For most people, the healthy fats in fish provide a huge benefit to your heart and overall health — even with a little mercury. Skeptical? Get this: Eating one to two 6-ounce servings of omega-3-rich fish each week reduces your risk of dying from heart disease by 36 percent! And your all-cause mortality rate drops by 17 percent.

Soon-to-be or currently breastfeeding moms need to be especially careful to avoid excess mercury. Still, most people can do their heart and body right by eating one or two servings a week of omega-3-rich fish that is relatively low in mercury. Unfortunately, most fish contain some mercury, thanks to industrial processing. But the less time fish spend simply living in a mercury-laden environment or eating other fish containing mercury, the lower the contamination levels will be. So for low-mercury fish, we’re talking small fish that don’t eat many other fish (or fish meal) and don’t have a long life span. Here are five good choices:

1. Salmon (wild): 1 gram of omega-3 fatty acids per 2 ounces of fish;* 0.014 parts per million mercury concentration

2. Herring: 1 gram of omega-3 fatty acids per 1 ounce of fish;* 0.044 parts per million mercury concentration

3. Sardines: 1 gram of omega-3 fatty acids per 2-3 ounces of fish;* 0.016 parts per million mercury concentration

4. Trout (freshwater): 1 gram of omega-3 fatty acids per 3-4 ounces of fish;* 0.072 parts per million mercury concentration

5. Pollock: 1 gram of omega-3 fatty acids per 6.5 ounces of fish;* 0.041 parts per million mercury concentration

*Oil content varies widely, depending on species, season, environment, diet, and packing and cooking methods.

Here’s the list of fish to avoid:

• King mackerel: 0.73 parts per million mercury concentration
• Shark: 0.99 parts per million mercury concentration
• Swordfish: 0.98 parts per million mercury concentration
• Tilefish (Gulf of Mexico): 1.45 parts per million mercury concentration

So where does the beloved tuna fall? Pretty close to the middle of the road, actually, with mercury concentration ranging from 0.12 to 0.69 parts per million, depending on what kind of tuna you eat. And you’ll need to eat anywhere from 3.5-12 ounces to get 1 gram of omega-3 fatty acids, depending on how you take your tuna: Fresh tuna has the most and canned chunk light tuna has the least. But chunk light tuna also has the least mercury.

Keep in mind that oil content estimates can be fairly rough, despite the best research efforts. A fish-oil supplement is a surefire way to get the omega-3 fatty acids you want and need. But talk to your doctor first. Fish-oil supplements are dangerous for certain people.

Fish intake, contaminants, and human health: evaluating the risks and the benefits. Mozaffarian, D., Rimm, E. B., Journal of the American Medical Association 2006 Oct 18;296(15):1885-1899.

Fish consumption, fish oil, omega-3 fatty acids, and cardiovascular disease. Kris-Etherton, P. M., Harris, W. S., Appel, L. J., American Heart Association. Nutrition Committee. Circulation 2002 Nov 19;106(21):2747-2757.