Tuna at Tokyo's Tsukiji Market—overfished and flown round the world

Koichi Kamoshida/Getty Images

There seems to be a sushi joint on every corner in every city in North America, and a lot of fish are being caught to feed this craze. It is an international market, with fish flying round the world to satisfy the demand. But many of these fish are under threat, are being overfished, are no longer safe to eat, or part of a complex chain that makes them unsustainable.

The Environmental Defense Fund has produced an excellent sushi selection guide that can help you out. It divides the fish among Eco-best, eco-OK, and Eco-worst along with the Japanese names for the sushi so that it is easy to find. When online, you can click on the particular fish and get a lot of detail; you can also print out a pocket guide or even get it on your mobile phone—it looks terrific on an iPhone.

Some examples of eco-worst fish: