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.