I find it all interesting, no one knows for sure. Every living thing has a nervous system however, its the way the brain communicates through the body. Out side of single celled organisms.
Do I believe fish feel pain, IMHO, no. One of the reasons I BELIEVE this to be true is...well ill use the hook example. If you remove the hook and place the fish in a reservoir to monitor it will most likely revert back to its normal routine. Ive caught fish before and after removing and placing in a bucket it calmly swam around the bucket. If a dentist drills an exposed area of your mouth you don't walk away as soon as the drill is removed.
I like dutch believe that all animals have reflexes that are both behavioral and defensive in nature that are triggered by natural triggers through evolution. His explanation of the burn was exactly how it was explained to me when I was in biology. The reaction is a reflex, the pain is a reminder not to do whatever it was again.
Anyways, its my little opinion probably not even worth the metal that 2 cents would be printed on, but Ive seen fish lose eyes, ive seen goldfish feed as food lose chunks out of there bodies and still swim around calmly. The eventually die due to the injuries, but if it was in pain I would think it would park a seat at the bottom of the tank and stay there.
I'll give NEMO a call and see what he has to say and update.