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A strange species of fish lurks in the dark waters of Chinese caves and looks suspiciously like a mythical equine creature. The bizarre new fish, which researchers have discovered hiding in a pitch-black pool the size of a kitchen table, have no scales or color, tiny rudimentary eyes that probably can’t see anything and a unusually large horn protruding from their forehead, a new study reveals.
Researchers found the dull unicorn-like fish while surveying cave fish of the genus Sinocyclocheilus. Fish of this genus are found only in China, usually in small ponds immersed in darkness. There are 76 known species of Sinocyclocheilus, most of which share similar characteristics with newly discovered species, such as reduced or no vision, lack of scales, and no pigmentation. However, only some Sinocyclocheilus fish possess a horn, and others have completely lost their eyes in a process known as regressive evolution, in which species lose complex characteristics over generations. There are also a handful of Sinocyclocheilus species that live in illuminated waters and lack the unusual characteristics associated with their strange cousins.
Researchers discovered the new fish swimming in a small pool measuring 5.9ft (1.8m) wide and 2.6ft (0.8m) deep, inside a cave in the province mountainous region of Guizhou. The team rounded up individuals to take them back to the lab and examine them, unaware that they were collecting a species never seen before. After comparing the fish with other known species and analyzing their DNAthe researchers realized what they had discovered.
In the new study, published January 17 in the journal Zoo Keys (opens in a new tab)the team described the species, which they named S. longhorned beetle. The fish are 4.1 to 5.7 inches (10.5 to 14.6 centimeters) long and have two pairs of whisker-like barbels that they use to navigate their way through the dark. But perhaps their most interesting feature is their unusually long, horn-like structure, which has no clear use and is not found in closely related species. (The name longhorn is derived from the Latin words longus, which means “long”, and cornu, which means “horn of the forehead”.)
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These horn-like structures differ widely among dark dwellings Sinocyclocheilus species; they vary in length and may be forked or unforked, as in S. longhorned beetle. Since species living in light don’t have horns, these appendages likely have something to do with living in darkness, but their purpose is unclear, the researchers wrote in the paper.
The most logical explanation would be that the horns help these fish “see” in the dark, but their barbels already allow them to navigate around their pool, which is not very large and would probably require minimal navigation skills. in any event. More Sinocyclocheilus cash, including S. longhorned beetlealso have a fully formed lateral line – an organ made up of highly sensitive cells that extends laterally across a fish’s body and detects changes in pressure, temperature and salinity – so it is unlikely that the horn is also necessary to detect them.
However, the unusual size of the horn on S. longhorned beetle, coupled with the fact that the new species is not closely related to other longhorn species, suggests that longhorns have appeared at least twice in the genus, the researchers wrote. Therefore, comparing the environmental conditions of S. longhorned beetle along with some of the other long-horned species might finally reveal what the mysterious structures are actually for.
