| The Fenneropenaeus chinensis and Litopenaeus vannamei were selected as the experimental subject.Quantitative feeding method was used to conduct WSSV infection experiment on them.The purpose of first study was to estimate the genetic parameters for growth and WSSV resistance in L.vannamei.The purpose of second study was to evaluate their different sensitivity to WSSV infection among the Wild-F.chinensis(W-Fc),Selected-F.chinensis(S-Fc)and Commercial-L.vannamei(C-Lv).The purpose of third study was to evaluate their different tolerance to WSSV infection between the L.vannamei “Renhai No.1” and F.chinensis “Huanghai No.2” under the condition of three kinds of temperatures(24??28?and 32?).The concrete research content is as follows:The genetic parameters for body weight and WSSV resistance of pacific white shrimp(L.vannmei)were estimated.The continuous 15 d WSSV tolerance challenge for a total of 3000 individuals from 101 families(4-month old)of L.vannmei was used for a continuous 15 d WSSV challenge.In this period,the body weight and survival time for per shrimp were recorded.And then variance components for body weight and survival time of L.vannmei were estimated through linear mixed model.The results showed that the heritability for body weight and survival was 0.10~4±0.276,0.145±0.073,belonged to lower level,respectively,and were significantly different from zero(P<0.05).There was a moderate phenotypic and genetic correlation between body weight and survival time(0.69 and 0.47),and were significantly different from zero(P<0.01).The results showed that the genetic improvement on body weight and WSSV resistance traits in L.vannmei had a great potential because they had abundant genetic variation.And the moderate genetic correlation between these two traits indicates that selective breeding for body weight can indirectly improve WSSV resistance.However,this method will not achieve obvious genetic progress.By utilizing economic weighting or percentage weighted and formulating multi-trait comprehensive selection program to cultivate a good variety of comprehensive traits.In the present study,quantitative feeding method was used to conduct WSSV infection experiment on shrimp of Wild-F.chinensis(W-Fc),Selected-F.chinensis(S-Fc)and Commercial-L.vanamei(C-Lv)to evaluate their different sensitivity to WSSV infection.The results showed that the average survival time of W-Fc,S-Fc and C-Lv 124.11±39.49 h,166.16±51.54 h,and 136.90±41.99 h.respectively,after fed with equal quantity of WSSV bait,indicating that there is significant difference among the three groups of prawns in terms of survival time(P <0.05).The death peak of W-Fc started from 96 h and continued to 216 h;while that of C-Lv and S-Fc occurred at 144 h.Alive shrimp of the three groups,which were sampled at eight time points(3 h,6 h,12 h,24 h,36 h,48 h,72 h and 144 h)were examined via absolute quantitative PCR to detect virus-load in muscle.It is showed that the virus loads of W-Fc,S-Fc,and C-Lv at 48 h are 1.22×106 copies/ng DNA,7.10×10~3 copies/ng DNA,and 1.50×10~4 copies/ng DNA,respectively;at 144 h,the virus loads in the three groups of prawn were 8.44×106copies/ng DNA,3.21×106copies/ng DNA,and 1.49×106 copies/ng DNA respectively.The present study indicates that W-Fc is more sensitive to WSSV,but S-Fc has higher resistance to WSSV.In the present study,the results suggested that it has different sensitivity to WSSV infection between S-Fc and C-Lv,indicating that the immune mechanism against WSSV in S-Fc might be different to C-Lv.In addition,the higher resistance to WSSV in S-Fc revealed that the resistance to WSSV of “Huanghai No.2” has been significantly improved by our continuous artificial selection.At the same time,the present study indicate that the effective way to prevention and cure of WSSV is disease resistance breeding,it also indicate that new varieties of promotion and application has greatly reduced the dangers of WSSV disease.In the present study,quantitative feeding method was used to conduct WSSV infection experiment in L.vannamei “Renhai No.1” and F.chinensis “Huanghai No.2” under temperature conditions(24??28?and 32?)to evaluate their different tolerance to WSSV infection(L represents L.vannamei,F represents F.chinensis).The results showed that the average survival time of group L-24?and F-24? was 184.05 ± 69.56 h and 101.68 ± 38.45 h,the average survival time of group L-28?and F-28? was 100.25 ± 26.79 h and 73.38 ± 22.22 h.Respectively,there were significant differences on survival time between two kinds of shrimps in common temperature(P<0.05).As of 15 d,the survival rates of group L-32?and F-32? was 45.74% and 23.47%.The survival time among three temperature groups was 178 h and 98 h,98 h and 74 h,292 h and 78 h when reached 50% mortality rate.The time of death peak was 5d and 4d,5d and 4d,10 d and 4d.The survival shrimp of the six groups,which were sampled at nigh time points(12 h,24 h,48 h,72 h,96 h,120h,144 h,168 h and 15d)were examined via absolute quantitative PCR to detect virus-load in muscle.It is showed that the virus loads of L-24?and F-24?at144h was 2.97×106 ±7.44×106 and 8.08×106 ± 3.22×106 copies/ng DNA,there were very significant differences between the groups L-24?and F-24? in terms of virus-load in muscle(P<0.01).The viral loads of L-28?and F-28?at144h was 6.73×106 ± 1.49×106 and1.20×107 ± 6.15×105 copies/ng DNA,there were very significant differences between the groups L-28?and F-28?(P<0.01).The virus loads of L-32?and F-32?at15d was5.18×10~3 ± 4.32×10~3 and3.78×10~4 ± 8.97×10~3 copies/ng DNA,there were significant differences between the groups L-32?and F-32?(P<0.05).The present study indicates that the tolerance of WSSV in L.vannamei tolerance was higher than F.chinensis,and the ability of multiplication of WSSV in muscle under different temperatures was as follows: 28? > 24? > 32?. |
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