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Is That Really Yellowtail? Sushi Gene Study Reveals Rampant Mislabeling

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Fatty tuna and salmon nigiri
Fatty tuna and salmon nigiri... or is it? | Photo: CLF, some rights reserved

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.

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.

But some fish were more often mislabeled than others. Red snapper, halibut, yellowfin tuna, and yellowtail were the most fraudulent, while salmon, albacore tuna, and bluefin tuna were only rarely mislabeled.

The conservation implications of that mislabeling are a mixed bag. While some fish are replaced with species that are of greater conservation concern, as with the tuna scenario described above, a 2016 analysis found that in most cases, mislabeling actually causes people to eat more sustainably. Willette and his students found that "vulnerable" red snapper was often replaced in Los Angeles with sea bream, for instance, which is classified as a species of "least concern."

And while seafood mislabeling is, the researchers write, "an egregious offense," this kind of sustainability information could allow conservationists to prioritize their efforts, given limited resources. In that way, conservationists could more aggressively pursue the issues related to tuna while setting red snapper aside, at least at first.

If the mislabeling is a supply problem, restaurants should be considered victims rather than perpetrators.

That seafood is routinely mislabeled isn't exactly news, but Willette hopes that by illustrating the extent of the problem and highlighting the menu items that are more likely to be problematic, sushi aficionados might become savvier diners. "Telling the consumer what to eat is not my place, [but] if informed, I think the consumer can make the right choice," he says. "The consumer is very powerful. It's a lot of money, and that can have an impact." Indeed, the global fish trade is worth some $135 billion, with between a fifth and a third of the global fish supply imported to the United States.

It may be a while yet before people will think of "Patagonian toothfish" as palatable, even though it’s routinely sold as "Chilean sea bass," so the influence of marketing on seafood labeling is not likely to diminish any time soon. Still, there's a critical difference between assigning a palatable moniker to an awkwardly named species, and serving one species when you've advertised something else entirely.

While consumer advocates, conservationists, fisheries, and the restaurant industry work to sort it all out, Willette cautions not to be too hard on the restaurants themselves; he argues that they should be considered victims rather than perpetrators. "Since every restaurant had at least one case, this could be a more systemic problem. This could be happening earlier in the supply chain," he adds, rather than a handful of restaurants independently trying to pull one over on their customers.

Banner: yellowtail swimming | Photo: actor212, some rights reserved

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