Susceptibility Of Shrimp Litopenaeus Vannamei To WSSV Under Ammonia And Nitrite Stress

Aquaculture water environment deterioration and disease-prone affected the current vannamei farming seriously. To reveale the relationship between aquaculture water environment and disease outbreaks, we conducted the present experimental study of the effect of vannamei under ammonia and nitrite stress.we carried out the experiment that the effect of mortality of infected by WSSV under ammonia, nitrite separate and jointly stress. 10-4 and 10-5 two virus dilution leaded to about 50% vannamei mortality within 144 h as attacked drug concentration by pre-determined experiments. We setted ammonia, nitrite separate and joint stress concentration at 20mg/L, while stress and stress-free environment were injected with PBS, 10-5 and 10-4 dilutions of virus solution. The results showed that 10-5 and 10-4 dilutions of charged virus solution mortality was 53.33% and 63.33% under ammonia alone Stress, higher than 40.00% and 60.00% under no stress conditions. The mortality reached 56.67% and 90.00% of stress groups by nitrite infected with 10-5 and 10-4 dilutions of virus solution, higher than 40.00% and 60.00% under no stress. Beside, stress 10-4 was significantly higher than other groups. The mortality of 10-5 and 10-4 dilutions of virus solution was 78.33% and 100.00% under ammonia and nitrite jointly stress, significantly higher than 40.00% and 60.00% stress-free environment(P<0.05). Stress Environment mortality is higher than non-stress environment under the same charged WSSV concentration, while under the same culture environment, higher dilutions of virus solution with higher mortality. PBS injected control group mortality rates were lower than 10.00%, the rest in good health. Experimental results shows that ammonia, nitrite both individually and collectively Stress accelerates the death of WSSV infection vannamei, and jointly stress group higher than alonely stress group.We study WSSV proliferation rate in vannamei under ammonia, nitrite separate and joint stress. Experimental vannamei was infected with 10-5 and 10-4 two dilutions WSSV virus solution under ammonia, nitrite individually and collectively Stress at the concentration of 20mg/L environment. The changed amount of WSSV particles was detected by real-time PCR experiments in vannamei shrimp gills tissue. The results showed that experimental groups WSSV particles are rapidly increasing from 48 h to 72 h, the amount at 72 h was significantly higher than 48h(P<0.05). The group that stress 10-4 reached the highest WSSV amount at 72 h, and fluctuations with prolonged stress time while Stress 10-5 group and non-stress group reached their highest amount after 72 h. During the rapid proliferation of 48 h to 72 h, the amount of WSSV particles in vannamei shrimp gills tissue was detected that the stress group faster than non-stress group under the same infectious dose, a high concentration of infected infection faster than the lower concentration under the same culture environment. Experimental results shows that both ammonia, nitrite individually and collectively stress contribute to the proliferation rate of WSSV in Litopenaeus vannamei body.This study further explores the effect of ammonia, nitrite on enzyme activity of immune-related in shrimp serum. Experimental consists of control, 6mg/L、12mg/L、20mg/L four concentrations sudden change groups and one concentration gradual change groups. The experiment conducted under ammonia, nitrite individually and collectively stress environment. The results shows that the stress of 12mg/L and 20mg/L two high concentration sudden change group on enzyme activity of immune-related in shrimp serum was stronger than 6mg/L group and the stress gradual change group. The activity of PO, ACP, AKP increased significantly firstly, then decreased significantly as stress prolonged. There was no significantly effect of 6mg/L group and gradual change group on the activity of PO, ACP, AKP. The experiment shows that high concentrations of ammonia, nitrite individually and collectively sudden change had a significant effect on enzyme activity of immune-related in Litopenaeus vannamei serum, while stress with low and gradual changed concentrations had not obvious effect.Basis on the laboratory research, we carried out a survey about the changes of enzyme activity of immune-related in Litopenaeus vannamei serum of pond cultured shrimp. The survey found that the activity of PO, ACP and AKP reached their highest at 23:00 and significantly higher than other sampling time points through detecting three ponds PO, ACP and AKP activity in Litopenaeus vannamei serum in a day. However, there is not significant consistency between the detected change of ammonia, nitrite, nitrate, dissolved oxygen, pH, temperature, hydrogen sulfide seven water quality parameters and the activity Changes of PO, ACP and AKP. The activity of the same immune enzyme in different breeding ponds also showed significant differences at 23:00. The specific reasons why the activity of PO, ACP, AKP in Litopenaeus vannamei serum reached highest at 23:00 in breeding ponds needed further explores.