OSMOTIC RESPONSES OF HEMOLYMPH IN RED SWAMP CRAYFISH (PROCAMBARUS-CLARKII) AND WHITE RIVER CRAYFISH (P-ZONANGULUS) TO CHANGES IN TEMPERATURE AND SALINITY

Haemolymph concentrations of chloride and sodium and osmotic pressure were measured in red swamp crayfish (Procambarus clarkii) and in white river crayfish (P. zonangulus) exposed to different temperatures and sodium chloride concentrations. Temperature affected the pattern of ionic concentrations of both species similarly with minimum concentrations at 24 degrees C. Red swamp crayfish exhibited no statistically significant changes in sodium or osmotic pressure; however, chloride was significantly lower at 24 degrees C than at higher or lower temperatures. White river crayfish had significantly higher values of all variables at temperatures higher and lower than 24 degrees C. Crayfish exposed to salinities up to 20 ppt NaCl tended to hyperregulate their haemolymph osmotic pressure and chloride and sodium concentrations at the lower salinities. At about 20 ppt, the haemolymph became isosmotic or hyposmotic to the external solution. In crayfish transferred from freshwater to 20 ppt NaCl at different temperatures, haemolymph osmotic pressure and concentrations of chloride and sodium initially increased and were stabilized by 48 h in animals acclimated to 10, 15, 25, and 30 degrees C.