A comparison of the gill physiology of two 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 salinity. Callinectes sapidus also inhabits more dilute waters, but C. similis is rarely found below 15 . Previous work suggests that C. sapidus may be a better hyperosmoregulator than C. similis. In this study, energy metabolism and the levels of transport-related enzymes in excised gills were used as indicators of adaptation to low salinity. Oxygen consumption rates and mitochondrial cytochrome content of excised gills increased in both species as acclimation salinity decreased, but to a significantly greater extent in C. similis gills. In addition, C. similis gills showed the same levels of carbonic anhydrase and Na+/K+-ATPase activities and the same degree of enzyme induction during low-salinity adaptation as has been 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-acclimated C. similis have a higher oxygen consumption rate and more mitochondrial cytochromes than C. sapidus gills and the same level of transport-related enzymes, C. similis cannot homeostatically regulate their hemolymph to the same extent as C. sapidus.