Fragmentation and interconnection of water bodies cause severe changes in the natural flow regime of continental water systems. However, assessments of these impacts on the freshwater fish distribution are still scarce. We investigated whether an artificial flow regime generated by discharges from an aqueduct would promote a longitudinal environmental gradient in an off-river reservoir. We tested the hypothesis that the incoming water from aqueduct discharges promotes environmental gradient between lotic and lentic conditions. We expect that environmental changes and the artificial flow regime promote the structuring of fish assemblage and that the lotic-lentic transition areas present the highest fish species richness. A longitudinal gradient in environmental characteristics with differing fish assemblage structure was found. Temporal changes in the fish assemblages occurred only in areas near the discharge of the aqueduct. The highest fish richness and diversity were recorded in the transition zone during the wet season, associated with the greater environmental heterogeneity of this ecotone, whereas the lowest was found in the lotic zone, probably associated with the altered flow regime. The greatest abundance was recorded in the upper lentic zone in the wet season, whereas the lowest was found in the lower lentic zone in both seasons. Our results corroborate the hypothesis that the artificial flow regime, modulated by the seasonality of discharges and the influence of environmental variables, promotes longitudinal gradients in reservoirs when rivers are not present. The findings are relevant in a scenario where ever more interconnections of aquatic bodies have been diffused around the world.

水体的破碎和相互连接导致大陆水系统的自然流态发生了严重变化。但是，对这些对淡水鱼分布的影响的评估仍然很少。我们调查了由渡槽排放物产生的人工流态是否会促进河流下游水库的纵向环境梯度。我们检验了以下假设：从渡槽排出的进水会促进抽水条件和透镜状态之间的环境梯度。我们期望环境变化和人为的流动机制能够促进鱼群的结构化，并且乐透-透镜过渡区的鱼类物种丰富度最高。发现了不同鱼类组合结构的环境特征的纵向梯度。鱼群的时间变化仅发生在渡槽出水口附近。在湿季过渡区记录的鱼类丰富度和多样性最高，与该过渡带更大的环境异质性有关，而在抽水区发现的最低，可能与水流方式的改变有关。在两个季节，在上透镜区的丰度最高，而在下透镜区的丰度最低。我们的结果证实了这样的假说：在不存在河流的情况下，由流量的季节性和环境变量的影响所调节的人工流态会促进水库的纵向梯度。