You wouldn't think that the fish on your plate contains neurotoxins, but many popular types of seafood exhibit moderate to high levels of mercury. Though moderate consumption isn't a danger for healthy adults, pregnant women should avoid eating any high-mercury fish due to the risk of passing toxins to their fetuses. In young children, mercury can cause nervous system disorders and developmental delays. To be safe, consumers should eat fish and shellfish with the least mercury, which the FDA classifies as species with less than 0.09 parts mercury per million.
Saltwater Fish
Fishes with short life spans have limited time to absorb harmful levels of mercury into their systems. Most of the following ocean-going fish enjoy large, stable populations, and the commercial fisheries catch them use nondestructive means-though consumers should always note where the fish was caught, because countries have widely varying laws regarding fishing methods and sustainability standards. Saltwater fish lowest in mercury include butterfish, also known as sablefish or black cod; North Atlantic and chub mackerel; anchovy, herring, mullet, ocean perch, Alaska plaice, pollock, sardine, Pacific sole and squid.
Freshwater Fish
Freshwater fish may contain high levels of mercury absorbed from farm runoff and industrial pollutants that collect in lakes and rivers. Even farmed species can absorb mercury from their diets. Consumers should consider buying four freshwater species with the least mercury: catfish, freshwater trout, tilapia and whitefish.
Shellfish
Some popular types of shellfish are safe to eat and pose low levels of mercury. Consumers should try to buy shellfish from sustainable populations and away from waters with high pollutants. Lowest-mercury species include clam, domestic crab, crayfish and oyster.
Fish to Avoid
According to the FDA, four types of commonly sold fish contain dangerously high levels of mercury: shark, swordfish, king mackerel and tilefish caught in the Gulf of Mexico. These fish are predators at the top of their food chains and absorb mercury through the smaller fish they eat. Tilefish also have extremely long life spans and absorb mercury over long periods of time.
References
- National Resources Defense Council: Consumer Guide to Mercury in Fish
- U.S. Food and Drug Administration: What You Need to Know About Mercury in Fish and Shellfish
- U.S. Food and Drug Administration: Mercury Levels in Commercial Fish and ShellfishUS Food and Drug Administration: Mercury Levels in Commercial Fish and Shellfish
- Monterey Bay Aquarium: Seafood Watch
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