<；P>；PROBLEM TO BE SOLVED: To provide a method for preventing/treating parasitic disease, which has no anxiety of residual pharmaceutical component in fishes, does not contaminate environmental water and has a slight influence on fishes. <；P>；SOLUTION: The method for preventing and/or treating parasitic diseases of marine fishes comprises bathing fishes in seawater or artificial seawater from which metal ions essential for existence of parasites are removed. One or more kinds of sodium ion, potassium ion, calcium ion and magnesium ion are preferably removed and both ions of calcium ion and magnesium ion are especially preferably removed as the metal ions essential for existence of parasites. Seawater or artificial seawater which is corrected for reduction in osmotic pressure caused by removal of the metal ions is preferably used. <；P>；COPYRIGHT: (C)2007,JPO&INPIT
