Taxonomy & naming
Acanthodoras depressus was described by the Austrian ichthyologist Franz Steindachner in 1881. It belongs to the family Doradidae, the thorny or talking catfishes of South America, and to the small genus Acanthodoras. The Catalog of Fishes (Eschmeyer, California Academy of Sciences) treats Acanthodoras depressus as the currently valid combination; older literature and aggregator records for this genus have at times shuffled between doradid genera as the family's internal classification was revised, so the same fish may turn up under older generic placements in historical sources.
The genus name Acanthodoras combines the Greek akantha, "thorn" or "spine", with Doras, the type genus of the family — a reference to the row of thorny, backward-hooked bony plates running down the flank. The species epithet depressus is Latin for "pressed down" or "flattened", describing the notably flattened head and body that set this species apart from more cylindrical doradids.
Morphology
This is a small doradid, reaching only about 3 in SL, with a body plan built for hugging the bottom: the head is large, broad and strongly flattened, and the body itself is depressed rather than the rounded, torpedo-like cross-section of many other thorny catfishes. Three pairs of barbels — a long maxillary pair and two shorter mandibular pairs — ring the small mouth and help it feel its way through sediment. The eyes are small, typical of a fish that relies more on touch and smell than sight.
Like other doradids it lacks true scales; instead a row of bony, keeled plates (scutes) runs along each flank, and in this genus those plates carry small thorn-like points, giving the family its "thorny catfish" name. The dorsal and pectoral fins each carry a stiff, sharp, serrated spine that can be locked erect — a genuine hazard to bare hands and to careless netting, and part of why doradids are nicknamed "talking catfish" (the spines can be rasped to produce an audible sound, though this has been documented mainly in other genus members rather than specifically confirmed here from the cached sources).
Habitat
Acanthodoras depressus is native to South America, recorded from the upper Orinoco River basin (Venezuela and Colombia) and the Rio Negro basin in Brazil — both part of the wider Amazon–Orinoco lowland river system. It is a demersal, freshwater, tropical species that lives on or near the bottom, typically among leaf litter, root tangles and soft sediment where its flattened profile lets it wedge into tight spaces.
The cached sources do not give precise temperature or pH figures for this species specifically; as an Orinoco/Rio Negro fish it can be expected to come from warm, generally soft, acidic-to-neutral blackwater-influenced habitat typical of that region, but keepers should treat exact water-chemistry numbers as data sparse rather than assume specifics not confirmed in the literature consulted here.
Feeding
FishBase places Acanthodoras depressus at trophic level 2.5, consistent with a primarily detritivorous and herbivorous diet supplemented with small invertebrates picked out of the substrate — a nocturnal benthic forager that sifts through sediment and leaf litter after dark rather than hunting actively in open water.
In the aquarium it accepts a wide variety of foods, per hobbyist reports, and does well on sinking pellets, algae wafers and frozen foods offered after lights-out so it is not out-competed by more active, diurnal tankmates. A soft substrate or fine, rounded gravel is worth providing both to match its natural digging behaviour and to protect its sensitive barbels from abrasion.
Mating
Detailed courtship behaviour for Acanthodoras depressus has not been documented in the sources available here — this is a poorly studied species outside of taxonomic and distribution records. What is reported from aquarium observations is that spawning has been achieved in captivity, with parents seen excavating a shallow depression in the substrate ahead of egg deposition, suggesting a substrate-nesting rather than open-water egg-scattering strategy. Specific detail on pairing, size of spawns, or triggers is data sparse and should not be assumed beyond what is recorded.
Breeding
Breeding in the home aquarium is uncommon but has reportedly occurred: hobbyist accounts describe adults digging a depression in the substrate to receive the eggs, pointing to a cavity or substrate-nest mode rather than the free-scattering habit seen in some other catfish groups. Parental guarding behaviour after spawning is not confirmed in the sources consulted, and this should not be assumed present.
Given how little is documented, this species sits closer to the "rarely bred, breeding poorly understood" end of the doradid spectrum than to the readily spawned callichthyid bubble-nesters. Keepers attempting to breed it should expect to be working from limited precedent and should record and share observations rather than rely on an established protocol.
In the aquarium
Acanthodoras depressus tops out at a modest 3 in SL, so unlike many of its larger doradid relatives it does not fall into the classic catfish size trap — a modestly sized tank suits it for life, provided there is ample cover. It is a scaleless, plated fish, which means it is more sensitive than scaled species to copper-based and some other medications; dose any treatment conservatively and remove carbon or other media as directed rather than relying on standard scaled-fish dosing.
It carries stiff, sharp, serrated dorsal and pectoral spines that lock erect and readily snag in aquarium nets, so it is best scooped and moved in a container rather than netted by hand — the spines can jab the keeper as well as tangle in mesh. It is a nocturnal, secretive fish that hides extensively by day, so caves, root tangles and dim cover are worth providing; expect to see it mostly once the lights go down. Reports describe it as a peaceful community fish, suited to soft-water tankmates from its native Orinoco/Rio Negro region, though it should not be housed with fish small enough to be mistaken for food during its nightly foraging.
Conservation
The IUCN Red List assessed Acanthodoras depressus as Least Concern in 2020. It is known from a reasonably wide range across the upper Orinoco and Rio Negro basins, and FishBase notes high resilience with a minimum population doubling time of under 15 months, consistent with a species not currently considered at risk.
As with many South American blackwater and river species, the main long-term pressures on its habitat are regional — deforestation, mining-related sedimentation and water-quality changes across the Orinoco and Rio Negro systems — rather than any pressure specific to this species or its aquarium trade, which appears to be a minor and largely incidental part of the wider ornamental-fish export from the region.