| 摘要 |
PROBLEM TO BE SOLVED: To control minute plankton causing a red tide or harmful plankton such as a crustacean adhering to fishing implements to obstruct fishery with good payability without generating a secondary injurious effect. SOLUTION: Mineral powder containing at least one of silica SiO2 and calcium carbonate CaCO3 as a main component is mixed with carbide powder of a nut shell to obtain mixed powder, which is, in turn, sprinkled over a harmful plankton floating area. Especially, a mixture comprising a combination of the carbide powder of the nut shell, the silica powder and oyster shell powder is selected. Alternatively, a sheet, a net or a rope-like material having the carbide powder of the nut shell supported thereon is immersed in the harmful plankton floating area. Further, solid matter coated with a coating material containing the carbide powder of the nut shell is immersed in the harmful plankton floating area.
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