A new species of fish discovered in a remote cave system in northeastern India displays a rare ability to survive both underground and on the surface—a trait not seen before among cave-dwelling species in the region.
Zoologist Khlur Baiaineh Mukhim first spotted the fish two years ago in a stream deep within Krem Mawjymbuin, a cave in the eastern Khasi Hills of Meghalaya. The fish stood out with its yellowish-green color, long whisker-like barbels near its mouth, and most notably, its visible eyes—a surprising feature for a cave species typically adapted to total darkness.
Fish that live exclusively in caves often lose their eyesight over generations, evolving to survive in lightless, oxygen-poor environments. This discovery quickly drew attention from researchers across the state.
Scientists officially classified the fish as a new species earlier this month, naming it ‘Schistura densiclava’ referring to thick black stripe on its tail. Their findings were published in the Journal of Fish Biology, a peer-reviewed scientific journal.
A rare ability to adapt to surface and subterranean life
What makes Schistura densiclava unique is how it can live in both a surface stream and subterranean pools nearly 60 meters underground. This dual habitat adaptation is rare among known cave fish and marks a significant find for researchers studying how species evolve in extreme environments.
Professor Dandadhar Sarma, one of the study’s authors, explained that the cave is a very harsh environment. Temperatures inside drop to around 18 degrees Celsius (64 degrees Fahrenheit), much lower than what tropical fish usually require. Oxygen levels are also extremely low.
Sarma said the fish’s ability to survive in both harsh and favorable conditions is remarkable. It is the sixth cave-dwelling fish species discovered in Meghalaya over the past few decades, but the only one known to adapt across two vastly different ecosystems.
Meghalaya’s New Cave-Dwelling Fish. [Schistura densiclava]
( Species in the news – Bookmark 🔖) pic.twitter.com/eyJGoa8pp2
— Sleepy Classes (@SleepyClasses) May 26, 2025
The state is home to one of the most complex cave networks in the world, with an estimated 1,500 to 1,700 limestone and sandstone caves. Many remain unexplored due to their location in rugged, forested terrain.
These caves harbor a wide range of life forms with distinct evolutionary traits, yet remain understudied due to limited access and resources. In recent years, a government-funded team of researchers has worked to map these systems and document new species.
The same team discovered Neolissochilus pnar in 2019, now recognized as the world’s largest known cave fish. It was found hundreds of meters underground in the Krem Umladaw cave in the western Jaintia Hills.
Extreme conditions drive remarkable evolutionary changes
Mukhim, who has spent over a decade exploring these caves, says the fish living in them have evolved extraordinary survival traits. They have lost their eyesight and body pigmentation in their pitch-dark environment. Instead, they rely on heightened senses of taste, smell, and vibration detection through specialized skin receptors.
“These fish usually live in perpetual darkness, stagnant, shallow water pools with dangerously low oxygen levels and sometimes, go for months with little to no food,” Mukhim said.
Food sources include decaying leaves, small aquatic life washed in during floods, and even bat droppings. Despite these challenges, many of these fish live for up to a decade and reproduce underground. Interestingly, their offspring are born with eyesight, a clue to their surface-dwelling ancestry, but lose vision as they mature in the caves.
Catching these elusive fish is no easy task. Researchers often rappel into deep cave shafts, squeeze through narrow tunnels with limited air, and sit motionless for hours in total darkness with only headlamps for light. The fish are quickly caught with nets when they appear at the water’s surface.
Mukhim believes documenting these rare fish species, like the one discovered in India, is vital for their protection. “Once a species is wiped out, you can never bring them back,” he said.