Biofloc-based co-culture systems of Nile tilapia (Oreochromis niloticus) and redclaw crayfish (Cherax quadricarinatus) with different carbon–nitrogen ratios

This study aims to evaluate the production performance of biofloc-based co-culture systems of Nile tilapia and redclaw crayfish with varying carbon–nitrogen ratios (C/N). The experiment was conducted for 80 days in plastic-lined ponds with dimensions of 1 x 1 x 0.6 m. Two biofloc systems with two C/N ratios (10 and 15), using molasses as the carbon source and a control system without molasses were compared. Mixed-sex Nile tilapia with an initial average body weight of 7.00 ± 0.25 g were stocked at a density of 30 fish m⁻². After 30 days of culture, redclaw crayfish with initial average body weight of 11.50 ± 0.55 g were added to the culture system at a density of 10 crayfish m⁻². There were no significant differences in total animal biomass or total weight gain between treatments (P > 0.05). The total feed and overall feed conversion ratio (FCR) differed significantly (P < 0.05) between the biofloc systems and the control. Total ammonia nitrogen (TAN), nitrite nitrogen (NO₂−N) and nitrate nitrogen (NO₃−N) concentrations in biofloc systems with a C/N ratio of 15 were generally lower than those of other treatments. Dissolved oxygen concentrations decreased with the increase in the culture period in (4.13–4.40 mg L⁻¹). Based on the results of this study, it can be concluded that an increase in the C/N ratio has positive effects on the feed utilization efficiency and water quality in biofloc-based tilapia–redclaw crayfish co-culture systems.