Facts About Mercury in Fish and Shellfish

by Diane, M.P.H, M.S.

Stock image of 'fish in pan with vegetables isolated on white'

Fish and shellfish are an important part of a healthy diet. They contain high-quality lean protein, omega-3 fatty acids, vitamin D, selenium, are low in saturated fat, and easy to digest. A well-balanced diet that includes a variety of fish and shellfish can contribute to heart and brain health and children’s proper growth and development. Women and young children in particular should include fish or shellfish in their diets due to the many nutritional benefits.

Unfortunately, almost all fish and shellfish contain traces of mercury. The risks from mercury in fish and shellfish depend on the amount of fish and shellfish eaten and their respective concentrations of mercury. Fish and shellfish that contain higher levels of mercury may harm an unborn baby or young child’s developing nervous system. Therefore, the Food and Drug Administration (FDA) and the Environmental Protection Agency (EPA) are advising women who may become pregnant, pregnant women, nursing mothers, and young children to avoid some types of fish and eat fish and shellfish that are lower in mercury.

Follow these recommendations for selecting and eating fish or shellfish, but serve smaller portions to a young child

1. Avoid seafood containing high levels of mercury:

  • Shark
  • Swordfish
  • King Mackerel
  • Tilefish
  • Albacore tuna, tuna steaks
  • The FDA has indicated that orange roughy and marlin may be added to this list in the future.

2. Eat up to 12 ounces (2 average [6 oz.] or 3 small [4 0z.] meals) a week of a variety of fish and shellfish that are lower in mercury:

  • Commonly eaten fish that are low in mercury are U.S.A. shrimp, Wild Alaskan salmon (fresh and canned), freshwater Coho Salmon (farmed in tank systems, from the U.S.), farmed rainbow trout, pollock, catfish, wild-caught Pacific sardines, anchovies, Sablefish/Black Cod (from Alaska and Canadian Pacific), and canned light tuna.
  • Another commonly eaten fish, albacore (“white”) tuna has more mercury than canned light tuna. Americans get about 1/3 of their methyl mercury exposure from tuna. When choosing 2 meals of fish and shellfish, you may eat up to 6 ounces (one average meal) of canned light tuna per week. (According to the FDA, a limit of  6 ounces per week of albacore tuna is allowed, as long as women do not eat it to the exclusion of low-mercury fish. If you must eat tuna, select canned light tuna over albacore, whenever possible. Otherwise, Michael Bender, the executive director of the Mercury Policy Project advises that pregnant and nursing women avoid tuna altogether.)

3. Check local advisories about the safety of fish caught by family and friends in your local lakes, rivers, and coastal areas: If no advice is available, eat up to 6 ounces (1 average meal) per week of fish you catch from local waters, but don’t consume any other fish that week.

Facts about Mercury in Fish and Shellfish

What is mercury and methylmercury?
Mercury occurs naturally in the environment and can also be released into the air through industrial pollution. Mercury falls from the air and can accumulate in streams and oceans and is turned into methylmercury in the water. It is this type of mercury that can be harmful to your unborn baby and young child. Fish absorb the methylmercury as they feed in these waters and so it builds up in them. It builds up more in some types of fish and shellfish than others, depending on what the fish eat, which is why the levels vary.

Why should women of childbearing age be concerned about methylmercury?
If you regularly eat types of fish that are high in methylmercury, it can accumulate in your blood stream over time. Methylmercury is removed from the body naturally, but it may take over a year for the levels to drop significantly. Thus, it may be present in a woman even before she becomes pregnant. This is the reason why women who are trying to become pregnant should also avoid eating certain types of fish.

Is methylmercury in all fish and shellfish?
Nearly all fish and shellfish contain traces of methylmercury. However, larger fish that have lived longer have the highest levels of methyl mercury, because they’ve had more time to accumulate it. These large fish (swordfish, shark, king mackerel, tilefish, and tuna) pose the greatest risk. Other types of fish and shellfish may be eaten in the amounts recommended by FDA and EPA.

What should I do about fish not listed in the advisory?
For more information about the levels in the various types of fish you eat, see the FDA food safety website or the EPA website at www.epa.gov/ost/fish.

What about fish sticks and fast food sandwiches?
Fish sticks and “fast-food” sandwiches are usually made from fish that are low in mercury.

The advice about canned tuna is in the advisory, but what’s the advice about tuna steaks?
Tuna steak generally contains higher levels of mercury than canned light tuna. When choosing two meals of fish and shellfish, adults may eat up to 6 ounces (one average meal) of tuna steak per week.

What if I eat more than the recommended amount of fish and shellfish in a week?
One week’s consumption of fish does not significantly change the level of methylmercury in the  adult body much. If you eat a lot of fish one week, cut back for the next week or two. Just make sure you average the recommended amount per week.

Where do I learn about the safety of fish caught recreationally by family or friends?
Before you go fishing, check your Fishing Regulations Booklet for information about recreationally caught fish. You can also contact your local health department for information about local advisories. Check local advisories, because some kinds of fish and shellfish caught in your local waters may have higher or much lower than average levels of mercury. This depends on the levels of mercury in the water in which the fish are caught. Those fish with much lower levels may be eaten more frequently and in larger amounts.

Does the FDA advisory apply to fish oil supplements that contain omega-3 fatty acids?

No. Supplements do not provide as many health benefits and nutrients as seafood.

 If you have questions or think you’ve been exposed to large amounts of methylmercury, see your doctor or health care provider immediately.


  1. “What You Need to Know About Mercury in Fish and Shellfish: Advice for Women Who Might Become Pregnant, Women Who are Pregnant, Nursing Mothers, Young Children.” EPA-823-R-04-005. U.S. Food and Drug Administration/U.S. Environmental Protection Agency. March 2004. Last updated 05/19/14.
  2. For information about the risks of mercury in fish and shellfish call the U.S. Food and Drug Administration’s food information line toll-free at 1-888-SAFEFOOD or visit FDA’s Food Safety website.
  3. For information about the safety of locally caught fish and shellfish, see the Environmental Protection Agency’s Fish Advisory website or contact your State or Local Health Department. A list of state or local health department contacts is available. Click on Federal, State, and Tribal Contacts. For information on EPA’s actions to control mercury, visit  EPA’s mercury website.
  4. U.S. Food and Drug Administration: 10903 New Hampshire Avenue, Silver Spring, MD 20993. (Tel.1-888-INFO-FDA or 1-888-463-6332).

Comments on this entry are closed.

Previous post:

Next post: