ABSTRACT
The concentration of plasma calcium and the activity of the gill Ca2+ - ATPase has been measured in roach from several waters. Plasma calcium concentrations in these fish vary very little (2·62 ± 0·17 him) despite great variation in the external calcium concentration between waters (0·40 to 2·92 mm). There is, however, a close correlation between Ca2+ ATPase activity and external calcium concentration, consistent with the view that differences in the requirement for calcium transport are accommodated by variation in the Ca2+ ATPase system.
These results are discussed in relation to those of a previous experiment, where the short term effects of changing external calcium were considered. It is suggested that variation in the absolute level of Ca2+ATPase activity represents the long term adaptation of the roach to different calcium concentrations.
