Taxonomy & naming
Enteromius stigmatopygus was originally described as Barbus stigmatopygus by Boulenger in 1903 — the type locality is the White Nile River in Sudan, and the description appeared in the Annals and Magazine of Natural History (Series 7, volume 12, issue 71). The old combination Barbus stigmatopygus persisted in the literature for most of the twentieth century; iNaturalist and other aggregators still cross-reference that name as the former valid combination.
The genus Enteromius, resurrected as a valid clade for many African small barbs within the broad revision of Smiliogastrinae, now holds the species under the Catalog of Fishes. Enteromius is a large and taxonomically complex assemblage of African cyprinids, and phylogenetic work has continued to refine the boundaries of the genus and the relationships among its many members. The placement of stigmatopygus in Enteromius — rather than the old Barbus — reflects current consensus, though the group as a whole is still under active systematic study.
Morphology
The midspot barb is a small, moderately slender cyprinid. Detailed published size data for the species are sparse, but members of the Enteromius assemblage in this size class typically reach 2.5–4 in in total length at maturity. The body is fusiform and laterally compressed in the manner of a typical river barb, with a pointed snout, a subterminal mouth suited to picking invertebrates from the substrate or water column, and a well-forked caudal fin.
The most distinctive external feature is the dark spot at the base of the anal fin, the marking encoded in the specific epithet stigmatopygus (see Etymology). Otherwise the fish is typically pale to silvery on the flanks with darker dorsal pigment — a cryptic pattern common to many African small-river barbs that spend time over sand and gravel substrates in open flowing water.
Habitat
Enteromius stigmatopygus is a benthopelagic, potamodromous species of freshwater rivers and streams across sub-Saharan Africa. Its documented range spans multiple large drainages — the Nile, Niger, Volta, Lake Chad basin and Bandama — a breadth that implies tolerance of a considerable variety of lotic habitats, from the broad, slow reaches of major river systems to smaller tributary streams.
The species is classed as potamodromous, meaning it undertakes migrations within freshwater rather than between fresh and salt water — a behaviour typical of seasonally flooding African river systems where fish move up into feeding or spawning areas with rising water and retreat to deeper permanent channels during the dry season. Specific water chemistry parameters for the wild range of this species are not well documented in the available literature; values will vary substantially across the wide geographic footprint.
Feeding
Like the majority of small African Enteromius, the midspot barb is an opportunistic omnivore. River barbs of this size class typically graze on small invertebrates — aquatic insect larvae, crustaceans, worms — algae and organic detritus picked from the substrate and from the surfaces of submerged vegetation and wood. The subterminal mouth position is consistent with a benthic-leaning foraging mode, though open-water feeding on drifting invertebrates is also typical of the group.
No detailed dietary study specific to E. stigmatopygus has been published in the accessible literature; the generalisation to African small-barb feeding ecology is the most defensible position given available data.
Mating
Enteromius stigmatopygus is an egg-scattering, non-guarding spawner in the manner of virtually all barbs. No nest is built, no territory is defended beyond brief courtship chasing, and no parental bond forms. In the wild the potamodromous habit of the species likely links spawning to seasonal cues — rising water, warming temperatures and increased food availability that accompany the flood pulse across the West and Central African river systems it inhabits.
Courtship follows the typical barb pattern: a driving male pursues a gravid female through vegetation or over the substrate, and the two release eggs and milt together in a brief, repeated spawning act. The adhesive eggs settle among plants or on the substrate; the adults take no further interest in them.
Breeding
Reproduction in E. stigmatopygus follows the egg-scattering mode universal among barbs. Eggs are scattered over plants, fine gravel or other substrate during courtship chases and receive no parental care whatsoever — adults will consume eggs and fry if given the opportunity. Fecundity for the species is not documented in detail in the accessible literature.
In an aquarium setting, spawning can be induced with the standard approach used for African small barbs: a separate, shallow spawning tank with fine-leaved plants or a spawning mop, soft slightly warm water, and well-conditioned adults fed generously on live or frozen foods beforehand. The adults should be removed after spawning to protect the eggs. Fry are raised initially on infusoria and then small live foods as they grow. The species is not commonly kept or bred in the hobby, and captive breeding accounts are sparse.
In the aquarium
The midspot barb is an uncommon species in the aquarium trade and is rarely encountered in hobbyist literature or specialist stocklists. It has no particular track record in captivity to draw on, and the practical recommendations that follow are extrapolated from the general care requirements of similar-sized African Enteromius and river barbs.
As a potamodromous, flowing-water fish, it would benefit from good filtration creating a moderate current, a spacious tank with open swimming areas alongside some plant cover, and a substrate of sand or fine gravel. A shoaling approach — keeping several individuals together — is appropriate for any small barb. Temperature should reflect tropical to subtropical West African river conditions. The species' diet in captivity would be straightforward: quality dry foods supplemented with small live or frozen invertebrates. Given the scarcity of data, aquarists keeping this species are encouraged to document their observations.
Conservation
Enteromius stigmatopygus is assessed as Least Concern (LC) on the IUCN Red List, with the assessment dated 2009. The population trend is recorded as unknown. The species' wide distribution across multiple large and relatively intact river systems in West and Central Africa — the Nile, Niger, Volta, Chad and Bandama drainages — underlies the Least Concern determination; no major range-wide threats are documented.
The broad geographic range does not, however, preclude localised pressure in parts of the species' distribution where river quality has deteriorated through agricultural runoff, deforestation, wetland drainage or overextraction of water. The potamodromous behaviour of the species also makes it potentially sensitive to barriers such as weirs and dams that interrupt migratory routes within freshwater. A reassessment using more recent survey data would provide a clearer picture of population status across the range.