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November 16, 2014

Fish, Levels of Mercury and Omega-3 Fatty Acids

Fitness First USA

Fish is a good source of protein and, unlike fatty meat products, it’s not high in saturated fat. It’s also a good source of omega-3 fatty acids, which benefit heart health.

The American Heart Association recommends eating fish at least twice a week. However, some types of fish may contain high levels of mercury, PCBs (polychlorinated biphenyls), dioxins and other environmental contaminants. Levels of these substances are generally highest in older, larger, predatory fish and marine mammals. Levels of mercury and omega-3 fatty acids for various fish and shellfish are shown below.

The benefits and risks of eating fish vary depending on a person’s stage of life.

Children, pregnant and nursing women usually have low CVD risk but may be at higher risk of exposure to excessive mercury from fish. Avoiding potentially contaminated fish is a higher priority for these groups.

For middle-aged and older men, and women after menopause, the benefits of eating fish far outweigh the risks within the established guidelines of the FDA and Environmental Protection Agency.

Eating a variety of fish will help minimize any potentially adverse effects due to environmental pollutants.

Top 10 fish and shellfish consumed in the United States

Mean mercury level in parts per million (ppm)Omega-3 fatty acids (grams per 3-oz. serving)
Canned tuna (light)0.120.26–0.73
ShrimpND*0.27
Pollock0.060.46
Salmon (fresh,frozen)0.010.68–1.83
Cod0.110.13–0.24
Catfish0.050.15–0.20
ClamsND*0.24
Flounder or sole0.050.43
Crabs0.060.34–0.40
Scallops0.050.17

Other common seafoods

Mean mercury level in parts per million (ppm)Omega-3 fatty acids (grams per 3-oz. serving)
Lobster0.310.07–0.41
Grouper0.550.21
Halibut0.260.40–1.00
OystersND*0.37–1.17
Mahi mahi0.190.12
Herring0.041.71–1.81

Fish with the highest levels of mercury (about 1 ppm Hg)

Mean mercury level in parts per million (ppm)Omega-3 fatty acids (grams per 3-oz. serving)
Shark0.990.90
Swordfish0.970.70
Tilefish (golden bass or golden snapper)1.450.80
King mackerel0.730.34

Advice from the FDA

Women who are pregnant, planning to become pregnant or nursing — and young children — should not eat these fish. Everyone else can eat up to 7 ounces of high-mercury fish per week.

Fish with about 0.5 ppm Hg

Mean mercury level in parts per million (ppm)Omega-3 fatty acids (grams per 3-oz. serving)
Fresh or frozen tuna0.380.24–1.28
Red snapper0.600.27
Orange roughy0.540.002

Advice from the FDA

Minimizing exposure to methylmercury is particularly important for pregnant women, women who are planning to become pregnant, nursing women and young children. These people should limit their consumption of all fish with much lower mercury levels than 1 ppm Hg (see above). The guideline for them is 12 ounces per week (about 3 to 4 servings). Other people can eat 14 ounces a week of fish with mercury levels that average 0.5 ppm.

* ND - mercury concentration below the Level of Detection (LOD=0.01ppm)