Deep beneath the surface of southern China is a stream which flows between the stones in complete darkness. Although the hidden environment seems unreachable, life has found a way in the form of a pink fish that navigates the stones and current while being completely blind.
Guiyang Golden-Line Barbel
Just recently, scientists announced the discovery of a new species of cave fish which lives deep in the underground streams of Wujiang River System. The team discovered seven specimens of the eyeless fish, each with a golden stripe on its back. Unfortunately, the newly discovered species is at risk of extinction due to invasive species and pollution.
The first sample of the cave fish was identified by ecologists and conservationists in 2019. However, it took years of field surveys deep in the subterranean river systems to catch enough samples to prove that it is indeed a new species.
The cave fish was officially named Sinocyclocheilus guiyang. It is also known as "Guiyang Golden-line Barbel," named after the closely related golden-line barbel species and the Guiyang city which is near its cave river home. Unfortunately, the newly discovered species is at risk of extinction due to invasive species and pollution.
According to researchers, the diversity of fish in the Yangtze River Basin of Guiyang City has long been underestimated. There are almost 66 related Sinocyclocheilus fish species found in the Pearl River Basin to the south of Guizhou, but only six species have been discovered in Yangtze River Basin and its local Wujiang River tributary.
The survey team suspects that more undiscovered fish can still be found in the vast river caves of the Wujiang system. The geology of this river system is mostly limestone and carbonate rocks called "karst." This substance dissolves easily in water and creates sinkholes and drainages across south-central China. Just like the Pearl River Basin, the Wujiang River System possesses extensive and well-developed karst landforms which offers ideal conditions for the formation of underground river systems.
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Evolutionary Mysteries
The Guiyang Golden-line Barbel species are blind with their eyes appearing as black dots under their skin. What makes this animal remarkable is the fact that some of them have weak vision. According to the researchers, this feature provides exceptional cases for evolutionary studies.
The cave fish also grows up to 5 inches (12.7 centimeters) long. They have shorter-than-average 'barbels' or protuberances around their faces which they rely on to find food and to navigate.
According to researchers, it is common to see extended barbels in this fish species, since they better detect water flow and help in foraging in underground water systems with permanent darkness and food scarcity. Still, it remains a mystery why Guiyang fish cave did not evolve with longer, more useful barbels, or why they lack the horn-like structure commonly seen in its barbel cave fish cousins.
Additionally, they were found to have degenerated scales, a shorter snout, and shorter fins than other Sinocyclocheilus species. But just like the other related barbel fish, the new cave fish possesses a brilliant golden marking between its head and its dorsal fin.
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