a method for directing the displacement of aquatic crustaceans after feeding by utilizing their biological tendency responding to a bright and dark contrast is provided . this method comprises steps to generate the visual effect of this bright and dark contrast at a predetermined place within the water body of culture . light coming from light emitters directly or from reflection of protrusions and / or painted patterns / figures , and / or filtration of light filters , with the existence of illuminating light , are used for generating visual effect of the bright and dark contrast .