Study On Cultivation Of Planktonic Microalgae And Water Quality Control Technology In The Enclosure System Of Medium Alkalinity Leuciscus Pond

In recent years,due to the continuous decrease of freshwater resources available for aquaculture,the development of aquaculture and its future industry has been restricted,and more researchers have focused on the fishery development and utilization of saline-alkali water resources.to alleviate the shortage of fresh water resources.China is rich in saline-alkali water resources,which are mainly distributed in the inland three northern areas of China,in which the saline-alkali waters in Northeast China are mainly carbonate-type,which has a low salinity（1-5）,but the carbonate alkalinity is high,p H and ion coefficient are also at a high level,so that the biological resources in the water environment are scarce,the water quality is thin,the water quality is unstable in production and culture,and the growth of fish is slow and even death.The fishery yield is low.Leuciscus waleckii because of extremely high alkali resistant ability to adapt to the water.Five years ago,small-scale pond breeding was carried out.Now,problems such as large-scale breeding of seedlings have been solved,but there are problems such as incomplete breeding techniques for domestication in medium-high alkali-saline waters（10-30mmol/L）.In the process of aquaculture,problems such as low dissolved oxygen,high content of toxic substances such as ammonia nitrogen and nitrite nitrogen and slow growth of fish often occur,resulting in low fishery yield.In this study,in view of the alkalinity jarraud these problems that exist in the Leuciscus pond,under alkalinity jarraud phytoplankton investigation,water quality and phytoplankton factor correlation analysis,and to carry out targeted vaccination to aquaculture ponds to manage beneficial algae phytoplankton community structure in order to achieve improvement effect of water quality,build based on micro algae ecological regulation For the basicity of the pond green,ecology,efficient utilization and jarraud fish farming in the promotion of carbonate type saline waters in northeast China to provide technical support.The main results are as follows1.Phytoplankton community investigation and correlation analysis of phytoplankton and water quality factors in Leuciscus pondFrom August to October 2020,a total of 65 species and 6 phyla of phytoplankton were identified.The dominant species were different in different months of each pond,but they all showed a large number of dominant species and a low degree of dominance.The distribution of phytoplankton was relatively uniform and the ecosystem was relatively stable.The water quality of each aquaculture pond was evaluated based on the biodiversity index of phytoplankton community.The results showed that pond 1#and pond 2#were in eutrophication state as a whole,and pond 4#was always in a clean-oligo polluted state.The results of Pearson correlation analysis showed that the total biomass and abundance of phytoplankton in the three ponds had different correlations with water quality factors.Ammonia nitrogen,dissolved oxygen,temperature,total phosphorus,total nitrogen,nitrite nitrogen,alkalinity and p H value all had different degrees of influence on the phytoplankton community structure.Among them,cyanobacteria are mainly affected by ammonia nitrogen,dissolved oxygen,temperature and total nitrogen,green algae are mainly affected by nitrite nitrogen,dissolved oxygen and temperature,diatoms are mainly affected by p H and temperature,and eutrophic algae are mainly affected by dissolved oxygen and temperature.2.The changes of physical and chemical indexes of cultured water after inoculation of beneficial algae and the effect of cultivationAfter inoculation of beneficial algae,there were significant differences in dissolved oxygen（DO）and transparency（SD）between the experimental group and the control group.The average value of total phosphorus and total nitrogen in the experimental group was lower than that in the control group,and the average value of chlorophyll A in the experimental group was 45.47%higher than that in the control group.During the experiment,the mean mass concentrations of nitrite nitrogen and ammonia nitrogen in the experimental group decreased by 60.94%and 41.67%,respectively,compared with that in the control group.The results showed that Chlorella vulgare played a good role in regulating the water quality of the medium alkalinity yarrow fish culture pond.By the end of the experiment,the average body weight of the experimental group was 65.84g,and the average body length was 15.26cm;The average body weight of the control group was 55.32g and the average body length was 14.65cm.Both growth indexes in experimental group were significantly higher than those in control group（P<0.05）.3.Phytoplankton community structure in aquaculture water after inoculation of beneficial algaeDuring the experiment,48 species（genera）of 5 phyla were identified in the experimental group and 46 species（genera）of 5 phyla in the control group.The maximum total phytoplankton density was 27.41×10⁶ ind/L in the control group and 74.07×10⁶ ind/L in the experimental group.Control group identification to the advantage of 19 species during test,the experimental group during the test to identify to 14 species of the dominant species.The variation of phytoplankton species in the experimental group was more stable than that in the control group.In the experimental group,microcystis and other toxic algae in cyanophyta were inhibited,and the density of algae cells continued to decrease.In addition,the mean values of the three diversity indexes in the experimental group were larger than those in the control group,and the Pielou index in the experimental group fluctuated more slowly than that in the control group.The above results indicate that the vaccination of common chlorinated algae increases the diversity of water-floating plants and the stability of the community structure,and has also played a role in the improvement of water quality cleaning.4.Relationship between phytoplankton and physicochemical indexes in cultured water after inoculation of beneficial algaeDuring the experiment,phytoplankton in the cultured water was affected by the physical and chemical indexes of nitrate nitrogen（NO₃^--N）,total phosphorus（TP）,temperature（T）,total nitrogen（TN）,dissolved oxygen（DO）,alkalinity（TA）,transparency（SD）and ammonia nitrogen（TAN）.In the RDA analysis of 10 water physical and chemical factors and the cell density of dominant phytoplankton species in each group,dissolved oxygen（DO）,total phosphorus（TP）,total nitrogen（TN）,nitrite nitrogen（NO2^--N）and temperature（T）had a great influence on the density of dominant phytoplankton species in cultured water.