When you order fish, do you really know what you're eating?

When you order fish, do you really know what you're eating?

So you ordered the grilled mahi-mahi special — but are you really sure that's what you ate?

With seafood sales on the rise in stores across the U.S., research labs like Applied Food Technologies, recently profiled by a Smithsonian blog, are all the more important.

Applied Food Technologies is one of several labs that look at the DNA of seafood to verify it's been labeled correctly for restaurants, grocery stores, distributors, government agencies and importers. A report from Oceana, a nonprofit that aims to help conserve the Earth's oceans, says that roughly a third of all fish is labeled incorrectly.

"Of the most commonly collected fish types, samples sold as snapper and tuna had the highest mislabeling rates (87 and 59 percent, respectively)," according to the report. Approximately 44 percent of all grocery stores, restaurants and sushi retailers Oceana visited were selling mislabled seafood.

LeeAnn Applewhite, founder and CEO of AFT, told the Smithsonian that mislabeling isn't a new phenomenon.

"A fisherman goes out, harvests massive quantities of fish, whatever's in at harvest gets filleted, and once the head, tail and scales are gone, you really can't tell what it is," Applewhite said.

And of course, mislabeling is sometimes intentional. Asian catfish will fetch a higher market price if you say it's grouper.

And consumers in the U.S. could be particularly vulnerable to mislabeling. The Smithsonian noted that 90 percent of U.S. seafood is imported. Applewhite believes the problem is growing and the Oceana report might only scratch the surface.

"The FDA sometimes orders DNA testing for seafood imports, but right now, it only has the resource to do this for about 2 percent of shipments," she told the Smithsonian.

Aside from getting ripped off, mislabeled fish also pose a health risk. According to the Smithsonian, "In 2007, more than 600 people in Hong Kong got sick after eating escolar — a fish known to cause digestive issues — which they’d thought was cod."

So how does AFT do its magic?

From the Smithsonian: To identify a piece of fish, AFT staff slice off a tiny sample from a fillet, heat it up to break down the tissue and open up its cells, and spin it in a centrifuge to extract the DNA. They put this genetic material through a technique that uses polymerase chain reactions (PCR) to produce many copies of a particular DNA segments. By amplifying just a few different genes — most often, the COI gene — researchers can readily distinguish similar-looking pieces of fish and determine their species.