Taxonomy & naming
Mastacembelus marchei was described by Henri Émile Sauvage in 1879. The Catalog of Fishes (Eschmeyer, CAS), the governing authority for valid names, records it in the genus Mastacembelus, the type genus of the family Mastacembelidae within the order Synbranchiformes. This taxonomic placement is the essential context for the fish: although it resembles a true eel, it is not one. True eels belong to the order Anguilliformes; the spiny eels of Mastacembelidae evolved their elongate, burrowing body plan independently, and the similarity is convergent rather than indicative of close relationship.
The genus Mastacembelus is large and ranges across both Africa and tropical Asia. Its African members were historically divided among several satellite genera — including Aethiomastacembelus, Caecomastacembelus, and Afromastacembelus — before being consolidated back into the broader Mastacembelus by modern phylogenetic work. Mastacembelus marchei has been consistently placed in Mastacembelus throughout its taxonomic history. The type locality is recorded in the area of Doumé Falls on the Ogooué River in Gabon (approximately 00.843°S, 12.96°E), though Sauvage's original material also came from the Cameroon and Congo region.
Morphology
Mastacembelus marchei is a medium-sized spiny eel reaching a reported maximum of 13 in standard length. The body is greatly elongate and laterally compressed toward the tail, covered in small embedded scales overlaid by a smooth mucus coat that gives the fish its superficially scaleless appearance. The snout is drawn out into the characteristic fleshy, trunk-like rostral projection tipped with tubular nostrils that is diagnostic of the spiny eels, used to probe the substrate for benthic prey.
Running along the back ahead of the soft dorsal fin is the row of isolated, short dorsal spines that gives the family its common name. Fin ray counts recorded for this species fall in the ranges of 23–28 dorsal spines, 60–75 soft dorsal rays, 2–3 anal spines, and 61–83 soft anal rays, with vertebral counts of 71–85. The soft dorsal and anal fins meet around the tapering tail, forming a continuous fin that wraps the posterior end of the body. Detailed colouration data from field specimens is sparse in available literature, but the species shares the typical brownish, cryptically patterned ground colour common to West African riverine Mastacembelus.
Habitat
Mastacembelus marchei occupies lowland freshwater environments across a belt of West and Central African river drainages. Its confirmed range spans the Kribi River (Cameroon), rivers of Gabon including the Ogooué and its tributaries, the Kouilou-Niari system of the Republic of Congo, the lower Congo River, and Pool Malebo on the Congo River between the Democratic Republic of Congo and the Republic of Congo. The Dja River, a Congo basin tributary, is also part of its recorded distribution.
As a benthopelagic freshwater species associated with the lowland river systems of the Congo and adjacent basins, it is presumed to inhabit slow to moderate riverine and floodplain environments with soft or sandy substrates into which it can burrow. Like other West and Central African spiny eels, it is a fish of the lower reaches of large river systems, where it shelters by day in the substrate, among root masses and leaf litter, and forages nocturnally. It is a freshwater species and there is no evidence of catadromous migration or marine phase.
Feeding
Mastacembelus marchei is a nocturnal carnivore in common with the rest of its family. The elongate body and probing, sensitive rostral projection are adaptations for hunting along the substrate — rooting through soft sediment, leaf litter, and root tangles after dark to locate benthic invertebrates such as insect larvae, worms, and small crustaceans. Small fishes may also be taken opportunistically.
In the aquarium, as for other medium-sized African spiny eels, appropriate foods include bloodworm, earthworms, small pieces of prawn, and other meaty benthic invertebrate foods offered in the evening after lights have been reduced. Like most of its genus it is likely a shy, methodical feeder that performs best in a well-structured tank with sufficient cover, and competition from faster-swimming tankmates at feeding time should be avoided.
Mating
Spiny eels, including Mastacembelus marchei, are egg-scattering spawners. They are not true eels and do not undertake the oceanic spawning migrations of Anguilliformes; all reproduction takes place in fresh water. Courtship in Mastacembelus involves the pair entwining among fine vegetation, roots, or substrate structures before scattering adhesive eggs, and spawning across the genus appears to be triggered by the onset of seasonal rains, rising water levels, or flooding conditions.
No parental bond is formed, and neither parent tends the eggs or larvae after spawning. Detailed field observations of M. marchei mating behaviour are not documented in available literature, but the pattern is consistent across the family as established from studies of related spiny eel species.
Breeding
As a spiny eel, Mastacembelus marchei is an egg-scatterer that deposits adhesive, demersal eggs among vegetation, root masses, or leaf litter in fresh water and provides no parental care. Research on Mastacembelus breeding biology, including work on M. aculeatus, documents green, sticky eggs that hatch within roughly 31–37 hours at temperatures around 82–84 °F; fecundity varies with female size and can range from several thousand to over twenty thousand eggs. Spawning is triggered by flood or monsoon conditions.
Mastacembelus marchei is not known to have been bred in the home aquarium, and captive reproduction of West and Central African spiny eels of this size class is generally rare. There is no bubble-nest construction, no mouthbrooding, and no post-spawning parental investment. For any keeper attempting to condition this species for breeding, simulating seasonal rainfall through large, slightly cooler water changes and the addition of fine-leaved plants or spawning substrate would be the approach supported by family-level breeding data.
In the aquarium
Mastacembelus marchei is occasionally encountered in the specialist aquarium trade as part of the general West African spiny eel assortment, though it is far less common in the hobby than the Asian fire eel or the African peacock eel. At a maximum size of around 12.5 in SL it is manageable by spiny-eel standards, but it still requires a well-filtered aquarium with a deep bed of fine sand to burrow into, plenty of caves, pipes, and shaded retreats, and a tight, fully sealed lid — spiny eels are determined escape artists that will exploit even small gaps in cover and can die if they leave the water.
Being scaleless, it is sensitive to copper-based medications and to deteriorating water quality; a mature, stable system is essential. It is a nocturnal predator and will take small tankmates after dark, so companions should be chosen accordingly. Dim light, sandy substrate, meaty evening feeds, and minimal disturbance are the keys to keeping this species well. Detailed care information in the hobbyist literature is sparse, and much of what applies is extrapolated from the broader Mastacembelus husbandry knowledge base.
Conservation
Mastacembelus marchei has not been formally assessed by the IUCN Red List; no published assessment appears in the IUCN database as of 2026. The species' status is therefore Not Evaluated (NE), and nothing can be stated with confidence about population trends or threat levels based on official conservation data.
It is a freshwater species of the lower Congo River system and adjacent basins — one of the most biodiverse freshwater systems on earth but also one under increasing pressure from artisanal and commercial fisheries, habitat modification, and the rapid expansion of hydroelectric infrastructure. The Congo basin hosts a very high number of endemic fish species, many with ranges far narrower than M. marchei's, and broad-scale threats to river integrity in this region are real and documented. A formal assessment of this species would be a useful step toward understanding whether its apparent wide range translates to genuine population security.