基于表型值和育种值的中国对虾生长、抗逆性状相关分析

利用单性状动物模型估计中国对虾170d的体重、抗WSSV存活时间和存活率3个性状的育种值,在家系水平上进行性状间表型值和育种值相关分析。估计的3个性状的遗传力分别为:0.22±0.16、0.14±0.12和0.03±0.021,并据此计算各性状个体育种值。家系性状表型值的相关分析表明,家系170d体重和抗WSSV存活时间之间存在一定程度相关(r=0.35,P<0.05),其余性状间相关系数很小,且差异不显著。3个性状家系育种值间的相关系数均较小,170d体重与抗WSSV存活时间的相关系数最高(0.038),170d体重与存活率,抗WSSV存活时间与存活率之间为负相关(r=-0.24,r=-0.027),并且统计检验未达到显著性水平。研究结果表明,利用多性状复合育种技术,培育综合性状优良的中国对虾新品种是一个正确而必要的育种策略。     

凡纳滨对虾抗WSSV选育家系的建立及其抗病特性

2002-2007年在人工感染白斑综合征病毒(white spot syndrome virus,WSSV)的基础上进行一代个体选育(G1)后,对凡纳滨对虾连续进行4代家系选育,共建立120个抗WSSV家系,感染实验结果显示,G2～G5选育家系对虾平均成活率分别为5.57％ ±9.83％,8.66％±11.52％,9.52％ ±8.84％和13.79％±12.86％;G2～G5选育家系对虾平均成活率的变异系数分别为1.77、1.40、0.97和0.87.根据每个家系对虾的成活情况每个世代可分为敏感、中等抗性和高抗性家系,G2～G5敏感家系在各代选育家系中的比例逐年下降,分别占76.5％、55.2％、51.4％和33.3％,抗病成活率分别为0.44％±1.09％、0.78％±1.70％、2.27％±2.76％和2.44％±3.09％,感染WSSV后2～3d出现1个急性死亡高峰;中等抗病家系在各代选育家系中的比例逐年上升,分别占0、20.7％、31.1％和38.5％,抗病成活率分别为0、9.08％±1.46％、10.7％±1.41％和11.36％ ±3.30％,感染WSSV后出现2个死亡高峰,第1死亡高峰值大于第2高峰;高抗家系在各代选育家系中的比例逐年上升(G4除外),分别占23.5％、24.1％、17.1％和28.2％,抗病成活率分别为22.23％±5.21％、22.70％±12.30％、24.45％ ±6.56％和28.98％ ±8.09％,感染WSSV后出现2个死亡高峰,第1死亡高峰值小于第2高峰.经连续的定向选育,对虾抗病性状一代比一代强,表现出明显的抗病性能,特别是高抗对虾不仅死亡率低且其死亡高峰推迟2～3d,延缓了对虾WSSV暴发的时间,但是每代每尾对虾平均产卵量逐年下降.     

聚合酶链反应（PCR）检测养殖对虾的白斑症病毒（WSSV）感染

对虾WSSV病是亚洲对虾养殖业中的一个棘手问题。本研究采用Kimura引物 ,用PCR技术对不同生长期的中国对虾 (Penaeuschinensis)进行了WSSV的检测 ,同时也检测了对虾发病时养殖池中多见的野生厚蟹 (Helicesp .)和矛尾刺虎鱼 (Acanthogobiushasta)。检测结果表明 :分别在检测的 5尾亲虾中的 1尾 ,6尾仔虾中的 1尾 ,5尾稚虾中的 3尾及所检测的 5尾病虾和 2只厚蟹中获得到 982bp的PCR扩增产物 ,说明为WSSV感染阳性。在检测的 2尾矛尾刺虎鱼中均未获得PCR扩增产物 ,说明为WSSV感染阴性。在亲虾、虾苗以及虾池内的野生厚蟹中检测到WSSV感染的阳性结果表明 :WSSV感染的亲虾有可能是病毒的储主 ,WSSV感染的野生厚蟹有可能是病毒中间宿主或病毒的携带者 ,它们在对虾WSSV病的感染、传播中起了重要的作用     

