As of February 2013, all McDonald's fish will come from certified sustainable fisheries.

Pop quiz: If you want to buy sustainable seafood, are you better off going to McDonald's or that fancy sushi place down the street?

If you guessed the sushi restaurant…you'd be wrong. Not only did a recent report from the nonprofit Oceana find that most sushi restaurants are mislabeling fish in a way that could endanger your health, but also they often use rare, overfished (but highly valued) species.

McDonald's on the other hand? It could well be the greenest fish purveyor in the country. The chain has just announced that, as of February 2013, all the fish served in its U.S. locations will come from fisheries certified as sustainable by the Marine Stewardship Council (MSC), a UK-based independent agency that certifies fisheries that follow responsible management and fishing techniques. The chain already requires MSC certification for fish sold in all its European restaurants.

It's certainly a bold move—McDonald's officials say it's the only U.S. restaurant chain to require MSC certification for all locations—but the corporation uses just one fish variety, Alaskan Pollock, in its Filet-o-Fish sandwiches and in a new product, Fish McBites, also coming out in February. All those fish come from the same fishery, so the move isn't likely to make huge waves.

Still, the fast-food giant is the largest single purchaser of fish in the country, and its choice to purvey only sustainable fish could drive other businesses to follow suit. Walmart and Whole Foods are the only other two national chains to require MSC certification for fish sold at their stores. And at a mere 390 calories, the Filet-o-Fish is one of the chain's lower-calorie food alternatives. So if you're stuck on the road and need a fast meal, a low-cal sustainable fish sandwich isn't the worst choice you could make.