ATLANTA — The menu offered fried catfish. But Freddie Washington, a pastor in Tuscaloosa, Ala., who sometimes eats out five nights a week and was raised on Gulf Coast seafood, was served tilapia.

It was a culinary bait and switch. Washington complained. The restaurant had run out of catfish, the manager explained, and the pastor left the restaurant with a free dinner, an apology and a couple of gift certificates.

“If I’m paying for a menu item,” Washington said, “I’m expecting that menu item to be placed before me.”

The subject of deceptive restaurant menus took on new life last week when Oceana, an international organization dedicated to ocean conservation, released a report with the headline “Widespread Seafood Fraud Found in New York City.”

Using genetic testing, the group found tilapia and tilefish posing as red snapper. Farmed salmon was sold as wild. Escolar, which can also legally be called oil fish, was disguised as white tuna, which is an unofficial nickname for albacore tuna.

Every one of 16 sushi bars investigated sold the researchers mislabeled fish. In all, 39 percent of the seafood from 81 grocery stores and restaurants was not what the establishment claimed it was.

“This thing with fish is age-old; it’s been going on forever,” said Anne Quatrano, an Atlanta chef who opened Bacchanalia 20 years ago and kick-started the city’s sustainable food movement. “Unless you buy whole fish, you can’t always know what you’re getting from a supplier.”

Swapping one ingredient for a less expensive one extends beyond fish and is not always the fault of the person who sells food to the restaurant. Many a pork cutlet has headed to a table disguised as veal, and many an organic salad is not.

The term organic is regulated by the Agriculture Department, but many other identifying words on a menu are essentially marketing terms. Unscrupulous chefs can falsely claim that a steak is Kobe beef or say a chicken was humanely treated without penalty.

In cases of blatant mislabeling, a chef or supplier often takes the bet that a local or federal agency charged with stopping deceptive practices is not likely to walk in the door. “This has been going on for as long as I’ve been cooking,” said Tom Colicchio, a New York chef and television personality. “When you start really getting into this stuff, there’s so many things people mislabel.”

The line between marketing something like Patagonian toothfish as Chilean sea bass or serving langostino and calling it lobster is a fine one.

In 2005, a customer sued Rubio’s, a West Coast taco chain, for misleading the public by selling a langostino lobster burrito. The FDA ruled that practice acceptable, which allowed chains like Long John Silver’s and Red Lobster to sell the crustacean called langostino and legally attach the word lobster to it. Maine lobstermen and lawmakers fought the decision unsuccessfully.

The battle often plays out on an international scale, where millions of dollars in tax revenue are at play.