中国对虾新品种“黄海2号”的培育

选取中国对虾“黄海1号”、“即抗98”2个养殖群体,朝鲜半岛南海群体、乳山湾群体、青岛沿岸群体及海州湾群体4个自然群体,采用不平衡巢式交配设计方案,于2005年建立了中国对虾育种的基础群体.设计并建立了中国对虾的多性状复合育种技术,选育的目标性状为生长速度、白斑综合征病毒(white spot syndrome virus,WSSV)感染后的存活时间及养殖存活率.结果显示,养殖170 d收获体质量的遗传力为0.22,抗WSSV存活时间的遗传力为0.14,存活率的遗传力为0.03.采用BLUP法估算个体育种值,通过百分比加权的形式,分别赋予生长速度、抗WSSV存活时间和存活率的加权值为80％、15％和5％,并对性状育种值进行标准化,获得综合选择指数;按照每个家系及个体的综合选择指数大小进行家系间及家系内留种,并根据系谱信息,设计交配方案,将每代的近交系数控制在1％以内.选育4代后的统计结果表明,平均每代的遗传进展为生长速度,13.56％;抗病力,6.76％;存活率,5.05％.3个性状中,收获体质量的遗传力最高、加权最大,每代获得的遗传进展稳定在12％以上;抗WSSV存活时间与存活率遗传力较低,每代获得的遗传进展相对小且不稳定.实验培育的新品种“黄海2号”于2009年通过全国水产原良种委员会审定,可在适合中国对虾的养殖区进行推广养殖.     

凡纳滨对虾(Litopenaeus vannamei)抗WSSV选育家系的建立及其抗病特性

2002-2007年在人工感染白斑综合症病毒(white spot syndrome virus, WSSV)的基础上进行一代个体选育（G1）后,对凡纳滨对虾连续进行了4代家系选育,共建立120个抗WSSV家系,感染实验结果表明：G2~G5选育家系对虾平均成活率分别为5.57%±9.83%, 8.66%±11.52%, 9.52%±8.84% 和 13.79%±12.86%;G2~ G5选育家系对虾平均成活率的变异系数分别为1.77、1.40、0.97和0.87。根据每个家系对虾的成活情况可分为敏感、中等抗性和高抗性家系,G2至G5敏感家系在各代选育家系中的比例逐年下降,分别占76.5%、55.2%、51.4%和33.3%,抗病成活率分别为0.44%±1.09%、0.78%±1.70%、2.27%±2.76%和2.44%±3.09%,感染WSSV后2~3 d出现1个急性死亡高峰;中等抗病家系在各代选育家系中的比例逐年上升,分别占0、20.7%、31.1%和38.5%,抗病成活率分别为0、9.08%±1.46%、10.7%±1.41%和11.36%±3.30%,感染WSSV后出现2个死亡高峰,第1死亡高峰值大于第2高峰;高抗家系在各代选育家系中的比例逐年上升（G4除外）,分别占23.5%、24.1%、17.1%和28.2%,抗病成活率分别为22.23%±5.21%、22.7%±12.30%、24.45%±6.56%和28.98%±8.09%,感染WSSV后出现2个死亡高峰,第1死亡高峰至小于第2高峰。经连续的定向选育,选育对虾抗病性状一代比一代强,表现出明显的抗病性能,特别是高抗对虾不仅死亡率低且其死亡高峰推迟2～3d,延缓了对虾WSSV暴发的时间,但是每代每尾对虾平均产卵量逐年下降（P<0.05）。     

