Meet Cave Loach, Europe’s First Cave Fish – Sci-News.com

A team of scientists and cave divers has discovered and described the first European cave fish a loach of the genus Barbatula.

Loaches Barbatula sp. Top: two cave loaches in their natural habitat. Center: adult male loach with typical adaptations to living in caves: reduced eyes, enlarged barbels and pale body coloration. Bottom: typical epigean loach from the surface population in the Danube. Image credit: Jasminca Behrmann-Godel et al, doi: 10.1016/j.cub.2017.02.048.

The cave fish occur in Southern Germany, near the Swabian Alb, home to an elaborate karst region that includes many famous caves.

The fish were found in the 250 sq. km underground karst water system embedded in the limestone formation of the White Jura known as the Danube-Aach system, which formed 400,000-450,000 years ago.

The cave fish were found surprisingly far in the north in Southern Germany, said Dr. Jasminca Behrmann-Godel, a researcher at the Limnological Institute, the University of Konstanz, Germany, and lead author of a study on the cave fish published this week in the journal Current Biology.

This is spectacular as it was believed before that the Pleistocene glaciations had prevented fish from colonizing subterranean habitats so far north.

The cave loaches were first observed and photographed in August 2015 by cave divers in the DanubeAach system entering the cave from the Aach spring and diving roughly 550 m northwards.

During 15 trips between August 2015 and November 2016, several individuals of various size classes were observed, and five cave fish were caught by hand netting: two were adult fish (8.2 cm and 6.5 cm long), and the remaining three were small juveniles (less than 3 cm long).

No more than 30 divers have ever reached the place where the fish have been found, said co-author Joachim Kreiselmaier, a diver from the caving club Freunde der Aachhhle e.V.

Due to the usually bad visibility, strong current, cold temperature, and a labyrinth at the entrance, most divers do not come back again for diving.

The genetic studies of the fish together with knowledge on the geological history of the region suggest that the cave loach arose recently, within the last 20,000 years.

It was only when the glaciers retreated that the system first became a suitable habitat for fish, said co-author Dr. Arne Nolte, a researcher at the University of Oldenburg in Oldenburg and the Max Planck Institute for Evolutionary Biology in Pln, Germany.

Despite that relatively short period of evolutionary time, the fish already show adaptations characteristic of real cave fish.

Their eyes are much smaller, appearing almost as if curved inwards, and their color has all but disappeared, said co-author Dr. Jrg Freyhof, a researcher at the Leibniz Institute for Freshwater Ecology and Inland Fisheries in Berlin, Germany.

The fish also have elongated whisker-like barbels on their heads and larger nostrils than related fish living closer to the surface.

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Jasminca Behrmann-Godel et al. 2017. The first European cave fish. Current Biology 27 (7): R257-R258; doi: 10.1016/j.cub.2017.02.048

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Meet Cave Loach, Europe's First Cave Fish - Sci-News.com