This study was performed to investigate the effect of Ca and P on rearing and biological indices of crayfish (Astacus leptodactylus). Twenty-five isonitrogenous and isoenergetic diets were used. The experimental diets were made of the basal diet that was contained casein and gelatin. The basal diet was supplemented with five levels of calcium (0, 1, 2, 3, 4 %) from calcium chloride and five levels of phosphorus (0, 0.5, 1, 1.5, 2%) from natrium phosphate monobasic. The study was conducted in two phases and four experiments. In each experiment the diets with three replicates, totally in the 75 culture tanks containing 100l were used for feeding crayfish with average weights 1-2g and 8-9g for 80 days. In the first and second experiments, 5 and 3 indivisiual crayfish (miniatures) with average weights 1.22±0.21g and 1.31±0.29 g respectively and during the third and fourth experiment 10 and 4 indivisiuals crayfish with the average weights 8.48 ±1.03g and 9.06±1.41g respectively were stocked in each cultural tanks. The physicochemical factors of water (temperature, dissolved oxygen, pH as daily and hardness, nitrite, nitrate and phosphate as weekly) were measured for monitoring the condition of farming. The crayfish were fed about 5% of body weight for 3 times per day. The graded levels of Ca did not affect the growth indices. In crayfish (1-2g), weight gain and specific growth rate was significantly affected by the phosphorus levels. The average weight gain, survival, biomass increment in the different treatments was significantly affected by the graded levels of phosphorus. The crayfish were fed with diet containing calcium with 3-4% and phosphorus 1% showed the better growth. In the both group of experimental crayfish, were showed the graded levels of dietary Ca were caused the reduction the body ash and P values were increased. The clear correlation was not observed between the dietary levels of P and body ash and phosphorus in crayfish (1-2g). However, high levels of dietary phosphorus developed the body calcium. In Crayfish (8-9g) showed strong and negatively correlation between the dietary P levels and body ash and calcium. The graded dietary levels of Ca and P were caused increase in molting frequency and weight increment in molting. The optimum dietary levels of Ca and P were analyzed by broken –line regression showed 3-4%, 1% for crayfish 1-2g and 2-3, 1 -1.5% for crayfish 8-9g respectively. The results showed the presence of Ca and P are necessary for normal growth and molting in both group of crayfish. The proper growth was obtained at levels of 2-3% Ca and level of 1% P. Furthermore, the Ca and P ration in diet could not describe the interaction between Ca and P levels on growth function. So the determined Ca and P ratio were not obtained base of growth indices in the freshwater crayfish, Astacus leptodactylus.
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