Risk Evaluation Of Food Organisms Carrying The Mounts Of WSSV And The Effect Of Feeding Potamocorbula Rubromuscula On Anti-disease Ability Of Litopenaeus Vannamei

1The study of f food organisms carrying WSSV and the spread risk assessment in differentseasons in Northern areaPotamocorbula rubromuscula,Gammardea,Corophium acherusicum,Nereidae,Assimineaviolacea,Artemia were sampled in Dalian, Tangshan, Hangu, Dongying, Jiaozhou, Haiyang,Lianyungang and examined the quantity of WSSV carried by these food organisms by Taqmanreal-time PCR.The result shows that every examined bait organisms are infected with WSSV, but there is asignificant difference among the species. Nereidae has the highest level of WSSV, Potamocorbularubromuscula has the lowest, Assiminea violacea has the relatively higher level thanPotamocorbula rubromuscula but in the same magnitude; Corophium acherusicum has higherlevel than Gammardea, Artemia has lower level of WSSV. There is a seasonal trend of the WSSVlevel in different regions, the highest level happened in July, the relatively low level was in Apriland September. Four grades were decided after the examination of WSSV on the baitorganisms(copy/mg tissue): level1:<103low-grade infection; level2:104～105moderate infection;level3:106～107severe infection; level4: above108WSSV erupt. All the bait organismsexamined in April carried the102and103magnitude of WSSV, belong to level1low-gradeinfection. The bait organisms examined in July carried the104and105magnitude of WSSV,belong to level2moderate infection. The bait organisms examined in September carried the103and104magnitude of WSSV, some belong to level1low-grade infection, others belong to level2moderate infection.2The effect of feeding Potamocorbula rubromuscula on growth, immune parameters andanti-disease ability of Litopenaeus vannameiIn this paper, we viewed Potamocorbula rubromuscula Zhang et Cai as nature food forLitopenaeus vannamei, studying the effect of feeding Potamocorbula rubromuscula on growth,immune parameters and anti-disease ability by setting four experimental groups: feed group, P.rubromuscula group, combination group and homogenate group. The result as follows: The growth rate of the shrimps in the combination group and homogenate group are significantlyhigher than that in the feed group (P<0.05), but the growth rate of shrimps in P. rubromusculagroup are lower (P<0.05), and the survival rate among the groups have no significant differences（P＞0.05）. After30days, there was a significant increase of SOD and antibacterial activity ofthe shrimps in the P. rubromuscula group and homogenate group (P<0.05), a significant increasein POD、PO and antibacterial activity could been found in the combination group (P<0.05).After60days, feeding P. rubromuscula could significant improve the activity of POD and PO in thehaemolymph of Litopenaeus vannamei (P<0.05), while combination feeding could significantimprove the activity of POD and SOD (P<0.05). But there was no significant difference betweenhomogenate group and feed group in the immune parameters(P＞0.05). A TaqMan real-time PCRwas conducted to quantify the white spot syndrome virus (WSSV) infections.5.32×102copy/mgtissue WSSV was found in the P. rubromuscula, and the shrimps were carried with the magnitudeof102～103WSSV during the feeding process, after60days, the mounts of WSSV carried on theshrimps of feed group was much higher than that in all the other groups (P<0.05).The medianlethal time (LT50) in P. rubromuscula group has lengthened24%more than that in feed group afterchallenged with WSSV, and the relative percent survival in P. rubromuscula group are significanthigher than that in combination group and homogenate group. When the shrimps began to die, thenumber of WSSV on the shrimps surpassed106copy/mg tissue, the shrimps in P. rubromusculagroup had the highest resistance to the virus, reached to8.5×108copy/mg tissue. According to theresults, we can conclude that the combination of fresh P. rubromuscula and formulated diet or thehomogenate feed made of P. rubromuscula have a positive effect on the growth of Litopenaeusvannamei, but the homogenate feed should be well preserved.Feeding P. rubromuscula couldincrease the immune parameters of the shrimps to some extent and decrease the growth-rate ofWSSV in the latent infection and increase the resistance of the shrimps to acute infection withWSSV.3Effects of adding Bacillus sp. Z5in diet on growth, immune parameters and anti-diseaseability of Litopenaeus vannameiThe effects of adding Bacillus sp. Z5in shrimp pellet with the amounts of108CFU/g on growth,immune parameters and anti-disease ability of shrimp Litopenaeus vannamei were studied. The result shows that the shrimps grew faster in Bacillus treatment group and the yield was24%morethan that in the control. After21days, the activity of PO in Bacillus group significantly increased.After42days, the activity of PO, POD and SOD all increased significantly. The median lethaltime (LT50) in Bacillus group has lengthened35%more than that in the control after challengedwith WSSV. Consequently, it was concluded that Bacillus sp. Z5could increase the survival of theshrimps, enhance the immunity and anti-disease ability of the shrimps.4Effects of the synergy of Potamocorbula rubromuscula and Bacillus on anti-disease abilityof Litopenaeus vannameiThe artificial marked15N was used in the research of assimilation and accumulation effect onPotamocorbula rubromuscula filter-feeding bacillus. The Litopenaeus vannamei were dividedrandomly into five groups and each groups have six parallel experiment.The results showed that the bacillus can be utilized by Potamocorbula rubromuscula and theassimilation rate was29.88%and the carry rate was18.15%,while some bacteria just passed by.After five days feeding with Potamocorbula rubromuscula, the assimilation rate in the shrimporganization was46.72%, and the assimilation and engraftment rate in the intestinal were0.24%.The results showed that the bacillus can be used by Potamocorbula rubromuscula and finallycolonized in the shrimp gut through the food chain system bacillus-Potamocorbula rubromuscula-shrimp.The survival rate of the experimental groups was significantly higher than the feed group (P <0.05). The LT50of Potamocorbula rubromuscula and bacteria group and the filter-feedingPotamocorbula rubromuscula group were respectively longer than the feed group by61.76%and52.94%. The serum superoxide dismutase (sod) activity in Potamocorbula rubromuscula andbacteria group is distinctly higher than the feed group (P <0.05).These results showed that thesynergy of Potamocorbula rubromuscula and bacillus can improve the immune function andenhance the disease resistance of the Litopenaeus vannamei, and the live bacillus were moreeffective than the crushed.