Is That Really Yellowtail? Sushi Gene Study Reveals Rampant Mislabeling

2017-01-25T14:26:33+00:00 January 25, 2017|
New study uses genes to show widespread mislabeling of seafood. (Credit: Wikimedia Commons/Alpha)

New study uses genes to show widespread mislabeling of seafood. (Credit: Wikimedia Commons/Alpha)

Diners piling their leftovers into to-go boxes isn’t an unusual sight at a Los Angeles sushi bar, but for the last few years, some of those leftover slices of raw fish wound up in the most unexpected of settings: UCLA classrooms. Over the course of four years, undergraduate students taking a course called Introduction to Marine Science took nearly 400 pieces of sushi from 26 LA sushi restaurants back to the lab. Their goal? To see if the fish they were being sold was truly the fish they were being served.

(From KCET / By Jason Goldman)– Fraud in seafood has become an area of concern not just for consumers who want to know what they’re eating, but also for conservation biologists, who are concerned about the health and sustainability of global fisheries. Even when mislabeling doesn’t threaten human health – as it might when people inadvertently consume oilfish or escolar, which can lead to oily orange diarrhea, or when one kind of tuna is replaced with another, which can result in higher mercury levels – it can threaten the health of fish populations.

For example, albacore tuna is often replaced with bigeye tuna, which is not only a different species, but is also of higher conservation concern. (To confuse things even further, both the “vulnerable” bigeye tuna and the “near threatened” yellowfin tuna are commonly called “ahi,” and any of the above can be and sometimes are sold as simply “tuna.”) For even the most conscientious of sustainable seafood diners, seafood labeling is tricky business.

As identifying fish species by its DNA has become easier and cheaper, researchers have increasingly turned to a method called DNA barcoding to assess the severity and pervasiveness of seafood mislabeling. By comparing small stretches of DNA extracted from their fish to a database compiled from known species, the UCLA undergraduates and their teachers identified the species that once rested atop clumps of rice in their to-go boxes.

The students focused on nine fish in particular: albacore, yellowfin, bigeye, and bluefin tuna, along with red snapper, yellowtail, halibut, mackerel, and salmon. In addition, they sampled fish generically sold as “tuna,” which could have included any number of critters. The students also analyzed the DNA in fresh fish filets from premium grocery stores.

“We’re not the first ones to use DNA barcoding to look at seafood,” says UCLA biology instructor Demian A. Willette, “but [most of] the other papers only looked at one year.” By repeating the study four years in a row, Willette and his students were in the unique position to see whether the same restaurants sold mislabeled fish year after year, or whether mislabeling could be thought of as a series of one-time mistakes. “We were surprised to see that [mislabeling] sits between 40 and 50 percent, with the average being 47 percent each year,” he said.

In other words, nearly half of all the fish slices they tested proved fraudulent, and every single restaurant they attended – by Willette’s estimation, perhaps representing 10 percent of all LA sushi bars – had at least one case of mislabeling. And grocers were also culpable, though at a slightly lower rate of 42 percent. The study was published in the journal Conservation Biology.

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