
In early 2013 it became apparent that many beef products sold around the UK in supermarkets, shops and restaurants actually contained horsemeat. The scale of this scandal soon became apparent and almost all of the major supermarket chains were implicated (1). Beef products which had been sold as ready meals in shops and supermarkets, and consumed in schools, hospitals and care homes had actually contained horsemeat. The scale of the scandal meant that it was clear that this was no simple labelling mistake but an industrial-scale fraud motivated by the fact that horsemeat costs significantly less than beef (1).
In the years following this scandal there has been an increased level of attention placed on the origin of many types of food. Seafood has come under particular scrutiny due to the fact it is one of the most traded food products in the world and has extremely complex and convoluted supply chains which are open to fraud through mislabelling species. Unscrupulous fishermen, fish merchants and sellers have ample opportunities to mislabel fish, and the chances of being detected are extremely low.
Investigations into Mislabelled Seafood
A 2016 investigation by Oceana, the world’s largest ocean conservation organisation, analysed 25,000 seafood samples collected from around the world (2). There were eighteen examples of pangasius (a species also known as basa and Vietnamese river cobbler) being sold as more expensive species such as cod. In Italy, 200 samples of swordfish, grouper and perch were taken, with 82 per cent identified as being mislabelled, and in Hong Kong it was found that of twenty-nine samples of abalone (a type of mollusc) only one was correctly labelled (2). In total one in five of the samples analysed by the organisation was mislabelled.

In 2018 the first in-depth, large-scale study of seafood mislabelling in Europe was carried out. Over 100 scientists covertly collected samples of seafood from 180 restaurants across twenty-three European countries. DNA samples from the seafood were analysed in a laboratory and checked against the species listed on the menu. It was discovered that one-third of the restaurants had sold mislabelled seafood and in half of the samples of zander, sole, bluefin tuna and yellowfin tuna there was a 50 per cent chance that the species being sold was not the same as the one listed on the menu. In some samples, the species was swapped for a similar but less expensive alternative (such as bluefin tuna being on the menu but a cheaper species being served) but in other cases, a completely different species were supplied. Examples included pangasius being served instead of cod or haddock and in one case a sample of prawn balls was found to contain pig DNA. The results of this study were published in the academic journal Food Control (3).
There are plenty of cases of fish fraud happening in the UK. In 2013 Sainsbury’s was forced to apologise after jellied eels were sold from the supermarket’s fish counters under a sign which said the eels were “from sustainable sources from around the British Isles.” It later emerged that the eels had been imported from New Zealand (4). A 2017 study saw the Food Standards Agency collect ninety-one samples of fish and seafood from restaurants and small retailers around the UK and seven of the samples turned out to be labelled as the wrong species (5).

Subway, one of the world’s largest fast food companies, is [at the time of writing in late 2022] being sued by a consumer who claims that the chain’s tuna sandwiches “partially or wholly” lack tuna. Nilima Amin of Alameda County, California is suing the company for misleading her and other consumers over the content of the chain’s tuna sandwiches. Her lawsuit states that a marine biologist analysed twenty tuna sandwiches from twenty different Subway restaurants and found “no detectable tuna DNA sequences whatsoever” in nineteen of the samples, but chicken and pork DNA was detected. Subway has attempted to get the case thrown out, but District Judge Jon Tigar has said that the lawsuit can progress, noting that the allegations “refer to ingredients that a reasonable consumer would not reasonably expect to find in a tuna product” (6). Subway strongly maintains that their sandwiches do contain skipjack tuna with Subway North America President Trevor Haynes telling Yahoo Finance: “Our tuna is nothing but 100 per cent fantastic tuna … it’s delicious” (7).
How Does Fish Fraud Happen?
While mislabelling can happen accidentally, in the vast majority of cases it is a low-value fish being re-classified as a higher-value species, indicating that it is deliberate fraud for financial gain rather than inattention or negligence being the reason for the mislabelling. The way fish are presented to consumers makes them especially susceptible to being mislabelled as it is almost impossible to tell which species a skinned fish fillet or processed fish product comes from without DNA analysis.

