Résumé
In aquaculture,fish are exposed to unavoidable stressors that can be detrimental for their health and welfare.However, welfare in farmedfish can be difficult to assess, and, so far, no standardized test has been universallyaccepted as a welfare indicator. This work contributes to the establishment of behavioural welfare indicators in amarine teleost in response to different water quality acute stressors. Groups of tenfish were exposed to highTotal Ammonia Nitrogen concentration (High TAN, 18 mg.L-1), Hyperoxia (200 % O2saturation), Hypoxia (20 %O2saturation), or control water quality (100% O2saturation and TAN < 2.5 mg.L-1) over 1 hour. Fish were thentransferred in a novel environment for a group behaviour test under the same water quality conditions over 2hours. Videos were recorded to assess thigmotaxis, activity and group cohesion. After this challenge, plasmacortisol concentration was measured in a subsample, while individual behavioural response was measured in theotherfish using novel tank diving test. Prior to this study, the novel tank diving test was validated as a beha-vioural challenge indicative of anxiety state, by using nicotine as anxiolytic drug. Overall, all stress conditionsinduced a decrease in activity and thigmotaxis and changes in group cohesion while onlyfish exposed toHypoxia and High TAN conditions displayed elevated plasma cortisol concentrations. Inpost-stress condition,activity was still affected but normal behaviour was recovered within the 25 minutes of the test duration. Ourwork suggests that the activity, thigmotaxis and group cohesion are good behavioural indicators of exposure todegraded water quality, and could be used as standardized measures to assessfish welfare.