Taxonomy & naming
Auchenipterichthys coracoideus was described by Carl H. Eigenmann and William Ray Allen in 1942. It belongs to the family Auchenipteridae, the driftwood catfishes, within the order Siluriformes, and is one of a handful of species in the genus Auchenipterichthys. The Catalog of Fishes (Eschmeyer, California Academy of Sciences) treats Auchenipterichthys coracoideus as the currently valid combination; the species has also circulated in the aquarium trade under the older name Auchenipterichthys thoracatus, a name now applied to a different, related species, so older literature and some retailer listings still mix the two up.
The genus name Auchenipterichthys combines the family name Auchenipterus with the Greek ichthys, "fish" — literally an "Auchenipterus-like fish". The species epithet coracoideus refers to the coracoid, a bone of the pectoral girdle, likely describing a distinctive feature of that bone structure noted in the original description.
Morphology
This is a compact, deep-bodied driftwood catfish with a blunt head, small eyes suited to nocturnal life, and long, branched barbels used to feel out food in dark or turbid water. The body is dark grey to blackish-brown, giving rise to the trade name "midnight catfish", sometimes with faint mottling. Like other catfishes it is scaleless, with naked, sensitive skin rather than scales or bony plates.
Adults reach roughly 3.5–4.5 in standard length according to aquarium-standard sources, making it one of the more modestly sized driftwood cats — though some published records (FishBase) list larger maximum lengths for the species, so a keeper should plan for a fish that may exceed the smaller figure rather than assume it will stay tiny. As in all catfish, the dorsal and pectoral fins carry stiff, serrated spines that lock erect; these can snag a net and jab bare skin, so the fish is best moved in a cup or bag rather than netted.
Habitat
Auchenipterichthys coracoideus is native to the upper and central Peruvian and Brazilian Amazon basin, with a further population in the Essequibo drainage of Brazil and Guyana. It lives in turbid, slow-to-moderate lowland rivers, sheltering by day among submerged roots, sunken tree stumps and aquatic vegetation, and emerging to feed as light fades.
Water in these habitats is warm and on the soft, slightly acidic-to-near-neutral side: reported parameters are roughly 72–77 °F, pH 6.0–7.2, and low hardness (0–179 ppm). It is not an extreme blackwater specialist, but it does best in warm, gently soft-to-neutral water rather than hard or alkaline conditions.
Feeding
In the wild this species is a nocturnal benthic omnivore, taking aquatic insects and their larvae along with other small invertebrates picked out of leaf litter and root tangles after dark. Its barbels do much of the work of finding food in low light and turbid water.
In the aquarium it readily accepts live and frozen foods (bloodworm, brine shrimp and similar) as well as sinking pellets and other prepared foods. Because it is most active at night, feeding after the lights go out lets it forage naturally and keeps it from being out-competed by more visible daytime tankmates.
Mating
Driftwood catfishes are one of the few catfish groups with internal fertilisation, and Auchenipterichthys coracoideus follows the family pattern. The male's anal fin is modified into an intromittent organ used to transfer sperm directly to the female during mating. The female then stores the sperm — in a saclike structure associated with the oviduct — and can go on to lay fertile eggs afterwards, with fertilisation occurring at the moment of spawning rather than requiring a male to be present.
This is genuinely unusual among catfish, most of which spawn externally, and it means courtship and copulation in this species look nothing like the broadcast spawning typical of the order. It is rarely observed or deliberately triggered in home aquaria, but wild-caught or long-held females have been known to produce fertile eggs well after any contact with a male.
Breeding
Breeding follows directly from the internal-fertilisation biology above: after mating, the female deposits her eggs directly onto the substrate, and there is no reported parental care from either parent once the eggs are laid. This combination — internal fertilisation plus sperm storage, followed by an unguarded, substrate-scattered clutch — sets Auchenipterichthys and its relatives apart from both the open-water egg-scatterers and the nest-building, guarding catfishes found elsewhere in the order.
Deliberate captive breeding is uncommon and not well documented for this species; most aquarium stock is wild-collected. Keepers who maintain a healthy shoal in soft, warm, stable water may see it spawn, but a keeper should not expect a repeatable, home-breedable protocol the way one might with a nest-building callichthyid.
In the aquarium
Give this species a mature aquarium with soft sand, plenty of driftwood, and caves or root tangles to shelter in by day — it is shy and nocturnal, and will rarely be seen out in the open under bright light. It is gregarious and does best kept in a group of five or more rather than singly. Water should be kept warm (around 72–77 °F) and on the soft, slightly acidic-to-neutral side (pH roughly 6.0–7.2); minimal water movement suits it better than a strong current.
Because it is scaleless, it is more sensitive than scaled fish to copper and to many medications, so treatments should be dosed conservatively. Its dorsal and pectoral spines lock and can snag a net or jab a hand, so move it in a container rather than a net. It is generally peaceful with tankmates too large to swallow, but as a nocturnal predator of invertebrates it will take very small fish given the chance, so choose companions accordingly. Size the tank for an adult of at least 3.5–4.5 in SL — treat the smaller end of published sizes as a floor, not a guarantee, given the size discrepancy across sources.
Conservation
The IUCN Red List assesses Auchenipterichthys coracoideus as Least Concern, reflecting a wide distribution and stable populations across the upper Amazon basin in Peru and Brazil and the Essequibo drainage in Brazil and Guyana, with no quantified population declines.
The main long-term pressures on its habitat are deforestation and mining activity in the upper Amazon, which degrade the turbid rivers and root-tangle habitats it depends on. It is not a heavily targeted trade species, and its wide range across multiple river systems gives it some buffer against localised habitat loss.