The Environmental Characteristics And Regulation Techniques Of Freshwater Fish Pond

Pond aquaculture,a traditional farming model,occupies an important position in aquaculture industry of China.In recent years,the deterioration of aquaculture pond environment is severe with the development of intensive and high-density aquaculture.Therefore,it is urgent to investigate a low-cost,efficient and effective way to regulate the pond environment to maintain the sustainable and healthy development of pond aquaculture.This study investigated the changes characteristics of environment in the culture pond,by monitoring the changes of denitrifying microorganisms during pond-drying and the pond-drying and a simulation to explore the feasibility of using pond-drying to regulate pond environment.Besides,the pond culture parameters,microbial structure,and metabolic characteristics of different modules in the pond recirculating aquaculture system were studied,and feasibility of pond recirculating aquaculture system in maintaining the sustainability of pond aquaculture was discussed.The main findings were as the follow:1.The variation characteristics of freshwater fish pond environmentThe present study took the traditional tilapia?Oreochroms mossambcus?freshwater aquaculture ponds as research objects to investigate the changes of freshwater fish pond environment and the composition of microbial community structure.The contents of ammonia nitrogen?NH₄⁺?,nitrite?NO₂^-?,nitrate?NO₃^-?,total nitrogen?TN?,total phosphorus?TP?were detected,and the Biolog-ECO as well as high-throughput sequencing were used to analyze the changes of microbial community structure in water and sediment.The results showed that Biolog-ECO technology indicated that the microorganisms in the water and sediment had a higher utilization of carbohydrates and polymers,and a lower utilization of phenolamines and amine compounds.High-throughput sequencing revealed that Firmicutes and Bacteroidetes were the absolute dominant bacteria in the water and sediment.The changes of physicochemical indexes and the differences in the selective utilization of carbon sources by microorganisms might be related to the relative abundance of microorganisms.For example,Bacteroidetes as the relatively abundant bacteria in ponds could make better use of carbohydrates.The content of NO₂^-was negatively correlated with the relative abundance of Lactobacillus.2.The effect of pond-drying on the regulation of freshwater fish ponds environmentThe present study investigated the effects of pond-drying on the aquaculture environment and microbial community structure in the water and sediment before and after pond-drying in the eel?Anguilla japonica?culture pond.The contents of NH₄⁺,NO₂^-,NO₃^-,TN,TP were measured and the changes of microbial community structure were analyzed through high-throughput sequencing.The results showed that pond-drying had significantly positive effect on the contents of NO₂^-,NO₃^-,TN and TP in water?P<0.05?as well as the contents of TP in sediment?P<0.05?.The results of high-throughput sequencing analysis showed that Proteobacteria was the main kind of bacteria in the water and sediment after pond-drying,and the abundances of Proteobacteria,Nitrospirae and Bacteroidetes were increased,while the pernicious microbe such as Cyanobacteria was decreased in the pond at the level of the phylum.At the genus level,the beneficial bacteria such as Novosphingobium,Sediminibacterium,Limnohabitans and Rhodobacter were increased,while the pernicious microbe such as Microcystis and Ellin6067 were decreased.This current study showed that pond-drying could change the microbial community structure in the water and sediment,and have a significant effect on the pond environment regulation.3.Exploration on the sediment regulation of the freshwater fish pondsThe present study took the sediment of aquaculture pond as research objects to discuss the effect of the sun and probiotics on the pond sediment.The Alcaligenes faecalis?Y311 strains??Bacillus cereus?NY5 strains?and Bacillus megaterium?P5-2strains?were splashed into the sediment?10⁶ CFU/m L?indoor and outdoor,respectively.It was found that the removal rates of TN,NH₄⁺and NO₂^-in sediment by insolation were 10.8%,34%and 36%,respectively.The removal rates of NH₄⁺in sediment by Y311,NY5 and p5-2 were 67%,65%and 64%,respectively.The removal rates of NO₂^-and NO₃^-in sediment by NY5 were 25%and 28%.Y311 and P5-2 could inhibit the increase of NO₂^-.The above results showed that both insolation and probiotics could effectively remove N from sediment and could be used as ecological maintenance measures for healthy pond aquaculture.4.The dynamic change characteristics of different modules in pond recirculating aquaculture systemIn current study,the physicochemical indexes and the microbial structure of different modules of the system were detected and analyzed in the pond recirculating aquaculture system.The results showed that the average removal rates of NH₄⁺,NO₂^-,NO₃^-,TN and TP were 81.9%,93.2%,35.6%,81.0%and 56.4%in the clean water area of the system,which could effectively remove NH₄⁺,NO₂^-,NO₃^-,TN and TP in the pond and improve the pond environment.The microbial communities in water and sediment of different modules in the system have different selectivity of carbon source at different sampling time.High-throughput sequencing indicated that the most dominant bacteria in different modules of the pond recirculating aquaculture system were Bacteroidetes and Firmicutes.The improvement of the pond environment by the pond recirculating aquaculture system showed certain limitations for the accumulation of metabolites of cultured animals with time.