Being underground, many places where cavefish may live have not been thoroughly surveyed. New cavefish species are described with some regularity and undescribed species are known. As a consequence, the number of known cavefish species has risen rapidly in recent decades. In the early 1990s only about 50 species were known, in 2010 about 170 species were known, and by 2015 this had surpassed 200 species. It has been estimated that the final number might be around 250 obligate cavefish species. For example, the first cavefish in Europe, a Barbatula stone loach, was only discovered in 2015 in Southern Germany, and the largest known cavefish, Neolissochilus pnar (originally thought to be a form of the golden mahseer), was only definitely confirmed in 2019, despite being quite numerous in the cave where it occurs in Meghalaya, India. Conversely, their unusual appearance means that some cavefish already attracted attention in ancient times. The oldest known description of an obligate cavefish, involving Sinocyclocheilus hyalinus, is almost 500 years old.
