Polyculture is a sustainable aquaculture system because it can reduce environmental pollution and increase feeding efficiency. The purpose of this study was to analyze the performance of growth, biomass and food competition for tilapia as the main commodity and lemeduk fish as a secondary commodity with a polyculture system in floating net cages. The research method used a Completely Randomized Design (CRD) consisting of 5 treatments and 3 replications, namely: treatment A (60 tilapia fish), Treatment B (40 tilapia fish + 20 lemeduk fish), Treatment C (30 tilapia fish + 30 lemeduk fish), Treatment D (20 tilapia fish + 40 lemeduk fish), and Treatment E (60 lemeduk fish). The research container uses floating net cages with a size of 0.5 × 0.5 × 1m. Parameters observed were absolute length growth, absolute weight growth, specific growth rate, biomass production, competition index, and water quality. The results showed that the polyculture system of tilapia and lemeduk at different stocking densities had a significant effect on absolute length growth, specific growth rate, biomass production, and had low competition between tilapia and lemeduk. The best treatment was found in treatment B (N 40+ L 20) and treatment C (N 30+ L 30) with absolute length growth value 3.20 cm±0.17, specific growth rate 3.83%±0.36, biomass of tilapia 94.36 g/0.5m2±16.45 and total biomass 100.69 g/0.5m2±5.49. Hence, the polyculture system is better than the monoculture system and the absence of competition between tilapia and lemeduk in using food.