''Caecobarbus geertsi'', the African blind barb or Congo blind barb (known as ''Nzonzi a mpofo'' in the local

Kikongo Kongo or Kikongo is one of the Bantu languages spoken by the Kongo people living in the Democratic Republic of the Congo, the Republic of the Congo, Gabon and Angola. It is a tonal language. It was spoken by many of those who were taken from th ...

language, meaning "blind barb"), is a species of

cyprinid Cyprinidae is a family of freshwater fish commonly called the carp or minnow family. It includes the carps, the true minnows, and relatives like the barbs and barbels. Cyprinidae is the largest and most diverse fish family and the largest verte ...

fish. This

threatened Threatened species are any species (including animals, plants and fungi) which are vulnerable to endangerment in the near future. Species that are threatened are sometimes characterised by the population dynamics measure of ''critical depensat ...

cavefish Cavefish or cave fish is a generic term for fresh and brackish water fish adapted to life in caves and other underground habitats. Related terms are subterranean fish, troglomorphic fish, troglobitic fish, stygobitic fish, phreatic fish and hypog ...

is only known from

Democratic Republic of the Congo The Democratic Republic of the Congo (french: République démocratique du Congo (RDC), colloquially "La RDC" ), informally Congo-Kinshasa, DR Congo, the DRC, the DROC, or the Congo, and formerly and also colloquially Zaire, is a country in ...

, and it is the only member of the

monotypic In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unispec ...

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

''Caecobarbus''.

George Albert Boulenger George Albert Boulenger (19 October 1858 – 23 November 1937) was a Belgian-British zoologist who described and gave scientific names to over 2,000 new animal species, chiefly fish, reptiles, and amphibians. Boulenger was also an active botani ...

described this fish in 1921 and it apparently lacks any close relatives in the Congo region. Despite its common name, "African blind barb", other blind cave cyprinids are indigenous to Africa, notably the Somalian ''

Barbopsis devecchi The Somalian blind barb (''Barbopsis devecchi'') is a ray-finned fish species in the family Cyprinidae. It is the only member of the genus ''Barbopsis''. This troglobitic fish is found only in Somalia Somalia, , Osmanya script: 𐒈� ...

'' and ''

Phreatichthys andruzzii ''Phreatichthys andruzzii'', a species of cyprinid fish, is the only species of the genus ''Phreatichthys'', and is endemic to Somalia. This cave-adapted fish is whitish (not pigmented) and blind. It is considered to have evolved in the cave en ...

''.

Range

The Congo blind barb is found only in the

Thysville Cave The Thysville Caves are a cave complex in the Democratic Republic of the Congo, located near the town of Mbanza-Ngungu (formerly Thysville). The cave complex is fed by tributaries of the Lower Congo River, and extends across an area of 750 square ki ...

system, a part of the lower

Congo River basin The Congo River ( kg, Nzâdi Kôngo, french: Fleuve Congo, pt, Rio Congo), formerly also known as the Zaire River, is the second longest river in Africa, shorter only than the Nile, as well as the second largest river in the world by discharge ...

(notably Kwilu and Inkisi tributaries) in the

. The area where found covers about , and is located at an altitude around above sea level. It was initially known from seven caves in the Thysville system and an additional seven were discovered in the 2000s (decade). The caves where found have high levels of

calcium bicarbonate Calcium bicarbonate, also called calcium hydrogencarbonate, has the chemical formula Ca(HCO3)2. The term does not refer to a known solid compound; it exists only in aqueous solution containing calcium (Ca2+), bicarbonate (), and carbonate () ions ...

in the water and high variations in flood levels, meaning that animals such as

terrestrial Terrestrial refers to things related to land or the planet Earth. Terrestrial may also refer to: * Terrestrial animal, an animal that lives on land opposed to living in water, or sometimes an animal that lives on or near the ground, as opposed to ...

cave insects are absent.

Conservation

In the seven caves where first discovered, the total population has been estimated at perhaps 7,000 individuals in the 1950s; no estimates are available for the seven more recently discovered populations. Among the first seven, one has disappeared entirely following

quarry A quarry is a type of open-pit mine in which dimension stone, rock, construction aggregate, riprap, sand, gravel, or slate is excavated from the ground. The operation of quarries is regulated in some jurisdictions to reduce their envi ...

ing of

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...

that began in the 1930s. The caves where it lives are considered sacred by the locals and this restricts access to most of them. A local law passed in 1937 limits fishing and the species has been listed on

CITES CITES (shorter name for the Convention on International Trade in Endangered Species of Wild Fauna and Flora, also known as the Washington Convention) is a multilateral treaty to protect endangered plants and animals from the threats of interna ...

since 1981, which limits international trade. Before its listing on CITES

Appendix II CITES (shorter name for the Convention on International Trade in Endangered Species of Wild Fauna and Flora, also known as the Washington Convention) is a multilateral treaty to protect endangered plants and animals from the threats of interna ...

