How long should you cook fish for?

It depends on what method your using to cook the fish, what kind of fish you're trying to cook, and the size and quantity. Classical French method would be to pierce the side of the fillet or the whole fish with a thin metal wire or cake tester, leaving it there for about 5 seconds. Remove the wire and hold it to your lip, if it's warm or tepid, you're fish is ready. If it's hot, it's probably over cooked. Keep in mind that all things will continue to cook after they have been removed from the heat.