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Which Fish to Choose: The Mercury Question

“What about mercury in fish?” That’s a frequent question at our seafood counters that we’ll try to tackle here.

Which Fish to Choose: The Mercury Question

“What about mercury in fish?” That’s a frequent question at our seafood counters that we’ll try to tackle here.

Let’s start with lists of fish based on FDA testing of mercury. Then we’ll wade into some details so you can learn the science to help you make good choices.

The highest levels of mercury are found in large, longer-lived predatory fish:

  • King Mackerel

  • Shark

  • Swordfish

  • Tilefish (from the Gulf of Mexico)

Some seafood choices that are lower in mercury include:

  • Anchovies

  • Catfish

  • Clams

  • Cod

  • Crab (Blue, King, Snow)

  • Flounder/Sole

  • Haddock

  • Herring

  • Lobster

  • Ocean Perch

  • Oysters

  • Rainbow Trout

  • Salmon (farmed and wild)

  • Sardines

  • Scallops

  • Shrimp

  • Spiny Lobster

  • Tilapia

  • Trout (farmed)

And some of the fish that fall in the middle range:

  • Bass (Saltwater, black, striped, Chilean)

  • Grouper

  • Halibut

  • Marlin

  • Orange Roughy

  • Skate

  • Snapper

  • Tuna (amount varies by species; see note below)

For more species and details, see the FDA list of Mercury Levels in Commercial Fish and Shellfish.

Okay, so now you have a list of fish. What do you do with it? That depends.

Some people, like pregnant women and small children, are at greater risk from mercury than others.

It also depends on how much and how often you eat fish. If you eat swordfish (higher in mercury) once every few months, it’s not likely to affect you. But if you eat a sandwich made with albacore tuna (moderate level of mercury) every single day, that might be a greater concern.

Here’s some info to help you strike a balance.

Who should be concerned about mercury in fish?

The Food and Drug Administration (FDA) and the Environmental Protection Agency (EPA) advise pregnant women, women of childbearing age who may become pregnant, nursing mothers and children to avoid eating fish that might contain high levels of mercury.

Effects from too much mercury can also occur in men and in women not of childbearing age. High levels of mercury in humans can be harmful to neurological development.

Should pregnant women and children avoid eating fish?

The FDA and EPA don’t think so. They just released a draft of Fish: What Pregnant Women and Parents Should Know, which includes this advice:

“There is longstanding evidence of the nutritional value of fish in the diet. Fish contain high quality protein, many vitamins and minerals, omega-3 fatty acids, are mostly low in saturated fat, and some fish even contain vitamin D. Eat 8 to 12 ounces of a variety of fish and shellfish each week from choices that are lower in mercury. The nutritional value of fish is important during growth and development before birth, in early infancy for breastfed infants, and in childhood.”

Note: smaller portion sizes for children are detailed in their advice.

How does mercury get into fish?

Mercury is emitted into the air by industrial activities, such as manufacturing or burning coal for fuel, and from natural sources, like volcanoes.

Through rain, snow and runoff, mercury can accumulate in oceans, lakes and rivers where, aided by bacteria, it undergoes a chemical transformation into methylmercury, which can be toxic.

Fish absorb methylmercury from water as they feed on aquatic organisms like plankton.

Are all fish affected the same way?

No. The bigger the fish and the older the fish, the more mercury builds up. That’s because little fish eat plankton with mercury and then little fish that now also have mercury are eaten by bigger fish who are eaten by even bigger fish and so on. Each step up the food chain adds more mercury.

Other factors come into play too: where the fish live, what they eat, how deep the water is, the temperature of the water and many other complex variables.

What about farmed fish?

Farmed fish live for a relatively short time so they do not accumulate as much mercury as some species of wild fish. And if they are fed fish as part of their diet, it is usually types that are low in mercury. Learn more about our industry-leading farm-raised seafood standards.

What about canned tuna?

Canned tuna is the second most popular seafood choice in the US, but all canned tuna is not alike when it comes to mercury. Larger and longer-lived albacore tuna has almost three times the mercury as canned “light” tuna, which is made from smaller species. Assess your personal consumption to limit mercury exposure.

Can we avoid methylmercury completely?

It’s not likely. According to the EPA, “Almost all people in the world have at least trace amounts of methylmercury in their bodies, reflecting its pervasive presence in the environment.”

Can we clean or prepare fish in a way to avoid the mercury?

No, cooking preparation and heat does not reduce mercury levels since it’s found throughout the tissue of the fish.

What about Omega-3 fatty acids?

The FDA provides a table with the levels of mercury and Omega-3s side by side to help you choose. Here are a few of the top choices for balancing both:\

  • Anchovies

  • Salmon

  • Sardines

  • Mackerel

  • Trout

  • Herring

At Whole Foods Market, we offer the highest quality seafood caught and farmed from the best sources around the world. And we provide you with the health and environmental information you need to make the best choices for you and your family. The next time you shop, pick up a copy of our brochure, Methylmercury in Seafood.

Does mercury affect the choices you make at the seafood counter? Tell us about it in the comments below.

*** Update 7/18/14: Supplements can be a good solution for those concerned about mercury who would like to increase their intake of omega-3s. We carry fish oil supplements that have been purified (or molecularly distilled) during the manufacturing process, as well as algae-based omega-3 supplements. ***

Sources and additional reading:

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