Taxonomy & naming
The species was described by the German aquarist-ichthyologist Joachim Knaack in 2002, from material collected at Chené, Santiesteban, in the Santa Cruz Department of eastern Bolivia — the type locality. The epithet bilineatus is Latin for 'two-lined', for the dark longitudinal markings on the body. The holotype is held in Dresden (MTD F 25925), with paratypes distributed among several European and Bolivian collections.
It was described in, and long held in, the enormous genus Corydoras Lacépède, 1803. That genus proved to be an artificial grouping of several lineages, and in 2024 Dias, Tencatt and colleagues published a phylogenetic revision (Zoological Journal of the Linnean Society) that broke it apart. Eschmeyer's Catalog of Fishes now lists the species as valid as Gastrodermus bilineatus (Knaack 2002) — Gastrodermus being the resurrected genus built around the small, slender 'elegans / pygmy' corys. The hobby still uses 'Corydoras bilineatus', which we retain as the heading while recording the current combination.
Morphology
This is a small cory, reaching about 2 in in standard length. It has the standard Corydoradinae form — a compact, armoured body sheathed in two rows of overlapping bony scutes, a blunt head, and three pairs of barbels around the downturned mouth used to probe and taste the substrate; the dorsal and pectoral fins carry stiff defensive spines.
The diagnostic feature is the pattern that gives the fish its name: dark longitudinal lines along a paler body, used to separate it from the several similar small striped corys of the upper Madeira drainage. As a member of the Gastrodermus lineage it is on the slender, lightly built end of the cory spectrum rather than a deep-bodied form.
Habitat
Corydoras bilineatus is known from the Madeira River basin in Bolivia — the Andean-foreland tributaries draining toward the upper Madeira, in the Santa Cruz region. These are warm, soft, often clear to lightly stained streams over sand and fine sediment, with leaf litter and submerged wood along the margins.
No focused ecological study has been published, so its tolerances are inferred from the genus and from its collecting localities: warm temperatures broadly in the low-to-mid 20s Celsius, acidic to near-neutral, soft to moderately hard water. Like other Corydoradinae it is a facultative air-breather, surfacing to gulp atmospheric oxygen and absorb it through a modified, vascularised hindgut, which lets it cope with warm, oxygen-poor shallows.
Feeding
No diet study exists for this species, but it is a benthic omnivore and sediment-sifter like all corys. It forages over the bottom, using its barbels to detect small invertebrates, insect larvae, micro-crustaceans, worms and organic detritus in the sand, taking in mouthfuls of substrate and venting the cleaned grains through the gills. In the aquarium fish of this type accept sinking prepared foods, frozen bloodworm and brine shrimp and small live foods, grazing the bottom continuously.
Mating
Spawning has not been documented for Corydoras bilineatus, but the Corydoradinae share a uniform, well-studied courtship. They are egg-laying shoalers without a pair bond: a ready female cleans a spawning surface, a male assumes the 'T-position' at right angles to her head, she takes milt into her mouth, and the sperm passes through her gut to fertilise the small batch of eggs held in a pelvic-fin basket, which she then presses onto the cleaned site. The cycle repeats a few eggs at a time.
Breeding
There is no published aquarium-breeding record for this species, so reproductive detail is extrapolated from its relatives. Small Gastrodermus / Corydoras-type fishes lay adhesive eggs in small batches on cleaned surfaces, frequently triggered by a cool, large water change simulating the rainy season. They give no parental care and will eat their eggs, so breeders of related corys move 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 free-swimming. Whether C. bilineatus has been bred deliberately is not on record.
In the aquarium
Corydoras bilineatus is uncommon in the trade and little kept, so practical experience is limited; treat it as a typical small Bolivian cory. Keep it in a shoal of six or more over soft sand or very smooth, rounded fine gravel — sharp or coarse substrate abrades and infects the barbels these sand-sifters rely on. Provide warm, well-filtered, well-oxygenated water (broadly 72–79 °F), soft and slightly acidic to neutral, with leaf litter, wood and a gentle current. It is a peaceful fish for a calm community of small tetras, pencilfish and similar. As with all corys, the fin spines can catch in nets, so move them in a cup, and avoid crowding them in transport, where a stressed cory's skin toxin can foul a small bag.
Conservation
The IUCN Red List lists this species (as Corydoras bilineatus) as Data Deficient, assessed in 2014 — meaning there is not enough information on its range, population or threats to assign a category. It is known from a limited area of the Bolivian upper Madeira drainage, and as a Data Deficient species its true status is genuinely uncertain rather than reassuringly secure. The streams of the Andean foreland face deforestation, agriculture and sedimentation, any of which could affect a narrowly known fish; further survey work would be needed to assess it properly.