Fish High in Omega-3 and Low in Mercury

Omega-3 are polyunsaturated fatty acids that have been associated with a number of health benefits, including anti-inflammatory effects. In fish, these essential fatty acids occur in two forms: eicosapentaenoic acid (EPA) and docohexaenoic acid (DHA). These long-chain forms of omega-3 are considered particularly valuable because they don't have to be converted into other substances before the human body can make use of them, which is why fish that are rich in omega-3 fatty acids are generally considered the best dietary sources of omega-3s. In plant-based sources such as walnuts and flaxseed, the omega-3 fatty acids occur in the form of alpha-linoleic acid, or ALA, which has to be converted into DHA and EPA before the body can make use of it. Unfortunately, however, this conversion is usually very slow.

If you are looking to increase your intake of omega-3s by eating more fish, look for species that are not only high in omega-3s but also low in mercury. Mercury is a nasty heavy metal that can cause damage to your brain, heart, lungs, kidneys and immune system if you are exposed to it at high levels. What's more, this toxic heavy metal can harm fetuses, infants and young children even at relatively low levels, which is why the Environmental Working Group (EWG), a non-profit, non-partisan organization dedicated to protecting human health and the environment, advises pregnant and breastfeeding women as well as young children to avoid fish that are high in mercury, even if they are a good source of omega-3 fatty acids. To make your life easier, EWG has identified six fish species that it recommends as "good choices" for people who are looking for high omega-3, low-mercury fish. Listed in alphabetical order, these are anchovies, herring, salmon, sardines, shad and trout. The chart below shows the omega-3 content and mercury levels of these "top choices", along with other popular fish consumed in the US.

Chart: Omega-3 and Mercury Levels in Selected Fish Species

The amounts shown are per 4 oz of cooked fish

Fish	Mg of omega-3 (EPA + DHA)	Mcg of mercury
Anchovies, Herring and Shad*	2,300 - 2,400	5 - 10
Salmon: Atlantic, Chinook, Coho*	1,200 - 2,400	2
Mackerel: Atlantic and Pacific (not King)	1,350 - 2,100	8 - 13
Tuna: Bluefin and Albacore	1,700	54 - 58
Sardines: Atlantic and Pacific*	1,100 - 1,600	2
Shark	1,250	151
Trout: Freshwater*	1,000 - 1,100	11
Marlin, Striped	1,030	69
Tuna: White (Albacore), Canned	1,000	40
Tilefish from the Gulf of Mexico	1,000	219
Swordfish	1,000	147
Salmon: Pink and Sockeye*	700 - 900	2
Pollock: Atlantic and Walleye	600	6
Mackerel: King	450	110
Flounder, Plaice and Sole (Flatfish)	350	7
Tuna: Light canned	150 - 300	13
Tuna: Skipjack and Yellowfin	150 - 350	31 - 49
Marlin, Blue	250	69
Cod: Atlantic and Pacific	200	14
Haddock and Hake	200	2 - 5
Catfish	100 - 250	7
Tilapia	150	2
Orange Roughy (aka Deep Sea Perch)	42	80

*Promoted as a good, healthy source of omega-3 fatty acids by the Environmental Working Group due to high omega-3 content and low mercury levels

Note: The omega-3 contents and mercury levels shown in the above chart are based on an analysis included in Dietary Guidelines for Americans 2010, a white paper published jointly by the U.S. Department of Agriculture (USDA) and the U.S. Department of Health and Human Services. While the chart can give indication as to which fish are likely to be high in omega-3 and low in mercury, it is important to note that the data has been criticized by the Environmental Working Group (EWG) for a number of reasons. For example, according to EWG, the federal government's mercury monitoring program is incomplete and underestimates the true mercury levels for many species of seafood sold in the U.S. The public-interest watchdog has also pointed out that omega-3 fatty acid estimates for fish and shellfish in the USDA nutrient database are based on very few samples and may not reflect real-world exposures.

References

S. Lunder and R. Sharp (2014). US Seafood Advice Flawed on Mercury, Omega-3s. Environmental Working Group (EWG). Link
References: Dietary Guidelines for Americans 2010, Appendix 11. U.S. Department of Agriculture (USDA) and the U.S. Department of Health and Human Services.