The phsyiological and locomotive reaction to factors that influence environmental behaviour of Nordic krill from the Gullmarfjorden were studied in terms of swimming energetics, predator avoidence and food utilization. In a newly developed experimental approach, individuals were maintained under defined conditions in flow through chambers and continuously monitored for swimming activity and oxygen consumption. Chemical, physical and biological parameters were applied and the reaction of the krill determined. Stress levels, defined this way, will serve as a reference for unfavourable conditions in the field. Thermal characteristics of digestive enzymes from the midgut gland were furthermore identify the optimum conditions for nutrient assimilation. The results will contribute to the understanding of diel vertical migration, dispersion and aggregation of krill which, in turn is essential for the interpretation of ecosystem dynamics and trophic interactions.