The Role And Mechanism Of Microbial Regulation In White Shrimp Litopenaeus Vannamei Farming Ponds

White shrimp Litopenaeus vannamei is one of the important culture species of shrimp in China.In 2016,the total yield?1,672,200 tons?of marine and freshwater white shrimp aquaculture accounted for 50.6%of the total aquaculture production of shrimp in China.In high-stocking density and high-feed input intensive white shrimp ponds,with the prolongation of farming time,nutrients waste accumulates increasingly.The microbial regulations,by the supplementation of microbial product and exogenous organic carbon,to manipulate "microbial loop" to adjust nutrient cycle and improve aquaculture environment,have been used in aquaculture practices widely.Currently,microbial manipulation to improve water quality in aquaculture ponds has shown inconsistent results,especially the supplementation of microbial product.Understanding the role and mechanisms of the supplementation of microbial product and exogenous organic carbon in affecting the environment for aquaculture might be helpful to evaluate the effect of microbial manipulation correctly.In the present study,we evaluated the efficiency of supplementation of two microbial products and four carbon sources in improving water quality and bacterial community of white shrimp culture based on field investigation and in situ mesocosm,and the effective component of one microbial product in affecting water quality was analysed.The function of indigenous phytoplankton community in microbial regulation was studied.The main results are listed as follows:?1?The physicochemical environment and phytoplankton in 12 white shrimp ponds located in the diked flat in Binhai New District,Shaoxing were surveyed in 2016 and 2017.In these ponds,the mortality of white shrimp was high;the salinity was lower,dissolved oxygen?DO?,pH,total organic carbon?TOC?and C/N ratio were high;blue algae and green algae were dominant in phytoplankton community,and the biomass of blue algae and green algae were high;the chlorophyll a?Chl.a?concentration was positively correlated to the biomass of blue algae;the nitrite?NO₂^--N?and nitrate?NO₃^--N?were negatively correlated to pH.?2?In white shrimp aquaculture water under different situations of carbon and nitrogen?C/N ratio<1;C/N ratio at 10?,the supplementation of microbial product "Huodi No.1" could not decrease ammonia?TAN?,NO₂^--N and NO₃^--N;could affect relative abundance of some dominant phyla and genera,but Bacillus,Lactococcus and Oceanobacillus in microbial product did not colonize in aquaculture water successfully.?3?No significant differences were found in the effects of supplementation of microbial product "Huodi No.1" and sterilized microbial product on aquaculture environment.The supplementation of burning microbial product could affect water quality and microbial community significantly.?4?TAN,NO₂^--N and NO₃^--N were significantly lower in treatments with the supplementation of glucose to adjust C/N ratio at 4.53 and 9.07 than in treatment with non supplementation of glucose?C/N ratio 1.02?;C/N ratio at 9.07 was recommended as the optimal C/N ratio.The supplementation of four carbon sources such as glucose,sucrose,acetic acid and ethanol could not significantly decrease TAN,NO₂^-N and NO₃^-N in aquaculture water nitrification and denitrification dominated in;furthermore,NO₂^--N and N03--N were significantly higher in treatment with supplementation of glucose than in treatment with supplementation of other three carbon sources.?5?The supplementation of microbial product "Novozymes PondPlus" could not decrease TAN,NO₂^--N and NO₃^--N in the benthic environment of white shrimp ponds.?6?TAN,NO₂^--N and NO₃^--N were significantly higher in treatment with phytoplankton removal and the supplementation of glucose than in treatment with the supplementation of glucose;in treatment with phytoplankton and bacteria removal and the supplementation of microbial product "Huodi No.1" than in treatment with the supplementation of microbial product.The mainly conclusions are listed as follows:?1?The supplementation of microbial product "Huodi No.1" in white shrimp culture ponds had limited function in improving water quality and shaping microbial community.The effect of supplementation of microbial product "Huodi No.1”on aquaculture environment might be attributed to the role of organic matter.?2?The supplementation of microbial product "Novozymes PondPlus" could not improve benthic environment in white shrimp culture ponds.?3?The supplementation of different dosage of glucose and different types of carbon sources such as glucose,sucrose,acetic acid and ethanol could improve water quality.C/N ratio and carbon sources types could affect the effect of supplementation of carbon source in improving aquaculture environment.?4?The indigenous phytoplankton community in white shrimp culture ponds played a major role in reducing TAN,and stabilizing pH and DO.