Theoretically, the nutrient content of a diet can be manipulated to make the relative proportions of nutrients excreted by fish more similar to the relative proportions of nutrients assimilated by plants. With such a diet, there would exist an optimal ratio of fish to plants and optimal nutrient concentrations could be maintained over prolonged periods without nutrient supplementation. However, the commercial promise of such a diet would require that the fish fed the diet grow at commercially acceptable rates.