In this study, significant differences in NKA activity within the rectal
gland tissue with respect to environmental salinity were not apparent,
providing further evidence that the osmotic threshold for the maintenance
of osmotic homeostasis in C. punctatum had not been exceeded.
As environmental salinity increases, maintenance of relatively stable
plasma Na+ and Cl− concentrations despite increases in the environmental
ion concentrations exacerbates the inward ionic gradients, leading to a
significant rise in the passive gain of these ions thereby increasing the
need for active salt secretion by the rectal gland (Burger, 1965). It is
well established that excess Na+ and Cl− ions are removed from the