Postlarvae (PL) of Macrobrachium rosenbergii (de Man 1879) were stocked at 1, 2, 3 and 4 PL m-2. Prawns were fed only pellets (P) and a combination of pellets and snail meat (PS) with three replications in 100 m 2 plots in the rotational prawn-rice system. Water levels were 0.3-0.6 m in rice growing areas. The water temperatures at noon in the hot months were higher than the suitable range for prawns. The final mean weights of prawns in treatments 1, 2 and 3 PL m-2 were significantly higher than in treatment 4 PL m-2 (P-1 and increased significantly with the increases in prawn densities (P0.05). The total cost significantly increased at higher densities (P0.05). Net profit and cost benefit ratio of treatment PS were significantly higher than in treatment P. In the present study, treatment 3 PL m-2 and treatment PS offered the optimal results. © 2006 The Authors.