Osmotic and ionic regulation in Callianassa kraussi Stebbing (Crustacea: Decapoda: Thalassinidea)

Callianassa kraussi Stebbing in southern Africa has been recorded in salinities down to 1‰ Experiments suggest that because of the burrowing activities of the prawns, the substratum is unlikely to provide insulation against transient low surface salinities. Investigation of osmotic and ionic regulation in this species has shown that hyper-osmoregulation occurs in salinities below $\text{\$}\text{?}$20 ‰: hyper-osmoregulatory ability decreases in salinities below $\text{\$}\text{?}$3.5 ‰ Previous work on the genus Callianassa suggested that there was no osmo-regulatory ability in this group and a possible reason for the development of this faculty in the southern African species is discussed.