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 21parts per thousand salinity. Haemolymph osmolality, chloride and sodium concentrations of prawns transferred to 7, 14 and 21parts per thousand 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 0-14parts per thousand. The isosmotic point was 14.5 and 15.6parts per thousand, the iso-ionic point of chloride was 14.5 and 14.7parts per thousand, and the iso-ionic point of sodium was 16.5 and 15.7parts per thousand for males and females respectively. The adults lost their hyper-regulatory ability and became osmo-conformic over the media of 14.5-21parts per thousand and 15.6-21parts per thousand and ion-conformic with respect to sodium over the media of 16.5-21parts per thousand and 15.7-21parts per thousand for males and females respectively. The adults displayed hypo-ionic to the media at 21parts per thousand with respect to chloride.