Studies On The Affecting Factors To Microalgae Community Succession And Its’ Relevance To Shrimp Diseases In Industrial Aquaculture Of Litopenaeus Vannamei

For a long time, traditional pond shrimp aquaculture are the main modes ofshrimpproduction.But these modes exposed too many problems in recent years, such as high frequency of diseases, severe pollution, constrainted by weather and low yield per unit area. All this proplems had restricted the sustainable development ofshrimp aquaculture. Industrial shrimp farming model having less environmental pollution, can effectively prevent the outbreak of epidemics,and high yield.Based on these, shrimp industrial farming model developed rapidly in Qingdao, Rizhao, and other regions in recent years. However, there are still many shrimp pondshappened diseaseregularly every year, despite this industrial mode prevented the ponds from disease outside, more standardized and more scientific management for cultivation water.This may had certainconnections with microalgae community succession.Therelationship of outbreak ofshrimpdisease and microalgae had not seen systematic studyin recent yearsso far.As a special aquaculture mode, shrimp growth, the occurrence of disease, as well as dynamic community of microalgae in shrimp ponds were different from other modes for its own characteristics. Therefore, this paper studied on laws of microalgaecommunity succession and it’s relationship with main physical-chemical factors in water in Litopenaeus vannamei’s industrial aquaculture ponds.And it also explored the rules for outbreaking of shrimp diseases and connections with microalgae. The main contents are as follows:1. The studies on innestigations of the microalgae dominant speciesand it’s relationship with environmental factors in different density Litopenaeus vannamei’s industrial aquaculture pondsWe conducted theexperiments from2015 June 13 to September 6 in the indoorshrimpindustrial aquaculture ponds of Baorong Aquatic Science and Technology Co. Ltdat Jiaozhou in Qingdao.Coosing 3 different aquaculturedensityponds : 300ind/m2, 400ind/m2 and 500ind/m2,for periodically sampling and analyzing the main physical-chemical factors,species and nunbers of microalgae. And used Redundancy Analysis(RDA), to find the major ecological factorsin water which affectedmicroalgae dominant species succession. The results showed that a total of 14 dominant species of microalgae were identified,including 3 species of chlorophyte: Chlorella vulgaris, Chlorella pyrenoidesa and Nannochloris oculata; Including 5 species of bacillariophyta: Coscinodiscus lineatus, Cyclotella comta, Thalassiosira norden, Chaetoceros lorenzianus and Chaetoceros muelleri; Including 3 species of cyanophyta: Microcystis incerta, Oscillatoria willei and Oscillatoria tenuis;Including 2 species 0f Pyrroptata: Prorocentrum minimum and Peridinium depressum and including only 1 species of Cryptophyta: Cryptomonas ovata.We also found that:The species and quantity of microalgaedominant species in different density shrimp ponds were entirely different.In general, the dominant species were mainly green algae, diatoms and part dinoflagellates in the early stage.Microcystis and Oscillatoriaof Cyanophyta become dominant species in the middle and late Period,and some species which preference eutrophicated water also became the dominant species. From a different point of view of rearing densities in shrimp ponds, low-density ponds trended more stable compared to the high-density ponds.The harmful microalgae Oscillatoria rapidly growing easily in high-density ponds,and which trended that the higher the rearing densities, the larger Oscillatoria dominance in the late period of breeding. The RDA analysis shows the greatest environmental factors which impacted on the succession of microalgae dominant species were various nutrients and temperature in water.2. Exploration oninnestigations of the microalgae community succession in different periodsand its relationship withshrimp diseasesin Litopenaeus vannamei’s industrial aquaculture pondsThe experimentanalyzed the physical and chemical factors, the species and quantity of microalgae, heterotrophic bacteria and Vibrio regularly in shrimp industrial aquaculture ponds. The survival rateswere taken as indexes for degree of shrimpdisease,and analyzed the quantity of microalgae, survival rates of shrimp, quantity of heterotrophic bacteria and Vibrioto find their correlation. The results showed that density and biomass of microalgae significantly affect the degree of shrimp disease.Excessivedensity of microalgae, especially dominant species of cyanobacteria in late Period, resulting in the continuous shrimp diseases.The experimentrecommended the dominant species Oscillatoria’s density in 5.0′108 cell / L or less, and biomass at 60 mg / L or less;Low density and biomass of microalgaeresulting inpoor capacity of microalgae to regulate shrimp ponds ecosystem.This may caused of slow growth and unevenheadsof shrimp.The experimentrecommended the density of microalgaein the late stage in not less than 4.3′107cell / L, biomass at 7.5mg / L or more.We also found that diversity index of microalgae was significantly correlated with the degree of shrimp disease. We should regularly monitor the diversity index of microalgae.If the number and biomass diversity index were less than 1, indicating that the ecological structure of shrimp ponds with poor stability, should pay attention to the growth of shrimp in this stage,in case of shrimp disease.There excisedcomplicated relationship of coexistence and mutually wih microalgae and bacteria. There was significantly negative correlation between Chlorella and heterotrophic bacteria and Vibrio, whilethe bad algae Oscillatoriahad a positive correlation with heterotrophic bacteria and Vibrio,and the Microcystis had no significantly correlation with them.The experiment showed that harmful pathogens was inhibited, shrimp grew well, when the Chlorella were the absolute dominant species of shrimp ponds.There with high density of harmful pathogens, expressed as a double stress to shrimp when the Oscillatoria was the dominant species.We should emphatically considered the relationship between algae and bacteria in the process of shrimp breeding.The Microcystin blooms and became dominant species in the rainy weather.Shrimp was found acute symptoms of illness During this phase,may had some relation with weather,and the specific reasons need verified by follow-on experiments.