Taxonomy & naming
The many-spotted cory was described by the British ichthyologist Charles Tate Regan in 1912, in his revision of the South American siluroid fishes of the genus Corydoras, based on specimens in the British Museum. The type locality is the upper Río Paraguay at Descalvados, in Mato Grosso, Brazil. Regan placed it in Corydoras Lacépède, 1803 — the large genus of South American armoured catfishes in the family Callichthyidae — and it has been known as Corydoras polystictus in the hobby and literature ever since.
That genus had grown unwieldy, with well over 170 nominal species, and molecular work showed it was not a single natural lineage. In June 2024 Dias, Tencatt and colleagues published a large phylogenomic revision of the subfamily Corydoradinae (Zoological Journal of the Linnean Society, DOI 10.1093/zoolinnean/zlae053) that split the old Corydoras into several genera, including Brochis, Hoplisoma, Gastrodermus and Osteogaster. Under that scheme the many-spotted cory falls in the resurrected, short-bodied, lineage-9 genus Hoplisoma, and because Hoplisoma is grammatically neuter the species epithet changes ending to agree: Eschmeyer's Catalog of Fishes now lists the valid combination as Hoplisoma polystictum (Regan, 1912). The change is recent and not yet universal, and the trade still says 'Corydoras polystictus', so we keep that as the heading while recording the new combination. The fish is also frequently confused with the similar Corydoras similis; the cleanest distinction is the plainer, unpatterned caudal peduncle of polystictus.
Morphology
This is among the smallest of all corys: a stocky, deep-bodied little catfish reaching only about 1.5 in in standard length (roughly 1.5–2 in including the tail). Females grow a touch larger and noticeably rounder than males. Like all members of the genus it is armoured rather than scaled — two rows of overlapping bony plates run down each flank, the head is a hard blunt helmet, and three pairs of barbels fringe the downturned mouth for sifting the substrate.
The ground colour is a pale, sandy fawn to greyish-tan, overlaid across the body and the upper flank with many small, fine dark spots — the pattern that gives the fish its scientific and common names. A faint dark band may run through the eye, and there is often a diffuse darker shoulder area, but the caudal peduncle is left comparatively plain and unmarked, which is the most reliable feature separating it from its close look-alikes. As in all corys the dorsal, pectoral and adipose fins each carry a stiff, mildly venomous spine that can jab a careless hand and snag in a net.
Habitat
Corydoras polystictus comes from the upper Río Paraguay basin in the Brazilian state of Mato Grosso, with its range extending into the adjacent Río Guaporé (Iténez) system on the Brazil–Bolivia border, so the species spans parts of Brazil, Bolivia and Paraguay. Rather than the main river channels it favours small tributaries, creeks, the margins of flooded forest and quiet sand banks — shallow, soft-bottomed water over sand and mud, often with leaf litter and submerged wood.
These are warm, generally soft and gently acidic to near-neutral waters. Across its range the species sits comfortably in a band of roughly 68–82 °F, a pH around 6.0 to 8.0 and soft to moderately hard water (about 1–25 dH). Like other corys it is a facultative air-breather, darting to the surface to gulp air and absorb oxygen through a vascularised hindgut — an adaptation that lets it survive the warm, oxygen-poor shallows and shrinking dry-season pools it often occupies.
Feeding
The many-spotted cory is a benthic omnivore and detritivore. It works the soft bottom continuously, burying snout and barbels in sand to taste out small invertebrates, insect larvae, tiny worms, crustaceans and the organic film of detritus, and expelling cleaned sand through the gill openings as it feeds. It is an opportunist rather than a specialist, with a trophic level placing it among the small invertebrate-feeders. In the aquarium it is easy to feed, taking sinking pellets and tablets formulated for bottom-dwellers along with frozen and live bloodworm, Daphnia and brine shrimp; given its very small size it should be given its own ration on the substrate rather than left to scavenge leftovers.
Mating
Like all corys, the many-spotted cory is an egg-laying shoaler with no pair bond and the distinctive, well-studied T-position 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', and she appears to take his milt into her mouth. The sperm is thought to pass rapidly through her gut to fertilise the few eggs she clasps in a basket formed by her pelvic fins, which she then carries to the cleaned surface and presses into place. The sequence repeats, a few eggs at a time, until dozens of sticky eggs are distributed across plants, substrate and the tank glass.
Breeding
Corydoras polystictus can be bred in the aquarium with a little preparation. Condition a group — best skewed to more males than females — on varied live and frozen foods for a couple of weeks, then trigger spawning with a large water change using cooler water, mimicking the cool inflow of the rainy season. The adhesive eggs, laid in small batches and scattered over plants, glass and substrate, receive no parental care; the 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, once the yolk sac is absorbed, take microworm, newly hatched brine shrimp and powdered foods. Because the adults and fry are both tiny, fine first foods and clean water matter, but the species is no harder to raise than other small corys.
In the aquarium
The many-spotted cory is a charming little community fish, well suited to nano and small planted tanks, but it has the same handful of real requirements as its relatives. First, it is a shoaling species and is genuinely stressed kept alone or in pairs — keep six or more, and the group becomes confident and busy. Being so small, a group is comfortable in a modest tank from around 17.5 in; bottom area and footprint matter more than height.
Second, substrate is not decoration. Provide soft sand or very smooth, rounded fine gravel: corys feed by sifting, and this species in particular is prone to barbel erosion and infection on sharp or dirty gravel, leaving the stubby, blunted faces that are a classic sign of poor husbandry. Keep the bottom clean. Water should be warm but not hot (about 72–79 °F), well-filtered and well-oxygenated, with gentle current and regular changes; the species tolerates a broad pH and hardness range. It is utterly peaceful and, given its small size, is best matched with similarly small, calm tankmates — small tetras, pencilfish, dwarf rasboras and the like — never anything large enough to bully or eat it. Two standing cautions apply to all corys: the fin spines can catch in nets, so a cup is safer; and a badly stressed fish can release skin toxins that, in the small volume of a bag or bucket, may kill the whole group, so transport them with care.
Conservation
Corydoras polystictus is assessed by the IUCN as Least Concern. It is reasonably widespread across the upper Paraguay and Guaporé drainages, ecologically flexible and tolerant of the small marginal habitats it favours, and aquarium specimens are increasingly captive-bred, so collection pressure on wild stocks is modest. That does not exempt it from the broad pressures on these headwater systems — agricultural expansion in the Mato Grosso cerrado, run-off, deforestation and damming all degrade the shallow tributaries and sand banks it lives in — but as a species it is in no immediate danger. As with the rest of its lineage, its move into the redefined genus Hoplisoma is part of an ongoing effort to sort the many similar small spotted corys into natural groups.