Clarias cavernicola

Geographic Range

Clarias cavernicola , or golden cave catfish, are a species of hypogean freshwater fish found solely in Aigamas Cave, located about 40 kilometers northwest of Otavi in the northcentral area of the Otjozondjupa region in Namibia. Aigamas cave has yet to be fully explored. Golden cave catfish were likely first discovered in 1921 by Fritz Jaeger and Leo Waibel, yet the species was first recorded by Dr. Karl Jordan in 1933. Within the cave, golden cave catfish are only found in one freshwater pool that is about 18 by 2.5 meters in total surface area and is between 30 and 52 meters deep. Golden cave catfish have only been found to inhabit the upper 17 meters of the water column in the pool. How this species found its way into Aigamas Cave is unknown, as the nearest surface waters to the site are Guinas and Otjikoto Lakes (26 and 41 kilometers away, respectively) and the Kavango and Kunene Rivers (250 and 370 kilometers away, respectively).

• Biogeographic Regions
• ethiopian ethiopian
  • native native

Habitat

Golden cave catfish are found in only one subterranean pool in Aigamas Cave. The pool is located 81 meters below the mouth of the cave and the depth ranges 30 to 52 meters. Aigamas Cave has not yet been completely explored. Currently, explorers have only made it 100 meters below the surface when exploring the caverns. Jacobs et al. (2019) suggested that C. cavernicola move to other locations through undiscovered links in the aquifer, as one study counted a 75-fish difference between counts performed in February and May, but other populations have yet to be identified.

• Habitat Regions
• freshwater freshwater

• Other Habitat Features
• caves

Physical Description

The common name for Clarias cavernicola , the golden cave catfish, is derived from its skin color, which ranges from cream-colored flushed with pink or golden-yellow. Golden cave catfish are otherwise devoid of pigments, with the exception of the eyes, which are notably degenerate or completely absent, depending on the individual. Golden cave catfish were reported to grow to a mean length of 104 mm (measured from snout to the tip of the hypural plate), with a minimum recorded length of 42 mm and a maximum recorded length of 153 mm (Jacobs et. al, 2019). Like all Clariidae species, they possess alternative air-breathing organs located above the gills that allow the fish to breathe air. This function is stimulated by a gulping behavior that uses specialized muscles to close the gills and, in turn, exposes the air-breathing organs to air (Harvey, 2014). Other notable characteristics include four pairs of barbels (sensitive whiskers), long dorsal and anal fins, and a bony and depressed head (Bruton, 1995).

• Other Physical Features
• ectothermic ectothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• sexes alike

Development

Little is known about the developmental life cycle of Clarias cavernicola , which is largely due to failure to breed the species in captivity (Bruton, 1995; Jacobs et. al, 2019; Trajano et. al, 2013).

Reproduction

Mating behaviors of Clarias cavernicola are not well studied or understood (Bruton, 1995; Jacobs et. al, 2019; Trajano et. al, 2013).

Reproduction in Clarias cavernicola is not well studied or understood (Bruton, 1995; Jacobs et. al, 2019; Trajano et. al, 2013). Existing research on C. cavernicola is limited, especially regarding reproduction. Most other Clarias species distribute eggs as open-substrate spawners. In 1991, C. Hays injected pituitary extract into C. cavernicola females to induce egg production (Jacobs et al., 2019). The eggs produced in this experiment had a transparent green-tinted yolk, characteristic of a precocial lifestyle that would allow the fry to be capable of feeding almost immediately after hatching (Bruton, 1995).

• Key Reproductive Features
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• fertilization fertilization
  • internal internal
• oviparous oviparous

Little is known about the parental investment of Clarias cavernicola . Bruton (1995) suggests that the appearance of C. cavernicola eggs, as observed in the experiment conducted by C. Hays in 1991, may be indicative of a precocial lifestyle. Other Clarias species show diverse levels of parental involvement. Male walking catfish ( Clarias batrachus ), for example, exhibit protective behaviors over egg deposits and free-swimming young (Robins, 2017).

Lifespan/Longevity

Little is known about the natural lifespan of Clarias cavernicola . It is important to note that this species is critically endangered, so research attempts and specimens held in captivity are heavily restricted. Additionally, C. cavernicola have not yet been successfully bred in captivity, but female fish have been induced to produce eggs in hatchery conditions (Jacobs et. al, 2019).

