The second most intimidating factor, after the act of buying the fish, is how long to cook it. It can go from undercooked to overcooked in a heartbeat. In general, fish cooks in 9 minutes per inch of total thickness (in the case of whole fish, at the thickest part, near the base of the head), but this can vary depending on the shape and size of the fish. The species, in contrast, makes little difference, and most can be cooked in the same way.
Unlike meat, which is cooked to different degrees depending on the type and the cut, fish is almost always cooked to about 135°F., the point at which it loses its translucency. Cooking it beyond this point will only dry it out. Despite what many recipes say don’t cook fish until it flakes, or it will be overcooked.