Derivation of scientific name: The etymology of the term ‘holothurion’ is traced back to ancient Greek roughly meaning ‘unknown animal’ or ‘animal of obscure origin’. Holothuria is a type genus of the family Holothuroidea; ‘nobilis’ is Latin for ‘noble’ or ‘noteworthy’.
Introduction
The black teatfish is a species belonging to the class of exclusively marine invertebrates, Holothuroidea (commonly known as sea cucumbers). The genus Holothuria includes four species commonly known as teatfish, which are distinguished by the presence of a teat-like projection on their ventral side. They are highly valued species in the commercial seafood market.
How to recognize the black teatfish
Holothurid sea cucumbers generally have a cucumber-like elongated body arched dorsally with an oral and aboral end. On the oral end of the black teatfish, the mouth is located ventrally with 20 tentacles and positioned below the mouth area are six to ten lateral protrusions (teat-like), while on the aboral lies the anus with five calcareous teeth. The dorsal side have small, bulging structures known as papillae, while on the ventral side these structures are more elongated with disc-like ends and are known as tube feet. The definitive difference that teatfish have over other holothurids is the presence of teat-like projections (large papillae) close to the ventral side. The maximum recorded length of the black teatfish is 60 cm with the average length being 35 cm, and they can weigh anything between 230 g and 3 000 g. Morphologically, juvenile black teatfish differ from their adult form. Juveniles also can occupy different habitats, such that they are often misidentified in the field.
Getting around
Locomotion in black teatfish can be generally described as a ‘creeping along’ movement based on a water vascular or hydraulic system, moving along slowly with retractable tube feet that can stick or unstick to a substratum during movement. The movement patterns can be influenced by a number of factors such as substrate type, depth, sediment and light intensity.
Communication
The ocean is vast and often times visibility and hearing are limited. Therefore, chemical communication is vital for benthic organisms such as the black teatfish. These chemicals known as pheromones play a number of roles in the communication process of the black teatfish. The pheromones effect behaviours such as migration, inter-individual recognition, marking of territory and reproduction.
Distribution
The distribution of H. nobilis is limited to the Indian Ocean; it is found in the east coast of Africa. However, it is likely that this species may be limited to the western Indian Ocean.
Habitat
The black teatfish are benthic, living primarily on the ocean floor, and are found in the shallow coast of the Indian Ocean, in waters up to 40 m in depth. They are mostly associated with coral reef ecosystems.
Food
Holothuria nobilis are sediment feeders, feeding on deposit and detritus on the ocean floor. Organisms such as bacteria, cyanobacteria and fungi are digested in the sediment.
SEX AND LIFE CYCLE
Sex
Black teatfish are broadcast spawners, the male and female release their gametes into the water and fertilisation occurs externally. As such, successful fertilisation depends on the density of the male and female teatfish in the area. The success of reproduction is also individually varied and depends on the body size of the individual with larger individuals having greater chances of success due to larger gonads.
Family life
Due to fertilisation occurring externally, male and female black teatfish meet only when it’s spawning season. Fertilised eggs of the black teatfish are buoyant and they rapidly develop into free-swimming larvae. The plankton stage is a month and a half to three months, during which they feed on algae and are possibly dispersed by ocean currents.
THE BIG PICTURE
Friends and foes
Over 66 species of fish, sea star, crustaceans and gastropods have been known to prey on sea cucumbers. Other marine animals such as mammals, birds, sea turtles are possible predators of sea cucumbers. Teatfish have a commensal relationship with polychaeta species such as Arctonoe and Gastrolepidia (scale worms). Black teatfish do not appear to be competition to marine macroherbivores as they have not yet been found to feed on seagrass or macroalgae.
Smart strategies
Many sea cucumber produce chemical defences, which aid in some degree to reduce predation. The most characteristic defence mechanism of holothurians is evisceration, where the sea cucumber would release its guts to entangle a predator and allow the sea cucumber to escape. These guts can regenerate. Furthermore, the anal teeth discourage other organisms from trying to invade the body cavity of the sea cucumber, as have been observed in other sea cucumber species.
Poorer world without me
Black teatfish play a major role in the coral reef ecosystems by nutrient recycling, chemistry regulation and oxidation of coral reef ecosystems and their absence can have cascading effects. Furthermore, black teatfish, as sediment feeders, can potentially control parasites and pathogens along the sea floor.
People and I
Among approximately 70 harvested sea cucumber species, the teatfish is one of the most valued. Overfishing and commercial trade are the primary threats facing the black teatfish. Black teatfish are highly vulnerable due to a number of biological traits they exhibit. They have a slow growth rate, they sexually mature late, have limited mobility and are captured easily because of their large size.
