While cave-dwelling fish might be somewhat of a regularity in certain parts of the world, you used to be able to count Europe out of that equation. Cave fish were unheard of in the region and it was long believed that Pleistocene glaciations caused roadblocks for their Northerly development and habitation.
It wasn’t until recently that a hobby diver equipped with an underwater camera named Joachim Kreiselmaier discovered what appeared to be Europe’s first-known cave-dwelling fish in the depths of the Danube-Aach system. The fish appeared unique to him at first sight, so he grabbed some photographs to take with him to the surface. It has been described in the journal Current Biology as pale and having small eyes.
Image Credit: Jasminca Behrmann-Godel
"The cave fish was found surprisingly far in the north in Southern Germany," said study lead author Jasminca Behrmann-Godel from the University of Konstanz in Germany. "This is spectacular as it was believed before that the Pleistocene glaciations had prevented fish from colonizing subterranean habitats so far north."
It appears to be a loach of some sort; a type of bottom-dwelling fish that scavenges the deepest depths of the sea floor for opportunistic food sources.
Not only was it surprising to find a cave-dwelling fish in Europe to begin with, but the specimen was also the Northernmost cave fish ever discovered in the world. No researchers ever believed that a cave fish would ever be discovered so far North in the first place.
Because the Pleistocene glaciations would have kept them from migrating to Europe from another location in the world, it's believed that they might have evolved recently, within the last 20,000 years or so, and are specific to this particular region.
"It took someone with the 'right eye' to realize that this might be something special and I believe that, on top of the right conditions and the difficult trip, this discovery depended on an exceptional diver like Joachim to realize in the first place that the fish might be special," Behrmann-Godel continued.
Because it caught so much attention, Kreiselmaier reportedly went diving again just a few months later to capture a live specimen for scientists to study up close. Since the photographs were just the tip of the iceberg for researchers, getting a live specimen was the best way to really study the creature up close and realize they had been looking at something special.
The discovery of this loach in a region where it was supposedly never supposed to exist is bringing with it a lot of attention and excitement to explore the region where Kreiselmaier originally dove. On the other hand, not too many divers have successfully explored the region due to its dangerous conditions, and Kreiselmaier explains why:
"No more than 30 divers have ever reached the place where the fish have been found," he noted. "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."
It should be interesting to see what future diving missions might uncover, and whether or not there could be more undiscovered species in the region that could challenge our scientific understanding of what exists there.
At this point in time, Antarctica is the last remaining continent in the world where cave fish have never been discovered.