Effect of sulfide on the immune response and susceptibility to Vibrio alginolyticus in the kuruma shrimp Marsupenaeus japonicus

Kuruma shrimp Marsupenaeus japonicus held in 34‰ seawater were injected with tryptic soy broth (TSB)-grown Vibrio alginolyticus (2.7 × 106 cfu shrimp−1), and then placed in water containing concentrations of sulfide at 0 (control), 51, 106, 528 and 1050 μg l−1, respectively. After 12–144 h, mortality of V. alginolyticus-injected shrimp exposed to 528 and 1102 μg l−1 sulfide was significantly higher than that of shrimp exposed to 51 μg l−1 sulfide and the control solution. In another experiment, M. japonicus which had been exposed to 0, 56, 112, 525 and 1076 μg l−1 sulfide for 6, 12, 24 and 48 h were examined for immune parameters, and phagocytic activity and clearance efficiency of V. alginolyticus. Sulfide concentrations at 525 μg l−1 or greater for 12 h resulted in decreased total haemocyte count (THC) and phenoloxidase activity, phagocytic activity and bacterial clearance efficiency, whereas a sulfide concentration at 1076 μg l−1 for 24 h caused a significant increase in respiratory burst and superoxide dismutase activity of M. japonicus. It is concluded that concentrations of sulfide at 528 μg l−1 or greater increased the susceptibility of M. japonicus against V. alginolyticus infection by a depression in immune ability. The increased production of superoxide anion by M. japonicus exposed to 525 μg l−1 sulfide or greater was considered to be cytotoxic to the host.