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It was found that there is a certain correlation between the change of communitystructure and shrimp disease in the previous study about prawn aquaculture. Theoutbreak of dominant microalgae specie in shrimp ponds may play a certain role inthe crisis of WSSV, which may be the potential factor. But there was few researche onthe ralationships among dominant microalgae specie, WSSV and shrimp. In this paper,three kinds of ponds dominant microalgae specie (Chlorella pyrenoidosa, Microcystisaeruginosa, Phormidium chirinum) was used to study the quantitative relationbetween dominant microalgae specie and WSSV, the influence of the three kinds ofdominant microalgae specie to healthy Litopenaeus vannamei, impact of two kinds ofcyanobacteria on WSSV carried shrimp. The main contents are as follows:1. Relationship between three dominant microalgae species and WSSVBG11medium was used to culture Microcystis aeruginosa, Phormidiumchirinum and Chlorella pyrenoidosa. Four groups were set which relate to a highdensity group, a medium-density group, a low-density group and a control group(without algae). WSSV extract was added in each group until initial concentration of4.32×105copies/ml. Algae solution was centrifuged respectively in the first2h,24h,72h,120h, and supernatant was resuspended in PBS. Finally qPCR was used todetect WSSV copies in supernatant and the algal cells were counted. Partialcorrelation analysis was used to clarify the ralationship among the amount of WSSVin both algae and supernatant and algae density.It turns out that at2h, the amount of WSSV in supernatants of high densitygroup, medium-density group and low-density group were105copies/ml, and whichin algal were104copies/ml,104copies/ml and103copies/ml from high to low densitygroup. At24h, WSSV amount in supernatant of high, medium and low density groupswere reduced by98.1%,97.9%,87.6%. WSSV amount of algae in high and mediumgroup was reduced by98.6%and90.1%, which is significantly reduced by one or twoorders of magnitude (P<0.05), while low-density group shows the opposite result(P>0.05). At72h, the WSSV amount of each group in supernatants and algaecontinued to decline, most free WSSV had disappeared. Partial correlation analysisshowed that no significant correlation (P>0.05) between the amount of algae andWSSV carried by algal cells. Each group showed a declining trend of WSSV, in whichthe total WSSV of each group reduced to104copies/ml or103copies/ml within24h, while the control group stayed105copies/ml. The total amounts of WSSV in algaegroup reduced faster compared to the control group with the data of103copies/mlcompared to104copies/ml in72hours. We conclude that Microcystis aeruginosa,Phormidium chirinum and Chlorella pyrenoidosa are able to carry a small amount ofWSSV, their carrying capacity continue to decrease over time. The correlationbetween WSSV amount in algae and numbers of algae cells is non-significant. Thethree algae are able to accelerate the subtraction of WSSV in shrimp pond water.2. Effect of three dominant microalgae species on shrimpEight groups was set which were refer to Microcystis aeruginosa live algaegroup, Phormidium chirinum live algae group, Chlorella pyrenoidosa live algae group,Microcystis aeruginosa dead algae group, Phormidium chirinum dead algae group,Chlorella pyrenoidosa dead algae group, pond water group and control group. Eachgroup had1.2×106cells/ml algae cells. Shrimp pond water was used in the pond watergroup, which contains rich organics and approximately104cells/ml algae cells(mainly Scenedesmus, Chlorella, Merismopedia glauca, etc.). Other groups used thewater via sedimentation which contains less organics and without microalgae.10shrimps detected for WSSV negative were put into each group, and were checked theshrimp life-or-death situation at9:00,15:00and22:00every day. At last, cumulativemortality was figured out.The results show that cumulative mortality of Microcystis aeruginosa living ordead algae groups rise up over time, which are significantly higher than the pondwater group and the control group. Shrimp mortality of living and dead Microcystisaeruginosa group reached94%and87%in42hours, while the pond water group was37%and the control group was only3%. Within90h, shrimps in living or dead algaegroups of Microcystis aeruginosa were totally died, while the pond water and controlgroup only reach50%and13%of cumulative mortality. The living or dead algaegroup of Phormidium chirinum shows the same increase in the cumulative mortalitywhich was close to80%and significantly higher than the57%of shrimp pond watergroup and the control group of23%. Shrimp mortality of dead algae group ofChlorella pyrenoidosa increased rapidly, while it increased slowly in living algaegroup of Chlorella pyrenoidosa which shows the similar mortality to the controlgroup. At the end of the experiment, the mortality rate of dead algae groups reached70%while only23%in living algae group of Chlorella pyrenoidosa. During theexperiment, each group living algal cells was keep in the initial density, water pH,temperature and dissolved oxygen were in the suitable range for shrimp. Microcystis aeruginosa and Phormidium chirinum living or dead algae are able to bring aboutstress and hasten the death to farming shrimp, while the living Chlorella pyrenoidosadidn’t hasten the death to shrimp, but its dead algae also had a negative impact andhasten the death to shrimp.3. Effect of two dominant cyanobacteria species on WSSV infected shrimpEffect experiment of Phormidium chirinum and Microcystis aeruginosa onWSSV infected shrimp:4groups were set in each cyanobacteria experiment whichwere refer to living algae group with1.2×106cells/ml living algae, dead algae groupwith1.2×106cells/ml dead algae, positive control group, and negative control group.WSSV negative shrimps were put into the negative control group, while shrimpsinjected with WSSV were put into the rest three groups. Check the dead shrimps at9:00,15:00and22:00every day. At last, cumulative mortality was figured out.The results show that cumulative mortality of each group rised up. Within63h,shrimp mortality of living and dead algae groups of Phormidium chirinum increasedrapidly. In the end, shrimp cumulative mortality in living and dead algae groupsreached96%and89%, while the positive control group and negative control grouponly reach64%and11%. Shrimp cumulative mortality in living and dead algaegroups of Microcystis aeruginosa rised up after52h, two groups are in consistenttrend. In the end, shrimp cumulative mortality in living and dead algae groups reached82%and89%, while the positive control group and negative control group only reach64%and31%. Microcystis aeruginosa and Phormidium chirinum living or deadalgae are able to bring about stress and hasten the death to WSSV injected shrimp, theharmful have additive effects upon cyanobacteria and latent infection of WSSV,enhance the toxic effects.
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