Amblyopsidae
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. Description Amblyopsids are generally small, the northern cavefish (largest species in family) reaching up to in length. 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. The cave-dwellers typically lack pigment and are somewhat translucent. They have a naked, moderately depressed head and an elongated body, covered with small cycloid irregular flakes, with tiny or absent pelvic fins. The anal opening is so far forward that it is in the throat region. The premaxilla, a bone of the upper jaw, is segmented, and the vomer has no teeth. They have no ventral fins. The lateral line is incomplete, but well developed in some species. Its spine has between 27 and 35 vertebrae. Externally, they resemble killifishes in many respects, although their internal anatomy more closely resembles the trout-perches, with which they are currently classified. 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. Although some cave-dwellers have tiny, vestigial but functional eyes, others, such as the Amblyopsis and Typhlichthys have no eyes at all. Blindfish do, however, have rows of sensory papillae on their skin, which they use to help navigate. Similar darkness-adaptive traits can be seen in many fish families where members live underground and is known as convergent evolution. 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 does not contain cavefish. Ecology Although the cave habitat generally offers a poor food supply, the advantages of the environment include extremely