| Abstract | This study was carried out to assess the dynamics of bacterial population and identify the dominant bacterial species in the water column of both Aquamimicry and Biofloc systems applied for nursery rearing of Nile tilapia (Oreochromis niloticus). There were two triplicated treatments with total of six cylindrical cement tanks. In each tank, 4,000 fish with initial weight of 0.1732 ± 0.0036g were stocked and maintained for 55 days. Water samples were collected every 3 day for analyzing total bacterial count, zooplankton density, microbial activity and alkalinity, whereas TAN, NO2, NO3 and floc volume were monitored daily. Every 2 weeks, basing on the colony morphological characteristics, 3-4 representative bacterial colonies per each tank sample were isolated and preserved for identification. Bacterial identification was done by applying PCR 16s rDNA sequencing and the sequenced data was checked by Blast search (NCBI) program. Furthermore, fish growth performance as well as the relationships of bacterial quantity (TBC) with zooplankton, water quality parameters (TAN, NO2, NO3, floc volume, and alkalinity) and microbial activity parameters were also checked. The results showed that there were no significant differences (P>0.05) in fish weight and length at harvest, daily weight gain (DWG), specific growth rate (SGR), survival, total fish biomass, productivity and FCR of fish reared in the Aquamimicry and Biofloc systems. However, the number and biomass of fish that individual weight is greater than 5g at harvest were significantly higher in the Aquamimicry system. Besides, this study did not find any significant correlations (P>0.05) between bacterial quantity and microbial activity parameters (NEP, RR, GPP), floc volume, alkalinity and zooplankton density during the water preparation as well as rearing period in both systems. However, significant correlations (P<0.05) were found between TBC and NO3 (before fish stocking), TBC and TAN (after fish stocking) in the Aquamimicry system. Also, there was a significant correlation (P<0.05) found between TBC and NO2 (before fish stocking) in the Biofloc system. In both systems, the total bacterial count varied from 105 – 107 CFU/ml during the rearing period. Furthermore, this study identified 10 bacterial species and 1 genus as dominant bacteria in the Aquamimicry and Biofloc systems. Among these, 8 bacterium were found in both systems, including: Aeromonas hydrophila, Bacillus megaterium, Pseudomonas alcaligenes, Pseudomonas nitroreducens, Chryseobacterium indologenes, Vibrio cholerae, Shewanella xiamenensis and Bacillus subtilis. Meanwhile, Pseudomonas putida, Flavobacterium sp and Bacillus pumilus were found to be dominant species in the Aquamimicry system. |