Study On The Effect Of Microalgae In Regulating Carbon And Nitrogen In Litopenaeus Vannamei Factory Farming Environment

Litopenaeus vannamei has a short rearing cycle,is easy to survive and is one of the main species of shrimp farmed in China.The factory farming model is an intensive,high-density farming model with high land utilisation,which can significantly increase shrimp farming yields,but there is also greater pressure for environmental regulation.The accumulation of waste from shrimp factory farming has a significant impact on the health of Litopenaeus vannamei,which is not only more costly but also more polluting to the environment.In order to solve the above problems,the following studies were carried out using microalgae to regulate elements such as carbon and nitrogen in the culture system and to optimise the culture environment:Monitoring the characteristics of the aquatic environment of the culture system for two representative models of Litopenaeus vannamei factory water exchange and recirculating water,and analysing the characteristics of the microalgal community composition of the culture system using high-throughput sequencing techniques;Different concentrations of Picochlorum（1*104,2*104,4*104 cells/ml,each treatment group named KH₁,KH₂,KH₄,control group KH_D）and different species of microalgae（Chlorella,Tetraselmis,Chaetoceros muelleri,named RZ_Q,RZ_L,RZ_J in order,control group RZ_D）were used to optimise shrimp aquaculture water environment,and analyse the effect of adding microalgae on the microalgal community,water quality indicators,carbon balance and shrimp growth by calculating the amount of feeding,the weight of harvested shrimp and collecting sediment to count the carbon balance of the aquaculture system;Three types of microalgae and probiotic bacteria such as Bacillus sp.were used to regulate the water environment of shrimp culture in the beneficial algae group（zao）,the beneficial bacteria group（jun）and the mixed bacteria-algae group（hun）,and the effects of each treatment group on the optimisation of water quality,microbial community and shrimp growth in shrimp culture systems were analysed.The main findings are as follows:1.Characteristics of microalgal communities in shrimp factory farming systemsWhen the microalgal communities of the two shrimp culture modes were analysed at the generic level,7%-20%of the microalgae in the water exchange mode were either unclassifiable or extremely under-represented.The top three dominant populations in terms of relative abundance included Cyclotella（19.45%）,Nannochloropsis（15.74%）and Synechococcus（6.84%）;Approximately 6%to 40%of the microalgae in the recirculating water culture model were unclassified or extremely under-represented.The dominant species in the recirculating water culture model also included Nannochloropsis（9.96%to 25.4%）,with a change in the structure of the dominant population compared to the water exchange group,with an increase in the dominant population of unclassified f Akkeemansiaceae（LC group,8.61%）,Hyella（MC group,9.06%）and the proportion of microalgae that could not be classified or were extremely under-represented increased by about 20%,with Nannochloropsis accounting for 9.96%to 25.4%.The effect of different concentrations of microalgae on the community structure of microalgae,the absolute dominant population in the KH_D group was Isochrysis（69.59%）,and the relative abundance was significantly higher than that of KH₁,KH₂ and KH₄（P<0.05）.After inoculation of microalgae in the culture water,the absolute dominant population in the KH₁,KH₂ and KH₄ groups were all Picochlorum,and the relative abundance The relative abundance of Picochlorum was 70.03%,71.69%and 95.65%respectively,and was significantly higher than that of Picochlorum in KH_D（P<0.05）.The KH₁ group had the highest species diversity and richness,but the KH₂ and KH₄ groups had lower species diversity and richness than the KH_D group.Different species of microalgae had significant effects on the microalgal community structure,and species with relative abundance higher than 10%at the genus level in the RZ_D group included Nannochloropsis（20.14%）and Isochrysis（25.75%）.Inoculation of different microalgae had certain effects on the microalgal community structure of the cultured water bodies,and the RZ_Q,RZ_L and RZ_J groups The relative abundance of Nannochloropsis changed significantly,with 95.79%,41.52%and 8.24%respectively,and increased by 75.65%and 21.38%in the RZ_Q and RZ_L groups and decreased by 11.9%in the RZ_J group compared with the control group.Different farming patterns,as well as inoculation of shrimp farming systems with microalgae,can significantly influence the characteristics of microalgal communities in the aquatic environment and change the structure of the dominant populations.2.Water environment regulation of shrimp factory farming systemInoculation of different concentrations of micro-green algae could enhance the water environment of shrimp culture,among which the KH₄ group had the best effect on the removal of ammonia nitrogen,nitrite,phosphate and COD,with the removal rate of 68.99%,85.57%,72.4%and 60.82%,respectively,The hepatopancreas lysozyme（LZM）and superoxide dismutase（SOD）enzymes in the treatment groups increased by 16.93%-73.74%and 