Calcium Balance at the Postmoult Stage of the Freshwater Crayfish Austropotamobius Pallipes (Lereboullet)

Net uptake of calcium by Austropotamobius begins 15–30 min after the moult and rapidly reaches a maximum level (2 μmoles/g/h at 10°C) which is maintained throughout stages A and B. At stage C1 the rate of net uptake falls sharply to a lower level which is gradually reduced until equilibrium is reached at C4. The uptake mechanism is near-saturated at 0·4 mm-Ca/l and half-saturated at 0·13 mm-Ca/1. In the absence of external HCO3− net uptake is reduced. Calcium uptake is against an electrochemical gradient. The concentration of ionised calcium in the haemolymph remains unchanged during the intermoult cycle.