Catch and Release Fly Fishing Techniques
Play the Fish Quickly
You have hooked up with a nice fish. You want to enjoy the fight but still land it quickly enough so the fish has energy to recover. As a fish fights to get away, they build up an oxygen deficit just as humans do in physical activity. This lack of oxygen stresses the fish. Playing a fish too long may prevent it from recovering upon release.
When the fish's head comes out of the water and it no longer sprints off or makes a run, it is just fatigued enough to bring in and let it go.
Remove the hook and handle the fish gently
If possible, remove the hook without removing the fish from the water. Keeping the fish in the water will replenish some of the oxygen lost during the fight.
Generally a trout will be hooked in the upper or lower jaw or in the side of the jaw. Occasionally a fish will become hooked near the eye or swallow the hook into its throat. In such a case take a pair of clippers and cut the leader as close to the hook as possible. Over time, the hook will rust out. Bronzed or steel hooks rust out faster than stainless steel or gold plated ones.
Keeping the fish's head just out of the water, use a pair of forceps or needle nosed pliers try to grasp the hook at the bend. Then back the hook out. This is where barbless hooks facilitate removal.
Most fish have a protective "slime" coating. This coating is a protective shield against parasitic and fungus attacks and is easily damaged by handling or netting. Gills are another sensitive area. The gills supply oxygen from the water. Never grab a fish by the gill plates or gills.
If you must remove a fish from the water to remove the hook, untangle a dropper fly or take a photo, handle the fish gently and return it to the water as soon as possible.
Wetting your hands before picking up a fish will help to minimize damage to the fish's slime coating. If you are using a net, use one with a seamless soft mesh and a shallow bag that minimizes damage to the fish and the slime coating. Such nets also facilitate revival and release of the fish.
Please don't use some piece of junk net with that old large green hard knotted netting.
Smaller trout can often be immobilized by picking them up by the lower jaw. Don't try this with large trout. Temporarily immobilize larger trout or other species by gently grasping them around the belly and turning them upside down. Then use the other hand to remove the hook.
Never squeeze a fish, you may damage it's internal organs. Imagine a giant squeezing you and what would happen. You may especially damage a fishes air bladder that it uses for buoyancy and to keep itself upright.
Remember to:
wet your hands first
handle the fish gently
protect the slime coat
use a net with a soft seamless or new rubberized bag for netting a fish
not squeeze a fish or grab by the gills or gill covering
grasp just in front of the tail and under the belly just behind the gill coverings. NEVER insert your fingers into the gill coverings.
remove the hook as gently as possible, this will improve the fish's chances of surviving being caught.
Revive and release the fish
During a long fight, handling and hook removal, a fish can become exhausted and starved for oxygen. This final stage of Catch and Release can mean the difference for the fish's survival and death.
First, never throw a fish into the water, you may damage its internal organs. If it is oxygen starved, you have just added to the stress level and the fish will likely die. Respect your quarry. Throwing a fish into the water is not respectful.
Grasp the fish loosely in front of the tail and cradle the belly in your other hand.
Place the fish in slow water with the head facing the current so it can regain equilibrium.
If necessary, gently rock the fish forward and back so water passes over the gills allowing the fish to re-oxygenate and recover.
The fish will tell you when it is ready to go by swimming away on it's own.
Often a fish may finish its recovery by hiding behind your boots or a nearby rock.
--taken from Fly Fishing Colorado