Which is the Least Toxic Fish to Eat? Your Guide to Safer Seafood Choices

October 21, 2025 •

5 min read

According to the FDA, nearly all fish contain traces of methylmercury, but levels vary significantly depending on the species. This guide will help you understand which is the least toxic fish to eat and how to select seafood to maximize health benefits while minimizing the risk of contamination.

Quick Summary

This guide outlines the factors contributing to toxicity in fish, such as mercury and other environmental pollutants. It highlights the best low-mercury choices, explains why larger predatory fish should be limited, and offers practical tips for sourcing and preparing seafood safely. A comparison table provides a quick overview of popular fish options.

Key Points

Least Toxic Fish: Small, short-lived, non-predatory fish like sardines, anchovies, and farmed tilapia (from reputable sources) are among the least toxic choices.
Mercury Accumulation: Larger, older, predatory fish, such as shark, swordfish, and king mackerel, accumulate the highest levels of mercury and should be avoided.
Sourcing is Key: For farmed fish like tilapia and catfish, knowing the source is crucial; opt for products certified as sustainably and responsibly farmed.
Vary Your Intake: Diversifying the types of fish you eat helps minimize exposure to any single toxin, promoting overall healthier consumption.
Check Certifications: Look for certifications like ASC and MSC, which indicate seafood that is responsibly and sustainably harvested or farmed.
Health Benefits Outweigh Risks: For most people, the health benefits of eating recommended amounts of low-mercury fish far outweigh the risks of toxin exposure.

The Primary Concern: Methylmercury Accumulation

For most people, the main toxicological concern when eating fish is methylmercury. This naturally occurring element is released into the environment through industrial pollution and natural processes, eventually settling in oceans and rivers. Once in the water, microorganisms convert it into methylmercury, which is then absorbed by aquatic life. The process of bioaccumulation means that methylmercury levels increase as you move up the food chain.

Larger, older, predatory fish, like shark and swordfish, consume many smaller fish over their long lifespans, accumulating significantly higher concentrations of mercury in their flesh. In contrast, smaller, shorter-lived fish and species lower on the food chain, such as sardines and anchovies, have far less time to accumulate these toxins, making them generally safer choices.

Your "Best Choice" Low-Toxin Fish Options

To reap the nutritional benefits of fish—including omega-3 fatty acids, high-quality protein, and essential minerals like selenium and vitamin B12—without the high toxic load, focus on smaller, non-predatory species. The FDA and EPA maintain lists of "Best Choice" fish that are low in mercury and safe for frequent consumption, even for vulnerable groups like pregnant women and young children.

Recommended low-toxin fish include:

Sardines: These small, oily fish are packed with omega-3s, calcium (from their soft, edible bones), and vitamin D. Their low position on the food chain makes them one of the lowest-mercury options available.
Salmon: A widely recognized superfood, salmon is rich in omega-3s and protein. Wild-caught Alaskan salmon is typically a very low-mercury option, and canned wild salmon offers a budget-friendly source of nutrients and calcium.
Cod: A flaky, mild-flavored white fish, cod is a lean source of protein and vitamin B12. It has consistently low mercury levels and is a British classic for good reason.
Catfish: When sourced from U.S. farms with proper practices, catfish is a reliable low-mercury option. However, imported catfish (often labeled as basa or swai) can carry higher risks due to varying farming standards.
Tilapia: A popular and affordable white fish, tilapia is low in mercury. When purchasing, choose tilapia from reputable sources like farms in the U.S., Ecuador, or Indonesia, and avoid varieties from China due to historical concerns over farming practices.
Pollock: A mild, flaky white fish commonly used for fish sticks and imitation crab meat. It is a budget-friendly source of protein with very low mercury levels.
Herring: An oily fish known for its high omega-3 content, herring is a great choice. Atlantic herring from well-managed fisheries is a sustainable and low-mercury option.

Other Contaminants and Sourcing Practices

While mercury is a key concern, other contaminants like polychlorinated biphenyls (PCBs), dioxins, and pesticides can also be found in fish. These fat-soluble toxins also accumulate in the food chain. For fish that contain these, you can reduce exposure by trimming away the skin and fat before cooking, as this is where these compounds concentrate.

Additionally, sourcing matters. Wild-caught fish can still pick up contaminants from their environment. Farmed fish, especially from open-net pens, can have issues with antibiotics and waste. However, sustainably certified farmed options, often from recirculating aquaculture systems, can be excellent and safe choices. Always look for certifications like the Aquaculture Stewardship Council (ASC) or the Marine Stewardship Council (MSC) on seafood labels.

