Taxonomy & naming
Corydoras rikbaktsa was described by Flávio C. T. Lima and Marcelo R. Britto in 2020, in a paper in the journal Zootaxa, from material collected in the rio Juruena system of the upper rio Tapajós drainage, Amazon basin, in Mato Grosso, Brazil. The holotype is a female. Before its formal description the fish circulated among hobbyists under the collection code CW154.
The specific name honours the Rikbaktsa (also written Rikbaktsa or Erikbaktsa) Indigenous people of the upper Juruena region, on whose traditional lands the species occurs. It belongs to the family Callichthyidae, the South American armoured catfishes, and was placed in the long-snouted, intermediate-bodied assemblage of Corydoras. The authors noted that, on the morphological evidence available, the species could be assigned to either of the lineages later formalised by the 2024 revision, because no clean diagnosis then separated them. In the 2024 revision of the subfamily by Dias, Tencatt and colleagues, which split the old, oversized Corydoras into several genera, this species falls in lineage 9 and takes the resurrected genus name Hoplisoma — Hoplisoma rikbaktsa. The aquarium world still overwhelmingly writes 'Corydoras rikbaktsa', so we keep that as the heading while noting the current combination.
Morphology
This is a small cory, the female holotype measuring about 1.5 in in standard length and the species reaching roughly 2 in; males stay a little smaller than females. The body is the familiar Corydoras build — stocky and deep through the shoulders, flat-bellied, and clad in two longitudinal rows of overlapping bony plates instead of scales, with a hard helmet of a head and three pairs of barbels around the downturned mouth. The snout is moderately elongate rather than blunt.
The single most distinctive feature is the sexual dimorphism. Mature males develop numerous, well-developed odontodes — tiny tooth-like dermal spines — scattered conspicuously over the lateral surfaces of the head, across the pectoral girdle, and along the pectoral-fin spines, giving those regions a rough, bristly texture. This degree and distribution of odontode development is unusual within the genus and is the feature that most readily sets the species apart from its relatives. Females lack the dense odontode fields. The ground colour is a pale brownish body marked with dark blotching and a darker saddle and fin markings rather than bold stripes.
Habitat
Corydoras rikbaktsa is known from a small number of localities in the rio Juruena basin, part of the upper rio Tapajós system, in northern Mato Grosso, Brazil. The recorded sites include small tributaries of the rio Juína-Mirim, west of the town of Juína, and a tributary of the rio Papagaio. These are clear, flowing upland streams of the southern Amazon shield rather than large lowland rivers.
Like other corys it is a bottom-oriented fish of shallow, well-oxygenated water over sand and fine gravel with leaf litter and submerged wood. No detailed in-situ water chemistry was published with the description, but the species is associated with the soft, slightly acidic, warm waters typical of clearwater shield streams in this part of Brazil. Its known range is small, and because it has only recently been described the full extent of its distribution within the upper Juruena is not yet established.
Feeding
No dedicated study of the diet of Corydoras rikbaktsa has been published, but its anatomy and its membership of the genus make its feeding ecology clear enough. Like all corys it is a benthic forager: it works over sand and leaf litter, burying its barbels and snout to taste and sift out small invertebrates, insect larvae, micro-crustaceans, worms and the organic detritus that collects between grains and among fallen leaves. The moderately elongate snout suits probing into the substrate. It is best understood as an opportunistic bottom-feeding omnivore and detritivore, taking whatever small animal and plant matter the streambed offers.
Mating
The reproductive behaviour of Corydoras rikbaktsa has not been documented in detail, but corys as a group share a well-known and remarkably uniform spawning style, and there is no reason to expect this species to depart from it. They are egg-laying shoalers with no pair bond. A receptive female cleans a spawning surface and the group becomes active; a male takes up the classic 'T-position', placing his body at right angles to the female's head, and she appears to take his milt while clasping a small batch of eggs in a basket formed by her pelvic fins. She then carries those eggs to a cleaned surface and presses them into place. The dense male odontodes, concentrated on the head and pectoral region that contact the female during this clasp, are thought in similarly armed corys to play a role in the spawning embrace, though their exact function in this species is unconfirmed.
Breeding
There is no published account of Corydoras rikbaktsa being bred in captivity, and it remains an uncommon, specialist fish rather than a commercially farmed one. By analogy with its many congeners, spawning would be expected to follow the general cory pattern: adhesive eggs laid in small batches and scattered across firm surfaces such as plants, wood, stones or aquarium glass, typically triggered by a cool, large water change mimicking the onset of the rains. Corys give no parental care and will eat their own eggs, so any breeder would need to separate eggs from adults. Eggs of comparable species hatch in a few days, after which the fry take microfoods and small live foods. Until a documented spawning exists, all of this should be read as the expected pattern for the genus rather than confirmed for this particular species.
In the aquarium
Corydoras rikbaktsa is a rarely traded fish that reaches hobbyists mainly through specialist channels and under its CW154 code, so it is not a beginner's species in terms of availability, though its care needs are those of a typical small cory. It is a shoaling fish and should be kept in a group of six or more; corys kept singly or in pairs are visibly stressed. Provide soft sand or very smooth fine gravel — corys feed by sifting the substrate, and sharp or coarse gravel erodes their barbels and leads to infection and blunted, stubby faces, one of the commonest husbandry failures with the genus.
As a fish of clear, flowing shield streams it appreciates clean, well-oxygenated water with gentle current, warmth in the mid-20s Celsius, and the soft, slightly acidic chemistry of its home waters; regular water changes suit it as they do all catfish. It is peaceful and best matched with similarly calm, small community fish — small tetras and the like — rather than anything boisterous or large enough to bully it. As with all corys, two practical cautions apply: the stiff fin spines can tangle in a net, so a cup is safer for moving them, and a badly stressed cory can release a skin toxin that, in the small volume of a bag or bucket, can kill the whole group, so transport them carefully.
Conservation
Corydoras rikbaktsa has not been assessed by the IUCN and currently carries no Red List status; on Planet Catfish's Cat-eLog it is listed as Not Evaluated. As a recently described species with a small known range confined to the upper rio Juruena, it has simply not yet been the subject of a formal conservation assessment. That narrow, localised distribution is itself the main reason for caution: range-restricted upland species are inherently more vulnerable than widespread lowland generalists to habitat change. The headwaters of the Juruena and Tapajós face pressures from agricultural expansion, deforestation and hydropower development across the southern Amazon, all of which can degrade the clear shield streams this fish depends on. Until its full distribution and population are better known, its status is best regarded as genuinely uncertain rather than secure.