What is mercury in fish?

Mercury is a metal found naturally in the air, soil, and water. Fish can take in mercury from water. When you eat fish containing mercury, you can also take in the mercury. The metal builds up in your bloodstream over time. It slowly leaves the body through urine, stool, and breast milk.

For most people, eating a small amount of fish high in mercury isn't a health concern. Fish are part of a healthy diet. But in a fetus or child, too much mercury can harm the brain and nerves.

If you might become pregnant, are pregnant, are breastfeeding, or are the parent or caregiver of a child age 11 or younger, talk to your doctor about which fish are safe for you and your child to eat. If you eat a lot of fish high in mercury, it may take up to a year for your mercury levels to drop.

This is the advice from the U.S. Food and Drug Administration (FDA) and the U.S. Environmental Protection Agency (EPA) for choosing fish that's low in mercury. This advice is for children ages 1 to 11 and for people who might become pregnant, are pregnant, or are breastfeeding. Eating fish and shellfish that are low in mercury can be part of a healthy diet.

The EPA divides fish into these three lists.

• Best Choices. These fish are lowest in mercury. Some examples from the Best Choices list are salmon, canned light tuna, trout, and shrimp.
• Good Choices. These fish have more mercury than fish in the Best Choices list. Some examples from the Good Choices list are halibut and canned, fresh, or frozen white albacore tuna.
• Choices to Avoid. These fish have the highest levels of mercury. Avoid eating tilefish from the Gulf of Mexico, swordfish, and shark. Also avoid king mackerel, bigeye tuna, orange roughy, and marlin.

The EPA suggests eating 2 to 3 servings of fish a week from the Best Choices list, or 1 serving a week from the Good Choices list. A serving size is 4 oz (ounces) for people age 11 or older.

Children ages 1 to 11 can have 2 servings of fish a week from the Best Choices list. Avoid serving children fish from the Good Choices or Choices to Avoid list. Those fish may have too much mercury. A serving size is 1 oz for children ages 1 to 3, 2 oz for children ages 4 to 7, and 3 oz for children ages 8 to 10.

If you're unsure about fish that has been caught locally, check local fish advisories about the safety of the fish. If no advice is available, eat only 1 serving a week. And eat no other fish that week.