A survey by the Oceana group found that up to 30 percent of America's favorite seafood is being misrepresented and the practice may extend to the rest of the world.

In the only known study of its kind in the U.S. DNA testing confirmed that 30 percent of the 143 shrimp products tested from 111 grocery stores and restaurants were misrepresented. Oceana, the largest international advocacy organization focused solely on ocean conservation, found that consumers are often provided with little information about the shrimp they purchase, including where and how it was caught or farmed, making it difficult, if not impossible, for them to make informed choices.

"The results are not suprising," said marine biologist Nancy Bailey. "We've been tracking farmed shrimp for years and it's some of the most unregulated and mislabeled seafood in the world."

But it's not only shrimp that is the problem. About 27 percent of the seafood Americans eat comes from China -- and the shipments that the FDA checks are frequently contaminated, the FDA has found. The agency inspects only about 2.7 percent of imported food. Of that, FDA inspectors have rejected 1,380 loads of seafood from Vietnam since 2007 for filth and salmonella, including 81 from Ngoc Sinh, agency records show. The FDA has rejected 820 Chinese seafood shipments since 2007, including 187 that contained tilapia.

SNIP