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Environmentally sound poly-eco-aquaculture enables the preservation of aquatic environments to be compatible with that of sustainable aquaculture. With this method, not only healthy fish can be cultured in purified water, but also the productivity will increase by recycling seaweed to feed the fish. The maximum nitrogen uptake rate of each seaweed per square meter of seaweed area was 2.9 mg N/ms2/day for “Konbu” Laminaria japonica, 3.1 mg N/ms2/day for “Wakame” Undaria pinnatifida, and 3.6 mg N/ms2/day for sea lettuce Ulva pertusa. The maximum phosphate uptake rate was 0.43 mg P/m2/day, 0.54 mg P/m2/day, and 0.19 mg P/m2/day, respectively. The calculated values of nitrogen and phosphate uptake rates, obtained by integrating the nutrient concentrations, light intensity, and water temperatures, corresponded well with each observed value. The minimum seaweed cultural density necessary per unit area of yellowtail Seriola quinqueradiata farm was calculated using the values of the maximum nitrogen uptake rate. The maximal production rates were 0.75 mg O2/g wet/h for L. japonica, 0.83 mg O2/g wet/h for Un. pinnatifida, and 6.39 mg O2/g wet/h for Ul. pertusa. The minimal weight of cultured seaweeds necessary to accommodate the oxygen consumption of an individual S. quinqueradiata was calculated as 1.17 kg wet/fish, 0.83 kg wet/a fish, and 0.21 kg wet/fish.