But these weren’t cases in which tilapia was being sold as snapper. In most of the mislabeled samples, the DNA matched a closely related species and wasn’t an egregious substitution.

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The study discovered “pretty mild substitutions,” Crandall said. “We didn’t see anything that looked like some kind of comprehensive fraud, to swap out an expensive piece of seafood for something much less expensive.”

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Still, there were a few restaurants whose results might raise an eyebrow. At Bobby Van’s steakhouse, a dish advertised as a rock shrimp tempura was a DNA match with whiteleg shrimp, which is typically a much cheaper, farmed shrimp.

The testing was performed in 2015, and Bobby Van’s doesn’t have a rock shrimp tempura on the current menu. Jonathan Langle, the chain’s head of operations for Washington, said he doesn’t recall it being on the menu, and that it may have been a special.

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“We buy products that we trust and we know, and I pray to God that we didn’t get a bait and switch, where we bought something, and they switched the box,” Langle said. “It’s something that we are always concerned about.”

Restaurants have good reason to be concerned about seafood fraud, which was the subject of a wide-ranging 2013 study by the advocacy group Oceana. That organization found that one-third of all seafood sold in restaurants and grocery stores is mislabeled, sometimes fraudulently. When seafood is substituted, it could mean swapping a pricey fish for a less-expensive one and charging a brand-name markup.

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It could also have environmental and health impacts. Some instances of fish fraud could conceal overfished species that aren’t recommended on the Monterey Bay Aquarium’s Seafood Watch list, a guide that helps consumers buy sustainable seafood. Others could conceal farmed fish, which may have been raised with antibiotics and fungicides, or fish that come from countries with poor labor practices.

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Legislation in Washington authorizes consumers to sue companies for selling products that aren’t properly labeled. That was one of the motives behind the study, which was co-authored and partly sponsored by attorney Jason Rathod of Migliaccio & Rathod LLP, a law firm specializing in consumer protection and unfair trade practices.

Because the discrepancies were slight — as in the substitution of a different types of tuna or toothfish that have close genetic links — Rathod felt that a class-action suit was unlikely to succeed.

“At least from a scientific perspective, as fraud,” Rathod said. “We decided that it wasn’t worth pursuing.”

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Still, consumers might be curious to know that, at Joe’s Seafood, Prime Steak and Stone Crab, an advertised ahi tuna tartare was actually albacore tuna, which is “half the price” at wholesale, according to Glenn Casten, a fishmonger with ProFish, a seafood distributor in Washington.

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Ahi is a Hawaiian word that restaurants often use to refer to both bigeye and yellowfin tuna. Though some sushi restaurants call albacore “tombo ahi,” “you would not see, on a non-sushi menu, albacore being called ahi — or you shouldn’t,” Casten said.

“We have no knowledge of anything such as this happening at our restaurant,” a spokeswoman for the restaurant said in an email. “Joe’s Seafood, Prime Steak & Stone Crab is committed to working with our vendors to source the highest quality products and ingredients possible.”

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Another dish on Joe’s menu, the Chilean sea bass, was a perfect genetic match with its menu listing. Many of the restaurant dishes passed with flying colors; Gordon Biersch’s yellowfin tuna, McCormick and Schmick’s Chilean sea bass and the Oceanaire’s Australian barramundi were exactly as advertised. The snapper salsa verde on Legal Sea Foods’ menu was, indeed, snapper. And, curiously, McCormick and Schmick’s sesame-crusted albacore tuna turned out to be yellowfin tuna — typically, a more expensive fish.

“I’d give them a pretty good grade,” Crandall said, even of the restaurants with slight substitutions. “I’d eat at these places.”