A 62-d trial was conducted to evaluate the effects of different C/N ratios on water quality, growth performance, digestives activity, and antioxidant indicators of tilapia fingerlings in BFT systems. Three biofloc treatments (added molasses) with a C/N ratio of 14 (BFT14), 17 (BFT17), and 20 (BFT20) were tested against control in clear-water, each treatment in triplicate. Four hundred twenty tilapias (24.2±0.1 g) were distributed on 12 tanks of 350 L. The dynamics of water quality parameters showed a shift from a predominantly autotrophic to a predominantly heterotrophic biofloc with an increase in the C/N ratio from 14 to 20. The growth and Feed conversion of tilapia were not significantly different between the control, BFT14, and BFT17 groups. A low weight gain and high FCR were found in the BFT20 treatment (0.61±0.07 and 1.11±0.12 g/d) compared to the control (0.84±0.05 and 1±0.07 g/d). Activities of proteases and alpha-amylase in the liver and digestive tract were similar in all treatments. As a measure of stress, CAT and SOD activities did not differ significantly among the four groups. Overall, it was possible to reduce the C/N ratio to14, without negatively affecting the biofloc development, growth performance, and physiological parameters of juvenile tilapia.

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