Multiple fish species identified from China's roasted Xue Yu fillet products using DNA and mini-DNA barcoding: Implications on human health and marine sustainability

Highlights

• Roasted fish fillet products sold as Xue Yu in China were collected.

• DNA and mini-DNA barcoding revealed an alarming misrepresentation rate of 58%.

• Implications on human health and marine conservation have been discussed.

Abstract

Roasted Xue Yu fillet is among the most common fish products in China and the market appealing can be reflected by its high price that occasionally exceeds 300 RMB/kg in local supermarket. However, due to the lack of harmonization around the definition of Xue Yu, as well as the disability of visual inspection for transformed fish products, China's roasted Xue Yu fillet products are quite deep in the scandal of species adulteration. The objective of this study is to apply DNA and mini-DNA barcoding for the species identification of 153 roasted Xue Yu fillet products, on behalf of 30 brands, collected from 16 cities of China. The mislabeling rate was assessed according to three increasingly stringent definitions: 1) Xue Yu meaning Gadiformes species; 2) Xue Yu meaning Gadidae species; 3) Xue Yu meaning Gadus spp.

Results highlighted a very high mislabeling rate, which reached 58% even with the least stringent definition. Only 42% of the samples were identified as belonging to Gadiformes, while the others were Scorpaeniformes, Tetraodontiformes and Lophiiformes. Moreover, the implications on human health and marine sustainability were also discussed, given the identification of poisonous Lagocephalus spp. from 37 samples and the China's rising consumption of marine resources.

Introduction

The catalytic growth of scientific literature dealing with seafood traceability during the last five years demonstrated that seafood species adulteration has emerged as a very common issue prevailing on the global market (Armani et al., 2015, Cawthorn et al., 2015, Chin et al., 2016, Günther et al., 2017, Mu Oz-Colmenero et al., 2015, Shokralla et al., 2015, Wen et al., 2016, Xiong et al., 2015, Zhao et al., 2013). Several reasons accounting for this fraudulent conduct include the rising global seafood trade, particularly of processed seafood products (Armani, Guardone, La Castellana, Gianfaldoni, Guidi & Castigliego, 2015), the depleted fishery resources (Marko et al., 2004, Miller and Mariani, 2010), as well as the absence of policies governing seafood labeling and adequate enforcement in some countries (Barendse and Francis, 2015, Miller et al., 2012, Xiong et al., 2016). In addition to the financial loss, seafood species substitution has also been considered as a great threat to human health and even the protection of depleted species (Armani et al., 2015, Bornatowski et al., 2013, Cline, 2012, Triantafyllidis et al., 2010).

Recent advancements in molecular biology contributed a lot for suppressing seafood species adulteration. In particular, the power of DNA in discriminating even closely-related seafood species has been validated (Armani et al., 2012, Rasmussen and Morrissey, 2008). Over the past decades, many DNA-based identification methods have been developed and DNA barcoding of a ∼655 bp region of the mitochondrial cytochromec-oxidase I (COI) gene (Full DNA Barcoding, FDB) is among the most used approaches (Galimberti et al., 2013, Hebert et al., 2003). In addition, the utilization of a mini DNA barcoding (MDB) of less than 600 bp has recently been proved to be a feasible alternative for the identification of highly processed foods (Armani et al., 2015, Shokralla et al., 2015).

Roasted fish fillet (Fig. 1) is among the most common fish products in China. It is generally obtained from boneless fish fillet through a series of processing steps: soaking in seasoning for 1–2 h, pre-drying below 55 °C for 9–14 h followed by roasting at 150–250 °C for less than 10 min, and finally rolling to obtain the soft texture (Hsieh et al., 2010, Zhao, 2006). In particular, given the great popularity and preference with Xue Yu in Chinese public (Xiong et al., 2016), an increasing number of roasted fish fillets are now sold under the name Xue Yu. The market appealing of roasted Xue Yu fillet products can be reflected by its high price that occasionally exceeds 300 RMB per kg in local supermarket (Table 1).

The term Xue Yu, in a broad sense, generally refers to fish of the family Gadidae and to related species within the order Gadiformes (Xiong et al., 2015). However, since specific provisions for the labeling of fishery products and a standardized seafood nomenclature in China are still not available (Xiong et al., 2016), there is still not a harmonization around the definition of Xue Yu. In this circumstances, producers and distributors are tempted to use species even beyond Gadiformes for the preparation of roasted Xue Yu fillet products (Li et al., 2013).

The situation could become even worse as the residual characteristics of roasted Xue Yu fillet products are often inadequate for a morphological identification. Our previous work identified several different species from thirteen roasted Xue Yu fillet products collected on Chinese market (Xiong et al., 2015). More interesting is that all six samples from Shanghai and all three samples from Zhangzhou, Fujian province were identified at the genus level as pufferfish, Lagocephalus spp., while the other three samples from Qingdao, Shandong province, either failed the amplification or were identified as Theragra chalcogramma and Coryphaenoides acrolepis/Albatrossia pectoralis. Only one sample was collected in Wuhan, Hubei province, and was identified as T. chalcogramma.

In order to assess the extent of misrepresentation and substitution with roasted Xue Yu fillet products occurring on this market and to investigate the possible reasons behind it, in this work we enlarged the number of sample collection to 153, on behalf of 30 brands, from 16 cities of China. FDB and MDB were employed for species authentication. This work enabled the understanding of which species are currently used in the preparation of roasted Xue Yu fillet products and facilitated the protection of consumers' health and even the support of marine sustainability.