Conservation status and what the future holds
The black teatfish is listed as Endangered on the International Union for Conservation of Nature (IUCN) Red List. The Convention on International Trade in Endangered Species (CITES) classifies Holothuria nobilis as a Species of High Concern as a consequence of being overexploited.
Relatives
At least 188 species are listed in the Holothuria genus. Holothuria nobilis is currently assigned to the subgenus Microthele and is the only species within the subgenus found in South African waters. Three other species are included in the subgenus, namely H. fuscogilva, H. fuscopuntuata and H. whitmaei. Another species, H. sordida is assigned to the subgenus, but its taxonomic validity is unclear. H. fuscogilva has previously been misidentified as H. nobilis. Holothuria whitmaei is also commonly called the black teatfish, however it occurs exclusively in the Pacific Ocean. All three species can be differentiated by genetics.
Scientific Name and Classification:
Kingdom: Animalia
Phylum: Echinodermata
Class: Holothuroidea
Order: Holothuriida
Family: Holothuriidae
Genus: Holothuria
Species: H. nobilis (Selenka, 1867)
Common names: Black teatfish
References and further reading
- Bruckner, A.W. (ed.). 2006. Proceedings of the CITES workshop on the conservation of sea cucumbers in the families Holothuriidae and Stichopodidae, 1–3 March 2004, Kuala Lumpur, Malaysia, NOAA Tech.
- Cherbonnier, G. 1980. Holothuries de Nouvelle-Calédonie. Bulletin du Museum National d’Histoire Naturelle, 2: 615–667.
- Conand, C. 1981. Sexual cycle of three commercially important Holothurian species (Echinodermata) from the lagoon of New Caledonia. Bulletin of Marine Science, 31: 523-543.
- Conand, C. 1986. Les ressources halieutiques des pays insulaires du Pacifique: Deuxim̀e partie. Les holothuries. Food and Agriculture Organization of the United Nations, 272.
- Conand, C. 2005. Commercial sea cucumbers and trepang markets. Fisheries and Aquaculture, 2: 221-250.
- Conand, C. Purcell, S. Gamboa, R., and Toral-Granda, T.-G. 2013. Holothuria nobilis. The IUCN Red List of Threatened Species. Accessed at: https://www.iucnredlist.org/.
- Marquet, N. 2017. Study of the reproductive biology and chemical communication of sea cucumbers (Holothuria arguinensis and mammata). PhD Thesis. Doctoral program in Marine, Earth and Environmental Sciences Marine Sciences Branch Specialty in Marine Ecology. University of the Algarve, Portugal.
- Purcell, S.W. 2010. Managing sea cucumber fisheries with an ecosystem approach. In: Lovatelli, A. Vasconcellos, M. & Ye, Y. FAO Fisheries and Aquaculture Technical Paper. Rome.
- Purcell, S.W. Mercier, A. Conand, C. Hamel, J. Toral-Granda, M. Lovatelli, A. & Sven, S. 2011. Sea cucumber fisheries: global analysis of stocks, management measures and drivers of overfishing. Fish and Fisheries, 14: 34–59.
- Purcell, S.W., Conand, C., Uthicke, S. & Byrne, M., 2016. Ecological roles of exploited sea cucumbers. In Oceanography and Marine Biology, 375–394.
- Siegenthaler, A. Cánovas, F. & González-Wangüemert, M. 2015. Spatial distribution patterns and movements of Holothuria arguinensis in the Ria Formosa (Portugal), Journal of Sea Research, 102: 33–40.
- Shiell, G. 2004. Questionnaire on the field observations of juvenile sea cucumbers. Beche-de-Mer information bulletin, (19): 41.
- Stout, C. 2021. Endangered Species Act Status Review Report: Black Teatfish (Holothuria nobilis). Report to National Marine Fisheries Service, Office of Protected Resources, Silver Spring, 53.
- Thandar, A.S. 2022. A taxonomic monograph of sea cucumbers from southern Africa (Echinodermata: Holothuroidea). Suricata South African National Biodiversity Institute, Pretoria.
- Uthicke, S., O’Hara, T.D. & Byrne, M. 2004. Species composition and molecular phylogeny of the Indo-Pacific teatfish (Echinodermata: Holothuroidea) bêche-de-mer fishery. Marine and Freshwater Research, 55: 837–848.
- WoRMS (2024). Holothuria nobilis (Selenka, 1867). Accessed at: https://www.marinespecies.org/aphia.php?p=taxdetails&id=1672772
Author: Gift Speelman