Garra andruzzii explained

Garra andruzzii, a species of cyprinid fish, formerly the only species of the genus Phreatichthys, and is endemic to Somalia. This cave-adapted fish is whitish (not pigmented) and blind. It has no scales.^[1] It is considered to have evolved in the cave environment for some two million years.^[2] Its former generic name derives from the Greek words phreasatos for spring, and ichthys for fish. It grows to a maximum length of .

This fish is the first animal discovered that does not adjust its biological clock with the light of the sun. It has an unusual internal clock, which measures the passage of time with an extremely long period (up to 47 hours). It is also completely blind to all light stimuli.^{[3] [4]}

Two other cavefish species are found in Somalia: the cyprinid Barbopsis devecchi and the catfish Uegitglanis zammaranoi.^[5]

Notes and References

1. Web site: Fish living in dark caves still feel the rhythm of life. BBC News. 10 September 2011. 2 July 2023. Battison. Leila.
2. Web site: Gough. Zoe. Blind cavefish are able to 'count'. dead. BBC. 6 June 2014. https://web.archive.org/web/20140620151822/https://www.bbc.co.uk/nature/27663537. 20 June 2014.
3. Web site: University of Ferrara. Orologi biologici in un pesce cieco. Le Scienze Web. 8 September 2011. dead. https://web.archive.org/web/20111020012329/http://lswn.it/comunicati/stampa/2011/orologi_biologici_in_un_pesce_cieco. 20 October 2011.
4. Cavallari, N.. Frigato, E.. Vallone, D.. Fröhlich, N.. Lopez-Olmeda, J. F.. Foà, A.. Berti R.. Sánchez-Vázquez, F.J.. Bertolucci, C.. Foulkes, N. S. . 2011. A Blind Circadian Clock in Cavefish Reveals that Opsins Mediate Peripheral Clock Photoreception. PLOS Biology. 9. 9. e1001142. 10.1371/journal.pbio.1001142. free. 21909239. 3167789.
5. Book: Romero, A.. 2001. The Biology of Hypogean Fishes. Developments in Environmental Biology of Fishes. Springer . 978-1402000768.