Seasonal drift patterns of fish eggs and larvae were analysed along the river section downstream the Iguaçu River Falls to the confluence with Paraná River, over three spawning seasons. This river section is situated in a narrow rocky canyon characterized by a steep slope, which leads to highly turbulent and fast flowing conditions in a series of rapids. Water transit time in this river stretch of 20 km was short (5–11 h), the flow-velocity in rapids can reach values of more than 6 m s⁻¹. Densities of drifting eggs and larvae varied between three spawning seasons, and differences of eggs were more pronounced compared to larvae. Eggs and larvae were observed all along the river section. A spatial, longitudinal distribution pattern of larvae was found, with higher numbers in the upper section. A distinct spatial sequence of different embryonic stages was observed, with the highest abundance of early stages. Larval densities were low in comparison to egg densities, and preflexion and flexion stages predominated. High abundance of buoyant eggs in drift indicates fish spawning in rapid and turbulent waters of the Iguaçu River, particularly downstream from the Iguaçu Falls. Rainfall and turbidity may be the main trigger for spawning. Spawned eggs drifted quickly towards the confluence, most are likely to hatch in the Paraná River, while larvae disperse to nursery habitats even in the river section below the falls. Thus, inshore zones along the whole stretch provide nursery habitats for larval development of fish species exhibiting different reproductive strategies.

中文翻译：

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巨大瀑布下方湍流河段对鱼类产卵的重要性：早期生命阶段漂移和分散模式的迹象

在三个产卵季节，沿伊瓜苏河瀑布下游至与巴拉那河汇合处的河段分析了鱼卵和幼虫的季节性漂移模式。该河段位于狭窄的岩石峡谷中，其特点是陡峭的斜坡，导致一系列急流中高度湍流和快速流动的条件。该河段 20 km 的水流过境时间较短（5-11 h），急流中的流速可达 6 m s ^-1以上. 漂流卵和幼虫的密度在三个产卵季节之间存在差异，与幼虫相比，卵的差异更为明显。沿河段观察到卵和幼虫。发现了幼虫的空间纵向分布模式，上部数量较多。观察到不同胚胎阶段的不同空间序列，早期阶段的丰度最高。与卵密度相比，幼虫密度较低，并且以预屈期和屈曲期为主。漂流中大量浮力卵表明鱼在伊瓜苏河湍急的水域中产卵，特别是伊瓜苏瀑布下游。降雨和浊度可能是产卵的主要诱因。产卵迅速向汇合处漂流，大部分可能在巴拉那河中孵化，甚至在瀑布下方的河流部分，幼虫也会分散到苗圃栖息地。因此，整个沿岸的近岸区域为表现出不同繁殖策略的鱼类的幼虫发育提供了育苗栖息地。