of processed flatfish products from both public health and economic points-of-view. Our findings reinforce other evidence in calling for increased traceability of food products and the assessment of authenticity of raw material by competent supervisory authorities.