Intensive shrimp aquaculture can generate excess nutrients that negatively affect pond environments and production sustainability. This study evaluated an integrated polyculture system using Guam sea grape (Caulerpa sp) to mitigate environmental impacts while improving the production performance of specific pathogen-free (SPF) white shrimp (Penaeus vannamei) and salt-tolerant red tilapia (Oreochromis sp.). The 8-week experiment was conducted using six treatments in triplicate tanks: a shrimp monoculture control (no seaweed) and five polyculture treatments with increasing sea grape densities (1, 2, 3, 4, and 5 kg m⁻³). Growth performance, total biomass, survival, and feed efficiency were evaluated for both shrimp and tilapia.
Polyculture treatments significantly improved growth rate, biomass, and survival of both species compared to monoculture (p < 0.05). Shrimp survival ranged from 78.10–81.90% in polyculture compared to 77.14% in monoculture, while tilapia survival ranged from 81.90–97.14% compared to 87.62% in monoculture. Sea grape density was positively correlated with growth and biomass of both cultured species. Although shrimp performance did not differ significantly among polyculture treatments, a sea grape density of 1 kg m⁻³ produced the highest shrimp growth and feed efficiency. For seawater-tolerant red tilapia, optimal performance was observed at 3 kg m⁻³, with higher densities (3–5 kg m⁻³) supporting increased biomass production.
These results demonstrate that integrating indigenous sea grape into shrimp–tilapia polyculture systems can enhance production performance while offering a practical approach to nutrient management. Sea grape densities of 1–2 kg m⁻³ are recommended for shrimp-focused systems, while 3 kg m⁻³ is optimal for tilapia production, supporting the application of environmentally sustainable, multi-trophic aquaculture systems.