Be gentle and quick. Use thumb and index finger to grasp lower jaw, while holding the fish under water to release hook. Keep fingers out of gill area. Delicate internal organs need the water cushion. Internal organs can be ruptured easily when handled.
Gravity forces acting on a fish while it's out of the water can be harmful.
Use hemostats to remove barbless hooks. Revive an exhausted fish be holding upright, pointing upstream to force water through gills until the fish starts to struggle strongly. Slack in your line may allow a trout to free itself, making it unnecessary for you to handle it. The mortality of trout held out of the water for mere 15 to 20 seconds is 87 percent. Mortality of properly release trout is less than three percent.