Dietary protein level and carbon/nitrogen ratio manipulation in bioflocs rearing of Cyprinus carpio juvenile: Evaluation of growth performance, some blood biochemical and water parameters

The increasing demand for aquatic products has caused the need to increase production, trying to minimize environmental damage, which has begun to be succeeded with the recent development of new systems such as bioflocs technology (BFT), which is based on the manipulation of Carbon to Nitrogen (C/N) ratios. So, the purpose of this study was to evaluate the effects of increasing C/N ratios with different dietary protein levels in bioflocs (BFT) system on growth performance, body composition, water quality and blood biochemical parameters of juvenile common carp. A total number of 750 fish with initial average weight of 17 ± 0.05 g were randomly divided and stocked into 30 fiberglass tanks with a volume of approximately 250 L of water (1.7 kg/m3). Treatments used in this study included 3 levels of C/N ratio, (C/N15, C/N20, C/N25) and 3 levels of dietary protein contained 25%, 30% and 35% in three replicates with a control group contained 35% dietary protein and water change during the 8 weeks of experiment. Fish were fed three times a day with the different diets at the daily rate of 3% body weight. Also, molasses just was added as a carbon sources to the bioflocs treatments after each feeding. Based on the result, the poor growth parameters and feed utilization were observed in C/N ratio of 25 at 35% dietary protein which were significantly different compared with control. The result of body composition showed that different C/N ratios at different dietary protein levels significantly effected body composition of fish in compared with control. The blood biochemical parameters showed different C/N ratios at different dietary protein levels significantly affected the amount of total protein, globulin, albumin and glucose values of fish in BFT treatments compared with control. Furthermore, the C/N ratio of 15 showed the lower variation of water total ammonia and nitrite than other C/N ratios in different dietary protein levels. In general, growth and feeding parameters, body composition, blood biochemical parameters of fish and water quality was suitable for common carp juveniles rearing in bioflocs system with C/N ratio of 15 at 25% dietary protein level. •C/N ratios and protein levels had effects on the culture of Cyprinus carpio in a biofloc-based system.•High C/N ratio with high protein level reduced growth and increased fish FCR.•Manipulating C/N input can serve as a useful management tool in biofloc-dominated systems•Low C/N ratio with low protein level