Adulteration: DNA project reveals fishy nature of fish labeling

In a restaurant, it’s usually obvious when the server brings out the wrong order. Sometimes, however, it may require advanced DNA testing to even realize the order isn’t what you expected.

Dr. Jennifer McDonald, a biology professor at Fanshaw College in Ontario, Canada, directed her molecular biology students on a homework assignment that would reveal a lot about the food they ate every day.

“Their Super Important Homework Assignment™ was to go out for sushi and take a small sample home in a Ziploc bag,” she said in a series of tweets that have spread rapidly on Twitter. (She also directed students to eat the rest of the meal. “Wasting food is uncool.”)

The students labeled their samples with the species they, and likely the restaurants that served them, believed the fish to be. Back in the campus lab, they extracted the DNA from the fish, and amplified the CO1 gene using polymerase chain reaction (PCR). The class nailed it, with every student successfully executing the difficult method.

“So now my class of 16 will have a set of samples to look at real-life prevalence of food fraud in the seafood industry,” McDonald tweeted.

And the results did, indeed, reveal evidence of food fraud. Of nine workable sequences, just two were labelled correctly. Fish labelled as red tuna was tilapia, rainbow trout was coho salmon, Pacific cod was Atlantic cod. Worryingly, fish labeled as albacore (or “white”) tuna was escolar.

“This is dangerous,” McDonald said. “(It) can cause extreme gastrointestinal distress.”

Most worryingly of all, one sample of supposed salmon came back as matching the DNA profile of a body louse, meaning the sample was contaminated to the point where students couldn’t identify what species of fish it belonged to.

Food fraud — what gives?

McDonald and her class have elaborated on a known issue. Food fraud, known as “adulteration” in the industry, is a big problem in the seafood business, much to the frustration of honest restaurants, retailers and processors who are just trying to sell good products. Your local sushi joint often has no idea the fish they sell isn’t what it’s labeled to be — they’re commonly lied to about it from somewhere else on the supply chain.

In a bigger study conducted by the conservation group Oceana, DNA tests revealed that 21% of fish sampled had been inaccurately labelled. Usually, fish considered higher quality were substituted for less expensive varieties. A similar number was found by another study conducted by the state of New York — 27% of samples were falsely labelled.

As our food supply chain becomes more global, and more complicated, it can be tricky to stop these bumps along the line. This problem affects more than just seafood, for instance, in 2013 the European food industry was rocked by a scandal in which horse meat was found in many products advertised as containing only beef.

Speciation tests and other adulteration screening methods are one way food companies can protect their consumers — and their brand — from unintended adulteration. Still food fraud remains a high profile topic today, but blockchain and other new technologies may allow us to see a more secure food supply chain in the near future.