Pain associated behaviour
The question whether fish experience pain or suffering is still a matter of debate. Fish have a nociceptive system, i.e. a system that detects (tissue)injury in the organism and mediates appropriate behavioural and physiological responses to such injury. Several studies have demonstrated the presence of the neuronal and physiological building blocks of this system, i.e. nociceptors, afferent nerves (A-delta fibers and C fibers) and opiate receptors. Research into the motivational-affective aspect of the system – an “awareness” of pain as something unpleasant – suggests that this element of the system is also present in fish.
Although fish can detect whether they are injured and most likely also experience pain, they differ from other vertebrates such as rats, mice and humans. For instance, fish have more A-delta fibers than C fibers, whereas the reverse is true for other species. This suggests that their pain sensation may be short-lived, because A-delta fibers appear to mediate brief, “acute” pain and C fibers longer-lasting, “dull” pain. The neuroanatomy of the fish system also appears to differ from that of mammals.