Taxonomy & naming
Brachypetersius altus was described by George Albert Boulenger in 1899, with the type locality recorded as Lake Tumba (Bikoro) in what is now the Democratic Republic of Congo. The species has accumulated several synonyms over the years — Micralestes altus, Petersius nummifer, and Micralestes rochefoucauldi have all been placed in synonymy with it — reflecting the complex taxonomic history typical of African alestid characins. Under Eschmeyer's Catalog of Fishes, the valid combination is Brachypetersius altus (Boulenger, 1899), with the parenthetical authority indicating the species was originally described under a different genus.
The genus Brachypetersius was erected by Hoedeman in 1956, and B. altus is its type species. Brachypetersius belongs to the tribe Petersiini within the family Alestidae, the African tetras — a family broadly distributed across sub-Saharan Africa and entirely distinct phylogenetically from the Neotropical characid tetras familiar to most aquarists, despite superficial similarities in body form and behaviour.
Morphology
Brachypetersius altus is a slender, laterally compressed tetra reaching a maximum reported size of approximately 4 in standard length (SL), with FishBase citing 2.5 in total length (TL) for typical specimens. The body is moderately elongate with a silvery ground colour and the fine-scaled, compact profile characteristic of the Petersiini.
The species' defining external feature is a large, black, rounded spot on the lower caudal peduncle — the 'spottail' of its common name — which is clearly visible in life and distinguishes it from related Brachypetersius. Additional diagnostic characters noted in the literature include 4½ transverse scale rows and 21–26 scales along the lateral line. The fins are mostly hyaline, and the overall impression in a healthy shoal is of a bright, active, silver fish with a prominent black tail spot.
Habitat
This species is found throughout the middle Congo River basin, with records from Cameroon, the Central African Republic, the Republic of Congo, and the Democratic Republic of Congo. Key localities include the Congo River at Pool Malebo, Lake Tumba (the type locality), and Lake Mai Ndombe — all large, shallow floodplain water bodies fed by the Congo system.
In the field, Brachypetersius altus occupies slow-moving tributaries and marginal habitats characterised by leaf litter, submerged roots, and soft, slightly acidic water. FishBase records water parameters at capture sites of 75–81 °F and pH up to 6.2, with hardness up to 15 dH, consistent with the blackwater and clearwater tributaries typical of much of the Congo basin.
Feeding
Brachypetersius altus is an omnivore, as is typical of small African alestids. In nature it likely forages on small invertebrates — insect larvae, microcrustaceans, and zooplankton — supplemented by plant material and organic detritus in the leaf-littered habitats it favours.
In the aquarium the species is undemanding and readily accepts a varied diet of quality flake, small pellets, and frozen or live foods such as Daphnia, brine shrimp, and bloodworm. As with most small shoaling tetras, a mixed diet that includes live or frozen invertebrate foods improves condition and colour, particularly in fish being brought into breeding readiness.
Mating
Brachypetersius altus is an egg-scattering species with no parental care, a reproductive strategy shared across most of the Alestidae. In common with other small Congo basin tetras, courtship likely involves brief chasing displays by males towards receptive females, with pair or group spawning occurring among fine-leaved vegetation or other dense cover.
The species shows no recorded territorial or nest-guarding behaviour. Spawning is triggered by the conditions — water temperature, chemistry, and food availability — rather than a discrete pair bond. In the aquarium, conditioning adults with live and frozen foods promotes spawning activity.
Breeding
Brachypetersius altus is an egg-scatterer that deposits adhesive eggs among fine-leaved plants or spawning mops, with no parental care after spawning. Aquadiction sources report a hatching time of 24–48 hours at typical aquarium temperatures, which is fast relative to many tetras and suggests relatively small, non-yolk-heavy eggs.
Adults will consume their eggs and newly hatched fry if given the opportunity, so standard tetra breeding practice applies: either remove adults after a spawning session, or use a spawning grid or densely planted tank to protect the eggs physically. Fry are very small at hatch and require infusoria or commercial micro-fry food as first foods before graduating to newly hatched brine shrimp nauplii. Detailed accounts of captive breeding are scarce in the hobby literature, reflecting the species' relative rarity in the trade.
In the aquarium
The African Spottail Tetra is a peaceful, shoaling fish best kept in groups of six or more, where the collective movement of the school and the black tail spots create an attractive display. It is suited to a moderately sized aquarium — around 23.5–31.5 in in length for a small group — with subdued lighting, a dark substrate, and plenty of cover in the form of plants, driftwood, and leaf litter to replicate its natural Congo basin habitat.
Water chemistry should reflect the species' soft, slightly acidic natural conditions: 75–81 °F, pH 6.0–7.5, and general hardness in the range of 3–10 dH are appropriate targets based on both field data and hobbyist keeping reports. The species is peaceful with similarly sized tankmates and will not harass plants or other fish. Because it remains relatively uncommon in the trade, sourcing typically means specialist African fish importers or hobbyist networks rather than general retail. Lifespan in captivity is reported at up to five years under good conditions.
Conservation
Brachypetersius altus is assessed as Least Concern (LC) on the IUCN Red List, an assessment made in February 2009. The evaluation noted no major threats to the species, which is broadly distributed across the middle Congo River basin in Cameroon, CAR, Republic of Congo, and DRC — a large, relatively intact drainage that still supports extensive natural habitat.
The Congo River basin, despite pressures from land use change and human population growth along its margins, remains one of the largest continuous tropical forest river systems on Earth, and the floodplain lake habitats used by this species are not subject to the kind of rapid, localised degradation that threatens narrowly endemic Congo basin species. No specific conservation measures are directed at this species, and the Least Concern assessment is considered appropriate given its wide range and lack of identified significant threats.