Swimming behavior of a school of fish in running water has not been investigated. Recently, Onitsuka et al. investigated on the swimming behavior of isolated or a couple of fish in running water. In this study, the swimming behavior of a school of ayu, consinting of 3 fishes, in running water was investigated. It was found that the streamwise length of a school increases and the spanwise length of that decreases with an increase of the flow velocity and also that the swimming speed in the streamwise direction increases with an increase of the flow velocity. The turning angle of swimming trajectory decreases with an increase of the flow velocity. The individual distance becomes larger when the velocity is increased.
