Fish fauna of small-order streams of savannah and forest fragments landscape in the lower Tapajós River basin, Amazonia

Abstract: To better understand the fish fauna of Amazonian streams, we assessed small streams in a landscape of forest fragments and savannah in the region of the lower Tapajós River, Brazil. We sampled the fish fauna using a well-tested active capture method during two dry seasons (October 2006 and 2018) and one rainy season (March to May 2018). Species richness was calculated using an abundance matrix and first-order jackknife estimator. Using qualitative and quantitative data, we present a cluster analysis in which each stream corresponds to a sampling unit. We collected 6,094 individuals of 43 species distributed in six orders. The sampling effort represents 73% of the estimated richness (58.69 ± 7.65). The most abundant species were Copella nattereri, Iguanodectes variatus and Laimosemion dibaphus that together represent almost half of the total sample (48.7%). The most frequent species were Aequidens epae, Helogenes marmoratus and Laimosemion dibaphus, which were collected in 11 of the 13 sampled streams. This is the first fish fauna list for small-order streams of savannah and forest fragments landscape in Amazonian Brazil. The richness of fish and the presence of many rare species underscore the contribution of small streams to the regional fish fauna composition, even in dynamic and spatially restricted landscapes.

摘要：为深入解析亚马逊溪流的鱼类区系，我们针对巴西塔帕若斯河下游区域的森林片段与稀树草原景观中的小型溪流开展了调查。本研究于两个旱季（2006年10月、2018年10月）及一个雨季（2018年3月至5月）期间，采用经过充分验证的主动采集法（active capture method）采集鱼类样本。通过多度矩阵与一阶刀切法估计量（first-order jackknife estimator）计算物种丰富度；基于定性与定量数据构建聚类分析模型，以每条溪流作为独立采样单元。本次调查共采集到6094尾个体，隶属于6目43种。实际采样覆盖了估计物种丰富度的73%（估计丰富度为58.69±7.65）。优势物种为纳氏亮银脂鲤（Copella nattereri）、变纹矮脂鲤（Iguanodectes variatus）与双斑拟四眼鳉（Laimosemion dibaphus），三者合计占总样本量的近半数（48.7%）；高频物种为埃普丽真盖丽鱼（Aequidens epae）、斑吻鼬鲶（Helogenes marmoratus）与双斑拟四眼鳉（Laimosemion dibaphus），在13条采样溪流中的11条均有采集记录。本研究是巴西亚马逊区域内稀树草原与森林片段景观中小溪流的首份鱼类区系名录。即便在动态且空间受限的景观中，鱼类物种丰富度与诸多稀有物种的存在，均凸显了小型溪流对区域鱼类区系组成的重要贡献。