The prey-predator relationship between the plankton and the pond-cultured bigheed at every growing stage has been studied in this paper. The fishconsumes the same species of phytoplankton, but it takes different species of zooplank-ton at its every growing stage. The abundance of phytoplankton as well as zooplank-ton in the pond are of the same importance in the feeding intensity of the fish.Since the zooplankton has higher calorie than that of phytoplankton, it becomes moreimportant in terms of quality. It is considered that the factor which influences theproduction of the bighead is the abundance of suspended nutritive matters in the water.So it is not nessary to divide the phytoplankton into "digestible or "undigestible".