The overarching conundrum of this master thesis was to study the movement behaviour and activity of hatchery reared marble trout (Salmo marmoratus) and rainbow trout (Oncorhynchus mykiss) after their release into natural habitat of the river Kanomljica. Since rainbow trout is a non-native species, originating from North America, it might present a certain amount of disturbance for the native marble trout. We investigated the general activity of fish, their diurnal preferences and habitat use and investigate potential differences between marble trout and rainbow trout regarding these parameters and determine if rainbow trout has negative impact on native marble trout. Fish were monitored using telemetry. Field work has been done in the late summer of 2017. Telemetry technology provided spatiotemporal stamps, which served as a basis of all the subsequent calculations. In the process of data analysis, we calculated distances between spatiotemporal stamps and analysed the swimming activity, diurnal preferences and habitat use of fish. Our results showed no differences in general activity between species and no differences in diurnal preferences. However, our results did show statistically significant differences between species in habitat use with marble trout residing mostly in rapids and laminar flow and rainbow trout residing mostly in pools. Our results did not show major negative impact of rainbow trout to the native marble trout. However, we imply that fish interactions might be too subtle for detection with our method of choice.