Flood Pulse Effects on the Growth of Pseudoplatystoma fasciatum in the Amazon Basin

Fish growth is a fundamental biological process driven by a multitude of intrinsic (within-individual) and extrinsic (environmental) factors that underpin individual fitness and population dynamics. Interannual variability in river hydrology regarding the intensity and duration of floods and droughts can induce interannual variations in the biotic and abiotic variables that regulate fish growth. However, the understanding of how interannual variability in river hydrology affects fish growth remains limited for most species and ecosystems. We evaluated how inter-annual hydrological variations within the Amazon River basin influence the growth of the catfish Pseudoplaystoma fasciatum. Our research questions were as follows: Do floods lead to the faster growth of P. fasciatum and droughts lead to the slower growth? And do floods and droughts affect all age classes in the same manner? We sampled 364 specimens of P. fasciatum from five sites in the Amazon basin, estimated their growth rates, and related the growth rates to indices of the intensity of floods and droughts. We fitted linear mixed-effects models to test the relationship between growth increments and hydrological indices (with F and D quantifying the intensities of floods and droughts, respectively), age as fixed effects, and basins and Fish ID as random effects. We found an inverse relationship between the increment width in the fish hard parts and hydrological indices. That is, intense floods and droughts negatively affected the growth rates. We also found that the growth of P. fasciatum was no different in years with intense and mild floods across age classes 1–5, although was different for age class 6. However, the growth of P. fasciatum was faster in years of mild droughts for all age classes. Our results showing that the growth of P. fasciatum was slower in years of intense droughts are supported by those of previous studies in the Amazon basin and elsewhere. However, our results showing for the first time that the growth of P. fasciatum is slower in years of intense flooding is the opposite of patterns found in other studies. These results thus suggest that the growth of P. fasciatum is maximized within an optimum range of hydrological conditions, where neither floods nor droughts are intense.

鱼类生长是一个基本的生物学过程，由众多内在（个体内部）和外在（环境）因素驱动，这些因素支撑着个体的适应性和种群动态。河流水文在洪水和干旱的强度及持续时间方面的年际变化，会导致调节鱼类生长的生物和非生物变量出现年际变化。然而，对于大多数物种和生态系统来说，人们对河流水文的年际变化如何影响鱼类生长的了解仍然有限。我们评估了亚马孙河流域内的年际水文变化如何影响鲶鱼（Pseudoplaystoma fasciatum）的生长。我们的研究问题如下：洪水是否会导致P. fasciatum生长加快，而干旱是否会导致其生长减慢？洪水和干旱是否以相同的方式影响所有年龄组？我们从亚马孙流域的五个地点采集了364个P. fasciatum样本，估算了它们的生长率，并将生长率与洪水和干旱强度的指标相关联。我们拟合了线性混合效应模型，以检验生长增量与水文指标（其中F和D分别量化洪水和干旱的强度）之间的关系，将年龄作为固定效应，将流域和鱼的个体编号作为随机效应。我们发现鱼的硬组织增量宽度与水文指标之间呈反比关系。也就是说，强烈的洪水和干旱对生长率产生了负面影响。我们还发现，在1 - 5年龄组中，P. fasciatum在强洪水年和弱洪水年的生长没有差异，但在6年龄组中有所不同。然而，对于所有年龄组，P. fasciatum在轻度干旱年份生长更快。我们的研究结果表明，P. fasciatum在严重干旱年份生长较慢，这得到了亚马孙流域及其他地区先前研究的支持。然而，我们首次发现P. fasciatum在严重洪水年份生长较慢，这与其他研究中发现的模式相反。因此，这些结果表明，P. fasciatum的生长在一个最佳的水文条件范围内达到最大，在这个范围内，洪水和干旱都不强烈。