New groundwater-dwelling fish species ‘Gitchak nakana’ discovered in Assam

In a significant scientific breakthrough, researchers have discovered a new genus and species of subterranean fish, Gitchak nakana, from a dug-out well in Assam, marking the first aquifer-dwelling (phreatobitic) fish recorded from Northeast India.

The findings have been published in the journal Scientific Reports, a Nature Portfolio publication. The research was led by Ralf Britz of the Senckenberg Naturhistorische Sammlungen Dresden, in collaboration with scientists including Wimarithy K. Marak of Assam Don Bosco University (ADBU), along with other national and international institutions.

The newly described species, Gitchak nakana, is a miniature, blind and pigmentless cobitid loach that exhibits several troglomorphic traits, characteristics typically associated with subterranean life, such as the absence of eyes and loss of pigmentation. The species was collected on three occasions from the same well in a village at the foothills of the Shillong Plateau near the Brahmaputra Valley in western Assam.

Among its most unusual anatomical features is the complete absence of a skull roof, with the brain covered dorsally only by skin, a trait not seen in other known cobitid genera. Due to these distinct morphological characteristics, the fish has been classified as a new genus and species.

While more than 300 fish species worldwide are known from subterranean habitats, the vast majority inhabit caves. Fewer than 10 per cent are known from groundwater aquifers, making such discoveries rare. The Shillong Plateau is already known for cave-dwelling fishes, including species of the genus Schistura and the large subterranean fish Neolissochilus pnar, but Gitchak nakana is the first aquifer-dwelling fish reported from the region and the first subterranean cobitid recorded from Northeast India.

The discovery not only expands scientific understanding of subterranean biodiversity in the region but also points to the presence of previously undocumented underground fauna in this part of Asia. Researchers have also provided insights into the species’ unusual skeletal anatomy and proposed hypotheses regarding its evolutionary position among cobitid loaches.

The study underscores the ecological significance of groundwater habitats and highlights the need for further exploration and conservation of fragile subterranean ecosystems in Northeast India.