Dopamine depresses immunity in the tiger shrimp Penaeus monalon

The total haemocyte count (THC), differential haemocyte count (DHC), phenoloxidase activity, respiratory bursts (release of superoxide anion), superoxide dismutase activity, phagocytic activity and clearance efficiency to the pathogen Photobacterium damsela were measured when tiger shrimp Penaeus monodon (13.5 +/- 1.5 g) were individually injected with saline or dopamine at 10(-8), 10(-7), or 10(-6) mol shrimp(-1). Results showed that a transient period of immunosuppression occurred between 2 and 8 It after injection of dopamine for all immune parameters except circulating haemocytes, and all immune parameters had returned to control values within 8-16 h after receiving dopamine. The injection of dopamine also significantly increased the mortality of P. monodon challenged with the pathogen Pho. damsela. These results suggest that stress-inducing dopamine suppresses the immune system, which in turn promotes the susceptibility of P. monodon to Pho. damsela. (c) 2006 Elsevier Ltd. All rights reserved.