Experimentally induced variation in hemocyte density for Ruditapes philippinarum and R. decussatus (Mollusca, Bivalvia)

Hemocytes represent the most important internal defense mechanism against foreign material in marine bivalve molluscs.Variations in their density were induced in the hemolymph of 2 economically important clam species (Ruditapes philippinarum and R. decussatus) after challenge with a pathogenic bacteria (Vibrio PI) and after starvation.The number of circulating hemocytes increased in both species 72 h post-challenge when compared to control animals.Following 1 wk starvation, a marked reduction of hemocyte density occurred compared to the control values.It is suggested that reversible migration of hemocytes from the tissues to the circulatory compartment or vice versa explains these variations.Consequently, the hemocyte density may be a quantifiable parameter of the immunodefense response of bivalve molluscs to physiological or pathological stress.