Real Simple asked Tim Fitzgerald, a marine scientist for the Oceans program of the nonprofit organization Environmental Defense, to list the healthiest picks for you―and for the environment. You can download and cut out a foldable pocket-size guide.

* Because this fish is high in mercury or other contaminants, those who are pregnant, nursing, of child-bearing age, or feeding young children should avoid it entirely. 

Twice a Week:

• Catfish, U.S.
• Caviar, U.S. farmed
• Char, Arctic; farmed
• Clams, farmed
• Crab, Dungeness and stone
• Herring, Atlantic
• Mackerel, Atlantic
• Mussels, farmed
• Salmon, wild Alaskan
• Scallops, bay; farmed
• Shrimp, U.S. farmed
• Striped bass, farmed
• Sturgeon, farmed
• Tilapia, U.S.
• Trout, rainbow; farmed

Once a Week:

• Halibut, Pacific
• Sablefish (a.k.a. black cod), Alaska or Canada
• Tuna, albacore (a.k.a. white); canned or fresh; U.S. or Canada*