Mercury in Seafood: Which Fish Are Safest to Eat?

Seafood is still one of the healthiest proteins you can eat, but it comes with a caveat. Every fish in the ocean, from the smallest sardine to the largest shark, contains some amount of mercury. This isn’t because fish are “toxic” by nature, but because mercury has become part of our global environment, eventually finding its way into lakes, rivers, and seas. When you sit down to a plate of seafood, you’re also eating trace amounts of this heavy metal.

The question isn’t whether mercury is there. It’s how much and how often you should eat certain types of fish without putting your health at risk.

This guide breaks down what mercury is, why it matters, and which fish are safer to enjoy regularly.

How It Gets Into Fish

Mercury is a naturally occurring metal. It gets into lakes, rivers, and oceans through volcanic activity, mining, industrial pollution, and coal burning. Inside water, microbes convert some of it into methylmercury, the form that accumulates in fish and makes its way into our diets. It’s most worrisome for human health.

The process works like a chain reaction:

Tiny plankton absorb methylmercury.

Small fish eat the plankton.

Bigger fish eat the smaller fish.

With each step up the food chain, mercury concentrations climb, a process called biomagnification.

That’s why small, short-lived fish like sardines carry far less mercury than predators like swordfish or tuna, which accumulate mercury over decades of eating smaller prey.

Why Some Fish Are Riskier Than Others

Here are the key factors that influence how much mercury a fish might carry:

Size and lifespan. Big, long-lived predatory fish eat smaller contaminated fish, so mercury builds up over time (a process called biomagnification).

Position in the food chain. Fish that are top predators have fewer checks on how much methylmercury they accumulate.

Geographic location & environmental contamination. Waters near mining, coal plants, or industrial sites tend to have more mercury inputs; fish from contaminated areas risk having higher levels.

Species biology. Some fish naturally grow faster or have greater fat content, which may dilute mercury a bit (though not enough in many cases).

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Why Mercury Exposure Is a Health Concern

Our body has no real use for mercury, and once it’s inside, it doesn’t leave quickly. Instead, it binds to proteins and builds up in tissues over time, especially in the brain, liver, and kidneys.

High exposure has been linked to:

Nervous system damage (affecting memory, coordination, and mood).

Developmental issues in children, including delays in learning and language when exposure happens during pregnancy.

Higher risk of long-term conditions such as cardiovascular problems and, in some research, neurodegenerative diseases like Parkinson’s (per NIH).

For adults, occasional meals of higher-mercury fish may not cause immediate harm. But for pregnant women, breastfeeding mothers, and young children, avoiding frequent exposure is critical because the developing brain is particularly sensitive.

Low, Moderate, and High Mercury

Instead of cutting out seafood altogether, the smarter move is choosing species with lower mercury levels. These give you the nutritional benefits omega-3 fats, protein, selenium, vitamin D—without the heavy metal baggage.

Low-Mercury Options and More Nutritious

These are smaller, short-lived species and shellfish that tend to stay clean:

Salmon: Low mercury burden; high in omega-3s, vitamin D, etc. (per OEHHA)

Sardines: Very low mercury; good fats; often more sustainable. U.S. Food and Drug Administration (FDA)

Trout: Freshwater trout are often low in mercury, especially in cleaner waters. (OEHHA)

Canned light tuna / skipjack tuna (limited): Good as an occasional option. However, canned albacore is higher in mercury; limit servings.Environmental Protection Agency (EPA)

Tilapia, catfish: Farm-raised or caught in lower-mercury waters, these are usually in “Best Choices” lists.

Clams, oysters, scallops, crab, and squid:Shellfish often rank among the lowest mercury levels. Plus, they bring trace minerals. (per FDA)

Canned light tuna / skipjack tuna (limited): Good as an occasional option. However, canned albacore is higher in mercury; limit servings. (per EPA)

Herring

Haddock

Anchovies

These can comfortably be eaten multiple times a week. They’re also budget-friendly and widely available.

Moderate-Mercury Options (Best Kept to Once a Week)

These fish have more mercury but can still fit into a balanced diet:

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Cod

Snapper

Monkfish

Lobster

Canned light tuna (skipjack)
They’re fine in rotation but not ideal for daily consumption.

High-Mercury Fish (Limit or Avoid Altogether)

Predatory, long-lived fish almost always top the danger list. These fish tend to have higher mercury levels, and health agencies often recommend minimizing or avoiding them, especially if you’re pregnant, nursing, or feeding young children.

Shark

Swordfish

King mackerel

Bigeye tuna and albacore tuna

Grouper

Sea bass

Bluefish

Orange roughy

For most people, these are best left as an occasional indulgence, once a month at most. For pregnant women and children, most public health agencies recommend avoiding them completely (per FDA/EPA guidance).

Other Things to Watch

Mercury isn’t the only factor that matters when choosing seafood. A few other points worth keeping in mind:

Wild vs. Farmed: Check fish origin. Wild-caught vs farmed matters, and local advisories about mercury in lakes/rivers make a difference. Not all farmed fish are problematic, but sourcing matters.

Freshness: Quality affects nutrition. Fresh fish should smell like the ocean, not “fishy.” Look for firm flesh, clear eyes, and bright red gills if buying whole.

Sustainability: Overfishing is a global problem. Opt for species certified by the Marine Stewardship Council (MSC) or check Seafood Watch for eco-friendly recommendations.

Rotate your fish. Don’t eat the same species every day; mix low-mercury fish with occasional higher ones depending on guidelines.

Watch portion sizes, especially for kids, use smaller servings frequently rather than large servings occasionally.

Read labels. For canned fish, pay attention to tuna type (light vs albacore/white).

Cooking doesn’t remove mercury. Unfortunately, mercury binds in tissue; cooking methods don’t significantly reduce it. So start with a safer source.

Tailor it to your needs: Pregnant women, children, and those with neurological conditions need stricter limits than the average healthy adult.

The body is equipped to flush out mercury gradually. Thankfully, Our bodies naturally eliminate mercury over time so dangerous levels are typically only reached if someone consumes large amounts of high-mercury fish on a frequent basis for many months.