Researchers at the Roslin Institute and the University of Edinburgh have produced convincing evidence that fish can perceive pain. The study revealed that rainbow trout possess receptors (called nociceptors) that respond to damaging stimuli. Moreover, the receptors also respond to the application of short-acting noxious agents by undergoing significant physiological and behavioral changes that are comparable to those observed in mammals following exposure to painful stimuli.

The Scotland-based researchers used electrophysiological recordings to monitor anesthetized fish following the application of mechanical, chemical, and thermal stimuli to the head. Additionally, the researchers injected bee venom and acetic acid into the fishes' lips. "Anomalous behaviors were exhibited by trout subjected to bee venom and acetic acid," stated Dr. Lynne Sneddon, who led the research team. She noted that fish demonstrated a "rocking" motion, "strikingly similar to the kind of motion seen in stressed higher vertebrates like mammals."

Sneddon explained that the research "demonstrates nociception and suggests that noxious stimulation in the rainbow trout has adverse behavioral and physiological effects. This fulfills the criteria for animal pain."

Sources: Press Release by Roslin Institute-University of Edinburgh research team (Scotland), News in Science