Sodium balance in the Australian crayfish Cherax destructor, Euastacus keirensis and E. spinifer (Decapoda : Parastacoidea)

Sodium balance was examined in C. destructor. E. spinifer and E. keirensis to assess the degree of adaptation to fresh water and to permit comparisons with the better known astacoid crayfish of the Northern Hemisphere. The crayfishes had blood ion concentrations close to those reported in the Astacoidea and permeability to sodium ions was similarly low. The affinities of the sodium pumps for sodium ions were relatively low but this was compensated for by an unusually high rate of uptake of sodium following depletion, which enabled sodium balance to be maintained at low external concentrations. Adaptation to fresh water in the species examined is less advanced than in the astacoid species studied.