近交对中国明对虾生长、存活及抗逆性的影响

以"中国对虾遗传育种中心"2个近交家系为基础培育近交群体,近交系数为0375;以"中国对虾遗传育种中心"选育的核心群体做对照群体.将实验对虾养殖60 d,每隔20 d测量体长与体质量.通过体长、体质量、存活率、耐盐力、耐温力和抗白斑综合症病毒(WSSV)感染能力6个指标来评价近交对中国明对虾生长、存活和抗逆性的影响.方差分析表明,近交群体和对照群体在体长、体质量和存活率这3个性状上差异显著(P＜0.05),近交衰退系数分别为-4.027 0%、-7.300 0%、-5.803 3%;而近交群体和对照群体在耐盐力、耐温力和抗WSSV感染能力3个抗逆性状上差异不显著(P＞0.05),近交衰退系数分别为0.084 1%、-0.739 4%、1.911 0%.研究结果表明,近交使中国明对虾生长、存活等性状产生显著的衰退,而对抗逆性这-性状没有显著影响.     

中国对虾“黄海2号”新品种的培育

选取中国对虾“黄海1号”、“即抗98”2个养殖群体,朝鲜半岛南海群体、乳山湾群体、青岛沿岸群体及海州湾群体等4个自然群体,采用不平衡巢式交配方案设计,于2005年建立了中国对虾育种的基础群体。设计并建立了中国对虾的多性状复合育种技术,选育的目标性状为生长速度、白斑综合症病毒感染后的存活时间及养殖存活率。为最大限度消除环境差异对遗传方差的影响,在中国对虾家系构建过程中采用标准化程序培育苗种,经过对体长为3cm左右的幼虾进行荧光标记,每个家系标记后混合养殖测试。随机从每个家系中抽取同等数目的标记对虾分成2组,一组共同养殖在养殖池中,测试生长速度和养殖存活率,另一组在封闭的水泥池中进行WSSV感染实验,测试病毒感染后的存活时间长短。中国对虾遗传参数的估计结果表明,养殖170天收获体重的遗传力为0.22,抗WSSV存活时间的遗传力为0.14,存活率的遗传力为0.03。采用BLUP法估算个体育种值,通过百分比加权的形式,分别赋予生长速度、抗WSSV存活时间和存活率的加权值为：80%、15%和5%,并对性状育种值进行标准化,获得综合选择指数;按照每个家系及个体的综合选择指数大小进行家系间及家系内留种,并根据系谱信息,设计交配方案,将每代的近交系数控制在1%以内。选育4代后的统计结果表明,平均每代的遗传进展为：生长速度,13.56%;抗病力,6.76%;存活率,5.05%。三个性状中,收获体重的遗传力最高、加权最大,每代获得的遗传进展稳定在12%以上;抗WSSV存活时间与存活率遗传力较低,每代获得的遗传进展相对小且不稳定。实验培育的新品种“黄海2号”于2009年通过全国水产原良种委员会审定,可在适合中国对虾的养殖区进行推广养殖。为更快地培育抗病新品种,解决对虾养殖病害问题,进一步的研究需查明对虾抗病的遗传机制,提高抗病性状的选择强度,快速培育对虾抗病新品种。     

控制环境养殖下近交对中国对虾早期体重和抗WSSV性状的影响

过量的捕捞和不合理的人工育种措施，使中国对虾野生和养殖群体的遗传多样性均遭到不同程度的降低。本试验在相似的环境条件下养殖了40个野生对虾产生的家系和3个兄妹交产生的家系，定量测定了平均体重(1.43~1.58) g 1 460尾中国对虾早期体重和感染白斑综合征病毒（WSSV）后存活时间的近交衰退系数。结果显示，野生对虾家系组的平均体重和平均存活时间分别为(1.58±0.01) g和(100.43±0.68) h，而兄妹交家系组平均体重和平均存活时间分别是(1.43±0.04) g和(85.84±1.70) h，平均体重和平均存活时间在两组间均存在极显著差异（P<0.01）。野生对虾家系组体重和存活时间的表型相关系数为0.16±0.00，而兄妹交家系组两者间的表型相关系数为0.20±0.00，但是两组间表型相关系数差异不显著（P>0.05）。近交系数每增加10％，体重和感染WSSV后存活时间分别衰退-3.80%±0.17%和-5.81%±0.11%，与近交能够降低生长和疾病抗性的观点相一致。实验结果表明，在选择育种和种质资源保护过程中都应该保证基础群体遗传背景最大化，从而有效控制近交。图0表2参39     

