|Abstract or Summary
- Osmotic and ionic regulation was studied in the Dungeness
crab, Cancer magister, after acute exposure to a range of five
salinities from 25% to 125% sea water (100% = 32%). Blood, urine
and muscle tissue were sampled at 24 and 48 hours after exposure.
Analyses were made of blood and urine osmotic concentrations, as
well as blood and urine sodium, potassium, calcium, and chloride
ion concentrations. Data were also obtained for these ions and the
total amino nitrogen (ninhydrin positive substances) in muscle tissue
from crabs at the experimental salinities. Measurements of muscle
extracellular space (interfiber water) and blood volume were determined
In dilute sea water, blood is hyperposmotic to the medium but
remains isosmotic at 100% sea water. Urine is slightly blood
hypoosmotic over the salinity range. Hyperregulation is also demonstrated
for the blood cations: sodium, potassium, and calcium.
Blood chloride, however, is weakly regulated and the blood:medium
gradient is low. Urine cation concentrations are blood hypoionic in
the salinities of 75% and 100% sea water compared to 25% and 50%
sea water where they are isoionic, Urine chloride is isoionic in
75% and 100% sea water, but blood hyperionic in 25% and 50% sea
Increases in tissue water content as well as muscle extracellular
(interfiber water) space occur when crabs are placed in dilute
sea water. The inulin extracellular space is 7.3% in 100% sea water
and this is lower than the chloride spaces (18%). Reductions in
muscle ions concentrations and free amino nitrogen compounds occur.
The blood:tissue gradient for potassium indicates intracellular regulation
of this ion, while no regulation of sodium and chloride is found.
Decreases in free amino nitrogen compounds in dilute sea water do
not contribute significantly to decreases in cell volume through loss
of osmotically active nonelectrolytes in the muscle.
In concentrated sea water (125%), there is some indication of
blood hypoosmotic regulation while urine is regulated blood hypoosmotic,
The pattern of blood sodium, potassium and chloride regulation
suggests slight hypoionic regulation. Urine sodium and potassium
are significantly blood hypoionic, while urine chloride is isoionic.
Muscle tissue in crabs at 125% sea water indicate decreases in
tissue water content, muscle sodium and muscle chloride in comparison
to controls. Muscle potassium is regulated. Large increases
in free amino nitrogen compounds are noted in muscle from crabs at
this stress, and appear to indicate intracellular compensation for the
cells to tolerate increased osmotic concentration.