Alterazioni antropogeniche nell'ittiofauna nativa di alcuni corsi d'acqua del bacino del fiume Ombrone (Grosseto-Siena, Toscana meridionale)

Sampling carried out using the same technique and in the same locations in the Ombrone River and some of its tributaries between 2003 and 2013, and then more than ten years later in 2024 and 2025, unfortunately revealed a drastic alteration in the ichthyofauna. In the Ombrone River , in terms of density, the ichthyofauna currently consists of over 90% non-native species and is largely dominated by the Spanish barbel (Luciobarbus graellsii) and the spotted catfish (Icta-lurus punctatus), while native species are sporadic with the exception of the italian chub (Squalius squalus). In the tributaries, the ichthyofauna is still predominantly composed of native species, however, a significant population decline has occurred, with density decreases ranging from a minimum of 40% (Merse) to a maximum of 95% (Tressa). Unfortunately, this decline primarily affects some endemic Italian species of great conservation interest: the Tiber barbel (Barbus tiberynus), the brook chub (Squalius lucumonis) and the brook goby (Padogobius nigricans). The data obtained show that the decline in the composition and number of fish populations is attributable to the poor state of conservation of waterways: climate change, water withdrawal, alterations in the morphology of waterways and banks, and the expansion of non-native fish species are responsible for this phenomenon, all clearly due to human activity. If urgent measures are not taken to address at least some of these pressures, most of the native species still present in the Ombrone basin will become extinct within a few decades.