I think they are confusing response to an irritation (like itching) to be pain.
They specifically injected TOXINS (bee stings are poison, right?) and things that cause swelling (another reactive thing) and watched the reaction of the fish. No doubt they reacted funny.
The question is, is how long after the affects of the test did the fish return to normal behaviour?
If it was true pain, they would never eat again. Like others have mentioned, fish eat sharp things all the time.
Tell a PETA person to check the sharpness of a catfishs fins, or the pinchers on a crawfish, the fins on a bluegill, etc....
Fish in aquariums can be conditioned. I have a 220 Gallon that I just set up. Caught several varieties of sunfish and a couple (trep size 3") of spotted bass.
WIthin a day or two I have ALL of the fish eating from my hands, nightcrawlers, aquarium flake food, etc... And no K&B needed.
Another true test for pain is the reaction... you dont pull against pain. watch a bull, put a ring in its nose and you can pull it anywhere. Put a hook in a fish, and it pulls awayf from you.
Blast them PETA people.
Beyond that, so what if fish feel pain? That doesnt make it unethical to fish for them.
They can take my fishing pole when they pry it from my cold dead fingers!