<;P>;PROBLEM TO BE SOLVED: To provide a feeding method effective for organisms wafting in water and passively feeding on materials floating in the water. <;P>;SOLUTION: The breeding aquarium is obtained by forming two or more stable layers in the breeding aquarium by utilizing the density regulation by a water-soluble polymer, and using the layer having a density higher than that of a breeding water layer as a liquid feed layer. <;P>;COPYRIGHT: (C)2010,JPO&INPIT