Effect of carbon and nitrogen ratio (C:N) manipulation on growth performance, immune response and stress index of common carp (Cyprinus carpio) acute exposure to ammonia stress in biofloc system

Biofloc is a novel technology that can improve aquaculture production and also pursue sustainable aquaculture goals. In this experiment, the impact of the different C/N ratios on water quality, growth performance and immune response of Cyprinus carpio (initial weight; 11.75±0.53g) reared under biofloc conditions were investigated. Four levels of C/N ratios, using the addition of a carbon source (sugar), 10, 15 and 20 and the control without adding carbon (Control group with 40-50% daily water exchange) were consisted of the experimental treatments. After 8 weeks, fish were subjected to acute ammonia stress (0.5mg/L) for 6 hrs. Stress indicators such as glucose and cortisol were measured and statistically compared before and after exposure to ammonia. Total ammonia nitrogen (TAN) concentration was significantly higher in C10. The growth of fish was significantly higher in C15 while the feed conversion ratio had no statistically significant difference. Serum immunoglobulin, lysozyme, ACH50 activities were significantly higher in the C/N groups than in the control. Stress indicators (glucose and cortisol) showed no significant change before exposure, while after ammonia stress, their levels increased in all groups and the highest level was observed in the control group. Overall, biofloc (C/N manipulation) had an anti-stress effect, and the culture of common carp in the biofloc system with the lowest daily water exchange could be recommended.