Roasted fish fillet (Fig.1) represents a popular snack food in China and a preliminary analysis of the label found only fish common names, without any reference to a particular species (Table 1). Since there is still not a harmonization around the definition of these common names in China, retailers are thus induced to mislabel roasted fish fillet products for lucrative profits. This study used direct sequencing method based on fragments of 16S rRNA gene and subsequent BLAST analysis to investigate the species composition of roasted fish fillet products circulated on Chinese market. An exclusive criterion was defined to determine the labeling accuracy and only the identified species beyond the expected family was considered as mislabeling. Results highlighted an inadequate enforcement of relative rules and a high mislabeling rate of 75.9%. A worse fact was the identification of multiple fish species not only from several packages under the same common name, but also from several specimens belonging to a single package. In order to protect the consumers from economic loss and even health risk, we recommended the amendments to the existing legislations and the compilation of list of acceptable market names for fish species in China.

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BACKGROUND Species adulteration has been widely revealed around the world, and the possible reasons include declining stocks in most source areas of the world, poor transparency in the global supply chain, and difficulty in distinguishing the features of processed products. The present work selected Atlantic cod (Gadus morhua) as a case study, and developed a novel loop‐mediated isothermal amplification (LAMP) assay for Atlantic cod authentication, where a self‐quenched primer and a newly designed reaction vessel were used to realize the endpoint visual detection of the target‐specific products. RESULTS A novel LAMP primer set was designed for Atlantic cod, and the inner primer BIP was selected to label the self‐quenched fluorogenic element. The fluorophore's dequenching only occurred along with LAMP elongation for the target species. No fluorescence could be observed with both single‐stranded DNA and partially complementary dsDNA of the non‐target species. With the novel reaction vessel, both amplification as well as detection were operated in an enclosed device, and visual differentiation of Atlantic cod, negative control, and false positive generated from primer dimers was achieved. The novel assay has proved its specificity and applicability, and could detect as little as 1 pg of Atlantic cod DNA. Moreover, Atlantic cod adulteration as low as 10% could be detected in haddock (Melanogrammus aeglefinus), and no cross‐reactivity was observed. CONCLUSION The established assay could be a useful tool to detect mislabeling incidents involving Atlantic cod considering the advantages of speed, simplicity and accuracy. © 2023 Society of Chemical Industry.

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