Taxonomy & naming
Corydoras apiaka was described in 2014 by Espíndola, Spencer, Rocha and Britto in a paper in Papéis Avulsos de Zoologia that also examined the species' phylogenetic placement. The holotype was collected in the Ribeirão Oito de Julho, a right-bank tributary of the Rio Arinos in the Rio Tapajós basin, near Porto dos Gaúchos, Mato Grosso, Brazil. The epithet honours the Apiaká, an Indigenous people who originally occupied the middle and lower Rio Arinos and lower Rio Juruena; the word means 'people' in Tupi, and it is treated as a noun in apposition rather than a Latinised adjective.
The species belongs to the family Callichthyidae, subfamily Corydoradinae. It was described in, and for a decade carried under, the genus Corydoras. When Dias, Tencatt and colleagues revised the Corydoradinae in 2024 (DOI 10.1093/zoolinnean/zlae053) and split the oversized genus into several lineages, apiaka was placed in the resurrected genus Hoplisoma, and the Catalog of Fishes now records the valid combination as Hoplisoma apiaka (Espíndola, Spencer, Rocha & Britto 2014). As the trade and most hobby literature still use 'Corydoras', we keep that as the heading and note the current name here.
Morphology
This is a small cory, reaching only about 1.5 in in standard length — distinctly compact even by the standards of the genus. The body carries the usual Corydoradinae armour of two interlocking rows of bony scutes, a hard bony head, a downturned mouth with three pairs of barbels, and stiff leading spines in the dorsal and pectoral fins. The fin-ray counts given in its description are a dorsal fin with two spines and eight branched rays and an anal fin with eight rays.
Its diagnostic feature is colour. The head and trunk are covered in numerous dark-brown spots scattered in a somewhat random pattern, with diffuse rather than sharply defined edges — a look that separates it from striped relatives and from spotted species whose marks are arranged in rows. The paired, pelvic and anal fins are hyaline (clear), and the adipose fin is clear or carries at most a single spot; the spots do not extend onto the anal-fin base. The describers also noted a naked ventral region, lacking the small belly platelets present in most congeners — a useful technical distinction within the spotted-cory group it resembles.
Habitat
Corydoras apiaka is endemic to the upper Rio Tapajós basin of Brazil, known from tributaries of the Rio Arinos, the Rio Teles Pires and the Rio Preto. It is principally a fish of lotic — flowing — habitats. The Rio Arinos itself is described as a muddy-brown river with a soft bottom of clay and sand, but the species is collected mostly in small forest streams of black or clear water, and in marginal ponds along them.
These are warm tropical headwater environments. FishBase does not publish detailed water-chemistry figures specific to the species, but the soft, often acidic to neutral clear- and black-water streams of the Tapajós headwaters are the relevant template, and the values used for husbandry below are conservative ones typical of such corys rather than direct field measurements. As with all members of the subfamily, C. apiaka is a facultative air-breather, able to gulp air at the surface and take up oxygen across a vascularised section of the gut.
Feeding
No dedicated diet study has been published for C. apiaka, but as a member of the Corydoradinae it is a benthic omnivore and detritivore. In its forest streams it would work the sand and leaf litter with its barbels, taking small invertebrates, insect larvae, micro-crustaceans and organic detritus and sifting substrate through the gills. In the aquarium it can be expected to accept the standard cory diet — sinking micro-pellets and wafers, frozen and live bloodworm, daphnia and brine shrimp, and other small foods that settle to the bottom — with food sized appropriately for so small a fish.
Mating
Courtship has not been described specifically for Corydoras apiaka, and the following is the standard, well-documented pattern of the genus. Corys are egg-laying shoalers without a pair bond: a gravid female cleans a spawning site, the group becomes active, and a male takes up the classic 'T-position' at right angles to the female's head. She appears to take milt into her mouth, the sperm passing rapidly through her gut to fertilise the small batch of eggs she holds in a basket formed by her pelvic fins, which she then presses onto the cleaned surface. The sequence repeats a few eggs at a time.
Breeding
There is no published captive-breeding account for C. apiaka. By analogy with better-known corys, spawning would likely be triggered by a cool, rain-simulating water change, with adhesive eggs scattered on firm surfaces and given no parental care; the adults will eat their own eggs, so a breeder removes either the spawn or the parents, and the eggs hatch in a few days. Its small adult size means correspondingly small fry, which would need very fine first foods such as infusoria and microworm before graduating to baby brine shrimp. Because the species is only sporadically available, these remain reasonable expectations rather than a tested protocol.
In the aquarium
Corydoras apiaka is an uncommon import, of most interest to keepers who specialise in spotted and small Tapajós corys. The basics are those for the genus, adjusted for its small size: keep it in a shoal of six or more, never alone, in a tank whose value is measured by bottom area rather than height. A bed of soft sand is close to mandatory — sharp or coarse gravel abrades and infects the barbels, and a small, fine-snouted cory is especially vulnerable to that damage.
Given its origin in clear and black-water forest streams, it suits soft, gently acidic, clean and well-oxygenated water with modest flow, warm but not hot, with shade from wood and plants and an open sand area for foraging. It is entirely peaceful and belongs in a calm community of small tetras, pencilfish and similar species; it should not share a tank with anything large or boisterous. The familiar cory cautions apply — fin spines catch in nets, so a cup is the safer way to move them, and a stressed cory can release a skin toxin that may prove lethal in the confined volume of a transport bag.
Conservation
Corydoras apiaka was assessed by the IUCN in 2018 and listed as Least Concern. It is a small-ranged endemic of the upper Tapajós, but it is recorded from several different tributary systems — the Arinos, Teles Pires and Preto — and no immediate, range-wide threat was identified at assessment. The upper Tapajós is nonetheless a region under real pressure from agricultural expansion (the soy and cattle frontier of Mato Grosso), deforestation and a series of hydroelectric projects on the Teles Pires and Tapajós, all of which alter flow, sediment and connectivity in exactly the kind of headwater streams this fish occupies. A Least Concern listing therefore does not mean an absence of concern for a narrowly distributed clear- and black-water specialist of this sort.