Anguilla mossambica

Geographic Range

African longfin eels ( Anguilla mossambica ) are native to the eastern and southern coastal and inlands parts of Africa. Their range includes the Western Indian Ocean and the southeastern Atlantic Ocean around Africa, in the tropical region. Their range extends northward to coastal and inland portions of Kenya rivers ending at Uganda. They range southward to coastal and inlands of Tanzania rivers, and also freshwater rivers in Rwanda. Southward of coastal and inlands of Mozambique rivers and inlands Malawi. From Mozambique to southern Africa (including Eswatini and Lesotho), African longfin eels can be found in inland waterways, including the southeastern South African rivers. These eels' range includes the entirely of coastal and inland Madagascar waterways. They also inhabit islands east of Madagascar, including the entirely of the coastal and inlands of Reunion, Mauritius, and Rodrigues.

• Biogeographic Regions
• ethiopian ethiopian
  • native native
• oceanic islands oceanic islands
  • native native
• indian ocean
  • native native
• atlantic ocean atlantic ocean
  • native native

Habitat

African longfin eels are freshwater and marine fish. Their habitat during the non-breeding years is inland freshwater locales that include rivers, streams, and creeks. In South Africa, a telemetry study suggested that they utilized pool habitats in rivers in winter and spring months, and switched to glides (slow-moving waters downstream of pools) and moderately-fast-moving runs in the summer and fall months.

These eels also live in inlands bogs, marshes, swamps, fens, and peatlands. During their passage season, these eels migrate to feed and reproduce. They migrate 1,000 to 2,000 km from their inland freshwater habitats to spawning sites in marine environments. When spawning, these eels utilize the pelagic zone, specifically moving between the epipelagic and the mesopelagic zones.

• Habitat Regions
• tropical tropical
• saltwater or marine saltwater or marine
• freshwater freshwater

• Aquatic Biomes
• pelagic pelagic
• lakes and ponds
• rivers and streams

• Wetlands
• marsh marsh
• swamp swamp
• bog bog

Physical Description

African longfin eels as adults are slender and long, reaching total lengths of 150 cm and weights of 5.7 kg. As adults, these eels are silver and possess relatively big eyes. Sexual dimorphism exists, as female eels are larger in weight and generally longer than male eels. Female eels can be 5 kg in mass while males are just 2 kg. Most adults are about 120 cm long. Eels have thick skin, with small scales embedded in it. These longfin eels possess a bicolored pattern. Eels have a pectoral fin, caudal fin, and dorsal spine. They are ectoderms. They have sharp teeth for hunting as they mainly hunt at night. They have 2 rows of teeth but the number of teeth they have varies.

As larvae called leptocephalus, these marine-dwelling eels have wide mid-regions with tapered anterior and posterior ends. they are just 5 to 6 cm long at this stage. The eels transform to glass eels when they reach freshwater, looking transparent and flat. In this stage their length reaches 12.7 to 15.2 cm long. As juveniles, their body color eventually turns yellow - and they stay yellow until reaching the migrating adult stage. Their length at this yellow stage isn't reported.

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

• Sexual Dimorphism
• female larger

Development

African longfin eels lay eggs in oceanic waters, which hatch after 1-2 days. The hatchlings develop into leptocephali and grow to 50-60 mm. The timing of their growth depends on the temperature of the environment. The larvae proceed through a metamorphosis into their “glass” eel stage. Here, eels are transparent. They migrate to freshwater environments after 6 months to a year to feed and continue to develop. Glass eels become elvers, which are brownish red, later becoming yellow; their length as elvers isn’t reported.

In freshwater, African longfin eels develop into silver eels. In this stage, their eyes get larger, and their skin darkens and turns silver. Reaching this silver stage may take 8-18 years but depends on the habitat, temperature, and food. In their silver stage, eels migrate to back to the Indian Ocean to mate.

These eels exhibit indeterminate growth, meaning they never stop growing. The eels make one spawning migration event to the open ocean, and then they die. These eels do not exhibit temperature sex determination.

