The split-beam echo sounders were used in the No. 1 ship lock and the adjacent areas of the Gezhouba Dam Reach separately, to observe fish spatial distribution and the behavior of local fish about the Gezhouba Dam, and figure out whether the ship lock could served as a channel for fish migration in a way. The resulted showed that there were significance difference in both fish size (converted from the of individual fish) and abundance in the five marked sub-areas. Beyond that, there was an analogical fish distribution format in the analogical environmental condition. It might well be that fish species distributed in this area with the regioselectivity, which might resulted in the spatial differentiation. The horizontal fixed-location detection of the No. 1 ship lock revealed that, there were many ups and downs in the fish density with significant difference during a diurnal period, which might be resulted by the law of diel vertical distribution. There were all together 38 fishes moving up- or downstream the ship lock were detected during the period of ship-lock opening. In spite of the fact that, we cannot regard that the ship lock can served as the channel for fish migration. Because the evidence originated from the fish spatial differentiation and behavior in preference to that, it was the general behavior of that the fish swam backwards and forwards across the ship lock.
