Tackling seafood fraud - Fisheries forensics

Trawl of mixed fish

Bewildering species diversity in mixed trawl of fish from Malaysian waters collected for genetic analysis - you won't spot any cod in here!

1 June 2012 by Gary Carvalho and Stefano Mariani

Media attention to mislabelled seafood is helping bring the scale of illegal and unregulated fishing to consumers' attention. Gary Carvalho and Stefano Mariani explain how genetic tools can promote sustainability and make sure the fish we buy is what it says on the label.

Hardly a day goes by without more media coverage of the fragile state of our fisheries, or exhortations from TV chefs to give up high-street favourites like highly threatened Atlantic cod in favour of more sustainable dab or pollock. Such high-profile attention is not misplaced; recent estimates indicated around 88 per cent of fish stocks in European waters were overexploited last year.

Globally the situation is no better; over the last 50 years, 366 out of 1519 world fisheries have collapsed - nearly one in four. Estimating sustainable rates of fishing is notoriously difficult, partly because natural fluctuations in many fish populations make it difficult to estimate the numbers needed to replace those that are caught. The situation is made worse by an alarming level of so-called IUU fishing (illegal, unreported and unregulated), which is not included in stock assessment.

The global value of legal fishing is estimated at €55-60 billion. The estimated global value of IUU activities is €10-20 billion. Before 2010 (when new regulations were introduced), €1·1 billion of that illegal fish was imported into the EU every year. IUU fishing remains the biggest global threat to the sustainable management of fish stocks, and it's not restricted to remote areas with limited governance; estimates from the first decade of this century revealed IUU tuna and swordfish in the Mediterranean was 40-50 per cent, North Sea cod up to 50 per cent, and sharks across European waters up to 75 per cent.

How do we know what fish we're eating?

While protein from land animals comes almost entirely from a handful of artificially selected species (cattle, sheep, pigs, chickens) over which humans have exerted complete control for millennia, protein from the oceans is still harvested from large wild populations, comprising hundreds of species whose biology we don't yet fully understand. Public knowledge even of emblematic species like Atlantic cod - a mainstay of European and American food culture for over 500 years - is surprisingly poor. In a recent survey less than one person in three was able to identify a cod when shown a photograph of a freshly caught specimen - never mind less popular fish species!

IUU fishing remains the biggest global threat to the sustainable management of fish stocks.

Part of the problem stems from the fact that, in many countries, fish is marketed in such a processed state it's hard to know what you're looking at. Together with over-exploitation, this practice has created the ideal conditions for product substitution, whereby less valuable, and often more readily available, species are mislabelled as more sought-after ones. Such activity causes serious harm at many levels: fraudulent seafood industry operators make huge profits; consumers won't understand the diversity of natural food resources nor how threatened some of them are; and some people might unknowingly be exposed to the risk of food allergies when they buy mislabelled products.

All this is a significant threat to consumer trust and to the livelihoods of diligent fish-industry operators who do the right thing.

What we urgently need is a framework to promote compliance with regulations, and the political will and mechanisms to enforce those regulations, through prosecution where necessary.

Tackling seafood mislabelling and IUU activities

Relatively strict EU legislation on labelling and traceability has existed since 2000, and a new regulation to stop imports of IUU fish products into the Community came into force in January 2010.

The problem is that traditional certification is vulnerable to fraud, especially since fish are processed at sea and many of the features that distinguish different species are removed. What regulators need is an independent forensic test that will work equally well from the moment they are caught to when they are served up on our plates, to identify whether they have been caught illegally, or to check whether a product in a supermarket or restaurant is what the label says.

Sampling fish in Malaysia

Gary Carvalho (middle) and colleague, Martin Taylor (left) from Bangor University, with fisheries officer Abdul Rahman, sampling fish in Malaysia for genetic analyses

The only reliable approach is to use DNA-based technologies, and that's where our work comes in. DNA tests are sensitive enough to distinguish species and even populations, quick enough to be cost-effective, and reliable enough to provide robust forensic validation and evidence in a court of law.

