Using DNA barcoding to stop seafood fraud

The dual flavours of vinegar, salt, and fresh seafood mix in your mouth while the crashing of ocean waves provides a soothing background as you catch up with friends over fish and chips. For Australians, it’s a quintessential meal and often evokes fond memories. Would you still remember that meal fondly if you knew you were eating an endangered shark?

Overfishing has been cited as the greatest threat to sharks for years now. A study released in 2021 found that one-third of chondrichthyans (sharks, rays, skates and chimaeras) are threatened with extinction. In addition, a recent study found that nearly two-thirds of coral reef shark and ray species are threatened with extinction. With these sobering statistics in mind, what’s the reason for some South Australian fish and chip stores selling endangered shark meat as ‘flake’ fillets?

The seafood industry faces a growing issue of food fraud, which includes a lack of confidence in the authenticity and provenance of seafood products and complex and obscure supply chains. The total amount of seafood traded includes a small proportion of sharks. Globally, they are fished for their meat, fins (e.g. shark fin soup), liver oil, cartilage (for medicinal purposes), and skin (for leather). A number of shark species are traded in Australia under the generic term ‘flake’. However, this ambiguous nomenclature makes it difficult for regulatory agencies to determine which species are being traded. As the authors of the new study point out, the use of the commercial label flake has been recommended by the Australian Fish Names Standards (AFNS) AS SSA 5300 to only include gummy shark (Mustelus antarcticus) and New Zealand rig (Mustelus lenticulatus), both of which have sustainable populations for fishing.

The seafood industry faces a growing issue of food fraud, which includes a lack of confidence in the authenticity and provenance of seafood products and complex and obscure supply chains.

“However, the use of AFNS is not mandatory in Australia, and this creates the risk of multiple species of shark being sold under the umbrella label of flake,” they explain. “Ultimately, the lack of clear national guidelines or labelling laws that safeguard authenticity and compliance on the sale of shark meat (e.g., show species or origin of catch) potentially opens the door to fraudulent practices.” To find out what kind of fish was being sold in Adelaide and regional South Australia, a team of researchers at the University of Adelaide analysed DNA of fish fillets sold by more than 100 retailers.

“Only 27% of all samples were identified as gummy shark (Mustelus antarcticus), […] one of only two species that is recommended to be labelled as flake in Australia,” first author Ashleigh Sharrad explained. According to the study published in the journal Food Control, at least nine species were identified, including some species that are not found in Australian waters. A total of four species, including the CITES Appendix II listed shortfin mako (Isurus oxyrinchus) and smooth hammerhead (Sphyrna zygaena), were listed. 

---

Read more: Most flake served in the humble fish and chip shop is mislabelled (and might even be endangered)

---

A small percentage (11%) of the samples and shops identified their fish species correctly, another 20% were mislabelled, and the remaining had only ambiguous labels. But does the blame lay on the shop owners? Not quiet, says Sharrad: “It is important to note that while a broad variety of species are being sold as flake, smaller retailers can’t be accused of mislabelling because they are most likely unaware when they purchase bulk, processed or frozen fish fillets. Our results highlight the need for clearer national guidelines or labelling laws for shark fillets.”

“It is important to note that while a broad variety of species are being sold as flake, smaller retailers can’t be accused of mislabelling because they are most likely unaware when they purchase bulk, processed or frozen fish fillets.”

Ashleigh Sharrad

Professor Bronwyn M. Gillanders, Deputy Dean Research and Deputy Executive Dean of the University of Adelaide, had some tips on what shop owners can do to make sure their flake is what it’s supposed to be: “They can request greater clarity around species identity and where it comes from – I suspect there is an element of ‘it’s flake’ without realising that’s a broad umbrella term. [Shop owners] can [also] help push for mandatory species and country of origin labelling (CoOL). The government currently has a discussion paper on country of origin labelling for seafood in hospitality that everyone can contribute too (noting I think this needs to be more than CoOL; species identity should also be part of it).”

Despite the frustration of scientists who work to protect these animals, these findings shows that DNA barcoding continues to be an effective tool to test ambiguous fish labels. This is especially good news for regions that are resource poor as it requires intensive resources, time, and expertise to conduct traditional taxonomic research. As cheaper and faster genetic techniques have developed, however, a greater number of biodiversity sources can be assessed using methods such as DNA barcoding. Using short segments of DNA, or a barcode, DNA barcoding has been used worldwide for rapid species identification based on DNA sequences. An efficient method for assessing biodiversity, including marine life, it has been found to be highly effective. There are many advantages to using DNA barcoding in marine life studies, for example identifying the occurrence of cryptic species common to marine ecosystems, improving identification of larvae and their adult forms, identifying non-indigenous species and potentially invasive species, detecting the illegal trade of protected species, or identifying species used in shark finning.

DNA barcoding is also useful for monitoring changes in biodiversity (e.g. expanded/contracted distribution ranges) as a result of the periodical El Niño–Southern Oscillation (ENSO) events. With the current biodiversity crisis scenario, DNA barcoding provides important opportunities for species conservation and management. Accurate species diagnosis with DNA barcoding may also be beneficial for conservation efforts when species extinction rates exceed species discovery rates. However, some say an approach based on genetics alone is insufficient to delineate new species, and it wastes funds that are desperately needed for taxonomy. The traditional morphological methods for identifying species, however, require specialized training and time. Furthermore, barcoding allows systematic quantification of groups whose identification and sampling are difficult with conventional taxonomy, such as cryptofauna. A combination of genetic and taxonomic approaches has been suggested as the best practice for integrated taxonomy by many, especially in countries that are resource-limited (e.g. many island nations in the Pacific).

The DNA barcoding of seafood seems to be an effective way to stop seafood fraud, according to some. In light of how much it affects our lives, this is a good thing. In addition to threatening the conservation of species, food fraud also is potentially damaging human health and the economy. Seafood is one of the top food allergens and anaphylactic and systemic immunological reactions can result from accidental allergic exposure to seafood due to mislabelling of species. And according to a study conducted in 2020, illegal, unreported, and unregulated (IUU) fishing costs the global economy US$26-50 billion since it accounts for as much as 55% of product sold in some countries. Some companies and countries are turning to blockchain while others have adopted DNA tissue sampling and barcoding to make sure their products are what they’re supposed to be. By doing so, policy, management, and compliance efforts can mitigate mislabelling, empowering consumers to make informed choices and promote sustainable fishing. “This is the key to building trust across the supply chain, boosting demand for local, sustainable catch and importantly, empowering consumers and retailers to make informed choices,” Sharrad said.

In addition to threatening the conservation of species, food fraud also is potentially damaging human health and the economy.

Would you like to help ensure that your seafood is sustainably caught? Designed for iPhone and Android users, the GoodFish Australia app offers consumers a comprehensive assessment of over 160 seafood options available in Australian fishmongers, supermarkets, and restaurants (covering 90% of what is available at the market).