The Amazon River Basin, one of the world’s most threatened ecosystems, has an enormous diversity of fish species, a result of temporally and spatially complex habitat containing biogeochemically different river systems. The annual hydrologic cycle results in floodplain lakes during low water and inundates forests during high water, exposing fish to different resources and environmental conditions. The two principal river systems in the central Brazilian Amazon are blackwater, with nutrient-poor acidic water, and nutrient-rich whitewater. Although species-rich, the Amazon Basin is data-poor in terms of comparative studies on a regional scale. We analyzed data sets from independent sampling studies of pelagic fish in16 floodplain lakes, nine whitewater (Rio Solimões) and seven blackwater (Rio Negro), in the central Amazon Basin of Brazil. Our findings suggest striking similarities in pelagic fish diversity patterns. Species richness was virtually equal (165 in whitewater and 168 in blackwater), Both species richness, and number of migratory species, per lake increased toward the confluence of the rivers in both systems in our study. The proportion of unique species was also similar in whitewater lakes and blackwater (41% and 43%, respectively), boosting total regional richness to 237 species. However, species composition in whitewater lakes was more homogenous (lower β diversity), and species composition was associated with conductivity and pH in whitewater, but with dissolved oxygen and transparency in blackwater. Therefore, regional fish diversity cannot be represented by sampling one lake or even one drainage system, but must include multiple lakes from both systems. These two systems may differ in sensitivity to anthropogenic stressors such as damming and deforestation.

中文翻译：

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巴西亚马逊河流域中部白水和黑水排水系统泛滥平原湖泊中的远洋鱼类多样性模式

亚马逊河流域是世界上受威胁最严重的生态系统之一，由于时空复杂的栖息地包含生物地球化学不同的河流系统，因此鱼类种类繁多。一年一度的水文循环导致低水位时泛滥平原湖泊，高水位时淹没森林，使鱼类暴露于不同的资源和环境条件。巴西亚马逊中部的两个主要河流系统是黑水（含有贫营养的酸性水）和营养丰富的白水。尽管物种丰富，亚马逊盆地在区域范围内的比较研究方面数据不足。我们分析了来自巴西亚马逊盆地中部 16 个泛滥平原湖泊、9 个白水湖 (Rio Solimões) 和 7 个黑水湖 (Rio Negro) 中上层鱼类的独立抽样研究的数据集。我们的研究结果表明中上层鱼类多样性模式具有惊人的相似性。物种丰富度几乎相等（白水为 165，黑水为 168），在我们的研究中，每个湖泊的物种丰富度和迁徙物种数量都随着河流汇合而增加。白水湖和黑水湖中独特物种的比例也相似（分别为 41% 和 43%），将区域总丰富度提高到 237 个物种。然而，白水湖中的物种组成更均匀（β多样性较低），物种组成与白水的电导率和 pH 值有关，但与黑水的溶解氧和透明度有关。因此，区域鱼类多样性不能用一个湖泊甚至一个排水系统的样本来代表，而必须包括两个系统的多个湖泊。