Optimization of Phosphorus Fertilizer in Supplemental Feed-Fed Based Nile Tilapia (Oreochromis niloticus) Ponds

An experiment was conducted in earthen ponds at the Asian Institute of Technology, Thailand to determine different phosphorus fertilizer dose effects on Nile tilapia production, water quality variables, nutrient utilization and cost-benefit under supplemental feeding. Five phosphorus fertil- ization rates were used as treatments e.g. 100%, 75%, 50%, 25% and 0% of 7 kg P ha week1. Nitrogen fertilization rate was fixed at 28 kg N ha week1 for all the treatments. Sex-reversed Nile tilapia were stocked at 3 fish m2, and 30% CP floating feed fed at 50% satiation feeding rate. Nutrient budget showed higher phosphorus fertil- izer input resulted in higher phosphorus sink in the sediment. Mean weight, mean weight gain, daily weight gain and net yield were not signifi- cantly different among treatments (P > 0.05). Total Kjeldahl nitrogen, total phosphorus and sol- uble reactive phosphorus were significantly differ- ent among treatments. Economic analysis showed phosphorus fertilization resulted in positive net returns. Though the gross income was not affected by different fertilization rates, significantly lowest cost was found in the treatment using 25% phos- phorus fertilizer. It can be concluded from the research that 25% phosphorus fertilization might be used as an alternative strategy of Nile tilapia pond culture in terms of economic return and nutrient loss in sediment.