Taxonomy & naming
Mastacembelus brachyrhinus was described by George Albert Boulenger in 1899. It belongs to the family Mastacembelidae and the order Synbranchiformes — the same order that contains the swamp eels (Synbranchidae), not the true eels of the Anguilliformes. The eel-like body plan is convergent, not a shared ancestry with Anguilla.
The species was for many years assigned to the African segregate genus Caecomastacembelus under the combination Caecomastacembelus brachyrhinus, before molecular phylogenetic work on African Mastacembelidae collapsed Caecomastacembelus and the related Aethiomastacembelus back into the broader genus Mastacembelus. The Catalog of Fishes (Eschmeyer, CAS) records the current valid name as Mastacembelus brachyrhinus (Boulenger, 1899). The epithet brachyrhinus is Greek for 'short-nosed' (brachys, short; rhinos, nose/snout), apparently describing the proportionally abbreviated rostral proboscis relative to some congeners.
The genus Mastacembelus is diverse across tropical Africa and Asia; the African species flock is especially rich in the Congo Basin and in the East African rift lakes. M. brachyrhinus sits within the African group, likely allied to the Lower Congo or adjacent river drainages based on its type locality and phylogenetic placement.
Morphology
Mastacembelus brachyrhinus is a small spiny eel reaching a maximum of approximately 6.5 in in standard length (SL), making it one of the more compact African members of the genus. FishBase records 78 vertebrae, reflecting the elongate body plan shared across Mastacembelidae. Like all spiny eels the body is greatly elongate and laterally compressed toward the tail, with a continuous dorsal-anal fin running around the rear of the body.
The snout terminates in the characteristic fleshy rostral proboscis of the spiny eels, used to probe the substrate for food, though in M. brachyrhinus this projection is proportionally shorter than in some larger congeners — a feature likely referenced in the species epithet. The skin is scaleless to the eye, protected by a heavy mucus coat. A row of short, isolated dorsal spines precedes the soft dorsal fin. Specific data on coloration in life are sparse in the literature, but African Mastacembelus of riverine origin are typically brown to olive-brown on the back and flanks, paler ventrally.
Habitat
Mastacembelus brachyrhinus is an African freshwater fish associated with Congo drainage river systems. It inhabits the typical Mastacembelid biotope of lowland freshwater rivers, streams and floodplain habitats, where it buries into soft substrates of sand and mud and shelters among submerged roots, leaf litter and debris. Like its congeners it is largely nocturnal, most active after dark.
Water parameters for M. brachyrhinus are not extensively published, but the broader genus in West and Central African river systems generally tolerates warm soft-to-neutral water: temperatures in the mid-to-upper 20s Celsius and pH in the 6.0–7.5 range are characteristic of Congo-basin tributaries. The species is scaleless and shares the family-wide sensitivity to copper and to deteriorating water quality.
Feeding
Like other African spiny eels, Mastacembelus brachyrhinus is a nocturnal benthic carnivore. It uses its fleshy rostral proboscis to probe the substrate for small invertebrates — insect larvae, worms, and small crustaceans — which it locates by scent and tactile sensation in low-light conditions.
In the aquarium, such species accept a diet of bloodworm, small earthworms, and other meaty invertebrate foods offered in the evening after lights dim. Its small adult size means prey items should be appropriately sized. Competition from faster or more aggressive tankmates at feeding time should be avoided.
Mating
Mastacembelus brachyrhinus is a spiny eel and, as such, an egg-scattering spawner in fresh water. It is not a true eel and does not undertake the long-distance marine migration of catadromous Anguilla species; it breeds entirely in freshwater habitats. No dedicated field or aquarium observations of M. brachyrhinus courtship have been documented in the accessible literature.
Based on the biology of the Mastacembelidae family as a whole, spawning is presumed to be triggered by seasonal environmental cues such as rising water temperature, increased rainfall and flooding associated with the wet season. A courting pair would be expected to entwine and scatter adhesive eggs among fine vegetation, roots or leaf litter, with no pair bond maintained afterward.
Breeding
Mastacembelus brachyrhinus has not been documented as successfully bred in the home aquarium, and it is unlikely to appear in the trade with any regularity. African spiny eels as a group are rarely bred in captivity: their requirements for large, mature set-ups, difficulty of sexing, and the triggering role of seasonal water changes (cooler, rain-mimicking top-up water) make accidental or deliberate spawning uncommon.
Where captive spawning of Mastacembelus has been documented in related species, eggs are small and adhesive, hatching in a few days, with the resulting larvae requiring very fine first foods. There is no parental care: eggs and larvae are entirely on their own once scattered. Given the scarcity of M. brachyrhinus in the hobby and the absence of breeding accounts, the species should be assumed difficult to breed in the aquarium.
In the aquarium
Mastacembelus brachyrhinus is a seldom-seen African spiny eel that, at roughly 6.5 in adult size, is one of the few Mastacembelus genuinely manageable in a modestly-sized tank — though it still requires considered care. A tank of 23.5–35.5 in with a deep bed of fine sand for burrowing, multiple caves and shaded retreats, and stable, well-filtered water is appropriate. It is scaleless and sensitive to copper-based medications and to organic pollution; a mature, cycled system is essential.
Like all spiny eels it is an escape artist of the highest order. Even a small individual can squeeze through surprisingly tight gaps, climb silting, and exit an inadequately covered tank; a sealed, weighted lid with no gaps is mandatory. It is nocturnal and will hide by day, emerging to forage after dark, so evening or post-lights-out feeding is advisable. Tankmates should be peaceful and too large to be swallowed. Very little aquarium husbandry literature exists specifically for this species, so care guidance should be extrapolated from the broader genus.
Conservation
Mastacembelus brachyrhinus is assessed as Least Concern on the IUCN Red List (2020.2 assessment). The assessment indicates no evidence of a range-wide population decline sufficient to approach threatened thresholds.
The Congo Basin and adjacent West/Central African river systems that the species inhabits are broadly intact across much of their extent, though they face increasing pressure from artisanal mining, deforestation, and hydrological modification in some areas. As a small-bodied species with no recorded presence in the ornamental trade at scale, it is unlikely to face significant collection pressure. Its status as Least Concern reflects an adequate population across its range, but continued monitoring of Congo-region freshwater biodiversity is warranted given the pace of land-use change in the region.