The fingerprints of fish in their DNA are powerful tools for tracing them to source. In a world rife with food fraud, consumers who choose fish from sustainable sources will be reassured to know that the certification process is standing up well to this scientific scrutiny. Successive years of DNA testing carried out by the Marine Stewardship Council (MSC) since 2009 have found less than 1% of mislabelled fish in hundreds of samples bearing the organisation's logo.
That's not to say there's nothing fishy on the seafood scene: far from it. Overexploitation has caused the collapse of one in four of some 1500 wild capture fisheries worldwide in the last fifty years, and put many of the rest under intolerable pressure, though the MSC's expanding global programme has seen 200 certified as sustainably managed. Once-plentiful species are under threat, and it's not easy to deflect consumer demand from those that are most prized.
With many modern fishing fleets doing much of their processing out at sea, the substitution of less valuable varieties could easily go undetected. In how much of what you can buy today, from frozen meals to fish fingers or fancier restaurant dishes, could you confidently claim to recognise what you are eating? It's a situation ripe for fraud – even within regulated fisheries. Meanwhile, the global value of illegal, unreported and unregulated fishing is estimated at €10-20 billion a year.
Small wonder, then, that some shocking scandals surfaced with the advent of DNA testing. What's tended to grab the headlines is the passing off of something cheaper as cod – or haddock, hake, tuna, sea bass and so on. There's a special problem, though, if fraud disguises the exploitation of fish stocks under particular pressure; where North Sea cod is sold as Arctic cod, for instance.
That's why the MSC, in its Traceability and Assurance in the Supply Chain (TASC) programme, is helping develop DNA checks that can even determine a fish's population of origin.
Nearly all the tests use fish cell DNA from the mitochondria rather than from the cell's nucleus, as Alison Roel, the MSC's product integrity manager, explains. It's more plentiful, its form (in closed rings rather than open threads) means it better endures the rigours of cooking and freezing, and its lineage is easier to decode because it's entirely inherited through the female line.
Comparing a gene sequence against samples in a growing worldwide bank of barcodes of different species will tell you definitively what species you're looking at. Establishing which fishery it comes from, however – and so knowing whether it merits the MSC's “sustainably sourced” logo – depends on looking for the markers of point mutations in the gene sequence. Each fishery has developed over time its characteristic pattern of these mutations, known in the jargon as “snips”. Gary Carvalho, professor of molecular ecology at Bangor University, says snip tests now provide a cost-effective way of tracing fish from ocean to fork that's “reliable enough to provide robust forensic validation and evidence in a court of law”.
The MSC tests sample products without forewarning the producer, acting as both a check and a deterrent in the MSC’s wider traceability programme. A viable DNA snip test can also help a fishery meet MSC criteria, if its certification is conditional on effective traceability, as is the case for South Georgia toothfish (‘Chilean sea bass’), the only regional stock that's sustainably managed.
Even the “negatives” – three out of 381 in the most recent round, which included the first “region of origin” testing for Atlantic cod – can help strengthen the chain of custody. They're referred back to the certifier for investigation, with the right to follow the document trail, and can show where procedures need tightening up. And so far they've found no worrying patterns of anomalies, nor had to revoke a trader's right to use the logo. Transparency, in fact, is proving positive all round.
Marine Stewardship Council is a Forum for the Future partner.