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 /imoles/g/h at io°C) which is maintained throughout stages A and B. At stage Cx 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/1 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.