Researchers have discovered a new genus and species of underground earthworm eel living beneath the Indo-Gangetic Plain in Bihar, northern India. The small, colourless creature, named Gangaichthys indonepalicus, is the first subterranean fish to be recorded from the Gangetic Basin.

The research, published in ZooKeys, was carried out by an international team of scientists from the Thackeray Wildlife Foundation in Mumbai, India; Shivaji University in Kolhapur; the Shanghai Synchrotron Radiation Facility at the Chinese Academy of Sciences; and the Zoological Survey of India in Gopalpur-on-Sea. The investigation began after a short video clip posted on TikTok in 2024 showed an unusual tiny fish emerging from a water borewell near the border between India and Nepal.

“The unique morphology of the fish in the video, and the fact that there are no known stygobitic fish known from the region, motivated us to track down the species to ascertain its identity,” the research team stated.

Securing physical samples required an intensive fieldwork effort in Bihar, where the scientists manually pumped thousands of litres of water from local handpumps.

“Procuring samples of this unusual fish was challenging,” researcher Akshay Khandekar of the Thackeray Wildlife Foundation explained. “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 2000 litres of water but sustained damage during the process and died immediately. 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.”

The newly described fish measures roughly four centimetres in length and features physical adaptations suited to life in total darkness, including reduced eyes covered by skin, an unpigmented translucent body, and an apparent absence of ribs. Advanced micro-CT scanning and genetic analysis confirmed that it represents a completely distinct genus within the earthworm eel family Chaudhuriidae.

“Gangaichthys means fish of the Ganga,” Agarwal explained 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.”

As for the naming of the species itself, Tejas Thackeray commented: “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.”

Agarwal also reflected on the broader context of the find and the challenges of studying 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, both Linnaean and Wallacean shortfalls, with many more species yet to be discovered.

This exciting discovery is in some ways symptomatic of general biodiversity research in India, though sampling subterranean habitats is especially challenging.”

Khandekar A, Thackeray T, He Y, Mohapatra A, Agarwal I (2026) Gangaichthys indonepalicus, a new genus and species of miniature stygobitic earthworm eel (Synbranchiformes, Chaudhuriidae) from alluvial aquifers in the Indo-Gangetic Plain, Bihar, northern India. ZooKeys 1289: 185-202. https://doi.org/10.3897/zookeys.1289.188089