In order to conserve wild fish stocks, it is essential to know how to handle fish causing the minimum of distress. Firstly fish with barbless hooks, you will hook more anyway (even if you do loose a few more - in fact with floating lines the difference is in the angler's favour). Next, long drawn out fights kill fish. A long fight causes a build up of lactic acid which can be fatal to fish.
The days of impressing people with talk of huge fish taking hours to land are over. Nowadays, the bigger the fish and the shorter the fight; the greater the respect. Whereas anglers lied before with stories of three hour battles, now they exaggerate in seconds.
Handle fish with knotless mesh nets and wet hands. Dry hands and knotted nets remove fish's protective slime. Warm hands cause heat stroke, damaging fish's sensory organs.
Holding fish upside down causes them to struggle less. Struggling fish get damaged. Hold them gently, but firmly, away from gills and eyes (sensitive areas).
When returning them, hold them facing upstream (if in a river) and help them to get oxygen flowing over their gills by nudging them forwards. Take your time in returning, these fish are the future.
In the UK there are still people around who seem to have to justify their desire to fish by concepts of food hunting. It is a moral issue for them, and in my opinion a completely false one. The simple fact is that if wild fish continue to be treated in this way, there will come a time when there are no wild fish left anymore. They are a pretty rare commodity already. As regards to wild fish stocks, catch and release must be practised.
In other counties, such as the States and New Zealand for example, there are many no-kill rivers. Also, especially in the States, there are many anglers who would never dream of fish killing. Indeed the moral issue has taken full circle.
I personally think a small controlled cull is good for healthy trout populations. However this does not mean the killing of the largest fish in the best of condition. These fish carry the best genes. I never kill wild fish of larger then average size, let alone trophy fish.
If you want fish for the table then please take them from stocked waters. And if you are lucky enough to own a water of your own please only stock it if there are no indigenous fish already there. Introduced pig-fish have already destroyed the finest river fishing in the UK.
One thing that is completely beyond me is that with the drastic reduction in salmon and sea-trout population in Scotland and Ireland, anglers are still killing fish and complaining that things are really in a shambles all the while. If they can't bear to return fish then they should take up golf or something similar and let the fish get on with their survival struggles.