What fish have the highest amount of mercury and why?

January 14, 2026 •

5 min read

According to the U.S. FDA, certain fish, particularly large predatory species like swordfish and shark, have the highest concentrations of methylmercury. Understanding what fish have the highest amount of mercury is crucial for making healthier dietary choices, especially for pregnant women and young children who are most vulnerable to its effects.

Quick Summary

Examines why some fish species contain higher levels of mercury than others due to their position in the food chain. Details the most contaminated fish to avoid and provides practical advice for safer seafood consumption, including options with lower mercury content.

Key Points

Apex Predators Accumulate the Most Mercury: Large, predatory fish like shark, swordfish, and bigeye tuna have the highest mercury levels due to biomagnification in the food chain.
Mercury is a Neurotoxin: Methylmercury can damage the nervous system, with unborn babies and young children being the most vulnerable.
Choose a Variety of Low-Mercury Fish: Diversifying your seafood intake with low-mercury options like salmon, sardines, and tilapia can minimize exposure while retaining nutritional benefits.
Pay Attention to Health Advisories: Pregnant women and parents of young children should follow specific FDA/EPA guidelines to limit or avoid high-mercury fish.
Cooking Does Not Eliminate Mercury: Because mercury binds to fish proteins, it cannot be cooked out or removed by any preparation method.

The Science of Mercury in Fish: Biomagnification

Methylmercury is the primary form of mercury found in fish, and its concentration is a result of a natural process called biomagnification. Mercury is released into the environment from both natural sources (like volcanoes) and human activities (primarily industrial pollution from sources like coal-fired power plants and mining). This elemental mercury is converted into methylmercury by bacteria in aquatic environments.

This highly toxic compound is then absorbed by microorganisms, which are consumed by small fish. The process of biomagnification occurs as larger, predatory fish eat these smaller, contaminated fish. Because mercury is slowly excreted, its concentration builds up in the fatty tissues of fish as you move up the food chain. As a result, the largest and longest-living predatory fish accumulate the highest levels of mercury, making them the most contaminated seafood choices.

The Top High-Mercury Fish to Watch Out For

Several species are consistently flagged by health organizations like the FDA and EPA for their high mercury content. It is generally recommended to limit or completely avoid consumption of these fish, especially for sensitive groups.

Tilefish (Gulf of Mexico): This species, particularly those from the Gulf, are often cited for their extremely high mercury levels.
Shark: As apex predators with long lifespans, all species of shark contain very high concentrations of mercury.
Swordfish: Another large, long-lived predator, swordfish are known to have high mercury content.
King Mackerel: The larger, older king mackerel accumulate significant amounts of mercury over their lifespan.
Bigeye Tuna: This type of tuna is listed among the most contaminated species, with higher levels than canned light tuna.
Marlin: Similar to swordfish and shark, marlin is a large predator with elevated mercury levels.
Orange Roughy: This fish can have high mercury concentrations and is also a very long-lived species.
Chilean Sea Bass (Patagonian Toothfish): This deep-sea species also ranks on the higher end for mercury.

Health Risks Associated with High-Mercury Fish

The methylmercury found in fish is a powerful neurotoxin that poses a particular threat to the nervous system. While most people have small, non-harmful amounts of mercury, regular consumption of high-mercury fish can lead to a dangerous buildup over time.

Specific Vulnerable Groups

Unborn Babies and Young Children: The developing brain and nervous system of a fetus and infant are extremely sensitive to the toxic effects of methylmercury. High exposure can lead to cognitive and developmental issues.
Pregnant and Breastfeeding Women: Because mercury can pass from the mother to the fetus through the placenta and is transferred in breast milk, these individuals should be especially cautious about their seafood choices.

Symptoms of Mercury Toxicity

Though rare from typical dietary exposure, high-level methylmercury poisoning can lead to several symptoms, including:

Loss of peripheral vision
Numbness or tingling in the hands, feet, or mouth
Lack of coordination
Muscle weakness
Impairment of speech and hearing

A Comparison of High vs. Low Mercury Fish

To better visualize safe seafood options, here is a comparison of fish species categorized by their mercury levels based on FDA/EPA advice.


High Mercury Species (Avoid or Limit)	Low Mercury Species (Best Choices)
Gulf of Mexico Tilefish	Salmon
Shark	Sardines
Swordfish	Catfish
King Mackerel	Tilapia
Bigeye Tuna	Canned Light Tuna
Marlin	Shrimp
Orange Roughy	Scallops
Chilean Sea Bass	Haddock

Practical Guidelines for Safer Seafood Consumption

Making informed choices can help you enjoy the health benefits of fish without the risk of high mercury exposure. Consider these tips:

Choose a Variety: Mix up the types of fish you eat. By choosing a wide variety of seafood, you reduce the risk of over-consuming mercury from a single source.
Prioritize Low-Mercury Options: Make fish like salmon, sardines, and canned light tuna a staple of your diet, as they are rich in omega-3s and low in mercury.
Follow Serving Recommendations: Pay attention to recommendations from health authorities. For vulnerable groups like pregnant women, the advice is typically to consume 8-12 ounces per week of low-mercury fish and limit or avoid higher-mercury species.
Check Local Advisories: If you consume recreationally caught fish, consult local advisories from your state or regional health department, as mercury levels can vary significantly by location.
Bigger Isn't Better: A simple rule of thumb is to choose smaller, shorter-lived fish rather than larger, long-lived predatory fish.

