Microbial Consortia Modulate Carbon–Nitrogen Dynamics and Nile Tilapia Production in Biofloc Technology Systems

Biofloc technology (BFT) promotes nutrient recycling through microbe-mediated carbon–nitrogen transformations. However, the roles of heterotrophic and nitrifying bacteria in biofloc systems remain incompletely understood. This study examined the effects of microbial inoculation on carbon–nitrogen dynamics, biofloc development, water quality, and production performance in Nile tilapia (Oreochromis niloticus). Four treatments were evaluated: a natural microbial community (BFT1), a Bacillus consortium (BFT2), a nitrifying consortium (BFT3), and a combined consortium (BFT4). Fish were reared for 35 days following a 10-day biofloc maturation period. The treatments showed different patterns of carbon and nitrogen dynamics and production performance. BFT2 exhibited the largest biofloc volume (28 mL/L), the highest growth rate (GR = 0.696 g/day/fish), and the lowest feed conversion ratio (FCR = 1.10). BFT3 showed the highest nitrogen assimilation estimate (Nass = 385.05 mg/L), survival rate (SR = 91.67%), and harvested biomass (Hf = 646.37 g). BFT4 exhibited the highest apparent carbon consumption (Ccon = 624.32 mg/L), the lowest residual carbon concentration (Cyield = 167.01 mg/L), and the lowest calculated C/N ratio (4.42). Adding bacterial consortia was also associated with lower NH4+ and NO2− concentrations than those observed in BFT1. Overall, the different microbial inoculation treatments were associated with distinct carbon–nitrogen dynamics and production outcomes.