Taxonomy & naming
Corydoras treitlii was described by the Austrian ichthyologist Franz Steindachner in 1906, from material collected in a tributary creek of the rio Parnaíba in north-eastern Brazil. It was placed in Corydoras Lacépède, 1803, the great genus of South American armoured catfishes in the family Callichthyidae, and there it has stayed.
That genus had grown to well over 170 species and was shown to be non-monophyletic, and in 2024 Dias, Tencatt and colleagues published a large revision (DOI 10.1093/zoolinnean/zlae053) that split it into several genera — Brochis, Hoplisoma, Gastrodermus, Osteogaster and others. Crucially, the long-snouted lineage that includes the type species of the genus was retained as Corydoras in the strict sense, and C. treitlii sits within it. So unlike most of the trade's 'corys,' which have been reassigned to other genera, this species keeps the familiar name as its current valid combination. The Catalog of Fishes treats Corydoras treitlii as a valid species.
Morphology
This is one of the long-snouted corys, and the elongate, gently down-curved snout is its signature — the source of the 'hognose' and 'longsnout' common names. The body is more streamlined than the deep, stocky bronze-cory shape, reaching about 2.5 in standard length. As in all the subfamily, it is armoured rather than scaled: two rows of overlapping bony plates run down each flank and meet along the back, the head is a hard helmet, and sensory barbels fringe the down-turned mouth — barbels that the long snout puts to good use probing deeper into the substrate than the short-snouted species can manage.
The colouring is muted and workmanlike: a pale to brassy ground with fine darker mottling and speckling over the body, without the bold blotches of the spotted corys. The dorsal, pectoral and adipose fins each carry a stiff leading spine, the standard defensive armament of the group.
Habitat
Corydoras treitlii lives in the coastal drainages of north-eastern Brazil and the rio Parnaíba system, the type material having come from a tributary creek of the Parnaíba near Alto Parnaíba in Maranhão. These are warm lowland streams and creeks; like other corys the fish favours quieter water over soft sand and fine substrate with leaf litter and submerged wood.
FishBase gives an indicative temperature band of about 68–77 °F and a broad pH range of roughly 6.0–8.0 for the species, reflecting the warm, soft-to-moderate waters of its range. Like all corydoradines it is a facultative air-breather, surfacing to gulp air and absorb oxygen through a vascularised hindgut — an adaptation for the warm, sometimes low-oxygen shallows it inhabits.
Feeding
Corydoras treitlii is a benthic omnivore and detritivore, and its long snout is a feeding tool: it lets the fish push further into sand and crevices than the blunt-faced species, rooting out small invertebrates, insect larvae, worms and the organic detritus of the stream bed, then expelling cleaned sand through the gill openings. It is an opportunist rather than a specialist. In captivity it takes sinking pellets, frozen bloodworm and brine shrimp and other small sinking foods, sifting the bottom continuously, but should not be left to live on leftovers alone.
Mating
No detailed spawning account specific to Corydoras treitlii has been published, and the description here is the standard corydoradine pattern offered as the expected behaviour. These are egg-laying shoalers with no pair bond: a ready female cleans a site, a male takes the classic 'T-position' at right angles to her head, and she clasps a few eggs in a basket formed by her pelvic fins before pressing them onto a cleaned leaf, stone or root. The sequence repeats a few eggs at a time until a clutch of sticky eggs is scattered across the chosen surfaces.
Breeding
There are no reliable aquarium breeding reports for Corydoras treitlii; the long-snouted corys in general are bred far less often than the hardy short-snouted staples, and available fish are wild-caught and seasonal. By analogy with the group, spawning would be expected to follow the familiar pattern — adhesive eggs laid in small batches on firm surfaces, no parental care, and a cool, large water change as the likely trigger. Until the species is bred and documented, this should be read as informed expectation rather than established husbandry.
In the aquarium
Corydoras treitlii is an occasional, seasonal import rather than a tank-bred staple, and the long-snouted corys can be a touch more demanding than the bread-and-butter species — they want clean, well-oxygenated water and a genuinely soft, fine sand bed into which the long snout can dig. Sharp or coarse gravel is especially damaging here, eroding and infecting the barbels. Keep it as a shoal of six or more; it is a peaceful, sociable fish that frets when kept singly. Warm water in roughly the low-to-mid 20s Celsius, gentle current, good filtration and regular water changes suit it, and it makes a calm community companion for small tetras, rasboras and dwarf cichlids. As with all corys, the fin spines can catch in nets, and a stressed fish can release a skin toxin that may prove lethal in the small volume of a transport bag, so move it with care.
Conservation
Corydoras treitlii is assessed by the IUCN as Least Concern, in an evaluation dating to 2018. It has a reasonably wide distribution across the coastal and Parnaíba drainages of north-eastern Brazil, and is not subject to the kind of heavy targeted collection that would threaten it. As with all freshwater fishes of the region it is exposed to the broad pressures of deforestation, agriculture, water abstraction and pollution that degrade lowland streams, but as a species it is not presently considered at risk.