Which Kinds of Fish Have Mercury?

While mercury occurs naturally in the environment and is released through industrial pollution, a more serious form of environmental contamination, methylmercury, can be harmful to people. When mercury disperses in the air, the mercury will fall into water sources, contaminating fish. Methylmercury can accumulate over time in fish. Once consumed by humans, mercury can cause illness. Levels of methylmercury vary depending on the species of fish and what that fish consumes.

Highest Levels

• Species with the highest concentration of mercury are of concern.

  Predatory species of marine life -- such as swordfish, sharks and king mackerel -- have the highest quantities of methylmercury. Contaminants in food are measured by parts per million. Fish such as sharks and swordfish have nearly 1 part per million, which is high. Some have levels of between 0.01 ppm and 0.5 ppm. The U.S. Food and Drug Administration asserts that larger fish have had time to ingest larger doses of methylmercury because they have lived longer than smaller of fish. Other fish that contain the highest levels of mercury include grouper, marlin, golden bass and orange roughy. Fish with the highest doses of mercury should not be eaten.

Lowest Levels

• Fish containing lower levels of mercury are safe to eat, in small quantities. These include shrimp, crab and salmon. It's acceptable to consume two meals a week of fish that are low in mercury, according to the Environmental Protection Agency. Catfish, clams, tilapia and herring are fish that also contain low mercury levels.

Advice

• Even game fish can be contaminated.

  The Natural Resources Defense Council says that all 50 states have advisory warnings on fish that are unsafe for human consumption. Some fish can be unsuitable for consumption by younger children because of the high concentration of mercury. The Environmental Protection Agency has an advisory list for fish that is unsafe to eat, by state.

Concerns About Tuna

• Light canned tuna is safe to eat about once a week.

  While tuna doesn't contain as much mercury as the fish you should avoid eating, tuna does contain high levels of mercury, reports the National Research Center for Women & Families. White tuna, or albacore tuna, contains higher levels of mercury than canned tuna. Tuna steaks also contain high levels of mercury. Pregnant women and young children should avoid eating fresh tuna because of the potential neurological damage that the fetus or child can sustain.