Taxonomy & naming
Nannocharax altus was described by the French ichthyologist Jacques Pellegrin in 1930. It sits in the genus Nannocharax, within the family Distichodontidae — the African characin family that also holds the much larger, plant-grazing Distichodus and the deep-bodied citharinids are sometimes treated as a separate family, Citharinidae, depending on the classification followed. The Catalog of Fishes (Eschmeyer, California Academy of Sciences) lists Nannocharax altus as a currently valid name, with its type locality in the Kouilou River drainage spanning the Republic of the Congo and Gabon.
Nannocharax is a large genus of small, elongate, bottom-associated African characins, quite distinct in build and habit from the deep-bodied, plant-shredding Distichodus and the grazing citharinids that share the family. Unlike those relatives, species in this genus are not defined by aggressive herbivory; they are small invertebrate feeders, and N. altus in particular is known from very few records, reflecting how poorly surveyed much of its home basin remains.
Morphology
Nannocharax altus is a genuinely small fish: FishBase records a maximum length of just 2.5 in total length, placing it among the smaller members of a genus that already runs to modest, elongate body forms built for life near the riverbed. Like other Nannocharax, it is expected to show the genus's characteristic slender, subcylindrical body, a underslung or subterminal mouth suited to picking food from the substrate, and the small, banded or spotted patterning typical of many species in the group, though detailed morphological description specific to this species is not available from the sources consulted here.
Because N. altus has not been documented in the aquarium trade and few published accounts exist beyond its original description and catalog entries, finer details of colouration, fin shape and any sexual dimorphism have not been confirmed and are not reported here rather than guessed at.
Habitat
The species is known only from the Kouilou River basin in the Republic of the Congo, part of the Lower Guinea freshwater ecoregion of West-Central Africa — a single-river endemic in the strictest sense, with no confirmed populations reported outside that drainage. FishBase classifies it as a freshwater, pelagic-associated fish within that system.
Specific water chemistry data (temperature range, pH, hardness) for N. altus itself is not available in the sources consulted. As a general pattern, Lower Guinea rivers such as the Kouilou run warm and are often soft and slightly acidic to neutral, sometimes tannin-stained, but applying that regional pattern as if it were measured data for this exact species would overstate what is actually known — so no specific figures are given here.
Feeding
Nannocharax altus is a benthic invertebrate feeder. FishBase notes it accepts small live foods such as bloodworm and Daphnia in aquarium contexts, consistent with the genus's general habit of picking small aquatic invertebrates and associated matter from the substrate and lower water column, rather than grazing plant material the way Distichodus does. There is no documentation of the species taking dried or prepared foods.
Given how little this species has been kept, its feeding account in the literature is limited essentially to that one FishBase note; broader statements about its dietary preferences beyond small live invertebrate foods would not be supported by the available sources.
Mating
No courtship or spawning behaviour has been documented for Nannocharax altus in the sources available. The species has not been established in the aquarium hobby, and no field or captive observations of pairing, colour changes, or breeding condition were found. Rather than extrapolate from other, better-known Nannocharax or from the wider Distichodontidae, this account reports the gap honestly: mating behaviour in this species is undescribed.
Breeding
Breeding has not been established for Nannocharax altus, either in the aquarium hobby or as a documented event in the field. FishBase explicitly notes that reproduction has not been documented in captivity for this species. This mirrors the pattern across much of the Distichodontidae and the citharinid grazers, where most species — Distichodus included — are egg-scatterers that are rarely, if ever, bred at home; for N. altus specifically there simply is no record of a successful spawn to describe, and no parental-care behaviour has been reported. Any claim of a specific breeding mode for this species would be invented rather than sourced, so none is given.
In the aquarium
Nannocharax altus is essentially absent from the aquarium trade. It has not been established as a captive-bred or regularly imported fish, and detailed husbandry parameters (tank size, groups, water chemistry targets) specific to this species have not been published. What can be said with confidence from FishBase is that individuals that have been kept accepted small live foods such as bloodworm and Daphnia, consistent with a genus of small benthic invertebrate feeders best suited, in principle, to a modestly sized, gently run nano or species setup rather than anything resembling piranha- or pacu-scale housing.
Given the near-total absence of hobby data, a prospective keeper should treat this species as effectively unavailable and unproven in captivity, and should not assume it shares husbandry needs with larger, well-documented Distichodontidae relatives without direct evidence.
Conservation
Nannocharax altus is assessed as Endangered on the IUCN Red List, a status consistent with its extremely restricted distribution — confined to the Kouilou River basin shared by the Republic of the Congo and Gabon — which leaves the species vulnerable to any localized habitat degradation, pollution or hydrological change within that single system. Species endemic to a single river basin in West-Central Africa are characteristically data-poor and carry elevated extinction risk simply by virtue of having nowhere else to persist if conditions in that one basin decline.
There is no indication in the available sources that N. altus supports any fishery or aquarium trade that would create collection pressure; its conservation concern stems from habitat-based vulnerability rather than exploitation. Given how sparse the documentation is for this species, any conservation account beyond its Red List status and range would risk overstating what has actually been studied.