The discovery of a golden scaleless fish in China is helping scientists understand how animals evolved to live in caves.
Newly Discovered Golden Cave Fish in China Is Still Evolving
Researchers have discovered a never-before-seen golden cave fish in southwestern China, providing fresh insight into how species adapt to life underground.
The scaleless fish is a newly identified species of golden-line fish (Sinocyclocheilus), a group found exclusively in and around Chinese caves. The discovery sheds light on the evolution of these unique cave dwellers.
Unlike some golden-line fish that have lost both their scales and eyes due to the perpetual darkness of their habitat, the newly discovered species—named the “Xingren golden-lined fish” (S. xingrenensis) after the nearby city of Xingren—has large eyes but no scales. This suggests it is still undergoing evolutionary changes to better suit its environment, according to a study published on Feb. 24 in the journal Zoosystematics and Evolution.
Evolutionary Adaptations to Cave Life
Golden-line fish are believed to have moved into caves when China experienced a period of drying towards the end of the Miocene epoch (23 million to 5.3 million years ago) and into the Pliocene epoch (5.3 million to 2.6 million years ago). By analyzing their evolutionary history, researchers found that Xingren and similar species likely lost their scales during the Pleistocene epoch (2.6 million to 11,700 years ago), around the same time some members of the group began losing their eyesight.
“This further suggests that most cave fishes may not have lived in cave ecosystems for more than a few million years,” the researchers wrote. “Together with the eyes and scales, we hypothesize that the new species may be undergoing a gradual evolutionary process towards caves.”
A Unique Addition to the Most Diverse Cave Fish Group
With 80 previously recognized species, Sinocyclocheilus is the most diverse group of cave fish in the world. The discovery of the Xingren golden-lined fish brings the total to 81. Researchers collected specimens of this new species in southwestern Guizhou province between 2012 and 2020.
Golden-line fish display remarkable variation in appearance. The Xingren golden-lined fish is distinguished by a scaleless body with irregular black markings, setting it apart from its relatives. It also lacks the horn-like structure seen in S. longicornus, a unicorn-like blind fish discovered in 2023.
The Role of Eyes in Evolution
Although much remains unknown about Xingren golden-lined fish, its eyes offer clues about its adaptation to cave life. Unlike completely blind fish that live in total darkness, Xingren has significantly larger eyes, suggesting that it still relies on detecting light.
“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. Photoperiods refer to the length of daylight an organism experiences within a 24-hour period, meaning this species may still interact with light in its environment.
As scientists continue studying Xingren and other golden-line fish, this discovery offers a rare glimpse into the evolutionary process in action.