Abstract
To determine whether fish welfare matters morally, we need to know what characteristics or capacities beings need to have in order to be morally considerable, and whether fish have such characteristics. In this paper I discuss a group of theories, Kantian practical reasoning theories, in which agency (or practical rationality) is traditionally thought to be a necessary condition for moral considerability. An individual must have quite sophisticated capacities to be a (moral) agent in such theories: she must be able to act on rational principles. It seems unlikely that nonhuman animals such as fish have such capacities. I argue, however, that on the basis of certain Kantian arguments, moral agents have reason to accept duties to nonrational animals if they are agents in a much less demanding sense: if they are motivated to pursue the objects of their desires. If fish have this capacity, their welfare matters morally.