Seafood Fraud

Image by Kevin Phillips from Pixabay

Seafood fraud is one of the biggest unsung food issues of the 21st century. It not only means the illegal mislabeling and mis-selling of fish but in some instances a criminal disregard for health and safety.

In March 2021, the Guardian newspaper analysed 44 studies on fish fraud and found that 40% of roughly 9,000 seafood products collected from various places like markets, fishmongers and restaurants in 30 countries were fake. The fish had been mislabelled. In their vernacular it was “seafood fraud on a vast global scale”.

It is fair to say that very often the consumer has no clue about whether cod is really cod or a haddock actually a haddock. Our ability to recognise fish is much worse than our ability to recognise different meats even if it might turn out to be horse in beefburgers. In fact there are 1,700 different species of seafood available globally so it seems wholly unrealistic that we would all be able to recognise the fish and shellfish being served us at the table.

The other economic factor contributing to fraud is the rise in the price of fish. In the USA, the consumer price index for seafood and risen over 27 per cent in the past ten years. It is steadily rising and with that comes an extreme incentive to illegally fish as well as commit fraud. No wonder the Guardian newspaper had hit upon a situation with enormous ramifications.

Fraud of any sort is a an unceasing challenge for authorities. There is a constant rise and evolution of fraudulent practices. The New York Times has been looking at fraud in canned tuna. This is a fish of very high value for its high protein and low fat. It is the most popular canned fish and supersedes canned salmon. 

In one of the most extreme cases, Subway — the world’s largest sandwich chain — is facing a class-action lawsuit in California that claims its tuna sandwiches “are completely bereft of tuna as an ingredient.”  To date it has been difficult to establish the provenance of the fish but the story was enough to prompt severe legal action.

Catfish fraud seems another extraordinary case in point. One of those fish is a Vietnamese catfish called Pangasius which we often eat called basu. Basu itself is not a fraudulent fish by any means and in fact is a welcome addition to the range of seafoods that can be bought off the shelf. I’ve tried it and it is versatile with all sorts of other flavours. However, it is so cheap that operators have tried to pass it off as higher value fish food such as cod, haddock and sole. Basu is very similar to sole in texture so it’s a difficult one to recognise.

Shrimp fraud is an issue globally. It’s difficult to know if the shrimp or prawn you buy at the market was caught locally or thousands of miles away. One recent report from a shrimp catcher off the coast of North Carolina was complaining of those fisherman who have tried to cash in on the Carolina prawn marketplace. A number of fresh and local sellers have started obtaining their seafood from other countries and mis-labelling it too. 

In 2020 there were two North Carolina-based crab meat companies who admitted in federal court that they were labeling crab as a U.S. product when plenty of that meat was foreign (, 2021). It happens in Cornwall in the UK too.

How Can We Recognise Fraud?

One way is to compare a suspect fish with a known species. The most appropriate method is to compare particular DNA fragments that indicate similarities an differences. The latest technology in this field uses devices found in the medical field for detecting cancer. That device is the PCR test i.e. polymerase chain reaction test which has made DNA testing almost a routine measure which is very hard to fake.

There are other studies which make use of DNA technology such as BLAST  (Basic Local Alignment Search Tool) analysis. One study used DNA authentication methods in 2016 to examine the labelling accuracy of Spanish semi-preserved anchovies (Velasco et al., 2016). The key gene of interest was the Cytb gene which is a gene coding for the protein cytochrome b that is found in electron-transport chains. 

Cytb is diverse enough to allow differentiation between closely related species and has proved invaluable in differentiating species in the  Engraulidae (anchovy) family (Santaclara et al., 2006; Velasco et al., 2016).

The mislabeling rate in the Velasco study was higher than 15%. The most substituted anchovy was the Argentine anchovy (Engraulis anchoita). Whilst there might be genuine reasons for misidentifying fish like anchovy there is also a strong liklihood that this is also done deliberately.

In a similar study reported by Giusti et al., in 2019, they looked at the authenticity of 111 products of ready-to-eat anchovy sold in Italian markets. This study used BLAST analysis of a cytb fragment amplified with a new primer pair for the anchovy family. In their study they found just one case of mislabelling where the European anchovy (Engraulis encrasicolus) was substituted  with the low-valuable Peruvian/Chilean anchoveta (Engraulis ringens).

The PCR method has been used to check shrimp species (Wilwet et al., 2021). The key as in the Giusti paper is to develop species-specific primers. In their studies of 68 commercial shrimp products, 16 per cent were mis-labeled.


Giusti, A., Tinacci, L., Sotelo, C. G., Acutis, P. L., Ielasi, N., & Armani, A. (2019). Authentication of ready-to-eat anchovy products sold on the Italian market by BLAST analysis of a highly informative cytochrome b gene fragment. Food Control97, pp. 50-57. (Article).

Santaclara, F. J., Cabado, A. G., & Vieites, J. M. (2006). Development of a method for genetic identification of four species of anchovies: E. encrasicolus, E. anchoita, E. ringens and E. japonicus. European Food Research and Technology, 223(5), pp. 609-614

Velasco, A., Aldrey, A., Pérez-Martín, R. I., & Sotelo, C. G. (2016). Assessment of the labelling accuracy of
spanish semipreserved anchovies products by FINS (Forensically Informative Nucleotide Sequencing).
Heliyon, 2(6), e00124

Wilwet, L., Shakila, R. J., Sivaraman, B., Nayak, B. B., Kumar, H. S., Jaiswar, A. K., & Jeyasekaran, G. (2021). Rapid detection of fraudulence in seven commercial shrimp products by species-specific PCR assays. Food Control124, 107871. (Article).

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