Report: The more expensive the sushi, the higher the mercury level

"The most expensive fish have the highest mercury," said Grimur Valdimarsson, director of the Fisheries Industries Division at the United Nations Food and Agriculture Organization (FAO) in Rome. "The biggest, oldest fish have the most mercury. They are also the most highly priced - going to the sushi market."

In a survey conducted by New Jersey researchers for The New York Times that was published last week, laboratory tests found high concentrations of mercury in a sampling of tuna used in sushi in New York City restaurants, some so high the U.S.