Nutrition
What Do You Know About Mercury in Fish?
Nearly all fish and shellfish have some mercury in them, the federal government says. Find out how much you know about mercury in fish by taking this quiz.
1. Mercury in the environment can cause health problems when it is in which form?
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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.
2. Which of these ocean creatures have the highest amount of methylmercury in them?
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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.
3. People are more likely to get the most methylmercury by eating:
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Because tuna is at the top of the food chain, it has the most mercury.
4. Mercury is most harmful to:
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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.
5. Which agency is responsible for watching mercury levels in bodies of water?
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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.
6. High levels of methylmercury can cause:
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Mercury harms the brain. It can cause a wide range of brain and nerve problems.
7. Which fish should not be eaten by pregnant or breastfeeding people, or children?
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Shark, swordfish, king mackerel, tilefish, orange roughy, and big-eye tuna have such high levels of mercury that pregnant people, people 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.
8. How much fish should a pregnant person have each week?
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People who are pregnant or breastfeeding should consume between 8 and 12 ounces per week of a variety of seafood from choices that are lower in mercury. Seafood low in mercury include anchovy, cod, herring, oyster, salmon, freshwater trout, and canned light tuna.
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Author: Lambert, J.G. M.D.
© 2000-2026 The StayWell Company, LLC. All rights reserved. This information is not intended as a substitute for professional medical care. Always follow your healthcare professional's instructions.
