Certain tuna types contain more mercury than others

Japanese men load frozen tuna from a cold room on to carts after a tuna auction at the Tsukiji fish market in Tokyo in this Jan. 24, 2007 photo. Japan will cut its Atlantic bluefin tuna catch by 23 percent by 2010 in an effort to help preserve stocks of the endangered fish, the country's fisheries agency announced Wednesday, Jan. 31, 2007. (AP Photo/David Guttenfelder) (AP Photo/David Guttenfelder)

April 21, 2010 2:26:26 PM PDT
Those who prefer their sushi from upscale restaurants, rather than the local supermarket, could be getting something extra with their meal.

New research which linked DNA and mercury contents shows that levels of the metal are elevated in certain species of tuna. They were higher in blue fin , sushi from lean dark red tuna, and big eye tuna samples. Yellowfin , the type typically sold by supermarkets tested lower.

Researchers at Rutgers University say the likely reason is that mercury accumulates differently in certain tissue types. The leanest fish tend to have the highest concentrations.

Also, yellowfin are typically harvested at a younger age, so the mercury does not have a lot of time to build up.