Some fish ought not to be eaten, because we have so overfished them that these fish and other sea creatures are becoming endangered. Bluefin tuna, Atlantic cod and Chilean seabass are just a few popular examples. If you want to eat them again down the road, it's time to give them a break now -- here is a list of some especially endangered seafood along with some sustainable alternatives. Where I can, I will also give you the few exceptions where an otherwise threatened fish is being caught sustainably somewhere.
1. Bluefin TunaBluefin tuna is one of the tastiest -- and most threatened fish in the ocean. They are overfished everywhere they live, which is all the world's temperate oceans. The popularity of sushi has largely done in these gigantic, slow-maturing fish; one tuna can bring tens of thousands of dollars at the great fish markets of the world. Alternatives would be yellowfin and bigeye tuna, often sold under the Hawaiian name "ahi." Be sure to buy tuna caught by American fishermen, who are subject to strict environmental rules foreign fleets are not.
2. Red SnapperRed snapper is a great fish, but it has been hammered everywhere it swims, particularly in the Caribbean. From a taste standpoint this reef fish is excellent -- but not so fine that the more plentiful gray or yellowtail snappers can't substitute for them. And honestly, avoid the problem altogether and buy black seabass if you are on the East Coast, or Pacific Rockfish if you are in the West. If you must have real red snapper, make sure you buy the varieties that live around the Hawaiian Islands -- these are not overfished. Yet.
striped bass or Pacific white seabass as an alternative.
Pacific halibut and Pacific cod are both virtually identical to their Atlantic cousins, and neither is in bad shape.
tilapia or Pacific sole -- Petrale sole, especially -- or flounder as an alternative.