• Development - Life Cycle
• metamorphosis metamorphosis
• indeterminate growth indeterminate growth

Reproduction

Female African longfin eels release pheromones for mate attraction, and the male eels pick up the chemical signature of the pheromones. Spawning events occur in the Indian Ocean. However, mating rituals have not been documented. The eels are monogamous because they only mate once throughout their lifespan. Further, it is unknown if these eels' mate once or multiple times, but they are classified as semelparous. The eels make one spawning migration event to the open ocean, and then they die. Eels are broadcast spawners; they breed utilizing external fertilization. When they reach adult stage and are ready to mate, they turn a silver color, their eyes become enlarged, and they migrate to the ocean for breeding.

• Mating System
• monogamous monogamous

African longfin eels are catadromous fish; they spend most their lives in freshwater, but they migrate to the Indian Ocean for spawning event. African longfin eels depend on their internal high fat for egg production. They reproduce between June and November. During their semelparous breeding effort, eggs hatch after 1-2 days. Offspring receive no parental care. These eels are broadcast spawners, they reproduce from external fertilization, and the number of eggs laid is not reported. However, other members of the genus can lay 1 million eggs. After hatching, the larvae will migrate to freshwater at the age of 6 months and undergo several life phases until they reach adulthood. They reach sexual maturity at 10 years old, and they grow larger eyes and gain a silvery appearance and return to ocean to breed once. Some individuals may reach ages of 20 before spawning.

• Key Reproductive Features
• semelparous semelparous
• seasonal breeding seasonal breeding
• sexual sexual
• fertilization fertilization
  • external external
• broadcast (group) spawning
• oviparous oviparous

At hatching the larvae are independent, as neither parent provides care beyond the act of mating. Indeed, the parents die after breeding.

• Parental Investment
• no parental involvement

Lifespan/Longevity

The lifespan of African longfin eels is reported to be 20 years. The eels are expected to live 10 years before reaching sexual maturity and up to 10 more years until they spawn and reproduce. They then die after spawning. Limitations to longevity include predation, even from larger conspecifics. They can also be threatened by parasites. Although raised in captivity for food markets, these fish are not kept in captivity beyond their harvest dates.

Behavior

African longfin eels are nocturnal and solitary. They are catadromous, moving from saltwater (after the first 6 months to one year of life) to freshwater (up until age 10 or later) and back to saltwater (for final breeding effort). As broadcast spawners, they release gametes and then die in the ocean. They are hunters and predators to smaller species of fish and shrimp. The eels don’t eat daily, instead relying on internal high fat reserves. With elongated bodies, they can forage in small spaces. These eels can swim in a side-to-side movement, or they crawl in the sediment.

They are territorial, contesting dominance as they fight for food and shelter. This aggression can be with conspecifics or other species. They use chemical communication to communicate with other members of their species as a way to let them know they are ready to mate. When they are ready to mate, they migrate 1000 to 2000 km from inland waters to marine environments. In the spawning area, during the day they inhabit the lower mesopelagic layer and at night they move to shallow areas in the upper mesopelagic layer.

• Key Behaviors
• natatorial natatorial
• nocturnal nocturnal
• motile motile
• migratory migratory
• solitary solitary
• territorial territorial

Home Range

In a South African river study, Hanzen et al. (2021) reported home ranges of 2 larval African longfin eels (65 cm, 57 cm total lengths) to be over 25,000 square meters (32,432 m^2 and 25,600 m^2), with a core area of about 9,764 an 6,098 square meters for the individuals. The linear distances reported for these 2 individuals were just under 1,000 meters.

These ranges varied seasonally, with winter areas covering less than 820 square meters. Although territorial defense has been noted, territory size is not reported.

