Taxonomy & naming
Lepthoplosternum tordilho was described by Roberto E. Reis in 1997 as part of his taxonomic revision of the neotropical genus then known broadly as Hoplosternum. That revision split several small, slender species out of Hoplosternum into a new genus, Lepthoplosternum, and this fish — originally named Hoplosternum tordilho — was reassigned to it. The Catalog of Fishes treats Lepthoplosternum tordilho as the valid combination, and the species remains in the family Callichthyidae, subfamily Callichthyinae, the armoured catfishes.
The genus name Lepthoplosternum combines Greek leptos, "slender" or "fine", with Hoplosternum, literally naming these fish as the slender-bodied relatives of the larger Hoplosternum. The species epithet tordilho is not Latin but Portuguese, a regional Brazilian term for a dappled, grey-roan horse coat — a direct, descriptive nod to the fish's light brownish-grey background peppered with small darker spots.
Morphology
Like every Callichthyinae, Lepthoplosternum tordilho is armoured rather than scaled: two overlapping longitudinal rows of bony dermal plates (scutes) run along each flank in place of true scales, the hallmark of the subfamily. The body is slender and compact even by the standards of a genus defined by its slenderness, and the ground colour is a light brownish-grey overlaid with small, irregular dark spots — the mottled "tordilho" pattern the species is named for.
Maximum recorded size is only about 2 in standard length, making this one of the smallest armoured catfishes in the hobby's orbit, well under half the size of the Hoplosternum species it was split from. As in its relatives, the skin beneath and around the scute rows is scaleless, so the fish should be treated as medication-sensitive in the same way as any naked-skinned catfish. Like other callichthyines it is an obligate air-breather, gulping surface air into a highly vascularised section of hindgut modified for accessory respiration — an adaptation that lets it survive in water too oxygen-poor for gill-only fish.
Habitat
The species is endemic to a small stretch of range: the lower Jacuí River drainage in Rio Grande do Sul state, southern Brazil, including the coastal lagoon systems that give it its common name, Lagoon catfish. It is a warm-water, freshwater species associated with slow-flowing, vegetated backwaters and lagoon-margin habitat rather than fast open river channel.
Specific published pH, hardness and temperature ranges for this species are sparse, but related Lepthoplosternum and Hoplosternum species in similar coastal river and lagoon systems favour warm, soft to neutral, often acidic water low in dissolved oxygen — conditions consistent with the accessory air-breathing anatomy this species shares with its relatives. Its restricted single-drainage range makes it vulnerable to any large-scale change in that habitat, including river damming and coastal development, which is reflected in its conservation status.
Feeding
Detailed dietary studies specific to Lepthoplosternum tordilho are not available, but the species can be expected to follow the same pattern as its Callichthyinae relatives: a nocturnal, benthic omnivore that forages the bottom mostly after dark for small invertebrates, detritus and organic matter sifted from sediment and leaf litter.
In an aquarium setting this translates to sinking pellets, small frozen foods and prepared bottom-feeder foods offered after lights-out, when a small, retiring catfish like this one is far more likely to find food before faster tankmates clear it. Given its very small adult size, food particles should be sized accordingly rather than assuming a catfish-scale appetite.
Mating
No detailed field or aquarium account of courtship in Lepthoplosternum tordilho has turned up in the available literature, but the species' subfamily placement is informative: Callichthyinae — Hoplosternum, Megalechis, Dianema and Lepthoplosternum alike — are floating bubble-nest builders. In related species, a male blows a raft of mucus-coated bubbles at the surface, often anchored beneath a floating leaf or plant, and entices a female to release eggs into it, fertilising them as they are placed in the nest.
Given the consistency of this reproductive mode across the subfamily and the shared morphology with its close relatives, Lepthoplosternum tordilho is presumed to follow the same bubble-nest strategy, though species-specific courtship behaviour has not been documented in the sources available here.
Breeding
As in other armoured callichthyids, breeding in this species is expected to centre on a floating bubble-nest that the male constructs and then guards, fanning and tending the raft of eggs until they hatch — one of the few genuinely home-breedable reproductive strategies among catfishes generally. This makes the group notable: unlike most catfish families, which are either essentially unbred in captivity or reliant on hormone induction at commercial scale, callichthyids like Hoplosternum and Megalechis are regularly spawned by hobbyists.
That said, no specific aquarium-breeding account for Lepthoplosternum tordilho itself was found in the sources consulted here — the species is little-known outside its native range and does not appear to have an established hobbyist breeding record. Anyone attempting it should expect the general callichthyid pattern (male-built bubble-nest, male guarding) rather than assume it has been proven in the aquarium.
In the aquarium
This is a genuinely small catfish — adults top out around 2 in standard length — so it does not carry the size trap that catches out keepers of many larger armoured catfishes; a modestly sized, well-planted tank suits it. It nonetheless shares the family's other care considerations: the bony scute armour means it lacks true scales, so it should be treated as sensitive to copper-based medications and dosed conservatively; and as an obligate air-breather it needs unobstructed access to the surface to gulp air; a lid with an air gap is worth keeping, not a fully sealed cover.
Data on captive husbandry specific to this species is sparse — it is not an established or widely traded aquarium fish, and most of what can be said follows from its Callichthyinae relatives. Provide soft leaf litter or fine sediment for foraging, floating plants or cover for a nocturnal fish to shelter under by day, and gentle, well-oxygenated but not fast-flowing water reflecting its lagoon and backwater habitat. As with any wild-range endemic, sourcing should be scrutinised given its restricted distribution and NT status.
Conservation
The IUCN Red List assesses Lepthoplosternum tordilho as Near Threatened, assessed 7 November 2018. The species is endemic to a single, restricted range — the lower Jacuí River drainage and associated coastal lagoons of Rio Grande do Sul, Brazil — which is precisely the kind of narrow-range distribution that elevates conservation concern even without evidence of steep population decline.
The principal pressures identified are habitat-scale: damming of the Jacuí River system and "coastal squeeze" affecting the lagoon habitats it depends on, both of which fragment or shrink the limited area this fish can occupy. There is no evidence in the sources consulted of an established aquarium trade or captive-breeding programme for the species, so any conservation value from the hobby side is effectively absent; its future is tied to the health of its one home drainage.