When it comes to your favorite sushi bar, grocery store and local diner, what's listed as "catch of the day" may actually be the one that got away.

What you really have in front of you is, well, a net gain for someone, but not you.

DNA testing on 1,200 seafood samples in 21 states revealed that 87 percent of fish sold as "snapper" and 59 percent of fish labeled "tuna" just aren't. Every - yes, every - sushi restaurant served imposter fish, and 33 percent of fish countrywide were mislabeled.

Mislabeling fish isn't just a scam, it's a health hazard.

Tilefish is served in place of red snapper, and it's on the government's do-not-ever-eat list because of high mercury content. In New York City, 94 percent of fish labeled "white tuna" turned out to be escolar, a snake mackerel with toxins that act as a "fish laxative" after a few bites, plus a high mercury content.

But eating fatty fish, loaded with heart-loving omega-3 fatty acids, is good for you, and we don't want this fish-fraud to turn you off.

So we suggest:

1. Become an informed consumer and learn how to identify fish by their appearance (skin color and texture are important clues).

2. At the fish store, check out the whole fish before they cut a filet.

3. Order whole fish or fish with skin attached in restaurants so you can identify imposters, and speak up.

4. Your healthiest choices? Salmon delivers 1,500-2,300 mg of omega-3 in every 4-ounce filet. Ocean trout contains 1,380 mg in 5.25 ounces.

Mehmet Oz, M.D., is host of "The Dr. Oz Show," and Mike Roizen, M.D., is chief medical officer at the Cleveland Clinic Wellness Institute. To live your healthiest, visit sharecare.com. Distributed by King Features Syndicate, Inc.