WASHINGTON — Consumers who purchase mislabeled seafood can overpay by significant amounts, according to a new report by ocean conservation group Oceana.

Although the report noted seafood prices vary based on a number of factors, Oceana contends supermarket shoppers can overpay by as much as $4 for an 8-ounce filet when a less expensive fish like tilapia is swapped for a higher priced one like grouper.

At restaurants, Oceana found the price difference can be as much as $12.

“Swapping a lower cost fish for a higher value one is like ordering a filet mignon and getting a hamburger instead,” report author and Oceana senior scientist Margot Stiles said in a statement. “If a consumer eats mislabeled fish even just once a week, they could be losing up to hundreds of dollars each year due to seafood fraud.”

Oceana based its figures on online prices at Costco, Sam’s Club, FreshDirect and Peapod; menu prices at over 300 seafood restaurants in 12 cities; interviews with industry experts; and published estimates from the National Marine Fisheries Service and Urner Barry.