Why Does Tuna Have Mercury and Which Types Have the Lowest Levels?

Tuna soak up methylmercury from their prey as they grow, and canned light tuna packed from skipjack carries the least mercury of any common type.

For the full breakdown, see our best Low Mercury Tuna guide.

A can of white tuna looks like the gentler pick on the shelf, and it is not. Albacore holds roughly three times the mercury of canned light tuna, so the wording on the label tells you more than the brand or the price does.

Mercury reaches tuna through their food chain rather than the water they swim in, and no cooking method takes it back out. That leaves two practical questions for anyone who eats tuna: which type to buy, and how often it can land on the plate.

How Does Mercury Get Into Tuna?

Mercury enters tuna through their diet, not through the water passing over their gills. Mercury from natural sources and human activity settles into oceans, bacteria and other microorganisms convert it into methylmercury, plankton absorb that, small fish eat the plankton, and tuna eat the small fish. The compound climbs the food web and ends up stored in muscle tissue.

Tuna are large, predatory, and long-lived, which means they collect more methylmercury than smaller fish do. The biggest, oldest tuna carry the heaviest loads, and muscle tissue is exactly what becomes a tuna steak or a can of tuna. Cooking does not reliably reduce methylmercury, so species and serving size are the controls that work.

The main health concern is methylmercury’s effect on a developing nervous system, which puts fetuses, infants, and young children under the strictest guidance. Tuna caught by a friend or family member at a local spot follows state or local advisories first; with no advisory in place, the federal advice is one serving that week and no other fish.

Which Tuna Types Have The Lowest Mercury Levels?

Canned light tuna, usually skipjack, is the lowest-mercury tuna among the types sold in the US. Albacore, yellowfin, and tuna steak sit at one serving a week, and bigeye tuna, often sold as ahi, is the FDA’s Choice to Avoid.

Light and white are not interchangeable labels. White tuna means albacore, which generally runs higher in mercury than canned light tuna, and light tuna commonly means skipjack — the species line on the can is still worth a look. The FDA’s advice about eating fish also notes that ahi is a market name rather than a species: it can be yellowfin or bigeye, and those two land in different categories.

Labels do not always name the species, and brands switch suppliers, so an ingredient line can settle the question at the store. If sorting through cans is not how you want to spend a Saturday, our tested low-mercury tuna picks group brands by species and price.

Counting Tuna Against The Weekly Seafood Allowance

The strict numbers come from joint EPA and FDA guidance for people who are pregnant, may become pregnant, breastfeeding, or feeding children: 8 to 12 ounces of varied, lower-mercury seafood a week, or 2 to 3 servings of 4 ounces each. The advice is aimed at pregnancy, breastfeeding, and childhood rather than at a blanket limit for every adult.

Tuna counts inside that total rather than on top of it. Canned light tuna fits 2 to 3 times a week, albacore and yellowfin each fit once, and bigeye does not fit at all during pregnancy or for young children. For pregnant people, cooked fish is the recommendation, which leaves raw tuna off the list — Mayo Clinic’s pregnancy guidance says the same.

• Pick canned light tuna when mercury is the deciding factor.
• Hold albacore, yellowfin, and tuna steak to one 4-ounce serving in a week.
• Skip bigeye, and skip anything sold only as ahi when the species is unclear.
• Subtract tuna servings from the weekly 8 to 12 ounces instead of adding them.