Effect of Different Levels of Calcium on Growth Criteria and Survival of Freshwater Crayfish, Astacus leptoductylus

The study was conducted to compare the efficiency of diets containing various levels of calcium(0, 1, 2, 3 and 4 percentage) in feeding freshwater crayfish, Astacus leptoductylus. 150 cray fish (10 individuals per tank) with mean weight of about 8-9 gram were stocked in each of 15 tanks, containing 100 L of water. In this research, The results showed that the mean values of some parameters such as weight gain (WG), weight increment rate (WIR), length increment rate (LIR), specific growth rate (SGR), biomass increment (BI), food efficiency rate (FER) and survival rate (SR) of animal fed on different diets were 0.75-1.46gr, 9.8-24.54%, 6.57-15.33% and 0.12-0.29% respectively. However, the diet with high levels of calcium (3-4%) showed the good weight and length increment, but there were no significants difference among these indices using different trial diets. The biomass of crayfish increased with increasing of calcium concentration. So, the highest biomass (11.65gr) of crayfish was observed in the diet containing calcium about 4%. Optimal calcium requirement in the freshwter crayfish was estimated about 3.4% with broken-line regression analysis. The lowest survival rate (30%) was obtained in the diet containing 2% calcium level. There were significant differences among survival rates in various experimental diets (p<0.05). These results indicate that the dietary calcium supplement is nesessary for crayfish. The diets with high levels of calcium had a good efficiency in freshwater crayfish feeding. So it is recommended to use 3-3.5% of calcium in formulated diets for freshwater crayfish