Osmolality and ion balance in giant river prawn Macrobrachium rosenbergii subjected to changes in salinity: role of sex

Haemolymph osmolality, chloride and sodium concentrations of giant river prawn Macrobrachium rosenbergii adults were determined 15 days after they were transferred from freshwater to 0 (control), 7, 14 and 21‰ salinity. Haemolymph osmolality, chloride and sodium concentrations of prawns transferred to 7, 14 and 21‰ reached a constant level within 0.5, 2 and 3 days respectively. Both male and female adults exhibited strongly hyper-osmotic and hyper-ionic over the range of 0–14‰. The isosmotic point was 14.5 and 15.6‰, the iso-ionic point of chloride was 14.5 and 14.7‰, and the iso-ionic point of sodium was 16.5 and 15.7‰ for males and females respectively. The adults lost their hyper-regulatory ability and became osmo-conformic over the media of 14.5–21‰ and 15.6–21‰ and ion-conformic with respect to sodium over the media of 16.5–21‰ and 15.7–21‰ for males and females respectively. The adults displayed hypo-ionic to the media at 21‰ with respect to chloride.