If you like fish, you will not like this: A February 2013 report revealed that seafood fraud is running rampant, and a large percentage of fish tested—namely sushi—was falsely labeled. Meaning, what’s in between those chopsticks may not be what you think.MORE: Does Your Food Contain Fake Ingredients?From 2010 to 2012, Oceana, an international nonprofit focused on ocean conservation, conducted one of the largest seafood fraud investigations ever. And their findings were, well, fishy. Of the more than 1,200 seafood samples genetically tested from 674 retail outlets in 21 states, one-third were mislabeled and replaced with cheaper, lower-grade fish, according to FDA guidelines.Among the biggest places to deceptively dupe customers—you guessed it: sushi bars. Of those tested, a whopping 74 percent of the fish was fraudulently marketed. Restaurants and grocery stores followed with 38 percent and 18 percent of fish wrongly labeled, respectively.And this isn’t just an isolated instance, according to Kimberly Warner, Ph.D., author of the report and senior scientist at Oceana. Warner says mislabeled fish has been reported since the 1930s. “We knew there was a potential this was still going on, but we didn’t know it would be this big,” she says about the study.The findings about deceptive sushi were especially surprising to Warner. “I didn’t realize sushi would be as high as it was,” she says. Case in point: 84 percent of white tuna in sushi bars was really a cheaper fish called escolar, which can cause diarrhea and is illegal in some countries outside of the U.S. “You’re not supposed to call tuna [escolar] unless it’s in a can,” Warner explains. “This wasn’t tuna at all. It can make you sick. Sushi is everywhere now—it’s profitable and popular, and they need to call it what it is.”MORE: How Eating Out Sabotages Your DietCertain Fish Are More Likely to be FraudulentThe report also found that certain types of fish were more likely to be frauds. Snapper and tuna topped the list with 87 and 59 percent mislabeled, respectively. In fact, only seven of the 120 samples of red snapper purchased nationwide was actually red snapper. Other commonly swapped fish included grouper and cod.So why do restaurants and markets do this? The answer is simple: money.“When it comes to not following the rules by the government on naming fish, some of it could be an honest mistake, but primarily it’s done for an economic gain,” explains Warner. “There’s a lot of money to be made with the billions of dollars spent in the U.S. every year on fish.”Beyond the disparity between what you bought and what you got, eating fraudulently-labeled fish could put your health at risk. For example, if you stick to “wild” salmon to avoid artificial dyes, pesticides and antibiotics, nearly two-thirds of the supposed wild salmon tested was actually found to be “farmed” salmon. Then there’s tilefish—a species that is often high in mercury content and one that pregnant women should avoid. It was often fraudulently marketed as red snapper or halibut.And if you think the FDA is cracking down on this fish fraud, think again. Today, more than 90 percent of the seafood consumed in the U.S. is imported, and less than one percent is inspected by the government specifically for fraud. That means it’s up to the consumer—you—to be more diligent.MORE: Is Ground Beef the Most Dangerous Meat to Eat?How to Safeguard Your HealthHere are three ways to protect yourself:Ask questions. When buying or ordering fish, ask: What kind of fish is this? Is it farmed or wild? Where and when was it caught? “Develop a good relationship with the people who supply you with that fish,” advises Warner. “Some restaurants are more willing and transparent in what they tell you about the fish. It’s always worth asking.”Check the price. Become familiar with the going rates for fish. As with many things, if you see a very low price that’s too good to be true, it probably is—and you are most likely getting a lower-quality fish.Purchase whole fish. Educate yourself on what your favorite fish looks like. It’s a lot easier to know what you’re getting when you buy a whole fish versus fillets or ready-made sushi.And don’t forget to lobby for better seafood tracking. “Tell your congressperson that you support the traceability law,” says Warner. This would require that all seafood is traceable from boat to plate in order to prevent seafood fraud and keep illegal fish out of the U.S. market. “If people who sell us our fish know that we want to know what we’re eating and where it came from, they will respond,” she says.MORE: The Top 14 Foods You Should Buy Organic