What Do You Know About Mercury in Fish?

Mercury is an element that is usually not harmful. But in the environment, mercury changes to methylmercury. This organic form is easily absorbed by living things. It builds up in fish and animals. The more mercury in a fish or animal, the more harm it can cause.

Tuna is a large predatory fish at the top of the food chain. It has the most methylmercury. Plankton is tiny food for almost all small and some large marine animals. Smaller marine animals are food for bigger marine animals. As mercury moves up the chain, the larger fish and the longest-lived fish end up with the mercury that has been absorbed by the smaller plants and animals.

Because tuna is at the top of the food chain, it has the most mercury.

The fetus is very sensitive to the harmful effects of mercury. The harm done cannot be reversed even when the fetus is no longer exposed to the mercury. Mercury is always harmful. But it causes less harm as you get older. An adult seems to be less harmed by higher amounts of mercury, compared with a fetus, child, or adolescent.

State and tribal health programs regularly post information about mercury in area fish. They offer guides on how much fish from certain lakes, rivers, and coastal waters a person can safely eat.

Mercury harms the brain. It can cause a wide range of brain and nerve problems.

The FDA says that shark, swordfish, king mackerel, and tile-fish have such high levels of mercury that pregnant women, women who are breastfeeding, and young children should not have even a single serving of these types of fish. All of these fish are higher up the food chain.

The FDA made this recommendation to lower the effects of mercury on the fetus.

Freshwater fish include fish from rivers, streams, lakes, and reservoirs. Six ounces is about half the amount allowed for ocean (marine) fish. It is important to take into account the type of fish and where they were caught. Some areas are so polluted that fishing is not allowed. You should check with your state health department if you are unsure about the pollution status of the area where the fish were caught.