My dog yelps if I accidentally step on her paw. No further “studies” needed for me to know if animals….. feel pain. Fish? IDK. The catfish starts “croaking” when he’s removed from the water signifying some type of stress. Flip side is “God gave man dominion over all the animals, birds, fish…” thus they were created for mans use. Never purposely be cruel to anything but past that: ITS A FISH!