From the U.S. Food and Drug Administration

June 2014

Eat 8 to 12 ounces of a variety of fish* each week from choices that are lower in mercury. The nutritional value of fish is important during growth and development before birth, in early infancy for breastfed infants, and in childhood.

Who should know
Women who are pregnant (or might become pregnant) or breastfeeding.
Anyone who feeds young children.

What to do
1. Eat 8-12 ounces of a variety of fish a week.
That’s 2 or 3 servings of fish a week.
For young children, give them 2 or 3 servings of fish a week with the portion right for the child’s age and calorie needs.
2. Choose fish lower in mercury.
Many of the most commonly eaten fish are lower in mercury.
These include salmon, shrimp, pollock, tuna (light canned), tilapia, catfish, and cod.
3. Avoid 4 types of fish: tilefish from the Gulf of Mexico, shark, swordfish, and king mackerel.
These 4 types of fish are highest in mercury.
Limit white (albacore) tuna to 6 ounces a week.
4. When eating fish you or others have caught from streams, rivers, and lakes, pay attention to fish advisories on those waterbodies.
If advice isn’t available, adults should limit such fish to 6 ounces a week and young children to 1 to 3 ounces a week and not eat other fish that week.
5. When adding more fish to your diet, be sure to stay within your calorie needs.

Why this advice is important
Fish contains important nutrients for developing fetuses, infants who are breastfed, and young children. Fish provides health benefits for the general public. Many people do not currently eat the recommended amount of fish.

Note
*This advice refers to fish and shellfish collectively as “fish.”

Mercury occurs naturally in the environment and can also be released to the environment through many types of human activity. Mercury can collect in streams, lakes, and oceans and is turned into methylmercury in the water. It is this type of mercury that is present in fish. Methylmercury is a neurotoxin that can be harmful to the brain and nervous system if a person is exposed to too much of it.

Nearly all fish contain at least traces of methylmercury. As they feed, fish absorb methylmercury. Methylmercury tends to build up more in some types of fish than others, especially in larger fish with longer life spans.

You should avoid these four types of fish that are highest in mercury*

Tilefish from the Gulf of Mexico
Shark
Swordfish
King mackerel
As you can see from the above table, those fish are notably higher in mercury on average than the other listed fish.
*Mercury concentration data come from the FDA database located at http://www.fda.gov/Food/FoodborneIllnessContaminants/metals/ucm115644.htm.