Hobby Cave Diver Discovers First European Cave Fish

A hobby cave diver exploring the deepest parts of the Danube-Aach underground water system in South Germany discovered the first confirmed cave fish in Europe. The fish, described in a paper published in the journal Current Biology, appears to be a loach in the genus Barbatula.

"The cave fish was found surprisingly far in the north in Southern Germany," said lead author Jasminca Behrmann-Godel from the University of Konstanz in Germany through a press release. "This is spectacular as it was believed before that the Pleistocene glaciations had prevented fish from colonizing subterranean habitats so far north."

Hobby diver Joachim Kreiselmaier first spotted the "strange looking" fish in August 2015 while exploring the hard-to-reach part of the Danube-Aach system, which can only be explored under particularly dry conditions in summer and fall. Kreiselmaier took a photo of the fish and showed it to hobby geologist Roland Berka.

Kreiselmaier successfully captured a live specimen of the loach in November 2015. About a year later, he caught more of the same fish. Genetic and morphological comparison to surface fish that are caught in the upstream and downstream areas of the cave revealed that the cave loaches are indeed an isolated population and the fist cave fish found in Europe.

The researchers noted that the underground water system first became a suitable habitat for the fish when glaciers retreated. Based on the geological history of the region and genetic studies of the fish, the researchers estimated that the fish came to existence within the last 20,000 years.

However, the researchers observed that the fish already shows adaptation characteristics of "real" cave fish despite having a relatively short period of evolutionary time.

Their eyes are much smaller and appear to almost curve inward. The fish also have elongated whisker-like barbels on their heads and larger nostrils than other fish living closer to the surface. Additionally, their color has all but disappeared.

With the discovery of the cave fish, the researchers noted that animals living in subterranean habitats can adapt to their environment faster than previously thought, requiring only a few thousand years.