Taxonomy & naming
Lepthoplosternum altamazonicum was described by the Brazilian ichthyologist Roberto E. Reis in 1997, part of his broader revision of the callichthyid catfishes that split the old, crowded genus Hoplosternum into several smaller, better-defined genera — Hoplosternum sensu stricto, Megalechis, Dianema and Lepthoplosternum among them. Older literature and some aquarium-trade references may still list callichthyids of this group under Hoplosternum; that combination is outdated, and the Catalog of Fishes recognises Lepthoplosternum altamazonicum as the valid current name.
The species belongs to family Callichthyidae — the armored catfishes, which also contains the much more familiar Corydoras — and specifically to the subfamily Callichthyinae, the larger-bodied, air-breathing armored catfishes that build bubble nests rather than scattering eggs. The species epithet altamazonicum references its range in the upper ("alta") Amazon basin.
Morphology
Like all callichthyids, Lepthoplosternum altamazonicum has no true scales; instead its flanks are covered in two overlapping rows of bony dermal plates (scutes) running the length of the body, giving it the armored look shared by corydoras and its larger callichthyine cousins. The body is elongate and only moderately deep, with a flattened underside suited to life on and near the bottom, and it carries the paired barbels typical of the family for probing sediment.
Maximum recorded size is a modest 2 in standard length, making this one of the smaller members of the armored-callichthyid group — considerably more modest than the well-known Hoplosternum thoracatum or Megalechis picta, which can exceed 6–8 in. As in other callichthyids, the pectoral and dorsal fins carry stiff, sharp spines that can lock erect; these catch easily in aquarium nets and are best handled by moving the fish in a container rather than netting it directly.
Habitat
The species is native to the upper Amazon River drainage, recorded from Peru and extending downstream to around the confluence of the Rio Solimões and Rio Japurá in Brazil. It occupies the slow-flowing and still (lentic) freshwater habitats typical of Amazon floodplains — the sluggish channels, backwaters and seasonally flooded várzea forest that characterise much of the upper basin.
These floodplain waters are often warm, soft and low in dissolved oxygen, especially where leaf litter and organic decay draw oxygen down; this is precisely the pressure that has shaped Lepthoplosternum, like the rest of the Callichthyinae, into an obligate air-breather, gulping atmospheric air at the surface to supplement what its gills can extract from the water. Specific temperature and pH figures were not captured for this species in research; typical upper-Amazon floodplain water is warm and circumneutral to mildly acidic, and that range is a reasonable starting point for the aquarium pending firmer data.
Feeding
Lepthoplosternum altamazonicum is a nocturnal benthic omnivore, sitting at a fairly low trophic level typical of bottom-foraging callichthyids — it works the substrate for detritus, small invertebrates and other micro-prey rather than hunting larger animals. Most feeding activity happens after dark, when the fish is less exposed and competition from diurnal fish is reduced.
In the aquarium it takes sinking pellets and wafers, frozen foods such as bloodworm and daphnia, and other prepared foods without fuss. Because it is most active at night, offering a portion of food after the lights go out helps ensure a shy or small specimen is not out-competed by more visible tankmates.
Mating
Mating in Lepthoplosternum, as in the other armored callichthyids (Hoplosternum, Megalechis, Callichthys), centres on a floating bubble nest rather than open-water spawning. The male produces a raft of mucus-coated bubbles at the water's surface, often anchored beneath a broad leaf, a piece of floating cover, or the underside of an emergent object, and works to hold the raft together.
A receptive female is drawn to the nest and eggs are laid and fertilised in or beside it, then tucked up into the bubble mass, where the surface air trapped in the raft keeps them oxygenated even in the low-oxygen floodplain water the species calls home. No specific published account of courtship detail was found for this species; the pattern described here follows the well-documented callichthyine bubble-nest strategy shared across the genus.
Breeding
This is one of the more genuinely home-breedable catfishes in the atlas: once the bubble nest is built and the eggs deposited, the male stations himself beneath or beside the raft and guards it, driving off potential egg predators and topping up the nest's air supply until the fry hatch and become free-swimming. This male-only parental care is the callichthyine pattern seen across Hoplosternum, Megalechis and Dianema, and there is no reason from the available record to expect Lepthoplosternum altamazonicum to differ.
Aquarists attempting a spawn should provide floating cover (broad leaves, floating plants, or a foam square) at the surface, softened, warm water, and good but gentle surface movement rather than strong current, which can break up a fragile bubble raft. As with related callichthyids, a slight cooling and refill with softer water — mimicking a floodplain rain event — is a plausible trigger, though this has not been specifically documented for the species.
In the aquarium
At a maximum of 2 in SL this is a genuinely small catfish, one of the few in this family that will not outgrow a modest aquarium — but its air-breathing habit still means it needs unobstructed access to the surface, so tall, densely covered tanks without any open water at the top are a poor fit. A soft, sandy substrate suits its barbelled, bottom-probing habits and protects the skin from abrasion.
Because it lacks true scales and is armored instead with bony plates, treat it with the same medication caution given to other scaleless catfish: dose copper-based and other harsh treatments conservatively, as this skin type is more sensitive than a fully-scaled fish's. Its pectoral and dorsal spines lock and can snag in a net or jab a careless hand, so scoop it in a cup or container rather than a net. Keep it in a group if possible — like other callichthyids it is a sociable bottom-dweller — with peaceful, similarly modest-sized tankmates, and expect it to be most active after the lights go down.
Conservation
The IUCN Red List assesses Lepthoplosternum altamazonicum as Least Concern, with the assessment dated 2020. It occupies a substantial stretch of the upper Amazon floodplain across Peru and Brazil, habitat that remains extensive relative to the species' modest ecological footprint as a small detritivore/omnivore.
As with many upper-Amazon floodplain fish, the longer-term outlook is tied to the health of the várzea system itself — deforestation, water-level regulation and habitat conversion pressure on Amazon floodplains generally — rather than to any species-specific threat. The species is not known to be significant in the aquarium trade, so collection pressure is not considered a driver of its conservation status.