The previously unknown golden-lined xingren fish appears to be still evolving for cave life. (Image credit: Xiao MY, Wang JJ, Luo T, Zhou JJ, Xiao N, Zhou J (2025), Zoosystematics and Evolution (CC BY 4.0).)
Scientists have discovered a previously unseen golden cave fish in southwest China that is still adapting to underground life.
This scaleless fish is a new species of golden-lined fish (Sinocyclocheilus) that lives exclusively in and around Chinese caves. The discovery thus provides scientists with a unique opportunity to study the evolution of these unusual cave organisms.
Some gold-lined fish have lost their scales and eyes as they adapt to cave life — there’s no need for eyes when it’s too dark to see. The new species, named the Xingren gold-lined fish (S. xingrenensis) after the city near where it’s found, has large eyes but no scales, suggesting it’s still evolving to suit its environment, according to a study published Feb. 24 in the journal Zoosystematics and Evolution.
Previous research has suggested that gold-lined fish moved into caves during a period when China's climate was becoming drier — meaning there was less water outside — toward the end of the Miocene (23 million to 5.3 million years ago) and into the Pliocene (5.3 million to 2.6 million years ago). By examining the evolutionary history of gold-lined fish, the study's authors concluded that Xingren and other gold-lined fish like it likely lost their scales during the Pleistocene (2.6 million to 11,700 years ago), similar to how some members of the group are thought to have begun losing their eyes.
“This further highlights that most cave fishes may not have lived in cave ecosystems for more than a few million years,” the researchers wrote in their paper. “Thus, together with the eyes and scales, we suggest that the new species may be undergoing a slow evolutionary process toward cave life.”
Sinocyclocheilus is the most diverse group of cavefish in the world, with 80 recognized species, including 81 species of the golden-lined Xingren fish. According to the study, the scientists discovered this new addition to the group while collecting golden-lined fish in the southwestern province of Guizhou between 2012 and 2020.
Goldfish are remarkably diverse in their appearance. The new species stands out among known goldfish due to a unique combination of characteristics, including a lack of scales on its body with irregular black markings. Xingrens also lacks the horn-like structure that is present in some goldfish, notably S. longicornus, a blind, unicorn-like fish found in 2023.
Researchers still have a lot to learn about Xingrens, but their eyes offer some clues about how the species might exist. Scientists speculate that Xingrens' lives are tied to photoperiods, which refer to the amount of light an organism receives in a 24-hour period. After all, Xingren's eyes are noticeably larger than those of blind fish living in total darkness deep in caves, and thus can still detect light.
“This is related to the habitat, where the new species may be connected to surface water flows through cave windows, and their life rhythms may be closely linked to photoperiods,” the study authors conclude.
TOPICS caves China
Sourse: www.livescience.com
