Effect of Copper Ion Sterilization on Bacterial Community in a Freshwater Recirculating Aquaculture System

The study aimed to evaluate the safety of copper ion sterilization based on copper ion residues in zebrafish (Brachydanio rerio), as well as bacterial community structure and diversity in recirculating aquaculture systems (RASs). The copper ion content was determined using national food safety standard GB 5009.13-2017. Bacterial community structures and alpha and beta diversity indexes were examined using the 16S rRNA gene sequences produced by Illumina HiSeq sequencing. The results revealed no significant copper ion enrichment in B. rerio when the copper ion concentration was 0.15 mg/L. The relative abundances of Erythrobacter, nitrite bacteria, and Flavanobacteria were clearly higher in the treatment group than in the control and differences in bacterial species richness and diversity were obvious. In addition, there was no sharp decrease in the microflora at the outflow of the copper ion generator. In conjunction with the changes in ammonia nitrogen, nitrate, and nitrite concentrations during the experiment, the results indicated that there were no significant effects on the purification efficacy of the biological filter, but the abundances of beneficial bacteria increased significantly. This is of great relevance in order to understand the response of bacterial communities affected by changing environmental conditions, such as copper ion sterilization.