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Abstract Tilapia is one of the most important aquaculture species due to the desirable characteristics as easy reproduction and quick growth in several farming systems, including the recirculating aquaculture systems RAS. In this, the high flow of water to remove waste casually stimulates the fish to swim backset, and growth performance may be improved. Increasing the speed of swimming can improve performance within certain limits, in which however if exceeded can be harmful. Fish may be exhausted leading to impaired growth or even mortality. The objective of this work was to evaluate the growth performance of tilapia juveniles under sustained swimming exercise at different speeds. Additionally, the fish stocking density effect was tested in the sustained swimming exercise condition. In the first experiment, Nile tilapia juveniles were submitted in triplicates to sustained swimming exercise in speeds of control (not exercised), 1 BL/s (body length per second), 1.5 BL/s and 2 BL/s. In the second experiment, two fish stocking densities were tested in triplicates in sustained swimming exercise in speed of 2 BL/s and control not exercised. Fish growth performance was improved by sustained swimming exercise in speeds up to 2 BL/s. No expressive fish mortalities were observed in both experiments. The comparison between the two stocking densities does not allow us to safely say tilapia can be reared at stocking densities in order of 1,000 fish/m3, even under sustained swimming exercise. Other densities need to be tested.