Taxonomy & naming
Enteromius greenwoodi was originally described by Max Poll in 1967 as Barbus greenwoodi, named in honour of the British ichthyologist Peter Humphry Greenwood of the Natural History Museum in London. The original description was based on material from the Congo Basin ichthyofauna surveys that Poll conducted over several decades, which yielded a substantial number of new small barb species from central Africa.
The genus Barbus, once a vast catch-all for barb-like cyprinids across Africa and Eurasia, has been progressively partitioned since the early 2000s through molecular and morphological work. African small barbs formerly grouped under Barbus (sensu lato) are now largely accommodated in Enteromius, a genus originally proposed by Cope in 1867 and resurrected for this purpose. Under the Catalog of Fishes the current valid combination is Enteromius greenwoodi (Poll, 1967), the parenthetical authority marking the transfer out of Poll's original genus.
Morphology
Enteromius greenwoodi is a small, slender barb reaching approximately 1–1.5 in standard length. It displays the generalist body plan common to the genus: a moderately compressed, fusiform profile, a slightly arched dorsal contour, a terminal mouth, and the two pairs of barbels characteristic of Enteromius. Specific colour pattern details are sparse in the available literature, though small Congo Basin Enteromius typically show silvery or pale flanks with variable dark spotting or banding and a dusky dorsal fin.
Sexual dimorphism follows the pattern seen in related species: females become visibly deeper-bodied and more rounded in the abdomen when gravid, while males tend to remain slimmer. Given the species' small maximum size, it falls at the diminutive end of the Enteromius size range.
Habitat
The species is endemic to the Congo Basin in the Democratic Republic of Congo, where it inhabits tropical freshwater streams and slow-moving areas with aquatic vegetation. The Congo drainage is the world's second-largest river system, encompassing a wide range of habitat types from fast-flowing mainstreams and rocky rapids to small forest streams and flooded marginal areas.
Small Enteromius of the central Congo region typically occupy the calmer margins of streams and shallow tributaries, where fine sediment, leaf litter, submerged roots and low-growing vegetation provide both cover and foraging substrate. Water chemistry in the inner Congo Basin is generally soft to moderately hard, with a mildly acidic to neutral pH in the range of approximately 6.0–7.5 and tropical temperatures of around 72–79 °F.
Feeding
Enteromius greenwoodi is a small omnivore in the manner typical of the genus. In its natural stream habitat it forages for microcrustaceans, small invertebrates, fine organic detritus, and algae, browsing among vegetation, leaf litter and the upper substrate layer. The small terminal mouth and modest body size constrain it to fine-particulate food items.
In an aquarium setting it would be expected to accept most small-particle prepared foods — finely crushed flakes, micro-pellets, and small live or frozen invertebrates such as brine shrimp nauplii, micro-worms, and daphnia. Vegetable matter and algae-based foods would complement the diet. Its feeding behaviour is unremarkable for the group, grazing actively throughout the day.
Mating
Like all barbs, Enteromius greenwoodi is an egg-scattering, non-guarding spawner. No pair bond is formed, and no territory is held beyond the transient chase of courtship. When a gravid female is ready to spawn, a driving male pursues her through vegetation or over the substrate, pressing close to her flank as eggs and milt are released simultaneously.
The adhesive eggs drift or fall among plants, onto gravel, or into the substrate interstices. Adults take no further interest in the spawn and will consume eggs if they encounter them. Courtship is typical of small Enteromius: energetic and brief, without elaborate display.
Breeding
Enteromius greenwoodi is an egg-scatterer that gives no parental care, in keeping with the universal barb breeding pattern. Spawning is likely triggered by rising temperatures, good feeding condition, and seasonal rainfall cues in the wild. Females broadcast adhesive eggs among fine-leaved vegetation or over gravel and sandy substrate, and the eggs are left to develop without attendance.
No aquarium breeding accounts for this species are documented in the available literature. By analogy with closely related small Congo Basin Enteromius, a soft, mildly acidic spawning tank with fine-leaved plants or a spawning mop, a mesh layer to protect eggs from the adults, and temperatures in the mid-twenties Celsius would be appropriate starting conditions. Egg hatching times and larval development would follow the general small-barb pattern of hatching within 24–48 hours and free-swimming larvae a few days later.
In the aquarium
Enteromius greenwoodi is not a species commonly encountered in the aquarium trade, and dedicated husbandry literature is absent. As a small Congo Basin barb it would be expected to thrive under conditions appropriate to the region: soft to moderately hard water, a pH in the 6.0–7.5 range, and tropical temperatures of 72–79 °F. A well-planted aquarium with subdued lighting, some driftwood, and leaf litter would replicate the shaded stream margins of its native habitat.
Being a small schooling barb, it should be kept in groups to express natural behaviour and reduce stress. Suitable tankmates would be other small, peaceful Congo Basin species — small tetras, dwarf cichlids such as Nanochromis, and other diminutive barbs — that share its water requirements and are unlikely to compete aggressively. Its small size makes it vulnerable to larger or predatory tankmates. Feeding presents no special difficulties given the species' omnivorous habits.
Conservation
Enteromius greenwoodi has not been formally evaluated by the IUCN Red List; its status is recorded as Not Evaluated (NE). This is common for the many small, narrowly distributed Enteromius species of the Congo Basin, which are often described from limited material and receive little subsequent survey attention. Small endemic African barbs are frequently considered locally common within their stream systems, but the absence of assessment data means that population trends and pressures are effectively unknown.
The Congo Basin faces ongoing threats from forest clearance, artisanal and industrial mining (particularly in the east of the DRC), and subsistence fishing pressure on river systems. For a species with a restricted type locality in the Congo region, any significant degradation of its stream habitat could have outsized consequences. A formal IUCN assessment would require targeted field surveys to establish its distribution limits, abundance, and habitat condition.