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<p>The common bleak, <i>Alburnus alburnus</i> (Linnaeus, 1758), is a widespread cyprinid fish, highly abundant in the Danube River basin and also recognised as a successful invader in non-native environments. Its ecological success is driven by pronounced phenotypic plasticity, expressed in morphology and life-history traits, enabling the species to thrive across diverse environmental conditions. In this study, we analysed 24 external morphometric characters (including SL) in 1109 individuals collected from 16 sites along the Danube and 12 sites in its tributaries. Discriminant analyses revealed a clear separation between populations from the main channel and tributaries. Within the main channel, five morphotypes were recognised, differing mainly in gape size, head proportions, eye diameter, and fin-related traits. In tributaries, four morphotypes were distinguished, with weaker yet still significant divergence, driven primarily by gape and fin-related distances. Overall, our results reveal high morphological variability in <i>A. alburnus</i>, which likely reflects strong phenotypic plasticity shaped by local environmental conditions. These results support the idea that the bleak’s morphological variability enables a high degree of adaptation to different types of habitats and, at the same time, represents the potential for successful invasive spread.</p>

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Spatial morphological variation of common bleak (Alburnus alburnus) across the Danube basin and its implications for invasiveness hypotheses

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年8月4日

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  • Erik Safko,
  • Mária Balážová,
  • Kristína Slovák Švolíková,
  • Maroš Kubala,
  • Barbora Števove,
  • Eva Záhorská

摘要

The common bleak, Alburnus alburnus (Linnaeus, 1758), is a widespread cyprinid fish, highly abundant in the Danube River basin and also recognised as a successful invader in non-native environments. Its ecological success is driven by pronounced phenotypic plasticity, expressed in morphology and life-history traits, enabling the species to thrive across diverse environmental conditions. In this study, we analysed 24 external morphometric characters (including SL) in 1109 individuals collected from 16 sites along the Danube and 12 sites in its tributaries. Discriminant analyses revealed a clear separation between populations from the main channel and tributaries. Within the main channel, five morphotypes were recognised, differing mainly in gape size, head proportions, eye diameter, and fin-related traits. In tributaries, four morphotypes were distinguished, with weaker yet still significant divergence, driven primarily by gape and fin-related distances. Overall, our results reveal high morphological variability in A. alburnus, which likely reflects strong phenotypic plasticity shaped by local environmental conditions. These results support the idea that the bleak’s morphological variability enables a high degree of adaptation to different types of habitats and, at the same time, represents the potential for successful invasive spread.