Understanding Seafood Safety: What is the least contaminated fish to eat?

October 8, 2025 •

4 min read

According to the U.S. Food and Drug Administration (FDA), nearly 90% of fish consumed in the United States falls under the 'Best Choices' category for low mercury levels, making it safe for regular consumption. This statistic highlights that while contamination is a concern, many delicious and nutritious options are available when asking, what is the least contaminated fish to eat?

Quick Summary

This guide provides a comprehensive overview of seafood contamination, explaining how certain toxins like mercury accumulate and offering clear recommendations for choosing the safest fish. It details the best low-contaminant choices, lists high-mercury varieties to avoid, and provides tips for maximizing the nutritional benefits of seafood.

Key Points

Choose smaller fish: Fish lower on the food chain, like sardines, anchovies, and herring, contain significantly less mercury due to less biomagnification.
Select 'Best Choices': The FDA and EPA provide lists of low-mercury fish (e.g., salmon, trout, tilapia) recommended for consumption of 2-3 servings per week.
Avoid high-mercury predators: Large, long-lived predatory fish such as shark, swordfish, and king mackerel accumulate high levels of mercury and should be avoided or limited.
Consider source and farming: Opt for responsibly sourced seafood, whether wild-caught from pristine waters or farmed using controlled, sustainable practices.
Prioritize omega-3s from safe sources: Fish like salmon and sardines offer high levels of essential omega-3 fatty acids with minimal mercury risk, providing major heart and brain health benefits.
Diversify your fish intake: Eating a variety of low-contaminant fish helps minimize exposure to any single type of pollutant.

Understanding Fish Contamination

Fish and shellfish are a vital part of a healthy diet, providing high-quality protein, essential vitamins, and heart-healthy omega-3 fatty acids. However, environmental pollutants can be absorbed by fish, accumulating in their bodies over time. The primary concern for human health is methylmercury, a neurotoxin that can cause neurological and developmental problems, especially in vulnerable groups like pregnant women and young children.

Biomagnification is the process by which contaminants like mercury become more concentrated as they move up the food chain. This is why larger, longer-lived predatory fish tend to have the highest levels of mercury, as they consume many smaller fish that have also accumulated the toxin. Conversely, smaller fish lower on the food chain, such as sardines and anchovies, have much lower mercury levels. Other contaminants, like polychlorinated biphenyls (PCBs) and dioxins, can also be a concern, with farmed fish potentially having higher levels depending on their feed source.

Low-Contaminant 'Best Choices' and High-Risk Fish

Health authorities like the FDA and EPA provide clear guidance to help consumers navigate seafood choices. By focusing on smaller, shorter-lived species, you can significantly reduce your exposure to contaminants.

Best Choices: Low Contaminants

For most people, enjoying two to three servings of these fish per week is an excellent way to get nutrients with minimal risk. These include:

Salmon: Both wild Alaskan and many farmed varieties have low mercury levels and are excellent sources of omega-3s.
Sardines: These small, quick-reproducing fish are very low in mercury and packed with omega-3s.
Anchovies: Similar to sardines, they are an abundant, low-mercury source of nutrients.
Trout (especially farmed rainbow trout): Farm-raised in U.S. recirculating tanks is often a low-contaminant option.
Tilapia: When sourced responsibly from well-managed farms, tilapia is a low-mercury choice.
Cod: A flaky white fish generally known for its low mercury content.
Pollock: A staple in many seafood dishes, it is consistently low in mercury.
Shellfish: Most types, including shrimp, clams, oysters, and scallops, are very low in mercury.

Choices to Avoid: High Contaminants

Because of the high levels of mercury, the FDA advises against or recommends limiting consumption of these fish, especially for pregnant or nursing women and young children.

