There might be something fishy going on in the kitchen of your favorite restaurant.
At randomly selected sushi restaurants in Chicago, the Chicago Sun-Times recently found cheaper, lower-end fish being passed off as expensive fish.
It's not an isolated finding. A wave of investigations, from Miami to Los Angeles to New York to Chicago, found that in many cases consumers were not getting what they paid for when it came to pricier foods like fish.
Dave Pasternak, the owner and head chef of New York's Esca restaurant, looks at thousands of pounds of fish every year to make sure his customers get what they're paying for.
"It should be illegal," Pasternak said. "It's like going to a gas station where they're selling bogus gasoline. What's the difference?"
He says some restaurants -- knowingly or unknowingly -- switch out higher-end fish with second-rate varieties behind kitchen doors.
"Well, they say [red] snappers and groupers are very commonly replaced," Pasternak said.
Red snapper usually sells for about $10 a pound, while a less-expensive fish like tilapia sells for much less.
The Sun-Times investigation of 14 restaurants found nine substituting tilapia for red snapper, four sneaking in cheaper red sea bream and one inconclusive finding.
"We were surprised that we didn't find any red snapper at all," said Janet Fuller, a staff reporter at the Chicago Sun-Times.
The ABC News affiliate in Fort Myers, Fla., looked at restaurants selling grouper. Out of eight fish sampled, only three came back as genuine grouper. At one restaurant, the expensive grouper was really emperor fish, a cheaper Southeast Asian substitute.
Some restaurant owners say they, too, are being fooled.
"Our boxes say grouper. Our invoices say grouper. It should be grouper," said Suzanne Grady, owner of the Shrimp Shack in Fort Myers.
Florida's attorney general even tested 26 samples from Tampa-area restaurants, and 17 came back as something else.
More than 100 Florida restaurants have been cited for selling bogus grouper.
"We think it's a major problem, not just in Florida, but everywhere," said John Fruin, chief of the Florida Bureau of Food and Meat Inspection.
Experts say the problem is greatest with imported fish, for which the breakdown can occur with suppliers, food labelers or restaurants.
"In every element of the food distribution chain, there are people to be blamed," Fruin said.
Experts say another common fish switch is selling farm-raised salmon as wild salmon. Some researchers say farm-raised salmon can contain more pollutants.
To protect yourself, buy from a knowledgeable vendor and go to well-known, respectable places.
Also, know what the price should be. For example, if a market is selling grouper for less than about $9 a pound, be skeptical.
In some cities like Chicago you can call the Department of Consumer Services to file a complaint if you believe you were served the wrong fish.