Which fish has the highest mercury? A guide to making safe seafood choices

October 19, 2025 •

4 min read

According to the U.S. FDA, certain fish like king mackerel, shark, swordfish, and bigeye tuna have the highest levels of mercury, a neurotoxin. Understanding which fish has the highest mercury is crucial for minimizing health risks, especially for vulnerable populations, while still enjoying the health benefits of seafood.

Quick Summary

Large, predatory fish at the top of the food chain contain the highest mercury levels due to biomagnification. Vulnerable populations, like pregnant women and young children, should be especially cautious with certain species. Focusing on smaller, lower-mercury alternatives is the best strategy.

Key Points

King Mackerel, Shark, and Swordfish: These large, long-lived, predatory species have the highest mercury content and should be limited or avoided, especially by at-risk individuals.
Biomagnification: Mercury levels increase up the food chain, meaning apex predators accumulate the most, explaining why larger fish are a greater concern.
Safer Alternatives: Smaller fish with shorter lifespans, including salmon, sardines, and canned light tuna, contain much lower mercury levels and are safer for regular consumption.
High-Risk Populations: Pregnant women, breastfeeding mothers, and young children are most vulnerable to the neurotoxic effects of mercury and should follow conservative consumption guidelines.
Cooking Does Not Remove Mercury: Since methylmercury is bound to the protein in fish muscle, preparation methods like cooking or cleaning will not reduce its concentration.
Don't Avoid Fish Entirely: Many low-mercury fish are packed with heart-healthy omega-3s. The best practice is to choose wisely rather than eliminating fish from your diet.

Understanding the Source of Mercury in Fish

Mercury is a naturally occurring element, but human activities such as industrial processes and the burning of fossil fuels have significantly increased its presence in the environment. Once released, it makes its way into aquatic ecosystems where it is converted by bacteria into methylmercury, a highly toxic organic form. Fish absorb methylmercury through their gills and from the food they eat. It then binds to proteins in their muscle tissue.

The Role of Biomagnification

The primary reason some fish have higher mercury levels is a process called biomagnification. As mercury moves up the food chain, its concentration increases in each successive trophic level. Smaller fish consume plankton and smaller organisms containing low levels of methylmercury. Larger predatory fish then eat many of these smaller fish throughout their long lifespans, causing mercury to accumulate to much higher, and potentially dangerous, levels in their own tissues. Therefore, long-lived, predatory fish consistently show the highest concentrations.

The Fish with the Highest Mercury

Large, predatory species are at the highest risk for mercury accumulation. These are often the fish that are a primary concern for high-risk individuals, such as pregnant women, breastfeeding mothers, and young children. The following list identifies some of the most common high-mercury species:

Shark: A long-lived, top-tier predator.
Swordfish: Known for its high mercury content due to its predatory diet and size.
King Mackerel: This species, particularly those from the Gulf of Mexico, has significantly higher mercury levels than other mackerel varieties.
Marlin: A large, highly predatory billfish.
Tilefish (from the Gulf of Mexico): This specific variety is a notorious source of high mercury levels.
Bigeye Tuna (Ahi): This tuna species is a top predator and contains considerably more mercury than smaller tuna species.
Orange Roughy: A deep-sea fish with a very long lifespan, allowing for significant mercury accumulation.

Lower Mercury Fish: The Safer Seafood Choices

Many fish and shellfish are excellent sources of lean protein and heart-healthy omega-3 fatty acids, and they have very low mercury levels, making them safe for regular consumption. Smaller fish with shorter lifespans and lower on the food chain are the best choices. This list highlights some of the best options:

Salmon: An excellent source of omega-3s and very low in mercury.
Sardines: Small, oily, and packed with nutrients, with negligible mercury.
Shrimp: One of the most popular and safest seafood options.
Canned Light Tuna (Skipjack): A much lower mercury alternative to albacore or bigeye tuna.
Cod: A versatile, low-mercury white fish.
Tilapia: A popular, low-mercury farmed fish.
Catfish: A consistently low-mercury option, especially if farmed.
Pollock: Commonly used in fish sticks and sandwiches, it has a very low mercury content.

Comparing Mercury Levels in Common Fish

This table provides a snapshot of the typical mercury levels in a range of seafood, based on FDA and EPA data.


Fish Species	Typical Mercury Level (PPM)	FDA/EPA Recommendation
King Mackerel	0.730	Avoid (Highest Mercury)
Swordfish	0.995	Avoid (Highest Mercury)
Shark	0.979	Avoid (Highest Mercury)
Bigeye Tuna	0.689	Avoid (Highest Mercury)
Albacore Tuna (Canned)	0.350	Good Choice (Limit to 1 serving/week for at-risk groups)
Canned Light Tuna	0.126	Best Choice (2-3 servings/week)
Salmon	0.022	Best Choice (2-3 servings/week)
Sardines	0.013	Best Choice (2-3 servings/week)
Shrimp	0.001	Best Choice (2-3 servings/week)

Recommendations for Safe Fish Consumption

For most healthy adults, consuming a variety of fish and following general guidelines poses little risk. The primary concern is for vulnerable populations, including pregnant or breastfeeding women and young children, whose developing nervous systems are more sensitive to the effects of methylmercury. The U.S. FDA and EPA offer specific advice to help these groups make informed choices. The key is to consume a variety of fish, favoring those lower in mercury, and to limit or avoid the highest-mercury species. You can explore the full guidance from the FDA on their website.

The Health Benefits of Eating Fish

It's important to remember that fish remains a cornerstone of a healthy diet, providing essential nutrients that can benefit brain function and cardiovascular health. The goal is not to eliminate fish but to be a mindful consumer. Many low-mercury fish are also rich in omega-3 fatty acids (EPA and DHA), such as salmon and sardines, meaning you can get the maximum health benefits with minimal risk.

Conclusion

While some large, predatory fish like swordfish, shark, and king mackerel have dangerously high levels of mercury, many other popular and nutritious seafood options are perfectly safe for regular consumption. The risk of mercury poisoning is primarily linked to frequent, high intake of the most contaminated species. By choosing a variety of low-mercury options such as salmon, shrimp, and sardines, and being aware of which fish to limit, you can enjoy the significant health benefits of seafood while minimizing mercury exposure for yourself and your family.

Frequently Asked Questions

Bigeye (ahi) and Albacore (white) tuna have significantly higher mercury levels than canned light (skipjack) tuna. Health experts recommend limiting albacore consumption and avoiding bigeye tuna.

Biomagnification is the process where chemical concentrations increase as they move up a food chain. Fish higher up the chain eat smaller, mercury-containing fish, causing the neurotoxin to accumulate to much higher levels in their bodies.

No, cooking or cleaning fish does not remove mercury. The mercury is bound to the protein in the fish's muscle tissue, so it remains present even after cooking.

High exposure to methylmercury can cause nervous system damage, leading to symptoms like loss of peripheral vision, tingling sensations, lack of coordination, and impaired speech or hearing. The developing brains of fetuses and young children are particularly susceptible.

Often, yes. Farmed fish tend to have lower mercury levels than their wild-caught counterparts because their feed and environment are more controlled and less exposed to contaminated waters.

The U.S. FDA recommends that most people can safely eat two to three servings (about 8 to 12 ounces) of low-mercury fish per week. Vulnerable populations should be mindful of these amounts.

Yes, generally, larger and older fish have higher mercury concentrations. Because they live longer and prey on other fish, they have more time to accumulate methylmercury in their bodies.