Discarding fish organs into the water may be illegal. Chill the fish with plenty of ice. Cooling fish is critical. Spoilage begins as soon as the fish dies. All fish, gutted or not, spoil rapidly if they aren't chilled right away.
Ice is the best choice for chilling fish.
Cold sea or lake water is the next best choice, followed by covering the fish with a wet cloth. Note the temperature of the water in which you're fishing. Keeping fish in water that warm isn't a good idea. If you plan to be out all day in a boat, bring ice. Never let fish lie in the sun.