Extensive Chinese fish fraud revealed by DNA study

Almost 60 per cent of a popular roasted fish fillet in China is fraudulently mislabelled, according to a sampling study using DNA barcoding.

Published in the journal Food Control, the study, which built on a previous smaller investigation, applied DNA and mini-DNA barcoding to identify the species of 153 roasted Xue Yu fish fillet products of 30 brands.

The researchers from Italy and China found that 58 per cent of the products were mislabelled, with the fish in the products found to come from different species, and note in the paper that seafood species substitution ca be “a great threat to human health” and the “protection of deplete species.”

Roasted Xue Yu fillets, which go through a series of processing steps, are among the most common fish products in China, proving to be popular with consumers and sporting a premium price tag, which can be in excess of 300 yuan (around $46) per kilogram.

However, Xue Yu (Mandarin for cod) is often a target for adulteration.

“The term Xue Yu, in a broad sense, generally refers to fish of the family Gadidae and to related species within the order Gadiformes,” the researchers said, noting that “cod” is a generic name for many species and the name itself does not assist specific species identification.

“Since specific provisions for the labelling of fishery products and a standardised seafood nomenclature in China are still not available, there is still not a harmonisation around the definition of Xue Yu. In this circumstance, producers and distributors are tempted to use species even beyond Gadiformes for the preparation of roasted Xue Yu fillet products.”

They added: “The situation could become even worse as the residual characteristics of roasted Xue Yu fillet products are often inadequate for a morphological identification.”

The researchers identified the various fish species in the Xue Yu fillets using DNA and mini-DNA barcoding, which have been developed as a means to identify species substitution, notably in high-processed foods. The DNA findings were then cross-referenced for species identification and compared with those reported on the product labels.

“The mislabelling rate was calculated considering three increasingly strict definitions of Xue Yu: 1) Xue Yu meaning Gadiformes species [cod and hake]; 2) Xue Yu meaning Gadidae species [cod, haddock, whiting, pollock]; 3) Xue Yu meaning Gadus spp.,” the report said.

According to the results, the Xue Yu fillets were identified to contain T. chalcogramma (Alaska Pollock), Liparis sp. (snailfish), and Lophius litulon (monkfish). The researchers were particularly concerned about the finding of Lagocephalus (pufferfish) DNA in 37 samples, which was a health risk.

Meanwhile, several of the package labels cited the fish Plecoglossus altivelis (sweetfish), which the researchers said would “amplify the confusion on Xue Yu”.

The mislabelling represented a threat to marine sustainability, the researchers said, as it created a “false perception” of healthy stock and market availability of the Gadiformes species.

Furthermore, the mislabelling meant Chinese consumers could not make informed choices when buying seafood, they added.

The researchers called for a standardised fish list that assigns a specific commercial name to each fish species available on the market, as well as a more stringent and mandatory requirement for how fish products are labelled.