In recent years, biofloc technology has grown rapidly for various reasons, including improved water quality, cost-effectiveness, sustainability, and environmental friendliness. Therefore, the purpose of this study was to evaluate the impact of fish culture systems (a traditional system (TRS) and biofloc system (BFS)) on growth, hematological parameters, serum biochemical markers, and flesh quality of O. niloticus reared in different stocking densities (SDs). A total of 900 on-grown O. niloticus, weighing 53.17±3.32g, as initial body weight, were randomly distributed into continuously aerated tanks in two different culture systems (BFS and TRS) and stocked at densities of 50 and 100 fish/m³ for 60 days. As the SD increased, all growth performance and feed efficiency indices decreased significantly. Fish reared in the BFS showed superior growth performance and feed conversion ratio (FCR) compared to the TRS group. Fish stocked in the BFS at a density of 100 fish/m³ showed much better growth performance than TRS. Hematological indicators were enhanced in fish cultured in the BFS, especially at higher SD. Conversely, fish reared in the TRS displayed significant increases in levels of serum cortisol, glucose, total cholesterol, and triglycerides than fish reared in the BFS. Fish stocked at SD of 100 fish/m³ and reared in the BFS exhibited a significant decrease in cortisol levels and improvements in flesh quality, as indicated by decreased drip loss and frozen leakage rate compared to those in the TRS. Overall, the findings indicate the BFS's ability to mitigate the adverse effects of increasing SD on fish, emphasizing its potential as a promising technology for enhancing fish productivity and obtaining a healthy product.