Taxonomy & naming
Corydoras costai was described in 2016 by Ottoni, Barbosa and Katz, in the journal Spixiana, from a swamp beside the BR-030 road near Guanambi in Bahia State, Brazil — within the São Francisco river basin. It was originally named in Corydoras Lacépède, 1803 (subfamily Corydoradinae, family Callichthyidae).
That large genus was shown to be unnatural, and in 2024 Dias, Tencatt and colleagues published a phylogenomic revision (Zoological Journal of the Linnean Society) that split Corydoras into several genera, resurrecting Brochis Cope, 1872 for one well-supported lineage. Under that scheme this fish becomes Brochis costai (Ottoni, Barbosa & Katz, 2016) — the combination now used by the Catalog of Fishes and FishBase. The change is recent and the aquarium trade still overwhelmingly says 'Corydoras costai', so we keep that hobby-familiar heading while recording the current genus as Brochis. The epithet honours the Brazilian ichthyologist Wilson Costa, who first collected and recognised the species as new.
Morphology
This is a small, short-headed catfish reaching only about 2 in in standard length. Its most conspicuous feature is the bold colour pattern described in the original account: a series of large, irregular dark-brown blotches across the dorsal and lateral surfaces of the body, running from the front plates back to the caudal peduncle, with five well-defined large blotches strung along the midline from the base of the tail to the rear edge of the gill cover, and a dark lower cleithrum.
Like all members of the family it is armoured rather than scaled, with two rows of overlapping bony plates along each flank and three pairs of barbels around the small mouth. The describers diagnosed it on a suite of internal characters — reduced, separated parapophyses on the fourth free vertebra (not fused into a haemal arch), five pairs of ribs, odontodes on the infraorbitals and opercle, a nuchal plate not contacting the supraoccipital, and a short head — that distinguish it from its relatives. As in the rest of the subfamily, the dorsal and pectoral fins each carry a stiff leading spine.
Habitat
Corydoras costai is restricted to the São Francisco river basin in north-eastern Brazil — a single large drainage isolated from the Amazon and from the coastal rivers, and one that hosts a distinctive, partly endemic fish fauna. The type series came from a roadside swamp near Guanambi in Bahia, at around 1706 ft elevation, which points to a fish of shallow, still or sluggish standing waters rather than open river channel.
Detailed water chemistry for the species in the wild has not been published, but as a small corydoradine of warm tropical lowland-to-upland freshwaters it would be expected to occupy the usual range for the group. Like its relatives it is presumably a facultative air-breather, able to gulp surface air and absorb oxygen through a vascularised hindgut — an asset in the warm, oxygen-poor swamps and seasonal pools of the semi-arid São Francisco country.
Feeding
No dietary study has been published for C. costai, but its body plan and habits place it among the benthic omnivore–detritivores typical of the subfamily. It would work soft substrate with its barbels and downturned mouth, taking small invertebrates, insect larvae, worms, micro-crustaceans and organic detritus, and expelling sifted sediment through the gills. In the aquarium, by analogy with related species, it would take sinking pellets and tablets, frozen bloodworm and brine shrimp, and other small prepared and live foods reaching the bottom — best offered as a varied diet rather than scavenged leftovers.
Mating
There is no published spawning account for C. costai, but corydoradine catfishes are highly uniform in their reproductive behaviour and it is expected to follow the group pattern. These are egg-laying shoalers with no pair bond. A receptive female cleans a surface; a male takes up the 'T-position' at right angles to her head, and sperm is thought to pass quickly through her gut to fertilise a few eggs held in a basket formed by her pelvic fins. She presses those eggs onto the cleaned site, and the sequence repeats a few at a time until the clutch is distributed across the chosen surfaces.
Breeding
No breeding report exists for C. costai, and the species is rare in aquaria. By analogy with related corydoradines, spawning would likely be prompted by a cool, large water change mimicking the onset of the rains, with groups holding more males than females proving most productive. The adhesive eggs receive no parental care — the adults will eat them, so breeders move the eggs or the parents. Eggs typically hatch within a few days, and the fry, after absorbing the yolk sac, take micro-foods such as baby brine shrimp and powdered fry feeds. All of this is inferred; the species' own captive reproduction is undocumented.
In the aquarium
C. costai is seldom kept and not commercially traded, but as a small corydoradine its care would mirror that of its relatives. It is a shoaling fish that should be kept in a group of six or more for its wellbeing, over soft sand that lets it sift and forage without eroding its barbels, with shade from wood, rock or plants and an open feeding area.
Water should be warm, clean, well-filtered and well-oxygenated, with a gentle current and regular changes; specific tolerances for this species have not been published, so a typical corydoradine regime is the safe default. It would be a peaceful occupant of a calm community of small, gentle tankmates. The usual cory cautions apply: the fin spines tangle in nets (a cup is safer), and a stressed corydoradine can release a skin toxin that, in the small volume of a bag, can harm a whole group, so any specimens should be transported with care.
Conservation
Corydoras costai has not been evaluated by the IUCN Red List, so it carries no formal conservation status. That gap matters more than usual here: the species appears to be narrowly endemic to part of the São Francisco basin, a heavily used and partly semi-arid system under pressure from water abstraction, agriculture, damming and habitat loss. A small-bodied fish known from few localities in such a basin warrants attention, and a formal assessment would be valuable; for now its true range, population and trend are essentially unquantified.