Taxonomy & naming
Enteromius melanotaenia was described by Melanie Stiassny in 1991 from material collected in the River Via, part of the St. Paul's River basin in Liberia. The original description placed it in the then-broadly-defined genus Barbus, which for most of the twentieth century served as a receptacle for small African and Eurasian cyprinids. Ongoing phylogenetic work on African small barbs has redistributed many of these species into Enteromius — a genus validated by Cope in 1867 but largely resurrected in modern usage — and that placement is followed here per the Catalog of Fishes (Eschmeyer, CAS), the authority for valid names.
The World Register of Marine Species (WoRMS) places Enteromius in the family Cyprinidae, subfamily Smiliogastrinae. African Enteromius form a large, species-rich assemblage across sub-Saharan Africa and differ considerably in their ecology, morphology and conservation status. Enteromius melanotaenia's combination of very small size, a strongly developed lateral stripe, and a highly restricted type locality distinguish it readily from congeners recorded elsewhere in the Upper Guinea coastal river systems.
Morphology
Enteromius melanotaenia is a small, slender cyprinid reaching a maximum of 1.5 in standard length (female). The dorsal fin carries 12 soft rays and the anal fin 8, counts in keeping with the diagnostic formula for the species as recorded by FishBase. The body is laterally compressed and moderately elongate, consistent with a fish that exploits the water column in slow and moderately flowing environments.
The species' most conspicuous feature is the broad, ribbon-like black lateral stripe from which its name derives — melanotaenia means "black-banded" in the original Greek. This stripe runs from behind the operculum along the full length of the lateral line to the base of the caudal fin, contrasting with a pale body. Beyond this defining mark, detailed colour descriptions are sparse in the available literature, and no account of sexual dichromatism or secondary sexual characters in males has been documented.
Habitat
The species is known from the River Via in the St. Paul's River basin, Liberia — a West African coastal drainage that descends through tropical forest and secondary vegetation to the Atlantic. FishBase categorises the species as a freshwater, benthopelagic fish of tropical Africa with a pelagic habitat association, suggesting it occupies the water column rather than being strictly benthic.
A closely related Enteromius species documented from West African forest streams by Seriously Fish inhabits shaded, slow-flowing streams over substrates of sand, gravel and leaf litter — an ecological template that fits the Upper Guinea forest rivers of Liberia well. Water temperatures in comparable West African forest streams typically fall between 22 and 79 °F, and chemistry tends toward soft, mildly acidic conditions under intact forest canopy. Precise physico-chemical data for the River Via itself are not documented in the available literature.
Feeding
No dedicated feeding study exists for Enteromius melanotaenia. Related West African Enteromius from comparable forest-stream habitats are documented feeding on small invertebrates — insect larvae, microcrustaceans and worms — as well as algae and organic detritus, reflecting the opportunistic omnivory typical of the genus across the continent.
The species' small adult size and a pelagic habitat category on FishBase suggest it targets zooplankton and fine particulate matter in the water column, supplemented by invertebrate prey picked from the surface of leaves and submerged wood. In the absence of published dietary data specific to this species, a cautious inference from congener ecology is the most honest account available.
Mating
No direct observation of spawning behaviour in Enteromius melanotaenia has been published. All barbs — including African Enteromius — are egg-scattering, non-guarding spawners. Courtship in the group follows a consistent pattern: males in breeding condition drive gravid females through vegetation or over the substrate, and eggs and milt are released in close contact. No nest is constructed, no territory is guarded beyond the brief act of courtship, and no pair bond persists after spawning.
Given the Critically Endangered status and the species' restriction to a single river, captive observations remain entirely absent from the literature. Analogues from West African forest-stream barbs suggest spawning may be linked to seasonal rainfall pulses that raise water levels and trigger peak reproductive condition, but no direct evidence is available for this species.
Breeding
Enteromius melanotaenia has not been bred in captivity, and no aquarium or research breeding account has been published. Like all barbs, it is an egg-scatterer that releases adhesive eggs over fine-leaved plants or onto the substrate with no parental care whatsoever. Adults would be expected to consume eggs opportunistically once spawning is complete, as is universal in the family.
The extremely restricted wild range and the difficulty of obtaining legal specimens mean that captive husbandry and controlled breeding remain unlikely in the foreseeable future outside of any future conservation programme specifically targeting the St. Paul's River basin fauna.
In the aquarium
Enteromius melanotaenia is not a hobbyist fish. It is not found in the ornamental trade, and its collection is both impractical and — given its Critically Endangered status — deeply problematic from a conservation standpoint. The species is of interest primarily to ichthyologists and conservation biologists rather than aquarists.
For completeness, a tank keeping analogous tiny West African forest-stream barbs would replicate soft, slightly acidic water at 72–79 °F, moderate filtration producing gentle flow, a dark substrate, shaded areas and fine-leaved plants. These parameters broadly describe the Upper Guinea forest-stream environment from which the species originates, but they are offered only as ecological context, not as a husbandry guide for a fish that should not be in the trade.
Conservation
Enteromius melanotaenia is assessed as Critically Endangered (CR) on the IUCN Red List. It is endemic to the River Via, a single tributary of the St. Paul's River basin in Liberia — a range so restricted that any significant disturbance to that catchment represents an existential threat to the species. The St. Paul's River and its tributaries flow through a region that experienced prolonged civil conflict, large-scale deforestation, artisanal and industrial mining, and substantial agricultural conversion during the late twentieth and early twenty-first centuries, all of which degrade freshwater habitat through sedimentation, chemical runoff and altered hydrology.
No targeted conservation measures for Enteromius melanotaenia are known to be in place, and the species is absent from formal captive-breeding programmes. Its conservation fate is tied to the broader protection of Liberia's remaining forest cover and the integrity of the St. Paul's basin catchment — a challenge that requires sustained national and international commitment to a country still recovering from decades of instability.