I fish a lot and I do know the hole, depending on how big, does scar. Having caught a few fish myself and noticed scarring from pervious catch and releases. I always wondered about pain, because I know Bass are a very smart fish and will often not bite again for several days after being caught and usually not on the same lure. I always wondered if it was because they associated the lure with pain, and didn’t bite again for a few days because they hurt.
I have caught fish with most of their mouths ripped open..with hooks still inside the mouth, the belly, the gills. The hooks do eventually work themselves out or fall apart and it is always better to cut the line and leave the hook if it is buried too deep in the mouth. This doesn’t always mean the fish will survive but it has a better chance than if you try to pull the hook out.
How long it takes for these wounds to heal is a mystery to me, but having a fish tank and having worked in a pet store, I have seen “hole in the head” a disease that a certian type of fish gets. It is an actual hole that develops in the head it can take months for the hole to heal. For some fish it never completely heals and there is always a scar. http://en.wikipedia.org/wiki/Hole_in_the_head_disease I can only assume it would take a while for the hole to heal depending on how big and where it is located. The mouth of a fish is not as dense as the head/body tissue so it may be a long heal time for the mouth.
Catch and release works quite well, as long as you don’t allow the fish to swallow the hook. Once the fish has swallowed the hook it’s chances of survival become very slim.
I catch and release all my fish.