When you order blackened red snapper at a restaurant, you expect to be served a beautifully peppered red snapper. But a new study found that the seafood we order in a restaurant or buy at the grocery store isn’t always what we think it is.

It’s called seafood fraud. At some point between the fish being plucked from the water to its arrival on your plate, the grocery store or seafood market, someone has mislabeled it, intentionally, to make a buck. Oceana, an international research and advocacy group, undertook a large study, collecting more than 1,200 seafood samples of fish from across the country. They purchased 46 different varieties of fish from sushi bars, restaurants, supermarkets and fish markets. “Overall, 33 percent of fish was mislabeled,” says Kimberly Warner, PhD, senior scientist at Oceana.

In response to fraudulent mislabeling of seafood, the White House organized a task force to crack down on seafood fraud as well as illegal, unreported and unregulated fishing. The task force just released an aggressive plan of action, which includes domestic and international agencies enforcing much stricter regulations on seafood traceability.

Related: Farmed Fish: Yay or Nay?

Reeling from fish fraud

In the Oceana study, the most highly substituted fish was red snapper, which was replaced by 28 cheaper species, including tilapia, other types of snapper and tilefish, which is high in mercury. “We also found fish that are not known to be sold in the U.S.,” says Warner.

Fish fraud is not just a case of getting less than what you paid for. Consuming mislabeled fish can have serious negative health consequences. For instance, some fish are high in mercury or other contaminants, which many people want or need to avoid, especially pregnant women. Some contain toxins including ciguatera, which can cause gastrointestinal, neurologic and cardiovascular symptoms.Yet mislabeling makes it more difficult to track outbreaks. Some people are also allergic to specific allergens in certain seafood.

And then there are the conservation and sustainability concerns. When Oceania tested grouper, they found that some endangered or threatened species of grouper were being sold rather than more sustainably caught grouper. Likewise, some people may prefer wild to farm-raised fish, but it’s nearly impossible to know where your fish comes from or which country it is coming from. “We put out a shrimp report where we found that in the Gulf region, farmed shrimp were being substituted for wild shrimp, and you couldn’t tell where the farmed shrimp were farmed,” says Warner. The shrimp could have come from countries that employ slave labor on their shrimp boats, she says.

“A lot of consumer are trying to make responsible choices when they buy seafood, but without some kind of accountability, there is no way to know,” says Warner. Oceana is advocating for a tracking system that would identify the species and where it was caught or farmed. “Seafood passes through many hands before it arrives to us, and it’s a very opaque supply train,” she adds.

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How to protect yourself

Until stricter tracking and labeling systems are put into place, there are a few things you can do to help ensure the seafood you’re eating is the real deal:

  • Choose your sushi carefully. Consider avoiding the varieties most likely to be swapped out: white tuna and snapper. The study found that 74 percent of sushi samples were mislabeled.
  • Eat your fish at home. Grocery stores had the lowest level of mislabeling at 18 percent, followed by restaurants at 38 percent.
  • Buy from grocery stores and fish sellers you trust, or from those that say they can trace their seafood. Whole Foods and Wegmans, for instance, offer traced seafood. Other stores may as well.
  • Ask the waiter to double-check exactly what species the restaurant is serving. If he doesn’t come back with specifics on the species and where the seafood was harvested and purchased, you may want to choose another fish.
  • Choose fish that’s widely available. “If a fish is plentiful in a certain year, you’re likely getting the real thing,” says Warner. These often included cheaper fish, like farm salmon, tilapia or Pangasius (catfish).
  • Be wary of fish in short supply. These fish are most likely to be mislabeled, and include red snapper, grouper and fresh wild salmon in winter. Fish that are mislabeled typically include local delicacies, or favorites like Atlantic Cod when sold outside of its region.

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Laurie Tarkan is an award-winning health journalist for the New York Times, national consumer magazines and websites.