The exponentiating use of fish for food, biomedical research, or as ornaments has prompted an increased interest in their welfare, with one question in particular—their capacity to experience pain—receiving major attention. Those dismissing this possibility argue that fish neither possess the neuroanatomical and physiological processes necessary for the full (presumably mammalian) capacity to feel pain nor the behavioural repertoire necessary to convince human observers that they do. However, using the sentience framework developed by Birch et al. (Review of the evidence of sentience in cephalopod molluscs and decapod crustaceans. LSE, The London School of Economics and Political Science, 2021) this chapter provides evidence that fish experience pain and that optimising fish welfare depends on accurate pain recognition and the subsequent delivery of effective analgesic strategies. The chapter reveals the various signs that are used to assess pain in fish, e.g. physical appearance, production-related, physiological and behavioural changes, and discusses the role of anaesthetics, e.g. MS-222 and isoeugenol, and analgesics, e.g. morphine and lidocaine, in pain management.