Immune response and energy metabolism of Chlamys farreri under Vibrio anguillarum challenge and high temperature exposure

The complex interactions among host, pathogen and environment are believed to be the main causes for the mass mortality of cultured scallops during summer period. In the present study, the temporal variations of immune and energy parameters of Chlamys farreri under Vibrio anguillarum challenge, higher temperature (29 °C) exposure as well as their combined treatment were investigated in order to better understand the energetic mechanisms of scallop immune defense. After the treatments, the superoxide anion level, the activities of superoxide dismutase (SOD) and acid phosphatase, as well as heat shock protein 70 expression level in the hemolymph of scallops increased substantially within 48 h. And as time progressed, the malondialdehyde content in the serum of scallops in the higher temperature treated and the combined stress treated groups were significantly increased, while the SOD activity was significantly depressed (96 h, P < 0.05). After 3 h, a significant decline (P < 0.05) in glycogen reserves was observed in the examined tissues of all the scallops in the bacteria challenged, higher temperature treated and the combined stress treated groups. The cellular energy allocation (CEA) in the examined tissues dropped considerably when the treatments lasted 48 h. There was a significant decline in the CEA and a significant increase in the energy consumption in the examined tissues compared with other treatments when the scallops were exposed to the combined stress for 96 h (P < 0.05). All the results demonstrated that the antioxidant systems and acute phase response system in scallops were not enough to wholly repair oxidative damage caused by higher temperature and the combined stress with bacteria challenge, and glycogen reserved in relative tissues were mobilized to meet the increased energy demands during the process of immune defense. Immune defense against the combined stress imposed greater costs on scallopʹs energy expenditure than either stressor alone, and CEA could be a useful tool to evaluate energetic allocation. The information provided valuable insights into possible mechanisms of scallop mass mortalities during summer period.