Taxonomy & naming
Enteromius sylvaticus was described by Paul V. Loiselle and Robin L. Welcomme in 1971. The original description placed it in the genus Barbus — the sprawling catch-all that once contained most of the world's small carps — under the combination Barbus sylvaticus, and older literature and museum records will be found under that name. Following a succession of revisions that progressively dismembered the polyphyletic Barbus, the species is now assigned to Enteromius, the genus that accommodates the majority of small sub-Saharan African barbs. The Catalog of Fishes (Eschmeyer, California Academy of Sciences), the governing authority for valid names used here, confirms the current combination as Enteromius sylvaticus (Loiselle & Welcomme, 1971).
The specific epithet sylvaticus is Latin for "of the woods" or "forest-dwelling", a reference to the forested stream environment of the type locality, the Ignidi River at Lagbe in Benin. No common names are in wide circulation for this species in the aquarium trade or the scientific literature; it is known almost entirely from museum material and field surveys.
Morphology
Enteromius sylvaticus is a dwarf barb, with a maximum recorded size of 0.5 in standard length — placing it among the smallest of the African Enteromius. The body is benthopelagic in habit and typical of the genus in general proportions: fusiform and moderately compressed, suited to life in open water close to the bottom and among vegetation. The species lacks barbels entirely, which distinguishes it from many larger African barbs.
The scale formula runs to 20–23 scales in the longitudinal series, with 8–9 scales around the caudal peduncle. The dorsal fin has a smooth (unserrated) last simple ray on its hind margin and carries 7 branched rays, a combination consistent with the broader Enteromius diagnosis. Specific coloration details are not captured in the available literature, which is based primarily on preserved specimens; the live colour pattern has not been formally documented in accessible sources.
Habitat
The type locality of Enteromius sylvaticus is the Ignidi River at Lagbe in southern Benin, a small watercourse draining into the coastal plain near the Bight of Benin. The species is also known from the lower Niger Delta in Nigeria, indicating it occupies tropical freshwaters of the Guinea–Nigeria coastal lowlands. These are warm environments; FishBase records a temperature range of approximately 72–77 °F for the species, with some habitat data suggesting up to 79 °F in the warmer season.
The "forest" element of the name points to shaded, vegetated stream habitat — likely slower-moving reaches with leaf litter, submerged roots and aquatic vegetation providing cover for a schooling dwarf fish. Water quality in such environments is typically soft to moderately mineralised and slightly acidic to neutral. The species is noted as sensitive to abrupt parameter changes and elevated nitrogenous compounds; FishBase records that nitrate should remain below 25 mg/L for maintained animals.
Feeding
No detailed dietary study of Enteromius sylvaticus has been published in the accessible literature. By analogy with other small, benthopelagic Enteromius from West African forest streams, it almost certainly feeds as a micro-omnivore: picking small invertebrates — midge larvae, microcrustaceans, worms — from the substrate and the water column, supplemented with algae, detritus and organic particles.
The shoaling habit recorded for the species is consistent with active, constant foraging in the open water close to the bottom, scanning substrate and vegetation for small prey items. In aquarium conditions such dwarf barbs typically accept fine-particle commercial foods readily, though their very small adult size means appropriately sized food particles are essential.
Mating
Like all barbs, Enteromius sylvaticus is an egg-scattering, non-guarding spawner. No parental bond or territory is maintained, and there is no nest-building of any kind. In related small African Enteromius, a ready male pursues a gravid female through vegetation or over the substrate, pressing close as eggs and milt are released together. Eggs are adhesive and fall into fine-leaved plants or substrate interstices where — absent the adults — they develop unattended.
The species has not been spawned under controlled conditions in the literature available, so specifics of courtship coloration or behaviour at this scale are not documented. Given its minimal size at maturity (maximum 0.5 in SL), breeding groups would presumably consist of multiple individuals spawning as a loose school rather than a single pair.
Breeding
No captive breeding account for Enteromius sylvaticus has been documented in accessible hobby or scientific literature — this is an essentially unknown fish in the aquarium trade, and almost all records come from field collections and museum specimens. Inferences from the biology of comparable dwarf African Enteromius suggest it would scatter small adhesive eggs among fine vegetation or onto the substrate, with no parental care whatsoever; adults are likely to consume eggs given the opportunity, as is typical across the barb tribe.
Any serious attempt to maintain and breed this species would require appropriately small live or frozen foods, very gentle filtration, and careful attention to water quality given the documented sensitivity to parameter fluctuations and nitrogenous waste noted in the FishBase account.
In the aquarium
Enteromius sylvaticus is not an aquarium fish in any practical sense: it is unknown in the ornamental trade and has never been established in hobbyist collections as far as the available literature records. Its extreme small size — under 1 in at maximum — means it would require a species-only or very carefully chosen micro-fish setup, with tankmates equally tiny and gentle. The documented sensitivity to water-parameter fluctuation and elevated nitrate points to the need for stable, well-maintained, soft to moderately mineralised tropical water, filtered gently so as not to overwhelm fish barely larger than a thumbnail.
Shoaling behaviour is confirmed for the species, meaning any maintained group should be kept in numbers sufficient to allow natural schooling. The primary interest in this species is ichthyological and conservation-oriented rather than ornamental.
Conservation
Enteromius sylvaticus is assessed as Vulnerable (VU) on the IUCN Red List under criterion B2ab(iii), with the assessment published in May 2019. The B2 criterion reflects a restricted area of occupancy; the ab(iii) qualifier indicates that the occupied area is fragmented or declining, and that the quality of its freshwater habitat is in ongoing decline. The species is known from only two areas: the Ignidi River drainage in Benin and the lower Niger Delta in Nigeria.
The Niger Delta and the coastal lowlands of Benin face substantial and accelerating pressures — agricultural expansion, urban growth, oil-industry pollution, and modification of watercourses — that degrade the forested stream habitats this species depends on. As a dwarf with a restricted, low-lying coastal range, Enteromius sylvaticus has little buffer against habitat deterioration: the loss or degradation of even a small number of forest stream catchments could eliminate a significant portion of its range. There is no targeted conservation measure in place for the species, and its existence is little known outside specialist ichthyological circles.