Interactive effects of stocking density and dietary protein level on some growth parameters, hematology and immune response of juvenile common carp ( Cyprinus carpio) to Aeromonas hydrophila in modern biofloc System

The present study investigated the impact of stocking density and dietary protein level on the growth, hematology, immunity and resistance against Aeromonas hydrophila in common carp reared under biofloc conditions for 60 days.  Fish (12.09±0.99g) were stocked into 15 tanks in a 2×2 factorial design consisting of two stocking densities and two protein levels in biofloc system include: moderate stocking density (10kg.m-3) with 25 and 35% protein (MD25 and MD35) and high stocking density (20kg.m-3) with 25 and 35% protein (HD25 and HD35). The control group of fish was in clean water with moderate density (10kg.m-3) and 35% protein. The growth of fish was significantly higher and the FCR was lower in MD35 group, when compared to other groups. WBC, hemoglobin and hematocrit values were reduced while red blood cell count increased in fish reared in MD35 group. IgM, ACH50 and bactericidal activity of fish serum were significantly higher in MD35 group than other groups. Based on the present results, it is recommended to culture of common carp in the biofloc system with stocking density of 10 kg.m−3. As well as, the biofloc system can compensate for up to a 10% reduction in the diet in MD group.