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.

[Analysis of Microbial Diversity in a Fluidized-Sand Biofilter Based on High-Throughput Sequencing Technology].

In order to understand the microbial community composition and mechanism of purifying aquaculture water with a biofilter that was been applied to spotted parrotfish recirculating aquaculture systems with microglass beads as the biofilter filler, the changes in the nutrients of different biological filter beds and the water treatment performance of a fluidized-sand biofilter were analyzed. By using high-throughput sequencing technology, the microbial community structure of the surface area and bottom area at different times were studied. The results show that the fluidized-sand biofilter successfully start-up after one month under marine culture. Nitrification of the biofilter occurred mainly in the lower bed layer; the surface area played a small role in eliminating the NH4+-N. The average removal rates of NH4+-N, TN, BOD5, and SS were 68.3%±2.24%, 49.54%±3.56%, 60.35%±4.98%, and 45.21%±2.11%, respectively. The average NH4+-N removal load reached (343.28±75.5) g·(m3·d)-1, which showed a better performance of wastewater treatment. In this experiment, 31 phyla and 490 genera were identified, thus the biological diversity was significantly higher than that of the other conventional microbial biofilter. Start-stop cycling of the self-cleaning device in the biofilter had no effect on the microbial diversity of different regional, but had some effect on the dominant bacterial community of the microglass beads surface. Under opening self-cleaning device regularly condition, the microbial species of the surface and bottom areas became significantly similar. With time, the microbial species of the superficial area and bottom area had no significant change, and the microbial population structure was relatively stable. In the biofilm training period, the diversity of microbial communities was significantly lower than it was after biofilm maturation. At the time of biofilter stable operation, the dominant bacteria of the superficial zone essentially remained unchanged and mainly included Anaerolineaceae_uncultured (8.4%-28%), Flavobacteriaceae_unclassified (1.1%-32%), Rhodobacteraceae_uncultured (2.3%-17%), Nitrospira(1%-7%), and Caldilineaceae_uncultured (1%-6%). The dominant bacteria of the bottom zone changed over time and mainly include Nitrospira (12.45%-17.06%), Candidatus_Microthrix (2.6%-8.8%), Muricauda (4.8%-6.3%), Defluviimonas (6%-7%), and Rhodobacteraceae_uncultured (2%-6.2%). Among them, the abundance of Nitrospira was significantly higher than that in the other biofilter.