Taxonomy & naming
Mastacembelus sexdecimspinus was described by Roberts and Travers in 1986, placing it in the genus Mastacembelus, the type genus of the spiny-eel family Mastacembelidae. The Catalog of Fishes (Eschmeyer, the authority for valid names) recognises the name in Mastacembelus. The family Mastacembelidae sits within the order Synbranchiformes — the same order that contains the swamp eels (Synbranchidae) — and has no close relationship to the true eels of the order Anguilliformes. The eel-like body of Mastacembelus is convergent: it evolved independently for a burrowing, benthic way of life.
The genus Mastacembelus is large and spans both Africa and tropical Asia. African spiny eels were for many years partitioned into smaller genera — Aethiomastacembelus, Caecomastacembelus, Afromastacembelus — but modern treatments fold most of these back into Mastacembelus. The African members of the genus include species from West and Central African river systems as well as a notable species flock in Lake Tanganyika. The specific epithet sexdecimspinus is Latin, meaning "sixteen-spined," most likely referring to the count of isolated dorsal spines that characterise the species and give the spiny eels their common name. Detailed morphological data from the original description are not readily available in accessible sources, and the species remains data-sparse in secondary literature.
Morphology
Like other members of the genus Mastacembelus, this species has a greatly elongate, laterally compressed body covered in tiny embedded scales and a coat of mucus rather than obvious external scales — a feature that makes spiny eels sensitive to copper-based medications and abrasive handling. The snout is extended into the fleshy, trunk-like rostral organ tipped with tubular nostrils that is characteristic of the group, used to probe the substrate for food. Along the dorsal midline ahead of the soft dorsal fin runs a series of short, isolated spines — the "spiny" of spiny eel — and the dorsal and anal fins are continuous around the tapering tail.
Specific size data for Mastacembelus sexdecimspinus are not available in accessible sources, and the species is not annotated in secondary databases at the time of writing. Based on its placement in a group of small-to-medium Central African Mastacembelus and the pattern seen across the genus, it is likely a moderately sized spiny eel, but an authoritative maximum length cannot be stated without access to the original description or a reliable secondary source. Coloration and further morphological details are similarly data-sparse.
Habitat
Mastacembelus sexdecimspinus is a Central African freshwater species, as indicated by the Roberts and Travers (1986) description. The broader genus Mastacembelus in Central Africa occupies warm lowland rivers, streams, swamps and floodplain habitats, typically over soft substrates of sand and mud into which individuals burrow, often with only the head exposed. Water chemistry in these environments tends toward soft to circumneutral conditions, in keeping with the Congo basin and associated Central African drainages.
The precise type locality and detailed distributional data for this species are not accessible in available secondary sources. It has not been annotated on FishBase or widely treated in hobbyist literature, and its natural range within Central Africa must be considered uncertain based on current data. Like its congeners, it would be expected to favour sheltered microhabitats — submerged roots, leaf litter, soft sand — that provide cover during the day and hunting grounds at night.
Feeding
Mastacembelus sexdecimspinus is expected to share the carnivorous, benthic feeding strategy of the genus. Spiny eels are nocturnal hunters that use the sensitive fleshy snout to probe the substrate for prey: insect larvae, worms, small crustaceans and other benthic invertebrates form the core of the diet in the wild. The elongate body and downward-directed mouth are adaptations to hunting at and within the substrate rather than in open water.
No species-specific feeding observations are available in the accessible literature. In the aquarium, congeners are fed live and frozen invertebrates — bloodworm, earthworms, and similar meaty foods offered in the evening when the fish are naturally most active. Newly imported spiny eels frequently refuse food in daylight or while observed, and feeding after lights-out typically produces better results.
Mating
No mating observations specific to Mastacembelus sexdecimspinus have been published in accessible literature. Based on the biology of the family Mastacembelidae, this species is expected to be an egg-scattering spawner that breeds in fresh water — it is emphatically not a true eel and does not undergo the semelparous oceanic migration of Anguilla. In congeners, spawning is typically triggered by seasonal cues such as rising water levels and warming temperatures associated with the wet season, which mimics the flooding of marginal habitats.
Courting pairs of spiny eels have been observed circling and entwining among fine aquatic vegetation before scattering adhesive eggs, with no nest construction and no pair bond maintained beyond the spawn. Whether M. sexdecimspinus follows this pattern precisely is unknown, but the family-wide pattern of open-water egg-scattering with no parental investment is well established.
Breeding
Mastacembelus sexdecimspinus has not been bred in the aquarium hobby to any documented extent, and data on its reproduction are absent from the accessible literature. Its family-level breeding biology follows the typical spiny-eel pattern: eggs are adhesive and scattered among vegetation or root tangles in fresh water, there is no parental care, and the adults disperse after spawning. Eggs hatch in a few days under warm conditions, and the larvae are small and require fine first foods.
Most African spiny eels in the hobby, where they appear at all, are wild-caught imports. The combination of unclear provenance, data-sparse taxonomy and likely rarity in trade means that captive breeding programs for this species are essentially non-existent. Hobbyists wishing to attempt breeding any small Mastacembelus typically follow the approach used for other Central African congeners: a soft, deep sand substrate, caves and leaf litter, conditioning with live foods, and large water changes with slightly cooler water to simulate the onset of the rains.
In the aquarium
Mastacembelus sexdecimspinus is rarely encountered in the aquarium trade and is not a species routinely available through normal hobby channels. Should it be obtained — for example through specialist importers of rare African fish — care requirements would follow those of small-to-medium Central African Mastacembelus: a soft sand substrate deep enough for burrowing, caves and shaded retreats, dim lighting or well-planted cover, and meaty evening feedings. Like all spiny eels it is scaleless and acutely sensitive to copper-based medications; only copper-free treatments should be used in any tank housing this family.
Spiny eels are notorious escape artists: they climb, squeeze through tiny gaps, and can breathe at the surface for short periods, so a fully sealed lid with no openings is essential. Tankmates should be peaceful and large enough not to be swallowed; the species should not be kept with invertebrates it could predate. Water quality must be stable and well-oxygenated, as the lack of scales makes spiny eels more vulnerable to deteriorating conditions than scaled species of comparable size.
Conservation
Mastacembelus sexdecimspinus has not been assessed by the IUCN Red List at the time of writing. The species is poorly documented in secondary literature and its range, population size and ecology are not well quantified — all factors that typically result in a species remaining unassessed or being listed as Data Deficient when it is eventually reviewed.
Central African freshwater systems face significant and growing pressures from deforestation, agricultural runoff, artisanal mining (particularly in the Congo basin), and habitat degradation from expanding human settlement. Narrow-range or recently described Central African fish species are inherently vulnerable to local extinction even in the absence of formal threat assessments. Until a survey of the species' range and population status is carried out, its conservation needs cannot be meaningfully evaluated.