Taxonomy & naming
Mastacembelus cunningtoni was described by the Belgian–British ichthyologist George Albert Boulenger in 1906, based on material collected during William Alfred Cunnington's 1904–1905 zoological survey of Lake Tanganyika — the expedition that produced the type specimen. The Catalog of Fishes (Eschmeyer, the authority for valid names) places the species in the genus Mastacembelus, the type genus of the family Mastacembelidae within the order Synbranchiformes. This is a critical distinction: the fish is not a true eel. True eels — Anguilla and its relatives — belong to the order Anguilliformes; the spiny eels of the Mastacembelidae are not closely related to them, and their elongate, sinuous body is a product of convergence on a burrowing way of life rather than any common heritage with the marine eels.
The African members of Mastacembelus were for many years divided among segregate genera including Aethiomastacembelus, Caecomastacembelus and Afromastacembelus. These have largely been folded back into the broad Mastacembelus as currently recognised by the Catalog of Fishes. M. cunningtoni sits within the Lake Tanganyika species flock — a group of spiny eels that radiated within the rift lake just as cichlids did — and has 89 vertebrae recorded for the species, a meristic detail noted in FishBase.
Morphology
Mastacembelus cunningtoni reaches a maximum recorded length of 23 in total length (TL), making it one of the larger spiny eels in the Tanganyikan flock. The body is greatly elongate and strongly compressed toward the tail, outwardly scaleless — the tiny embedded scales are concealed under a layer of mucus — and bears the distinctive row of isolated short dorsal spines ahead of the soft dorsal fin that gives the family its common name. The fleshy, trunk-like proboscis characteristic of the genus tips the snout, housing paired tubular nostrils used to probe the substrate.
The soft dorsal and anal fins run continuously around the tapered tail in the typical mastacembelid fashion. No detailed coloration description from confirmed field or museum data is available in the sources consulted, but African rift-lake spiny eels are generally cryptically patterned in browns and tawny hues suited to blending with rocky and sandy lake margins. Ripe females are likely fuller-bodied than males, as in other members of the genus, but no formal description of sexual dimorphism is recorded for this species.
Habitat
The species is endemic to the Lake Tanganyika basin, the deepest lake in Africa and the second-deepest in the world. Its recorded range extends from the lake itself into the Lukuga River — the sole outflow — downstream as far as the Kisimba-Kilia rapids, which represent a dispersal barrier. It occurs across parts of all four countries bordering the lake: Burundi, the Democratic Republic of the Congo, Tanzania, and Zambia.
Within the lake it occupies the littoral zone, living over rocky, sandy and muddy bottoms in shallow to moderately deep water. Unlike the soft, slightly acidic lowland rivers that many Asian Mastacembelus species inhabit, Lake Tanganyika is hard and distinctly alkaline — pH values of 8.6–9.0 are typical, water hardness is high, and dissolved oxygen is abundant in the surface and littoral waters. M. cunningtoni is adapted to these stable, chemically demanding conditions. The lake's thermal regime is warm year-round, with surface temperatures broadly in the 75–82 °F range, falling slightly in the cool austral winter.
Feeding
Like other mastacembelids, M. cunningtoni is a benthic carnivore that uses its probing, sensitive snout to locate prey within and on the substrate. In the littoral habitats of Lake Tanganyika it likely forages on invertebrates — insect larvae, crustaceans, worms and molluscs — and potentially small fishes, hunting mostly at night in the manner typical of the family.
No specific feeding observations or stomach-content studies for this species are recorded in the sources available. Given its size — up to 23 in — and habitat, it is plausible that small cichlids and other benthic prey enter the diet when available, as observed in comparably-sized African spiny eels from other systems. Its fleshy rostral proboscis and downturned mouth are the anatomical signatures of a substrate probe-feeder rather than a pursuit predator in open water.
Mating
Mastacembelus cunningtoni is a spiny eel, and spiny eels are substrate egg-scattering spawners that give no parental care. This species is not a true eel and does not undertake any catadromous spawning migration; it breeds in fresh or rift-lake water. No specific mating observations have been published for M. cunningtoni, and no captive spawnings are recorded in the literature consulted.
By analogy with the broader genus and with other African Mastacembelus from lake and river systems, spawning is likely triggered by seasonal cues — changes in water temperature, day length, or the inflow of river water during wet periods — and probably involves a courting pair that scatter adhesive eggs among rocky crevices, vegetation, or substrate debris in the littoral zone. No nest is built and no pair bond persists beyond spawning.
Breeding
No captive breeding of Mastacembelus cunningtoni is recorded in the hobbyist or scientific literature consulted. It is not maintained widely in the aquarium trade or in public aquariums as a breeding project, and the demanding water chemistry of Lake Tanganyika adds an additional barrier beyond the usual difficulties of inducing mastacembelid spawning in captivity.
For the family in general, the breeding mode is scatter-spawning: a pair releases adhesive eggs among vegetation, roots, or rocky crevices, the adults provide no further care, and the eggs hatch within a few days at tropical temperatures. The larvae require very fine live foods initially. Given the combination of specialist water chemistry, adult size, and the absence of a captive-breeding tradition for this species, M. cunningtoni must be considered extremely rarely if ever bred outside its native lake.
In the aquarium
Mastacembelus cunningtoni is an uncommon species in the hobby, encountered occasionally in specialist Tanganyika cichlid circles rather than in general tropical fish retail. Any keeper attempting to maintain it must replicate the lake's distinctive chemistry: hard, alkaline water with a pH in the 8.0–9.0 range, high carbonate hardness, stable temperatures around 75–79 °F, and excellent oxygenation — the opposite of the soft, acidic conditions suited to Asian spiny eels like the fire eel.
Like all spiny eels it is scaleless and highly sensitive to copper-based medications and to organic pollution; water quality must be impeccable. It is a burrower and needs a fine sandy substrate and plenty of rocky caves and crevices to shelter in during the day. It is principally nocturnal and should be fed meaty foods — worms, crustaceans, sinking carnivore pellets — after lights-out. A tight-fitting, fully sealed lid is non-negotiable: mastacembelids are notorious escape artists that can climb out of the smallest gap and will die on the floor overnight. Given its 23 in potential size, a large, mature aquarium of at least 59 in length is needed for an adult, combined with compatible Tanganyikan tankmates robust enough not to be swallowed.
Conservation
Mastacembelus cunningtoni is assessed as Least Concern on the IUCN Red List (assessment version 2022.2). The basis for this assessment is the species' apparent wide distribution through the Lake Tanganyika basin, and the lack of evidence of rapid population decline. The lake itself, however, faces real and growing pressure: sedimentation from deforestation in the surrounding catchment, overfishing of littoral communities including cichlids and associated species, and the long-term threat of climate-driven warming to the lake's thermal stratification and oxygen distribution.
As an endemic confined to a single lake basin — with the Lukuga River outflow representing a small secondary range extension — M. cunningtoni has no refugia outside its native system. Any large-scale deterioration of Lake Tanganyika's littoral habitat or water quality could affect it and the broader spiny-eel flock. The species is not known to be a significant target of fisheries, but bycatch in artisanal nets operating in the littoral zone is plausible given its habitat overlap with commercially fished cichlid assemblages.