The Seafood Watch Program from the nonprofit Monterey Bay Aquarium rates seafood according to its environmental and health impacts.
The following “Super Green List" meets guidelines for being ocean-friendly, high in omega-3 fats and low in contaminants (including mercury, PCBs and pesticides): oysters (farmed), Pacific sardines (wild-caught), rainbow trout (farmed), salmon (wild-caught, from Alaska), freshwater Coho salmon (farmed in tank systems in the U.S.) and albacore tuna (troll- or pole-caught, from the U.S. or British Columbia).
Other healthful green choices include arctic char (farmed), barramundi (farmed, U.S.), squid (wild-caught Atlantic) and mussels (farmed).
By the way, you may wonder why troll- or pole-caught albacore (white) tuna gets a green light, since albacore tuna is generally high in mercury. These fishing methods catch younger tuna, which have accumulated less mercury. In contrast, long-line gear (what’s typically used in the tuna industry) catches older tuna in deeper waters that have higher mercury levels.