Comparison between recirculating aquaculture and biofloc systems for rearing juvenile common carp (Cyprinus carpio): Growth performance, haemato-immunological indices, water quality and microbial communities

In a 2-month trial, four different aquaculture systems, viz., (a) rearing at 50% daily water exchange without filtration (WE), (b) biofloc system (BFT1), without water exchange or filtration, (c) biofloc system (BFT2), similar to BFT1 but 10% of daily feed deducted, and (d) recirculating system (RAS), without water exchange, were compared through monitoring water quality as well as measuring the growth, haematological and immunological indices of common carp (Cyprinus carpio). Metagenomics was also applied to characterize the microbial profile of the waters through screening 16S rDNA gene sequences. BFT systems demonstrated lower values of pH, dissolved oxygen but did higher concentration of total suspended solid (TSS) and 5-day biochemical oxygen demand (BOD5). No significant change was observed in haematocrit, haemoglobin, albumin, total protein and total cholesterol of the fish kept in all treatments. Metagenomics analysis revealed the highest abundance for Proteobacteria in BFT1, BFT2 and RAS systems, whereas Firmicutes was the dominant phylum in WE treatment. At the genus level,Flavobacterium(in BFT treatments),Sphingobacterium(RAS) andRhodoluna(WE treatment) were the dominant bacteria. Taken together, BFT treatments could improve water quality and feed utilization. Moreover, BFT and RAS rearing conditions might change microbial structure of water.