Effect of ammonia on the immune response of white shrimp Litopenaeus vannamei and its susceptibility to Vibrio alginolyticus

Growth of Vibrio alginolyticus was not affected by TSB medium containing ammonia-N concentration in the range of 0-20 mg l(-1). White shrimp Litopenaeus vannamei (7-12 g in the intermolt stage) were challenged with V alginolyticus, which had been incubated for 24 It in the TSB medium containing different concentrations of ammonia-N (0, 1, 5. 10 and 20 mg l(-1)). There was no significant difference in cumulative mortality for shrimp incubated in the TSB medium containing 0, 1, 5, 10 and 20 mg l(-1) ammonia-N after 120 h of challenge. The shrimps were challenged with V alginolyticus previously incubated in the TSB medium for 24 h, then placed in water containing concentrations of ammonia-N at 0.01 mg l(-1) (control), 1.10, 5.24, 11.10 and 21.60 mg l(-1). Mortality of shrimp in 5.24, 11. 10 and 21.60 mg l(-1) was significantly higher than those in the control solution (0.01 mgl(-1)) after 48-168 h. Shrimps which had been exposed to control, 1.10, 5.24, 11.10 and 21.60 mg l(-1) ammonia-N for 7 days were examined for THC (total haemocyte count), granular cells, hyaline cells, phenoloxidase activity, release of superoxide anion, superoxide dismutase (SOD) activity, phagocytic activity and clearance efficiency to V alginolyticus. No significant difference in THC, hyaline cells and granular cells were observed among shrimps at different ammonia-N concentrations. Phenoloxidase activity however, decreased when the shrimps were exposed to 5.24 mg l(-1) ammonia-N and greater after 7 days. The release of superoxide anion increased significantly, whereas SOD activity decreased significantly at 21.60 mg l(-1) ammonia-N. With shrimps exposed to 11.21 and 21.22 mg l(-1) ammonia-N for 7 days, phagocytic activity and clearance efficiency to V alginolyticus significantly decreased. It is therefore suggested that ammonia in water caused a depression in the immune response and an increase in mortality of L. vannamei from the V. alginolyticus infection. (C) 2003 Elsevier Ltd. All rights reserved.