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

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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.

Data availability

All newly generated sequences analysed during the current study are available in the Genbank repository (https://www.ncbi.nlm.nih.gov/genbank/) under accession numbers PX277237-PX277247 for COI, PX289534-PX289537 for cyt b and PX289538-PX289541 for RAG1 and the data sets generated and analysed for our study are available as supplementary information files.

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Acknowledgements

We are very grateful to the people of the unnamed village in Assam for their help and support while collecting and studying individuals of Gitchak. We acknowledge financial support of VKD by a Senckenberg Global Fellowship. We are especially grateful to Leminard K. Marak for his unfailing skills in collecting Gitchak from the well. We thank the National Biodiversity Authority, Government of India, for allowing us to study specimens in Dresden under permit no. INBA13202500003/25/24-25/72. The µCT scans were obtained with a Zeiss Context, which was acquired through the financial support of the European Regional Development Fund (EFRE) and processed and imaged with software acquired through a grant from the Sächsisches Staatsministerium für Wissenschaft, Kultur und Tourismus (SMWK) through their TG-70 funding stream. We thank Andreas Hartl, Beta Maharatvaraj, Heok Hui Tan, and Frank Schäfer for providing images of various cobitids used in Fig. 3. Help rendered by Lekiningroy Dann (KUFOS) in the laboratory is gratefully acknowledged. We thank Jose Palely, Vice Chancellor of the Assam Don Bosco University, Gauhati, for encouragement and support. And finally, we are grateful to two anonymous reviewers for their critical comments, which improved our manuscript.

Funding

Open Access funding enabled and organized by Projekt DEAL. Senckenberg Global Fellowship, European Regional Development Fund (EFRE) and Sächsisches Staatsministerium für Wissenschaft, Kultur und Tourismus (SMWK).

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Authors and Affiliations

  1. Senckenberg Naturhistorische Sammlungen Dresden, Dresden, Germany

    Ralf Britz & Amanda K. Pinion

  2. Assam Don Bosco University, Guwahati, Assam, India

    Wimarithy K. Marak & Kangjam Velentina

  3. Dhanamanjuri University, Imphal, Manipur, India

    Yumnam Lokeshwor

  4. Department of Fisheries Resource Management, Kerala University of Fisheries and Ocean Studies (KUFOS), Kochi, India

    Rajeev Raghavan

  5. Naturhistorisches Museum Bern, Bern, Switzerland

    Lukas Rüber

  6. Aquatic Ecology and Evolution, Institute of Ecology and Evolution, University of Bern, Bern, Switzerland

    Lukas Rüber

Authors

  1. Ralf Britz
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  2. Wimarithy K. Marak
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  3. Kangjam Velentina
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  4. Yumnam Lokeshwor
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  5. Rajeev Raghavan
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Contributions

R.B., L.R. and R.R. designed the study and all authors contributed to the writing. R.B., W. K. M., V. K., Y. L., and L.R were responsible for obtaining the specimens and DNA samples. R.R. and L.R. provided the sequencing and L.R. performed the molecular analyses. A.K.P. was in charge of the CT scanning and A.K.P. and R.B. analysed the CT scans and were responsible for the rendering of the skeleton.

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Ralf Britz.

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Britz, R., Marak, W.K., Velentina, K. et al. A miniature, subterranean, blind cobitid loach, Gitchak nakana, new genus and species, is the first groundwater-dwelling fish from Northeast India.
Sci Rep (2026). https://doi.org/10.1038/s41598-026-40425-6

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