Researchers in China have discovered a previously unknown golden scaleless cavefish, shedding light on how species continue to evolve in underground environments.
The newly identified Xingren golden-line fish was found in caves in southwestern China and marks the 81st known species in the Sinocyclocheilus genus, the most diverse group of cave fish in the world.
The study, published Feb. 24 in the journal Zoosystematics and Evolution, suggests the fish is still adapting to its dark habitat. Unlike some of its relatives, which have lost both their eyes and scales, the Xingren golden-line fish has large eyes but no scales, indicating an ongoing evolutionary shift.
Golden-line fish are unique to China’s caves and have developed extreme adaptations to life in darkness. Some species have lost sight, while others have evolved without scales.
Scientists believe these changes began millions of years ago when shifting climates forced fish into underground water systems.
A closer look at evolutionary patterns suggests that golden-line fish first moved into caves between 23 million and 2.6 million years ago. These fish adapted to their new environment as surface water sources became scarce.
Researchers estimate that many species, including the newly discovered Xingren golden-line fish, lost their scales between 2.6 million and 11,700 years ago, around the same time some species started losing their eyesight.
The Xingren golden-line fish stands out due to its scaleless body with irregular black markings, a feature not seen in many relatives. It also lacks a horn-like structure, a distinct trait of some golden-line fish, such as the unicorn-like S. longicornus, discovered in 2023.
Unlike fully blind cavefish, the Xingren species has large, functioning eyes, suggesting it still relies on some level of light detection. Researchers believe this may be due to its habitat, where cave openings allow limited access to surface light. This could mean that photoperiods, the natural cycle of light and darkness, still influence the species.
“This is related to the habitat, where the new species can be connected to surface streams through cave windows, and their life rhythms may be closely related to photoperiods,” the study authors wrote.
The discovery of the Xingren golden-line fish raises further questions about how cave species evolve. Scientists continue to study its behavior, genetic adaptations, and how it compares to other golden-line fish.
As experts continue exploring China’s vast cave systems, even more undiscovered species might be waiting to reveal the secrets of underground evolution.
