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

Abstract 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 × 7 m × 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 g·m−2 and 200 g·m−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 °C (P   0.05). The specific growth rates (SGR), survival rates (SR) and net yields (NY) of mirror carp did not show significant differences among the different treatments or from the control (P > 0.05). The total feed conversion rate (TFCR) of fish in the control was significantly higher than that of the fish in the BFT treatments (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.