Fish species richness is one of the most common descriptors of aquatic biodiversity and an important indicator of the ecological condition of stream reaches and regional biological diversity. However, inadequate sampling effort underestimates the true number of species and, consequently, might provide erroneous information about the ecological conditions of, and trends in, aquatic environments. We sampled 24 to 39 stream reaches (each 150 m long) in seven megadiverse hydrologic units in the Brazilian states of Pará (Amazonia biome) and Minas Gerais (Cerrado biome) to estimate the sampling effort needed to reach asymptotes at hydrologic unit spatial extents. We also estimated how much of the local richness would have been captured if the sampled reach was 50 or 100-m-long. Our results indicate that up to 53 reaches must be sampled per hydrologic unit for attaining an estimated 90% of the fish species richness, depending on the relative number of rare species. In most units, 100-m-long reaches suffice for collecting about 90% of the local sampled richness. We conclude that the effort frequently used in neotropical streams is adequate to capture most of the local fish fauna. However, complete inventories of hydrographic regions would only be feasible with efforts and resources far greater than those commonly employed. Before sampling programs are implemented for estimating true species richness, adequate levels of sampling effort should be assessed wherever that richness is expected to be high.

鱼类物种丰富度是水生生物多样性最常见的描述之一，也是河流河段生态状况和区域生物多样性的重要指标。然而，抽样工作不足低估了物种的真实数量，因此可能会提供有关水生环境生态条件和趋势的错误信息。我们在巴西帕拉州（亚马逊生物群落）和米纳斯吉拉斯州（塞拉多生物群落）的七个大型水文单元中对 24 到 39 个河流河段（每个 150 m 长）进行了采样，以估计在水文单元空间范围内达到渐近线所需的采样工作。我们还估算了如果采样范围为 50 或 100 米长，将会捕获多少当地丰富度。我们的结果表明，根据稀有物种的相对数量，每个水文单位必须对多达 53 个河段进行采样，以获得估计 90% 的鱼类物种丰富度。在大多数单位，100 米长的河段足以收集约 90% 的当地采样丰富度。我们得出结论，在新热带溪流中经常使用的努力足以捕获大多数当地鱼类群。然而，完整的水文区域清查只有在努力和资源远远大于通常使用的资源的情况下才是可行的。在实施用于估计真实物种丰富度的抽样计划之前，应在预期丰富度较高的任何地方评估适当的抽样工作水平。在大多数单位，100 米长的河段足以收集约 90% 的当地采样丰富度。我们得出结论，在新热带溪流中经常使用的努力足以捕获大多数当地鱼类群。然而，完整的水文区域清查只有在努力和资源远远大于通常使用的资源的情况下才是可行的。在实施用于估计真实物种丰富度的抽样计划之前，应在预期丰富度较高的任何地方评估适当的抽样工作水平。在大多数单位，100 米长的河段足以收集约 90% 的当地采样丰富度。我们得出结论，在新热带溪流中经常使用的努力足以捕获大多数当地鱼类群。然而，完整的水文区域清查只有在努力和资源远远大于通常使用的资源的情况下才是可行的。在实施用于估计真实物种丰富度的抽样计划之前，应在预期丰富度较高的任何地方评估适当的抽样工作水平。只有在努力和资源远远大于通常采用的资源的情况下，才能对水文区域进行完整的清查。在实施用于估计真实物种丰富度的抽样计划之前，应在预期丰富度较高的任何地方评估适当的抽样工作水平。完整的水文区域清查只有在努力和资源远远大于通常使用的资源的情况下才可行。在实施用于估计真实物种丰富度的抽样计划之前，应在预期丰富度较高的任何地方评估适当的抽样工作水平。