中国对虾雄性生殖系统感染WSSV在其垂直传播中的作用

通过人工感染实验,对中国对虾(Fenneropenaeus chinensis)雄性亲虾进行投喂感染。在确定其携带WSSV粒子后,将被WSSV感染的精荚人工移植到健康的雌虾纳精囊内。在无其他病源的情况下,促其产卵繁殖,统计各组子代的受精率、孵化率及无节幼体至溞状幼体的变态率贸?式PCR技术对亲虾及子代进行WSSV检测。结果表明,受WSSV感染的精荚能够把病毒传播给健康雌虾,雌虾能产出携带WSSV的卵子,培育出带毒幼体。各组子代的受精率、孵化率及变态率的统计结果表明,感染组和对照组在受精率上没有明显区别,受WSSV感染的精卵细胞可以正常结合。对照组受精卵的孵化率明显高于感染组,差异显著(P=0.045<0.05)。对照组无节幼体的变态率也高于感染组。说明WSSV的入侵对受精卵及幼体的发育有影响,WSSV感染导致部分受精卵及幼体不能正常发育或死亡。     

应用BLUP法对中国对虾一代选择的遗传进展

为了评估中国对虾最佳线性无偏预测(Best liner unbiased prediction,BLUP)的育种效果,利用2005年评估的个体育种值,组建3个高育种值家系为实验组,3个平均值育种值家系为对照组,进行了生长对比测试。2006年,6个家系的苗种经过独立培育、中间暂养,体重达到1g左右时用荧光标记进行了标记,标记后的幼虾同时放养于对虾养殖池中。在生产养殖池中养殖63d后进行生长性状的测定。BLUP法预测结果显示,中国对虾一代选育后的预期遗传进展为0.78g,相对于选育前全群的平均值6.68g提高了约11.68%。实际对比测试结果表明,高育种值家系后代平均体重为21.55g,平均育种值家系的平均体重为19.03g,选育一代的体重提高13.28%。结果表明,BLUP育种技术对中国对虾生长性状的选育效果显著。     

Development of a multiplex PCR system for the simultaneous detection of white spot syndrome virus and hepatopancreatic parvovirus infection

A multiplex PCR kit for simultaneous detection of white spot syndrome virus (WSSV) and hepatopancreatic parvovirus (HPV) was developed and field testing was conducted. A 604‐bp target sequence was selected from the vp28 gene of WSSV. A primer set was developed to amplify a 338‐bp DNA fragment at the junction of the NS2 and NS1 protein genes of HPV after alignment of eight sequences from different strains. Another internal positive control primer set produced a 139‐bp PCR fragment from the β‐actin gene by alignment of this gene from Litopenaeus vannamei, Fenneropenaeus chinensis and Penaeus monodon. The detection limits, tested using purified plasmids, for WSSV and HPV were 21.4 and 19.0 copies respectively. The optimum ratio for HPV, WSSV and β‐actin was 3:1:1, with an optimum annealing temperature of 57°C. Field test of the multiplex PCR with 170 L. vannamei individuals from 17 aquaculture farms showed 41.8% coinfection with WSSV and HPV, and 40.0% and 3.5% single infection with WSSV and HPV respectively. No virus‐free shrimp farm was found. Ten wild catch F. chinensis individuals showed 60% coinfection, and 40% were infected with HPV.     

