When you order beef from a butcher and he hands you chicken, you know something’s screwy. But if you order a flounder at a restaurant, would you be able to tell if your waiter brought you tilapia?  It happens every day, with seafood lovers across the country being scammed into eating fish that isn’t what they paid for and, worse, could be putting their health at risk. Those are the conclusions of a new report from ocean conservation group Oceana, which found that 39% of seafood samples purchased in New York City were labeled as another species. While startlingly common, the practice is actually illegal according to Food and Drug Administration guidelines.  The investigators behind the report sent volunteers to collect seafood samples from restaurants (including sushi spots), as well as grocery stores. After performing DNA tests on the fish, they concluded that 15 of 19 “red snapper” samples were actually imitators. One of the faux red snappers was tilefish, which is on the FDA’s list of fish that shouldn’t be consumed by pregnant women or children because of mercury content. Seventeen out of 18 samples of tuna were, in reality, escolar, a species of snake mackerel that can cause acute gastrointestinal problems. And salmon marketed as contaminant-free, wild fish was actually farmed salmon in 25% of samples.  More from Prevention: 7 Gross Things In Your Food Other fish species being swapped with lesser versions included halibut, sole, Pacific cod, grouper, and striped bass. In most cases, the seafood was being replaced with cheaper, more abundant fish, even at high-end restaurants. So not only is your health in jeopardy, you’re paying more for a cheaper product.  And it’s not just happening in New York. “We’re seeing it everywhere we look,” says Beth Lowell, a campaign director at Oceana, adding that tests of seafood in Boston, LA, and Miami have all turned up similar levels of fish fraud. To avoid falling victim to faux fish, take the following steps:  Stick with the big chains. Stores like Whole Foods have fewer problems with seafood fraud than smaller chains or independent groceries, Lowell says, because most have internal auditing procedures designed to prevent the problem.  Buy certified. A few different programs, including the Marine Stewardship Council, certify fisheries as sustainable. Others, including Gulf Wild and Rhode Island Trace & Track, certify that fish hail from a particular state or region. These programs aren’t specifically designed to prevent fraud, Lowell says, but certified companies tend to operate under more rigorous ethical standards.  Don’t order the fish special. The report found that 39% of seafood samples purchased at regular restaurants and a whopping 76% of those from sushi restaurants were mislabeled. You can find a chef who emphasizes sustainable seafood through the Fish2Fork certification program, but if you’re unsure whether your favorite restaurant is committed to accurate seafood labeling, stick with a land-based or vegetarian protein when you eat out. More from Prevention: The 7 Most Fraudulent Foods Questions? Comments? Contact Prevention’s News Team!