Effect of bio-floc on water quality and the production performance of bottom and filter feeder carp fed with different protein levels in a pond polyculture system

A 90-day experiment was conducted with the aim of investigating the effect of bio-floc on water quality and the production performance of bottom and filter feeder carp fed with different protein levels in a pond polyculture system. For this purpose, three bioflocs treatments with carbohydrate referred to as 'BFT-24% (24% feed protein)', 'BFT-27% (27% feed protein)' and 'BFT-30% (30% feed protein)' and a control referred to as 'CW-30% (30% feed protein)' without carbohydrate addition were performed in three replicate enclosures (7 m x 7 m x 1.5 m) each. Young bottom feeder mirror carp (Cyprinus carpio specularis) and filter feeder bighead carp (Hypophthalmichthys nobilis) with initial mean individual body weights of 691.34 ( +/- 6.73 g) and 327.13 ( +/- 3.54 g), respectively, were stocked altogether in polyculture at biomass of 800 gm(-2) and 200 gm(-2) in the control and treatment enclosures. There was a significant positive correlation between the bioflocs volumes and water temperatures from 19.3-28.5 degrees C (P < 0.05). The pH values and the concentrations of total ammonia nitrogen (TAN), nitrite nitrogen (NO2-N), nitrate nitrogen (NO3-N), total inorganic nitrogen (TIN) and orthophosphate (PO4-P) in all the treatments of BFT were significantly lower than those in the control (P < 0.05), while the total alkalinity, the concentration of chlorophyll a and the chemical oxygen demand (COD) did not show significant differences among the treatments and the control (P < 0.05), while the digestive enzyme activity in the BFT treatments did not show significant differences compared with that in the control (P > 0.05). This study demonstrated that a protein-restricted diet did not affect the productive performance or body condition index of mirror carp and bighead carp in a BFT polyculture system with improved water quality.

Automated summary

The experiment demonstrated that bio-flocs treatments improved water quality and had a positive impact on the production performance of bottom and filter feeder carp, without significant effects on productivity or body condition index of the fish under protein-restricted diet.