A COMPARISON OF THE GILL PHYSIOLOGY OF 2 EURYHALINE CRAB SPECIES, CALLINECTES-SAPIDUS AND CALLINECTES-SIMILIS - ENERGY-PRODUCTION TRANSPORT-RELATED ENZYMES AND OSMOREGULATION AS A FUNCTION OF ACCLIMATION SALINITY

Callinectes sapidus and C, similis co-occur in estuarine waters above 15 parts per thousand salinity, Callinectes sapidus also inhabits more dilute waters, but C, similis is rarely found below 15 parts per thou sand. Previous work suggests that C. sapidus may be a better hyperosmo regulator than C. similis, In this study, energy metabolism and the le vels of transport-related enzymes in excised gills were used as indica tors of adaptation to low salinity, Oxygen consumption,rates and mitoc hondrial cytochrome content of excised gills increased in both species as acclimation salinity decreased, but to a significantly greater ext ent in C. similis gills, In addition, C. similis gills showed the same levels of carbonic anhydrase and Na+/K+-ATPase activities and the sam e degree of enzyme induction during low-salinity adaptation as has bee n reported for C. sapidus gills, However, hemolymph osmolality and ion concentrations were consistently lower in C. similis at low salinity than in C. sapidus. Therefore, although gills from low-salinity-acclim ated C, similis have a higher oxygen consumption rate and more mitocho ndrial cytochromes than C. sapidus gills and the same level of transpo rt-related enzymes, C. similis cannot homeostatically regulate their h emolymph to the same extent as C. sapidus.