, the species was often caught and exported for the

freshwater aquarium A freshwater aquarium is a receptacle that holds one or more freshwater aquatic organisms for decorative, pet-keeping, or research purposes. Modern aquariums are most often made from transparent glass or acrylic glass. Typical inhabitants include ...

trade, but few exports have happened after. Currently, the main threat is

habitat loss Habitat destruction (also termed habitat loss and habitat reduction) is the process by which a natural habitat becomes incapable of supporting its native species. The organisms that previously inhabited the site are displaced or dead, thereby ...

: The human population in its range is increasing and farming near the caves can result in

sedimentation Sedimentation is the deposition of sediments. It takes place when particles in suspension settle out of the fluid in which they are entrained and come to rest against a barrier. This is due to their motion through the fluid in response to the ...

and pollution. The region was formerly covered in rainforest and grassland, which limited

erosion Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is distin ...

. Other potentially serious threats are changes to the

hydrology Hydrology () is the scientific study of the movement, distribution, and management of water on Earth and other planets, including the water cycle, water resources, and environmental watershed sustainability. A practitioner of hydrology is calle ...

(for example, large-scale water extraction) of the small rivers that feed the caves and predation by ''

Clarias ''Clarias'' is a genus of catfishes (order Siluriformes) of the family Clariidae, the airbreathing catfishes. The name is derived from the Greek ''chlaros'', which means lively, in reference to the ability of the fish to live for a long time out ...

'' catfish found in at least some places inhabited by the Congo blind barb.

Appearance

Like other

, the Congo blind barb has reduced pigmentation and no externally visible eyes. Because of the lack of pigment, it appears pale whitish-pink overall. The operculum and

lateral line The lateral line, also called the lateral line organ (LLO), is a system of sensory organs found in fish, used to detect movement, vibration, and pressure gradients in the surrounding water. The sensory ability is achieved via modified epithelial ...

region are purplish-red due to the

gill A gill () is a respiratory organ that many aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow respiration on land provided they are ...

s and lateral line

vein Veins are blood vessels in humans and most other animals that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenated b ...

s, respectively. The eye completely lacks a

lens A lens is a transmissive optical device which focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements''), ...

, and the

retina The retina (from la, rete "net") is the innermost, light-sensitive layer of tissue of the eye of most vertebrates and some molluscs. The optics of the eye create a focused two-dimensional image of the visual world on the retina, which then ...

and

optical nerve In neuroanatomy, the optic nerve, also known as the second cranial nerve, cranial nerve II, or simply CN II, is a paired cranial nerve that transmits visual information from the retina to the brain. In humans, the optic nerve is derived from ...

are rudimentary and located deep inside the head. Despite this, the fish is

photophobic Photophobia is a medical symptom of abnormal intolerance to visual perception of light. As a medical symptom photophobia is not a morbid fear or phobia, but an experience of discomfort or pain to the eyes due to light exposure or by presence o ...

, actively avoiding light. Its maximum total length is . Minor differences have been described between the different cave populations; some have a spot on the opercular and one has a serrated

dorsal fin A dorsal fin is a fin located on the back of most marine and freshwater vertebrates within various taxa of the animal kingdom. Many species of animals possessing dorsal fins are not particularly closely related to each other, though through conv ...

spine.

Behavior

The Congo blind barb mainly relies on food items that flow into the cave during the rainy (flood) season, but it may also feed on small crustaceans. Its

longevity The word " longevity" is sometimes used as a synonym for "life expectancy" in demography. However, the term ''longevity'' is sometimes meant to refer only to especially long-lived members of a population, whereas ''life expectancy'' is always d ...

is estimated to be 9–14 years, but it may be able to live longer. It is slow-growing and likely has a slow reproduction rate. The adhesive eggs are spawned freely, ending up in crevices and pores in the bottom, which protects them from predation.

References

{{Taxonbar, from1=Q16189690, from2=Q513217 Barbs (fish) Endemic fauna of the Democratic Republic of the Congo Cyprinid fish of Africa Taxa named by George Albert Boulenger Monotypic fish genera Cave fish Taxonomy articles created by Polbot Taxobox binomials not recognized by IUCN