Taxonomy & naming
Corydoras lymnades was described in 2013 by Luiz Tencatt, Juan Vera-Alcaraz, Marcelo Britto and Carla Pavanelli, in Neotropical Ichthyology, from the rio Guarda-Mor in Guarda-Mor, Minas Gerais — a tributary system of the upper rio São Francisco. The holotype is a 1 in SL specimen, underlining just how small the fish is. The species name comes from the Lymnades, small water-dwelling creatures of Greek mythology, chosen both for the species' tiny size and for its colour-pattern resemblance to Corydoras garbei.
The genus Corydoras Lacépède, 1803 (family Callichthyidae) had become a catch-all of more than 170 species and was shown not to be monophyletic. The 2024 revision by Dias, Tencatt and colleagues split it into several genera — Brochis, Hoplisoma, Gastrodermus, Osteogaster and a restricted Corydoras — and under that classification this species becomes Hoplisoma lymnades. The change is recent and not yet universally followed; the hobby still writes 'Corydoras lymnades,' so that remains our heading while we note the new combination. The Catalog of Fishes (Eschmeyer, CAS) lists the name as a valid species.
Morphology
This is a true dwarf cory, reaching only about 1 in in standard length. It has the standard armoured Corydoras body plan — twin rows of overlapping bony plates along each flank, a hard helmeted head, a downturned mouth with three pairs of barbels, and stiff leading spines in the dorsal and pectoral fins — but in miniature.
The colour pattern is its defining feature and the basis of the original description. The body is pale, scattered with small rounded or short streak-like dark blotches over the dorsal region, with oblong blotches concentrated along the junction of the lateral plate rows and a further series of marks running below that junction between the pelvic and caudal fins. A diagnostic skeletal trait noted by the describers is a greatly enlarged, anteriorly expanded first infraorbital bone that almost entirely covers the lateral margin of the snout — hence the 'nose-striped' common name applied to it. Females, as usual in the genus, grow somewhat larger and rounder than males.
Habitat
Corydoras lymnades is endemic to the upper and middle rio São Francisco basin in eastern Brazil, recorded from small headwater streams in Minas Gerais State down to the main channel of the river in Bahia State — a notable distribution, because the São Francisco is an old, isolated drainage separate from the Amazon and Paraná systems, with comparatively few Corydoras of its own.
It is a benthic fish of clear to slightly turbid running waters over sand and fine gravel, among the shallow margins, leaf litter and submerged structure of streams and river reaches. Specific published water chemistry for the type localities is limited, but the basin's clearwater streams are generally warm and circumneutral to mildly acidic; the genus as a whole tolerates temperatures of roughly 72–79 °F and a pH band around 6.0 to 7.5. Like all Corydoras it is a facultative air-breather, surfacing to gulp air taken up through a vascularised hindgut.
Feeding
As a small benthic corydoradine, Corydoras lymnades is an omnivore and detritivore that works the bottom continuously, sifting sand and fine sediment with its snout and barbels to extract micro-invertebrates, insect larvae, tiny crustaceans, worms and organic detritus, and venting cleaned substrate through the gills. Being dwarf-sized it takes correspondingly small prey. In captivity its relatives accept micro-pellets, crushed tablets, frozen and live daphnia, cyclops, microworm and finely chopped bloodworm; the fine particle size matters for so small a fish.
Mating
Reproduction in the wild has not been documented for this species, but the courtship of Corydoras is strikingly uniform across the genus and is expected to hold here. They are egg-scattering shoalers with no pair bond. A ripe female cleans a spawning surface while the group becomes active; a male assumes the characteristic 'T-position' at right angles to her head, and the female takes milt into her mouth and passes it through her gut to fertilise the few eggs she carries in a pelvic-fin basket, pressing them onto the cleaned surface. The process repeats a few eggs at a time over the spawning bout.
Breeding
No species-specific breeding account has been published for Corydoras lymnades, and it is rarely if ever bred in the hobby; the following is the general genus pattern. Spawning is typically triggered by a large, cooler water change mimicking the rainy season, in a mature group with a surplus of males. The adhesive eggs are deposited in small batches on plants, wood, stone or glass and receive no parental care — the adults will eat them, so a breeder separates eggs from parents. Hatching usually takes three to five days, and the tiny fry need correspondingly tiny first foods (infusoria, microworm and powdered fry food) before graduating to baby brine shrimp. The species is not established in the trade and is essentially unknown as an aquarium fish.
In the aquarium
Corydoras lymnades is effectively a collector's or specialist species rather than a common import, and almost everything about keeping it is inferred from other dwarf corys. If kept, it should be treated as a small, sensitive shoaler: a group of at least six (ideally more) in a tank with a generous footprint, where it can forage in confident company rather than hide.
A soft, clean sand substrate is essential — these fish feed by sifting, and abrasive gravel wears down and infects the barbels, leaving the blunted faces typical of bad husbandry. Warm, soft to moderately hard, well-oxygenated water (about 72–79 °F) with gentle flow and regular changes suits it, alongside fine-leaved planting and leaf litter for cover. As a dwarf species it belongs only with similarly small, peaceful tankmates — nano tetras, pencilfish, small rasboras — and must never be housed with fish large enough to eat or bully it. The usual cory cautions apply: the fin spines snag in nets, so a cup is safer for moving them, and a badly stressed cory can self-poison the water of a transport bag, endangering the whole group.
Conservation
Corydoras lymnades has not been assessed by the IUCN Red List and carries no formal conservation status. It is a narrow-range endemic of the rio São Francisco — a heavily exploited basin subject to damming, water abstraction, agricultural and urban pollution and habitat fragmentation — and small-bodied endemics of such systems are exactly the kind of species that can be vulnerable to localised habitat loss. At the same time it is recorded across a fair stretch of the upper and middle basin, from Minas Gerais headwaters to the Bahia main channel, which is reassuring. Without a formal assessment its population trend is genuinely unknown, and a proper evaluation would be needed before anything firmer could be said.