The Astyanax mexicanus is a cavefish that is distributed in Louisiana, Oklahoma, Arizona, New Mexico, Central Mexico, and Texas. This species is native to the Rio Grande and possibly Nueces River drainages (Texas Freshwater Fishes Texas State University 2013).

Caves are typically formed in karst, which is a landscape made from limestone, dolomite, and gypsum rocks. Acidic water flows through the Earth and creates a network of passages, creating an underground plumbing system (National Geographic 2013). In caves they have formations called speleothems, which hang from the ceiling of the environment. This environment is draped in a shadow of darkness and hides the uniqueness of the environment, but also allows for this organism to thrive in (National Geographic 2013). For a similar organism in this habitat click here!

 The Astyanax mexicanus originally camefrom a surface-dwelling species that once in a while invaded caves, but then reproduced multiple cave-adapted lineages. These surface dwelling populations of the Astyanax mexicanus prefer rocky and sandy-bottomed pools and creeks, streams and rivers (Arkive 2013). In the cave-adapted lineage, there are certain limitations due to the darkness of this specific habitat; such limitations include: food (because there is no primary productivity in caves) (Gallo and Jeffery 2012), reproduction, and spatial orientation. This habitat has also been a cause for the loss of coloration and loss of functioning eyes. However, the dark cave environment has allowed for the Astyanax mexicanus to evolve vibration attraction behaviors (click here for more information). The cavefish responds to low frequency water vibrations toward their source (Gallo and Jeffery 2012).  Astyanax mexicanus can determine the size of its' environment and grow based on other sensory cues besides their sight.

Other organisms have been known with similar characteristics to the Astyanax mexicanus, also live in the same environment. Many troglolbites, or cave dwelling animals, assume similar life cycles as this organism. They have evolved to live in this perpetual darkness by having no skin pigmentations and may even be blind like the Astyanax mexicanus (see form and function). (Cave of the Winds 2013)

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