Taxonomy & naming
Mastacembelus trispinosus was described by Franz Steindachner in 1911 from specimens collected at the Ituriflusse bei Mawambi — the Ituri River near Mawambi — in the northeastern Congo Basin. The Catalog of Fishes (Eschmeyer, the authority for valid names) places it in the genus Mastacembelus, the type genus of the family Mastacembelidae within the order Synbranchiformes. This order also contains the swamp eels, and despite the common name 'eel' the spiny eels share no close evolutionary relationship with the true eels of the order Anguilliformes; their elongated, burrowing body plan evolved independently.
African spiny eels have experienced considerable generic-level churn: older literature placed many Congo Basin species in the separate genera Aethiomastacembelus and Afromastacembelus, and M. trispinosus was cited under both combinations. A further African segregate, Caecomastacembelus, was also placed in synonymy with Mastacembelus in post-2005 revisions. The current valid name Mastacembelus trispinosus is the result of that consolidation. The specific epithet trispinosus is Latin for 'three-spined', most likely alluding to a distinctive feature of the dorsal-spine series.
Morphology
Mastacembelus trispinosus reaches a recorded maximum of 13 in total length, placing it among the smaller members of its genus. Like all spiny eels it has a greatly elongated, laterally compressed body, covered not in the obvious scales of typical bony fishes but in a layer of small embedded scales overlaid with mucus. The snout is produced into the characteristic fleshy, tubular proboscis of the mastacembelids, bearing paired nostrils used to probe soft substrate for food. Along the anterior dorsum runs the row of short, isolated dorsal spines that gives the family its common name, followed by a continuous soft dorsal fin that merges around the tapered tail with the anal fin.
Detailed colour descriptions for this species are not available in the published literature, and its appearance is not well documented in aquarium or field sources. In the absence of reliable morphological data beyond size and general body plan, precise details of colour pattern remain unknown and are not speculated upon here.
Habitat
The only known collection locality for Mastacembelus trispinosus is the Ituri River system of the northeastern Democratic Republic of Congo, in the Congo Basin drainage. The Ituri flows through equatorial rainforest at relatively low elevation, and like most Congo Basin rivers it carries warm, typically soft and slightly acidic to neutral water typical of large tropical lowland river systems.
Based on the habitat preferences of congeners from similar river systems, the species likely inhabits slow to moderate riverine reaches with soft substrates of sand, silt and leaf litter, burrowing during daylight hours and emerging to forage at night. Beyond the type locality, no field surveys documenting habitat associations for this species appear to have been published, and data on its distribution within the wider Ituri or Congo Basin remain very sparse.
Feeding
Mastacembelus trispinosus has not been studied in terms of diet, but the morphological toolkit shared by all spiny eels — the sensitive, downward-pointing probing snout and elongate benthic body — is well adapted for hunting invertebrates along and within soft substrates at night. In closely related African Mastacembelus, the diet consists mainly of benthic invertebrates including insect larvae, worms and small crustaceans, and occasionally small fishes.
In any aquarium setting, feeding meaty foods of appropriate size in the evening, after lights dim, is consistent with the nocturnal foraging habits common to all mastacembelids. Given the small size of this species (maximum around 13 in) food items should be scaled accordingly — bloodworm, chopped earthworm, and small frozen invertebrates are appropriate.
Mating
No observations of mating behaviour in Mastacembelus trispinosus are recorded in the literature. As a member of Mastacembelidae, it is a freshwater egg-scatterer and is not a true eel; it does not undertake any migratory spawning journey to the sea. In the wild, spawning in African spiny eels is thought to be triggered by seasonal cues — the rising water levels and temperature changes associated with wet-season flooding — when adult fish move into flooded marginal areas with dense vegetation.
In the related and better-studied spiny eels, a courting pair entwine and circle among plants before scattering small, adhesive eggs over the substrate, roots, or leaf litter. There is no nest construction and no pair bond beyond the act of spawning itself.
Breeding
No captive breeding records for Mastacembelus trispinosus are known, and the species is essentially unrepresented in the aquarium trade. Based on the pattern documented across the family Mastacembelidae, the breeding mode is substrate egg-scattering: adhesive eggs are scattered among vegetation, roots, or leaf litter in fresh water, and neither parent attends the eggs or larvae. The eggs hatch after a few days and the larvae are small and require fine live foods.
For the wider genus, captive spawnings remain rare because the combination of adult-sized tank requirements, difficulty in conditioning and sexing a compatible pair, and the need for seasonal-mimicking water changes all stand in the way. There is no parental care, no bubble-nest, and no mouthbrooding — the adults play no role beyond fertilisation.
In the aquarium
Mastacembelus trispinosus is essentially unknown in the aquarium hobby and is not available in normal trade. It is known only from scientific material collected from the Ituri River, and no care accounts have been documented. General principles applicable to small African Mastacembelus would apply: a fully sealed aquarium is mandatory, as all spiny eels are escape artists capable of squeezing through the smallest gaps; a deep layer of soft sand is needed for the burrowing behaviour essential to the fish's welfare; and dim, naturalistic lighting with ample cover in the form of driftwood, leaf litter and caves accommodates the nocturnal lifestyle.
Like all mastacembelids, this species is scaleless and therefore sensitive to copper-based medications and to deteriorating water quality. It should be housed with peaceful tankmates that cannot be swallowed, and food should be offered in the evening. Any hobbyist who encounters this species should treat it as a rare, data-sparse import and document care conditions carefully.
Conservation
Mastacembelus trispinosus has not been formally assessed by the IUCN Red List and its conservation status is Not Evaluated. The species is documented only from a single collection locality — the Ituri River near Mawambi in the northeastern Democratic Republic of Congo — and no subsequent surveys appear to have confirmed additional populations or clarified its range within the broader Congo Basin.
The Congo Basin is one of the world's most biodiverse and hydrologically significant river systems, but it faces growing pressure from artisanal and industrial mining, logging, and agricultural expansion, particularly in the Ituri region. A species with a known range of a single river locality and no recent records is inherently vulnerable to these pressures, but the absence of any assessment means that neither the population size nor the trend is known. Given the data deficit and restricted known range, a future IUCN evaluation would likely consider a Data Deficient listing as a minimum starting point.