excellent post, imotep.
fish have similar nervous systems as all mammals. yes it hurts.

Dr. Sylvia Earle, one of the world's leading marine biologists, said, "I never eat anyone I know personally. I wouldn't deliberately eat a grouper any more than I'd eat a cocker spaniel. They're so good-natured, so curious. You know, fish are sensitive, they have personalities, they hurt when they're wounded."

"[I]t has been shown that fish (like other vertebrate animals, including humans) have a highly developed system that may help protect them from severe pain--pain which could endanger their lives if they were seriously handicapped by it following some injury to their bodies, such as might be inflicted by a large predator. This system releases natural opiate-like substances (enkephalins and endorphins) once an animal is injured. ... The presence of this pain-dampening opiate system implies that there must be some capacity to experience pain, otherwise there would be little point in animals having evolved such a system in the first place. ..." --- Fox, Michael W., D.V.M., Ph.D., "Do Fish Have Feelings?," The Animals' Agenda, July/August 1987, pp. 24-29.



"Fish cry out in both pain and fear. According to marine biologist Michael Fine, most sound-producing fishes 'vocalize' when prodded, held or chased. In experiments by William Tavolga, toadfish grunted when electrically shocked. What's more, they soon came to grunt at the mere sight of an electrode."

-- Dunayer, Joan, "Fish: Sensitivity Beyond the Captor's Grasp," The Animals' Agenda, July/August 1991, pp. 12-18.