Talked to the guys at kelly tarltons a few years back, any fish they catch (they use barbless hooks tho) that is gut hooked, they simply put the fish into a tank and 3 days later thay find the hook on the bottom of the tank... fish pass them thru without any seeming difficulty.
Caught a hapuku once out at White that had a big sinker hanging out its butt, nylon went right thru its gut, and the circle hook was still in its jaw. It was rusting out slowly, so it had been there for a fair while, the puka was a fat as a tick and no sign of any particular distress.... it certainly had still been actively feeding.
Guess we just have to accept that fish register such things differently from us, not so much of the pain thing I think, more annoyance at the irritation probably, well, that is my thoughts anyhow. All those eedjits who liken hooking a fish with hooking a puppy or a person are total wastes of space in the cranial department.... and with no experience in animal life.