Responsible anglers humanely dispatch their fish before cleaning or icing them. Fish welfare is a relatively new area of research, but over 500 studies on fish intelligence and sentience show that fish are feeling, social creatures who can learn from other fish, use tools, build nests, experience distress and feel pain. Fish can be quickly and easily killed with minimal distress using the simple method of percussive stunning and bleeding.
The quickest, easiest humane method of killing a fish is percussive stunning. Percussive stunning involves striking a quick, hard blow to the top of the fish's skull, just behind the eyes. The blow to the brain immediately kills or renders the fish unconscious. You want the blow's mechanical force, when absorbed by the brain, to disrupt neurological activity without necessarily crushing the skull.
Smaller fish can be held in one hand for percussive stunning. Larger fish can be laid on the belly on a boat deck or other firm surface. Many anglers use a priest, or small club, made specifically for the job, such as the Delta Tackle Fish Wacker. Once you determine that your fish is dead or unconscious, percussive stunning should be followed by bleeding.
There are a couple of quick tests you can use to determine if you have indeed dispatched your fish. Test the eye roll reflex by rotating the fish in your hands and watching the eye. If the fish is unconscious or dead, the eye will not move as the fish is rolled around. If the fish has been dispatched, there will be no rhythmic movement of the operculum, the bony plate that covers the gills. Finally, if the percussive stun was successful, the fish will not attempt to swim when placed in water.
Percussive stunning should be followed by bleeding to maintain a high fish flesh quality. To bleed the fish, turn the fish belly-up and find the thin flap of skin between the gills at the base of the throat. Hold the fish by the head in one hand. Point the fish's throat away from you and hook your finger around the skin flap. Pull to sever it. This will open up two large blood vessels in the throat. Allow the fish to bleed out before cleaning it or putting it on ice.
There are methods of dispatch that have been deemed unacceptable by the Humane Slaughter Association and FishCount.org.uk due to the pain and distress they cause prior to death. These include: live chilling in ice water, which causes suffocation; cutting the gills to bleed out without prior stunning, which causes pain; and removal from water, which causes a violent suffocation.