Ultrastructural and cytochemical characteristics of phagocytes in kuruma prawn

Abstract

Five types of phagocytes were observed in kuruma prawn Penaeus japonicus. Two of them were fixed phagocytes and three were hemocytes. Fixed phagocytes were detected in the heart and lymphoid organ. Phagocytes in the heart were observed on basal lamina covering sarcolemma of heart muscles and the cells had many lysosomal granules (0.1 μm in diameter). Phagocytes in the lymphoid organ was characterized by numerous interdigitating cell processes and few cytoplasmic granules. The hemocytes were classified into three types, hyaline cell (HC), small granular cell (SGC) and large granular cell (LGC), according to the presence of cytoplasmic deposit and size of granules. The HC had cytoplasmic deposits and a few small granules (0.2 μm in diameter). The SGC had small granules (0.2 μm in diameter) but the LGC contained large granules (1 μm in diameter). Lysosomal enzymes, such as acid phosphatase, β-glucuronidase and α-naphthyl butylate esterase, were detected in all five phagocytic cell types. Esterase activity was higher in the LGC than in any other phagocytes. Peroxidase activity was also detected in all phagocytes, although it was weak. Prophenoloxidase activity was found only in the SGC and LGC. These results indicate that the fixed phagocytes are different from the hemocytes both in their ultrastructural and cytochemical characteristics.