Effects of different C/N ratios on formation of biofloc, water quality and microflora in aquaculture water of Chinemys reevesii

In order to determine the feasibility and the best addition amount of biofloc technology in turtle culture, we studied the formation of biofloc and its effects on water quality and microflora by regulating the C/N ratio in the culture water of Chinemy sreevesii. We carried out an experiment with the addition of sucrose at 10∶1 (CN-10), 15∶1 (CN-15), 20∶1 (CN-20) and the control group for 40 d. The results show that the biofloc volume index of each group of biofloc became stable after 28 d, and the treatment effect of ammonia nitrogen and nitrite was significant with the C/N ratio≥10∶1. Among them, the removal rate of ammonia nitrogen and nitrite after 40 d of the group with a C/N ratio of 15∶1 were 76.7% and 64.4%, respectively, which indicates that the C/N ratio of 15∶1 can promote the formation of biofloc, and reduce the level of ammonia nitrogen and nitrite in the water effectively. The biological flocs of the experimental group (CN-15) and the control group were sequenced by high-throughput sequencing, and the results show that the dominant phyla of biofloc in the two water bodies were Proteobacteria, Bacteroidetes and Actinobacteria, but the proportion of each dominant bacteria phylum was different. In conclusion, the addition of different C/N ratios can affect the formation of biofloc, water quality and microflora of C. reevesii ponds. 15∶1 is the optimal C/N ratio for the formation of biofloc, which can promote the formation of biofloc and has a strong ability to regulate water quality.