Taxonomy & naming
Enteromius sensitivus was described by Tyson Roberts in 2010 under the original combination Barbus sensitivus, with the type locality given as the Sanaga River, Cameroon. The original description emphasised the species' extensive pit-line system — exposed neuromasts organised into canals across the head and body scales — as the primary diagnostic character, distinguishing it from all other African small barbs then known.
Subsequently, molecular phylogenetic work on African cyprinids prompted the wholesale reclassification of the old paraphyletic genus Barbus; most small sub-Saharan species were moved into Enteromius, and sensitivus was transferred accordingly. The Catalog of Fishes records the current valid combination as Enteromius sensitivus (Roberts, 2010), with parenthetical authority marking the change of genus from the original description. No junior synonyms are recorded.
Within Enteromius — a large and heterogeneous assemblage of several hundred African small barbs — sensitivus is morphologically distinctive enough that its placement is not in dispute, though the internal relationships of the genus remain an active area of cyprinid systematics.
Morphology
Enteromius sensitivus is a small, slender barb with a notably slim caudal peduncle, reaching a maximum recorded standard length of 1.5 in. The body form is consistent with life in fast-flowing water: streamlined rather than deep-bodied, and well suited to holding position over coarse substrate in strong current.
The species' defining feature is the exceptional development of its lateral-line and pit-line sensory system. Free neuromasts — mechanosensory hair-cell clusters normally enclosed in lateral-line canals — are here exposed across most of the head surfaces and extend onto the scales of much of the body. These sensory papillae, visible as minute pit-like organelles, are far more extensive than in any closely related species and prompted Roberts's choice of the specific epithet. The functional significance is presumed to be enhanced detection of water-flow disturbances in the turbulent habitat the species occupies, though detailed behavioural study has not been published.
Colour pattern and fin details were not described in the cache sources beyond the general barb body plan; no sexual colour dimorphism has been formally documented, though breeding tubercles on the rostrum and dorsal head surface of males are noted from FishBase, indicating at least one secondary sexual character.
Habitat
The Sanaga is Cameroon's largest river by discharge, draining a broad highland catchment before crossing the western coastal plain to the Gulf of Guinea. Within this system, Enteromius sensitivus is associated with reaches of very swift current over coarse gravel and smooth stones — a habitat characteristic of upland rapids and fast riffles rather than the slower lowland sections.
The Sanaga basin spans both montane and lowland forest zones, and the river carries the soft, slightly acidic chemistry typical of forest-influenced West African drainages. Water temperatures at mid-elevation sites in the region range from roughly 63–75 °F seasonally, with pH in the region of 5.0–6.8 and generally low conductivity reflecting the granitic and gneissic geology of the highland catchment. These conditions — warm, soft, moderately acidic — contrast with harder savanna-river barb habitats and reflect the forest-stream ecology more common to small Enteromius species of the Congo-Atlantic divide.
Feeding
No detailed dietary study of Enteromius sensitivus has been published. By analogy with other small fast-water Enteromius of West and Central Africa, the species is presumed to be a generalist omnivore feeding on invertebrates — insect larvae, small crustaceans and worms — dislodged from the coarse substrate by current, as well as biofilm, algal scraps and organic detritus.
The slender body and well-developed mechanosensory system suggest a fish highly attuned to detecting prey movement in turbulent flow, consistent with an invertivore-dominated diet in high-energy riffle habitats. In the aquarium, related small Enteromius and Barbus-complex species typically accept a wide range of live, frozen and prepared foods without difficulty.
Mating
Enteromius sensitivus is an egg-scattering, non-guarding spawner, following the standard reproductive strategy of virtually all barbs. No specific courtship observations have been published for this species, but males bear breeding tubercles on the rostrum and dorsal head surface — structures that in other barbs function in tactile stimulation during spawning chases and in competitive interactions among males.
In the manner typical of the group, a ripe male would pursue a gravid female through the water column or over the substrate, pressing alongside her briefly as eggs and milt are released simultaneously. No pair bond is formed, and no territory is maintained beyond the transient activity of a spawning bout. Eggs are scattered onto or among the substrate and receive no subsequent attention from either parent.
Breeding
No captive breeding account for Enteromius sensitivus has been documented in the published literature or hobby sources consulted. In the wild, breeding is presumed to be seasonal, cued by the hydrological cycle of the Sanaga basin — rising water levels, temperature shifts or increased food availability associated with the rainy season.
As with other small fast-water African barbs, spawning likely takes place over coarse gravel in riffle zones, where the current carries eggs downstream into interstices among stones, partially sheltering them from adult predation. Parental care is absent. For aquarists who may attempt to breed the species, the general principles applicable to fast-water African barbs apply: cool, soft, well-oxygenated water with significant current, a coarse gravel or pebble substrate, and removal of adults following spawning.
In the aquarium
Enteromius sensitivus is essentially unknown in the aquarium trade. Its restricted range within a single Cameroonian river system, its association with turbulent fast-water habitat, and the absence of any distinctive colour pattern that would attract collector or hobbyist attention combine to make it a scientific curiosity rather than a traded species.
Should specimens become available, the husbandry requirements can be inferred from the habitat: a well-filtered, highly oxygenated tank with significant water movement, a temperature in the range of 68–75 °F, soft and slightly acidic water (pH 5.5–6.8), and a substrate of smooth stones and coarse gravel. It is a small species at just over 1.5 in standard length and would suit a species tank or a community with other small, peaceful West African stream fishes. Its exceptional sensory apparatus makes it a fish of real biological interest, even if it lacks the ornamental appeal that drives commercial trade.
Conservation
Enteromius sensitivus has not been evaluated by the IUCN Red List; its conservation status is listed as Not Evaluated (NE). As a species known only from the Sanaga River of Cameroon and described as recently as 2010, it falls within the very large backlog of African cyprinids that have not yet been formally assessed.
The Sanaga basin faces increasing pressure from hydroelectric development — several large dams have been constructed or planned on the main stem and tributaries — as well as agricultural expansion, deforestation along riparian corridors, and artisanal fishing. For a species apparently restricted to fast-water riffles in a single river system, these pressures represent a plausible threat, though no population surveys or trend data have been published. A formal IUCN assessment, ideally accompanied by systematic surveys of fast-water habitats in the upper and middle Sanaga, would be necessary to establish the species' actual range and abundance before conservation recommendations could be made.