To investigate the water quality variations and microbial community structure in the aquaculture zone of a freshwater pond with an embedded container recirculation aquaculture system, this study measured water quality indicators in the zone containing a three - stage biofilter (sedimentation tank, oxidation tank, purification tank, and filter dam) and biofill (filter cotton and brush). High - throughput sequencing was also employed to analyze the microbial community structure in the water column of each biofilter and on the biofill. Results indicate that the water purification system in the aquaculture zone operates stably and effectively, with the treated water quality meeting aquaculture requirements. The removal rates of ammonia nitrogen (NH4+-N), nitrite nitrogen (NO2--N), and total nitrogen (TN) were 52.97%, 63.23%, and 53.51%, respectively. The bacterial community in the aquaculture zone consisted mainly of 33 phyla, including Proteobacteria, Actinobacteria, and Bacteroidota. In the biofilter, the bacterial community structure of the biofilm differed from that of the water column, with a significantly higher relative abundance of Actinobacteria on the biofilm (P < 0.05). The water column samples had higher bacterial community diversity and richness than the biofilm samples. Correlation analysis revealed that NH4+-N, NO2--N, and TN significantly influenced the microbial community structure in the water column group (P < 0.05), while TP, AP, and DO had a more significant impact on the bacterial community structure in the biofilm group. In conclusion, the three - stage biofilter can effectively increase the microbial flora that promotes nitrogen and phosphorus metabolism, contributing to stable water quality. These findings provide theoretical support for the construction and water quality regulation of freshwater pond embedded container recirculation aquaculture systems.
