The telltale signs to spot whether your sushi is fake, according to science

Scientists have warned that raw fish such as tuna, salmon and prawns are being swapped out for cheaper alternatives and being mislabelled as premium products.

Studies have shown that customers may not be getting what they pay for when it comes to sushi, with it being virtually impossible to spot the difference once the fish has been prepared and sliced.

Dr Marine Cusa, a marine biologist and policy expert from the Technical University of Denmark, told MailOnline: “Because mislabelling rates depend on the species, if consumers want to avoid mislabelling then they should avoid certain species and prioritize others.

“White fish like cod, haddock, and saithe in general are rarely mislabelled in Europe apart from their geographical origin.

“But tuna, swordfish, groupers, snappers, sharks, rays, have a higher species mislabelling risk.”

open image in gallery

In many cases, fish are sold under more generic terms to avoid confusion, such as the name ‘tuna’ covering 68 different species.

However, this leaves a legal loophole which can be exploited for malpractice, with scientists warning that there is widespread evidence of fish being marketed with misleading labels.

The most commonly substituted fish in nearly every country where studies have been conducted is the red snapper, which is frequently targeted for fraud.

In a 2018 study, the UK was found to be one of the worst culprits with a mislabelling rate of 42 per cent, while in the US and Canada it ranges between 80 to 100 per cent. It is usually substituted by tilapia, which is farmed around the world and sold cheaply in markets.

Another commonly found cases of forgery include tuna, which is swapped for cheaper fish up to 40 per cent of the time.

open image in gallery

In 2018, a team of international researchers sampled 545 tuna samples in six European countries, with the results indicating that 6.7 per cent was a different species than what the label had advertised.

It is often substituted for the cheaper escolar, which is also known as the ‘laxative of the sea’ due to its gastrointestinal effect.

The sale of the escolar is banned in Italy and Japan due to side effects including diarrhoea, nausea, vomiting, abdominal pain, and headaches.

Salmon is also swapped out for cheaper options, with a 2024 study of seafood products showing that the labelling of 18 per cent of 107 products was misleading.

DNA analysis found that nine of those options were in fact the much cheaper rainbow trout, while another study by Harvard University in 2020 found that salmon was the second most commonly mislabelled fish.

Other pricier fish products such as yellowtail and swordfish are also often mislabelled, with some estimates showing that up to 40 per cent of the latter has been swapped with a cheaper alternative when sold in the UK.

Americans are also believed to purchase an estimated 20,000 tonnes of mislabelled prawns each year, which is usually replaced with whiteleg shrimp, while tiger prawns are commonly mislabelled.

Selling fish under false names or listing them as having false geographic locations makes it harder for scientists to keep track of fishing patterns.

While the research shows that deliberate fish fraud in restaurants is rare, as the swapping of products happens further up in the supply change, the mislabelling of fish in sushi is a common issue.

Dr Cusa says: 'In general, fish products that are sold in supermarket chains and that have thorough labels indicating the species, catch location and catching gear, are also good choices.

'On the other hand, processed products, canned products with little information if any are, almost by definition, mislabelled. I would avoid any product with poor labelling or where the species is not indicated.

'Perhaps finally, European-caught fish are less likely to be mislabelled than imported products.'