Taxonomy & naming
The spotted collar cory was described in 1947 by Alec Fraser-Brunner, the epithet brevirostris ('short-snouted') marking the blunt, rounded face that sets it apart from long-nosed relatives. Its taxonomic history is tangled: for a long stretch it was treated as a subspecies of the very similar Corydoras melanistius, traded and written about as 'Corydoras melanistius brevirostris,' and only later restored to full species rank. It has spent most of its history within the huge genus Corydoras Lacépède, 1803 of the family Callichthyidae.
That genus proved not to be a single natural lineage, and the 2024 revision by Dias, Tencatt and colleagues (DOI 10.1093/zoolinnean/zlae053) divided it into several genera, including the resurrected Hoplisoma. Under that classification the species becomes Hoplisoma brevirostris, the combination now used by FishBase and the specialist Corydoras World site. As the change is recent and the trade still says 'Hoplisoma brevirostre,' we keep that heading while recording the current lineage name. Because of its close resemblance to melanistius, reliable identification of this species leans heavily on collection locality.
This fish was long listed as Corydoras brevirostris; Eschmeyer's Catalog of Fishes places the species in Hoplisoma, and the current combination Hoplisoma brevirostre is followed here.
Morphology
This is a small-to-modest cory, reaching about 2 in in standard length — a deep-bodied fish with the short, blunt snout from which it takes its name. Like all the group it is armoured rather than scaled, with two overlapping rows of bony plates down each flank and the hard, helmeted bony head, and three pairs of barbels fringe the small, downturned mouth used to sift the substrate.
Its pattern is the source of the 'spotted collar' name: a dark band or blotch across the nape and shoulder region behind the head, set off against a paler ground, with fine spotting on the body and fins — a colouration close to that of C. melanistius, which is exactly why the two were long confused. The sexes differ chiefly in build, females growing larger and fuller-bodied (most obvious from above) while males stay slimmer. The dorsal, pectoral and adipose fins each carry a stiff leading spine, the standard corydoradine defence.
Habitat
Hoplisoma brevirostre is recorded from the Orinoco River basin and the coastal drainages of Suriname, a somewhat disjunct distribution that suggests it is also likely to occur in Guyana between the two. These are warm tropical lowland waters, and the fish lives over soft bottoms in quieter stream and river reaches where corydoradines forage.
The water is warm and broadly circumneutral to acidic: FishBase gives a temperature band of roughly 68–75 °F — somewhat cooler than many lowland corys — a pH range from about 6.0 to 7.8 and water up to moderately hard (to around 25 °dH). Like its relatives it is a facultative air-breather, surfacing periodically to gulp air and absorb oxygen through a vascularised hindgut, an adaptation to the warm, oxygen-poor margins and seasonal pools of its habitat.
Feeding
No species-specific dietary study has been published, but its anatomy and habits place it firmly with the rest of the group as a benthic omnivore and detritivore. It works the bottom with its barbels, sifting sand and leaf litter for small invertebrates, insect larvae, micro-crustaceans and organic detritus, taking in mouthfuls of substrate and expelling the cleaned grains through the gills. Its trophic level (around 3.0) reflects that mixed invertebrate-and-detritus diet. In the aquarium it takes the usual cory foods — sinking pellets and tablets, frozen bloodworm and brine shrimp, and small live foods delivered to the bottom.
Mating
Spawning has not been documented specifically for H. brevirostre, but the Corydoradinae share a highly uniform reproductive pattern, so the general account very probably applies. These are egg-laying shoalers with no pair bond. A ready female cleans a spawning site, and a courting male takes up the classic 'T-position', his body at right angles to her head; she appears to take milt directly, and a few adhesive eggs are clasped in a basket of the pelvic fins and pressed onto the cleaned surface. The sequence repeats, a few eggs at a time, until the clutch is complete.
Breeding
There is no well-established captive-breeding record specific to this species, so any account is by analogy with its better-known relatives rather than direct observation, which we state plainly. In the corydoradines generally, spawning is often triggered by a cool, large water change that mimics the rainy season; the adhesive eggs are laid in small batches onto plants, wood or aquarium glass and receive no parental care, the adults eating them unless the eggs or parents are separated. Eggs typically hatch in three to five days, and the fry take microworm, baby brine shrimp and powdered foods once the yolk is absorbed. Whether H. brevirostre follows this template in every detail awaits confirmation by aquarists who keep it.
In the aquarium
The spotted collar cory is a peaceful, shoaling catfish that turns up in the trade occasionally, sometimes still under the old 'melanistius brevirostris' label. Standard corydoradine husbandry applies. Keep it in a group of six or more — these are social fish, stressed when kept singly or in pairs — over soft sand or very smooth fine gravel, since they feed by sifting and sharp or coarse substrate erodes and infects their barbels.
A planted tank with a clean bottom, gentle current and good oxygenation suits it. Note that it prefers slightly cooler water than many lowland corys — around 68–75 °F — with a soft, near-neutral to mildly acidic chemistry, though it tolerates a fair range. It is entirely peaceful and belongs with small, calm community fish rather than anything boisterous. The familiar cautions hold: the fin spines tangle easily in nets, so a cup is safer, and a badly stressed cory can release a skin toxin that may kill the whole group in the confined volume of a bag or bucket, so move them with care.
Conservation
The IUCN assessed Hoplisoma brevirostre as Least Concern in 2020. It is fairly widely distributed across the Orinoco basin and the coastal Guianan drainages, and the assessment found no evidence of major threats or significant collection pressure. The broad pressures on northern South American freshwaters — deforestation, mining, agricultural run-off and pollution — degrade the lowland streams it favours, but as a species it is not currently considered to be at risk. The more persistent issue around this fish is taxonomic rather than conservational: its long confusion with C. melanistius means trade and occurrence records under either name should be read with care.