Optimizing shrimp growth and water quality in constructed wetland recirculating aquaculture systems: Effects of stocking density and shrimp size

Constructed wetlands integrated into recirculating aquaculture systems (RAS) offer an eco-efficient solution for water treatment in shrimp farming by reducing water exchange while maintaining water quality. However, the effects of stocking density on pollutant removal—and its interaction with shrimp size on growth performance—remain poorly understood. In this study, a 112-m² wetland-based RAS was developed to culture Litopenaeus vannamei under four stocking densities (90, 135, 180, and 360 ind/m³) over a 90-day period. The system included a reservoir, culture ponds, sedimentation tank, plant purification units, and a vertical-flow constructed wetland. Grid search–optimized ridge regression and particle swarm optimization–based gray relational analysis were employed to assess the effects of stocking density and shrimp size on nutrient removal and growth. Results showed that the vertical-flow wetland effectively removed ammonium nitrogen, nitrite nitrogen, and chemical oxygen demand, with removal efficiencies positively correlated with stocking density. By contrast, the removal of nitrate nitrogen and phosphate phosphorus decreased as stocking density increased. Larger shrimp (9–16 cm; 1.16–3.67 g; gray correlation: 0.819) were more sensitive to density effects than smaller ones (4–9 cm; 16.37–19.04 g; gray correlation: 0.667). While lower densities (180 and 360 ind/m³) had minimal impact on the growth of small shrimp, a higher density (540 ind/m³) significantly inhibited performance. These findings provide a quantitative foundation for optimizing stocking density in wetland-integrated RAS to enhance both water purification efficiency and shrimp yield.