The Amblyopsidae are a fish family commonly referred to as cavefish, blindfish, or swampfish. They are small freshwater fish found in the dark environments of caves (underground lakes, pools, rivers and streams), springs and swamps in the eastern half of the United States. Like other troglobites, most amblyopsids exhibit adaptations to these dark environments, including the lack of functional eyes and the absence of pigmentation. More than 200 species of cavefishes are known, but only six of these are in the family Amblyopsidae. One of these, Forbesichthys agassizii, spends time both underground and aboveground. A seventh species in this family, Chologaster cornuta, is not a cave-dweller but lives in aboveground swamps.
The amblyopsids are probably ancient in origin. Adaptations common to many cavefish include reduced susceptibility to light, pigment loss, or reduction in skin scales, as well as development of chemoreceptors in the sensory organs of the body surface and the lateral line. Three species exhibit efficient metabolism during swimming, as compared with a group of non-cave fish, and many cavefish species exhibit slender bodies adapted to swimming in fast-flowing waters.
Eyes
The name of the family, Amblyopsidae, refers to their eyes (compare amblyopia). Most in this family are either blind or can only detect the difference between light and darkness. The true cave-dwellers have only rudimentary eyes, like so many other fauna that live in the dark.
Distribution
All members of this family are small and typical of the fresh waters of the eastern and southern regions of the United States. Some live deep in the swamps, and others in the lakes and streams or in caves, significantly the Kentucky cave system called the Mammoth caves.
Cavefish can only be found in caves that have streams running into them; a cave with no inlets<!-- uncited, random , such as Blanchard Springs Caverns in Arkansas,--> does not contain cavefish.
Ecology
thumb|The [[Alabama cavefish (Speoplatyrhinus poulsoni) has a tiny range and is very rare]]
Although the cave habitat generally offers a poor food supply, the advantages of the environment include extremely stable conditions, few competitors, and few predators.
Life history and behavior
Cavefish breed only once a year, occupying about 10% of the population. Cavefish protect their eggs for the longest period of any fish.