Taxonomy & naming
Corydoras micracanthus was described by the British ichthyologist Charles Tate Regan in 1912, from material collected in the province of Salta, Argentina. The epithet — from Greek mikros (small) and akantha (thorn/spine) — refers to its small fin spines. It belongs to the family Callichthyidae and subfamily Corydoradinae.
For most of the twentieth century the species was a near-cipher, known essentially only from Regan's original account; it was redescribed by Aguilera, Mirande and colleagues in 2009 (published in the journal of the Argentine herpetological/ichthyological community) on the basis of fresh Salta material, which clarified its identity and distribution. In 2024 Dias, Tencatt and colleagues published a large revision splitting the oversized genus Corydoras into several lineages (including Brochis, Gastrodermus, Osteogaster and Hoplisoma), and under that scheme the Andes cory becomes Hoplisoma micracanthus — the combination now followed by FishBase and the Catalog of Fishes. The change is recent and the hobby still says 'Corydoras micracanthus,' so we keep that heading while noting the current placement in Hoplisoma.
Morphology
This is a small cory, reaching about 1.5 in in standard length, with the short rounded snout and deep, compact body of the saddle-and-spot lineage. Like all Corydoradinae it is armoured rather than scaled: two overlapping rows of bony plates run down each flank and meet along the back, the head is a hard bony casque, and three pairs of barbels fringe the downturned mouth.
Its colour pattern is the source of both its scientific and common standing — a pale body marked with dark blotching, typically including a darker saddle or band across the back and a patterning of spots and marks on the flanks, the details of which were a focus of the 2009 redescription. As the name micracanthus ('small spine') signals, its fin spines are relatively short. The dorsal, pectoral and adipose fins each carry the family's stiff leading spine. Females grow larger and broader than males, judged most easily from above.
Habitat
Corydoras micracanthus occupies the western tributaries of the Paraná system in Salta, north-western Argentina — streams draining the eastern Andean foothills. This is one of the southern and western extremes of the entire cory range, country higher and more seasonal than the lowland Amazon most corys inhabit, and FishBase accordingly classes it as subtropical rather than tropical.
These are clear, often cooler foothill streams with sandy and gravelly beds. FishBase gives an environmental envelope of pH about 6.0–8.0, hardness from soft to fairly hard (dH 2–25) and water temperatures around 72–79 °F, somewhat cooler on average than equatorial corys experience. As with the rest of the genus it is a facultative air-breather, able to gulp air at the surface and absorb oxygen through a vascularised hindgut, an adaptation for warm or oxygen-poor pools and for the shrinking water of the dry season.
Feeding
No dedicated dietary study has been published, but Corydoras micracanthus is a typical benthic cory: an omnivore and detritivore that works the stream bed. It sifts sand and fine gravel with its barbels and downturned mouth, taking small invertebrates, insect larvae, micro-crustaceans, fallen organic matter and detritus and venting cleaned substrate through the gills. In captivity corys of this type readily accept sinking tablets, granules and flake along with live or frozen bloodworm, Daphnia, grindal and white worm and brine shrimp; a varied diet keeps them in condition rather than leaving them to scavenge leftovers.
Mating
Spawning has not been documented for this species, but corys share a distinctive courtship it can be assumed to follow. They are egg-laying shoalers with no pair bond. A ripe female cleans a surface and the group becomes active; a male takes the classic 'T-position' at right angles to her head, and she appears to take his milt into her mouth. Sperm is thought to pass quickly through her gut to fertilise the few eggs she holds in a basket formed by her pelvic fins, which she presses onto the cleaned site. The cycle repeats a few eggs at a time until the clutch is complete.
Breeding
There is no published breeding report for Corydoras micracanthus, which is seldom kept and only sporadically available. By analogy with related Hoplisoma and Corydoras species, spawning would be expected to follow the family pattern — adhesive eggs laid in small batches on leaves, wood, stone or glass, often triggered by a cool, large water change mimicking seasonal rain or snowmelt, with no parental care (adults may eat the eggs, so a breeder separates eggs or parents). Given its subtropical, cooler-water origin, a meaningful temperature drop may be a particularly useful spawning cue. Eggs of related corys hatch in three to five days and the fry take microworm, baby brine shrimp and powdered foods. None of this is confirmed for C. micracanthus and is offered as informed inference.
In the aquarium
Corydoras micracanthus is an uncommon aquarium fish, more a collector's cory than a community-shop staple, and first-hand husbandry notes are limited. Its core needs are the usual ones: keep it in a shoal of six or more, never singly, with ample bottom area. Substrate should be soft sand or very smooth fine gravel — corys feed by sifting, and sharp or coarse grit erodes and infects their barbels. Provide clean, well-oxygenated, well-filtered water with gentle current and regular changes, planting and wood for cover.
The one point that sets this species apart is temperature: as a subtropical foothill fish it does not want tropical-hot water and is better kept toward the cooler end of the cory range (about 72–75 °F), with the seasonal cooling its home streams experience. It tolerates a broad pH and hardness window. It is peaceful and suits calm community fish — small tetras, rasboras and dwarf cichlids — but should be matched with tankmates that also accept cooler, well-oxygenated conditions.
Conservation
Corydoras micracanthus has not been assessed by the IUCN Red List, so it carries no formal conservation status (Not Evaluated). It is a narrow-range endemic of the Salta foothills in north-western Argentina, and restricted-range stream fishes of this kind are inherently more vulnerable to local pressures — water extraction for agriculture, sedimentation, pollution and habitat alteration — than the wide-ranging lowland corys. Its rarity in the trade means collection is unlikely to be a significant pressure. The honest position is that, lacking a formal assessment and detailed population data, its conservation status is genuinely unknown, and a species this localised would warrant evaluation on its own terms.