Effects Of Chlorella Pyrenoidosa And Haematococcus Pluvialis On The Water Quality Of Litopenaeus Vannamei Culture System

At present,china has become the country with the largest shrimp farming area and the highest production volume in the world.In recent years,the deterioration of water quality in the breeding environment has become one of the bottlenecks in the development of shrimp aquaculture.Among them,ammonia nitrogen（NH₄⁺-N）and nitrite nitrogen（NO₂^--N）are the main pollutants in the aquaculture water.It can cause fulminant shrimp disease,making the shrimp unable to grow normally,and even death by poisoning.Traditional pond aquaculture removes water pollutants by changing water,and most of the untreated aquaculture wastewater is directly discharged into the surrounding environment,which not only causes serious waste of water resources,but also pollutes the water environment.The recirculating aquaculture system model（RAS）has high investment,operating costs and technical requirements,and it is difficult to promote in a large area.The internal circulation prawn breeding model proposed by this research group puts the pre-filmed biological filler into the prawn breeding pond,makes full use of the space of the prawn breeding pond,and has the advantages of small footprint,simple process,and environmental friendliness.Microalgae are widely distributed in nature and have strong adaptability.They can not only provide nutritional supplements for prawns,improve their growth performance,but also use their own biological characteristics to effectively absorb nitrogen and phosphorus and other substances,increase the dissolved oxygen content of water,and improve The water quality of aquaculture water plays an important role.In this study,two types of microalgae,Chlorella pyrenoidosa and Haematococcus pluvialis,were selected to study their effects on the water quality of the Litopenaeus vannamei culture system,internal circulation and water exchange.Scanning electron microscopy was used.And high-throughput technology analyzed the morphology of the polyurethane filler biofilm in the internal circulation aquaculture system and the structure and diversity of the bacterial community.The following conclusions are obtained through research:（1）Four aquaculture systems were set up,namely,internal circulation+C.pyrenoidosa（D1）,internal circulation（D2）,water exchange+C.pyrenoidosa（D3）and water exchange（D4）4 culture systems.During the 60-day breeding process,the concentrations of NH₄⁺-N,NO₂^--N and NO₃^--N all showed an upward trend,and there were significant differences between systems.Among them,the concentration of NH₄⁺-N in each system is maintained at a relatively low level(<0.1 mg·L^-1),the average concentration of NO₂^--N is 1.77±1.18 mg·L^-1,0.28±0.14 mg·L^-1,4.11±2.50mg·L^-1,4.75±2.89 mg·L^-1,the average concentration of NO₃^--N is 36.97±14.48mg·L^-1,41.77±17.06 mg·L^-1,9.08±4.84 mg·L^-1,7.40±3.19 mg·L^-1,the survival rate of prawns was 75.0%,79.7%,70.3%,67.2%.（2）Four aquaculture systems were set up,namely,internal circulation+H.pluvialis（Y1）,internal circulation（Y2）,water exchange+H.pluvialis（Y3）,water exchange（Y4）4 culture systems.During the 60-day breeding process,the concentrations of NH₄⁺-N,NO₂^--N and NO₃^--N all showed an upward trend.Among them,the concentration of NH₄⁺-N in each system is maintained at a relatively low level(<0.1 mg·L^-1),Y1,Y2 are significantly less than Y3,Y4,there is no significant difference between Y1 and Y2,and there is a significant difference between Y3 and Y4.The average concentration of NO₂^--N is 0.37±0.28 mg·L^-1,1.14±0.95 mg·L^-1,2.17±1.45 mg·L^-1,3.41±1.73 mg·L^-1,and there were significant differences between systems.The average concentration of NO₃^--N is 26.22±12.10 mg·L^-1,23.32±11.63mg·L^-1,11.49±7.99 mg·L^-1,9.99±7.32 mg·L^-1,and there were significant differences between systems,the survival rate of prawns was 75.0%,68.8%,73.4%,61.1%.（3）The results of scanning electron microscopy showed that rod-shaped bacteria（7.5-8.5μm）were mainly in the adsorbent of polyurethane filler,accompanied by a small amount of spherical bacteria（1.0-1.5μm）and filamentous bacteria（7-8μm）.The polyurethane filler biofilm is mainly composed of short rod-shaped bacteria（1.5-2.0μm）,accompanied by a small amount of spherical bacteria（0.8-1.5μm）,which grow on the surface of the filler in the form of bacterial micelles.A large amount of C.pyrenoidosa residues were found on the filler of the dosing system of C.pyrenoidosa,but not observed in the dosing system of H.pluvialis.（4）The high-throughput sequencing method was used to analyze the bacterial community structure and diversity of polyurethane filler adsorbents and biofilms.The results showed that the bacterial community diversity and abundance of the filler of the C.pyrenoidosa system was lower than that of the non-administered system,and the system with H.pluvialis was higher than that of the non-administered system;the difference in bacterial community composition between the C.pyrenoidosa system and the non-administered system was significantly greater than that of the H.pluvialis system.（5）The dominant bacteria of the C.pyrenoidosa system are Acidobacteria（41.6%）,Proteobacteria（19.5%）and Desulfurization bacteria（8.3%）,and the dominant bacteria are Acanthopleuribacter,norank＿f＿＿norank＿o＿＿PB19,Catenovulum and SM1A02,etc.;The dominant bacteria of the dosing system are Proteobacteria（45.3%）,Bacteroides（27.6%）,and Planctomycetes（6.4%）.The dominant bacteria are Sungkyunkwania,Ruegeria,Rheinheimera and SM1A02,etc.（6）The dominant phyla of H.pluvialis system are Proteobacteria（47.6%）,Bacteroides（25.4%）and Phytomycetes（5.7%）,and the dominant bacteria are unclassified＿f＿＿Saprospiraceae,norank＿f＿＿norank＿o＿＿Kordiimonadales,Aliikangiella and Pseudohongiella,etc.;The dominant bacteria of the dosing system are Proteobacteria（40.8%）,Bacteroides（36.3%）and Acidbacteria（12.2%）,and the dominant bacteria are unclassified＿f＿＿Saprospiraceae,Acanthopleuribacter and norank＿f＿＿norank＿o＿＿Chitinophagales,etc.