Abstract
Blood of Pacific salmon was studied with particular interest in red blood cell (RBC) deformability in relation to migration. Blood samples were taken via cardiac puncture or chronic cannula placed in the dorsal aorta and heparinized. As an index of RBC deformability the mean passage time of single RBCs through micropores of 8μm in diameter and 10μm in length was determined under a pressure difference of 10cmH2O. Despite about 100mOsmol/l difference in plasma osmolality, there was no marked difference in RBC passage time between fish in seawater and those well acclimatized to freshwater. However, it seemed probable that a transient decrease in RBC passage time, i.e., an increase in RBC deformability, occurred immediately following transfer from seawater to freshwater. Plasma osmolality decreased to about 300mOsmol/l within 1hr after the transfer and showed no fluctuations thereafter. The temperature dependence of RBC deformability was much smaller in comparison with those previously observed in yellowtail and carp; salmon RBCs were still highly deformable even at 5°C, a possible temperature of cold river water.
