Taxonomy & naming
Corydoras urucu was described in 2009 by Marcelo R. Britto, Wolmar B. Wosiacki and Luciano F. A. Montag, in the journal Copeia, from the rio Urucu basin — a right-bank tributary of the rio Solimões near Coari, Amazonas, Brazil. The holotype, just 1 in standard length, came from the Igarapé da Onça, a small stream in that drainage. The species name is taken directly from the type locality, the rio Urucu.
It was placed in Corydoras Lacépède, 1803 (family Callichthyidae). That genus was subsequently shown to be non-monophyletic, and the 2024 revision by Dias, Tencatt and colleagues (DOI 10.1093/zoolinnean/zlae053) split it into several genera. Under that scheme C. urucu belongs to the resurrected genus Hoplisoma, and FishBase now lists it as Hoplisoma urucu, the current valid combination. The hobby still uses 'Corydoras,' so we keep that heading while noting the change. The Catalog of Fishes treats the name as valid.
Morphology
This is a dwarf cory — one of the smallest in the genus — reaching only about 1 in standard length, with the holotype measured at 1 in SL. The build is the familiar armoured one in miniature: two rows of overlapping bony plates down each flank meeting in a dorsal ridge, a hard helmet of a head, and short barbels around the down-turned mouth.
Its colouring is comparatively plain — a pale ground with fine dark speckling and markings rather than the bold blotches or wavy bands of the more flamboyant corys — which, together with its small size and the obscurity of its home river, helps explain why it remains little known in aquaria. The dorsal, pectoral and adipose fins each carry the usual stiff defensive spine.
Habitat
Corydoras urucu is known only from the rio Urucu basin, a right-bank tributary of the rio Solimões reaching Lago Coari, in Amazonas, Brazil; the type series came from the small forest stream Igarapé da Onça. This is lowland western-Amazon stream country — warm, soft water over sand and leaf litter, among submerged wood and roots in shaded creeks.
No published temperature or pH figures are tied specifically to this species, so the water values given here are conservative estimates drawn from the warm, soft, slightly acidic streams of the Solimões/Urucu region rather than from measurements at the type locality, and should be read as indicative only. Like all corydoradines it is a facultative air-breather, surfacing to gulp air and absorb oxygen through a vascularised hindgut, suiting the warm, low-oxygen shallows it inhabits.
Feeding
Like its relatives, Corydoras urucu is a benthic omnivore and detritivore, working the bottom of its small streams to sift out micro-invertebrates, insect larvae, tiny worms, micro-crustaceans and organic detritus, expelling cleaned sand through the gill openings. No diet study specific to this species has been published, but its mouth and feeding anatomy are those of a typical sand-sifting cory — scaled down — and there is no reason to think it departs from the omnivorous, opportunistic pattern of the group.
Mating
No spawning of Corydoras urucu has been documented, and the account here is the standard corydoradine pattern, offered as the expected behaviour. These are egg-laying shoalers with no pair bond: a ready female cleans a site, a male takes up the classic 'T-position' at right angles to her head, and she clasps a few eggs in a basket formed by her pelvic fins before pressing them onto the cleaned surface. The cycle repeats a few eggs at a time until a clutch of sticky eggs is distributed across leaves, stones or wood.
Breeding
There are no published breeding reports for Corydoras urucu, which is rare in the trade and seldom kept. By analogy with the group — and with other dwarf corys, which can be productive if delicate — spawning would be expected to follow the familiar pattern of adhesive eggs laid in small batches on firm surfaces, no parental care, and a cool, large water change as the likely trigger. Until the species is bred and documented, all of this should be treated as informed expectation rather than established husbandry.
In the aquarium
Corydoras urucu is a rarely seen dwarf cory, and its small size makes it both appealing and a little demanding: tiny corys want clean, soft, warm water and a fine sand bed, and are best kept in a species or small-fish setup where they are not outcompeted at feeding time. Keep it as a shoal of six or more — dwarf corys are especially gregarious and shy when understocked — with gentle filtration, good oxygenation and regular water changes. Offer small sinking foods sized for a little mouth. As with all corys, avoid sharp gravel that damages the barbels, net it with care or use a cup (the fin spines snag), and transport it gently, since a stressed cory can release a skin toxin that may prove lethal in the small volume of a bag.
Conservation
Corydoras urucu is assessed by the IUCN as Least Concern, in an evaluation dating to 2018. That status sits against a very restricted known range — the single rio Urucu drainage — which, for any narrowly distributed fish, is a genuine vulnerability should that catchment be disturbed. The rio Urucu region is notable for petroleum extraction, and the associated infrastructure and pollution risk are the most obvious local threats. As with many recently described, single-drainage Amazonian fishes, its true range and population remain poorly known, and an honest assessment records both the Least Concern listing and the narrowness of what is actually documented.