Growth performance, haematology, antioxidant status, immune response and histology of common carp ( Cyprinus carpio L.) fed biofloc grown on different carbon sources

A 10 weeks trial was performed to investigate how different carbon sources (sugar beet molasses: SBM + BFT , sugar: S+ BFT , corn starch: CS + BFT ) along with control affect welfare status of common carp ( Cyprinus carpio L.) fingerlings in biofloc‐based tanks. Three hundred healthy fingerlings (22.5 ± 0.2 g) were randomly distributed in 12 tanks (70 L) at a density of 8.02 kg/m 3 (25 fish/tank). The fish in BFT treatments fed only 75% feeding rate of control. At the end of the experiment no differences were seen between the groups in case of growth performance, but the fish reared in CS + BFT had a significant lower food conversion ratio compared with the others ( p  < .05). Different carbon sources did not affect on haematological parameters ( p  > .05). Total serum protein and antibody concentration differed in treatments, and the highest values were found in S+ BFT and CS + BFT treatments ( p  < .05). No significant differences were observed in case of lysozyme, superoxide dismutase and complement activity in treatments ( p  > .05), whereas the fish in BFT treatments showed a significant higher total antioxidant capacity and lower glutathione peroxidase than the control ( p  < .05). Different carbon sources resulted in no change in goblet and kupffer cells in intestine and liver respectively. The highest relative percentage survival was obtained in the CS + BFT and S+ BFT (50%) in comparison with SBM + BFT (20%) treatment. The results obtained in this experiment, suggest that corn starch improves immune response, diseases resistance and histology of digestive and respiratory systems in carp fingerlings when used as a carbon source in zero water exchange system.