The subterranean world is filled with a surprising array of life, from tiny microorganisms so small you can't see them with the naked eye, to burrowing invertebrates – and even large vertebrates. Now, researchers in India have found an entirely new species of underground creature: an earthworm eel, named Gangaichthys indonepalicus.
This small, colourless animal, which measures around 4cm long, is the first subterranean fish to be documented from the Ganges Basin – an enormous river basin spanning India, Nepal, Bangladesh and China.
Described in the journal ZooKeys, the fish has an unpigmented translucent body, tiny eyes covered by skin, and no ribs.
The quest to find and document this extraordinary fish came after a video was shared on TikTok in 2024. The footage shows the strange animal emerging from a water borewell in Bihar, a state in north-east India, bordering Nepal.
“The unique morphology of the fish in the video, and the fact that there are no known stygobitic [underground] fish from the region, motivated us to track down the species to ascertain its identity,” says the research team, which included scientists from the Thackeray Wildlife Foundation in Mumbai and the Zoological Survey of India in Gopalpur-on-Sea, among others.
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But finding the fish wasn’t easy, explains co-author of the study Akshay Khandekar from the Thackeray Wildlife Foundation. “Identifying potential handpumps (borewells) and wells, and obtaining permission from their owners to extract water for the purpose of searching for the fish proved difficult. This became more intensive when we finally began manually pumping water.
“The first specimen emerged after pumping approximately 2,000 litres of water but sustained damage during the process and died immediately,” says Khandekar. “The second and only intact specimen (later designated as the holotype of this species) was found from the same borewell after pumping an additional 500 litres of water.”
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Back in the lab, the team used advanced micro-CT scanning and genetic analysis to confirm that the fish is indeed a new species: Gangaichthys indonepalicus. The animal also represents a completely new genus – Gangaichthys – within the earthworm eel family Chaudhuriidae.
“Gangaichthys means fish of the Ganga,” explains co-author Ishan Agarmal, regarding the naming of the new genus. “The Ganga or Ganges is one of the most important rivers in India, both as a source of fresh water, food and livelihood for millions of people; besides having an important role in the Hindu religion. This is the first stygobitic fish from the Indo-Gangetic plains and from the Gangetic basin.”
Tejas Thackeray, another co-author, adds: “As the species occurs on the border between India and Nepal we picked indonepalicus as the specific epithet, which reflects the distribution of the species.”
Although the discovery of this strange underground animal is exciting, Agarwal says it shows just how little we know about subterranean habitats. “India is an incredibly diverse country, spanning huge gradients in climate and topography and multiple biogeographic regions. However, there is a huge gap in knowledge [of subterranean habitats].”
Read more about the study.
Top image credit: Akshay Khandekar/ZooKeys 2026
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