JuvenilePenaeus indicus osmoregulated well between 3–26‰ S for 24 and 48 h duration with isosmotic points ≈S 18‰ and ≈S 14‰ respectively. Adults also showed good osmoregulatory capability between 5–30‰ S with isosmotic points ≈ S 21‰ and ≈S 17‰ for 24 and 48 h duration respectively. A duration of 48 h is essential for prawns to adjust to the new medium. Influence of various neuroendocrine centres on the osmolal concentration of haemolymph was studied. In eyestalk ablated prawns osmolal concentration decreased with time and reached a lowest after 48 h. Eyestalk ablated prawns injected with extracts of eyestalk, brain and thoracic ganglia did not show any decrease in the values with time but remained on par with the values of normal ones.