Effect of four rearing water temperatures on some performance parameters of larval and juvenile crucian carp, Carassius carassius, under controlled conditions

The performance of larvae and juveniles of the crucian carp, Carassius carassius, held at temperatures of 22, 25, 28 and 31 degrees C was evaluated in terms of growth, survival and, only in juveniles, haematological indices. The best growth in both larvae and juveniles was recorded at 28 degrees C (relative growth rate (RGR) of 27.52% and 3.50%/day, respectively). The highest final survival rates were found at temperatures of 25-28 degrees C, exceeding 99% in larvae and equal to 100% in juveniles. Haematopoietic activity and leucocyte count were significantly disturbed at temperatures of 28 and 31 degrees C. These temperatures were stressing to the juveniles, as shown by the lymphopaenia and neutrophilia found in their peripheral blood and haematopoietic kidney. Thus, the optimum temperature for growth of larval and juvenile crucian carp is close to 28 degrees C. However, stress indicators found at this temperature in juvenile fish strongly suggest that the most favourable temperature range for long-term rearing is below 28 degrees C and near to 25 degrees C.