Introduction
The crucial roles of prokaryotes in the recirculating aquaculture system (RAS) highlight the need to characterize the prokaryotic communities in the system. U nderstanding the communities can lead to improvements in system control, system function, and future system design of RAS, and therefore are indispensable steps. Using two universal primer pairs and two Illumina sequencing runs, we characterized bacteria and archaea communities sampled from eight different sampling points from two identically designed commercial RAS systems (Fig 1).
Results
In this short abstract, we only shared the two most interesting findings. Firstly, we found that the bacterial communities in the biofilm and the water were different both in term of abundance and species present (Fig. 2) . The finding contrast with the general belief that r ecirculation of water in the system would promote the dispersal of bacteria communities between RAS compartments , which the biofilter may serve as the primary bacteria source through continuous seeding from the shedding of old biofilm. Secondly, the diversity of archaeal communities was not high as previously thought. We found only 30 ASVs, with Nitrosopumilus as the dominant group (Fig. 3). This study further supplements our existing knowledge on bacterial and the archaeal community in RAS.