中国明对虾眼柄微结构与其生长的关系

观察了采集于江苏南通近海的69只中国明对虾的眼柄微结构,分析了其体长和体质量的生长。结果显示,眼柄由表层、色素层、钙化层和膜层4个部分组成。眼柄内存在明显的生长宽带和细纹,其中宽带数0~1个,细纹数27~37个。最小AIC法拟合分析显示,中国明对虾体长、体质量的生长与眼柄细纹数都呈显著的Logistic关系。研究表明,中国明对虾眼柄中的宽带与其年龄相关,细纹可用来分析中国明对虾的生长,而细纹的形成周期是否与个体差异、生长环境差异等相关还需要进一步验证。     

Compensatory growth of Chinese shrimp, <Emphasis Type="Italic">Fenneropenaeus chinensis</Emphasis> following hypoxic exposure

Compensatory growth following stress is a strategy aquatic animals use to adjust themselves to a variable environment. Studies on the recovery growth of aquatic animals are not only of theoretical value in ecophysiology and evolution, but also important to applications in aquaculture and fisheries resource management. In this experiment, juvenile Fenneropenaeus chinensis with an initial average body weight of about 3.72 g were exposed to hypoxic water (about 2.08 and 3.11 mg/l of dissolved oxygen (DO) content) for 10 days and then switched to normoxic water (about 5.63 and 5.59 mg/l DO). Compared with juveniles in normoxia, juveniles in the hypoxia period allocated a greater proportion of energy to metabolism and exuviations but allocated less energy to daily metabolism per gram shrimp weight (J/g/day). This reduced feed conversion efficiency and feeding rate. Finally, F. chinensis suffered growth depression. The juveniles completely compensated for hypoxia-induced growth depression in 30 days after being switched into normoxic water and the compensation was achieved mainly by hyperphagia and slightly by improvement of feed conversion efficiency. During the recovery period the hypoxic-stressed shrimp showed higher daily metabolic energy (J/g/day) than controls (P < 0.05). Which means the stressed shrimp had more energy for feeding-related activities. So hyperphagia was observed. Energy analysis indicated that F. chinensis improved feed-conversion efficiency mainly by reducing the percentage of energy lost in feces and exuviations. The results showed that short-term non-lethal hypoxia would not affect the growth of juvenile F. chinensis if there were enough time for the stressed shrimp to recover. This suggested F. chinensis was capable of adapting to DO fluctuation to some extent and short-term non-lethal hypoxia would not have an obvious effect on natural, released, and cultured shrimp stock.     

Limited evidence for genetic variation for resistance to the white spot syndrome virus in Indian populations of Penaeus monodon

There has been a highly detrimental impact of the white spot syndrome virus (WSSV) on black tiger shrimp (Penaeus monodon) aquaculture in India. Currently, no cost‐effective measures are available for controlling the disease. One alternative is to improve WSSV resistance through a selective breeding programme for disease‐resistant shrimp, provided that genetic variation exists for this trait. The aim of this study was to evaluate the evidence for genetic variation in resistance to WSSV in P. monodon sourced from Indian populations. Post‐larval shrimp (n=1950) from 54 full‐sibling families were challenged with WSSV using WSSV‐infected mince meat. The heritability was estimated using four different statistical models fitted to the resulting time to death data, including two linear models and two Weibull proportional hazard frailty models. None of the estimated heritabilities were significantly different from zero. We suggest three possible explanations for these results: there actually is very little variation between P. monodon in WSSV resistance and all individuals are highly susceptible to the disease; there is genetic variation in resistance to WSSV in P. monodon but we did not find it in our experiment because the level of challenge in the experiment was too high to allow genetic differences to be expressed; the variation is due to mutations conferring resistance, which are at a low frequency in the population, and we did not sample a broad enough genetic base to capture these mutations.     

