Taxonomy & naming
Hoplosternum dukei was described by Cliff Emmens and Herbert Axelrod in 1968. It sits in the family Callichthyidae, the armoured catfishes, within the genus Hoplosternum — a small genus of South American callichthyids that also includes H. littorale, H. thoracatum, H. magdalenae and H. punctatum. The genus has had a tangled taxonomic history typical of Siluriformes: species now placed in Hoplosternum, Megalechis and Dianema have at various times been shuffled between genera as the callichthyid family was revised, and some literature still uses older combinations for close relatives.
Records for H. dukei are thin. It does not currently appear with a detailed profile on FishBase or on the PlanetCatfish Cat-eLog, the two most heavily used references for aquarium siluriforms, and no IUCN Red List assessment could be located. That gap does not mean the species is invalid — only that it has attracted very little documented attention since its description — so the genus placement is kept as published (Hoplosternum) rather than reassigned on guesswork.
Morphology
Like its congeners, Hoplosternum dukei should be built as a typical armoured callichthyid: a stocky, laterally compressed body covered in two overlapping rows of bony plates (scutes) rather than true scales, a flattened ventral surface, a short-based dorsal fin with a stout leading spine, and two pairs of barbels around the mouth used to feel out food on the bottom. The pectoral and dorsal fins carry stiff, serrated spines that lock into place — a genuine hazard when handling or netting the fish, since a locked spine can jab the keeper and readily tangles in net mesh.
No confirmed maximum size is available for H. dukei specifically. Related species in the genus reach a substantial size for a bottom-dwelling catfish — H. littorale is documented to around 10 in — so a similar adult size is plausible for H. dukei, but this has not been confirmed for the species itself and should be treated as an estimate, not a documented fact. Whatever its exact ceiling, prospective keepers should assume it is not a small fish and plan tank space accordingly rather than assuming it stays diminutive.
Habitat
Hoplosternum species as a group are found across northern and central South America, in slow-flowing rivers, floodplain pools, swamps and other still or sluggish freshwater habitats, often in water that is poorly oxygenated — a pressure that has driven the family's characteristic ability to breathe air at the surface. No specific locality, river system or country record could be confirmed for H. dukei from the sources checked here, so its precise native range is not stated with confidence; treat any specific-country claim for this species as unverified pending better documentation.
Feeding
As an armoured callichthyid, H. dukei is best assumed to be a nocturnal benthic omnivore, foraging along the substrate for invertebrates, detritus and organic matter, with activity concentrated after dark. In the aquarium, relatives in the genus take sinking pellets, frozen foods and other prepared foods readily and are not fussy feeders. Offering food after the lights go out better matches the fish's natural foraging rhythm and avoids it being out-competed by more visible, day-active tankmates.
Mating
Documented breeding behaviour specific to H. dukei was not found in the sources checked. Armoured callichthyids in the genus Hoplosternum breed as bubble-nest builders: the male blows a raft of mucus-coated bubbles at the surface, often anchored beneath a floating leaf or plant, and the pair spawns beneath or into the raft. On present evidence this is the mode to expect for H. dukei as well, following the pattern of its genus, though it has not been confirmed for this species by direct observation.
Breeding
Following the pattern documented for its congeners, H. dukei is expected to be a bubble-nest builder: the male constructs a floating raft of bubbles at the surface, the eggs are deposited into the nest, and the male then guards and tends the clutch and fry while the female takes no further part. This life history makes Hoplosternum one of the more genuinely home-breedable groups among catfishes generally — a soft, well-oxygenated aquarium with floating cover and a stable male can often be coaxed into a spawn. No aquarium breeding reports specific to H. dukei were located, so this account describes the expected genus-typical mode rather than a confirmed record for the species.
In the aquarium
Because a confirmed adult size for H. dukei is not available, keepers should size a tank generously and err toward the larger end suggested by its relatives (an estimated 8–10 in class) rather than assuming it will stay small — the size trap is the most common care failure with armoured catfish generally. Like all callichthyids it lacks true scales, wearing bony plates instead, so it should be treated as medication-sensitive: dose copper-based and other harsh treatments conservatively. Its pectoral and dorsal spines lock rigid and are serrated, so it should be moved in a container rather than scooped in a net, both to protect the fish's spines and the keeper's hands.
Hoplosternum species are facultative air-breathers, regularly rising to gulp air at the surface, so a tank should never be sealed tightly enough to prevent this and should include some open surface area. A soft substrate, subdued lighting and floating plants for cover suit its likely nocturnal, bottom-oriented habits. Given how little is documented about this particular species, keepers should treat any specific water-chemistry or feeding claim beyond the genus-level generalities here with appropriate caution.
Conservation
No IUCN Red List assessment for Hoplosternum dukei could be located, so its conservation status is presumed Not Evaluated. This is common for obscure, narrowly documented catfish species that have not been the subject of a dedicated population assessment. Given the general pressures on South American freshwater habitats — deforestation, water pollution and floodplain modification — a formal assessment would be valuable, but in its absence no status claim beyond Not Evaluated can be made responsibly.