Der Höhlenfisch

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The discovery of [cave fish](https://www.wissenschaft.de/erde-umwelt/ueberraschungsfund-erster-hoehlenfisch-europas/) in the Danube-Aach system in 2015 was a worldwide sensation. All media outlets reported on it after its publication in 2017, including numerous scientific media outlets. This cave fish is the first proven cave fish population in Europe and the northernmost cave fish population in the world. Until then, scientists believed that there were no cave fish this far north. The cave fish found are a species of stone loach (Barbatula barbatula), which probably separated from the stone loaches of the Danube on the surface around 20,000 years ago, were probably washed down through the cave passages and then adapted to the "underworld," the so-called "Black Danube," over the course of thousands of years. Over the years, the fish have adapted to the living conditions in the underground cave system. Compared to its above-ground relatives, the cave fish of the Danube-Aach system has greatly reduced eyes and is almost blind. Its color is pale pink and its nostrils are enlarged. To help them navigate in the dark, their barbels (tactile appendages on their heads) have gradually grown longer. Individual cave fish grow to a length of approximately 8.5 cm.

Source: DZT Knowledge Graph