Fish and seafood are valued for their nutritional benefits, including lean protein and omega-3 fatty acids. A common concern is the presence of mercury, a naturally occurring element that can accumulate in fish. Understanding which fish contain lower mercury levels helps individuals make informed dietary choices, allowing them to enjoy seafood’s health advantages while minimizing potential risks.
Understanding Mercury in Fish
While mercury exists in various forms, methylmercury is the primary concern in fish. This toxic compound enters aquatic environments through natural processes like volcanic activity and human activities such as coal burning and industrial processes. Once in water, microorganisms convert inorganic mercury into methylmercury, which is then absorbed by algae and plankton at the base of the food chain.
Methylmercury moves up the food chain through bioaccumulation and biomagnification. Bioaccumulation is the uptake and retention of methylmercury by an organism over time. Biomagnification occurs as methylmercury concentrations increase at each successive trophic level, as smaller organisms are consumed by larger ones. Consequently, larger, older fish higher on the food chain accumulate more methylmercury in their tissues.
Fish with Lowest Mercury Levels
Many fish offer nutritional benefits with very low mercury levels, making them suitable for regular consumption. These species are generally smaller and lower on the aquatic food chain. Salmon, for instance, is a popular choice with low mercury content, as it typically feeds on plankton and smaller organisms. Farmed salmon may have lower mercury levels than wild-caught varieties. Sardines and anchovies are also excellent options, containing some of the lowest mercury levels due to their diet of phytoplankton and small zooplankton. Other widely available fish with minimal mercury include Atlantic mackerel, cod, flounder, haddock, herring, pollock, and tilapia. Shellfish such as shrimp, clams, scallops, and oysters consistently rank among the lowest in mercury. Freshwater trout and catfish are also good choices for their low mercury concentrations.
Fish to Limit or Avoid Due to Mercury
Conversely, certain fish species accumulate higher mercury levels and should be consumed in moderation or avoided, especially by sensitive populations. These are typically large, predatory fish that accumulate significant methylmercury through biomagnification. Examples include shark, swordfish, and king mackerel, which consistently show elevated mercury concentrations. Tilefish, particularly those caught in the Gulf of Mexico, have the highest mercury levels and are generally advised against; bigeye tuna and marlin also fall into this high-mercury category. Other species like orange roughy, bluefish, grouper, and some tuna (yellowfin, certain albacore) tend to have moderate to high mercury levels, warranting careful consideration of consumption frequency.
Safe Consumption Guidelines
To minimize mercury exposure while enjoying fish, various organizations offer consumption guidelines. The U.S. Food and Drug Administration (FDA) and the U.S. Environmental Protection Agency (EPA) advise most adults to consume at least 8 ounces of seafood per week (a typical serving is 4 ounces), encouraging a variety of fish from their “Best Choices” list, which includes low-mercury species. For individuals who are pregnant or breastfeeding, or who may become pregnant, and for young children, the FDA and EPA recommend consuming 8 to 12 ounces per week from the “Best Choices” category. For children, serving sizes range from 1 ounce for toddlers aged 1-3 years to 4 ounces for those aged 11. Check local advisories for fish caught from local waters, as mercury levels can vary.