Like many cave-dwelling species, the Anguila ciega (Ophisternon infernale), otherwise known as the blind swamp eel, has lost its eyes and pigmentation, which are of no use in the dark depths of a cave (3). Instead, this fish has a large number of sensitive pores on its long, bulb-shaped head to detect environmental stimuli (2)(3). This is a very elongate fish with an exceptionally long tail, giving it a somewhat worm-like appearance (2).
The Anguila ciega builds mucus-lined burrows in organic rich sediments within the freshwater part of the aquifer. This species is able to tolerate low oxygen concentration levels and can even breathe atmospheric oxygen. The diet is thought to primarily comprise stygobitic shrimp (Creaseria morleyi), and reproduction is reportedly oviparous, or egg-laying (2).
The main threats to this species are various forms of water pollution caused by humans. In rural areas sewage is rarely treated before being discarded, and industrial and domestic waste is sometimes disposed of in caves. Another threat comes from over-harvesting of freshwater, which may lead to saline waters creeping into the normally freshwater zone. The human population of the Yucatan peninsula is growing, so a greater and greater strain on water resources can be expected in the future. Another potential threat is the modification and/or the intensive use of this fish’s habitat by humans for recreational or tourism purposes (2).
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