Communication and Perception

African longfin eels ( Anguilla mossambica ) use chemical signals to communicate, particularly during reproduction. They rely on their keen sense of smell to detect species-specific reproductive cues. Pheromones are released to help locate and attract mates, with bile fluid and skin mucus playing key roles in this attraction. Chemical communication is also essential for coordinating migration, guiding these eels from estuarine environments to freshwater habitats. These eels are not blind; in fact, they have larger eyes so they can see at night because they are nocturnal. African longfin eels have a lateral line sense water pressure. Eels have electroreceptors that help them distinguish electrical fields by movement of other species. These eels use tactile senses to mate and to capture food.

• Communication Channels
• visual visual
• tactile tactile
• chemical chemical

• Other Communication Modes
• pheromones pheromones

• Perception Channels
• visual visual
• tactile tactile
• chemical chemical

Food Habits

African longfin eels forage nocturnally and can be scavengers. Wasserman et al. (2012) studied the diets of African longfin eels in the elvers stage (4.5 50 11.6 cm long) in South African river. They report that these eels primarily are benthis feeders, opportunistically consuming aquatic insects (>85% of diet), especially from the orders Diptera (true flies) and Odonata (dragonflies). Non-insects included fish and copepods - both less than 2% of total volume in guts. When in larger stages, they eat crabs, frogs, and fish. They can also cannibalize conspecifics.

• Primary Diet
• carnivore carnivore
  • piscivore piscivore
  • insectivore insectivore
  • eats non-insect arthropods
  • scavenger scavenger

• Animal Foods
• fish
• insects
• terrestrial non-insect arthropods
• aquatic crustaceans

Predation

African longfin eels are preyed upon by humans ( Homo sapiens ). They’re also prey to larger aquatic animals like sharks, otters, seals, birds and larger conspecifics ( Anguilla mossambica ). To evade predators, long fin eels can be cryptic, hiding in crevices and burying themselves in the sediment.

• Anti-predator Adaptations
• cryptic cryptic

Ecosystem Roles

African longfin eels are both predators and prey, feeding on smaller organisms while being hunted by larger aquatic species. Many parasites are associated with this species, including nematodes Anguillicola papernai and monogeneans Pseudodactylogyrus anguillae . Additionally, they are hosts to two gastrointestinal nematodes, Heliconema longissimum and Paraquimperia africana , as well as other nematodes such as Heliconema africanum and Anguillicoloides crassus .

Other parasites affecting African longfin eels include an acanthocephalan, Acanthocephalus reunionesis and a cestode, Bothriocephalus claviceps .

Economic Importance for Humans: Positive

African longfin eels have a positive economic impact on humans through their importance in global seafood trade, especially in East Asia. With this global trade of eels, the exports were decreased then increased in a span of 10 years. The main exporter for eels is China, and Japan is a main importer. Global production of Anguilla species can increase due to eel farming. They are illegally fished for and traded as glass eels. Glass eels are imported from Africa to Asia and Europe. African longfin eels have interest by farms in East Asia, and there has subsequently been an increase in commercial harvesting in all their stages. Their skin serves as a source of valuable material used in the production of leather for fashion.

• Positive Impacts
• food food
• body parts are source of valuable material

Economic Importance for Humans: Negative

The negative impact on humans of African longfin eels is the increase of parasites. Some of the wild-caught eels are infected with the parasites that consumers could ingest.

• Negative Impacts
• injures humans
  • carries human disease

Conservation Status

African longfin eels are listed of “Near Threatened” on the IUCN Red List. There is no special status on the US Federal list, CITES, or the State of Michigan list. The IUCN Red List specific to the island of Réunion considers these eels to be "Critically Endangered."

African longfin eels migrate long distances from freshwater to saltwater environs. which subjects them to more threats across the aquatic landscape. Threats that impact their survival include climate change, invasive species, parasites, pollution, and predation. Dams may slow down progress from freshwater to saltwater breeding environs. These eels are subject to overharvesting, as well. For example, a 2012 press release indicated that a Japanese company was importing (from Madagascar populations) 1 metric tonne/week of African longfin eels.

African longfin eels are fished. After one eel species is over-exploited, the industry moves on to another Anguilla species. The River Health Programme in Reunion montors African longfin eel health and ecosystem services. Officials plan to facilitate river connectivity on the island of Réunion so the eels have a suitable migratory route. Future research should focus on species-specific legal and illegal harvest rates, and related patterns in regional abundance. Sustainability of harvests is a serious unknown.

