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Animals show a great variety in physiological and behavioural responses to stressors. These responses are often bimodally distributed within populations and show consistency on an individual level over time and across situations, which in terrestrial vertebrates have been identified as proactive and reactive stress coping strategies. Proactive animals show lower cortisol responses, higher sympathetic activation and brain serotonergic activity compared to reactive animals. Behaviourally, proactive animals are more aggressive, more active in avoiding stressors, they form routines and show fewer cases of conditioned immobility compared to reactive animals. Our aim has been to reveal if such stress coping strategies exist in fish. Our results show that rainbow trout with high (HR) or low (LR) cortisol responses to stressors differs in sympathetic activation and brain serotonin turnover in the same manner as proactive and reactive mammals. HR fish showed less locomotor activity when reared in large groups (30 individuals) compared to LR fish. When reared in isolation there were no differences between HR and LR fish when exposed to stressors within a familiar environment. The adaption of a proactive coping style among reactive coping individuals when they are challenged within a familiar environment has previously been shown to be distinction between proactive and reactive coping mammals. However, when they were transferred to unfamiliar environments a behavioural difference between the two lines was observed indicating different stress coping strategies akin to those described in mammals. Finally, we observed a consistency over time in the cortisol response of an unselected line of rainbow trout. Fish from this line also demonstrated a correlation between behavioural responses to different stressors. However, there was no apparent connection between these behavioural responses and the cortisol response. Overall, the results of this thesis have strengthened the hypothesis that different stress coping strategies exist in teleost fish.