DNA barcoding reveals chaotic labeling and misrepresentation of cod (鳕, Xue) products sold on the Chinese market

The increasing rate of seafood frauds, especially in the case of highly priced species, highlights the need of verifying the identity of fish products. This paper describes the application of DNA barcoding to the identification of 52 products commercialized with the Chinese term 鳕 (Xue, Cod) in supermarkets (Nanjing and Shanghai) and in the online market. Considering the lack of harmonization around the definition of Cod, the mislabeling rate was assessed according to three increasingly stringent definitions: Cod meaning Gadiformes species; Cod meaning Gadus spp.; Cod not meaning any specific species, since a qualifier (“Atlantic”, “Pacific” or “Greenland”) should be added in order to refer to Gadus morhua, Gadus macrocephalus or Gadus ogac, respectively.Results highlighted a very high mislabeling rate, which exceeded 60% even with the less stringent definition. Interestingly, only 42.3% of the samples were Gadiformes, while the others were Perciformes, Pleuronectiformes or toxic Tetraodontiformes species. Economic, ecological and health issues arising from the misuse of the term Cod are discussed in the light of the leading role of China in the seafood worldwide industry and of the increased national consumption of marine species.     

Towards more sustainable surimi? PCR-cloning approach for DNA barcoding reveals the use of species of low trophic level and aquaculture in Asian surimi

In recent years, authentication of commercialized seafood products has become a market priority. In this study, 29 Asian surimi products produced in China, India and Singapore, and commercialized in two Mediterranean countries (Egypt and Spain), were analyzed in order to authenticate species contained in surimi products. Due to the processing treatments, classical identification methods are not effective. Therefore, we conducted two molecular tracing methodologies for species identification: direct sequencing of 16S rDNA PCR products, and DNA mini-barcoding-based PCR cloning for Cytochrome oxidase subunit I (COI), with subsequent plasmid sequencing. In total, 10 fish species corresponding to 7 families were found. The Singaporean and Chinese surimi contained principally species of low trophic levels, like fringe scale sardines Sardinella fimbriata, and other, likely farmed, species such as striped catfish Pangasianodon hypophthalmus. The presence of low trophic level and aquaculture species suggests that current trends in surimi production are moving towards sustainability. The exception was a vulnerable shovelnose ray (Rhinobatos jimbaranensis) found in one product, which encourages further studies to detect the use of endangered species in such morphologically indistinct food items. We suggest PCR-cloning methodology for efficient species authentication in seafood controls, especially for mixed products.