When I worked at the fisheries research center, this came up and was part of our training. I think it all comes down to how you define pain. Do fish have a reaction in the nerves and brain in response to injury? Of course. If you define pain as feeling injury, yes they do feel pain. Then again, so do almost all living creatures I imagine.
Do fish feel the emotion we call pain? Much more difficult to judge and tell. Fish are primative creatures with a small brain in relation to body size. Do they really have emotions at all, or do they just respond to stimuli? There are some studies that have been done that we read (or were supposed to!) at the lab which concluded that fish lack the brain to form complex emotional “fear” that mammels do in response to pain. They basically just live to live and rely on instinct and reaction to survive.
There is probably alot of literature out on the subject.
My personal belief is that fish feel the hook and realize they are injured, but do not have the emotion that goes with it. I don’t get too worked up over fish. Hey, if they could eat you, they would just swallow you and let you digest. That would be a bad way to go!!
Went and did a quick search and foudnthis article. I’m sure there are many more out there.
http://www.cotrout.org/do_fish_feel_pain.htm