Screening Families Of Penaeus Monodon For Resistance To The White Spot Syndrome Virus (WSSV)

The shrimp culture industry of China had been devastated severely since theoutbreaks of White Spot Syndrome Virus （WSSV） in1993. While, with thedevelopment of researches on epidemiology and control technology about WSSV, aswell as the improvement of breeding technology and patterns, the production and scaleof shrimp in China have been restored and developed, and the production per year couldreach more than130tons at the present time. But WSSV is still a serious threat to thedevelopment of shrimp aquaculture. So cultivating new varieties of shrimp withdisease-resistance to a certain extent is an effective way to address the current plight ofshrimp culture industry in China.The phenomenon of shrimp with WSSV in the latent period is extremely extensivefor its widespread host in aquaculture process. Shrimp with a small count of WSSVcould survive in the suitable environment without the outbreaks of WSSV. In theprevious research on screening disease-resistance families, only the qualitative analyseson the death patterns of shrimp had been done, lacking from the quantitative view toselecte a suitable screening chroma and analysis the variation of WSSV in shrimpmuscle. The changes in mortalities of Penaeus monodon （with1×105copies/g WSSV）,WSSV loads in muscle, Total Haemocyte Count （THC） and the percentage of differenttype of haemocyte, activities of five kinds of immune enzyme （ACP、AKP、PO、POD、SOD） were studied by injection with three dosage WSSV solution containing3×10³,6×10²,2×10²copies/mL virus and PBS. Screening method for anti-WSSV familieshave been established and applied to37families of Penaeus monodon preliminarily.Five families which have better growth rate and diesase-resistance capacity have beenselected.The main structure of the study as follows:1. The cumulative mortalities were （93.33±2.89）%、（56.67±5.77）%、（45.00±5.00）%respectively, when the concentration of WSSV solution were3×10³、6×10²、2 ×10²copies/mL. The WSSV quantity in muscle reached maximum at48h postinjection under three WSSV groups. The WSSV quantity in death shrimp reached10¹⁰copies/g. WSSV virulence of death shrimp used in this experiment have no change thanpreviously reported. Shrimp with WSSV in the latent period had been caused eruptivedeath by a small amount of WSSV. No death was observed in the PBS group, indicatingthat latent infection of WSSV shrimp had not been caused death without stimulationfrom external pathogenic.2. Under three WSSV groups, the variation of THC and WSSV load werenegatively correlated except individual time points; semi-granular cells had the largestproportion under three kinds of cells, while it showed upward trend obviously earlypost-injection, but later remained at a high level although fluctuated; the percentage ofgranular and halinocyte cells showed downward trend early post-injection significantly,but the percentage of granular cells at the later stage of post-injection was significantlylower than that of early, while the level of hyaline cells between later and early stage ofpost-injection have no significant difference.3. The activity of ACP、AKP and SOD showed a trend of increased and thendecreased and then increased on the whole in the three group of WSSV infection, whileSOD activity was higher than the initial level significantly. The activity of PO and PODshowed a trend of decreased and then increased and then decreased, the last an upwardtrend on the whole in the three group of WSSV infection; while PO activity of later andearlier period were equally matched, but POD activity was higher than the initial levelsignificantly. There was a certain relationship between the reaction level ofimmuno-enzymes and the infection concentration of WSSV, and the most sensitivechanges of four enzymes activity except ACP was in the6×10²copies/mL WSSV group.The range of variation in the PBS group was lower than that of the three group ofWSSV infection.4.37different families of Penaeus monodon were injected by the WSSV solutionof25copies/g body-eight. Except2families with survival rate of about50%, there were17families survival rate of closed to100%, and the remaining18families of almost0.37families have been dividied into high and weak resisting disease groups according tothe disease-resistant appraisal system: Ki=（∑Ai×Mi+1×F）/N. Through acomprehensive analysis of the average weight of all families, anti-disease index、 weighting coefficient of body weight and disease-resistant, Y125*T115、S186、Y126*Y175、T179*S132、F20*S198were considered better relatively with growth rateand disease resistance. Five families with disease-resistant relatively have been selectedin the low dosage injection experiment. Results indicated that the method can be appliedto screening families of Penaeus monodon for resistance to the white spot syndromevirus.