The present invention provides a virus targeting red tide-causing plankton Heterocapsa; a method and an agent for preventing red tide using the virus; a method for isolating the virus; and a method for subculturing the virus. The elimination of this motion is achieved by the implementation of iterative algorithms, such as Resolution Recovery andor Wide Beam Reconstruction, which compensate for the Line Spread Function effect due to the collimator characteristics. The core is formed its both side edges with notches and respective regions of the cover sheet lying in these notches are provided with a pair of crotch region elastic members extending in a back-and-forth direction and intersecting folding guide lines.