What seafood has high levels of mercury?

October 22, 2025 •

3 min read

According to the U.S. Food and Drug Administration (FDA), nearly all fish and shellfish contain traces of mercury, but levels vary widely depending on the species. This makes it crucial to understand what seafood has high levels of mercury, particularly for vulnerable groups like pregnant women and young children.

Quick Summary

This article outlines which types of seafood are known to contain high levels of mercury, a neurotoxin that bioaccumulates in the food chain. It explains the biological factors influencing mercury content and provides expert-backed recommendations for safe consumption based on species and population risk.

Key Points

High-Mercury Seafood to Limit: Avoid or limit consumption of large predatory fish like shark, swordfish, and King Mackerel, as they accumulate the most mercury.
Low-Mercury Seafood is Safe: A variety of fish and shellfish, including salmon, shrimp, sardines, and canned light tuna, contain very low levels of mercury and are safe for frequent consumption.
Bioaccumulation is the Cause: Larger and older predatory fish have higher mercury concentrations due to biomagnification, accumulating mercury from the smaller fish they eat over their lifespan.
Vulnerable Groups Need Caution: Pregnant and breastfeeding women and young children should be most cautious about high-mercury seafood, as methylmercury can harm a developing nervous system.
Check FDA and Local Advisories: Consult guidelines from the FDA for general recommendations and local advisories for fish caught recreationally in your area.
Benefits Outweigh Risks for Most: For the general population, the nutritional benefits of eating low-mercury fish, including omega-3 fatty acids, typically outweigh the risks of mercury exposure.

Understanding Mercury in Seafood

Mercury is a naturally occurring element, but industrial activities like burning coal and waste release significant amounts of it into the atmosphere. It then falls into oceans and waterways, where bacteria convert it into methylmercury, a highly toxic organic form. Fish absorb methylmercury through their gills and diet. The process of biomagnification causes larger, older, and more predatory fish at the top of the food chain to accumulate significantly higher concentrations of mercury than smaller fish. When humans eat these fish, the methylmercury is absorbed and can accumulate in the bloodstream, with the nervous system being particularly vulnerable to its effects.

The Highest Mercury Seafood: What to Avoid

Certain fish species consistently top the charts for mercury contamination due to their size, longevity, and predatory habits. The FDA and other health organizations strongly recommend that certain populations, and suggest that the general public, limit or avoid these fish.

Shark: As a major apex predator, sharks have some of the highest mercury levels. A shark can carry an average mercury measurement of 0.979 ppm, with higher readings reaching 4.54 ppm.
Swordfish: Another top predator, swordfish typically have very high mercury levels, averaging around 0.995 ppm.
King Mackerel: This large, carnivorous fish, especially from the Gulf of Mexico, is known for its high mercury content.
Tilefish (from the Gulf of Mexico): This species consistently shows extremely high levels of mercury, averaging over 1.123 ppm. Note that Tilefish from the Atlantic have much lower levels.
Bigeye Tuna (Ahi): This species, often served as steak or in sushi, has significantly more mercury than canned light tuna.
Marlin: These large, powerful fish are at the top of the food chain and, therefore, are high in mercury.
Orange Roughy: A long-lived, deep-sea fish that accumulates high levels of mercury over its lifespan.
Chilean Sea Bass (Patagonian Toothfish): This large, long-lived fish has been shown to contain elevated mercury concentrations.

Low-Mercury Seafood: Healthier Alternatives

Many types of seafood are low in mercury and offer significant health benefits, such as being excellent sources of omega-3 fatty acids, protein, and other nutrients. These are generally safe for more frequent consumption. Some great low-mercury options include:

Salmon (Fresh, Frozen, or Canned)
Shrimp
Scallops
Crab
Canned Light Tuna
Cod
Tilapia
Catfish
Anchovies
Sardines

Seafood Mercury Levels: High vs. Low-Mercury Options

To help visualize the difference, this comparison table highlights the average mercury concentration (in parts per million, ppm) for some high and low-mercury options, based on FDA data.


Seafood	Mean Mercury (ppm)	Category	Notes
Tilefish (Gulf of Mexico)	1.123	High	Avoid for vulnerable populations
Swordfish	0.995	High	Limit to one serving per week
Shark	0.979	High	Limit to one serving per week
King Mackerel	0.730	High	Limit or avoid
Bigeye Tuna	0.689	High	Limit or avoid, especially for pregnant women
Salmon (Canned)	0.014	Low	Safe for frequent consumption
Shrimp	0.009	Low	Safe for frequent consumption
Scallops	0.003	Low	Safe for frequent consumption
Sardines	0.013	Low	Safe for frequent consumption

Making Smarter Seafood Choices

Balancing the nutritional benefits of seafood with the risks of mercury exposure is key. The U.S. Food and Drug Administration (FDA) provides specific guidance for different populations, including a detailed advisory that categorizes fish into 'Best Choices,' 'Good Choices,' and 'Choices to Avoid'. Always check for local advisories regarding fish caught recreationally, as mercury levels in local waters can differ based on industrial pollution and environmental factors. For more comprehensive information on safe seafood consumption, consult the FDA’s official advice regarding eating fish.

Conclusion

Understanding which seafood has high levels of mercury allows for informed dietary decisions that prioritize health while still enjoying the significant nutritional benefits that fish and shellfish provide. By limiting or avoiding large, long-lived predatory fish like shark, swordfish, and some types of tuna, and opting instead for a variety of low-mercury options, you can reduce your exposure to potentially harmful levels of methylmercury. This is especially important for pregnant women, breastfeeding mothers, and young children, who are most sensitive to mercury's effects on the developing nervous system. Making conscious choices based on size, species, and habitat ensures a healthy and balanced approach to consuming seafood.

Frequently Asked Questions

Larger, older, and predatory fish tend to have more mercury due to a process called biomagnification. They eat many smaller fish, which contain low levels of mercury, and over time, the mercury accumulates and becomes more concentrated in their bodies.

No, mercury levels in tuna vary by species. Bigeye tuna has very high levels and should be limited or avoided. However, canned light tuna, typically made from smaller skipjack tuna, is considered a 'Best Choice' for consumption with much lower mercury content.

Pregnant women, those planning to become pregnant, breastfeeding mothers, and young children are most at risk because the developing nervous system is particularly sensitive to the effects of mercury.

No, cooking methods like canning, freezing, or preparing fish do not significantly reduce the amount of mercury. The mercury is tightly bound to the muscle tissue of the fish.

For most adults, health organizations recommend eating 2 to 3 servings of low-mercury fish per week. The FDA advises pregnant women and young children to eat 8 to 12 ounces per week of 'Best Choice' options.

Mercury is a naturally occurring element. Methylmercury is the highly toxic organic form created when bacteria in water and soil convert mercury. It is this form of mercury that bioaccumulates in fish and poses a health risk to humans.

It is important to check local advisories before consuming fish from local waters, as mercury levels can be higher or lower than the national average depending on the area's specific environmental conditions. If no advisory is available, the FDA recommends limiting consumption.