What Kind of Fish Should I Avoid?

October 31, 2025 •

4 min read

According to the FDA and EPA, predatory fish species like shark, swordfish, and king mackerel contain the highest levels of mercury due to bioaccumulation. This guide will help you understand what kind of fish you should avoid and why, focusing on safety, sustainability, and environmental responsibility.

Quick Summary

Several fish species should be avoided due to high mercury content from bioaccumulation, unsustainable fishing and farming, or environmental pollutants like PCBs. Health-conscious consumers, especially pregnant women and young children, should choose smaller, lower-mercury fish.

Key Points

High-Mercury Predators: Avoid large, long-lived predatory fish like shark, swordfish, and king mackerel due to high mercury levels from bioaccumulation.
Check FDA Warnings: Vulnerable populations, including pregnant women and young children, should strictly follow FDA recommendations to avoid specific high-mercury fish.
Beware of Unsustainable Options: Conventional farmed salmon and Chilean sea bass raise environmental concerns due to pollution and overfishing.
Consider Smaller Fish: Opt for low-mercury alternatives like sardines, canned light tuna, and anchovies for a safer seafood intake.
Verify Sustainability: Use resources like Seafood Watch to ensure your choices are not contributing to overfishing or harmful environmental practices.
Watch for Mislabeling: Be aware of seafood fraud, where cheaper or different fish may be sold fraudulently, potentially containing different contaminants.

Health Risks Associated with Certain Fish

While fish is a valuable part of a healthy diet, rich in omega-3 fatty acids and protein, some species carry health risks that consumers should be aware of. The primary concerns are high levels of mercury, bioaccumulation of other pollutants, and unsustainable practices that harm ecosystems.

High Mercury Content

Mercury, particularly methylmercury, is a neurotoxin that can damage the brain and nervous system, and it is especially dangerous for a fetus and young children. This metal accumulates in fish over time, meaning larger, longer-living predatory fish have the highest concentrations, a process known as biomagnification. The FDA has issued specific warnings for certain groups to avoid these high-mercury species.

Common high-mercury fish to avoid:

King Mackerel: Known for high mercury levels, particularly from the Pacific Ocean, making it especially risky for pregnant women and children.
Shark: As an apex predator, sharks accumulate high levels of mercury and other toxins like arsenic and lead.
Swordfish: This large, long-lived predatory fish frequently contains high levels of mercury.
Tilefish (from the Gulf of Mexico): This species has some of the highest mercury levels of all fish.
Marlin: Another large predatory fish with high mercury content.
Orange Roughy: These fish can live for over 100 years, accumulating high mercury levels throughout their long lifespan.
Bigeye Tuna: This type of tuna has significantly higher mercury than canned light tuna and is recommended for avoidance, especially for sensitive groups.

Unsustainable Fishing and Farming

Beyond health concerns, some fish should be avoided for environmental and ethical reasons. Overfishing threatens marine ecosystems, and certain farming practices can lead to significant water pollution and other ecological damage.

Common fish to avoid for sustainability reasons:

Bluefin Tuna: Severely overfished and often contains high levels of mercury and other pollutants like PCBs.
Farmed Salmon (conventional): Many salmon farms use crowded open-net pens, which contribute to water pollution from waste and chemicals, and can spread disease and parasites to wild salmon populations.
Chilean Sea Bass (Patagonian Toothfish): This slow-growing, overfished species is often caught using destructive longlines that harm marine habitats.
American Eel: The population of wild American eels is in decline, and most farmed eels come from polluted sources.
Imported Shrimp: Certain imported shrimp can carry significant environmental risks and contaminants due to poor farming conditions.

Making a Safer Choice: What to Eat Instead

To balance health and environmental concerns, focus on smaller, faster-reproducing fish lower on the food chain. These fish generally accumulate less mercury and are often sourced more sustainably.

Safer, lower-mercury fish options:

Canned Light Tuna (Skipjack): A good alternative to fresh or canned albacore tuna, as it contains much lower mercury levels.
Salmon (wild-caught): Wild-caught salmon is a preferable choice over conventionally farmed salmon, offering high omega-3s with lower pollutant exposure.
Sardines: Very low in mercury and an excellent source of omega-3 fatty acids.
Tilapia (responsibly sourced): When sourced from well-managed farms, tilapia can be a low-mercury option.
Catfish: Also low in mercury and a common option for those seeking safer fish.
Anchovies: These small fish are a very low-mercury option and great for flavor.

Comparison Table: High-Mercury vs. Low-Mercury Fish


Feature	High-Mercury Fish	Low-Mercury Fish
Typical Species	Shark, King Mackerel, Swordfish, Bigeye Tuna	Sardines, Salmon, Anchovies, Canned Light Tuna
Position in Food Chain	Apex predators (high trophic level)	Lower on the food chain
Lifespan	Long-lived species (e.g., Orange Roughy)	Shorter-lived species
Bioaccumulation Risk	Very high	Low
Recommendation	Avoid or limit consumption, especially for sensitive groups	Generally safe to eat regularly
Primary Health Risk	Neurotoxicity from methylmercury	Minimal risk from mercury

The Problem with Mislabeling

Another concern for consumers is the issue of fish mislabeling, which can inadvertently lead people to eat fish they intended to avoid. Studies have found that a significant percentage of seafood sold in restaurants and markets is mislabeled. For instance, a cheaper fish might be sold as a more expensive one, or even a different type of fish entirely. A notable example is escolar, a fish linked to stomach issues, sometimes being passed off as "white tuna". To combat this, knowing the source of your seafood and shopping at reputable outlets is key. Source: Oceana Report on Seafood Fraud, a good resource for understanding the problem.

Conclusion

Making an informed choice about the fish you eat is crucial for both your health and the planet. By understanding which species accumulate high levels of contaminants like mercury and which are linked to unsustainable fishing and farming practices, you can make smarter decisions. Always check reputable sources like the FDA and Seafood Watch, especially if you are in a sensitive population group like pregnant women or young children. Opting for smaller, low-mercury, and responsibly sourced fish is the safest and most environmentally friendly approach to enjoying the nutritional benefits of seafood.

Frequently Asked Questions

The fish with the highest mercury levels are large predators such as shark, swordfish, king mackerel, marlin, bigeye tuna, and tilefish from the Gulf of Mexico.

Methylmercury, the form of mercury found in fish, is a potent neurotoxin that can disrupt the development of a fetus's or young child's brain and nervous system. For this reason, the FDA advises them to avoid high-mercury fish.

No, not always. While some conventional fish farms, especially open-net ones, raise environmental concerns about pollution and disease, responsibly managed farms can be a sustainable option. It depends on the specific species and farming methods.

Bioaccumulation is the process by which toxins like mercury build up in an organism faster than the organism can excrete them. It affects fish by causing larger, longer-lived fish at the top of the food chain to have higher concentrations of these toxins.

Yes, Polychlorinated Biphenyls (PCBs) are another type of pollutant that can accumulate in fish. They are a concern in certain species like bluefin tuna and farmed salmon, and have led to health advisories.

Yes, in addition to mercury, fish can contain other pollutants depending on their environment and position in the food chain, including dioxins, pesticide residues, and in some species like shark, even lead and arsenic.

The FDA recommends that pregnant or nursing women eat up to 12 ounces per week of low-mercury fish such as salmon, canned light tuna, shrimp, and catfish. Checking local advisories for locally caught fish is also important.