This chapter addresses the economic and societal importance of coastal and freshwater fishing during the Mesolithic of Eastern Norway. Here, new archaeological evidence of fishbone, fishing gear and site locations from different topographic environments – the coastal zone, the eastern interior zone and the mountain areas – are compiled and discussed. Increased use of aquatic resources is noticeable during the Middle and Late Mesolithic (c. 8200–6350 cal BC), even though the studied organic archaeological record are severely affected by techonomic loss. Based on general data from the region, selected key sites and comparison with diachronic finds from Western Norway, Sweden, and Southern Scandinavia, we maintain that increased use of temporally and spatially predictable aquatic foods are linked with socio-economic consequences such as reduced mobility, delay return systems, and economic and social differentiation. We further argue that rather than passively adapting to the environment, late Mesolithic populations actively intervened, transformed their landscapes and managed its resources. There is ample ethnographic evidence that indigenous non-agrarian people employed management techniques that allowed them to enhance the productivity of the local environment, and sustain supplies of key species. Based on archaeological evidence we suggest that such resource management included transportation of living trout to the upper part of the large watercourses during the last part of the Mesolithic period.