<;P>;PROBLEM TO BE SOLVED: To provide a safe and effective means for exterminating fungi and parasites without using chemicals in a live fish tank for marine fish or a circulating tank for on-land culture. <;P>;SOLUTION: A fish rearing method comprises the mixing of epigallocatechin to seawater at a weight ratio of 0.5-1.2 ppm and the culture of fish in the seawater. <;P>;COPYRIGHT: (C)2009,JPO&INPIT