That fish on your dish may not be what you wish, or even what you think it is, according to a new Canadian study.

Researchers at the University of Guelph tested more than 200 fish products from Canadian retailers, processing plants and importers by using DNA barcoding technology.

They found that 32.3 per cent of their samples did not include the type of fish they had been labelled as containing. Seven of those products originated in the U.S. and met labelling standards in that country, but failed to meet the different requirements of the Canadian system.

“At the end of the day, Canadian consumers don’t really know what type of fish they are eating,” Robert Hanner, the study’s lead author, said in a statement.

Only 17.6 per cent of the products studied were found to have been mislabelled when they arrived in Canada. The mislabelling rate was 27.3 per cent at processing plants and 38.1 per cent by the time the product arrived at stores.

“The higher mislabelling rate in samples collected from retailers, compared to that of samples collected from importers, indicates the role of distribution and repackaging in seafood mislabelling,” Hanner said.

Hanner said mislabelling can occur for various reasons. Sometimes it can be intentional, with cheaper fish purposely mislabelled as something more prestigious in an attempt to defraud customers. In other cases, common names such as tuna can be used to identify a wide variety of fish, even those which may not scientifically fit that classification.

“It creates ambiguity and opens the door for fraud or honest mistakes. It also makes it more difficult to track species at risk of indicate if a fish is a species that has higher mercury content,” he said.

DNA barcoding technology was created at the University of Guelph. It was used in 2017 to reveal that 20 per cent of studied sausages from Canada contained meats not listed on their labels. Last year, DNA barcoding led to a discovery that 52 per cent of fish samples taken from Canadian restaurants were not what they were believed to be.

Hanner says the study he authored was the first in Canada to look beyond restaurants and retailers to the broader food chain. He says researchers could learn more about fish mislabelling in Canada by tracing and testing the same batch of product at each step of the production process.