Osmotic and ionic regulation in the Dungeness crab, Cancer magister (Dana)

Osmotic and ionic regulation was studied in the Dungenesscrab, Cancer magister, after acute exposure to a range of fivesalinities from 25% to 125% sea water (100% = 32%). Blood, urineand muscle tissue were sampled at 24 and 48 hours after exposure.Analyses were made of blood and urine osmotic concentrations, aswell as blood and urine sodium, potassium, calcium, and chlorideion concentrations. Data were also obtained for these ions and thetotal amino nitrogen (ninhydrin positive substances) in muscle tissuefrom crabs at the experimental salinities. Measurements of muscleextracellular space (interfiber water) and blood volume were determinedwith inulin-C¹⁴.In dilute sea water, blood is hyperposmotic to the medium butremains isosmotic at 100% sea water. Urine is slightly bloodhypoosmotic over the salinity range. Hyperregulation is also demonstratedfor the blood cations: sodium, potassium, and calcium.Blood chloride, however, is weakly regulated and the blood:mediumgradient is low. Urine cation concentrations are blood hypoionic inthe salinities of 75% and 100% sea water compared to 25% and 50%sea water where they are isoionic, Urine chloride is isoionic in75% and 100% sea water, but blood hyperionic in 25% and 50% seawater.Increases in tissue water content as well as muscle extracellular(interfiber water) space occur when crabs are placed in dilutesea water. The inulin extracellular space is 7.3% in 100% sea waterand this is lower than the chloride spaces (18%). Reductions inmuscle ions concentrations and free amino nitrogen compounds occur.The blood:tissue gradient for potassium indicates intracellular regulationof this ion, while no regulation of sodium and chloride is found.Decreases in free amino nitrogen compounds in dilute sea water donot contribute significantly to decreases in cell volume through lossof osmotically active nonelectrolytes in the muscle.In concentrated sea water (125%), there is some indication ofblood hypoosmotic regulation while urine is regulated blood hypoosmotic,The pattern of blood sodium, potassium and chloride regulationsuggests slight hypoionic regulation. Urine sodium and potassiumare significantly blood hypoionic, while urine chloride is isoionic.Muscle tissue in crabs at 125% sea water indicate decreases intissue water content, muscle sodium and muscle chloride in comparison to controls. Muscle potassium is regulated. Large increasesin free amino nitrogen compounds are noted in muscle from crabs atthis stress, and appear to indicate intracellular compensation for thecells to tolerate increased osmotic concentration.