Taxonomy & naming
The flagtail cory was described by Warren Burgess in 1983 as Corydoras robineae, from the Rio Aiuana, a southern tributary of the middle Rio Negro in the Brazilian state of Amazonas — a strikingly late description for so conspicuous a fish, which had simply not reached science before the modern ornamental trade opened up the upper Negro. For four decades it sat in Corydoras Lacépède, 1803, the vast genus of South American armoured catfishes in the family Callichthyidae.
That genus proved not to be a single natural lineage, and in 2024 Dias, Tencatt and colleagues published a large revision of the subfamily Corydoradinae that split it into several genera. Among these was the resurrection of Brochis Cope, 1872 — a name long treated as a junior synonym or subgenus of Corydoras — for a clade of long-snouted, many-rayed corydoradines, and the flagtail cory was placed there. Under the current Catalog of Fishes classification the valid combination is therefore Brochis robineae (Burgess, 1983). The change is recent and the aquarium world still overwhelmingly says 'Corydoras robineae,' so we keep that heading while noting the new genus. The epithet honours Robine Schwartz: the collector and exporter Adolfo Schwartz supplied the type material and asked that the fish be named for his mother.
Morphology
This is a slender, fairly long-snouted cory, reaching only about 2 in in standard length (roughly 2.5–3 in total, females a little larger); it is a small fish whose impact is entirely in its pattern. The body plan is standard Corydoras armour — two rows of overlapping bony scutes down each flank meeting in a dorsal ridge, a hard helmeted head, three pairs of barbels on the downturned mouth, and the usual stiff, mildly venomous spines in the dorsal, pectoral and adipose fins.
The colour is what makes it. The ground is a pale silver-white, broken along the back and upper sides into a network of dark spots and short, irregular stripes; the dorsal fin carries a couple of faint dark stripes. The signature, though, is the caudal fin: five or six bold black bands run horizontally across a white tail, three of them carrying forward to merge into the body pattern and break up into spots by mid-body. No other corydoradine has a horizontally striped tail — in every other species the caudal is either clear or vertically barred — which makes the flagtail instantly identifiable and is the source of both 'flagtail' and 'bannertail'.
Habitat
Corydoras robineae is restricted to the upper and middle Rio Negro basin and its tributaries in the Brazilian Amazon — classic black-water country. These are the famously dark, tea-stained waters of the Negro: stained brown by dissolved tannins from decaying forest litter, very soft, acidic and nutrient-poor, flowing over white sand among submerged wood and leaf litter.
Despite that acidic, soft-water origin, the species is kept successfully across a fairly broad range — temperatures around 73–79 °F and a pH from about 6.0 to 8.0 in captivity — though it leans, like its home water, toward warm, soft and well-oxygenated conditions. Hobbyists consistently note that it likes clean, well-oxygenated water with a little more flow and surface movement than the average cory, a hint that in the wild it favours the more active, oxygen-rich reaches of its rivers. As a callichthyid it is also a facultative air-breather, surfacing to gulp air and absorb oxygen through a vascularised hindgut.
Feeding
The flagtail cory is a benthic omnivore that forages over sand, sifting snout and barbels through the substrate to find small invertebrates, insect larvae, worms, micro-crustaceans and organic detritus. In the wild that means working the leaf litter and sand of black-water margins; in the aquarium it takes sinking dried foods — pellets and tablets — as a staple, supplemented generously with small live and frozen foods such as bloodworm, brine shrimp, daphnia and chopped earthworm. A varied diet matters more for this species than for the toughest community corys, because conditioning it well is the first step to ever getting it to spawn, and a fish kept only on leftovers will neither colour up nor breed.
Mating
The flagtail cory shows the family's characteristic spawning behaviour: it is an egg-laying shoaler with no pair bond. When a female is ready she cleans a site and the group becomes active; a male adopts the classic 'T-position', lying at right angles to her head, and she appears to take his milt into her mouth, the sperm then passing quickly through her gut to fertilise the few eggs held in the basket of her clamped pelvic fins. She carries those eggs to a chosen surface — plants, wood, glass — and presses them into place before the cycle repeats. The clutch is built up a few sticky eggs at a time, and a balanced or male-skewed group spawns more readily than a single pair.
Breeding
This is regarded as one of the more challenging corys to breed, and home spawnings are uncommon enough to be worth reporting. Success starts with conditioning a group well on varied live and frozen foods, with the ratio tilted to more males than females (around two males per female). Spawning is then coaxed with large, distinctly cooler water changes (on the order of 50–70 per cent) and stepped-up oxygenation and flow, mimicking the cool inflows of the rainy season. The female lays a relatively small clutch — on the order of dozens of adhesive eggs — that receives no parental care; breeders remove either the eggs or the adults. Eggs hatch in roughly three to four days, and once the yolk sac is absorbed the fry take microworm and baby brine shrimp. Reliable captive production is rare, so a good share of fish in trade are still wild-caught from the Rio Negro.
In the aquarium
The flagtail cory is a rewarding but not beginner-proof fish. Like all corys it is a shoaler that is stressed in ones and twos — keep six or more, and a larger group both looks better and behaves more confidently. Bottom area matters more than height, and a tank of around 23.5–31.5 in gives a group room to forage.
Substrate must be soft sand or very smooth, rounded fine gravel: this species feeds by sifting, and sharp or coarse gravel wears down and infects the barbels, leaving the blunted faces that signal poor husbandry. Where it asks for a little more than the average cory is water quality and oxygen — it wants genuinely clean, well-oxygenated water with some current and surface movement, soft and warm, and it is less forgiving of neglect than the bronze or peppered corys. It is entirely peaceful and suits a black-water or Amazon community of small tetras, pencilfish, dwarf cichlids and similar calm fish; never house it with anything large enough to bully it. The usual cautions apply: the fin spines snag in nets, so move it in a cup, and a badly stressed cory can release a skin toxin that, in the small volume of a bag, can kill the whole group — so transport with particular care.
Conservation
Corydoras robineae is assessed by the IUCN as Least Concern. Although its range is narrow — essentially the upper and middle Rio Negro — that basin remains largely forested, sparsely populated and comparatively undisturbed, and the ornamental fishery there is generally regarded as a low-impact, even conservation-positive use of the river that gives local communities a reason to keep the forest standing. The species is not currently considered threatened. The watch items are the familiar ones for the Negro: any future expansion of deforestation, mining or damming in the basin would fall directly on a fish with nowhere else to go, and a black-water endemic with a small range warrants ongoing attention even when its present status is secure.