Production performance, inorganic nitrogen control and bacterial community characteristics in a controlled biofloc-based system for indoor and outdoor super-intensive culture of Litopenaeus vannamei

The aim of this study was to develop a commercial-scale biofloc-based tank system for shrimp culture in an efficient and environmental-friendly way. Eight independent and identical tanks (6 m/length x 6 m/width x 1 m/height, water volume of 30 m(3)) were randomly selected and prepared for the trial: four were from indoor and other four from outdoor. A complete production trial for super-intensive culture of L. vannamei was conducted under both indoor and outdoor environmental conditions simultaneously. In the trial, ten-day-old post larvae of L. vannamei were stocked at a density of 580 ind m(-3) and cultured for 13 weeks, obtaining survival rates of 82.7% and 81.3%, yields of 6.75 and 7.36 kg m(-3), and FCRs of 1.32 and 1.25 under indoor and outdoor culture conditions, respectively. For producing one kg of shrimp, the usages of water, molasses and sodium carbonate were 210 L, 0.23 L and 0.27 kg under indoor condition and 217 L, 0.15 L and 0.19 kg under outdoor condition, respectively. Throughout the trial, the concentrations of both TAN and NO2--N first increased and then decreased during the early to middle phases and then maintained below 1.0 mg L-1 until the end under both indoor and outdoor conditions. After mature bioflocs established in the culture water, diverse bacterial communities were detected from sampled bioflocs, with Shannon index significantly higher in outdoor than in indoor condition. Top eleven abundant phyla and top nine abundant genera of bacteria with relative abundance over 1% were all shared by both culture conditions, although most of them had significant differences in relative abundance between the two conditions. Notably, communities of nitrifying bacteria were detected in the bioflocs but with very low relative abundances under both culture conditions. Taken together, these results demonstrate the efficiency of a commercial-scale biofloc-based system for super-intensive culture of L. vannamei under limited water exchange. Moreover, the data suggest that the outdoor environmental conditions were more favorable in terms of production performance and inorganic nitrogen control of the system. Improved application of biofloc technology was also discussed and proposed for inorganic nitrogen control in intensive shrimp culture.