An investigation by the city attorney’s office has led to misdemeanor convictions against eight sushi restaurants whose “lobster rolls” apparently lacked a key ingredient.

Investigators bought the rolls at a sampling of restaurants and then sent them to a laboratory for DNA testing. The results revealed that less-expensive seafood, including crawfish or pollock, had been substituted for lobster.

“Every single one that was tested was found to be false,” said Kathryn Turner, chief deputy of the city attorney’s consumer and environmental protection unit. Consumers are “paying for a premium product. They should be getting a premium product.”

The “truth in menu” investigation was conducted in August and September 2014, outside the trapping season for California spiny lobster, which runs from October through March. Follow-up inspections were conducted by the city’s investigator and state Department of Fish and Wildlife.