How important is a clean kill to you? Would a stone shot be considered the only clean kill with a fish, or do you have other guidelines? If the only clean kill was a stone shot then it doesn't seem all that important as most of us enjoy the fight with a big fish. I usually feel good about it if the shot was such that I knew there was no way for a fish to rip off, something like an angled shot through body and head.
What about with other animals? As I explore my feelings I find that the common factor when I feel good about a kill is if there was no moment in the hunt where I worried the animal may be lost due to incompetence on my part.
In nature there is no such thing as a clean kill, just whatever worked. Or the other way to look at it is that in nature any kill is a clean kill. If a clean kill is wholly dependent on how you feel about it, does it even really matter? If it doesn't matter then why does the concept of a clean kill exist?