Additional Links

Encyclopedia of Life

Contributors

Mikeyia Brown (author), Radford University, Natalie May (editor), Radford University, Alexander McVicker (editor), Radford University, Karen Powers (editor), Radford University, Tanya Dewey (editor), University of Michigan-Ann Arbor.

References

Frankowski, J., K. Lubke, M. Coke, O. Weyl. 2019. Genetic variability and demographic history of Anguilla mossambica (Peters, 1852) from continental Africa and Madagascar. Journal of Fish Biology , 96/5: 1251-1259.

Hagihara, S., J. Aoyama, D. Limbong, K. Tsukamoto. 2012. Morphological and physiological changes of female tropical eels, Anguilla celebesensis and Anguilla marmorata, in relation to downstream migration. Journal of Fish Biology , 81/2: 408-426.

Hanzen, C., M. Lucas, G. O'Brien, P. Calvery. 2021. Spatial ecology of freshwater eels in South Africa: Implications for conservation. Hydrobiologia , 848: 2579–2593.

Hanzen, C., M. Lucas, O. Weyl, S. Marr, G. O'Brien, C. Downs. 2022. Slippery customers for conservation: Distribution and decline of anguillid eels in South Africa. Aquatic Conservation: Marine and Freshwater Ecosystems , 32/8: 1277-1290.

Huertas, M., A. Canario, P. Hubbard. 2008. Chemical communication in the genus Anguilla: A minireview. Behaviour , 145/10: 1389-1407.

Keith, P., E. Vigneux, P. Bosc. 1999. Atlas des poissons et des crustacés d'eau douce de La Réunion. Patrimoines Naturels , 39: 1-136.

Norton, M. 2020. Prawns, justice, and relationships of care in Stilbaai, South Africa. ICES Journal of Marine Science , 77/7-8: 2483-2490.

Parker, D. 2010. An Ecological Study of Anguilla mossambica Populations and their Associated Parasites from Three River Systems in the Eastern Cape, South Africa (Honors Thesis) . Grahamstown, South Africa: Rhodes University.

Parker, D., O. Weyl, H. Taraschewski. 2011. Invasion of a South African Anguilla mossambica (Anguillidae) population by the alien gill worm Pseudodactylogyrus anguillae (Monogenea). African Zoology , 46/2: 371-377.

Pike, C., V. Crook, D. Jacoby, M. Gollock. 2020. "Anguilla mossambica (amended version of 2019 assessment)" (On-line). The IUCN Red List of Threatened Species 2020: e.T183155A176495218. Accessed February 15, 2025 at https://dx.doi.org/10.2305/IUCN.UK.2020-3.RLTS.T183155A176495218.en .

Robinet, T., E. Reveillac, M. Kuroki, J. Aoyama, K. Tsukamoto, M. Rabenevanana, P. Valade, P. Gagnaire, p. Berrebi, E. Feunteun. 2008. New clues for freshwater eels (Anguilla spp.) migration routes to eastern Madagascar and surrounding islands. Marine Biology , 154: 452-463.

Wasserman, R., O. Weyl, N. Strydom, L. Pereira-da-Conceicoa. 2012. Diet of Anguilla mossambica (Teleostei, Anguillidae) elvers in the Sundays River, Eastern Cape, South Africa. African Journal of Aquatic Science , 37?/3: 347-349.

Williamson, M., C. Pike, M. Gollock, D. Jacoby, A. Piper. 2023. Anguillid eels. Current Biology , 33/17: 888-893.

U.S. Fish & Wildlife Service. African Longfin Eel (Anguilla mossambica) Ecological Risk Screening Summary. None. Washington, D.C.: U.S. Fish and Wildlife Service. 2017. Accessed April 19, 2025 at https://www.fws.gov/sites/default/files/documents/Ecological-Risk-Screening-Summary-African-Longfin-Eel.pdf .