To fillet a trout by gutting it, take the knife at the tail end and gently cut along the stomach of the fish to the throat. The insert the knife between the gils and collar bone and cut perpendicular to the belly until you can remove the head. Remove the guts of the fish and then rinse the fish in cold water. While the fish is in the water, scrape away the blood line by using a spoon. Then wash the fish on the inside and outside with lightly salted water.