To what extent fish can experience suffering and enjoyment is not just an empirical question, but one that also calls for ethical reflection. This is firstly, because animal welfare research is value laden and secondly, because the empirical evidence requires a normative framework in order to become action guiding in practices involving fish, such as aquaculture. In this chapter, we describe the role of ethics and different ethical theories that have been applied in animal ethics and that are relevant for discussions on fish welfare. We particularly focus on utilitarian, rights based, relational, and virtue ethical animal ethics theories. We furthermore argue that fish welfare is a term that combines moral norms and biological concepts. After all, when we implement fish welfare measures we have already made certain normative choices. We illustrate the integration between ethics and science in seven steps, from implementing fish welfare at the farm level, to weighing welfare against other values, defining and measuring welfare, to the questions of why welfare is morally relevant and what this means for the moral status of fish. We then consider the question of whether fish should be attributed to moral status and hence whether their welfare should be taken into account in our moral deliberations. However, not all moral concerns regarding our treatment of fish can be addressed by focussing on welfare. We discuss a number of concerns beyond welfare that need to be taken into consideration in a moral discussion on how to relate to fish: does the killing of fish constitute a moral harm? and how should we morally evaluate the process of domesticating fish in aquaculture? The chapter concludes by pointing out a number of moral issues in four practices involving fish: aquaculture, wild fisheries, experimentation, and recreation.