Résumé
Stress modifies energy allocation in fishes by redirecting energy from growth and reproduction to copingmechanisms. However, these adjustments become inappropriate when the challenge consists of sustained orrepeated stressors, with the animal entering a maladaptive state. Capacities to cope with additional threats arethen altered and compromise survival. The characterization of the responses to chronic stress in fishes helpsbetter understanding the physiological limits in an aquaculture or ecological context. Here, we investigate thecoping capacities of European sea bass to multiple and diverse stressors applied over a 3-weeks period. Multiplebehavioural (group dispersion and swimming activity) and physiological responses (blood cortisol, osmoregulatorymechanisms, stress-related gene expression, etc.) were evaluated in resting fish or in fish exposed toadditional challenges. Resilience to the chronic stress protocol was evaluated 4 months after the end of thechronic stress. Chronically stressed individuals showed reduced growth, lower cortisol response, increasedchloride and sodium concentration in the plasma and modified gill gene expression translating osmoregulatorydysfunctions. Chronic stress had no significant effect on plasmatic calcium, lysozyme concentration and osmoticpressure. Increased thigmotaxic behaviour was observed in a new environment behavioural test. Four monthsafter the chronic stress, no significant difference was observed in growth performances and in plasma parameters.Altogether, gills and more generally osmoregulatory functions were found to be the most sensitive to thechronic stress, while only limited changes in growth, activity of the HPI axis, immunity and swimming behaviourwere observed when assessed individually. This work demonstrates the necessity of using multiple and diverseendpoints related to different functions to properly assess health and welfare in fishes.