Taxonomy & naming
Auchenipterichthys longimanus was described by the German-British ichthyologist Albert Günther in 1864. It sits in the family Auchenipteridae, the driftwood catfishes, within the order Siluriformes, and in the genus Auchenipterichthys, a small South American genus of a handful of species. The Catalog of Fishes (Eschmeyer, California Academy of Sciences) treats Auchenipterichthys longimanus as the current valid combination; as with many nineteenth-century catfish descriptions, the species has at times been shuffled between older genus placements in historical literature, but Auchenipterichthys is the name that stands today.
The genus name Auchenipterichthys combines the family name Auchenipterus with the Greek ichthys, "fish" — literally "an Auchenipterus-like fish" — while the species epithet longimanus is Latin for "long-handed", from longus ("long") and manus ("hand"), a reference to the notably elongated pectoral and pelvic fins of mature males, which give the species part of its common name.
Morphology
This is a compact, deep-bodied catfish that reaches about 9 in total length, a real adult size that dwarfs many of the small tetras and dwarf cichlids it is sometimes sold alongside — buyers should plan for the full-grown fish, not the juvenile in the shop tank. The body is laterally compressed and rounded in profile, with a short head, an upturned mouth and three pairs of barbels. Colouration is a study in contrast: a dark grey-to-black body broken by pale, often silvery-white bands or blotches, giving rise to the "zebra" name used in the trade.
Like other members of Auchenipteridae, and like catfishes generally, it is scaleless — its skin is naked rather than protected by scales or bony plates, which makes it markedly more sensitive to medications than scaled fish; copper-based treatments and many standard remedies should be dosed conservatively, at reduced strength. It carries the stiff, serrated, locking spines typical of catfish at the leading edge of its dorsal and pectoral fins; these can snag in an aquarium net and jab an unwary hand, so the fish is best moved in a submerged container rather than netted. The species' defining feature, though, is sexual: mature males develop conspicuously elongated pectoral and pelvic fin rays, the "long hands" of the epithet, along with a modified anal fin used in mating (see Mating).
Habitat
Auchenipterichthys longimanus is native to the Amazon River basin, where it is recorded from Brazil. As a driftwood catfish it favours structurally complex habitat — submerged wood, root tangles, leaf litter and overhanging bank cover — in the basin's blackwater and clearwater tributaries and floodplain channels, sheltering there through the day and moving out to forage as light fades.
Aquarium-relevant water values reported for the species sit around pH 6.0–7.2 and a relatively cool 68–73 °F for a tropical fish, consistent with the moderate, slightly acidic-to-neutral conditions typical of many Amazonian forest streams. It is not documented as needing the extreme soft, tannin-stained blackwater some Amazon fish require, but stable, clean water and cover are important.
Feeding
This species is a nocturnal benthic omnivore and opportunistic micro-predator. In the wild it forages the bottom and among submerged wood after dark for aquatic invertebrates, detritus, and other small prey items it can overpower or scavenge.
In the aquarium it readily takes live and frozen foods such as bloodworm and earthworms, and it learns to accept sinking pellets and other prepared foods once settled. Because it feeds mainly at night, food is best offered after the lights go out, or it risks being out-competed by faster, diurnal tankmates for its share.
Mating
Auchenipterichthys longimanus breeds by internal fertilisation, the hallmark reproductive strategy of the driftwood catfish family Auchenipteridae and one of the genuinely unusual arrangements among catfishes. The mature male's anal fin is modified into an intromittent organ, and this — together with his elongated, thickened pectoral and pelvic fins, which likely help him grip and position the female — is used to transfer sperm directly to her during mating.
Unlike the vast majority of catfishes, which fertilise externally over a nest or scattered clutch, fertilisation here happens internally at the moment of mating. The female is then able to store sperm and does not necessarily spawn immediately; related auchenipterids are known to lay their fertilised eggs directly onto the substrate some time after mating, a reproductive quirk rare enough in the order that it is worth stating plainly rather than assuming the usual egg-scatter pattern.
Breeding
Because fertilisation is internal, breeding in Auchenipterichthys longimanus does not follow the open-water egg-scattering pattern common to many catfishes. Mating itself is the key event — the male transfers sperm via his modified anal fin, the female stores it, and eggs are laid onto the substrate afterward, with little or no reported parental care of the resulting clutch. This mode is documented for the wider driftwood catfish family, though detailed accounts of home-aquarium spawning specific to this species are sparse.
Sexing adults is straightforward once fish mature: males show the long, extended pectoral and pelvic fin rays that give the species its name, while females remain comparatively short-finned and typically deeper-bodied when carrying eggs. Deliberate captive breeding is not well documented in the hobby, and this is not a species aquarists should expect to spawn reliably at home; most specimens in the trade are wild-collected.
In the aquarium
Auchenipterichthys longimanus grows to a genuine adult size of nearly 9 in, and a tank should be sized for that fish from the outset rather than the small juvenile typically sold — the size trap is the most common care failure with driftwood cats. It is a scaleless catfish, so it is more sensitive than scaled fish to copper-based medications and many standard treatments; dose conservatively, often at half strength, and remove it before treating tankmates with anything stronger. Its dorsal and pectoral spines lock rigid and can snag a net or jab a hand, so it should be moved in a submerged container rather than chased with a net.
Provide plenty of driftwood, root tangles and shaded cover to match its wild habitat and give it daytime refuges; it is most active after dark and does best fed once the lights are off, using sinking pellets, frozen bloodworm and other meaty foods. Water in the cooler-than-typical-tropical 68–73 °F range and a pH of roughly 6.0–7.2 suits it well. It is generally peaceful toward tankmates too large to swallow, but as an opportunistic nocturnal predator it will take much smaller fish, so choose companions of a comparable size.
Conservation
The IUCN Red List assesses Auchenipterichthys longimanus as Least Concern, in an assessment dated 11 August 2020. The species is not currently considered threatened, and no major range-wide threats are documented.
It remains tied to the Amazon basin's wood- and root-rich habitats, so localised pressures — deforestation, altered river hydrology, and habitat degradation along its native tributaries — are the relevant long-term concerns even where the overall Red List status is favourable.