Get the best for omega-3s. Some seafoods have more of these than others. The best are salmon (wild and farmed), Pacific oysters, anchovies, herring, sardines, trout, and Atlantic and Pacific mackerel.

Monitor mercury. Some people avoid fish for fear of consuming methyl mercury, which might harm the developing nervous system of a fetus or young child. Some fish contain more mercury than others, including large fish such as albacore tuna.

Pregnant women in particular should steer clear of the top four mercury-containing fish: tilefish, shark, swordfish and king mackerel (also known as golden bass). As for tuna, the dietary guidelines say women who are pregnant or breast-feeding can eat any kind of tuna they like but should stick to no more than 6 ounces of white tuna per week because it contains more mercury.

Watch cholesterol. Shrimp is a "very lean source of protein," Thayer says, but some people shy away because it is loaded with cholesterol. (It's also lower in omega-3s than other seafood.) Thayer and Kris-Etherton agree that the science is fuzzy on how eating shrimp affects cholesterol levels in your body. American Heart Association guidelines call for consuming less than 300 milligrams per day of cholesterol; 4 ounces of shrimp deliver about 160 mg.

Keep it safe and fresh. Cook fish until its internal temperature measures 145 degrees on a food thermometer, Thayer advises. Just checking to see if it's flaky isn't good enough. And the best way to tell whether fish is fresh is to give it a sniff.

"If it smells fishy, it's probably not fresh," she says. "It should have just a faint smell of the sea."