Cortisol and finfish welfare Tim Ellis • Hijran Yavuzcan Yildiz • Jose Lo ´pez-Olmeda • Maria Teresa Spedicato • Lluis Tort • Øyvind Øverli • Catarina I. M. Martins Received: 9 July 2010 / Accepted: 24 October 2011 / Published online: 24 November 2011 Ó Her Majesty the Queen in Rights of the United Kingdom 2011 Abstract Previous reviews of stress, and the stress hormone cortisol, in fish have focussed on physiology, due to interest in impacts on aquaculture production. Here, we discuss cortisol in relation to fish welfare. Cortisol is a readily measured component of the primary (neuroendocrine) stress response and is relevant to fish welfare as it affects physiological and brain functions and modifies behaviour. However, we argue that cortisol has little value if welfare is viewed purely from a functional (or behavioural) perspective—the cortisol response itself is a natural, adaptive response and is not predictive of coping as downstream impacts on function and behaviour are dose-, time- and context-dependent and not predict- able. Nevertheless, we argue that welfare should be considered in terms of mental health and feelings, and that stress in relation to welfare should be viewed as psychological, rather than physiological. We contend that cortisol can be used (with caution) as a tractable indicator of how fish perceive (and feel about) their environment, psychological stress and feelings in fish. Cortisol responses are directly triggered by the brain and fish studies do indicate cortisol responses to psychological stressors, i.e., those with no direct T. Ellis (&) Cefas Weymouth Laboratory, Barrack Road, The Nothe, Weymouth, Dorset DT4 8UB, UK e-mail: tim.ellis@cefas.co.uk H. Y. Yildiz Department of Fisheries and Aquaculture, Ankara University, 06110 Ankara, Turkey J. Lo ´pez-Olmeda Department of Physiology, Faculty of Biology, University of Murcia, 30100 Murcia, Spain M. T. Spedicato COISPA, Stazione Sperimentale per lo Studio delle Risorse del Mare, 70126 Bari, Italy L. Tort Unit de Fisiologı ´a Animal, Faculty of Biosciences, Department of Cell Biology, Physiology and Immunology, Universitat Autonoma de Barcelona, 08193 Bellaterra, Spain Ø. Øverli Department of Animal and Aquacultural Sciences, Norwegian University of Life Sciences, PO Box 5003, 1432 Aas, Norway C. I. M. Martins CCMAR, Centro de Cie ˆncias do Mar, Universidade do Algarve, Campus de Gambelas, 8005-139 Faro, Portugal C. I. M. Martins Aquaculture and Fisheries Group, Wageningen University, PO Box 338, 6700 AH Wageningen, The Netherlands 123 Fish Physiol Biochem (2012) 38:163–188 DOI 10.1007/s10695-011-9568-y