Shark: A large, predatory fish high on the food chain.
Swordfish: Another large predator with elevated mercury levels.
King Mackerel: A large mackerel species with high mercury concentration.
Orange Roughy: A long-lived, slow-reproducing species that accumulates contaminants.
Bigeye Tuna: This type of tuna has significantly higher mercury than canned light tuna.
Tilefish (from the Gulf of Mexico): This specific variety is known for very high mercury levels.

Choosing Between Farm-Raised and Wild-Caught

Making a choice between farmed and wild fish depends on the species and sourcing. For instance, while wild Alaskan salmon is often cited for its lower contaminant levels, some farmed Atlantic salmon can have similar levels. The crucial aspect is transparency and responsible practices.

Farmed fish in enclosed or properly managed systems can offer better control over contaminants, as their feed can be monitored. However, poorly managed open-net pens can sometimes lead to localized pollution and disease.
Wild-caught fish depends entirely on the cleanliness of their natural environment. While some regions (like Alaska) have pristine, well-managed fisheries, others may be more polluted.

Look for certifications like the Marine Stewardship Council (MSC) or the Aquaculture Stewardship Council (ASC) to ensure both sustainability and responsible practices.

Comparison of Low vs. High Mercury Fish


Feature	Low Mercury Fish (e.g., Salmon, Sardines, Tilapia)	High Mercury Fish (e.g., Shark, Swordfish, King Mackerel)
Trophic Level	Lower on the food chain, consuming algae or small prey.	Higher on the food chain, preying on other fish.
Lifespan	Generally shorter lifespan, limiting contaminant accumulation.	Long lifespan, allowing for significant contaminant bioaccumulation.
Mercury Content	Minimal levels, safe for frequent consumption.	High levels, best to avoid or limit consumption.
Nutritional Profile	Excellent source of omega-3s, protein, and vitamins.	High in protein, but the risk of high mercury outweighs benefits for frequent intake.
Safety for Vulnerable Groups	Considered safe for pregnant women, nursing mothers, and young children in recommended amounts.	Should be avoided by pregnant and nursing women, and young children.

Conclusion: Making Informed Choices

For a nutritionally sound diet, the best strategy is to diversify your seafood intake and primarily choose fish from the 'Best Choices' category, as recommended by the FDA. Prioritizing smaller, oilier fish like salmon, sardines, and herring not only minimizes mercury exposure but also provides a high concentration of beneficial omega-3s. Always check the source and opt for responsibly harvested or farmed products. By staying informed about which species pose a higher risk, you can confidently enjoy the significant health benefits that fish offers while keeping contamination concerns in check. For the most up-to-date information and species-specific advice, consult resources from governing bodies like the FDA and EPA.

For more information, consult the official FDA guide to eating fish.

Frequently Asked Questions

The primary contaminant of concern is methylmercury. This organic form of mercury is toxic and accumulates in fish, posing health risks, particularly to pregnant women and children.

Fish higher on the food chain, like large predators (e.g., sharks, swordfish), accumulate more mercury through a process called biomagnification. They consume many smaller fish, absorbing and retaining the mercury from each prey.

Canned light tuna, which typically uses smaller skipjack fish, is a 'Best Choice' for low mercury levels and is safe to eat frequently. Canned white (albacore) tuna uses larger fish and has more mercury, so it should be consumed less often.

Safety depends on the species and farming practices. Some farmed fish raised in controlled environments can have lower contaminant levels, while others may contain different pollutants depending on their feed. Look for certifications like ASC or MSC to help make an informed choice.

Fish is a high-quality source of protein, vitamin D, and vitamin B2. It is especially prized for its omega-3 fatty acids, which are crucial for heart and brain health.

For most adults, health organizations recommend eating two to three servings (8 to 12 ounces) of low-mercury fish per week. Pregnant and nursing women, and young children, should follow specific guidelines from the FDA.

Contaminants like PCBs are fat-soluble. Removing the skin, fat, and belly flap before cooking can help reduce exposure, though this is less effective for mercury which is distributed throughout the fish's tissue.