The group bought 1200 samples from retailers and restaurants in 21 states and genetically tested it. Some of the fish swaps were benign, but not all were.
"Eighty percent of the fish we purchased was escolar. It can cause diarrhea. They call it the Ex lax of fish," says study author Dr. Kimberly Warner. "We also saw some of the higher mercury fish being swapped for safer fish."
The swaps can effect more vulnerable groups like pregnant women and children.
According to the study, retailers and restaurants are usually not behind the fraud. It comes higher up in the food chain, so to speak.
That chain is often so long that it's hard to determine where it happened. Eighteen percent of fish from retailers was mislabeled; thirty-eight percent from restaurants. Sushi restaurants were the worst.
The report singled out Revival Market and Captain Benny's as two examples of places that do it right.
Captain Benny's and it's distributor Dutchman's Seafood are owned by the same company.
Operations manager Hollis Harris says they know where everything comes from.
"The other day a guy came in with red fish. We were talking to the guy who owns the boats. Sometimes it's a farm. But we know exactly where it comes from, the quality, the whole nine yards," says Harris.