The total water hardness affects molting, calcification, growth and survival of Cryphiops caementarius (Palaemonidae)

The aim of this work was to evaluate the effects of different levels of total hardness on the molting, calcification of exoskeleton, growth and survival of Cryphiops caementarius prawn. Male prawns were collected from Pativilca river (Lima, Peru) and cultivated in individual containers inside aquariums (55 L). Four levels of the total hardness of water (100, 200, 300 and 400 mg CaCO L) were used, with three repetitions, respectively. Prawns cultured in water with hardness of 300 mg L has a shorter molting period (26.7 days) and a higher frequency of molts (three molts). The calcium content of the prawn exoskeleton increased (p < 0.05) from 25 to 31 % in water with hardness of 100 and 400 mg L, respectively. The greatest thickness of the exoskeleton (144 µm cephalothorax and 131 µm abdomen) was obtained in water with a hardness of 400 mg L and the smallest thickness (93 µm in the cephalothorax and abdomen) in 100 mg L. The growth in length was greater (p < 0.05) in water with hardness of 200 and 300 mg L. The weight growth was similar (p > 0.05) between treatments. The highest survival (> 94.4 %) was maintained in water with hardness up to 300 mg L and the lowest survival (77.8 %) was at 400 mg L. The total hardness of 200 and 300 mg L is suitable for prawn farming, but hardness high or lower than this range affects the molting, growth and survival due to deficiency or excess of accumulated calcium, respectively, in the prawn exoskeleton.