Which seafood has the highest mercury levels?

Large predatory fish consistently show the highest mercury concentrations, with shark, swordfish, king mackerel, and tilefish among the most contaminated species. Large tuna species such as bigeye and bluefin also tend to have high mercury, while smaller fish and shellfish generally have lower levels. U.S. Food and Drug Administration and Environmental Protection Agency guidance identify these specific species as carrying the greatest risk for mercury exposure and advise pregnant people, nursing parents, and young children to avoid them or limit consumption.

Why high-mercury seafood is concentrated in apex predators
Mercury enters aquatic systems primarily as inorganic mercury from natural sources and human activities such as coal combustion and artisanal gold mining. Microorganisms convert inorganic mercury into methylmercury, a form that bioaccumulates in organisms and biomagnifies up the food chain. Because methylmercury binds tightly to muscle tissue and is eliminated slowly, long-lived, large-bodied predators that eat other fish accumulate higher concentrations over their lifetimes. This ecological process explains why shark and swordfish, which are long-lived and high on the food web, routinely test highest for mercury compared with short-lived forage fish.

Health, environmental, and cultural consequences
Methylmercury is a potent neurotoxicant that can impair fetal brain development and reduce cognitive function in children, a risk emphasized by World Health Organization guidance on mercury and health. In adults, higher methylmercury exposure has been linked to cardiovascular effects in some studies. Public health advisories from U.S. agencies balance these risks against nutritional benefits of seafood, recommending lower-mercury choices such as salmon, sardines, and light canned tuna for frequent consumption.

Mercury contamination also has territorial and cultural dimensions. Indigenous and coastal communities relying on subsistence fishing can face disproportionate exposure because traditional diets often include locally caught large fish or marine mammals that concentrate mercury. Artisanal gold mining elevates local waterway mercury and can transform previously safe fishing grounds into sources of toxic exposure. Internationally, the Minamata Convention on Mercury under United Nations Environment Programme seeks to reduce emissions and releases, reflecting global recognition of mercury’s environmental persistence and human-health consequences.

Practical implications for consumers and policy
Knowing which species carry higher mercury helps individuals and policymakers reduce risk without eliminating the nutritional and cultural benefits of seafood. Regulatory monitoring programs and advisories from agencies such as U.S. Food and Drug Administration and Environmental Protection Agency provide species-specific guidance. Continued reduction of mercury emissions, targeted monitoring in vulnerable regions, and culturally sensitive advisories for subsistence communities are key strategies for lowering exposure while preserving food security and cultural practices.