Scientists have identified a previously unknown genus and species of subterranean fish living beneath the Indo-Gangetic Plain in Bihar, marking the first recorded stygobitic fish from the Gangetic Basin.

Named Gangaichthys indonepalicus, the tiny, colorless, earthworm-like fish was discovered in groundwater emerging from a borewell near the India-Nepal border. The findings were published in ZooKeys by an international team of researchers from the Thackeray Wildlife Foundation in Mumbai, Shivaji University in Kolhapur, the Shanghai Synchrotron Radiation Facility of the Chinese Academy of Sciences, and the Zoological Survey of India.

The discovery began with an unlikely clue: a short TikTok video posted in 2024 showing a tiny, unusual fish emerging from a water borewell in the region.

Researchers were intrigued because no stygobitic, or groundwater-dwelling, fish had previously been documented from the Gangetic Basin. The unusual appearance of the animal prompted the team to locate the site and determine its identity.

Thousands of Litres of Water Pumped

Finding specimens proved far more difficult than spotting the fish in the video. Researchers surveyed borewells and handpumps in Bihar, secured permission from local residents and manually pumped thousands of litres of groundwater in an effort to locate the animal.

The first specimen was recovered after about 2,000 litres of water had been pumped. However, it was damaged during collection and died shortly afterward. A second specimen was found from the same borewell after researchers pumped another 500 litres of water. It remained intact and was subsequently designated the holotype, the reference specimen used to formally describe the new species.

The fish is only about 4 centimetres long and displays several characteristics associated with life in perpetual darkness. Its eyes are greatly reduced and covered by skin, while its body lacks pigmentation and appears translucent. Researchers also noted an apparent absence of ribs.

Advanced micro-computed tomography scanning, combined with genetic analysis, showed that the animal is not simply a new species within a known group. Instead, it represents an entirely new genus belonging to the earthworm eel family Chaudhuriidae.

A Fish Adapted to Life Underground

The name Gangaichthys refers to the Ganga, or Ganges, reflecting the species’ association with the Gangetic Basin. The researchers noted the river’s importance as a source of water, food and livelihoods for millions of people, as well as its cultural and religious significance.

The species name indonepalicus refers to its occurrence near the India-Nepal border.

The researchers said the discovery highlights how little is known about India’s subterranean ecosystems. Although India has been extensively studied for its biodiversity, many species remain undocumented, particularly those living in habitats that are difficult to access.

Subterranean environments present an especially challenging frontier for biodiversity research because many organisms live deep below the surface and can rarely be encountered through conventional surveys.

The discovery of Gangaichthys indonepalicus therefore provides more than the description of a new fish. It also points to the possibility that groundwater systems beneath the Indo-Gangetic Plain may contain other previously unknown species.

Researchers said the finding underscores the continuing gaps in both species documentation and geographic biodiversity knowledge in India, suggesting that many more discoveries could emerge from habitats that have received relatively little scientific attention.

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