Levels of ions and organic metabolites in the adult freshwater crayfish, Cherax quadricarinatus, exposed to different salinities

Adult male crayfish, Cherax quadricarinatus, were exposed to the salinities of 0 (control), 7.5, 15, 25 and 35 g L-1 for 3 weeks. Survival, oxygen consumption rate, hemolymphatic levels of glucose, lactate, sodium, potassium, pH, and free amino acids (FAA), as well as FAA concentration in muscle, were determined. Survival was significantly reduced (p<0.05) only at the highest salinity assayed, together with a significant (p<0.05) increase of glucose and decrease of lactate. Concerning ions, a hyper-regulation of both hemolymphatic sodium and potassium was maintained up to a salinity of 15 g L-1, at which hemolymph became isoionic with ambient water. A certain degree of ionic hypo-regulation was also noted. Hemolymph pH levels decreased as salinity increased from 0 to 15 g L-1. FAA content in muscle showed an increase parallel to that of hemolymphatic sodium, in accordance with their expected function in the isosmotic regulation of muscular cells.