SALINITY EFFECTS ON THE ACTIVITY OF GRANULAR HEMOCYTES OF AMERICAN OYSTERS,<i>CRASSOSTREA VIRGINICA</i>

Abstract

American oysters, Crassostrea virginica, from a high-salinity(HS) and a low-salinity (LS) location in the Chesapeake Bay were acclimated to six salinities (6-36 ppt) in the laboratory for 3-4 weeks. After acclimation, hemolymph was drawn from oysters and granular hemocytes were tested in vitro. Measurements of time to hemocyte spreading (TTS) and rate of hemocyte locomotion (ROL) were made in six media ranging in salinity from 6-36 ppt. TTS measurements were fastest at the acclimation salinities and slowed with acute rises in salinity. The time to spreading may be a measure of the osmotic adjustment process. Locomotion was dependent on ameboid shape. ROL decreased with acute rises in salinity for both populations, and increased with acute reductions in salinity for all test conditions except HS hemocytes acclimated at 30 and 36 ppt salinity. ROL tested at the acclimation salinities showed no differences between HS oysters (complete acclimation to lower salinities) but LS oyster hemocytes at 30 and 36 ppt were still slower even after 27 days of acclimation. There were a greater number of agranular hemocytes for HS oysters at all salinities. These findings are discussed in relation to osmotic adjustment, ameboid locomotion, acclimation, and disease susceptibility.