Pain and stress responses in farmed fish.

Farming fish for human consumption continues to expand as an industry and, with this increasing interaction with captive fish populations, there is now a growing interest in determining how to create good welfare for the fish we farm. This article summarises recent advances in our understanding of pain and stress responses in fish and how these relate to farmed fish welfare. Over the last decade several studies have examined whether or not fish feel pain, how aversive the experience is, and how such experiences may be mitigated through the use of analgesics. The basic neural mechanisms that enable the detection of tissue damage, i.e. nociceptive mechanisms, appear to be broadly conserved from fish through to birds and mammals, however, there is debate about the extent of the negative feelings associated with pain and whether these are truly experienced by fish. The stress response that helps fish to cope with various challenges also appears to be largely conserved across vertebrates, and the physiological changes that occur in response to acute and chronic stress in fish are similar to those described for mammals. Therefore, fish appear to have the innate ability to experience negative states such as pain and stress in a way analogous to that experienced by other vertebrates. There are multiple situations in which farmed fish may experience pain and stress and there is now a growing recognition that, to deliver appropriate welfare, on-farm practices and procedures will have to change. It is also the case that the welfare requirements of the different fish species that we farm vary, with some species coping better in captive rearing environments than others. The topic of fish welfare is relatively new and more research on stress responses, allostasis, pain thresholds and analgesics is required to help promote good fish welfare.