一株芽孢杆菌PC024的鉴定及其抗WSSV感染效果的研究

为了筛选WSSV的防病益生菌株,从健康中国明对虾消化道分离纯化一株芽孢杆菌PC024,经Biolog碳源利用反应、ATB微生物自动鉴定系统、脂肪酸气相色谱分析得出该菌株与坚强芽孢杆菌的生理生化特性最为相似,该菌株为革兰氏阳性菌,有一根端极鞭毛;细胞呈球杆状,有椭圆芽孢;单个菌落呈圆形,中间略微凸起;16S rRNA序列分析表明,该菌株与坚强芽孢杆菌进化地位最接近,同源性均达到100％,综合以上4种方法的鉴定结果,该菌株被鉴定为坚强芽孢杆菌.将已鉴定的PC024菌株粘附于对虾饲料表面投喂给凡纳滨对虾20 d后,进行WSSV肌肉注射感染,测定投喂和感染后对虾血淋巴上清和肝胰腺的免疫相关酶活性,并对对虾肠道总菌数和添加菌PC024进行计数及鉴定.结果表明:添加该菌的实验组对虾相对存活率高,相对保护率达33.7％;投喂含该菌饲料的实验组对虾血清和肝胰腺的相关免疫酶活性较对照组显著提高,对虾肠道总细菌数始终显著高于对照组,并在实验组能够分离得到坚强芽孢杆菌,坚强芽孢杆菌PC024可作为WSSV的防病益生菌株应用于对虾养殖生产.     

Starvation resistance and metabolic response to food deprivation and recovery feeding in Fenneropenaeus chinensis juveniles

Starvation resistance in the juveniles of Chinese shrimp, Fenneropenaeus chinensis Osbeck, was studied by point-of-no-return (PNR) and point-of-reserve-saturation (PRS) experiments. Changes in oxygen consumption rate, ammonia-N excretion rate, and oxygen consumed to nitrogen excreted (O:N) ratio were investigated immediately before and after the period of recovery feeding for each regime to assess metabolic response during starvation and refeeding. There was a significant change in survival rate and wet weight of test shrimp throughout the PNR and PRS experiments (P < 0.05). The estimated PNR and PRS for F. chinensis juveniles could be directly calculated from the selected equations as PNR₅₀ = 7.86 days, PNR₁₀₀ = 21.42 days, PRS₀ = 1.16 days, and PRS₅₀ = 11.75 days. A decrease in metabolic rate during starvation as a means of conserving energy was found in F. chinensis juveniles. Furthermore, although F. chinensis juveniles only utilized protein as an energy source during starvation, they showed a shift from pure protein during starvation to an equal utilization of protein and lipid or a lipid-carbohydrate mixture during later satiate feeding. The results in the present study indicate that F. chinensis juveniles have the ability to withstand and recover from relatively prolonged starvation after longer initial feeding periods. The knowledge derived from the understanding of starvation resistance and the corresponding metabolic response of F. chinensis juveniles will be useful in the design of feeding regimes in this species.     

A Microsatellite DNA Marker Developed for Identifying Disease‐resistant Population of Giant Black Tiger Shrimp,Penaeus monodon

White spot disease caused by white spot syndrome virus (WSSV) poses major problems that result in huge economic losses each year in shrimp aquaculture throughout the world. In the present study, microsatellite‐based DNA fingerprints have been compared between naturally occurring WSSV disease‐resistant and susceptible populations of giant black tiger shrimp, Penaeus monodon, to find DNA markers. For the first time, we report here a microsatellite locus, which, after amplification by polymerase chain reaction, provides a highly statistically significant DNA fingerprint of 71 bp, only in disease susceptible populations but not in disease‐resistant shrimp populations, whereas a 317 bp band is common in both. The absence of the former DNA marker will be very useful to identify disease‐resistant broodstock of P. monodon for marker‐assisted selection in breeding programs to generate disease‐free shrimps (P. monodon) in the aquaculture industry.     

