Taxonomy & naming
Corydoras semiaquilus was described by Stanley H. Weitzman in 1964, in the Proceedings of the United States National Museum. The type locality is Igarapé Preto, a tributary of the upper Rio Solimões (the Brazilian name for the upper Amazon main stem) in Amazonas, Brazil. The specific name refers to the partly dark coloration of the upper body — semi- ('half, partly') with aquilus ('dark, swarthy') — describing a fish that is darkened over the back and flank but pale beneath.
For decades it was carried as Corydoras semiaquilus, a long-snouted member of the huge armoured-catfish genus Corydoras Lacépède, 1803 (family Callichthyidae). That genus grew past 170 species and was shown by molecular work not to be a single natural lineage, and in 2024 Dias, Tencatt and colleagues split it into several genera (Brochis, Hoplisoma, Gastrodermus, Osteogaster and others). Unlike many of its long-snouted relatives, however, semiaquilus was retained in Corydoras: the Catalog of Fishes lists it as valid as Corydoras semiaquilus Weitzman 1964, in Corydoras in the strict sense. So here the hobby name and the current scientific lineage genus coincide. In the trade it is usually sold as the 'Peru black cory,' and 'C. semiaquilus' is also applied loosely to similar dark long-snouts from the region.
Morphology
This is one of the larger corys and a distinctly long-snouted one, reaching about 2.5 in standard length. The snout is elongated and pointed, the head angular, and the overall build sturdy — a powerful, active fish rather than a dainty one.
The colour is what names it: the body is a solid grey-to-black wash over the upper flank and back, fading to a pale, whitish belly, so the fish reads as 'black' in the tank — hence 'Peru black cory.' A dark, diagonal band runs from the snout up and back through the eye toward the dorsal fin, and in semiaquilus this eye mask and the dark body shading are connected by a continuous dark band, a useful identification feature. There is sometimes additional fine spotting or banding about the head. As in all corys the body is armoured with two rows of overlapping bony scutes, the mouth is downturned and fringed with three pairs of barbels, and the dorsal and pectoral fins carry stiff, mildly venomous leading spines.
Habitat
Corydoras semiaquilus is a fish of the western Amazon basin. Its type locality lies in the upper Rio Solimões drainage of Amazonas, Brazil (the Igarapé Preto), and it is recorded more broadly from the western Amazon in Brazil and Peru — the fish reaching the hobby as the 'Peru black' generally being collected in Peruvian Amazonia. It belongs to the quiet-water guild of the genus: slow tributaries, forest streams and creek margins over soft sand and leaf litter.
These are warm lowland waters, soft and slightly acidic to neutral. Reported aquarium-relevant figures sit around 72–79 °F, with a pH band of roughly 6.0–8.0 and soft to moderately hard water (about 2–25 dH). Like the rest of the subfamily it is a facultative air-breather, surfacing to gulp air and absorb oxygen through a vascularised hindgut — an adaptation for the warm, oxygen-poor backwaters and dry-season shallows where it lives.
Feeding
The Peru black cory is a benthic omnivore and detritivore. It forages continuously over the bottom, driving its long snout and barbels into sand and leaf litter to taste out small invertebrates, worms, insect larvae, micro-crustaceans, fallen organic matter and detritus, expelling cleaned substrate through the gill openings as it sifts. The long, pointed snout suits probing deeper into and under the substrate than the blunt-nosed corys manage. In the aquarium it takes sinking pellets and tablets, frozen and live bloodworm, blackworm and brine shrimp, and other sinking foods; as with all corys it should be fed properly rather than left to scavenge leftovers.
Mating
Corydoras are egg-laying shoalers with the conserved 'T-position' courtship and no pair bond, and the Peru black cory follows the family pattern. A ripe female cleans a spawning site, the group grows active, and a male presses crosswise against her head to form the characteristic T as she takes his milt; the eggs are clasped in a pelvic-fin basket, carried to the cleaned surface and pressed into place a few at a time until the chosen spots carry sticky eggs. Specific spawning observations for semiaquilus are limited, but there is no reason to think it departs from this conserved corydoradine sequence.
Breeding
Aquarium breeding of C. semiaquilus is not commonly documented; it is largely a wild-collected import rather than a mass-bred staple, and as a long-snouted species it is regarded as a more demanding subject than the easy community corys. Guidance is mostly extrapolated from related long-snouts: a cool, large water change mimicking the rainy season triggers activity, adhesive eggs are laid in small batches on firm surfaces and the glass, and the adults give no parental care and may eat the eggs, so a breeder removes the eggs or the parents. Fry hatch in a few days and take microworm, baby brine shrimp and powdered foods once the yolk sac is absorbed. A mature group in cool, soft, clean water gives the best chance; repeatable published spawning reports for semiaquilus specifically remain scarce.
In the aquarium
The Peru black cory is a peaceful, shoaling fish and should be kept in groups of six or more — kept singly or in pairs it becomes stressed and withdrawn. As a larger, active, long-snouted species it wants a roomy tank with a generous footprint (comfortably more than 23.5 in for a group) and open swimming space. Substrate is critical: soft sand or very fine, smooth, rounded gravel only, because the long feeding snout is precisely what coarse or sharp grit erodes and infects, leaving the blunted faces that mark a badly kept fish.
Water should be warm but not hot (about 72–79 °F), soft to moderately hard, slightly acidic to neutral, clean and well-oxygenated with gentle current and regular changes. Its dark body shows best over pale-to-medium sand among wood and leaf litter, though it is striking either way. It is peaceful with calm community fish — tetras, rasboras, dwarf cichlids — and should never share a tank with anything large enough to bully it. The usual cory cautions apply: the fin spines snag in nets (use a cup), and a badly stressed cory can release a skin toxin lethal in the small volume of a bag, so transport with care.
Conservation
Corydoras semiaquilus is assessed by the IUCN Red List as Least Concern (assessment dated 2020). It is reasonably widespread across the western Amazon in Brazil and Peru and is not considered threatened, with aquarium collection at modest levels relative to its range. As with all Amazonian fishes, the broad regional pressures — deforestation, agricultural and extractive activity, run-off and habitat alteration — bear on the shallow tributaries and creeks it inhabits, but the species itself is not currently flagged as at risk. Because 'Peru black' is applied loosely to several similar dark long-snouts, some trade material may represent related or undescribed forms whose status would need separate assessment.