Effect of dissolved oxygen on the immune response of Haliotis diversicolor supertexta and its susceptibility to Vibrio parahaemolyticus

Taiwan abalone Haliotis diversicolor supertexta (13-16 g) were challenged with Vibrio parahaemolyticus at a dose of 2 X 104 colony-forming units (cfu) abalone(-1) previously incubated in TSB medium for 24 h, then placed in water having concentrations of dissolved oxygen (DO) at 7.70, 5.61, 3.57 and 2.05 mg l(-1). Onset of mortality occurred after 6-h exposure to 2.05 mg I-I DO, and after 12-h exposure to 3.57 and 5.61 mg l(-1) DO. Cumulative mortality of abalone at 2.05 mg l(-1) DO was significantly higher than that at 3.57 mg l(-1) DO, and cumulative mortality of abalone at 3.57 and 5.61 mg l(-1) DO was significantly higher than that at 7.70 mg l(-1) DO after 24 h. Abalones which had been placed in water for 0 to 96 h at 7.70, 5.61, 3.57 and 2.05 mg l(-1) DO were examined for the total haemocyte counts (THC), phenoloxidase activity, respiratory burst, phagocytic activity and clearance efficiency. No significant differences in THC and respiratory burst of abalone were observed among four treatments after 6 h. The abalone following 24-h exposure to 2.05 mg l(-1) DO decreased significantly its THC and respiratory burst by 27% and 24%, respectively. Phenoloxidase activity increased significantly by 38% and 69% when abalones were exposed to 3.57 and 2.05 mg l(-1) DO after 24 h, respectively. Phagocytic activity and clearance efficiency to V. parahaemolyticus decreased significantly for the abalone following 12-h exposure to 3.57 mg l(-1) DO, respectively. It is concluded that DO as low as 3.57 and 2.05 mg l(-1) causes depression in immune system of H. diversicolor supertexta, and increases its susceptibility to V. parahaemolyticus infection. (C) 2004 Elsevier B.V. All rights reserved.