Long‐lasting Effect Against White Spot Syndrome Virus in Shrimp Broodstock,Litopenaeus vannamei,by LvRab7 Silencing

The white spot syndrome virus (WSSV) remains the most devastating viral pathogen of shrimp culture worldwide. Gene silencing by RNA interference (RNAi) using double stranded RNA (dsRNA) has been considered a powerful tool for conferring protection against WSSV when viral genes are silenced, as documented in several shrimp species. However, this effect is not long lasting. Our results provide the first evidence that long‐term silencing of the LvRab7 endogen produced antiviral effect against WSSV, which endured at least 21 d after dsRNA treatment (dat). Until now, the most efficient way to implement RNAi with dsRNA into the shrimp is by injection. Consequently, its application to broodstock in hatcheries is possible, minimizing the risk of vertical transmission of the virus. We show that the expression of Rab7 in hemocytes is lowest at 2 dat and finally recovers to basal status. In contrast, in gills and pleopods, gene expression silencing continued for at least 21 d. We challenged Litopenaeus vannamei broodstock with WSSV at 7, 14, or 21 dat reaching mortality rates of 0, 40, and 27%, respectively. In conclusion, the LvRab7 gene silencing is progressive and effective against WSSV. However, further studies are necessary to elucidate the functions of Rab7 in shrimp cells before applying this methodology at a commercial level.     

Effects of Dietary Administration of Probiotic Halomonas sp. B12 on the Intestinal Microflora,Immunological Parameters,and Midgut Histological Structure of Shrimp,Fenneropenaeus chinensis

The experiment was conducted to investigate the effects of oral administration of probiotic Halomonas sp. B12 (previously isolated from the intestine of Fenneropenaeus chinensis) on the intestinal microflora, immunological parameters, and midgut histological structure of F. chinensis. Shrimp (initial weight: 4.00 ± 0.10 g) were fed diets containing Halomonas sp. B12 at 0 (control), 3.68 × 10⁷ (T1), and 7.18 × 10¹⁰ (T2) colony‐forming units per gram for 6 wk, respectively. The results showed that the total bacterial counts significantly increased (P < 0.05) with supplementation of dietary probiotic B12. However, Vibrio spp. counts significantly decreased (P < 0.05) in the intestine of shrimp with increasing dietary probiotic B12. Hemocyte counts in the shrimp fed the diets supplemented with probiotic B12 were significantly higher (P < 0.05) than the control group. Both phenoloxidase (PO) activity in plasma and hemocyte lysate supernatant were higher in the shrimp fed diets supplemented with probiotic B12 compared with the control group. No significant difference was found in PO activity in plasma between the T1 and the control (P > 0.05). PO activity in plasma was higher in T2 than that in T1. Cumulative shrimp mortality after 10‐d white spot syndrome virus (WSSV) challenge test significantly decreased with increasing dietary probiotic B12 (P < 0.05). No significant difference was found between T1 and control in cumulative shrimp mortality after challenge test (P > 0.05). The oral administration of probiotic B12 to F. chinensis was beneficial to protect the integrity of shrimp intestinal mucosal layer. In summary, even though the low dose (T1) had some effects on bacterial counts and immunological parameters, only the high dose (T2) significantly increased the resistance of the shrimp to WSSV.     

Studies on the rotifer (Brachionus urceus Linnaeus, 1758) as a vector in white spot syndrome virus (WSSV) transmission

The rotifer Brachionus urceus (Linnaeus, 1758) was experimentally infected with the white spot syndrome virus (WSSV) by the virus-phytoplankton adhesion route in order to assess the possibility of rotifer acting as a vector of WSSV to infect the shrimp Fenneropenaeus chinensis (Osbeck, 1765) larvae at zoea stage III. The nested-PCR test revealed WSSV-positive results in the rotifers exposed to WSSV by the virus-phytoplankton adhesion route. Among 10 replicates in the infection treatment, 40% of F. chinensis larvae became WSSV-positive when fed with WSSV-positive rotifers, whereas all were WSSV-negative for F. chinensis when fed with WSSV-free rotifers. Though the mortality of shrimp larvae in the infection treatment (39.47 ± 15.44%) was higher than that in the control treatment (34.67 ± 15.11%), there was no significant difference in the mortality between them (P > 0.05). These results indicated that the rotifer could serve as a vector in WSSV transmission when ingested.