Effects of Carbon‐to‐Nitrogen Ratio in Biofloc System on Water Quality, Growth Performance and Haematological Parameters of Nile Tilapia ( Oreochromis niloticus )

ABSTRACT A 10‐week indoor culture trial was carried out to assess the impact of various C/N ratios on the water quality, growth performance and haematology of Nile tilapia ( Oreochromis niloticus ) in a biofloc system. The experiment included four biofloc treatment groups with distinct C/N ratios (12:1, 15:1, 18:1 and 21:1) and a control group with a C/N ratio of 10:1. Molasses was used as an organic carbon source to adjust the C/N ratios in the biofloc‐treated groups, while no carbon source was added to the control. The study was carried out in 15 circular tanks (300‐L water capacity), where 45 Nile tilapia fingerlings (average weight 6.7 g) were stocked in each tank and reared for 10 weeks. The results indicated that the electrical conductivity and total dissolved solids of water increased with higher C/N ratios, while the average levels of total ammonia nitrogen and pH showed a decreasing trend. At the end of the trial, increasing the C/N ratio positively influenced weight gain, growth rate and specific growth rate. Among all treatments, a C/N ratio of 15:1 exhibited significantly ( p < 0.05) improved growth performance and feed utilisation. Furthermore, better haematological parameters were noted in the 15:1 C/N ratio treatment. The study also revealed variations in microbial biomass in water samples with different C/N ratios, showing that Vibrio dominance declined as C/N ratios increased, confirming the prevalence of heterotrophic bacteria in higher C/N ratio groups. In conclusion, the biofloc system at C/N15:1 demonstrated improved water quality, growth performance and immunity in Nile tilapia. Therefore, it is recommended to maintain a 15:1 C/N ratio for Nile tilapia culture in the biofloc system.