Taxonomy & naming
Brochis britskii was described in 1983 by the Dutch ichthyologists Han Nijssen and Isaäc Isbrücker, from material taken in marginal lagoons along the Transpantaneira road near Poconé, in Mato Grosso, Brazil — still the type locality. They placed it in Brochis Cope, 1872, the genus erected for the emerald catfishes and distinguished from Corydoras chiefly by a much higher dorsal-fin ray count and large adult size.
For much of the intervening period Brochis was treated as a synonym of Corydoras, and the fish was widely listed as Corydoras britskii; that combination still appears in older literature and aquarium price lists. The 2024 phylogenomic revision of the Corydoradinae by Dias, Tencatt and colleagues recovered the subfamily as seven well-supported lineages, each matched to an available older genus name, and on that basis Brochis was resurrected as a valid genus — so the giant brochis is once again Brochis britskii. Because the change restores a long-familiar name rather than coining a new one, it has been comparatively easy for hobbyists to adopt. The species sits alongside the type species B. splendens (the common emerald cory) and B. multiradiatus in a compact genus of only a handful of described species.
Morphology
This is a large, deep-bodied corydoradine, reaching roughly 3.5 in in standard length and noticeably taller and more robust than the everyday Corydoras of the trade; females grow larger and broader than males, a difference best judged looking down on the fish from above. As in all members of the family it is armoured rather than scaled, with two rows of overlapping bony plates running down each flank and a hard, helmeted head, and three pairs of barbels fringing the down-turned mouth.
Two features set Brochis apart from Corydoras. The first is the dorsal fin: where a typical Corydoras carries seven to eight dorsal rays, Brochis carries many more, and B. britskii sits at the top of the range with about 15 to 18 — a tall, broad-based fin that is its most reliable field mark. In britskii the dorsal spine and the first rays form a distinctive hook-like leading edge, the fin looking almost as if its trailing margin had been cut square with scissors. The second feature is the snout: it is conspicuously blunt and down-turned, the 'hognose' profile that gives the fish one of its common names. The body carries the metallic blue-green to emerald sheen typical of the genus, brightest over the flank, with reddish tones often appearing on the belly and fin bases of well-conditioned adults.
Habitat
Brochis britskii is a fish of the upper Río Paraguay basin, spanning the Pantanal wetlands of Mato Grosso in Brazil and reaching into adjacent Paraguay and Bolivia. This is the great seasonally flooded lowland of central South America, a mosaic of slow rivers, marginal lagoons, oxbows, weed-choked channels and temporary pools that expand and contract with the annual wet and dry cycle. The type series itself came from such marginal lagoons beside the Transpantaneira.
These are warm, quiet, often densely vegetated waters with little current. Reported aquarium parameters reflect the soft, slightly acidic to neutral end of the spectrum — roughly pH 6.0 to 7.0 and temperatures around 68–75 °F, somewhat cooler than many tropical community fish prefer. Like other callichthyids it is a facultative air-breather, periodically darting to the surface to gulp air that it absorbs through a vascularised hindgut, an adaptation that lets it persist in the warm, oxygen-poor, weed-clogged backwaters and shrinking dry-season pools of the Pantanal where many fish could not survive.
Feeding
The giant brochis is a benthic omnivore, working the bottom with its barbels to taste out small invertebrates, insect larvae, worms, crustaceans and organic detritus, sifting mouthfuls of sand and expelling the cleaned grains through the gills. Its larger size simply means a larger appetite for the same kind of substrate-bound fare. In the aquarium it readily takes sinking pellets, tablets, granules and larger flakes that reach the bottom, and relishes live or frozen foods such as bloodworm, whiteworm, grindal worm, Daphnia and Tubifex — the latter especially useful for bringing a group into spawning condition. As with all corys it should be fed proper sinking food of its own rather than left to scavenge the leftovers of faster tankmates.
Mating
Brochis are egg-laying shoalers that spawn in the same characteristic manner as their Corydoras relatives, with no pair bond. When a female ripens, the group becomes active and a male takes up the classic 'T-position', aligning himself at right angles to the female's head; she is thought to take his milt at the mouth, while clasping a small number of eggs in a basket formed by her pelvic fins. She then carries those eggs to a cleaned surface — a plant leaf, a stone or the aquarium glass — and presses them into place, the sequence repeating egg-batch by egg-batch. Sexes are told apart much as in Corydoras: females are larger and fuller-bodied, while males tend to have more pointed fin tips and, in some accounts, larger ventral fins.
Breeding
Captive breeding of Brochis britskii is uncommon and far less routine than the prolific egg-laying of small Corydoras, and documented spawning reports are scarce. The general approach mirrors that used for other emerald catfishes and corys: condition a group well on live and frozen foods, then simulate the onset of the rainy season. For this species that appears to mean first holding the fish at relatively warm temperatures and then triggering with cooler, fresh water — accounts suggest a pronounced cool change, dropping toward the low 20s °C, to imitate the Pantanal's seasonal flooding. The adhesive eggs are laid on firm surfaces and receive no parental care; as with all corydoradines the adults will eat them, so a breeder removes either the eggs or the parents. Its larger size, cooler-water preference and the relative rarity of the fish in the trade together make it a more demanding breeding project than the average cory.
In the aquarium
Despite its size and scarcity, Brochis britskii is not difficult to keep, and is as peaceful and sociable as any cory. It is a shoaling species and should be kept in a group of six or more; kept singly or in pairs it is withdrawn and stressed. Because it is a large, full-bodied fish that grazes a wide footprint, it wants more floor space than a small Corydoras — a tank with a generous bottom area rather than great height suits it best.
Substrate matters as much here as for any cory: provide soft sand or very smooth, rounded fine gravel, because these fish sift the bottom constantly and sharp or chipped gravel wears down and infects their barbels. The biotope it comes from suggests the right décor — soft, slightly acidic water, gentle filtration with minimal current, driftwood, leaf litter and dense or floating plants to provide shade, with open feeding areas left clear. It appreciates cooler water than many community tropicals (around 68–75 °F), so choose tankmates that share that preference; calm, similarly sized characins and other peaceful South American fishes are ideal, and nothing large or boisterous enough to bully it. The usual cory cautions apply: the stiff fin spines can snag in a net, so a container is safer for moving them.
Conservation
Brochis britskii is assessed by the IUCN as Least Concern, evaluated in 2018 (the assessment dates from when the fish was still being listed under Corydoras). It is a fairly widespread inhabitant of the upper Paraguay and Pantanal, one of South America's great and still comparatively intact wetland systems, and is not at present considered threatened. It is a relatively scarce and sought-after fish in the aquarium trade — wild-caught and historically expensive — but that demand is modest in scale. The broader long-term pressures on its habitat are the familiar ones for the Pantanal: agricultural expansion, altered flooding regimes from upstream development and hydropower, deforestation and pollution, all of which degrade the marginal lagoons and weed-choked channels this species depends on, even as the species itself remains secure for now.