Study On The Application Of Probiotics In Water Quality Management Of High-place Ponds Culture

With the rapid development of the coastal marine aquaculture industry,a large amount of marine aquaculture wastewater has been discharged,which leads to the eutrophication of the coastal marine environment to increase and seriously restrict the green and healthy sustainable development of the marine aquaculture industry.Carbonaceous organic substances,ammonia,nitrite,and other contaminants are the major factor in the deterioration of water aquaculture.Thus,it is very important for the further development of mariculture to control the concentration of the main pollutants in aquaculture water,improve the utilization rate of seawater,and reduce the discharge of aquaculture wastewater.Microorganisms can not only utilize organic carbon,ammonia nitrogen,nitrite,and other substances in the water to complete their proliferation,to achieve the effect of removing and purifying pollutants in the aquaculture water,but also inhibit the growth of pathogenic microorganisms,promote the growth of aquaculture organisms,improve their immunity and other functions.The purpose of this study is to investigate the impact of direct discharge of marine aquaculture wastewater on the microbial diversity of seawater in the neighborhood,and to isolate and screen high-quality strains that can degrade aquaculture water from the aquaculture water.This strain can effectively purify the main pollutants in aquaculture wastewater content,thereby increasing the use rate of aquaculture water,which has a certain probiotic effect on aquaculture organisms.The main findings are as follows:(1)Analysis of the community structure and diversity of microorganisms in the marine aquaculture ponds and adjacent waters of Dongzhai Bay found that the dominant gates of microbial communities in the samples were similar.The predominant gates of bacteria include Proteobacteria,Cyanobacteria,Bacteroidetes,and Actinobacteria,and the predominant gates of fungi include Ascomycota,Basidiomycota,Mortierellomycota,and Rozellomycota.And each environment there is a unique species.Besides,the species abundance and diversity of microbial communities in Penaeus vannamei culture ponds are lower than in other regions,but bacterial genera such as Halioglobus,Owenweeksia,and RS62?marine?group show higher relative abundance than other regions.We also found that the composition and diversity of microbial communities are mainly affected by environmental factors such as pH,NH₄⁺-N,COD(Chemical Oxygen Demand),and TN.The results of the study indicate that as the discharge of marine aquaculture water bodies spreads in different areas of the harbor,it will affect the diversity and composition of microbial communities in the marine environment of the neighborhood.(2)Four high-quality indigenous microbial strains were isolated from the Penaeus vannamei culture pond in Dongzhai Bay,which was two COD degradation bacterium DZG-E3 and DZG-F1,one heterotrophic ammonia oxidizing bacteria DZG-N1 and one heterotrophic nitrite removal bacteria DZG-N1 were identified by16S rRNA gene sequencing,was named:Acinetobacter sp.DZG-E3,Bacillus sp.DZG-F1,Acinetobacter sp.DZG-N1 and Bacillus sp.DZG-A1.(3)Selection and preparation of microbial immobilization materials.Coconut fiber and sodium alginate were selected to prepare microbial immobilization materials.Coconut fiber was modified by the sol-gel method to immobilized microbial strains by improving hydrophobicity.The results showed that the three microbial immobilization materials all showed good bacteria-fixing ability,and the modified coconut silk fibers had the best fixation effect on the four strains used in the test.Besides,the growth of the four strains after the modification with modified coconut fiber was significantly higher than that of the other two materials.(4)To investigate the ability of probiotics to purify water quality in a short time,a simulated penaeus vannamei culture pond and biological filter box were set up,and four strains of microorganisms fixed by modified coconut fiber were added to the biological filter box.After 16 days of testing,DZG-E3 has the best ability to regulate the quality of cultured water.DZG-F1 has a good control effect on the increase of NH₄⁺-N concentration in the early stage of the experiment.DZG-N1 has the best effective control effect on the concentration of NO₂^--N in culture water,with the growth rate of 0.071 mg/L/d at 0-10 days.DZG-A1 can reduce NO₃^--N in aquaculture water,which can maintain water quality stability in the early stage.Compared with the initial breeding period,P.vannamei grew better with time,and its body length increased by more than 5 times compared with the initial value.The survival rate of the shrimp in the experimental group was higher than that in the control group,and the survival rate of the shrimp in the F1 group was the highest,which was 92±4%.The experimental results show that the addition of strains can purify carbon-containing organic matter,ammonia nitrogen,nitrite and other pollutants in the aquaculture water body can maintain the stability of the aquaculture water quality,and improve the survival rate of Penaeus vannamei during the breeding process and promote the growth of Penaeus vannamei effect.(5)According to the characteristics of the test strains and their interactions,and the ability to purify water pollutants in culture,different strains are designed to form two groups of composite bacteria:A(DZG-E3+DZG-N1)and B(DZG-F1+DZG-A1),which are respectively fixed and added to the biological filter box simulating the shrimp culture pond of Penaeus vannamei.The pollutants in the two groups of complex bacteria culture water have a certain purification effect,which can slow down the accumulation of various pollutants in the culture water.The best effect is group B,which is effective for COD and NO₂^--N in the culture water.Besides,the complex bacteria's ability to purify pollutants has been significantly improved compared to the single bacteria test,and the survival rate of P.vannamei has been improved during the breeding process.Compared with the control group,the survival rate of shrimp has increased by 10-12%.