A large proportion of mislabelled fish sold in European countries may be intentionally misidentified at the point of being caught thousands of miles away. Rashid Sumaila, a fisheries economist from the Institute for the Oceans and Fisheries which is part of the University of British Columbia, led a 2020 study which calculated that between 8 and 14 million metric tons of illegally caught fish are illicitly traded across the world each year. Much of this catch is made by distant fleets which operate in international waters in the Pacific and Indian oceans beyond the jurisdiction of any country. Catches may be mislabelled on board and then mixed with legitimate shipments of fish which are exported to Europe and North America (8). In this way, the mislabelling starts at the very first stage of the supply chain, with restaurants and retailers being unaware that they are buying mislabelled fish from the wholesale markets.
However, individual businesses and retailers are also guilty of fish fraud, with the owners of small businesses and independent restaurants intentionally mislabelling the fish species on their menus to dupe consumers and boost their profits. Fishmonger Rex Goldsmith, speaking the i newspaper, said:
“There have always been rogue restaurants out there selling inferior products as superior (in many different forms) … Consumers have a right to know whether the fish they are eating is farmed or wild, fresh or previously frozen, where and how it was caught. All this information is available from their fish supplier … This can only be implemented to the restaurant [and] catering trade if substantial funding is made available to local authorities for spot checks and training” (9).
Despite this concern, the checks on fish and seafood are inconsistent and sometimes non-existent. Stefano Mariani, professor of conservation genetics at the University of Salford, told the BBC that the “largely intelligence-led” testing system sometimes lets rogue businesses get away with fish fraud. He said:
“In general, there’s very little testing for authenticity and traceability – at county level, they may decide other tests, for instance, testing for potentially harmful bacteria, is more important … No step of the supply chain is completely free [from the risk of foul-play], that’s why it’s very important to invest in control, traceability and other means to minimise this problem” (5).
Solutions
A number of different ideas have been put forward to end – or at least reduce – the level of seafood fraud and mislabelled seafood which is reaching consumers. The Marine Stewardship Council has a scheme which it says guarantees the provenance of wild-caught fish (a separate scheme also exists for farmed fish). Fisheries signed up to this must prove they have followed the MSC’s “chain of custody standard” which allows fish being sold to consumers to be traced back to a specific fishery. The MSC say that 38,000 sites around the world are signed up to this scheme. These include retailers that sell seafood directly to the public, such as supermarkets, fishmongers and restaurants, but also wholesale fish retailers (10). The MSC state that less than 1 per cent of the seafood products included in this scheme are mislabelled – a figure small enough to be put down to honest mistakes during the catching, sorting and transporting process. This was backed up by a study in the academic journal Current Biology which analysed 1,463 MSC-certified seafood products between 2009 and 2016 and found only thirteen products (0.92 per cent) where “the product label was inconsistent with the species identified by DNA barcoding” (11). However, the MSC scheme has been criticised for being too limited to solve the issue of seafood mislabelling on a national or international basis. Prof Alan Reilly from University College Dublin’s Institute of Food and Health told the Guardian that the MSC’s solution was a “private sector scheme where you have to pay to be a member” and it may be the case that only reputable retailers who already had legitimate supply chains signed up the scheme (10).
A different approach uses the ‘chemical fingerprints’ of seafood to trace its origin. Although still in its infancy, this method could potentially see seafood tracked and traced internationally. Natural chemical markers known as oxygen isotopes which are in the bones of fish and the shells of molluscs can be used to identify the origin of seafood, as they are caused by the environment the animal lives in and not its biology. Early studies have shown that it is possible to match the oxygen isotopes in marine animals to specific areas on a global map, with oxygen isotope analysis having a 90 per cent success rate in distinguishing between fish, shellfish and squid which had been caught in Southeast Asia from those which had been caught in waters off the coast of southern Australia. It remains to be seen if this method can be scaled up to identify seafood which is traded and sold on an everyday basis, but it does show that technological solutions can be used to fight against seafood fraud (12).
The Future

The reality of the situation is it is easy to mislabel fish and seafood. The long and convoluted supply lines of the global seafood industry give ample opportunities for unscrupulous people to boost their own profits by mislabelling fish. The chances of being detected are low, and the penalties are light for the small number who do get caught. It is likely that it will take an outcry from consumers and action from the government to see meaningful and positive improvements in the accuracy of seafood labelling. Indeed, the only way to absolutely guarantee that you are definitely eating the species of fish which you have paid for is to purchase it as a whole fish from a wet fish counter so you can identify it yourself.
References
- Lawrence, F., Horsemeat Scandal Timeline, The Guardian, 10 May 2013.
- Oceana, 1 in 5 Seafood Samples Mislabeled Worldwide, Finds New Oceana Report, 7 September 2016.
- Pardo, M. A. et al., DNA Barcoding Revealing Mislabeling of Seafood in European Mass Caterings, Food Control, Vol 92, Pages 7 – 16, October 2018.
- Rebecca Smithers, Sainsbury’s Admits New Zealand Jellied Eels Were Mislabelled as British, The Guardian, 28 Nov 2013.
- BBC News, Restaurant Fish Fraud Not Being Caught, Experts Warn, 15 October 2018.
- Chappell, B., NPR, A U.S. Judge Rules that Subway can be Sued Over its ‘100% Tuna’ Claim, 13 July 2022.
- Sozzi, B., Yahoo Finance, Subway Exec: Our Tuna is ‘Nothing but 100% Fantastic Tuna’, 7 November 2022.
- Sumaia, U. R. et al., Illicit Trade in Marine Fish Catch and its Effects on Ecosystems and People Worldwide, Science Advances, Volume 6 Issue 9, 26 February 2020.
- Barrie, J., Restaurants Have Been Casting Off Catfish and Whiting for Cod and Selling them to Unwitting Customers, i Newspaper, 15 October 2018.
- Fleming, A., Is Your Fish a Fake? How to Spot Seafood Fraud and What to do if You’re Suspicious, The Guardian, 15 March 2021.
- Barendse, J., DNA Barcoding Validates Species Labelling of Certified Seafood, Current Biology, Volume 29, Issue 6, 18 March 2019.
- The Conversation, Where is Your Seafood Really From? We’re Using ‘Chemical Fingerprinting’ to Fight Seafood Fraud and Illegal Fishing, 12 September 2022.