Effects of biofloc on growth performance, digestive enzyme activities and liver histology of common carp (Cyprinus carpio L.) fingerlings in zero-water exchange system.

Biofloc technology is considered as a method that degrades organic waste by microorganisms and produces microbial flocs. A 30-day experiment was performed to investigate the effects of partial replacement of daily feeding intake with biofloc on the growth performances, digestive enzymes activity and liver histology of the common carp Cyprinus carpio L. fingerlings. Two hundred and eight healthy fingerlings (58.6 ± 0.2 g) were randomly distributed in 12 tanks (30 L) at a density of 25.4 kg m(-3) and fed experimental treatments (100 % daily feeding rate as a control, biofloc + 75% daily feeding rate, biofloc + 50% daily feeding rate, biofloc + 25% daily feeding rate). At the end of experiment, the results indicated that the highest weight gain was observed in the fish fed BFT 75% and control which differed significantly from those fed BFT 25 % (P < 0.05). Diet BFT 75% improved total protease and pepsin activity compared with BFT 25 and 50% (P > 0.05). No significant difference was observed in case of lipase, amylase and alkaline phosphatase activity between the treatments. In the liver, histological alterations were found in the treatments, and feeding the fish with BFT 75% significantly improved hepatocellular quantification and qualification than the other groups. The results obtained in this experiment suggest that the biofloc improves growth performances, digestive enzyme activity and liver condition of the common carp fingerlings when 25% of daily feeding rate (BFT 75%) was replaced with one carbohydrate such as molasses in zero-water exchange system.