11-03-2025
Eyeless creature — with pink body — found in mountain caves in Oman. See new species
In the arid mountains of northern Oman, rocky caves hold pools of water.
Naturalists were exploring these subterranean lakes in the Al-Hoota cave in 1980 when they discovered a white, eyeless fish. It was a species new to science, but when other scientists later compared it to similar species found on the surface, they believed the one found deep below was just a 'cave morph' of the same fish.
Now, additional study of the fish found in the Oman cave, as well as other fish from the region, suggests not only that the underground fish is a unique species, but it's 'evolutionarily young.'
'Garra cavernicola is distinguished from other Garra occurring in the Hajar Mountains in Oman and the United Arab Emirates by lacking an external eye and having a whitish or pink-colored body without any pattern,' Jörg Freyhof, researcher at the Leibniz Institute for Evolution and Biodiversity Science in Germany, wrote in a March 7 study published in the peer-reviewed journal Zootaxa.
Garra cavernicola, or the subterranean Garra, earns its name from the Latin words 'caverna,' meaning 'underground chamber,' and 'cola,' meaning 'inhabitant of,' according to the study.
The fish is about 1.5 inches long with a 'stout' and 'compressed' body, Freyhof wrote.
The fish's eyes are 'absent' from the outside, its eye sockets instead 'filled with fatty tissue,' adapted to its subterranean environment, according to the study.
When freshly caught from the water, the fish is 'pink or whitish' and its fins are 'usually transparent' at the ends and whiter closer to the fish's body, Freyhof wrote.
Freyhof used what is called the 'evolutionary species concept' to determine whether this underground fish constituted its own independent species from similar fish on the surface, according to the study.
The evolutionary species concept says a unique species 'is a single lineage of ancestor-descendant populations of organisms which maintains its identity from other such lineages (in space and time) and which has its own evolutionary tendencies and historical fate,' as defined by Edward O. Wiley in 1981.
This means as soon as a population of animals is expressing physical differences from their species because of geographic or temporal separation, they can constitute a new species, according to the study.
'Subterranean environments are very different from surface waters, and as subterranean fishes genetically adapt to these environments, they follow their own evolutionary trajectory,' Freyhof wrote. 'As soon as these new adaptations, such as the reduction of the eye and pigmentation, become observable, they are a diagnosable unit fulfilling the criteria to be distinct species under the (evolutionary species concept).'
Garra cavernicola may have gone down its own evolutionary path relatively recently when the species was confined to caves, making the species 'young' on an evolutionary time scale, Freyhof wrote.
The Hajar Mountains are in northeastern Oman, a country on the southeastern coast of the Arabian Peninsula.
