The combination between ethics and science in the field of animal welfare is not novel. Nonetheless, when we think of this combination in the area of fish welfare, novel considerations arise (cf. Huntingford et al. 2006). This was the reason to organize an expert meeting aiming to bring together a variety of academic disciplines that are involved in welfare studies to discuss fish welfare. This expert meeting about fish welfare and its moral implications, organized on November 29 and 30, 2010, by the Ethics Institute of Utrecht University, has been the occasion of this Special Issue. The meeting involved international experts from diverse academic backgrounds, including marine biology, physiology, the philosophy of mind, and ethics. For this special issue we have approached a number of the speakers at the expert meeting, but we have also invited other researchers to make a contribution. During the meeting, it appeared that the focus on fish makes a relevant difference and raises challenges both to the individual disciplines and to the interplay between ethics and science. Fish are special. Special in a biological and physiological sense, as well as from an ethical perspective. In our view, moral decision making consists of a reflection process in which facts, intuitions, and moral principles play a role (cf. Van der Burg 2008; Van der Burg and van Willigenburg 1998). Each of these three tiers has its own input. For example, in order to reach a decision about the implementation of certain welfare measures in aquaculture, we need factual input about the consequences of different welfare measures, about levels of fish consciousness and suffering, etc. However, what particular facts one emphasizes or deems relevant, or how one interprets facts, is not objective or value-neutral. Research methodologies and the interpretation of research results are influenced by normative assumptions. In moral judgments, in turn, intuitions play a role; for example, intuitions can be a signal that something