ABSTRACT: It is of scientific and practical interest to consider the levels of cognitive ability in animals,
which animals are sentient, which animals have feelings such as pain and which animals
should be protected. A sentient being is one that has some ability to evaluate the actions of others in
relation to itself and third parties, to remember some of its own actions and their consequences, to
assess risk, to have some feelings and to have some degree of awareness. These abilities can be taken
into account when evaluating welfare. There is evidence from some species of fish, cephalopods and
decapod crustaceans of substantial perceptual ability, pain and adrenal systems, emotional
responses, long- and short-term memory, complex cognition, individual differences, deception, tool
use, and social learning. The case for protecting these animals would appear to be substantial. A
range of causes of poor welfare in farmed aquatic animals is summarised.