Interactions between peritoneal exudate cells (PECs) of gilthead seabream ( Sparus aurata) and Pasteurella piscicida. A morphological study

Abstract

Peritoneal exudate cells from gilthead seabream ( Sparus aurata) weighing 20–30 g and 0.5 g were studied using transmission electron microscopy at several time intervals after intraperitoneal injection with a virulent Pasteurella piscicida strain. Fish of 20–30 g were injected with 0.3 ml of a bacterial suspension containing 1 × 10 9 cells/ml of P. piscicida. Fish of 0.5 g were injected with 0.1 ml of a suspension of 1 × 10 6 cells/ml. The microscopic findings showed that peritoneal exudate cells (PECs) of the bigger fish were capable of phagocytosing and killing the bacteria during the first 24 h following injection and, in consequence, of controlling the infection. PECs of seabream of 0.5 g also phagocytosed P. piscicida; however, macrophages appeared to be unable to kill the microorganism. As a result, P. piscicida was able to establish an infection and kill the fish within 5 days. We conclude that the resistance of gilthead seabream to P. piscicida is dependant on the size of the fish and may be related to the efficiency of its phagocytes.