Morphology and Phagocytic Activity of Hemocytes from the Japanese Rock Oyster Crassostrea nippona and the Pacific Oyster C. gigas

Abstract

Hemocytes from the Japanese rock oyster Crassostrea nippona and the Pacific oyster C. gigas were divided into 5 types (Types A to E) based on the microscopic observation of specimens stained with May-Grünwald and Giemsa. Of these 5 types, Types A, B and E were agranular and Types C and D were granular hemocytes in both species. In vitro phagocytic experiments using hemocytes of these two oyster species collected monthly through a year (September, 2002 to August, 2003) against zymosan revealed that Types C, D and E had high, Type B had low, and Type A had no phagocytic activities through the year, although phagocytic activities of the three types of hemocytes (C, D and E) became lower in the post-spawning season from October to November. When compared collectively between granular (C and D) and agranular (B and E) phagocytes, granulocytes played more important role in phagocytosis than agranulocytes. These morphological features and phagocytic activities of the two species of oysters were quite similar to each other, but when exposed to lower temperatures and salinities, lower phagocytic activities were exhibited in the Japanese rock oyster than the Pacific oyster, reflecting the difference in ecological nature of the two species.