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| Gitchak nakana Britz, Marak, Velentina, Lokeshwor, Raghavan, Pinion & Rüber, 2026 |
Abstract
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.
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| Gitchak nakana. (a) ZSI FF11123, holotype, 20.8 mm SL, in life, sides reversed, showing overall appearance, note presence of large eggs in body cavity and numerous fat globules (reflective spheres) along dorsal midline and postanal ventral midline. (b) same specimen, after preservation. (c) same specimen, µCT-image to illustrate presence of eight large eggs arranged in a longitudinal series. (d) same specimen, in life, actively swimming in the water column; note large yellow eggs and blood red liver. (e) KUFOS2025.F.11.51, non-type, 16.4 mm SL, in life, close-up of lateral head and body; note swimbladder visible through body wall. (f) KUFOS:2025.FT.11.6, paratype, 20.0 mm SL, frontal view of head to illustrate crown of barbels; note large-calibre red blood vessels supplying rostral (rb), maxillary (mxb) and mandibular (mdb) barbels and small-calibre vessels supplying nasal (nb) and tiny mental barbels (marked by arrow). |
Taxonomy
Gitchak, new genus
Diagnosis. Gitchak is a member of the family Cobitidae as evidenced by (i) the modification of lateral ethmoid into a bifurcated subocular spine, which articulates with the orbitosphenoid, (ii) the reduction of the endopterygoid into a rod-like element, (iii) the absence of contact between orbitosphenoid and pterosphenoid and (iv) the outer arm of the os suspensorium completely surrounding anterior swimbladder chamber.
Etymology. The genus name is derived from the Garo word gitchak, meaning red, alluding to the striking red life colour of this loach. Treated here as a noun in the feminine gender.
Gitchak nakana, new species.
Etymology. The specific name is derived from the Garo words na·tok, fish, and kana, blind, referring to the absence of eyes in this species, a noun in apposition.
Ralf Britz, Wimarithy K. Marak, Kangjam Velentina, Yumnam Lokeshwor, Rajeev Raghavan, Amanda K. Pinion and Lukas Rüber. 2026. A miniature, subterranean, blind cobitid loach, Gitchak nakana, new genus and species, is the first groundwater-dwelling fish from Northeast India. Scientific Reports. 16: 7746. DOI: doi.org/10.1038/s41598-026-40425-6 [26 February 2026]
