Effects of using different C/N ratios in biofloc system on growth performance, feeding and water quality indices of common carp (Cyprinus carpio) culture

Effects of using various ratios of C:N in biofloc system on growth performance, feeding indices and culture water quality of common carp with mean weight of 14.17±0.36 g were investigated during 90 days in experimental treatments including control (no extra carbon source) and four treatments with different C:N ratios of 11, 15, 19 and 23 each with 3 replicates. The increase in C:N ratio had a significant effect on growth and feeding indices of cultured common carp in treatments (p<0.05). The highest final weight and weight gain, the lowest FCR and the highest SGR were observed in C:N ratio of 19. No significant difference was observed in survival rate among different treatments indicating that the culture condition was suitable for common carp in this biofloc system. Hepatosomatic and visceral indices did not show significant differences between treatments with different C:N ratios (p> 0.05). Water quality indices including DO, pH, TDS, EC, TSS, FV, TAN, nirtite and nitrate showed significant differences in biofloc system with different C:N ratios (p<0.05). The mean values of FV and TSS in biofloc system increased with increasing C:N ratio. The variation pattern of the mean TAN and nitrite were the same as each other and reverse to the trend of TSS and FV showed a decreasing trend with increasing C:N ratio. These trends indicate the significant removal of nitrogenous compounds by bioflocs. In conclusion, using C:N ratio of 19 with molasses as carbon source in biofloc system could be recommended to improve water quality, growth and feeding performance of cultured common carp.