Dr. P. Michael Bolger, a toxicologist who is head of the chemical hazard assessment team at the Food and Drug Administration, did not comment on the findings in the Times sample but said the agency was reviewing its seafood mercury warnings. Because it has been four years since the advisory was issued, Dr. Bolger said, “we have had a study under way to take a fresh look at it.”

No government agency regularly tests seafood for mercury.

Tuna samples from the Manhattan restaurants Nobu Next Door, Sushi Seki, Sushi of Gari and Blue Ribbon Sushi and the food store Gourmet Garage all had mercury above one part per million, the “action level” at which the F.D.A. can take food off the market. (The F.D.A. has rarely, if ever, taken any tuna off the market.) The highest mercury concentration, 1.4 parts per million, was found in tuna from Blue Ribbon Sushi. The lowest, 0.10, was bought at Fairway.

When told of the newspaper’s findings, Andy Arons, an owner of Gourmet Garage, said: “We’ll look for lower-level-mercury fish. Maybe we won’t sell tuna sushi for a while, until we get to the bottom of this.” Mr. Arons said his stores stocked yellowfin, albacore and bluefin tuna, depending on the available quality and the price.

At Blue Ribbon Sushi, Eric Bromberg, an owner, said he was aware that bluefin tuna had higher mercury concentrations. For that reason, Mr. Bromberg said, the restaurant typically told parents with small children not to let them eat “more than one or two pieces.”

Koji Oneda, a spokesman for Sushi Seki, said the restaurant would talk to its fish supplier about the issue. A manager at Sushi of Gari, Tomi Tomono, said it warned pregnant women and regular customers who “love to eat tuna” about mercury levels. Mr. Tomono also said the restaurant would put warning labels on the menu “very soon.”

Scientists who performed the analysis for The Times ran the tests several times to be sure there was no mistake in the levels of methylmercury, the form of mercury found in fish tied to health problems.

The work was done at the Environmental and Occupational Health Sciences Institute, in Piscataway, a partnership between Rutgers and the Robert Wood Johnson Medical School.