31.73%-78.05%,respectively,compared with the control group.The treatment groups inoculated with different species of microalgae（RZ_Q,RZ_L,RZ_J）were able to reduce ammonia,nitrite and phosphate levels by up to 86.37%,75.41%and 78.63%,respectively,compared to the RZ_D group,with a reduction of more than 50%in COD in the water column;in terms of shrimp growth and immune-related enzyme activity,the experimental groups inoculated with microalgae outperformed the RZ_D group.Compared to the RZ_D group,the hepatopancreas LZM and SOD enzyme activity of the Vannabei shrimp increased by 85.49%（RZ_J）and 79.18%（RZ_Q）,and the RZ_Q group had the highest specific growth rate of shrimp（7.77）.The use of microalgae to regulate the water environment of shrimp culture was effective in improving water quality,significantly enhancing the activity of shrimp immune-related enzymes and increasing the growth rate,specific growth rate and survival rate of shrimp（P<0.05）.3.Carbon balance study of shrimp factory farming systemsCarbon inputs to the shrimp culture system in this study mainly include feed inputs,microalgae addition and shrimp fry inputs;carbon expenditures mainly include sediment expenditures（residual bait and faeces,shrimp shells,pond wall residues,etc.）,shrimp growth utilization expenditures,phytoplankton primary production expenditures,water respiration expenditures（microalgae respiration,zooplankton respiration,bacterial respiration）,shrimp respiration expenditures,organic carbon expenditures（DOC,POC）,etc.Analysis of carbon income and expenditure in the inoculation of different concentrations of microalgae in the regulated culture system showed that the carbon input component was dominated by feed input in all treatment groups（more than 89%）,microalgae addition input accounted for about 0%to 1.58%and shrimp fry input accounted for about 8.95%.In all four treatment groups,the carbon expenditure component was dominated by shrimp growth and use and respiration,with the KH_D group spending 30.18%on sediment,25.87%on shrimp growth and use,4.49%on phytoplankton primary production,36.06%on respiration and 3.41%on organic carbon.Inoculation of cultured water with different concentrations of microalgae increased the proportion of shrimp growth use expenditure by up to 8.45%（KH₂）and phytoplankton primary production expenditure by up to 11%（KH₄）.Analysing the carbon income and expenditure in the inoculation of different types of microalgae in the regulated culture system,the carbon input component is also dominated by feed input（over 97%）,with microalgae adding about 0%to 1.68%and shrimp fry input about 0.52%.The proportion of expenditure on each component in the RZ_D group was 30.91%for sediment,29.78%for shrimp growth and use,7.26%for phytoplankton primary production,29.44%for respiration and 2.61%for organic carbon.The treatment groups inoculated with microalgae（RZ_Q,RZ_L,RZ_J）showed some changes in the expenditure on each component,with the proportion of expenditure on sediment decreasing by 9.86%to 16.65%and the proportion of expenditure on phytoplankton production increasing by 7.25%to 8.93%.The proportion of respiration expenditure also increased somewhat（2.68%to 6.75%）.In this study,the RZ_Q group had the best carbon sequestration effect,with the microalgae input being 0.90%of the carbon input to the farming system,but accounting for 7.72%of the carbon expenditure of the farming system.the KH₄ group had a smaller proportion of each component（within 5%）compared to the RZ_Q,RZ_L and RZ_J groups,and inoculation of microalgae in the shrimp farming system could significantly affect the carbon expenditure of the farming system.4.Effects of bacterial and algal regulation on Litopenaeus vannamei culture water and its growthIn terms of water quality control,compared with the control group,the beneficial bacteria group,the beneficial algae group and the mixed bacteria and algae group were all effective in removing ammonia nitrogen,nitrite,active phosphate and chemical oxygen demand（COD）from the Litopenaeus vannamei culture water,with the beneficial algae group having the best effect on the removal of ammonia nitrogen,nitrite and COD,and at the end of the test,they were reduced by 95.61%,65.86%and 51.45%respectively relative to the control group.95.61%,65.86%and 51.45%,and the beneficial algae group had the best effect on the removal of active phosphate,with a reduction of 89.94%compared to the control group;High-throughput sequencing analysis showed that the absolute dominant group in all treatment groups was Rhodobacteraceae,and the relative abundance of Rhodobacteraceae was 43.30%in the beneficial bacteria group,48.66%in the beneficial algae group,73.03%in the mixed bacteria and algae group,and 66.87%in the control group.The addition of beneficial bacteria significantly increased the relative abundance of Bacillaceae in the beneficial bacteria group（3.69%）;In terms of shrimp growth and immune-related enzyme activity,all three treatment groups increased the hepatopancreas SOD and LZM enzyme activities to different degrees and promoted shrimp growth,with the beneficial algae and beneficial bacteria groups having a significantly higher promotion effect on shrimp enzyme activity and growth than the mixed bacteria and algae group and the control group（P<0.05）.