Drifting in a free-flowing river: Distribution of fish eggs and larvae in a small tributary of a Neotropical reservoir

Abstract: We investigated spatial and temporal variations in the distribution of fish eggs and larvae in the Guareí River, a free-flowing tributary located in the upper section of the Jurumirim Reservoir, Paranapanema River, Brazil. Fish eggs and larvae were sampled ~ fortnightly from November 2017 to March 2018 (Cycle 1), and from November 2018 to March 2019 (Cycle 2), at three sites distributed along the entire course of the Guareí River. We collected 859 fish eggs and 1,340 larvae, comprising 19 taxa. We found reproductive activity of several fish species in the Guareí River, including long-distance migrants. However, there was no spatial differences in the assemblage structure and densities of fish eggs and larvae along the channel of Guareí River. We recorded temporal differences in larvae density only in Cycle 2. The consistent capture of fish eggs and larvae in two reproductive cycles is strong evidence that this river is a spawning site for a variety of fish species. Thus, we recommend maintaining its natural flow regime.

摘要：本研究针对巴西巴拉那帕内马河（Paranapanema River）茹鲁米林水库（Jurumirim Reservoir）上游的天然自由流动支流瓜雷伊河（Guareí River）内鱼卵与仔鱼的分布时空变化展开调查。研究于2017年11月至2018年3月（第1周期）、2018年11月至2019年3月（第2周期）以约两周一次的采样频率，在瓜雷伊河全河段布设的3个采样点采集鱼卵与仔鱼样本。本次采样共获取鱼卵859粒、仔鱼1340尾，隶属于19个分类单元。调查发现，瓜雷伊河存在多种鱼类的繁殖活动，其中包括长距离洄游鱼类。不过沿河道全长，鱼卵与仔鱼的群落结构及密度未呈现显著空间差异；仅在第2周期中，仔鱼密度存在显著时间差异。在两个繁殖周期中均持续采集到鱼卵与仔鱼，这一结果充分证明该河流是多种鱼类的产卵场。据此，本研究建议维持该河流的天然水文情势（natural flow regime）。