It can be really confusing as you stand before a case of fish to remember which ones are higher in contaminants, getting overfished, best for our health, and so on. Seafood Watch from the Monterey Bay Aquarium and the Environmental Defense Fund both offer guides you can print and fold to wallet size, which make shopping much easier. Seafood Watch also has downloads for certain smart phones. Both also have extensive and reliable information available on their web sites.
For additional information, see Sustainable Fish and Seafood Choices and The Best Sustainable Fish Sources of Omega-3s from Cooking Light. And look for the green fish icon in every issue of Cooking Light which highlights recipes that call for fish or shellfish with healthy populations that are caught or raised by environmentally friendly means such as Arctic Char with Blistered Cherry Tomatoes (pictured above).