The Physiological And Immune Response Of Zhikong Scallop (Chlamys Farreri) To Acute Viral Necrobiotic Disease (AVND) Virus

The Zhikong scallop (Chlamys farreri) is the important farming scallop specie in northern China. Before the bay scallop (Argopecten irradians) and Japanese scallop (Patinopecten yessoensis) were introduced into China, Zhikong scallop accounted for 80% of annual scallop output. However, Successive heavy mortalities in most farming areas in northern China since 1997 have seriously affected and damaged the aquaculture development of C. farreri. The massive mortality of C. farreri is caused by a variety of combined factors, including non-biological factors and biological factors. The non-biological factors include too high summer temperature, high stocking density, environmental degradation, and so on. Biological factors includes the pandemic biological pathogens and scallop germplasm degradation. The studies about C. farreri massive mortality caused by Acute Viral Necrobiotic Disease (AVND) virus have been carried out. This research studied the physiological and immune response of C. farreri to AVND virus by physiological and immunological technologies and means, try to help better understand the defensive mechanism of C. scallop to AVND virus and provide information for disease prevention and treatment.The oxygen consumption rate and ammonia excretion rate of Zhikong scallop (C. farreri) infected by AVND virus under different temperatures were measured. The results showed that at 17℃the oxygen consumption rate and ammonia excretion rate of the groups of C. farreri with virus and saline injection gradually increased, but there was no significant difference between both groups. The control group had no significant change; variance analysis showed that there was no significant difference among three groups. At 25℃, the oxygen consumption rate of C. farreri with virus and saline injection gradually increased, and acquired maximum at 12 hours after injection. The control group had no significant change. Variance analysis showed that there was significant difference among the virus injection group, saline injection group and control (P <0.05). The results showed that the infection of AVND virus on C. farreri is dose-and temperature-dependant.The effects of AVND virus on the activity of immune-related enzymes in the serum of Zhikong scallop (C. farreri) under 25℃were studied. The SOD activity in serum of C. farreri rose gradually in serum and reached the maximum at 48 hours after injection of AVND virus. The results of analysis of variance showed that there were significant differences among the time points (P<0.05). At 48 hours after infection, there is significant difference between the virus group and saline control group (P<0.05) and no significant difference at other time points. Acid phosphatase (ACP) activity rises in 2 hours after injection and declined in 12 hours, then rose and reached the maximum in 48 hours. The analysis of variance showed that there were significant differences among different time points. The virus group and saline control group has significant difference in 2 hours and 48hours (P<0.05). The change of alkaline phosphatase (AKP) had same trend with ACP. In 24 hours after infection, the AKP activity reached maximum, and there were significant differences among time points. The analysis of variance showed that there were significant differences between virus group and saline control group in 2, 12 and 48 hours (P<0.05). The phenoloxidase activity reached maximum in 48 hours after infection and there was no significant difference with saline control group. There was no significant difference of lysozyme activity between virus group and saline control group. The virus group scallop reached maximum in 2 hours and saline control group in 24 hours.The results indicated that C. farreri could increase or regulate protein synthesis immune-related enzymes to deal with the AVND virus infection.The expression of immune-related genes of Zhikong scallop (C. farreri) infected AVND virus was studied using fluorescent real-time PCR technology. The mRNA expression of SOD gene in serum of C. farreri gradually increased after injection of AVND virus at 17℃and reached maximum in 24 hours after injection, about 1.8 times of blank control. There were significant differences among different time points (P<0.05), but no between the virus group and saline control group. The mRNA expression of SOD gene rose gradually in 25℃water temperature and reached maximum in 6 hours after infection, about 1.5 times of blank control and 2.2 times of saline control group. There were significant differences among the time points and between the virus group and saline control group in 2, 6, 12, 24 hours after infection (P<0.05). After AVND virus infection, the Lysozyme gene expression in hepatopancreas of C. farreri increased, and reached maximum in 6 hours, about 1.5 times of saline control and 2.7 times of blank control group, and acquired minimum value in 48 hours after infection (lower than blank control group). There were significant differences of lysozyme gene expression among the times points after infection (P<0.05). The gene expression significantly increased in 6, 24, 48 hours after infection compared with saline control group (P<0.05). In 6 hours after AVND virus infection, the mRNA expression of lysozyme gene in hepatopancreas, gonad, muscle and gill sharply increased, and reached 4.7 times, 3.8 times, 13.43 times and 25.15 times of blank control group respectively. The analysis of variance showed that there were significant differences among different tissues of C. farreri (P<0.05). The results indicated that immune-related gene expression of C. farreri after AVND virus infection has time course dependence and tissue specificity.