Taxonomy & naming
Mastacembelus reygeli was described in 2009 by Emmanuel Vreven and Jos Snoeks, ichthyologists at the Royal Museum for Central Africa (MRAC) in Tervuren, Belgium. The type locality is the zone between 'La chute' 1 mi south of Rutungu and Magera, in Burundi on the western shore of Lake Tanganyika (3°44'S 29°21'E), and the holotype (MRAC 73-68-P-552) is held at MRAC. The species name honours Alain Reygel, an artist at that institution.
The Catalog of Fishes (Eschmeyer, CAS) records it in Mastacembelus, the type genus of the family Mastacembelidae. African spiny eels were historically shuffled among segregate genera — Aethiomastacembelus, Caecomastacembelus, Afromastacembelus — before being synonymised back into Mastacembelus; M. reygeli has always been placed in Mastacembelus with no recorded old combinations. No synonyms are known.
The fish is a spiny eel, order Synbranchiformes, and is not a true eel by any phylogenetic measure. The true eels belong to the order Anguilliformes; the elongate body of Mastacembelus is the product of convergent evolution toward a burrowing, benthic lifestyle in fresh water, not of shared ancestry with marine eels.
Morphology
Mastacembelus reygeli reaches a maximum recorded length of approximately 10 in standard length. The body is greatly elongate and sinuous in the manner of all spiny eels, with the skin scaleless in appearance, coated in mucus, and carrying only tiny embedded scales. The snout is drawn forward into the fleshy, trunk-like rostral organ characteristic of the genus — a sensory probe used to explore the substrate. Ahead of the soft dorsal fin runs a row of isolated dorsal spines, the defining character of the spiny eels; fin counts recorded for the species are 34–38 dorsal spines, 54–70 dorsal soft rays, 3 anal spines, and 56–71 anal soft rays, with 78–83 vertebrae.
As with most Tanganyikan Mastacembelus, the colouration is not documented in detail in published sources; the species was described from preserved material and specific live colouration data are sparse. The body form and proportions place it within the large and diverse Tanganyika radiation of the genus, a group that has colonised and diversified across the lake's varied rocky and sandy shorelines.
Habitat
Mastacembelus reygeli is endemic to Lake Tanganyika, known from the stretch between Kalemie in the Democratic Republic of Congo and Kigoma in Tanzania — a range spanning the central-eastern and central-western shore of the lake. FishBase records it as benthopelagic at depths of 0–33 ft, suggesting it inhabits the shallowest nearshore zone, likely among rocks, sand, and organic debris along the lake margin.
Lake Tanganyika is a rift lake with chemical properties entirely unlike the soft, acidic rivers occupied by many tropical spiny eels. The lake is alkaline throughout — pH 8.3–9.0, highest near the surface — and hard, with GH 16–18 °dGH and KH 7–11 °dKH. Water temperature ranges from roughly 75 °F during the austral winter (southern regions, August) to 82–84 °F during the rainy season (March). The water is highly oxygenated and exceptionally clear in the littoral zone. Mastacembelus reygeli is adapted to these conditions and should not be kept in the soft, acidic parameters suited to Asian spiny eels.
Feeding
No species-specific feeding study exists for Mastacembelus reygeli. By analogy with the broader genus and with other small Tanganyikan spiny eels, it is presumed to be a nocturnal or crepuscular benthic carnivore that uses the fleshy rostral organ to probe crevices and sediment for invertebrates — insect larvae, small crustaceans, worms — and possibly very small fishes.
In any aquarium setting, meaty benthic foods offered in the evening — bloodworm, small earthworm pieces, and live or frozen invertebrates — would match the natural feeding ecology. Like all Mastacembelus it would be expected to ignore prepared foods initially and to compete poorly with fast or aggressive tankmates at feeding time.
Mating
Mastacembelus reygeli is a spiny eel and, like all members of the family Mastacembelidae, is an egg-scatterer that gives no parental care. It breeds in fresh water; it is not catadromous and does not undertake any marine migration. No wild courtship observations are on record for this species specifically.
In other Mastacembelus species, courtship involves a pair circling and entwining among submerged vegetation or root masses before scattering adhesive eggs. Spawning in the broader genus appears to be triggered by seasonal cues — rising water temperature, increased rainfall, or changes in water chemistry — that in Tanganyika translate to the annual thermal and storm cycles of the rift basin rather than the monsoon rains of the Asian relatives.
Breeding
Spiny eels of the genus Mastacembelus scatter adhesive eggs among fine-leaved plants, root masses, or leaf litter; the eggs are non-floating and have been described in related species as light brown and 0.5 in in diameter. No parental care follows: the adults take no further interest in the eggs or larvae after spawning.
Mastacembelus reygeli has not been reported as bred in the home aquarium, and given its recent scientific description and limited distribution within a specialist rift-lake community, captive breeding accounts are essentially absent. Its rift-lake water requirements — high pH, hard water, warm temperatures — add a layer of difficulty compared to the soft-water spiny eels most hobbyists work with. Any attempt would need to replicate Tanganyikan conditions faithfully and provide suitable egg-deposition structure such as fine-leaved plants or moss.
In the aquarium
Mastacembelus reygeli is not an established aquarium fish and is rarely if ever seen in trade. As a Tanganyikan endemic its husbandry demands parallel those of the lake's cichlid community rather than the soft-water Southeast Asian spiny eel set-up most keepers know: hard, alkaline water (pH 8.3–9.0, GH 16–18), stable warm temperatures (75–84 °F), excellent oxygenation and filtration, and careful attention to water quality. It should never be kept in soft or acidic conditions.
Like all spiny eels it is scaleless and therefore highly sensitive to copper-based medications and to dissolved toxins; any treatment in the same system must be copper-free. It would require a soft sand substrate deep enough to burrow into, caves and crevices for daytime shelter, and meaty evening feeds. The most critical point of husbandry for any Mastacembelus is a tight, fully sealed lid: spiny eels are consummate escape artists, able to push through the smallest gap and capable of breathing air briefly as they move across moist surfaces — a fish found on the floor overnight will not survive. Given its small adult size (to roughly 10 in SL) and specialist water requirements, it is best housed in a dedicated Tanganyikan setup with compatible benthic species.
Conservation
Mastacembelus reygeli has not been evaluated by the IUCN Red List; it carries a status of Not Evaluated (NE). The species was described only in 2009 and inhabits a relatively narrow coastal strip of Lake Tanganyika between Kalemie, DRC, and Kigoma, Tanzania — a range that spans two countries with different conservation frameworks.
Lake Tanganyika faces significant pressure from overfishing, sedimentation driven by catchment deforestation, and climate-linked warming and deoxygenation of deeper water layers. Endemic species with restricted distributions, such as M. reygeli, are inherently more vulnerable to these pressures than widespread generalists. The species has not been assessed at all, meaning its population status is entirely unknown; a formal evaluation, particularly given its limited endemic range, would be a worthwhile step for the researchers who work on the lake's extraordinary biodiversity.