Preheat the oven to 350 degrees

Rinse the whole fish and pat it dry. In a heavy casserole large enough to hold the fish and all the salt, make a 2 inch layer of salt. Make a shallow, fish shaped impression in the salt and lay the fish on top. Distribute the remaining salt around and over the fish so that it is completely covered. Pat the salt down gently, cover the casserole and bake for about 1 hour. Remove the cover and tap the salt to break it (it will have formed an armorlike crust). Break the crust and pull off most of the salt. Then peel away and discard the skin. Serve the flesh immediately, accompanied by the Romesco sauce.