| We examined the effects of thalweg velocity on use of low-velocity zone by pale chub, Zacco platypus, using an experimental flume. Stripped-frictions were set on one side of the experimental channel to weaken velocity artificially. The thalweg velocity was manipulated to five conditions (0,10,26,42,71 ㎝/s). The cross section of the channel was divided into three equal parts in each of the height and width, and velocity and number of the small (ca. 5㎝) and large (ca. 10㎝) fish in the each part were estimated. Most of the small and large fish used the center part under low-velocity conditions (?10㎝/s), while small fish moved to the slowest part above the stripped-frictions and large fish moved to the deeper parts with lower velocity under high-velocity conditions (?26㎝/s). These location shifts can be explained by the velocity tolerance generally calculated as 2～3 BL (body length) per second. These results suggest that importance of low-velocity zone such as river shoreline is determined by a combination of exposed velocity conditions and swimming capability of fishes. |
