Taxonomy & naming
Corydoras araguaiaensis was described by David Sands in 1990 from the Rio Araguaia in Brazil, which remains its type locality, and the river gives the fish both its scientific epithet and its common name. It was placed in Corydoras Lacépède, 1803 — the enormous genus of South American armoured catfishes in the family Callichthyidae — and that is the name under which it is still listed and traded.
The genus had long been recognised as far too large and not a single natural lineage. In 2024 Dias, Tencatt and colleagues published a phylogenomic revision (Zoological Journal of the Linnean Society) that broke Corydoras into several genera — among them Brochis, Gastrodermus, Osteogaster and the resurrected Hoplisoma — and under that scheme this species becomes Hoplisoma araguaiaense, a member of the large lineage-9 Hoplisoma group. The combination is recent and not yet universally adopted; FishBase already lists it as Hoplisoma araguaiaense, while the aquarium trade still overwhelmingly says 'Corydoras araguaiaensis,' so we keep the familiar heading and note the new combination here. The Catalog of Fishes treats araguaiaensis as a valid species.
Morphology
This is one of the smaller corys, reaching only about 1.5 in in standard length — a true dwarf among the genus. Like all members of the group it is armoured rather than scaled, with two rows of overlapping bony plates running down each flank and a hard, blunt head; three pairs of short barbels fringe the downturned mouth.
The body is pale with a pattern of dark spots and blotches that tend to coalesce into rough lines along the flank, and a darker mask through the eye. As in most corys the dorsal, pectoral and adipose fins bear a stiff leading spine. Females grow somewhat larger and become noticeably rounder and broader than males when in breeding condition, which is the most reliable way to sex the fish.
Habitat
Corydoras araguaiaensis is native to the Rio Araguaia basin in central Brazil, part of the larger Tocantins–Araguaia system that drains north toward the lower Amazon. It is a fish of shallow, warmer waters — the margins of streams and rivers and connected pools, typically over sand and fine sediment with leaf litter and submerged wood.
The Araguaia runs through clear- and white-water reaches and floods extensively in the wet season, so the species experiences a wide annual swing in water level, clarity and temperature. Like its relatives it is at home in soft to moderately hard, near-neutral water in the warm tropical range, and like all corys it is a facultative air-breather, periodically darting to the surface to gulp air that it absorbs through a modified, vascularised hindgut — an adaptation for the warm, oxygen-poor pools left behind as the floods recede.
Feeding
Like other corys this is a benthic omnivore and detritivore. In the wild it works over sand and soft sediment, sifting the substrate with its barbels to take small invertebrates, insect larvae, microcrustaceans and organic detritus, expelling cleaned sand through the gills as it forages. It is an opportunist rather than a specialist feeder. In the aquarium it readily accepts sinking pellets and tablets, and small frozen and live foods such as bloodworm, Tubifex and Daphnia; a varied diet keeps a group in good condition, and it should never be expected to subsist only on leftovers from other fish.
Mating
No detailed spawning account specific to C. araguaiaensis has been published, but Corydoras-type catfishes share a well-documented courtship and there is no reason to expect this species to differ. They are egg-laying shoalers with no pair bond. When a female is ready she cleans a spawning site and the group becomes active; a male takes up the characteristic 'T-position' at right angles to her head, and the female clasps a small number of eggs in a basket formed by her pelvic fins while sperm passes to fertilise them. She then carries the eggs to a cleaned surface and presses them into place, and the sequence repeats until the clutch is complete.
Breeding
Captive breeding of this particular species is little documented, but it is expected to follow the familiar Corydoras pattern. Spawning is typically triggered by a cool, generous water change that imitates the onset of the rainy season. The adhesive eggs are laid in small batches on plants, wood and the aquarium glass and receive no parental care — adults will eat them, so breeders move either the eggs or the parents. Eggs hatch in roughly three to five days depending on temperature, and the fry take microworm, baby brine shrimp and powdered foods once the yolk sac is absorbed. As a small species the clutches are correspondingly modest. Honest note: figures here are drawn from the genus rather than from confirmed records for araguaiaensis itself.
In the aquarium
C. araguaiaensis is an undemanding but seldom-seen aquarium fish best suited to a quiet, well-planted tank. As a shoaling species it should be kept in a group of at least six; kept singly or in pairs it becomes withdrawn and stressed. Being small, it does not need a large tank, but it does need bottom area rather than height.
Substrate matters: provide soft sand or very smooth, rounded fine gravel, because corys feed by sifting and sharp or coarse gravel wears down and infects their barbels. Keep the bottom clean and the water warm (about 72–79 °F), well-filtered and well-oxygenated, with the gentle current and regular water changes any cory appreciates; it tolerates a broad pH and hardness range. It is utterly peaceful and makes an ideal companion for small tetras, rasboras, dwarf cichlids and other calm community fish, and is best not housed with anything large enough to bully it. As with all corys, the fin spines can tangle in a net (a cup is safer), and a badly stressed cory can release skin toxins that, in the confined volume of a bag, may harm the whole group — so transport them carefully.
Conservation
Corydoras araguaiaensis is assessed by the IUCN as Least Concern (assessed 2018). It has a reasonably wide distribution across the Araguaia basin and no specific major threats have been identified for it. That said, the Tocantins–Araguaia system faces broad and growing pressures — dam construction, agricultural expansion and run-off, and habitat degradation across the Cerrado — that affect the shallow marginal habitats this and similar small fishes depend on. There is no targeted conservation programme for the species, and the chief uncertainty is taxonomic: as the wider 'spotted dwarf' complex of the region is studied, the boundaries and ranges of species like this one may yet be refined.