The cave loaches were first discovered by a group of cave divers exploring the Danube–Aach system, a subterranean water system that formed over 400,000 years ago in present day Germany. Genetic studies of the fish and geological history of the area indicate that the cave loach arose within the past 20,000 years. Source: http://www.sci-news.com/biology/cave-loach-04760.html