Taxonomy & naming
The tail-spot cory was described by Wolfgang Rössel in 1961 from the main stream of the upper Río Guaporé, in Rondônia, Brazil, which remains the type locality. For more than sixty years it has been catalogued as Corydoras caudimaculatus, the small armoured catfish genus (family Callichthyidae) that long held the great majority of the hobby's 'cory cats.'
The genus Corydoras had grown unwieldy — well over 170 species — and molecular work showed it was not a single natural group. In June 2024 Dias, Tencatt and colleagues published a large phylogenomic revision (Zoological Journal of the Linnean Society, zlae053) that split the old Corydoras into several genera, including Aspidoras, Scleromystax, Gastrodermus, Osteogaster, Brochis and the resurrected Hoplisoma. Under that scheme the tail-spot cory falls in lineage 9 and becomes Hoplisoma caudimaculatum — the epithet shifting to neuter to agree with the neuter genus name, a point clarified in a published correction to the paper. Eschmeyer's Catalog of Fishes and FishBase now carry the Hoplisoma combination, but the change is recent and not yet universal, so we keep the familiar 'Corydoras' heading while noting the current valid name. The species is easily confused with the similar C. similis and C. ourastigma; it is told apart by the well-defined, solid blackish spot on the caudal peduncle rather than a diffuse smudge.
Morphology
This is a small, stocky cory, deep-bodied and flat-bellied, reaching only about 1.5–2 in in standard length; females grow visibly larger, rounder and higher-bodied than males. Like all members of the group it is armoured rather than scaled: two rows of overlapping bony plates (scutes) run down each flank and meet in a ridge along the back, and the head is a hard, blunt helmet. Three pairs of short sensory barbels fringe the downturned mouth — the tools it uses to taste and sift the substrate.
The ground colour is a pale, translucent pinkish-white, the flank scattered with fine dark and iridescent speckling that gives the fish a frosted, almost silvery sheen in good light. The single defining feature is a large, sharply outlined black blotch on the caudal peduncle, at the base of the tail — the 'maculatus' of the name. The fins are otherwise mostly clear, and the dorsal, pectoral and adipose fins each carry a stiff, mildly venomous spine, a defence that can give a careless hand a sharp jab and that occasionally tangles in a net.
Habitat
Corydoras caudimaculatus is endemic to the Río Guaporé drainage — known as the Iténez on the Bolivian side — in the upper Madeira basin straddling western Brazil and northeastern Bolivia. It is a fish of quieter water: the shallow margins and tributaries of the river, typically over soft sand with leaf litter and submerged wood, where it forages in loose groups.
These are warm, soft, often tannin-stained waters. Across its range the species sits in a tropical envelope — temperatures of roughly 72–79 °F, a pH band from acidic to neutral (about 6.0–7.0, with FishBase citing tolerance to 8.0) and soft to moderately hard water — which is why it adapts readily to captivity. Like other corys it is a facultative air-breather: it darts to the surface to gulp air and absorb oxygen through a modified, vascularised hindgut, an adaptation that lets it survive in warm, low-oxygen shallows and shrinking dry-season pools where most fish could not.
Feeding
The tail-spot cory is a benthic omnivore and detritivore. It works the bottom more or less continuously, burying its snout and barbels in sand to taste out small invertebrates, insect larvae, worms, benthic crustaceans, fallen seeds and the organic film of detritus, expelling cleaned sand through the gills as it goes. It is an opportunist rather than a specialist, and that catholic diet is part of its hardiness. In the aquarium it takes sinking dried foods, frozen and live bloodworm, Tubifex and brine shrimp, and anything its tankmates let fall — but it should never be left to subsist only on leftovers, and a varied diet keeps the group in colour and condition.
Mating
Corydoras are egg-laying shoalers with no pair bond and a distinctive, well-studied courtship. When a female is ready she cleans a site — a leaf, a stone, the aquarium glass — and the group becomes active; a male positions himself at right angles to her head, in the classic 'T-position,' and she appears to take his milt into her mouth. Sperm is then thought to pass rapidly through her gut and out to fertilise the few eggs she clasps in a basket formed by her pelvic fins, which she carries to the cleaned site and presses into place. The sequence repeats, a few eggs at a time, until dozens of sticky eggs are scattered across the chosen surfaces.
Breeding
The tail-spot cory is bred in captivity along the familiar Corydoras lines, if a little less prolifically than the bronze cory. Spawning is typically triggered by a large (50–70%) water change with cooler water and increased oxygenation, mimicking the arrival of the rainy season. A productive group skews to more males than females — around two males per female is a common ratio. The adhesive eggs are deposited on glass and vegetation and receive no parental care; the adults will eat them, so breeders move the eggs or the parents. Eggs hatch in about three to four days, and the fry, after absorbing the yolk sac, take microworm and Artemia nauplii; a clean sand substrate helps reduce fry losses to disease. Most fish in the trade are wild-caught from the Guaporé, though captive breeding is well established.
In the aquarium
The tail-spot cory is a rewarding, undemanding aquarium fish, but a few real requirements separate a thriving group from a struggling one. First, it is a shoaling species and is genuinely stressed when kept alone or in twos — keep six or more, and they reward you with constant, confident activity. A group is comfortable in a tank of around 15–20 US gal or more; footprint and bottom area matter more than height.
Second, substrate is not optional decoration. Provide soft sand or very smooth, rounded fine gravel: corys feed by sifting, and sharp or coarse gravel erodes and infects their barbels, leaving stubby, blunted faces — one of the commonest signs of poor husbandry. Keep the bottom clean, because they are always nosing in it. Water should be warm (about 72–79 °F), soft to moderately hard, well-filtered and well-oxygenated, ideally tinted with the tannins of leaf litter and wood that suit a Guaporé fish. They are utterly peaceful and make ideal companions for tetras, rasboras, pencilfish, dwarf cichlids and other calm community fish — never with anything large enough to bully them. Two cautions worth knowing: the fin spines can catch in nets (a cup is safer), and a distressed cory can release a toxin from its skin that, in the confined volume of a bag or bucket, can kill the whole group, so transport them with care.
Conservation
Corydoras caudimaculatus was assessed by the IUCN as Least Concern in 2020. It is reasonably widespread within the Guaporé drainage, ecologically flexible and tolerant of the warm, shallow, low-oxygen habitats it favours, and although it is collected for the aquarium trade there is no evidence that this threatens the wild population. None of that makes it immune to the broad pressures on Amazonian headwaters — deforestation, agricultural run-off, gold-mining sediment and damming all degrade the marginal habitats of the upper Madeira — but as a species it is, for now, in no danger. Because it is a relatively narrow-range endemic rather than a continent-spanning generalist, it is worth watching as land-use change accelerates in Rondônia and the Bolivian Iténez.