Taxonomy & naming
Corydoras zygatus was described by Carl Eigenmann and William Ray Allen in 1942, from the western Amazon River basin in Peru. The specific name derives from the Greek zygon, a yoke or crossbar, in reference to the dark band that crosses the body — the source of the common name 'black-band cory'. It was placed in Corydoras Lacépède, 1803, and belongs to the so-called aeneus group, the cluster of bronze-and-rust coloured corys built around the familiar bronze cory, with which and with C. rabauti it is frequently confused.
In 2024, Dias, Tencatt and colleagues split the oversized Corydoras into several lineage genera, resurrecting Osteogaster for the aeneus-group species. Under that revision the black-band cory becomes Osteogaster zygata, the valid combination FishBase now carries; the specialist site Corydoras World places it in the same Osteogaster lineage, and the Catalog of Fishes (Eschmeyer, California Academy of Sciences) recognises the species as valid. We retain 'Corydoras zygatus' as the heading because that is the name still used throughout the hobby, while noting the current valid combination is Osteogaster zygata. Because the aeneus complex is a tangle of similar, partly undescribed forms, the boundaries between zygatus and its close relatives are not always cleanly drawn.
Morphology
This is a small, stocky cory, reaching about 2 in standard length, deep-bodied and flat-bellied in the manner of its bronze-cory relatives, with females growing larger and rounder than males. The armour is the standard two rows of overlapping bony plates meeting along the back, the head a hard blunt helmet, and three pairs of barbels fringe the downturned, sand-sifting mouth.
The ground colour is a metallic pinkish-grey to coppery, with an iridescent bronze sheen along the flank reminiscent of the bronze cory — which is exactly why the two, together with the rusty C. rabauti, are so often mixed up in shipments. The distinguishing feature, when present, is the darker band that crosses the body and gives the fish its name. The dorsal, pectoral and adipose fins each carry the usual stiff, mildly venomous leading spine that defends the fish and snags readily in a net.
Habitat
Corydoras zygatus is recorded from the western Amazon River basin in Peru — the upper Amazonian lowlands fed by Andean tributaries. Like its aeneus-group kin it is a fish of quieter, shallow water: stream margins, slow reaches, pools and backwaters over soft sand and mud with leaf litter and submerged wood.
Reported tolerances mirror those of the bronze cory and suit a warm lowland habitat — temperatures around 72–77 °F and a broad pH band from acidic to slightly alkaline (roughly 6.0–8.0), with soft to moderately hard water. Like all members of the subfamily it is a facultative air-breather, darting to the surface to gulp air and absorb oxygen through a vascularised hindgut, which lets it persist in warm, oxygen-poor pools and shrinking dry-season puddles where many fish could not survive.
Feeding
The black-band cory is a benthic omnivore and detritivore, like the rest of its group. It forages continuously over the bottom, burying its snout and barbels in sand to taste out small invertebrates, insect larvae, worms, crustaceans, fallen seeds and the organic film of detritus, expelling cleaned sand through the gills. It is an opportunist rather than a specialist, and that flexible diet underpins its hardiness. In the aquarium it readily takes sinking pellets and wafers, frozen bloodworm and brine shrimp, and whatever its tankmates let fall, though it should not be left to live on leftovers alone.
Mating
Corydoras zygatus follows the egg-laying, T-position courtship typical of the aeneus group and the genus at large, with no pair bond. When a female is ready she cleans a spawning site and the group becomes active; a male positions himself at right angles to her head in the classic 'T', a few eggs are fertilised and clasped in a basket formed by her pelvic fins, and she carries them to the cleaned surface and presses them into place. The sequence repeats, a few eggs at a time, until the clutch — on the order of dozens to a couple of hundred sticky eggs — is scattered across the chosen surfaces.
Breeding
As an aeneus-group cory, C. zygatus breeds along the same reliable lines as the bronze cory and is reported to spawn readily in the aquarium. Spawning is typically triggered by a cool, large water change mimicking the onset of the rainy season, and a productive group skews to more males than females. The adhesive eggs are laid in small batches and receive no parental care — adults will eat them, so breeders move 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, baby brine shrimp and powdered foods, growing quickly and hardily.
In the aquarium
Corydoras zygatus is a hardy, peaceful, undemanding cory in the bronze-cory mould, and makes an excellent community fish, but it is a shoaling species and should be kept in groups of six or more — kept singly or in pairs it is visibly stressed. A group is comfortable in a tank of around 23.5 in or more, where bottom area counts for more than height.
Substrate is the key detail: provide soft sand or very smooth, rounded fine gravel, because corys feed by sifting and sharp or coarse gravel erodes and infects their barbels, leaving the blunted faces that betray poor husbandry. Keep the bottom clean, the water warm (about 72–77 °F), well-filtered and well-oxygenated with a gentle current, and offer the broad pH and hardness range it tolerates. It is utterly peaceful and suits tetras, rasboras, dwarf cichlids and other calm community fish, never anything large enough to bully it. The familiar cautions apply: the fin spines catch in nets, so a cup is safer, and a badly stressed cory can release a skin toxin that, in the confined volume of a bag or bucket, can kill the whole group — so transport them with care.
Conservation
Corydoras zygatus is assessed by the IUCN as Least Concern, in an evaluation dated 2020. As a fairly widespread western-Amazonian species that is also commercially bred and adaptable, it faces no immediate threat at the species level, and collection pressure is moderated by captive production. The usual broad pressures on Amazonian freshwaters — deforestation, agricultural run-off and pollution — degrade the shallow marginal habitats it favours, but as a species it is not currently considered at risk. As with the rest of the aeneus complex, the more interesting caveat is taxonomic: the group contains several similar, partly undescribed forms, and any forms separated out of 'zygatus' in future may need assessing on their own terms.