Guwahati: An international team of scientists from Germany, India, and Switzerland has described a remarkable new genus and species of blind, groundwater-dwelling fish from a dug-out well in Assam.
The discovery marks the first-ever record of an aquifer-dwelling (phreatobitic) fish from Northeast India and the Eastern Himalayan landscape, revealing hidden subterranean biodiversity beneath the region’s feet.
Named Gitchak nakana, the species draws from the Garo language, “Gitchak” meaning red, referencing its striking blood-red live colour, and “na-tok” and “kana” referring to a blind fish.
Belonging to a newly described genus within the family Cobitidae (loaches), the tiny fish grows to just 2 cm and displays classic subterranean adaptations, or troglomorphies: no externally visible eyes, a translucent, pigmentless body, and extreme miniaturization.
The species was first collected in March 2021 from a well in Assam’s Goalpara district by PhD scholar Wimarithy K. Marak of Assam Don Bosco University and her brother Leminard K. Marak. Initially unsure of their find, further examination with Dr. Lokeshwor Yumnam confirmed it as a loach. Only 13 individuals were collected over three visits from the same well, suggesting the species may be rare.
While caves of the Shillong Plateau host blind subterranean fishes such as Neolissochilus pnar, Schistura papulifera, and Schistura larketensis, these are cave-dwellers. Gitchak nakana is different. It lives in aquifers, groundwater habitats far more difficult to access. Such phreatic ecosystems are typically revealed only when wells are emptied for cleaning, making discoveries largely accidental. Similar chance findings in Kerala previously led to species such as Horaglanis populi and Pangio pathala.
One of the most extraordinary features of Gitchak nakana is its skeletal anatomy. Unlike most bony fishes, it completely lacks a skull roof. Its brain is covered only by skin. This rare condition has been reported in only three other highly miniaturized cypriniform fishes. Micro-CT scans conducted at the Senckenberg Collections in Dresden, Germany, allowed researchers to compare more than 30 cobitid species to confirm its uniqueness. Molecular analyses were carried out at the University of Bern and the Kerala University of Fisheries and Ocean Studies.
The discovery raises an exciting question: could Northeast India’s aquifers harbour more undiscovered subterranean species? Researchers believe this find signals the presence of a specialized and previously unknown groundwater fauna in the region, comparable to that known from the lateritic aquifers of the Western Ghats.
However, Gitchak nakana has so far been found in only a single well, and its exact location remains undisclosed to prevent over-collection. Past experience, such as the appearance of Meghalaya’s cave mahseer Neolissochilus pnar in the international aquarium trade, underscores the need for caution.
Beneath the soils and sediments of Northeast India, an invisible ecosystem may be thriving, one that science is only just beginning to uncover.