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.
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.
- Habitat Regions
- temperate
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.
- Other Physical Features
- ectothermic
- heterothermic
- bilateral symmetry
Development
Eggs are held in the gills of females until they hatch. Otherwise, little is known
of development in southern cavefish.
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.
- Key Reproductive Features
- iteroparous
- seasonal breeding
- sexual
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.
- Parental Investment
-
pre-fertilization
- provisioning
-
protecting
- female
-
pre-hatching/birth
-
provisioning
- female
-
protecting
- female
-
provisioning
Lifespan/Longevity
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.
- Key Behaviors
- natatorial
- motile
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.
- Primary Diet
-
carnivore
- eats non-insect arthropods
- Animal Foods
- insects
- aquatic crustaceans
Predation
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).
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
.
Additional Links
Contributors
Tanya Dewey (editor), Animal Diversity Web.
Molly Van Appledorn (author), University of Michigan-Ann Arbor.
- 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.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- 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).
- 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.
- 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.
- 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).
- 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
- carnivore
-
an animal that mainly eats meat
- natatorial
-
specialized for swimming
- motile
-
having the capacity to move from one place to another.
- tactile
-
uses touch to communicate
- chemical
-
uses smells or other chemicals to communicate
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.