In commercial aquaculture, knowledge about and means for predicting growth rates, feed intake and energy requirements of the farmed animal in different conditions is essential for the viability of the enterprise. As Eurasian perch (Perca fluviatilis L.) is relatively new in culture, no growth models or suitable models for evaluation of the daily feed allowance of this species was available. There was also a large gap in information regarding management practices and optimal culture environment for juvenile and adult perch. Therefore the focus of this thesis was to evaluate the growth potential and energy requirements of perch of different body size and at varying temperature conditions, and to assess the effect of different rearing conditions on growth and energy expenditures of perch. Growth, feed intake and energy requirements of perch reared under different conditions (temperature, size of fish, tank colour, light intensity and disturbance) were studied in experimental tanks. Growth (the Thermal Unit Growth Coefficient, TGC) of perch was found to be affected both by body size of the fish and by temperature. However, in limited temperature intervals, TGC was quite stable. Furthermore, the digestible energy need (DEN) of perch was found to be affected by body size of the fish, but not by temperature. A growth model and an energy requirement model were developed and then combined to create a model for estimation of the theoretical daily energy requirement of perch in intensive culture. The developed models produced realistic results if compared to reference and validation data. The sensitivity of perch to disturbance was found to be high. The effects of stress on growth and energy expenditures were dramatic, and care should be taken to reduce stress of perch in culture in order to improve welfare of the fish, growth rates and thus farm economics. No specific tank colour seemed to be preferred by the fish, which was attributed to the ability of perch to adjust its body colour according to the surroundings. However, tank colour in combination with light intensity affected growth and feed intake of the fish. Selection of a suitable colour for rearing tanks should therefore be performed in accordance with ambient lighting conditions in the rearing facility
