Cavefish
The cavefish (commonly: blindfish, swampfish) is found in caves and adapted to life in the dark. Notably, it lacks functional eyes and pigmentation. There are more than 80 known varieties of cavefish.
Cavefishes are generally small, ranging up to 11 centimetres (4.3 in) in length. Most do not have pelvic fins, although Amblyopsis spelaea has small ones with up to six rays. Externally, they resemble killifishes in many respects, although their internal anatomy more closely resembles the trout-perches, with which they are currently classified.
Although some species have tiny, vestigial, eyes, three have no eyes at all. Cavefishes do, however, have rows of sensory papillae on their skin, which they use to help navigate their lightless environment. The majority of cave fish have little to no pigment in their skin. These features are an example of regressive evolution. Cavefishes can only be found in caves that have streams running into them; a cave with no inlets (such as Blanchard Springs Caverns in Arkansas) will not contain cavefishes. One species, the swampfish Chologaster cornuta, inhabits above-ground swamps, rather than caves.
They are believed to have evolved from their aboveground counterparts.
That's nonsense to say a cave has to have an "inlet" to have cavefish. Most of the cave that have them are like Blanchard Springs, feed by rainwater. A good example would be Alexander Cave , located a few miles from Blanchard Springs Caverns.
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