CAVE FISH

any of the pale, blind, cave-dwelling fishes of the genera Amblyopsis and Typhlichthys, family Amblyopsidae. Cave fishes are small, growing to about 10 cm (4 inches) long, and are found in fresh water in dark limestone caves of the United States. There are three species: Typhlichthys subterraneus, Amblyopsis rosae, and A. spelaea. The first two lack pelvic fins; the third, the blind fish of Mammoth Cave, Kentucky, possesses these fins. All have small but nonfunctional eyes, and tactile organs that are sensitive to touch; these are arranged over the body, head, and tail and enable the fish to feel what it cannot see. Contrasting with these fishes are the swampfish (Chologaster), which belong to the same family. They are also small but are pigmented and have functional eyes. They live above ground in North American swamps and streams. Other cave-dwelling fishes unrelated to the Amblyopsidae have, in adapting to their habitat, also tended toward blindness and pale colouring. In Cuba and Yucatn, there are three species of brotula (family Ophidiidae or Brotulidae) found in caves. Among the large superorder Ostariophysi (minnows, carps, and catfish), one of the best known is Astyanax (or Anoptichthys) jordani, an eyeless, 7.5-centimetre characin (family Characidae) found in Mexico and often kept in home aquariums. Others include Caecobarbus geertsi, an African member of the minnow family (Cyprinidae), and certain catfish belonging to several families and found in the United States, Mexico, South America, and Africa. Karst topography As previously noted, karst landscapes owe their existence to the removal of bedrock in solution and to the development of underground drainage without the development of surface stream valleys. Within these broad constraints, karst landscapes show much variation and are usually described in terms of a dominant landform. Most important with respect to worldwide occurrence are fluviokarst, doline karst, cone and tower karst, and pavement karst. Fluviokarst In this type of karst landscape, the pattern of surface stream channels and stream valleys are still in evidence, though much of the drainage may be underground. Tributary surface streams may sink underground, and there may be streambeds that carry water only during seasons of high flow or during extreme floods. In addition, the floors of the valleys may be dissected into a sequence of sinkholes. Consider a normal stream valley that gradually deepens its channel until it cuts into underlying beds of limestone (or dolomite). As the valley cuts deeper and deeper into the carbonate rocks, the stream that flows through it loses water into the limestone through joints and fractures, which begin to enlarge into cave systems. At first, the cave passages will be very small and capable of carrying only a small amount of water. The stream flow on the surface will be reduced but not eliminated. As time passes, the cave passages become larger and capable of carrying more water. There will come a time when they are large enough to take the entire flow of the surface stream during periods of low flow, and during these low-flow periodstypically during summer and fallthe surface stream will run dry. With the passage of more time the cave system continues to enlarge, and more and more of the surface drainage is directed into it. The caves may become large enough to carry even the largest flood flows, and the surface channels will remain dry all year. The surface at this stage is called a dry valley, and it is no longer deepened because no more streams flow through it. Stream banks collapse, channels become overgrown with vegetation, and shallow sinkholes begin to form in the valley floor. Upstream from these swallow holes where surface streams are lost to the subsurface, the tributary valleys continue to deepen their channels. These evolve into so-called blind valleys, which end where a stream sinks beneath a cliff. At the top of the cliff is the abandoned floor of the dry valley. In short, fluviokarst is a landscape of active stream valleys, dry valleys, blind valleys, and deranged drainage systems. It is a common type of karst landscape where the soluble carbonate rocks are not as thick as the local relief, so that some parts of the landscape are underlain by carbonate rocks and others by such non-soluble rocks as sandstones or shales.