I think you're just missing something very important here. Unnecessary STRESS is what you should minimize in your life, or your fish's life, in order to be healthy and happy. For humans, and probably for many mammals, pain is an extremely potent stressor; in many non-mammalian animals, it is not.
Research on catch-and-release angling has shown that being pulled from the water is a much greater stressor on the fish than the hook in its mouth; humans would be far more stressed by such a wound than they would be by a brief involuntary dunking. Similarly, research on marking of amphibians and reptiles in mark/recapture studies has found that damaging but swift marking methods such as toe-clipping and shell-notching are far less stressful to animals than seemingly less hurtful marking methods that require greater handling time. In my own experience, frogs who react violently to having a leg trapped between thumb and forefinger react hardly at all to having a toe cut off. This is not shock; that is another largely mammalian phenomenon. This indifference to pain is rather counter-intuitive for us.
How fish interpret pain is far from being of metaphysical importance only; it affects how we treat them. While I'm certainly not suggesting it is OK to subject a fish to undue pain, it is far more important not to subject it to undue stress.
Just my $0.02.