Behavior

Little is known about the behavior of Clarias cavernicola . Golden cave catfish have a relatively calm and lethargic lifestyle (Jacobs et al. 2019). These catfish do congregate to feed, but this could be coincidental due to their isolation and specific habitat. Golden cave catfish are completely dependent on other species and environmental forces in the Aigamas Cave ecosystem, as they scavenge organic matter that falls or washes into the cave.

• Key Behaviors
• troglophilic
• natatorial natatorial
• motile motile

Home Range

Golden cave catfish are recognized as inhabiting only one aquifer located in Aigamas Cave, however, Jacobs et al. (2019) have suggested, based on their findings, that they could inhabit other unexplored subterranean locations that this aquifer could be connected to.

Communication and Perception

Whether and how Clarias cavernicola communicate amongst other individuals is still unknown. Golden cave catfish are completely blind, thus relying on their other senses, the most significant likely being touch (Honeyborne and Gunton, 2013). Golden cave catfish have highly sensitive barbels that are their primary methods of moving around in the environment and are how these fish sense the locations of other individuals for behaviors such as breeding (Jacobs et al., 2019; Honeyborne and Gunton, 2013).

• Communication Channels
• tactile tactile

• Perception Channels
• tactile tactile
• chemical chemical

Food Habits

Golden cave catfish are generalist scavengers. The isolated cave system they inhabit greatly restricts their available food sources. The stomach contents of three individuals were analyzed to reveal a diet largely based on detritus, occasional insects, and bat carcasses that fall into the aquifer - additional and more specific findings include eggshell fragments, a flatworm, a grub, baboon droppings, and an insect within a pupal case (Trewavas, 1936). Insectivorous bats have small intestinal tracts and leave many nutrients behind in their droppings, providing an important food source to C. cavernicola (Burton, 2017). Wild game as part of the diet of C. cavernicola is disputed because the skeletal remains of a greater kudu (Tragelaphus strepsiceros) have been found in the habitat despite its isolation (Jacobs et al., 2019).

• Primary Diet
• carnivore carnivore
  • eats eggs
  • insectivore insectivore
  • vermivore
  • scavenger scavenger
• detritivore detritivore
• coprophage coprophage

• Animal Foods
• mammals
• eggs
• carrion carrion
• insects
• terrestrial worms
• aquatic or marine worms

• Other Foods
• detritus detritus
• dung

Predation

Golden cave catfish have not been reported to have any predators.

Ecosystem Roles

Golden cave catfish are scavengers and detritivores in the Aigamas Cave ecosystem. Additionally, many troglobitic catfish are known to be trophic generalists, suggesting that they could have a fundamental niche that includes predation. In this case, golden cave catfish would likely be the top predator of the pool they inhabit within Aigamas Cave

Economic Importance for Humans: Positive

Golden cave catfish do not have an economic role as a food source or sport fish; however, they do play an important economic role in ecotourism. They are a figurehead species for the advertisement of the Aigamas Ranch as an outdoor adventure site. The owners of the ranch offer cave tours and cave diving expeditions as recreational opportunities for visitors ("Aigamas Adventure", 2008). The owners of the ranch also recognize the sensitivity of the species and only allow the harvest of specimens with a valid permit (Bruton, 1995). These catfish also play an important role in scientific studies regarding cave conservation, subterranean fish evolution, and subterranean ecology.

• Positive Impacts
• ecotourism ecotourism
• research and education

Economic Importance for Humans: Negative

Golden cave catfish do not have an explicit negative economic impact on humans, but the conservation of the species may put pressure on local communities, as Aigamas Cave and surrounding cave systems such as the Karstland Lakes are important groundwater sources for local communities.

Conservation Status

Golden cave catfish are listed as critically endangered on the IUCN Red List and are not listed under the CITES convention. Due to the little rainfall surrounding the area of Aigamas Cave, they are severely threatened by the tapping of the cave's groundwater sources. Since 1921, the water levels in Aigamas Cave have decreased by about 20 meters. Many of the pool's submerged ledges that are thought to be the prime feeding areas of C. cavernicola are at risk of exposure, which directly affects the fitness of the population (Proudlove, 2001; Burton, 1995). Golden cave catfish are also protected in part by the bans on polluting cave lakes and translocating alien fishes in Namibia and by the considerations of the Aigamas Ranch owner, Mr. Bayer (Burton, 1995). Mr. Bayer does not allow visitors into the cave nor the take of C. cavernicola specimens without a permit.

Other Comments

A common misconception regarding Clarias cavernicola is that they are found in the largest non-subglacial underground lake in the world: Dragon's Breath Cave, which is located about 55 kilometers west of Aigamas Cave.

