The environmental advocacy group Oceana said a two-year study released Thursday found that a third of all seafood samples collected in the United States were mislabeled.

The study gathered 1,215 seafood samples from 674 randomly selected grocery stores and restaurants in 21 different states.

According to the study, DNA testing found that based on U.S. Food and Drug Administration guidelines 33 percent of the fish samples collected were mislabeled.

Snapper and tuna were the most commonly mislabeled fish, at 87 and 59 percent respectively.

Cities with the highest percentage of businesses offering customers mislabeled fish were Houston, Boston, and Austin, Texas. Nearly half of the samples there were fraudulent, according to the study.

Regionally, Southern California proved to be the worst with 52 percent of the seafood samples collected by Oceana being mislabeled. Fish sampled in the state's north were mislabeled 38 percent of the time, as was the case in southern Florida. New York City fish sampled by Oceana was found to be mislabeled 39 percent of the time.

"Our findings demonstrate that a comprehensive and transparent traceability system – one that tracks fish from boat to plate – must be established at the national level," read an Oceana press release on the study. "Our government has a responsibility to provide more information about the fish sold in the U.S., as seafood fraud harms not only consumers’ wallets, but also every honest vendor and fisherman cheated in the process--to say nothing of the health of our oceans."

Cities where Oceana found the least number of mislabeled fish included Portland and Seattle, at 21 and 18 percent respectively.

For the New York City study released last December Oceana sampled 16 local sushi bars, 100 percent of which had mislabeled their fish. In the nation-wide study released Thursday, 74 percent of sushi restaurants sampled had mislabeled their fish.

Red Snapper was the most commonly mislabeled fish, with all but seven of the 120 samples collected being inaccurately labeled. Most frequent substitutions for red snapper included 13 different types of less expensive fish, among them tilapia, white bass, goldbanded jobfish, tilefish, porgy, and ocean perch.

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