Monterey Bay Aquarium regularly updates and releases a seafood watch report that specifies what foods people should choose to help maintain healthy, sustainable oceans. These are the listings in their most recent report.
The “EAT THIS” column lists what the MBA considers the best seafood choices. These fish are abundant, well managed, and caught or farmed in environmentally friendly ways.
The “NOT THIS” column lists fish to avoid, at least for now. They come from sources that are overfished and/or caught or farmed in ways that harm other marine life or the environment. Cut off from the bottom of this list are Yellowfin*, Bluefin*, and Canned tuna (except troll/pole caught).
For fishes marked with an asterisk, it is recommended you limit the consumption of them due to concerns about high concentrations of mercury or other contaminants.
For more information, as well as a list of good alternatives to the best choices, you can check out this pdf, or go to www.seafoodwatch.org.