Additional Links

Encyclopedia of Life

Contributors

Daniel Rice (author), Colorado State University, Nathan Dorff (editor), Colorado State University, Tanya Dewey (editor), University of Michigan-Ann Arbor.

References

Berti, R., G. Messana. 2010. Subterranean Fishes of Africa. Pp. 357-395 in Biology of Subterranean Fishes , Vol. 1. Boca Raton, Florida, United States: CRC Press.

Bichuette, M., E. Trajano. 2010. Conservation of Subterranean Fishes. Pp. 65-69 in Biology of Subterranean Fishes , Vol. 1. Boca Raton, Florida, United States: CRC Press. Accessed February 07, 2021 at https://books.google.com/books?id=z9E8DgAAQBAJ&printsec=frontcover#v=onepage&q&f=false .

Bills, R. 2007. "Clarias cavernicola" (On-line). IUCN Red List. Accessed February 07, 2021 at https://www.iucnredlist.org/species/63363/12662977 .

Bruton, M. 1995. Threatened fishes of the world: Clarias cavernicola Trewavas, 1936 (Clariidae). Environmental Biology of Fishes , 43: 162. Accessed February 07, 2021 at https://link.springer.com/article/10.1007%2FBF00002486 .

Burton, A. 2017. What's for dinner?. Frontiers in Ecology and the Environment , 15: 4: 224. Accessed February 07, 2021 at https://esajournals-onlinelibrary-wiley-com.ezproxy2.library.colostate.edu/doi/pdfdirect/10.1002/fee.1487 .

Churchill, S., R. Draper, E. Marais. 1997. Cave Utilisation by Namibian Bats: Population, Microclimate and Roost Selection. South African Journal of Wildlife Research , 27: 2: 44-50. Accessed February 07, 2021 at https://journals.co.za/doi/10.10520/EJC117031 .

Datry, T., N. Bronada, A. Boulton. 2017. Intermittent Rivers and Ephemeral Streams . Cambridge, Massachusetts, United States: Academic Press. Accessed February 07, 2021 at https://www.sciencedirect.com/science/article/pii/B9780128038352000103 .

Harvey, C. 2014. Fish out of water. Scienceline . Accessed March 26, 2021 at https://scienceline.org/2014/08/fish-out-of-water/ .

Honeyborne, J., M. Gunton. 2013. "Africa Season 1, Ep. 1 Kalahari" (On-line video). Accessed March 16, 2021 at https://www.amazon.com/gp/video/detail/B00AZ0Q7HA/ref=atv_dp_share_cu_r .

Jacobs, F., C. Hay, G. Jacobs, T. Næsje. 2019. "A baseline study of the critically endangered cave-dwelling catfish Clarias cavernicola in Namibia" (On-line pdf). Namibian Chamber of Environment. Accessed February 07, 2021 at https://n-c-e.org/sites/default/files/2019-12/Final_report_Clarias%20cavernicola_November_2019.pdf .

Jacobs, F., G. Jacobs, C. Hay, T. Næsje. 2020. Status update of the endemic and critically endangered cave catfish Clarias cavernicola Trewavas 1936, from the Aigamas Cave system, Namibia. African Journal of Aquatic Science , 4: 383-524. Accessed February 07, 2021 at https://www.tandfonline.com/doi/abs/10.2989/16085914.2020.1787125 .

Palomares, M., B. Samb, T. Diouf, J. Vakily, D. Pauly. 2003. "Fish Biodiversity: Local Studies as Basis for Global Inferences" (On-line pdf). Accessed February 07, 2021 at https://op.europa.eu/en/publication-detail/-/publication/b71ec309-b188-4fb5-9255-330906f9acad .

Proudlove, G. 2001. The Conservation Status of Hypogean Fishes. Environmental Biology of Fishes , 62: 201-213. Accessed February 07, 2021 at https://link.springer.com/article/10.1023/A:1011828726038 .

Robins, R. 2017. "Clarias batrachus" (On-line). Florida Museum of Natural History. Accessed March 26, 2021 at https://www.floridamuseum.ufl.edu/discover-fish/species-profiles/clarias-batrachus/ .

Trewavas, E. 1936. Dr. Karl Jordan's Expedition to South-West Africa and Angola : The Fresh-water Fishes . United Kingdom: Tring: Zoological Museum. Accessed February 17, 2020 at https://www.biodiversitylibrary.org/page/3331176#page/100/mode/thumb .

2008. "Aigamas Adventure" (On-line). Aigamas Adventure. Accessed March 16, 2021 at http://www.aigamas.com/ .