Taxonomy & naming
Enteromius cerinus was formally described in 2024 by Ilodiri, Huyghe, Costa, Baba, Mizani and Vreven in the Journal of Fish Biology. The type locality is the Angadiko River, a left-bank sub-affluent of the Nepoko River inside the Okapi Wildlife Reserve in north-eastern Democratic Republic of Congo, placing the species within the Aruwimi basin of the Middle Congo drainage. It was co-described alongside Enteromius ruforum, with which it shares part of its range.
The species was placed in the genus Enteromius, a large and biogeographically diverse group of African cyprinid barbs. The old catch-all genus Barbus was progressively dismembered over several decades and the majority of sub-Saharan species are now referred to Enteromius rather than the Eurasian Barbus sensu stricto. Molecular work using COI barcoding confirmed that E. cerinus is distinct from related taxa, including its closest congener E. kamolondoensis, from which it differs in having 10–11 circumpeduncular scales rather than 12, as well as in body proportions documented at the time of description. The Catalog of Fishes is the authority for the current valid combination.
Morphology
Enteromius cerinus is a slender barb with a body depth of 22.8–25.7% of standard length, placing it at the more elongate end of the genus. Like other members of Enteromius it has two pairs of barbels: the anterior pair measures 32.6–35.3% of head length and the posterior pair 41.6–43.9% of head length, the latter extending noticeably behind the corner of the mouth. The last unbranched ray of the dorsal fin is flexible rather than ossified — a character shared with close relatives in the complex and useful in distinguishing them from species with a hardened dorsal spine.
Beyond these published meristic and proportional data the detailed coloration and full osteological description remain in the primary literature. Because the species was described very recently (2024) and is known from a single collecting site, measurements and counts are based on type material; no supplementary population series has been examined at the time of writing.
Habitat
The species is known from the Angadiko River, a small, clear first-order stream draining the forest interior of the Okapi Wildlife Reserve in north-eastern DRC. The Nepoko River, of which the Angadiko is a tributary, belongs to the Aruwimi sub-basin of the Middle Congo — a vast equatorial drainage system whose headwaters include numerous forest streams with clean, well-oxygenated water.
No water chemistry measurements were published for this locality in the original description. Based on habitat type — shaded lowland forest stream in the Congo Basin — conditions are likely soft to moderately mineralised, warm (approximately 72–81 °F), and close to neutral or slightly acid in pH, consistent with values recorded for closely related Enteromius species in similar central African forest rivers. The species has not been recorded elsewhere and its full habitat requirements remain poorly characterised given the data-sparse nature of such newly described taxa.
Feeding
No dietary data specific to Enteromius cerinus have been published. As a member of the genus Enteromius and of the family Cyprinidae, it is presumed to be an omnivore in the manner typical of the group, exploiting a combination of algae, organic detritus, small invertebrates and plant fragments picked from the stream bed and water column. Related species such as Enteromius paludinosus feed on algae and small invertebrates in comparable river environments.
In the absence of stomach-content studies for this species, the generic account should be treated as provisional. The combination of barbels — adapted for tactile substrate searching — and flexible diet is characteristic of small Enteromius in forested African streams.
Mating
No spawning observations exist for Enteromius cerinus in the wild or in captivity. As a cyprinid barb, the species is expected to be an egg-scattering, non-guarding spawner in the manner universal among the Barbinae. In the spawning behaviour typical of African barbs, a driving male pursues a gravid female through vegetation or over the substrate, and eggs and milt are released simultaneously on contact. No nest is built, no territory is defended beyond the brief courtship chase, and there is no pair bond.
The adhesive eggs fall among plants or settle onto the substrate after release. Adults take no further interest in them and will consume eggs if the opportunity arises. Courtship intensity and colour brightness typically peak during the spawning act before returning to baseline.
Breeding
Enteromius cerinus has not been bred in captivity. The species is known only from wild-caught type material at a single locality and has not entered the aquarium trade in any documented way. Reproduction is assumed to follow the egg-scattering pattern uniform across the Barbinae: eggs are scattered over plants or substrate in small batches, hatch within one to two days at tropical temperatures, and larvae become free-swimming within a few further days. No parental care of any kind is provided at any stage.
The breeding seasonality and fecundity of this species in its native forest stream environment are unknown. Many central African barbs are tied to seasonal flood pulses, with spawning triggered by rising water levels, falling water temperatures, or increased current — a pattern likely relevant to E. cerinus given the seasonally variable nature of small Congolese tributaries.
In the aquarium
Enteromius cerinus is not available in the aquarium hobby. It is a recently described species (2024) known from a single protected locality within the Okapi Wildlife Reserve in DRC, where collection for the trade would be both logistically remote and ecologically inappropriate given its Vulnerable status. No captive populations are known to exist outside of the scientific type-series material.
Any future aquarium husbandry would presumably follow the approach used for small, active Enteromius species generally: roomy, well-oxygenated water of soft-to-moderate hardness at tropical temperatures, kept in a shoal, offered varied omnivorous foods, and housed with peaceful similarly sized tankmates. Its slender build and forest-stream origin suggest it would require clean, well-filtered conditions rather than tolerating the stagnant or organically loaded water that some hardier African barbs endure.
Conservation
Enteromius cerinus is assessed as Vulnerable (VU) on the IUCN Red List under criterion D2, reflecting its extremely restricted known range. The Angadiko River is the only confirmed locality, and even though it lies within the Okapi Wildlife Reserve — a UNESCO World Heritage Site — the reserve's protections are not absolute. The IUCN assessment identifies three principal threats: clearance and degradation of riverbank forest for agriculture; illegal fishing using plant-based ichthyotoxins (primarily rotenone from toxic plant parts), which indiscriminately kill fish at all sizes and stages; and dam construction and the associated hydrological alterations that affect small tributaries in the wider Nepoko basin.
The species was co-described with Enteromius ruforum, which shares part of the same range and faces comparable pressures, highlighting the vulnerability of the Okapi Wildlife Reserve's freshwater fauna to threats that penetrate even formally protected areas. Long-term monitoring of the Angadiko population and a search for additional populations elsewhere in the Nepoko and Aruwimi drainages would substantially reduce the uncertainty around the species' true range and conservation status.