Mercury in Fish: What You Need To Know

Fish has a long-standing reputation as one of the healthiest foods you can put on your plate. So, when talk turns to mercury levels in seafood, it can seem like your nutritious meal has a dark side.

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But that doesn’t mean fish should be off your menu. Instead, focus on choosing certain kinds of fish to eat to limit potential exposure to the toxic metal, says registered dietitian Julia Zumpano, RD, LD.

Here’s what to know before your next bite.

Why is mercury a health concern?

Mercury is a naturally occurring metal that can build up in your body over time if you take in too much of it. At high enough levels, it can lead to mercury poisoning and harm your brain, nervous system or other organs.

For most healthy adults, occasional exposure isn’t likely to cause problems, says Zumpano. Your body can eliminate small amounts on its own.

But consuming large amounts over time can lead to issues. Mercury is especially concerning if you’re pregnant, trying to become pregnant or breastfeeding, as well as for babies and young children.

“Mercury is something where you want to minimize your exposure,” explains Zumpano. “If you’re eating more than your body can handle, it can start to be a problem.”

How does mercury get into fish?

Mercury enters lakes, rivers and oceans through natural processes and pollution. Once it’s in the water, it moves up the food chain. Small fish absorb tiny amounts of mercury. Larger fish eat many smaller fish, causing the metal to accumulate in their bodies over time.

That’s why bigger, longer-living fish tend to have the highest mercury levels. “Size matters here,” notes Zumpano.

What fish are higher in mercury?

Mercury levels in fish, with ones to avoid and ones that are best to eat

Mercury levels vary widely from one species of fish to another. The U.S. Food and Drug Administration (FDA) classifies seven types of fish as “choices to avoid” given their high mercury levels, says Zumpano. The list includes:

Bigeye tuna
King mackerel
Marlin
Orange roughy
Shark
Swordfish
Tilefish

What fish are lower in mercury?

To limit mercury, opt for fish designated as “best choices” by the FDA. The list includes:

Anchovies
Catfish
Cod
Haddock
Herring
Pollock
Salmon
Sardines
Tilapia
Trout

An assortment of fish is also listed as “good choices.” These fish have more mercury than the “best” category, but don’t need to be avoided. This group includes:

Albacore tuna
Carp
Grouper
Halibut
Mahi-mahi

You can find the FDA’s full list here.

Tips to limit mercury intake with fish

You don’t have to give up seafood because of mercury, but you should limit how much you eat per week, states Zumpano. She suggests following these recommendations.

Healthy adults: Two to three 4-ounce servings from the “best choices” list or one serving from the “good choices”
Pregnant or breastfeeding women: One 4-ounce serving per week from the “best choices” list
Children: Two servings per week from the “best choices” list, with amounts varying by age — aim for 1 ounce for children ages 1 to 3; 2 ounces for kids 4 to 7; 3 ounces for those 8 to 10; and 4 ounces at age 11 and up.

In addition, try to mix up the types of fish you eat. Instead of eating the same fish every week, rotate among different “best” or “good” varieties. That helps limit repeated exposure to mercury from any one source.

Bottom line? Fish can be eaten safely. It’s just a matter of making educated choices.

“Fish is one of the most nutrient-dense foods out there, offering high-quality protein along with heart-healthy omega-3 fatty acids,” emphasizes Zumpano. “So, eat fish — but try to stay away from the ones that might have more mercury.”