Use of Spirulina and Tilapia as biological treatment for low salinity shrimp culture was conducted using 3x3 cpm[lately randomized design involved factorials. Three concentration of Spirulina platensis 0, 4.2x108 and 8.4x108 trichome/L and 3 densities of tilapia were used in treatment combination for controlling water quality in low salinity shrimp culture. The experiments were conducted of salinity 5 ppt with 150 litres experimental unit. The culture system was one water and outdoor. During 3 months of experiment, nutrients such as NH4-N, NO2-N, NO3-N and PO4-P and chlorophyll were determined every two days. Water temperature pH, DO, salinity and light intensity were determine daily. The results indicated that a treatment with Spirulina platensis 8.4x108 trichome/L and 3 tilapias gave a better reduction of nitrate concentration while a treatment with results showed that the cultured tank with Spilurina platensis 8.4x108 trichome/L and 3 tilapias reduced the most nitrate concentration while the treatment with Spilurina platensis 8.4x108 trichome/L and no tilapia could give better control of Phosphate during the whole culture period of Penaeus monodon. The results indicated that a treatment with Spilurina platensis 8.4 x108 trichome/L gave better yield of Penaeus monodon than other treatment without Spilurina platensis.
