Sustainable fish? (Image: Ian Waldie/Getty)

HOW can you tell whether the cod on sale in your local market was legally caught from a sustainable source? For now, the short answer is that you can’t. But relatively cheap, reliable genetic tests could soon give the authorities the means to identify illegally caught fish.

Many key species have been overfished in some locations but still have thriving populations elsewhere. In the North Sea, for instance, cod populations have become dangerously depleted, while the Baltic is home to some well-managed cod fisheries.

In 2005, WWF found that 100,000 tonnes of illegal cod were caught in the Barents Sea alone. Inspectors can check what species fishing fleets are bringing to shore, but it is a lot more difficult to check where they were caught.


Though fishing vessels are tracked by GPS, and are occasionally inspected while at sea, fishers can easily bypass these measures. The UK government estimates that illegal, unreported and unregulated fishing is worth between $10 and $24 billion per year worldwide – up to a quarter of the total value of the industry.

Now a consortium is claiming to have developed DNA tests that can rapidly, accurately and affordably verify claims about the origins of fish and fish products. The group, called FishPopTrace, presented their results at a meeting in Brussels, Belgium, on Wednesday.

“Successful identification of both species and fisheries lies at the core of all programmes to manage fish sustainably,” says Blake Lee-Harwood of the NGO Sustainable Fisheries Partnership. “An affordable technology that eliminates confusion and fraud will be really helpful.”

Under the leadership of Gary Carvalho of the University of Wales, Bangor, in the UK, FishPopTrace researchers from 15 groups in Europe and Russia have spent three years evaluating the test’s ability to verify the origins of fish.

They sequenced thousands of samples of Atlantic cod, European hake, common sole and Atlantic herring, and identified several hundred variations in their DNA called single-nucleotide polymorphisms (SNPs), which act as genetic markers.

Existing DNA tests that use a different type of marker, known as microsatellites, can distinguish between species but are less effective at identifying the smaller genetic differences between populations of the same species. SNPs are more common and easier to detect.

Based on these characteristic SNPs, FishPopTrace has developed “labs on a chip” to test hake, sole and herring. They have also provided data to improve a similar chip for cod that was previously developed in Canada for fish farm research.

The tests have been validated to ensure they work equally well when conducted by technicians in different labs and for fish processed in different ways. Running the test costs around $10 per sample.

The FishPopTrace team found that a test using 20 SNPs always correctly assigned Atlantic cod to one of the four major population groups. Using just one SNP, it got the origins of sole correct 96 per cent of the time, and with hake it was almost perfectly accurate with 10 SNPs.

“Fishermen sometimes wonder whether it is worth complying with the rules when it will put them at a disadvantage compared to those who are not complying,” says Jann Martinsohn, a European Commission scientific officer. “These tools will be very powerful when it comes to court cases for enforcement and will also act as a deterrent.”