Taxonomy & naming
Enteromius roussellei was described by Ladiges and Voelker in 1961 and was originally placed in the genus Barbus, the traditional catch-all for African and Eurasian barbs. The parenthetical authority in the current name, (Ladiges & Voelker, 1961), records that move: the species now sits within Enteromius, a large genus erected to accommodate the African radiation of small barbs that were progressively separated from the paraphyletic Barbus sensu lato in the light of phylogenetic work. The Catalog of Fishes (Eschmeyer, CAS) is the governing authority for valid names within this group.
Enteromius is a sprawling African genus whose boundaries and internal arrangement remain subjects of ongoing revision; many species are known only from their original descriptions and a handful of museum specimens. Roussellei appears to fall into this category — data on it in the scientific literature is scarce, and it has not featured in major revisions of West African cyprinids to the extent that would bring it wider attention. The epithet honours a person (Rousselle), following a long tradition in ichthyological nomenclature of naming species for collectors, patrons or collaborators.
Morphology
Detailed morphological data for Enteromius roussellei is not available in the accessible literature. Based on its placement in Enteromius and the Ladiges and Voelker (1961) description context, it is expected to be a small, modestly deep-bodied barb with the standard cyprinid complement of a forked tail, a single dorsal fin, paired pectoral and pelvic fins, and a toothless mouth equipped with pharyngeal teeth for processing plant and invertebrate material.
Small West African Enteromius typically reach 1.5–3 in in total length, have silvery to olive-bronze flanks sometimes marked with a lateral stripe or spot pattern, and may show orange or yellow tints on the fins — but without direct examination of type material or published figures these specifics cannot be confirmed for this species. Data are sparse.
Habitat
The precise type locality of Enteromius roussellei is not recorded in the accessible literature, though the authorship context — German ichthyologists working in the late 1950s and early 1960s — is consistent with collection from West or Central Africa, regions actively surveyed by German-speaking workers at that period. Small Enteromius in those regions typically inhabit forest-margin streams, savanna waterways, and tributary headwaters where water is soft to moderately hard and temperatures range across the warm tropical band of roughly 72–79 °F.
Many congeners are found in seasonal floodplain habitats or perennial headwater streams with clear to lightly turbid water, substrates of sand, gravel, or leaf litter, and varying amounts of riparian shade. Without a confirmed locality, the precise water chemistry and habitat structure for E. roussellei cannot be stated with confidence.
Feeding
No feeding data specific to Enteromius roussellei has been published. Small African Enteromius are broadly omnivorous, consuming a mix of algal biofilm, diatoms, detritus, aquatic insect larvae, microcrustaceans and other invertebrates picked from the substrate or water column. The species' small body size and the shallow, productive stream habitats typically occupied by the genus suggest a similar generalist diet.
In an aquarium setting, congeners are reliably fed on good-quality flakes and small pellets supplemented with live or frozen items such as daphnia, bloodworm and brine shrimp nauplii, and occasional vegetable material.
Mating
No courtship or spawning observations have been published for Enteromius roussellei. Like all barbs, it is expected to be an egg-scattering, non-guarding spawner. Spawning in small African Enteromius is typically prompted by a combination of seasonal water warming, rising water levels associated with rainfall, and increased food availability.
A driving male pursues a gravid female through vegetation or over the substrate; the pair press together briefly and release eggs and milt simultaneously. No pair bond is formed, no nest is built, and no territory is defended beyond the brief act of courtship. Adults — including the spawning pair — will eat the eggs immediately if given the opportunity.
Breeding
Enteromius roussellei has not been bred in captivity to the knowledge of the published aquarium literature, and no hobbyist breeding accounts were located. Based on the reproductive biology common to the genus, spawning would involve scattered adhesive eggs deposited among fine-leaved plants, roots or over a gravel substrate, with no parental care whatsoever.
In congeners that have been bred experimentally, a separate shallow spawning tank with soft, slightly acidic water, a mesh or fine-plant layer to protect eggs from the parents, and conditioning on live foods prior to introduction of a pair or small group has proved effective. Clutch sizes, incubation periods and larval development data are unavailable for this species.
In the aquarium
Enteromius roussellei does not appear in the mainstream aquarium trade and has not been documented in hobbyist literature. It would, if available, be expected to suit conditions typical of small West African barbs: a warm, well-filtered aquarium in the 72–79 °F range, broadly neutral to slightly acidic pH, and soft to moderately hard water. A shoal of at least six individuals would reduce inter-fish stress, as is standard practice for small schooling barbs.
Small Enteromius are generally peaceful community fish compatible with similarly sized, non-aggressive species. Their diet would be straightforward — standard small-barb fare of flakes, micropellets, and frozen invertebrates. The absence of this species from the trade means practical aquarium data remain unavailable.
Conservation
Enteromius roussellei has not been evaluated by the IUCN Red List; it carries Not Evaluated (NE) status. This is a common situation for the many small, regionally obscure African barbs that have not attracted sufficient scientific attention for a formal conservation assessment.
The pressures facing small endemic African cyprinids are well-documented at the regional level: deforestation and land clearance for agriculture, damming and water extraction from river headwaters, sedimentation from poor catchment management, and localised pollution from mining and agriculture. Species with restricted ranges — particularly single-river or single-basin endemics — are inherently vulnerable to these pressures even without formal recognition of their status. Until the type locality and current range of E. roussellei are confirmed and the species is revisited in a modern ichthyological survey, its conservation standing must remain unresolved.