BUDD, S.J.*; ROER, R.D.; KINSEY, S.T.: Energetic cost of osmoregulation as a function of size and salinity in Callinectes sapidus

In order to determine the energetic cost of osmoregulation in C. sapidus over a range of salinities, adult and juvenile crabs were acclimated to either sea water (1000 mOsm) or dilute sea water (150 mOsm). Oxygen uptake was measured in vivo with intact crabs and in vitro using gills removed from the crab and ligated at the proximal end. Data demonstrated that at each salinity there was a decrease in weight-specific oxygen uptake with increasing body mass and gill mass. Acclimation to dilute medium resulted in an increase in whole-animal oxygen uptake for crabs of all weights relative to that in sea water. Exposure of sea water-acclimated posterior gills to 150 mOsm resulted in a rapid and marked increase in oxygen uptake relative to sea water. Nuclear magnetic resonance spectroscopy on individual gills was able to resolve the relative concentrations of all the major phosphate compounds involved in energy metabolism (arginine phosphate, ATP and inorganic phosphate). Exposure of sea water-acclimated posterior gills to 150 mOsm resulted in a marked decrease in arginine phosphate and an increase in inorganic phosphate.