Effect of C/N ratio on water quality in zero-water exchange tanks and the biofloc supplementation in feed on the growth performance of crucian carp, Carassius auratus

•Biofloc technology (BFT) is a novel technique used to reduce nitrogen concentration, serve as in situ food source.•Biological flocs can be well formed when C/N ratio is greater than 15:1.•BFT can improve the culture water quality in Carassius auratus ponds.•10% biofloc added to the feed of Carassius auratus can promote the growth.

Biofloc technology (BFT) is a novel ecological farming technique used to reduce nitrogen concentration, serve as in situ food source and remove pollutants through processes such as adding carbon to control C/N ratio in aquaculture water. The purpose of this work is to explore the potential of the BFT in crucian carp, Carassius auratus aquaculture. The impact of biofloc with different C/N ratios on water quality was studied including the concentrations of ammonia nitrogen (NH4+–N), nitrite nitrogen (NO2−–N) and nitrate nitrogen (NO3−–N). Then the relationship between different C/N ratio and C. auratus growth was identified. Finally, the effects of biofloc serving as feed supplement on the growth of C. auratus, feed utilization and antioxidant indicators were explored. The results demonstrated that BFT could effectively reduce ammonia nitrogen, nitrite and nitrate concentration in C. auratus ponds when C/N ratio was greater than 15:1. In addition, weight gain rate (WGR), specific growth rate (SGR) and protein efficiency ratio (PER) of C. auratus were considerately increased when C/N = 20:1 or C/N = 25:1. Finally, as the protein source, 10% biofloc added to the feed of C. auratus was shown to promote the growth performance and liver antioxidation capability demonstrated by the increase of t-superoxide dismutase (T-SOD), glutathione S-transferase (GST), catalase (CAT) and malondialdehyde (MDA). Our findings demonstrate that BFT is effective and highly potential technology in C. auratus aquaculture from for water quality control and producing proteinaceous feed production.