COPEWELL aims to provide a better understanding of the underpinning mechanisms and basic knowledge about the physiology, biology, and behaviour of fishes and to give a deeper understanding of the basic mechanisms involved in coping styles. We will use an innovative hypothesis-driven multidisciplinary approach that aims to explore the links between brain function, behaviour and adaptive plasticity (WPs 1 and 2). Underlying mechanisms will be addressed by localising key elements of the stress-responsive serotonergic and learning and memory systems in the telencephalon, and for the first time also analyse rates of brain cell proliferation, neurogenesis, and expression of genes controlling other aspects of brain function, as learning and memory, in fish expressing different coping styles. The project will also focus on the understanding of how animals experience their world, based on appraisal theory and experimental studies of appraisal mechanisms in farmed fish, and not simply on the description of animal behaviour or stress responses (WP2 Appraisal). COPEWELL will further study the ontogeny of brain function and neuroendocrine stress responses in the call species Atlantic salmon (Salmo salar), European sea bass (Dicentrarchus labrax) and sea bream (Sparus aurata), and will provide new insights on the interrelations between different relevant husbandry practices, plasticity of brain function and stress response during early ontogeny. COPEWELL will explore potential consequences of early life stress experiences on the welfare and quality of juvenile fish, substantiate the concept of allostatic stress regulation in fish and determine thresholds between eustress that are considered positive for welfare and distress that can have severe negative consequences for fish welfare as: “it will attempt to discriminate between normal adaptive stress responses and situations of potential consequence to animal welfare, in relation to different relevant husbandry practices and rearing methods” (WP3Allostasis and WP4 Ontogeny). The expected impact the COPEWELL project is to deepen our knowledge on the development of the brain function, behaviour and stress response in relation to the different husbandry practises and rearing methods. It will also serve to define how short or long episodes of stress during the early life affect the welfare and quality of juveniles and adult fish (WPs 3 & 4). It will significantly contribute in providing and extending the knowledge basis for the development of tools such as new individual-based indicators for a better assessment of fish welfare, e.g. by identifying and verifying non-invasive indicators of coping styles. Perhaps most important, COPEWELL will provide a new framework, based on evolutionary principles and an understanding of subjective experience of welfare as an evolved survival mechanism, making welfare available for scientific inquiry.