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The swordfish you’re eating might actually be shark

Chase Purdy

Only a striking 1% of fish imported into the United States is tested to ensure that what’s marketed on the outside of a package matches what’s on the inside. For a nation that imports about 90% of its seafood, that can have profound consequences.

It’s not that we don’t know how to test fish products. There just isn’t a cheap and fast way to do it. Which is one reason a team of scientists in Italy set out to study shady swordfish.

Some 45% of the world’s swordfish is caught off the southern coast of Italy in the Mediterranean, making the region a prime market for counterfeit fish. Demand is often high, especially in the summer months, which drives up the price of swordfish—and invites fraud in the form of mislabeling and misbranding.

The most common thing people are eating when they think they’re biting into swordfish is shark—specifically shortfin mako or blue shark. That’s the case with about 15% of all swordfish, the team found in a study published on Nov. 1 in the journal Foods. Not only is that harmful for health (shark meat can contain a lot of arsenic), but it can also lead to biodiversity problems, hurt local businesses, and prop up illegal trading of threatened species.

That’s why this team of scientists is pushing for increased use of a testing method called COIBar–RFLP, which treats fish DNA like a barcode you’d scan at a grocery store. Genetic barcoding has been around for years, but the method has often been time consuming, and the genetic database for fish has been been limited to a short list of species, which includes cod, grouper, snapper, and tuna.

The Italian scientists are looking to consolidate the process by analyzing shorter sections of DNA. In practice, this has meant focusing on the cytochrome oxidase I gene, which has been found to be dissimilar-enough across fish species that it can be used to distinguish one species from another. By analyzing these shorter sections of DNA, the scientists behind the study are contributing to a growing database that can be checked to authenticate what’s being sold.

As an added boon, is is cheaper and faster. Compared to more thorough DNA sequencing, which costs about 17 euros (about $19) per sample and can take about 24 hours, the COIBar–RFLP method costs 10 euros (about $11) and takes about seven hours.

Those costs could go down over time. It would be crucial, though, for governments work together to adopt the technology. Right now, there is no international collaboration moving toward adopting a single method for combatting commercial fraud in fishing, nor is there a mandate making this technology the default for testing. Likewise, there is not agreed-upon list of reputable third parties to turn to for testing and authentication.

In the European Union, for example, legislation only suggests (pdf) that genetic barcoding should be used in seafood traceability. There is no mandate to enforce using the most effective technology. In the United States there are laws that prohibit seafood fraud, but the government has been criticized for not vigorously enforcing (pdf) those rules.

In March, the watchdog group Oceana released a report on fraud across the US in the fish supply, finding that 21% of fish is mislabeled. Swordfish isn’t as much of a problem in the country as it is in Italy, but buyer beware: The most commonly mislabeled fish were sea bass, snapper, halibut, flounder, sole, lobster, catfish, and scallops.

 

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