The purpose of this study was to determine the optimal stocking density, effects of tubifex (Tubifex tubifex) feeding and monosex culture on growth performance of guppy (Poecilia reticulata) in a recirculation system. Three separate experiments were conducted in 200-L cylindrical fiberglass tanks, at 1.5/h water turnover rate at 26 degrees C water temperature. In Experiment 1, the fish (2.71 cm and 0.21 g) reached 4.56-4.99 cm length and 1.28-1.83 g weight at the at end of the culture period of 100 days in four stocking densities (1, 2, 3 and 4 fish/L), and 3 fish/L was found to be the optimal density under the present experimental conditions. In Experiment 2, the fish (2.68 cm and 0.20 g) were fed four different tubifex feeding frequencies (0, 1, 2 and 3 days/week) during a rearing period of 80 days. The growth of fish was increased (4.25-4.47 cm and 0.96-1.26 g) depending on the feeding frequency of tubifex, and the best growth was obtained in 3 days/week tubifex feeding (P < 0.05). In Experiment 3, the fish (3.20 cm and 0.27 g) were found to grow significantly better in monosex culture (4.47 cm, 1.09 g) than in the mixed culture (4.32 cm, 1.01 g) during the rearing period of 80 days. Also, in both culture types, the growth performance of females was about twice that of males (P < 0.05). In all the three trials, the fish reached to marketable size in as short as 80-100 days with very high survival rates (97-99%) even under the high stocking density of 3 fish/L. The present results are very promising in terms of providing higher yields per unit area as well as raising guppies in subtropical and even temperate climatic regions using closed RAS culture systems that can be applied worldwide.