Taxonomy & naming
The emerald cory was described by the French naturalist François de Castelnau in 1855 as Callichthys splendens, from material out of the Rio Tocantins, Brazil — still the type locality, with the holotype held in Paris (MNHN). It was the type species of the genus Brochis Cope, 1872, the small group of large, deep-bodied, many-rayed callichthyid catfishes that aquarists have always called the 'brochis' to distinguish them from the ordinary corys. Under that name it was bred and sold worldwide as the emerald or green 'brochis,' and the long-used name Brochis dipterus is a junior synonym of it.
The modern confusion came in two waves. First, Britto's 2003 revision of the Corydoradinae synonymised Brochis with the enormous genus Corydoras, and for two decades the fish was correctly written Corydoras splendens — the heading under which most current FishBase, IUCN and hobby material still files it. Then, in 2024, Dias, Tencatt and colleagues published a large phylogenomic revision of the subfamily that broke the unwieldy old Corydoras into several natural genera and resurrected Brochis as a valid lineage, with B. splendens once again its type species. The Catalog of Fishes now records the valid combination as Brochis splendens (Castelnau, 1855). The change is recent and the trade still says 'Corydoras splendens' or simply 'emerald cory,' so both names will be seen on tanks and price lists for years yet.
Morphology
Brochis is built like a cory that has been inflated. B. splendens reaches roughly 3 in in total length — noticeably bigger and far deeper-bodied than the bronze and peppered corys it is usually mixed with — with a high, arched back, a broad head and the same hard armour of two overlapping rows of bony plates (scutes) down each flank. Three pairs of barbels fringe the downturned mouth.
The single feature that defines the genus, and the easiest way to tell a true brochis from a look-alike Corydoras, is the dorsal fin: it is long-based and tall, carrying about 10–12 branched rays in B. splendens, where an ordinary cory has only six or seven. (Among the ex-brochis, that 10–12 count separates splendens from the ~15 of the giant B. britskii and the 17–18 of the hognose B. multiradiatus.) The body colour is the source of every common name — a brilliant, mood-dependent iridescent green, from emerald to almost bottle-green or near-black, washed with pink and gold low on the body and flushing brighter when the fish is settled and confident. As in all corydoradines the dorsal, pectoral and adipose fins each bear a stiff, mildly venomous locking spine.
Habitat
B. splendens is a widespread fish of the western and central Amazon basin, recorded from Brazil, Peru, Ecuador, Colombia and Bolivia — the area around Iquitos, the Ucayali toward Pucallpa and the Ampiyacu are among the classic collecting grounds. It is not a fish of fast, open river; it favours the quieter margins — smaller tributaries, backwaters, oxbow lakes, flooded forest pools and still marginal lagoons — over soft sand and mud thick with leaf litter and submerged wood.
These are warm, soft, often tannin-stained 'blackwater-influenced' shallows. The species tolerates a broad envelope in keeping with such variable habitats: temperatures of about 68–82 °F, a wide pH band from acidic to slightly alkaline (roughly 5.0–8.0) and soft to moderately hard water. Like other callichthyids 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 persist in the warm, oxygen-poor, sometimes stagnant pools it favours.
Feeding
The emerald cory is a benthic foraging omnivore. In the wild it works soft sand and litter, sifting the substrate with its barbels for small invertebrates, insect larvae, worms, micro-crustaceans and the organic detritus and fallen plant matter of the shallows, expelling cleaned sand through the gills. Its larger size simply means it processes more substrate than a small cory. In the aquarium it readily takes sinking dried foods — pellets, tablets and granules — alongside frozen and live bloodworm, Tubifex and brine shrimp; a varied diet keeps the green colour bright and the body well-filled, and it should never be left to scavenge only what tankmates drop.
Mating
Brochis are egg-laying shoalers that spawn in the classic corydoradine manner, with no pair bond. When a female comes into condition the group grows active and a male takes up the characteristic 'T-position,' aligning himself at right angles to the female's head; she appears to take milt from him and, holding a small clutch of eggs in a basket formed by her clasped pelvic fins, carries them to a cleaned surface and presses them into place. High in the water column, glass, plant leaves and the underside of broad leaves are all used. The sequence repeats, a few eggs at a time, until the spawning surfaces carry a scattering of large, adhesive eggs.
Breeding
B. splendens has been bred in aquaria, though far less routinely than the bronze or peppered corys, and it asks for a mature, settled group and good conditioning before it will oblige. As with most corydoradines, spawning is encouraged by a large, cooler water change that mimics the onset of the rains, dropping the temperature several degrees, together with a high-protein diet of live and frozen foods. The adhesive eggs, laid high and on broad surfaces, receive no parental care and are readily eaten by the adults, so breeders move either the eggs or the parents to a separate rearing container. Eggs hatch in a few days, and once the yolk sac is absorbed the fry take microworm, baby brine shrimp and powdered foods, growing into the deep-bodied genus shape over the following months. Most fish in trade are still wild-caught or pond-raised on Asian and South American farms rather than home-bred.
In the aquarium
The emerald cory is a rewarding, peaceful and surprisingly substantial aquarium fish, but its size and shoaling nature set the terms. It is gregarious and genuinely happier in a group of six or more; kept singly or in pairs it becomes shy and inactive. Because it is bigger and bulkier than an ordinary cory and an active swimmer, give it room — a tank of around 35.5 in / a footprint of 100+ litres suits a proper group, with bottom area mattering far more than height.
Substrate is the husbandry detail that matters most: provide soft sand or very smooth, rounded fine gravel, because these fish feed by burying their snouts and barbels, and sharp or coarse gravel abrades and infects the barbels, leaving the stunted, blunted faces that betray bad keeping. Water should be warm (about 72–79 °F), clean, well-oxygenated and gently moving, with regular changes; the species accepts a wide pH and hardness range. It is utterly peaceful and an excellent companion for tetras, rasboras, larger pencilfish, dwarf cichlids and other calm community fish, with nothing aggressive enough to harass it. Two standard corydoradine cautions apply: the locking fin spines tangle easily in a net (a cup or container is safer), and a badly stressed fish can release a skin toxin that, in the closed volume of a bag, may kill a whole group in transit — so move them with care.
Conservation
Brochis splendens (assessed by the IUCN under the name Corydoras splendens) is listed as Least Concern. It is widely distributed across the western and central Amazon, ecologically flexible and tolerant of the variable, sometimes degraded marginal habitats it favours, and it faces no range-wide threat. Collection for the aquarium trade is long-established but is not considered a population-level pressure, and an increasing share of trade fish are pond-raised. The usual broad pressures on Amazonian freshwaters — deforestation, agricultural run-off, pollution and damming — degrade the shallow waters it lives in, but the species as a whole is secure.