Taxonomy & naming
Distichodus affinis was described by the German-British ichthyologist Albert Günther in 1873, in a paper on new fishes from Angola published in the Annals and Magazine of Natural History, with a type locality on the Congo River. It belongs to the family Distichodontidae within the order Characiformes, a strictly African radiation of characins that also includes the deep-bodied, algae-grazing citharinids and ranges from tiny Neolebias and Nannaethiops up to the large, heavily built Distichodus species kept for their size and appetite.
The Catalog of Fishes (Eschmeyer, California Academy of Sciences) lists Günther, 1873 as the valid authority for D. affinis, and the genus itself remains large and taxonomically busy, with dozens of described Distichodus species distinguished mainly by body depth, fin-ray counts and colour pattern — characters that overlap enough between species that field identification within the genus is not always straightforward. The epithet affinis is Latin for "related" or "similar", reflecting its original description as a close relative of other already-known Distichodus.
Morphology
Distichodus affinis has the elongated, slightly compressed, torpedo-like body typical of the smaller Distichodus species, with a small, underslung mouth adapted for grazing rather than seizing prey. FishBase records a maximum published length of 8 in total length, making it one of the more modestly sized members of a genus whose largest species can approach half a metre.
Base colouration is a clean silver over the flanks, without the bold vertical banding that marks D. sexfasciatus, though faint dusky striping can show depending on mood and condition. As fish mature, the fins — particularly the dorsal, anal and caudal — develop a wash of red to orange-red, the species' most distinctive field mark and the trait most often used to distinguish it from similarly proportioned Congo basin relatives. Sexes are not reliably distinguished externally.
Habitat
Distichodus affinis is native to the Congo River basin, documented from the lower and central stretches of the system across Cameroon, the Democratic Republic of the Congo, the Republic of the Congo and the Central African Republic. Within that enormous drainage it occupies river channels and associated habitats typical of the genus — moving water over varied substrate, often near submerged wood, roots and marginal vegetation that it grazes and shelters among.
Water across its native range runs warm and is generally soft to moderately hard with a wide tolerable pH band; aquarium references give roughly 73–81 °F and pH 6.0–8.0, broader and less extreme than the blackwater conditions associated with some South American characins. It has also been noted as introduced or present outside strict native records in a small number of areas, though the Congo basin remains its core range.
Feeding
Distichodus affinis is an omnivore with a strong herbivorous lean, grazing algae, soft plant matter and organic detritus in the wild alongside small invertebrates. Its small, downturned mouth is built for browsing surfaces rather than chasing prey, consistent with the genus's broader reputation as plant-eaters — a trait taken to an extreme in the much larger D. sexfasciatus and D. lusosso, which can strip a planted tank in short order.
In the aquarium it takes a varied diet readily: bloodworm, Daphnia and other frozen foods alongside a vegetable-forward staple such as blanched spinach, courgette, frozen peas and Spirulina-based flake or pellet. Because it grazes continuously in nature, keepers are advised to weight the diet toward vegetable matter and not rely on protein-heavy foods alone, both to match its natural feeding and to reduce the risk of it turning to aquarium plants out of hunger.
Mating
Little is documented about courtship behaviour in Distichodus affinis specifically. Like other African characins in this family, it is not known to form the kind of overt pair-bonding or nest-site courtship seen in substrate-spawning cichlids or true piranhas; available accounts describe it, in line with its relatives, as an open-water group spawner in the wild rather than a pair-forming species.
No reliable external sexual dimorphism is documented for this species beyond general condition — gravid females may appear fuller-bodied — and sex cannot be reliably determined by colour or fin shape in the aquarium.
Breeding
Distichodus affinis is, honestly, not an established home-aquarium breeding project. Distichodontids and the related citharinids are egg-scatterers that in the wild are believed to spawn in groups in open water rather than over a guarded nest, and this species has proven very difficult to reproduce in home tank conditions — the large volumes, current and group dynamics involved in natural spawning are hard to replicate.
Commercial breeding of D. affinis for the aquarium trade has been reported from farms in eastern Europe, which has reduced reliance on wild-caught stock for the hobby, but this is farm-scale production rather than a technique available to a typical hobbyist. No parental care is documented, consistent with an egg-scattering strategy; keepers should not expect to breed this species in a standard home setup.
In the aquarium
Distichodus affinis is one of the more manageable species in its genus: a maximum size of around 8 in calls for a long, spacious tank (roughly 65 US gal and up for a full-grown fish) rather than the room-dominating setup needed for D. sexfasciatus or D. lusosso, but it should still not be mistaken for a small community fish. It does best kept in a small group, since solitary individuals can become skittish, and appreciates open swimming space along with driftwood and rockwork to graze and patrol around.
Because it grazes plant matter, soft-leaved aquarium plants are at real risk; robust, tough-leaved species or a hardscape-only river-style layout are safer choices. Water should be kept warm (around 73–81 °F) with a wide acceptable pH range (roughly 6.0–8.0) and strong filtration to match its size and appetite. It is generally considered a peaceful member of its genus and can be combined with other robust Congo basin fish, though as with any Distichodus it should not be paired with slow, delicate or heavily planted setups.
Conservation
The IUCN Red List assesses Distichodus affinis as Least Concern, an assessment dated 16 February 2009, reflecting its wide distribution across the Congo basin and populations that remain stable across a large native range. It is not currently the subject of any targeted conservation programme or known major population decline.
The aquarium trade for this species draws on both wild collection from the Congo basin and, increasingly, commercial farm production in eastern Europe, which eases pressure on wild stock. As with many Congo basin fish, longer-term watch items are regional rather than species-specific — habitat pressure, water quality and development impacts across the basin — rather than any documented threat to D. affinis itself.