This file photo taken on Nov. 15, 2019 shows the Sinocyclocheilus guiyang, a new fish species without functional eyes. Chinese researchers discovered the new fish species in a subterranean river within a cave in southwest China's Guizhou Province. [Photo/Xinhua]

Chinese researchers have discovered a new fish species without functional eyes in a subterranean river within a cave in southwest China's Guizhou Province.

In a paper published in the international journal Zoosystematics and Evolution, Sinocyclocheilus guiyang is described as a pinkish fish that belongs to the genus Sinocyclocheilus. It is named after Guiyang, capital of Guizhou Province, where the species was found in 2019.

The fish is blind with its eyes having degenerated into black spots without a complete ocular structure. This is probably a result of the dark environment of its habitat in the underground river, located in a karst cave, said Zhou Jiajun, a co-author of the paper.

The species has an extremely small population, with only 25 individuals having been recorded. Recent surveys have indicated a further decline in their number, said Cheng Guangyuan, the co-author who first discovered the fish.

Researchers have warned that the new species is at high risk of extinction due to pollution from garbage and invasive crayfish species threatening its cavernous habitat, highlighting the need for immediate habitat protection measures.