The Catch: Although nearly all fish and shellfish contain traces of mercury, not all contain dangerous amounts. In general, large, long-lived fish such as albacore tuna, king mackerel, shark and swordfish have higher levels since they've had more time to accumulate the toxin.
Smart Move: Get hooked on our low-mercury choices. Visit gotmercury.org, where you can measure your seafood-related mercury intake with a handy calculator.
Fish Tale: Tuna is one of the healthiest fish I can eat.
Fish Fact: Tuna can be dangerous. Cheap and protein dense, canned tuna remains a top fish pick for many Americans. We devour nearly 1 billion pounds each year.
The Catch: Not all tuna is created equal. According to FDA data and a study published by Rutgers University researchers, canned chunk light pink tuna has lower mercury levels than the solid white variant. That's because white tuna comes from albacore, which is a larger fish than skipjack tuna, used most often to make the light variety.
What's more, white tuna frequently exceeds a reasonably safe mercury level of 0.5 parts per million. Generally, bigeye (commonly referred to as ahi) and bluefin tuna have the most heavy metal while albacore, yellowfin and skipjack contain relatively less.
Oceana, a marine conservation group, recently tested yellowfin, albacore, bluefin and bigeye tuna samples from grocery stores in 23 different cities and discovered that average mercury levels were nearly double what existing FDA data suggests.
At sushi restaurants, the group found more than 30 percent of sushi tuna samples exceeded 1 part per million--the level allowed by the FDA for fish intended for human consumption. Similarly, in 2007 the New York Times reported that one-fourth of sushi-grade tuna (nigiri, maki and sashimi) scooped up from Manhattan restaurants had mercury levels high enough that the FDA could take legal action to remove the fish from the market.
When you consider that the FDA tests less than 1 percent of imported seafood and only a percentage of that number is tested for contaminants, it's even more cause for concern.
Smart Move: Make your next tuna sandwich with light tuna and choose safer skipjack tuna steaks at the fish market. Or consider purchasing canned tuna from St. Jude (tunatuna.com) or Wild Planet (1wildplanet.com), both of which use sustainable fishing methods, such as troll fishing, and conduct in-house mercury testing to ensure very low levels. The Oceana report suggests mackerel or "saba" as a low-mercury sushi option.
Fish Tale: Farmed salmon is a healthy and eco-minded choice.
Fish Fact: Farmed salmon was once thought to be preferable to wild, since it doesn't deplete natural stocks and is available year-round at a more affordable price.
Times change. Carnivorous in nature, salmon that are farmed are often fed large amounts of contaminated fish, causing them to carry around more toxins (PCBs, dioxins) than their wild counterparts. In fact, a 2004 study in the journal Science warned that farmed salmon contains upward of 10 times more contaminants. While these levels remain below what is considered dangerous to human health, the environmental issues concerning farmed salmon cannot be brushed aside.