Wild trout are a precious resource and filling the freezer with them is not sustainable! Wild trout that are caught and released carefully will live to breed and be caught again. Catch-and-release can make a huge difference to the quality of fishing on a wild fishery.
Use tackle that is an appropriate strength for the size of fish you expect to catch, as this avoids you having to play fish for a long time before landing. Long fights in warm weather are especially damaging.
Use barbless hooks and have pliers to hand in case of difficulty. If the fish is deeply hooked, cut the line as the hook will work its way out and this is less damaging than a prolonged wrestling match.
Always use wet hands to handle fish, and handle as little as possible. Avoid squeezing it. Try to release in the water and avoid landing on the bank or on gravel as this removes the surface slime and leaves the trout vulnerable to fungal infections. Photograph your fish close to the water, holding it out of the water as briefly as possible. Measure it rather than weigh it.
Release the fish by pointing its nose into the current so that water is flowing over its gills. If necessary, move gently back and forth until it swims away (below).