Nutrients and Microbial Community in Recirculating Aquaculture System for Plectropomus leopardus Aquaculture

  Objective  Nutrients content and microbial community in a recirculating aquaculture system (RAS) for Plectropomus leopardus aquaculture were analyzed to provide theoretical and practical reference for the aquaculture operation.

  Method  Indicators for the water quality of the influent, fish ponds, effluent, biological filter, and ultraviolet disinfection tank as well as the Vibrio count and microbial community at various stages of the RAS were determined based upon the high-throughput sequencing results.

  Result  The concentrations of NH₄⁺-N, NO₃⁻-N and PO₄³⁻-P in the water increased at the stages where fish were present and declined where disinfection took place. It was the opposite on NO₂⁻-N. Vibrio count was fewer in the exogenous seawater than in any downstream points of RAS which rose significantly after flowing through the fish ponds and diminished after the biofiltration treatment. At phylum level, the dominant microbes in the system were Proteobacteria, Bacteroidota, and Firmicutes. At genus level, there are mainly Pseudoalteromonas, Photobacterium, Vibrio, and Lactobacillus. The main Vibrio species was V. ponticus, the ration of which was 66.17%.

  Conclusion   The RAS system was effective in reducing the  \rmNH_4^+ -N, NO₃⁻-N, \rmPO_4^3- -P, and vibrio population in the water. The composition of the microbial community in the circulating water was unveiled.