Osmotic and ionic concentrations of Scylla serrata (Forskal) subjected to different salinity levels

Scylla serrata (198.58 +/- 35.98 g) were transferred from 34 ppt to 14, 24, 34 (control), and 44 ppt. Salinity, haemolymph osmolality, and ionic concentrations were examined after 1.5, 3, 6, 12, 24, 72, 120, and 240 hr. Haemolymph osmolality, and Cl-, Na+, K+, Ca2+, and Mg2+ concentrations of crabs transferred to 14, 24, and 44 ppt and reached constant levels within 5 days. The isosmotic value was 968.6 mOsm/kg (33.4 ppt), and the isoionic value was 365.4, 322.1, 8.4, 11.3, and 28.7 mmol/l (24.0, 22.3, 22.2, 33.4 and 21.3 ppt) for Cl-, Na+, K+, Ca2+, and Mg2+, respectively. C. serrata is hypo-osmotic, and regulates haemolymph Ca2+ hyperionic to the medium at salinities between 14 to 33.4 ppt, and osmoconforms above 33.4 ppt. Sodium and chloride ions accounted for 83.1, 87.3, 83.4, and 84.3% of haemolymph osmolality at 14, 24, 34, and 44 ppt, respectively. S. serrata is a hyper/hypo-osmotic osmoregulator, with osmotic regulation being largely accounted for by ion regulation. (C) 1997 Elsevier Science Inc.