The aim of this study was to evaluate the effect of supplementation with Chlorella vulgaris and molasses application rates on water quality, zootechnical performance, proximate composition and health status of Nile tilapia (Oreochromis niloticus) fingerlings cultivated in low-salinity (10 g L-1) biofloc systems. Four treatments were tested in a factorial design (supplemented with microalgae and molasses application rates): BFT-C30 (Biofloc supplemented with C. vulgaris and molasses application rates of 30% of the total daily feed); BFT-30 (Biofloc with molasses application rates of 30% of the total daily feed); BFT-C50 (Biofloc supplemented with C. vulgaris and molasses application rates of 50% of the total daily feed) and BFT-50 (Biofloc with molasses application rates of 50% of the total daily feed), for 70 days. Fingerlings of O. niloticus (initial mean weight of 3.15 ± 0.5 g) were stocked at a density of 680 fish m-3 in experimental units (50L), where 50% of this volume was biofloc previously matured. Throughout the experiment, they were supplemented with C. vulgaris every five days at the concentration of 5x10 4 cells mL-1. A significant interaction between supplementation with C. vulgaris and molasses application rates for final weight and length, survival, feed conversion ratio, specific growth rate, water consumption, protein efficiency ratio, sedimentation time, planktonic community and hematological indices were observed. The results indicated that the high molasses application rates (50%) in the biofloc system affects the zootechnical performance, water consumption, sedimentation time and the hematological indices of the Nile Tilapia fingerlings, hampering their development. Therefore, molasses application rates of 30% of the total daily feed for the tilapia fingerlings culture in low-salinity biofloc system is recommended.