Living in perpetual darkness deep beneath the ground, cave fish are odd little creatures. With reduced eyes and pale coloration, they were thought to found on every continent except Antarctica and Europe. But that now changes, as researchers have just described the very first cave fish species ever discovered in Europe.
Found dwelling in the cave systems of southern Germany, the fish is not only the first of its type to be discovered on the entire continent, but also represents the furthest north any cave fish species has ever been recorded. Genetic analysis of the fish shows that it is closely related to a surface species known as the stone loach (Barbatula barbatula), and is thought to have started its subterranean lifestyle roughly 20,000 years ago as the ice sheets retreated.
“The cave fish was found surprisingly far in the north in Southern Germany,” explained Jasminca Behrmann-Godel, one of the co-authors of the paper published in Current Biology, in a statement. “This is spectacular as it was believed before that the Pleistocene glaciations had prevented fish from colonizing subterranean habitats so far north.”
Cave fish distribution around the world. Behrmann-Godel et al. 2017
Europe has extensive cave systems, which actually hold some of the greatest speleological diversity anywhere in the world. There are thought to be at least 400 species of critters that have adapted to live in the dark, dank caves of Europe, yet despite in other parts of the world cave fish being the most common underground vertebrate, none had been found in this region.
It was thought that the massive ice sheets that covered Europe for much of the last few tens of thousands of years prevented the animals from entering the caves, and that since they retreated, not enough time has passed for species to then evolve. Clearly, however, that is not the case. While the researchers did not have enough individuals of the new cave species to do a full morphological analysis, they were able to note some very obvious adaptations to the caves that they have already developed.
The eyes of the new species are dramatically reduced, and they have lost much of their coloration, as is typical for subterranean species. They have also developed more elongated whiskers on their heads, as well as larger nostrils compared to surface dwelling varieties, presumably to help them navigate through the total darkness deep underground.
The cave where the fish were found is incredibly remote and only accessible during the dry season – only around 30 people have ever managed to reach it – which is why the fish has remained secret for so long. Future expeditions are now planned to further study its genetics, morphology, and behavior.