An experiment was conducted with or without addition of Tilapia (Oreochromis niloticus) at different stocking densities in a polyculture system. The polyculture consists of catla, rohu, silver carp, prawn and mola at a stocking density of 10, 30, 30, 40 and 100, respectively in 100m2 ponds in each treatment with three replications. In treatment T0, no tilapia was added; in treatment T10 and T20 tilapia were added at 10% and 20% of total number of catla, rohu, silver carp and prawn, respectively. Formulated feed was given twice daily (8.00 h and 16.00 h) at the rate of 1.5% body weight throughout the culture period. Water quality analysis showed that the mean values of water temperature, pH, dissolved oxygen, ammonia-nitrogen, nitrite-nitrogen, nitrate-nitrogen, phosphate-phosphorus, chlorophyll-a were not significantly different among the treatments. Water transparency was found significantly different (P<0.05) among the experiments. A total of 45 genera of phytoplankton and 13 genera of zooplankton were identified from the pond water. The abundance of macrobenthic organisms was mostly dominated by Chironomidae. There was no significant difference in the total abundance of benthos among the treatments. The combined net yield increased significantly with the increasing stocking density of tilapia. A simple economic analysis revealed that higher cost-benefit ratio was obtained in treatment T20 followed by treatment T10 and treatment T0. Therefore, it is concluded that the polyculture of carp, prawn and mola with 20% tilapia may be a better option considering the production and economic benefits.