Taxonomy & naming
Enteromius sublineatus was first described by the French ichthyologist Jacques Daget in 1954, originally as Barbus sublineatus. The species has also appeared in the literature under the genus Puntius, which formerly served as a broad container for many small barbs across Africa and Asia, and FishBase continues to list the old combination Barbus sublineatus as a common synonym. The Catalog of Fishes (Eschmeyer, CAS), which is the authority for valid names, places the species in Enteromius — a large genus encompassing the bulk of sub-Saharan African barbs.
The epithet sublineatus is Latin, meaning "finely lined" or "subtly marked", a reference to the lateral patterning of dark pigment that runs along the midline. This patterning is geographically variable enough that the species could be described as a mosaic of local forms rather than a uniform type, though no separate subspecies are currently recognised under the Catalog of Fishes.
Morphology
The Morse barb is a moderately slender cyprinid with the typical fusiform build of small riverine barbs. FishBase records a maximum total length of 3.5 in for unsexed or male specimens; Seriously Fish gives a size range of 3–4 in, suggesting the largest individuals may approach 4 in. The head is relatively small and the mouth terminal.
The most notable and taxonomically interesting feature is the lateral patterning, which is highly variable across the species' range. Populations in the Upper Niger carry three elongate dark blotches along the midlateral line, resembling the dots and dashes of Morse code — presumably the origin of the common name. Fish from the Middle Niger show a continuous dark lateral band, while those from the Volta basin bear four discrete spots. This intraspecific variation underscores the broad geographic range and the likelihood of long-standing allopatric differentiation across the drainages.
Habitat
Enteromius sublineatus occupies rivers and streams across a wide band of West and Central Africa, including the Cavalla, Comoé, Bandama, Volta, Mono, Ouémé, Benue, Niger Delta, Cross and Mokoko drainages, as well as rivers in Senegal, Guinea, Liberia, Burkina Faso, Ghana, Togo, Benin, Nigeria, Cameroon and Mali. The species is classified as a full migrant, suggesting it undertakes lateral or longitudinal movements within its river systems — behaviour consistent with the seasonally flooded savanna and Guinea woodland streams that characterise much of its range.
Some sources describe it as a fish of rivers and streams preferring clean, oxygenated water with current; others note associations with slower-moving or still waters with abundant marginal vegetation. These apparently contradictory accounts likely reflect genuine habitat partitioning across its broad range — riverine fish in the main channels and stream populations in slower lateral habitats. Water chemistry records span a notable range: temperature 72–81 °F, pH 6.0–7.7, and hardness from roughly 36 to 215 ppm (approximately 2–12 °dGH), reflecting the considerable environmental heterogeneity across West African drainages.
Feeding
Enteromius sublineatus is an omnivore. In the wild it takes insects and other small invertebrates along with plant material, an opportunistic diet typical of small African barbs that forage through the water column and substrate of stream margins and flooded vegetation.
In the aquarium it accepts standard offerings readily: good-quality flake and small pellets supplemented with live and frozen invertebrates such as bloodworm and daphnia, and some vegetable matter. Like most small barbs it is an active feeder and benefits from variety in the diet.
Mating
Enteromius sublineatus is an egg-scattering, non-guarding spawner in the mode universal among barbs. There is no nest, no pair bond, and no parental involvement beyond the act of spawning itself. A driving male pursues a gravid female through vegetation or across the substrate, and eggs and milt are released together in brief contact, the adhesive eggs falling among plants or onto the bottom.
The species is a schooling fish, and courtship activity in a group context is animated and competitive. Males in breeding condition show heightened colour and increased activity as they compete for access to ripe females.
Breeding
Like other small barbs, Enteromius sublineatus can in principle be bred in captivity using standard egg-scatterer technique: a conditioning period on varied live and frozen foods, a separate spawning vessel with soft, slightly acidic to neutral water, fine-leaved plants or a spawning mop, and a substrate mesh or layer of glass marbles so that eggs fall out of the adults' reach. Spawning typically occurs in the morning hours with rising light.
Given the species' rarity in the hobby, documented accounts of captive breeding are sparse. Adults will eat their own eggs if not removed promptly. Eggs hatch in approximately 24–36 hours at tropical temperatures, and free-swimming larvae require infusoria or commercial equivalents before graduating to newly hatched brine shrimp. The IUCN notes the species as a full migrant, implying that seasonal cues — rising water levels or temperature shifts — may be relevant triggers in the wild, but the implications for captive breeding have not been widely explored.
In the aquarium
The Morse barb is a schooling species and should be kept in groups of at least six; smaller numbers produce nervous, unsettled fish that may become skittish or harass tankmates. A roomy aquarium with open swimming space, some planted zones for refuge, and steady filtration providing moderate current suits the species well. Water parameters should reflect the West African river and stream conditions it comes from: temperature 72–81 °F, pH 6.0–7.5, and soft to moderately hard water.
It remains genuinely rare in the trade and is not a species one is likely to encounter at a standard aquarium shop. Its relative obscurity in the hobby means that documented long-term husbandry experience is limited. Peaceful community companions of similar size and activity level would be appropriate tankmates.
Conservation
Enteromius sublineatus is assessed as Least Concern (LC) on the IUCN Red List (species ID 182252, assessment 126326392). Its broad distribution across multiple river systems and countries in West and Central Africa, combined with the absence of evidence for any major range-wide decline, underpins the LC rating. The species is recorded from Guinea, Liberia, Ivory Coast, Burkina Faso, Ghana, Togo, Benin, Nigeria, Cameroon, Senegal, Mali and Niger.
The IUCN notes the species as a full migrant, indicating seasonal movement within river systems. West African savanna rivers face ongoing pressure from agriculture, water extraction for irrigation, small-scale damming, and periodic drought intensified by climate change — pressures that affect migratory fish more acutely than resident populations. While none of these has driven sublineatus to a threatened category at the range-wide scale, localised population reductions in more degraded drainages cannot be excluded.