Based on an of the model, for the optimal solution we find the ng cost for one unit of net income is obviously less than the current cost, so our feeding strategy can produce better harvest. Ecological Perspective on polyculture Adding herbivorous fish as the middle stratum contributes to the decomposition of solid particles can suppress the over-multiplication of the algae, can enable the coral to grow normally, and thereby can restore the ecosystem and biodiversit However, in our model we don't take into account the soluble POc released by the algae, the accumulation of which is likely to hinder the im- provement of water quality. In view of this, some may doubt the restorative ability of our polyculture system. But bacteria in the waters can process PoC and rational measures can be taken to control the concentration of microbes, thus ensuring the improvement of water quality. So, in terms of ecology, our polyculture system bears the potential of improving water quality and promoting favorable development of the ecosystems References Chen, Chih-Yu, and Chong-Nong Chou. 2001. Ichthyotoxicity studies of milkfish Chanos chanos fingerlings exposed to a harmful dinoflagellate Alexandrium minutum. Journal of Experimental Marine Biology and ecolog 262(2):211-219 Shan, Yu-lin, and Jia-de Tang. 2007. Numerical solution of bait-predator model derived from three biological populations based on Matlab [Nu merical solution of predator-prey model with three groups, based on Matlab]( Chinese). Ordnance Industry Automation 26(12) 94-96 Sumagaysay-Chavoso, Neila S. 1998. Milkfish( Chanos chanos) production and water quality in brackishwaterponds at different feeding levels and frequencies. Journal of Applied Ichthyology 14(1-2 ): 81-85Rebalancing 139 Based on analyses of the model, for the optimal solution we find the feeding cost for one unit of net income is obviously less than the current cost, so our feeding strategy can produce better harvest. Ecological Perspective on Polyculture Adding herbivorous fish as the middle stratum e contributes to the decomposition of solid particles, 9 can suppress the over-multiplication of the algae, e can improve water quality, e can enable the coral to grow normally, and 9 thereby can restore the ecosystem and biodiversity. However, in our model we don't take into account the soluble POC released by the algae, the accumulation of which is likely to hinder the im￾provement of water quality. In view of this, some may doubt the restorative ability of our polyculture system. But bacteria in the waters can process POC and rational measures can be taken to control the concentration of microbes, thus ensuring the improvement of water quality. So, in terms of ecology, our polyculture system bears the potential of improving water quality and promoting favorable development of the ecosystems. References Chen, Chih-Yu, and Chong-Nong Chou. 2001. Ichthyotoxicity studies of milkfish Chanos chanos fingerlings exposed to a harmful dinoflagellate Alexandrium minutum. Journal of Experimental Marine Biology and Ecology. 262 (2): 211-219. Shan, Yu-lin, and Jia-de Tang. 2007. Numerical solution of bait-predator model derived from three biological populations based on Matlab [Nu￾merical solution of predator-prey model with three groups, based on Matlab] (Chinese). Ordnance Industry Automation 26 (12): 94-96. Sumagaysay-Chavoso, Neila S. 1998. Milkfish (Chanos chanos) production and water quality in brackishwater ponds at different feeding levels and frequencies. Journal of Applied Ichthyology 14 (1-2): 81-85