Effects of water salinity on acid-base balance in decapod crustaceans

Extracellular acid-base balance in decapod crustaceans is influenced by wat er salinity, although the nature of this relationship is unclear. In euryha line crabs, a decrease in salinity results in a metabolic alkalosis in the haemolymph and an increase in salinity results in a metabolic acidosis. Alt erations in acid-base status by external changes in salinity are thought to be secondary to the adjustments required for ionic and osmotic regulation. In the present study, acid-base adjustments in the haemolymph of Eriocheir sinensis after transfer to 30% sea water accompanied alterations in muscle pH and [HCO3-], as an initial acidosis coincided with an alkalosis in the leg muscle. By 48 h transfer, haemolymph pH increased as muscle pH and HCO3 - declined. Haemolymph [Cl-] decrease significantly 3 h after transfer to a new steady state but haemolymph [Na+] and muscle [Na+] and [Cl-] remained unchanged. Muscle free amino acid concentration increased twofold 6 h after transfer, followed by a 2.5-fold increase in the haemolymph after 24 h, In contrast, 30% sea water had no effect on haemolymph acid-base adjustments in the osmoconforming crab, Necora puber, which lacks ion and osmo-regulato ry mechansims, Collectively these observations support the view that salini ty-induced alterations in acid-base status are caused by adjustments consis tent with cell volume regulation.