The integration of seaweeds (extractive, low-footprint species) into aquaculture systems has been considered as an alternative approach for the sustainable development of the shrimp industry, which aims to expand in an environmentally friendly way. Two consecutive experiments were conducted to evaluate the effects of integrating various densities of black tiger shrimp Penaeus monodon postlarvae (PL) and red seaweed Gracilaria tenuistipitata on water quality and shrimp performance in the nursery phase. The first experiment involved a 3×4 factorial design with three levels of shrimp density (1,000; 2,000 and 3,000 PLs m^-3) and four levels of red seaweed density (0, 1.0, 1.5 and 2.0 kg m^-3) randomly allocated in triplicate tanks for 30 days. Shrimp PL (with a mean weight of 0.012±0.002 g and length of 1.12±0.09 cm) and red seaweed were reared in 150 L tanks at a salinity of 15 g L^-1. Significant synergistic effects between shrimp and seaweed densities were observed for the NO_3,^- total nitrogen (TN) and PO₄^3- contents, as well as for the survival (p significantly decreased the concentrations of nitrogen and phosphorus in the rearing tanks and greatly enhanced the survival and growth rate of shrimp. In particular, increased stocking density resulted in poorer growth performance but enhanced production. Applying stocking densities of 1,000 and 2,000 PL m^-3 obtained larger shrimp size, while a density of 3,000 PL m^-3 achieved the highest production output in the integrated system. In the second experiment, which followed the 30-day growth trial, shrimp quality was assessed via an immersion challenge test using pathogenic Vibrio parahaemolyticus (a concentration of 2 x 10⁸ CFU mL^-1 ) on the shrimp groups previously stocked at a density of 3,000 PL m^-3 and integrated with different quantities of seaweed. After 14 days of challenge, the cumulative mortality in the monoculture system averaged 75.6%, which was significantly higher (pP. monodon shrimp and G. tenuistipitata improved tank water quality as well as shrimp survival and growth while also enhancing the antibacterial activity of shrimp against V. parahaemolyticus infection in the nursery phase.