I certainly think some fish learn by their mistakes !!
I'm sure those of us who have been around Carp fishing for a number of years can think of carp that rarely if ever get caught on carp baits as they get older.
How many times do you hear that so and so carp has died or has been moved at some well known waters, only to find that the carp in question is still in the said water, it's just wised up to anglers baits and methods.
And of course it's not just Carp, many older fish that have seen the Bank when younger, can wise up.
Big Chub, Bream and Roach all seem to become extremely difficult on at times on pressurised venues.
Good angling skills or tricky rigs often fail to capture these clued up fish, I don't know if you can call it inteligence or just a heightened survival instinct, but there are certainly some very tricky fish that hardly ever get caught.
Bob