While exploring a water-filled cave in Southern Germany, diver Joachim Kreiselmaier spotted a funny-looking fish swimming in the recesses of the cave. It had a pale, elongated body, large nostrils, and tiny eyes that seemed to curve inward. Kreiselmaier sent a photo of the little guy to Jasminca Behrmann-Godel, an expert of fish evolution at the University of Konstanz in Germany, and later brought her a live specimen. In an interview with Matt McGrath of the BBC, Behrmann-Godel said that once she was able to take a peek at the fish, she realized she was looking at “something really new.”
Experts believe that Kreiselmaier inadvertently stumbled upon the only known cave-dwelling fish in Europe, and the most northern cavefish ever discovered. There are some 200 species of cavefish living in various locations throughout the world, but none had been sighted in Europe until now. The critter has been identified as “a loach in the genus Barbatula,” according to Science Daily.
The northerly habitat of the cave loach, which was found in the hard-to-reach crannies of Germany’s Danube-Aach cave system, came as a surprise to researchers. Experts had believed that if a cavefish would ever be found in Europe, it would likely be located in the fauna-rich caves of the western Balkans. Most of Europe’s cave dwelling species live in that region, according to a press release from the University of Konstanz, but the newly discovered cave loach was found in “an area that would not have occurred to anyone—in Germany.”
Researchers now suspect that a large population of cavefishes dwell in sinkholes and caves “where percolating water from the Danube flows to the Aach spring north of Lake Constance,” Behrmann-Godel says, according to the press release.
To date, researchers have been able to examine five live cave loaches from the Danube-Aach in a laboratory, but getting the creatures there is no mean feat. The Danube-Aach system can only be accessed by skilled divers who know how to navigate the area’s labyrinthine caves, finding their way through both strong currents and poor visibility. According to John Raphael of Nature World News, the trickiest crannies in the caves can only be access during the summer and fall, when conditions are especially dry.
Once divers had caught several elusive cave loaches, researchers were able to conduct detailed genetic analyses. Their findings, published in the journal Current Biology, suggest that the fish evolved relatively recently. As Andy Coghlan explains in The New Scientist, the cave loach seems to have diverged from surface fish some 20,000 years ago, when receding ice age glaciers made the Danube-Aach caves accessible. Throughout this short period of evolutionary time, the fish have developed signature adaptations of creatures that live in dark, deep-water habitats: small eyes, large nostrils that help with navigation through lightless waters, and long facial appendages known as “barbels,” which cavefish also use to explore their environment.
Scientists hope that by studying the loach, they will be able to better understand the early evolutionary phases of cave-dwelling creatures.