Typhlichthys subterraneusSouthern cavefish

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Geographic Range

Typhlichthys subterraneus is restricted in its geographic range to the North American continent. Some scientists believe their range was continuous in the past and may still be, but it is difficult to determine. Many scientists agree the range is now disjunct, with species inhabiting specific cave systems in Tennessee, Alabama, Missouri, Arkansas, Oklahoma, and Kentucky, but always south of the limit of glaciation. Dispersal is presumed to be through underground water channels. (Jones, 1985; Romero, 1998; Woods and Inger, 1957)

Habitat

Southern cavefish inhabit subterranean waters and are troglobitic. They prefer caves that are near the watertable and have low energy flows. These caves have water temperatures of 10 to 15 degrees C. Southern cavefish have adapted to life in an extreme habitat that includes factors such as low food supply, seasonal water level changes, and an aphotic environment. (Poulson, 1963)

Physical Description

Typhlichthys subterraneus is a small fish reaching a maximum length of 9 centimeters. Individuals have large broad heads with rudimentary eyes hidden under the skin. Normally there is no pigment on the body, although tests have shown that coloration does appear if a specimen is removed from its habitat and exposed to light. Southern cavefish do not have pelvic fins. There are 7-10 dorsal rays, 7-10 anal rays, and 10-15 caudal rays. The body, head, and caudal fin is covered by sensory papillae. (Etnier and Starnes, 1993; Poulson, 1963; Woods and Inger, 1957)

  • Range length
    9.0 (high) cm
    3.54 (high) in
  • Average length
    8.6 cm
    3.39 in

Development

Eggs are held in the gills of females until they hatch. Otherwise, little is known of development in southern cavefish. (Poulson, 1963)

Reproduction

There is little known of mating behavior in southern cavefish.

Breeding is presumed to occur in the spring season when, unfortunately, the caves are inaccessible due to high water levels.The rise in the water table drives a temperature and alkalinity decrease and also results in an increase in food availability. In response to such stimuli, a hormone is released and the gonads complete their maturation. Females are low in fecundity, producing an average of 49 eggs per female that range from 2.0-2.3 millimeters in size. It is estimated that 50% of adult females breed each year. Because of this, population sizes are small, and as a result, mates are difficult to find. Therefore, a great amount of energy is put into the rearing of young. (Poulson, 1963)

  • Breeding interval
    Breeding occurs each year.
  • Breeding season
    Breeding is thought to occur in spring.
  • Average number of offspring
    49
  • Range age at sexual or reproductive maturity (female)
    2.0 (high) years
  • Range age at sexual or reproductive maturity (male)
    2.0 (high) years

Eggs are incubated in the gill chambers of the parent female for an unspecified amount of time. Fry have been recorded in June and July. (Poulson, 1963)

  • Parental Investment
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female

Lifespan/Longevity

The expected life span is four years in the wild. (Poulson, 1963)

  • Typical lifespan
    Status: wild
    4.00 (high) years
  • Average lifespan
    Status: captivity
    4 years
    AnAge

Behavior

Little is known of behavior in southern cavefish. It has been found, however, that Typhlichthys subterraneus does have a strong thigmotaxis and keeps the top of its head touching and parallel to surfaces. They prefer to swim on substrates in quiet water. (Poulson, 1963)

Communication and Perception

Southern cavefish use touch and their thigmotaxic sense to maintain their position in the water column. Their use their sense of touch extensively to detect prey. Other sensory modalities are possible, but are unknown currently.

Food Habits

Food is scarce. Typhlichthys subterraneus forages using its sensory papillae in midwater and on the substrate. When prey is within 10 mm of the mouth, capture movements are commenced. Southern cavefish have distance perception and spatial memory which aid in foraging behavior. Their diet consists mainly of copepods (60-90%, by volume).

Foods eaten include trichopteran larvae, tendepedid larvae, cladocerans, isopods, crayfish, and copepods. (Poulson, 1963)

  • Primary Diet
  • carnivore
    • eats non-insect arthropods
  • Animal Foods
  • insects
  • aquatic crustaceans

Predation

There are no known predators of southern cavefish. (Poulson, 1963)

Ecosystem Roles

These animals are the top predators in the environments in which they live.

Economic Importance for Humans: Positive

Southern cavefish are important members of their ecosystems and important research subjects for understanding evolution in extreme environments.

  • Positive Impacts
  • research and education

Economic Importance for Humans: Negative

There are no adverse effects of southern cavefish for humans.

Conservation Status

Because the habitat of southern cavefish is so unique and because population numbers are normally low, they are regarded as a vulnerable species. Any amount of habitat that is destroyed or altered would have a significant impact. However, many of the cave systems inhabited by Typhlichthys subterraneus are protected by govenmental regulation (e.g., Mammoth Cave in Kentucky). (Poulson, 1963; Woods and Inger, 1957)

Other Comments

Southern cavefish are well-adapted for their environment. Low growth and metabolic rates as well as eye degeneration and pigment loss decrease the amounts of expended energy; parental care of young increases their chances of survival; and a well-developed sensory papillae network and spatial memory aids in navigation.

It has been suggested that the extent of eye and pigment degeneration may be a reflection of the length of isolation in caves and thus would be a helpful tool in determining the ancestral phylogenies of Typhlichthys subterraneus and other species within the family Ambloypsidae. (Poulson, 1963)

Contributors

Tanya Dewey (editor), Animal Diversity Web.

Molly Van Appledorn (author), University of Michigan-Ann Arbor.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

References

Etnier, D., W. Starnes. 1993. The Fishes of Tennessee. Knoxville: University of Tennessee Press.

Jones, S. 1985. A Range Revision for Western Populations of Southern Cavefish *Typhlichthys subterraneus* (Amblyopsidae). American Midland Naturalist, 113: 413-415.

Page, L., B. Burr. 1991. A Field Guide to Freshwater Fishes (North America north of Mexico). Boston: Houghton Mifflin Company.

Poulson, T. 1963. Cave Adaptation in Amblyopsid Fishes. American Midland Naturalist, 70: 257-290.

Romero, A. 1998. Threatened Fishes of the World: *Typhlichthys subterraneus* Girard, 1860 (Amblyopsidae). Environmental Biology of Fishes, 53: 74.

Woods, L., R. Inger. 1957. The Cave, Spring, and Swamp Fishes of the Family Amblyopsidae of Central and Eastern United States. American Midland Naturalist, 58: 232-256.