Apparent digestibility coefficients (ADCs) of macro- and micronutrients and energy of two diets were measured with common carp Cyprinus carpio reared at two water temperatures (18 and 25 °C). Two diets containing either soy protein concentrate (SPC) or Norwegian herring meal (FM) as a major protein source were formulated. Dicalcium phosphate was incorporated at a level of 4 % of the former diet. Duplicate groups of 20 fish (body weight: 55 g) were fed by hand twice a day to apparent satiety. After a 7-day conditioning period, faecal collection was made over 10 days using an automatic faeces collector. ADC of dry matter was not different (P > 0.05) between fish fed the two diets at 18 °C, but at 25 °C, we observed a higher ADC value in fish fed the FM diet than in those fed the SPC diet. ADC of protein was higher in fish fed the SPC diet than in the FM groups at either temperature. ADC of lipids was not different between the two groups at 25 °C but was found to be higher in fish fed the SPC diet than in the FM group at 18 °C. ADCs of energy and ash of the two fish groups remained constant at both water temperatures. Availability of phosphorus was significantly higher (P < 0.05) from fish meal based diets than from SPC based diets at both temperatures. A more striking effect of dietary protein source was found in the availability of calcium, which was lower in carp fed SCP based diets.