Morphology and immunological roles of hemocytes and fixed phagocytes in black tiger shrimp Penaeus monodon

Morphology and immunological roles of the three distinct types of hemocytes, hyaline, small granular and large granular cells in black tiger shrimp Penaeus monodon were studied. The study of functions of these hemocytes in the elimination of injected yeast (Saccharomyces cerevisiae) or Vibrio harveyi as foreign bodies showed a rapid response against those particles. Together with fixed phagocytes, the blood cells removed the yeast through the process of phagocytosis, nodule formation and encapsulation, which occurred at almost all parts of the body. The injection of the yeast caused a marked reduction in the blood cell counts in the hemolymph during the first 1 h. V. harveyi was efficiently removed within 3 h after injection. The granular cells (small granular and large granular hemocytes) were the major blood cells that are associated with phenoloxidase activity. The role of hemocytes and fixed phagocytes on defense mechanism in the shrimp were discussed.