Scientists have made an exciting discovery in southwestern China—a new fish called the Xingren golden-line fish (Sinocyclocheilus xingrenensis). This unique fish offers a fascinating glimpse into evolution happening right now. Unlike typical cave fish, the Xingren fish has no scales and disproportionately large eyes, indicating it is still adjusting to life underground.
The Sinocyclocheilus genus has over 80 species, many of which have completely lost their eyesight and scales. In contrast, the Xingren golden-line fish keeps its large, functional eyes but lacks scales. This unusual combo shows that it’s right in the middle of the evolution process, adapting slowly to its cave environment.
Research published in Zoosystematics and Evolution highlights that most cave fish evolve blind over millions of years. The Xingren fish, however, appears to be on a different track, still retaining some vision.
Cave fish in China developed their special features due to ancient climate shifts. Millions of years ago, as waters dried up, some fish found refuge in underground systems and adapted to darkness. Many became blind over time, as sight was no longer useful in pitch-black environments. Yet, the Xingren golden-line fish still possesses well-developed eyes, suggesting it might get some light, possibly from cave openings that let sunlight in.
Another interesting point is that the Xingren fish doesn’t have a horn-like structure seen in some relatives, such as S. longicornus, which was discovered in 2023. This variation shows how cave fish can evolve differently, even within the same family.
The fish’s smooth body without scales and its unique black markings make it visually striking. Researchers believe that the loss of scales probably occurred during the Pleistocene era, around 2.6 million to 11,700 years ago, a time of significant evolutionary change for many Sinocyclocheilus species.
The Sinocyclocheilus genus is already a rich group of cave fish, boasting 81 known species after this recent discovery. Each new find helps scientists understand how animals evolve in extreme conditions. From losing sight to shedding scales, these fish illustrate dramatic evolutionary shifts when isolated from their natural habitats. The Xingren golden-line fish, with its mix of traits, serves as a living example of evolution. It likely still uses light cues from its surroundings, indicating it’s not entirely disconnected from the outside world.
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