Osmoregulatory performance and immunolocalization of Na/K-ATPase in the branchiopod Artemia salina from the Sebkha of Sidi El Hani (Tunisia).

Artemia salina is an extremophile species that tolerates a wide range of salinity, especially hypertonic media considered lethal for the majority of other aquatic species. In this study, A. salina cysts were hatched in the laboratory and nauplii were acclimated at three different salinities (60, 139 and 212 ppt). Once in the adult phase, their hemolymph osmolality was measured. The animals were strong hypo-osmoregulators in the entire range of tested salinities, with up to 10 fold lower hemolymph osmolalities than their surrounding environment. Immunostaining of Na/K-ATPase was done on sections and on whole body mounts of adults in order to localize the ionocytes in different organs. An intense Na/K-ATPase immunostaining throughout the cells was observed in the epithelium of the ten pairs of metepipodites. A positive immunoreactivity for Na/K-ATPase was also detected in the maxillary glands, in the epithelium of the efferent tubule and of the excretory canal, as well as in the anterior digestive tract. This study confirms the strong hypo-osmotic capacity of this species and affords an overview of the different organs involved in osmoregulation in A. salina adults.