Effects of carbon source addition strategies on water quality, growth performance, and microbial community in shrimp BFT aquaculture systems

The current study evaluated the effect of a novel carbohydrate addition strategy that establishes a mixed biofloc technology aquaculture mode in which heterotrophic bacteria dominate in the early stage and autotrophic bacteria play a role in the latter stage. The new strategy is divided into three phases: In the early rearing stage, a high C/N ratio (>= 15:1) is created by daily input feed and a carbon source to promote the formation of heterotrophic bioflocs; when the ammonia nitrogen concentration is reduced to 1 mg/L, the input C/N ratio is kept at 10:1; stop adding carbon source once there is a clear decrease trend in the nitrite nitrogen. Fourteen water quality indicators, shrimp growth, and some economic data were selected to evaluate the feasibility of the new strategy at the macro level. The results showed that the water quality remained good; the survival rate (71.1%) and yield (5.11 kg/m3) of shrimps under the new strategy were significantly higher than those under the traditional BFT aquaculture system. Moreover, the new strategy also has a lower environmental impact. Highthroughput sequencing was applied to better understand the dynamics of microbial communities. Microbial structure analysis showed that Phyla Proteobacteria and Bacteroidetes were the dominant microbial for the whole rearing process. Further analysis revealed that heterotrophic bacteria (e.g., Microbacterium and Rhodobacteraceae) gradually switched into autotrophic bacteria (e.g., Nitrospira) with the C/N ratio decreased. The results indicated that the new strategy was a feasible and efficient way, providing a novel idea for BFT farming of whiteleg shrimp.