The effect of different application rates of triple superphosphate (22.4, 44.8, and 67.2 kg P 2 O 5 ha -1 ) was observed on total and available phosphorus concentrations in pond soil, total and filterable orthophosphate concentrations in pond water, chlorophyll a, and fish growth in a carp polyculture system during summer (22-32°C) months to determine the economical dose of P 2 O 5 . pH, hardness, calcium and alkalinity of soil and water did not differ significantly among treatments (P [ 0.05) and were within the desired ranges. Average total phosphorus concentrations in pond soil were not significantly different between treatments but available phosphorus (P [ 0.05) in pond soil, total phosphorus (P [ 0.001), and filterable orthophosphate (P [ 0.0001) concentrations in pond water, chlorophyll a (P [ 0.0001), and net fish production (P [ 0.01) were significantly higher in fertilized ponds than in controls. Overall, fish yield did not significantly differ among treatments, suggesting that a very high dose of P 2 O 5 may not be necessary for high yields. Reducing the dose of P 2 O 5 could reduce cost without reducing fish production.