A miniature, subterranean, blind cobitid loach, Gitchak nakana, new genus and species, is the first groundwater-dwelling fish from Northeast India

Subterranean animals are commonly met with considerable fascination, by both laymen and biologists. While most of these animals have been reported from caves, some species have adapted to other underground habitats. One special subterranean aquatic habitat are aquifers, which are home to a number of invertebrates and fishes. Of the more than 300 known subterranean fishes, fewer than 10% have been recovered from aquifers and are encountered only rarely and serendipitously. Here we report the discovery of a tiny, blind loach of the family Cobitidae from a dug-out well in Assam, India, which exhibits a number of characters commonly associated with subterranean life, so-called troglomorphies. This loach, described here as Gitchak nakana, represents a new genus and species, differing from all other genera of cobitids by a number of unique characters. The most unusual among these is the complete lack of a skull roof with the brain covered dorsally only by skin. Gitchak nakana is the first aquifer-dwelling (phreatobitic) fish from Northeast India, and marks the first discovery of a previously unknown subterranean fauna in this part of Asia.