If you buy your fish from a fish market, your fish will already be gutted and ready to cook. Simply rinse your fish under cool water and it will be ready to season. Frozen whole fish is also already gutted but may still have gills. Simply lift the flap and pull the gills on each side of the fish with your fingers and rinse the entire fish well under cool water. If you see any remnants of guts in the belly, remove and rinse the fish again. The fish will now be ready to season.