Low-Toxin Fish Comparison Table


Fish Species	Mercury Level	Omega-3 Content	Sustainability/Sourcing Tips
Sardines	Very Low	Very High	Generally excellent; wild-caught and often canned.
Wild Alaskan Salmon	Very Low	Very High	Best choice; look for wild-caught from Alaska.
Cod	Low	Moderate	Opt for cod from Iceland or the Arctic for sustainability.
US-Farmed Catfish	Very Low	Low	Look for U.S. farmed to ensure better practices.
Tilapia (non-China sourced)	Very Low	Low	Choose tilapia from the U.S., Ecuador, or Indonesia.
Pollock	Very Low	Low	A safe and sustainable option for protein.

High-Mercury Fish to Avoid or Limit

It is just as important to know which fish to avoid or consume sparingly. These species typically have high levels of mercury due to their position at the top of the food chain. For pregnant women, nursing mothers, and young children, these fish should be avoided entirely.

Shark: Long-lived apex predator with very high mercury.
Swordfish: Another large, predatory fish with high mercury content.
King Mackerel: High mercury, especially king mackerel (avoid Spanish mackerel too).
Bigeye Tuna: Higher in mercury than canned light tuna and should be avoided.
Orange Roughy: Long-lived, slow to reproduce, and high in mercury.
Tilefish (Gulf of Mexico): Specifically, this variety has very high mercury levels.

Practical Tips for Safer Fish Consumption

Making healthy seafood choices is a balance of weighing benefits and risks. Here are some actionable steps to ensure you're consuming the least toxic fish:

Vary Your Choices: Don't rely on just one or two types of fish. Rotating your seafood choices helps minimize exposure to any single contaminant.
Follow Official Guidelines: The FDA and EPA provide detailed, up-to-date recommendations on fish consumption, including how many servings are safe for different populations. Their advice is a reliable resource for making informed decisions.
Check Local Advisories: If you consume locally caught freshwater fish, check for local advisories from state or environmental agencies, as contaminant levels can vary significantly by waterway.
Prioritize Sustainable Sourcing: Certifications from organizations like the ASC and MSC indicate responsibly sourced seafood, often with controlled farming practices or sustainable wild fishing that reduces environmental impact.
Cook Smartly: For fattier fish, cooking methods that allow fat to drain, and removing the skin, can help reduce potential exposure to fat-soluble contaminants like PCBs.

Conclusion

Fish is an important and nutrient-dense part of a healthy diet, but concerns about toxins like mercury are valid. The key to safe and healthy seafood consumption is to be a knowledgeable consumer. By prioritizing smaller, shorter-lived fish like sardines, salmon, cod, and responsibly-sourced tilapia, you can enjoy the many benefits of fish while minimizing your exposure to harmful contaminants. By diversifying your choices and staying informed, you can make smarter, healthier decisions for yourself and your family. For more in-depth advice on fish and shellfish, consult the FDA's official recommendations.

Frequently Asked Questions

Mercury levels are highest in larger, older, and predatory fish at the top of the food chain. This is due to a process called bioaccumulation, where mercury builds up in their flesh over time as they consume smaller, contaminated fish.

Yes, responsibly farmed tilapia is safe to eat and is a low-mercury option. The safety concerns surrounding tilapia are often linked to outdated farming practices in some regions. Look for certifications like ASC or sources from countries like the U.S., Ecuador, or Indonesia.

Contaminants like PCBs and dioxins are fat-soluble. To minimize exposure, you can remove the skin and fatty portions of the fish before cooking. Cooking methods that allow fat to drip away can also help.

Pregnant women, nursing mothers, and young children should avoid fish with the highest mercury levels. This includes king mackerel, shark, swordfish, bigeye tuna, and tilefish from the Gulf of Mexico.

Absolutely. Low-mercury fish are excellent sources of omega-3 fatty acids, high-quality protein, and vital nutrients like selenium and vitamin B12. These nutrients support heart health, brain development, and overall bodily functions.

Canned light tuna, which primarily uses smaller skipjack tuna, is a 'Best Choice' for low mercury. In contrast, canned albacore (white) tuna has moderate mercury levels and should be limited, especially for pregnant women and children.

For most adults, the FDA and EPA recommend eating 2 to 3 servings (8 to 12 ounces) of lower-mercury fish per week to gain health benefits. It is important to vary your choices and follow specific guidelines if pregnant, nursing, or for children.