Conclusion

While high-mercury fish can pose health risks due to biomagnification, the solution is not to eliminate seafood entirely, but to make informed decisions about your consumption. By understanding what fish have the highest amount of mercury and prioritizing low-mercury alternatives, you can continue to enjoy the significant nutritional benefits of fish, like protein and omega-3 fatty acids, while protecting yourself and your family. Staying aware of which species to limit and which to choose more frequently is the key to maintaining a healthy, balanced diet. For the most comprehensive advice, consult health guidelines from the U.S. FDA, which publishes updated information on mercury levels in commercial fish.

Key Takeaways

Apex predators have the most mercury: The process of biomagnification means large, long-lived predators like shark, swordfish, and certain tuna species accumulate the highest mercury concentrations.
Vulnerable groups need extra care: Pregnant women, breastfeeding mothers, and young children should strictly limit or avoid high-mercury fish due to the neurotoxic effects on developing nervous systems.
Low-mercury options are abundant: Salmon, sardines, tilapia, and most shellfish are excellent, low-mercury choices that offer significant health benefits like omega-3 fatty acids.
Mercury levels can vary geographically: Even within the same species, mercury concentrations can differ depending on the specific body of water and local environmental conditions.
Cooking doesn't remove mercury: Mercury binds to the fish's protein, so cooking methods like grilling or baking will not reduce the mercury content.

FAQs

Question: How does mercury get into fish?

Answer: Mercury is released into the environment from both natural and man-made sources. In water, bacteria convert it to methylmercury, which is then absorbed by aquatic life. It accumulates up the food chain, a process called biomagnification, resulting in higher concentrations in larger, predatory fish.

Question: Why are some types of tuna high in mercury while others are not?

Answer: The mercury levels in tuna depend on the species and size. Larger, longer-lived species like Bigeye tuna have significantly higher mercury than smaller, younger species used for canned light or skipjack tuna.

Question: Can cooking fish reduce its mercury content?

Answer: No, cooking does not remove or reduce the mercury in fish. Methylmercury is tightly bound to the fish's protein and will remain in the flesh regardless of the preparation method.

Question: How often can a pregnant woman safely eat fish?

Answer: Health organizations like the FDA recommend that pregnant and breastfeeding women eat 8 to 12 ounces of a variety of low-mercury fish per week. They should completely avoid the highest-mercury species.

Question: What are some of the safest fish to eat regularly?

Answer: Safe and nutritious options low in mercury include salmon, sardines, shrimp, pollock, tilapia, and catfish. These can generally be consumed multiple times per week without significant risk.

Question: Are all shellfish low in mercury?

Answer: Most shellfish, including shrimp, scallops, and clams, are low in mercury. They are considered safe for regular consumption and are often recommended as part of a low-mercury diet.

Question: Is mercury in fish a new concern?

Answer: The presence of mercury in fish has been a known health concern for decades. Research and monitoring of mercury levels have increased over time, leading to more specific and widespread dietary advisories from public health organizations.

Frequently Asked Questions

Mercury is released into the environment from both natural and man-made sources. In water, bacteria convert it to methylmercury, which is then absorbed by aquatic life. It accumulates up the food chain, a process called biomagnification, resulting in higher concentrations in larger, predatory fish.

The mercury levels in tuna depend on the species and size. Larger, longer-lived species like Bigeye tuna have significantly higher mercury than smaller, younger species used for canned light or skipjack tuna.

No, cooking does not remove or reduce the mercury in fish. Methylmercury is tightly bound to the fish's protein and will remain in the flesh regardless of the preparation method.

Health organizations like the FDA recommend that pregnant and breastfeeding women eat 8 to 12 ounces of a variety of low-mercury fish per week. They should completely avoid the highest-mercury species.

Safe and nutritious options low in mercury include salmon, sardines, shrimp, pollock, tilapia, and catfish. These can generally be consumed multiple times per week without significant risk.

Most shellfish, including shrimp, scallops, and clams, are low in mercury. They are considered safe for regular consumption and are often recommended as part of a low-mercury diet.

The presence of mercury in fish has been a known health concern for decades. Research and monitoring of mercury levels have increased over time, leading to more specific and widespread dietary advisories from public health organizations.

High levels of methylmercury exposure can cause damage to the nervous system, kidneys, and other organs. Symptoms may include nerve damage, loss of peripheral vision, and impaired coordination. It is particularly harmful to the developing brain of a fetus or young child.

Methylmercury is an organic compound found in fish, posing risks through dietary consumption. Elemental mercury is typically found in products like thermometers and is dangerous primarily when its vapor is inhaled. Most mercury in seafood is the more readily absorbed and harmful methylmercury.

Mercury levels in canned tuna vary by species. Canned light tuna (typically skipjack) is relatively low in mercury, while canned white or albacore tuna has higher levels. The FDA advises limiting albacore tuna consumption, especially for sensitive populations.