Osmolality and chloride concentration in the hemolymph of subadult Penaeus chinensis subjected to different salinity levels

Abstract

Hemolymph osmolality, chloride concentration and tissue water of subadult Penaeus chinensis (12.65±2.55 g) transferred from 30 ppt to 10, 20, 30 (control) and 40 ppt seawater were examined after 0.25, 0.5, 1, 2, 5 and 10 days of exposure. No shrimp died during the experimental period. Hemolymph osmolality, chloride concentration and tissue water of shrimp transferred from 30 ppt to 10, 20 and 40 ppt reached constant levels within one-half day. Percentage tissue water decreased with external osmolality at a rate of 0.091% per one ppt. Isosmotic and isoionic values were 707 mOsm/kg (25.0 ppt) and 285 mM (18.4 ppt), respectively. Slopes of 0.39 and 0.34, obtained from the relationship between hemolymph osmolality and external osmolality and between chloride concentration and external chloride concentration, indicated that subadult P. chinensis osmoregulates between 10 and 40 ppt. It exhibited hyper-osmotic or hyper-ionic regulation in salinities below isosmotic or isoionic salinities, and hypo-osmotic or hypo-ionic regulation in those above.