Taxonomy & naming
Corydoras aurofrenatus was described by Carl Eigenmann and Clarence Kennedy in 1903, from Paraguay, with the type locality given as 'Aguada near Arroyo Trementina' — a tributary system of the Río Aquidabán in the Paraguay drainage. The epithet, not explained in the original description, is most plausibly from the Latin auro ('gold') and frenatus ('bridled'), in reference to the broad yellow band across the snout. It belongs to the long-snouted assemblage of the family Callichthyidae and was placed in Corydoras Lacépède, 1803.
Corydoras had long been understood to be far too large and not a single natural lineage. The 2024 phylogenomic revision by Dias, Tencatt and colleagues (Zoological Journal of the Linnean Society) split it into several genera — Brochis, Gastrodermus, Osteogaster, Hoplisoma and more — leaving a restricted Corydoras (sensu stricto), the lineage-1 group typified by C. geoffroy, into which aurofrenatus falls. It therefore keeps the name Corydoras, one of the species for which the hobby genus and the current Catalog-of-Fishes lineage genus coincide. Catalog of Fishes treats aurofrenatus as valid. There is some historical tangle around it: Axenrot and Kullander (2003) considered C. ellisae Gosline, 1940 a junior synonym of aurofrenatus, a view that has not been widely accepted, and material of the related C. areio has at times been misidentified as aurofrenatus because of overlapping flank patterns.
Morphology
This is a medium-small, long-snouted cory reaching about 2 in in standard length, the females being the larger sex. Like all corys it is armoured rather than scaled, with two rows of overlapping bony plates down each flank — about 24 to 26 lateral scutes — and a hard head, and it bears the genus's three pairs of barbels on a downturned mouth set on an elongate snout.
The colour pattern comprises two dark blotches on each flank — one below the adipose fin and one just behind the head — over a paler ground, with a broad gold or yellow band across the snout that gives the fish its name. The dorsal fin carries three or four dark stripes and the caudal fin up to eight, and the caudal lobes are long, the upper more extended than the lower. The dorsal, pectoral and adipose fins each bear a stiff leading spine. Females grow larger and become rounder and broader-bodied than males, especially when gravid.
Habitat
Corydoras aurofrenatus is understood to occur throughout much of the Río Paraguay–Paraná system in Paraguay, with records also from Argentina and Bolivia — part of the great La Plata basin. The type locality lies in the Río Aquidabán drainage, which flows through the departments of Amambay and Concepción before entering the Río Paraguay north of Concepción city.
It is a fish of streams, river margins and connected pools over sand and soft sediment with leaf litter and wood, in waters that swing strongly with the seasons. Reported aquarium-relevant conditions are warm and span a near-neutral to slightly alkaline band — about 72–79 °F and pH roughly 6.0–8.0, with soft to moderately hard water. As a typical cory it is a facultative air-breather, periodically rising to gulp air absorbed through a modified, vascularised intestine, an adaptation for warm, oxygen-poor water.
Feeding
Corydoras aurofrenatus is a foraging benthic omnivore. Over sand and soft sediment it uses its barbels and long snout to taste out and probe for small invertebrates, insect larvae, microcrustaceans and organic detritus, sifting mouthfuls of substrate and expelling them through the gills. In the aquarium it accepts most sinking dried foods — pellets, tablets and granules — as well as small frozen and live foods such as bloodworm, Tubifex and Daphnia. A varied diet keeps it in condition, and like all corys it should not be expected to live on the leftovers of other fish or to 'clean' the tank.
Mating
No detailed spawning account specific to C. aurofrenatus has been published, but as a Corydoras it is expected to share the genus's well-documented courtship. They are egg-laying shoalers with no pair bond: a ready female cleans a spawning site, the group becomes active, and a male takes the characteristic 'T-position' at right angles to her head. The female holds a small number of eggs in a basket formed by her pelvic fins while they are fertilised, then carries them to a cleaned surface and presses the sticky eggs into place, repeating the sequence until the clutch is laid.
Breeding
There is no published captive-breeding report for C. aurofrenatus, and it is only occasionally kept, but it is expected to follow the standard Corydoras pattern. Spawning in the genus is usually triggered by a cool, generous water change imitating the onset of the rains; the adhesive eggs are laid in small batches on plants, wood and glass and receive no parental care, with the adults inclined to eat them, so breeders remove either the eggs or the parents. Eggs hatch in roughly three to five days, and the fry take microworm, baby brine shrimp and powdered foods once the yolk sac is absorbed. Honest note: these details are inferred from the genus, not from confirmed records for aurofrenatus.
In the aquarium
C. aurofrenatus is a peaceful, gregarious cory that does well in a calm community setup, though it is not a common import. As with all corys it should be kept in a group of at least six; in smaller numbers it becomes withdrawn and stressed. It needs bottom area more than height and benefits from a planted layout with open foraging space.
Provide soft sand or smooth, rounded fine gravel — as a long-snouted sifter it is particularly vulnerable to barbel erosion and infection over sharp or chipped gravel. Give it some cover from wood and planting for security, keep the substrate clean and the water warm (about 72–79 °F), well-filtered and well-oxygenated, with gentle current and regular water changes; it tolerates a broad pH and hardness range. It is an ideal companion for tetras, rasboras, dwarf cichlids and other quiet fish, and should not be kept with large or aggressive tankmates. The usual cory cautions apply: the stiff fin spines can pierce skin and tangle in nets (use a cup), and a badly stressed cory can release skin toxins that may harm a whole group in the confined volume of a transport bag.
Conservation
Corydoras aurofrenatus is assessed by the IUCN as Least Concern (assessed 2020). It is reasonably widely distributed across the Paraguay–Paraná system, and its wide range buffers it against rapid global decline; no specific major threat has been identified for it. As with all freshwater fishes of the La Plata basin, the broad regional pressures — agricultural expansion and run-off, land-use change, damming and pollution — bear on the shallow stream habitats it uses. There is no species-specific conservation programme, and the principal uncertainties around it are taxonomic, given the historical confusion with C. ellisae and C. areio within this long-snouted complex.