The illegal substitution of one species for another is best tackled by a method known as 'COI barcoding', a process that works by analysing the 600 base-pair sequence of the mitochondrial DNA cytochrome c oxidase I gene. DNA results from fish samples can be matched against the Barcode of Life Data system - external link - which currently contains the DNA sequences of nearly a third of known fish species. The method is cost-effective and reliable. Virtually any product advertised or sold as a particular species, anywhere in the world, can be verified unequivocally using a COI barcoding test.

But this doesn't give us enough information to identify biological populations or regional stocks within a species, which is crucial if we want to know when a threatened or lower quality fish is being substituted for another of the same species. For this we need to look at an emerging class of genetic markers called SNPs (single nucleotide polymorphisms). These represent novel genetic differences in the DNA sequence, known as 'point mutations'. The frequencies of each SNP variant are different for (and so can be used to distinguish between) different regions or populations, because interbreeding fish that share a common spawning ground are isolated to varying degrees from other groups, allowing independent changes in SNP frequencies - a 'population signature'. SNPs are abundant and widespread across every genome and are highly informative for understanding the fundamental biology and conservation needs of different species, and ideally suited for traceability purposes.

Importantly, data from SNPs are especially good for creating a reference database, because they are easily reproduced among different laboratories; newly collected data can then easily be compared with reference data. Another benefit is that SNPs vary due to both demographic and environmental factors - that is, they vary because of migration and population isolation, and also because of adaptive changes in the genome through natural selection, as groups of fish adapt to specific local environments. This greatly improves the power to detect the distinct signatures of local and regional groupings.

Fish fingerprinting in practice

A flurry of COI barcoding studies over the last five years has revealed astounding levels of fish mislabelling in at least three continents, affecting major seafood species including cod, hake, red snapper, haddock and tuna. In most cases, cheaper and more plentiful species were being substituted for more sought-after produce; whereas in some cases, endangered and protected species were labelled under deceptively generic names.

Most recently, Atlantic cod (Gadus morhua) has been discovered marketed as the related, but less threatened, Pacific cod (Gadus macrocephalus). This kind of substitution is particularly detrimental to environmentally aware consumers, who rightly expect 'eco-labelling' will help them avoid species or stocks that are under severe pressure.

Five species of typical British fish

Family members - five species typical of British and Irish waters, from top to bottom: cod, saithe, pollock, haddock, whiting. DNA barcoding has shown that the latter four may often be sold labelled as cod.

A European consortium, FishPopTrace, recently used SNPs for the first time to trace fish and fish products back to their population of origin. They developed a 'SNP chip' for each of four species: sole, hake, cod and herring. These devices contain chemicals that recognise only those SNP markers specific to a species or population. DNA samples taken from the fish are exposed to the SNP chip in the lab, where the relative frequencies of each SNP are revealed. These devices enabled researchers to test the identity of 1,536 possible SNPs for each population. The result was a series of diagnostic patterns of SNP frequencies - the population signatures we mentioned earlier. This provides a baseline against which we can compare fish of unknown origin.

One application of SNPs has been to distinguish between different types of the same cod species. Cod from the Baltic are worth less than Atlantic cod because they tend to have lower quality flesh and more contaminants. Having established a reference database, researchers looked at 20 SNPs and identified the origin of every fish from a sample collected from both regions. Even with just 10 SNPs, 96 per cent of the unknown samples were still correctly identified. In another case, FishPopTrace distinguished between North Sea sole (Solea sole) and its more highly prized Mediterranean counterpart with similar accuracy - using just one SNP.

SNP markers are so reliable that they have direct applications for control and enforcement authorities, and ultimately for the confidence of those of us who like to know where our fish dish has come from. They should become the standard tool for identifying source populations, and for verifying the origin of landed fish and processed fish products. SNPs can provide the technology for fish traders, processors and retailers to self-certify, for governments to enforce regulations, and give law courts access to unambiguous scientific evidence.

If coordinated action is taken at national and transnational levels, the seafood industry has a fresh opportunity to operate in a more transparent way, letting us trace our fish 'from ocean to fork', with the many benefits for the environment and the consumer that this will bring.


Gary Carvalho is professor of molecular ecology at Bangor University.

Stefano Mariani is reader in wildlife biology at the University of Salford.