A pilot-scale experiment was conducted within an improved extensive pond to evaluate the efficiency of co-culturing black tiger shrimp (Penaeus monodon) and red seaweed (Gracilaria tenuistipitata) at different densities with partially reduced feed rations. Six treatments were established at random in triplicate with three stocking densities (2, 4, and 6 ind. m^-2), and each density monocultured with either a 100% feed ration or co-cultured with red seaweed and a 50% feed ration. The culture system consisted of eighteen net enclosures (16 m² each) installed in an improved extensive pond. After four months of culture, the growth rates of the shrimp decreased with increasing stocking density and shrimp yields at densities of 4 and 6 ind. m^-2 were similar to each other (p > 0.05) and significantly higher (p < 0.05) than at a density of 2 ind. m^-2. Notably, the growth rates, survival, and yield of shrimp in co-culture receiving a 50% feed ration were comparable to, and feed conversion ratio and feed cost were much lower than those in monoculture receiving a 100% feed ration at the same stocking density. The proximate composition of the shrimp meat in terms of moisture and protein levels was nearly equivalent in all treatments, while co-culture groups had lower lipid and higher ash content than monoculture groups. The results revealed that a co-culture of black tiger shrimp and red seaweed at a density of 4 ind. m^-2 with a 50% feed ration maintained normal growth and increased shrimp yield while saving 40.45% of feed costs compared with monoculture.