IONIC AND OSMOTIC CONCENTRATIONS IN BLOOD AND URINE OF PACHYGRAPSUS CRASSIPES ACCLIMATED TO DIFFERENT SALINITIES

Abstract

1. When specimens of Pachygrapsus crassipes were acclimated to 50%, 100% and 170% sea water the average blood osmotic concentrations were equivalent to 0.46, 0.57 and 0.89 normal NaCl, as compared with the medium of 0.29, 0.58 and 0.99, respectively. Urine osmotic concentrations in the same series were equivalent to 0.39, 0.53 and 0.90 normal NaCl.2. Thus the crabs are hyper-osmotic in a dilute medium and hypo-osmotic in a concentrated medium; the antennary glands may function slightly in hyper-osmotic regulation but not at all in hypo-osmotic regulation.3. Serum sodium concentrations in 50, 100 and 170% S.W. were 313, 465 and 668 mM, urine sodium 356, 318 and 264 mM corresponding to environmental concentrations of 229, 459 and 780 mM. Thus as the blood sodium increases the urine sodium decreases.4. The osmotic deficit in the urine is accounted for in part by magnesium which in 50, 100 and 170% S.W. was in blood 9, 29 and 33 mM, in urine 32, 144 and 345 mM while the medium was 26, 52 and 88 mM, respectively.5. In artificial sea water urinary sodium decreased at high external salinity but in the absence of MgSO4, the urinary sodium increased.6. Active outward transport of magnesium by the antennary glands in some way reduces the excretion of sodium.7. Potassium in blood is well regulated in dilute medium, less well in more concentrated sea water. Calcium in blood is more concentrated than in the dilute medium, less concentrated than in the higher salinity medium.