Taxonomy & naming
Mastacembelus decorsei was described by the French ichthyologist Joseph Pellegrin in 1919, with the type locality given as the Gribingui River in what is now the Central African Republic. The species epithet honours the French explorer and naturalist Fernand Decorse, who collected in equatorial Africa around the turn of the twentieth century.
For much of the twentieth century, African spiny eels were placed in separate genera from the Asian Mastacembelus, including Aethiomastacembelus, Caecomastacembelus and Afromastacembelus, and this species was long listed as Aethiomastacembelus decorsei. A taxonomic revision accepted by the Catalog of Fishes (Eschmeyer, the authority for valid names) synonymized these African genera back into Mastacembelus, and the fish is now correctly placed as Mastacembelus decorsei Pellegrin, 1919. FishBase notes that the generic identity remains tentative pending further anatomical analysis, so future nomenclatural adjustments are possible.
This species belongs to the family Mastacembelidae within the order Synbranchiformes, making it a relative of the swamp eels rather than of the true eels (order Anguilliformes). Its elongate, sinuous shape is convergent with true eels and not evidence of a close phylogenetic relationship.
Morphology
Mastacembelus decorsei is a small spiny eel, reaching a maximum recorded total length of approximately 9.5 in. The body is greatly elongate and laterally compressed toward the tail, and to casual inspection appears scaleless — the scales are tiny and deeply embedded in the skin, which is covered in a thick coat of mucus. The snout is produced into the fleshy, probing rostral appendage characteristic of the genus, tipped with tubular nostrils used to detect prey in the substrate.
A row of short isolated dorsal spines runs along the back ahead of the soft dorsal fin, which merges with the anal fin around the pointed tail — the arrangement that gives the spiny eels their common name. Detailed colour description in the scientific literature is sparse for this species; like other West and Central African Mastacembelus it is presumed to be brownish or mottled in life, suited to the riverine substrates it inhabits. Sexual dimorphism is not documented; in related species, ripe females may be more rounded in the belly.
Habitat
Mastacembelus decorsei is a freshwater demersal species native to the Gribingui River, a tributary system of the Sangha and Ubangi drainages within the Central African Republic. Its known range also extends to portions of the Chad and Niger basins, indicating it occupies the broad equatorial and sub-Sahelian river systems of west-central Africa.
Like other Central and West African spiny eels, it almost certainly inhabits the soft-substrate margins of rivers and streams — sandy or silty bottoms where it can burrow, sheltering among roots and leaf litter in shallow, warm freshwater. The rivers of this region are generally soft to moderately mineralised and neutral to slightly acidic in character during the rainy season, with warmer temperatures typical of equatorial Africa. Detailed field observations for this species are not available in the accessible literature.
Feeding
FishBase assigns Mastacembelus decorsei a trophic level of 3.7, indicating a carnivorous diet consistent with the feeding biology of other spiny eels. The genus as a whole forages nocturnally along the substrate, using the sensitive fleshy snout to probe for benthic invertebrates — insect larvae, worms and other small invertebrates concealed in soft sediment or leaf litter.
No specific dietary studies for this species appear to exist in the accessible literature. Its small adult size suggests a diet tilted toward smaller prey items than the large, piscivorous spiny eels of Asia; invertebrates would make up the bulk of natural intake. In the aquarium, related small African spiny eels generally accept live and frozen bloodworm, tubifex and small earthworm offered after dark.
Mating
Mastacembelus decorsei is a spiny eel in the family Mastacembelidae and, like all members of the family, is an egg-scatterer that breeds in fresh water. It is not a true eel and does not undertake any marine or catadromous spawning migration. There is no bubble-nest, no mouthbrooding, and no complex hermaphroditism of the kind seen in swamp eels.
No specific courtship observations have been published for this species. In related Mastacembelus, spawning appears to be triggered by seasonal rainfall and rising water levels. A courting pair entwine among aquatic vegetation or root masses and scatter adhesive eggs; the eggs adhere to fine plant material or substrate debris. The adults do not form a lasting pair bond and separate after spawning.
Breeding
Mastacembelus decorsei is an egg-scattering substrate spawner that gives no parental care. After spawning, the adhesive eggs are left to develop unattended among vegetation or leaf litter, and the adults take no interest in the clutch or the larvae. This is the standard Mastacembelidae breeding pattern: no nest, no guarding, no care.
No captive breeding of this species has been documented in the accessible literature. It is a little-known species rarely if ever encountered in the ornamental fish trade, so the hobbyist record is essentially absent. Were it to be kept and bred, the approach used for similarly-sized African spiny eels would apply: a soft-substrate, heavily planted tank, stable warm water, and a simulated rainy-season trigger of large water changes with slightly cooler, softer water. Eggs would be expected to hatch within a few days, with larvae requiring very fine first foods.
In the aquarium
Mastacembelus decorsei is not an established aquarium fish. It is a small, obscure Central African species rarely collected for the ornamental trade, and essentially no hobbyist literature exists on its care. Its modest adult size of around 10 in makes it more manageable than the large Asian fire or tire-track eels, but it would share the general care requirements of the family.
As a scaleless spiny eel it would be sensitive to copper-based medications and to poor water quality. A soft sand substrate that allows burrowing, caves or pipe retreats, dim or subdued lighting, and meaty foods offered after dark are the baseline for any Mastacembelus. A tight-fitting, fully sealed lid is non-negotiable: spiny eels are accomplished escape artists that will exit any gap and die on the floor. Tankmates should be robust and too large to be eaten, as the fish hunts by night and will take small invertebrates and fishes.
Conservation
Mastacembelus decorsei has not been formally assessed for the IUCN Red List and carries a status of Not Evaluated. Little is published on the species beyond its original description and basic distributional records in the Central African Republic, with extensions to the Chad and Niger basins.
Central African river systems face increasing pressure from habitat degradation, agricultural runoff, and artisanal and commercial fisheries, though the broad-basin distribution of this species across the Chad and Niger drainages suggests it is not immediately confined to a single threatened locality. Without a formal assessment, however, the true conservation picture remains unknown. Its absence from the ornamental trade means collection pressure is not a current concern, but data deficiency is itself a risk for a poorly-known species.