When you order beef from a butcher and he hands you chicken, you know something’s screwy. But if you order flounder at a restaurant, would you be able to tell if your waiter brought you tilapia? Maybe, maybe not.  Yet it happens every day, with seafood lovers across the US being scammed into eating fraudulent fish that could be putting their health at risk. That’s according to a new report, which found that 33% of seafood samples purchased from grocery stores, restaurants, and sushi bars across the country were labeled as another species, a practice that’s illegal according to Food and Drug Administration (FDA) guidelines.  The analysis, conducted by nonprofit ocean conservation group Oceana, used DNA tests to evaluate 1,215 different fish samples. What’d they find? Red snapper appears to be the biggest scam behind the fish counter: Only seven out of 120 samples that were labeled “red snapper” were in fact that variety of fish. As many as nine other species were sold as red snapper, including tilefish, which the FDA cautions pregnant women and children to avoid because of its mercury levels.  Tuna was another sketchy choice. In 84% of instances, white tuna was being subbed with something called escolar, a species of snake mackerel that can cause acute gastrointestinal problems.  Tuna substitutions are particularly common at sushi restaurants, says Beth Lowell, campaign director at Oceana. Indeed, sushi joints are most likely to sell you a fish variety that’s different from what you ordered: In New York and Chicago, every sushi restaurant visited sold at least one mislabeled fish. Other fraud-ridden species, the report notes, include 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.  “We’re seeing seafood fraud everywhere we look,” Lowell says. And unless you’re a walking seafood encyclopedia, you won’t be able to fully avoid fraudulent fish. Fortunately, there are a few concrete steps you can take: Stick with the big chains. Stores like Whole Foods had fewer problems with seafood fraud than smaller chains or independent groceries, Lowell says, because most have internal auditing procedures designed to prevent such scenarios.  Buy certified. At the grocery store, look for labels that certify sustainable fisheries (like the Marine Stewardship Council) or else certify that fish come from a particular region (like the Gulf Wild or Rhode Island Trace & Trust). These programs aren’t specifically designed to prevent fraud, but the fishermen and companies approved by the programs operate under more ethical standards.  Don’t order the fish special. Oceana found that 38% of seafood samples purchased at regular restaurants, and a whopping 74% from sushi restaurants, were mislabeled. You can find restaurants that serve sustainable seafood (which is less likely to be fraudulent) through the Fish2Fork certification program, but if you aren’t sure how committed your favorite restaurant is to accurate seafood labeling, stick with a land-based or vegetarian protein when you dine out.  More from Prevention: 11 Fraudulent Food Ingredients Questions? Comments? Contact Prevention’s News Team.