DNA Barcoding and Mini-DNA Barcoding Reveal Mislabeling of Salmonids in Different Distribution Channels in the Qingdao Area

There is an increasing demand for salmonid authentication due to the globalization of the salmonid trade. DNA barcoding and mini-DNA barcoding are widely used for identifying fish species based on a fragment of the mitochondrial cytochrome c oxidase subunit I (COI) sequence. In this study, rainbow trout (Oncorhynchus mykiss), steelhead trout (O. mykiss), and Atlantic salmon (Salmo salar) collected from two salmonid aquaculture bases in China were authenticated by DNA barcoding (about 650 bp) and mini-DNA barcoding (127 bp) to evaluate the accuracy of the two methods in the identification of different salmonid species. The results revealed that both methods could effectively distinguish O. mykiss and S. salar with 100% accuracy. However, the two methods failed to separate rainbow trout (O. mykiss) and steelhead trout (O. mykiss), which are the same species but cultured in different water environments. Moreover, salmonid samples from three main distribution channels in the Qingdao area (traditional supermarkets, online supermarkets, and sushi bars) were identified by the two methods. Substitution of S. salar with O. mykiss was discovered, and the 27.78% overall substitution rate of salmonids in the Qingdao area was higher than those in other regions reported in previous studies. In addition, the mislabeling rates of salmonids from traditional supermarkets, online supermarkets, and sushi bars were compared in this study. The mislabeling rate was significantly greater in sushi bars (50%) than in the other two channels (16.67%), suggesting that stronger monitoring and enforcement measures are necessary for the aquatic food catering industry.