| Summary: | Farming of Arctic charr takes mainly place in land-based farms applying intensive rearing methods with relatively high production costs. Depending on local conditions at each site, it is possible to regulate important environmental factors to improve productivity and well-being of the fish. Knowledge about how these different environmental factors affect various farming traits are therefore important to reduce production costs. The aim to this thesis was to investigate how rearing temperature, photoperiod, salinity and feeding rations can be used to enhance the production of land-based Arctic charr. Rearing temperature is a highly effective tool to improve growth rate of Arctic charr. (Paper I). Juvenile Arctic charr reared at a constant temperature of 15 °C had mean weights that were 44 % and 78 % higher than fish reared at constant temperatures of 12 and 9 C, respectively. Attempts to transfer the Arctic charr down in rearing temperature as an effort to follow the drop in temperature optima for growth resulted in a consistently negative effects on the growth rate. High growth rates as observed at the higher temperature groups (Paper I) with subsequent high condition factor lead to higher incidence of maturation. Rearing of Arctic charr at periodic restricted feed rations (50 %) in Paper II led to full growth compensation (CG) of the farmed Arctic charr. Restricted feed groups had both higher feed intake and feed conversion efficiency during the re-feeding periods compared to the full ration group. Periodical feed restriction regimes had lower maturation level compared to full ration groups. The application of a six week short photoperiod within other ways continuous photoperiod improved long term growth rate of Arctic charr reared in freshwater (Paper III). Short day groups weighed 10.7–13.9 % more than the group reared on continuous light. Feed intake and feeding conversion efficiency increased following transfer to continuous light after a period of short day (Paper III) explaining the growth enhancement ...
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