Taxonomy & naming
Ernstichthys taquari was described in 2021 by Dagosta & de Pinna from material collected in the Taquarizinho stream, part of the Rio Taquari drainage in the upper Rio Paraguay basin, Mato Grosso do Sul, Brazil. It belongs to the family Aspredinidae, the banjo catfishes, and to the small genus Ernstichthys, which the Catalog of Fishes (Eschmeyer, CAS) treats as the current valid placement for this and its close relatives. As with much of Siluriformes taxonomy, the classification of aspredinid genera has been revised repeatedly in recent decades; older literature on similar small Amazon/Orinoco banjo cats may use different generic combinations, but Ernstichthys is the name to use for this species.
The species epithet taquari refers directly to its type locality, the Rio Taquari system, rather than to any physical trait. Being described so recently, E. taquari has not yet accumulated a body of synonyms or a common name in general use — hobbyists and the scientific literature alike refer to it by its scientific name.
Morphology
Ernstichthys taquari is minute even by banjo-catfish standards: FishBase records a maximum size of just 1 in standard length, which corresponds to roughly 1 in total length once the caudal fin is included. Like all Aspredinidae it has the family's signature banjo-shaped outline — a broad, flattened, bony head and forebody tapering to a long, slender, whip-like tail — and, notably, scaleless, naked skin rather than true bony plates, which makes it (like loaches, puffers and eels) more sensitive to medications such as copper than a scaled fish.
Aspredinids typically carry stiff, serrated pectoral spines that can lock erect; these tangle easily in a net and can jab careless hands, so any handling of this genus is best done by scooping the fish into a container rather than netting it. Detailed morphological description of E. taquari beyond size and family-typical body plan is not documented in the sources consulted here; data is sparse for this newly described species.
Habitat
The species is known from the Rio Taquari drainage of the upper Rio Paraguay basin in Mato Grosso do Sul, Brazil, with its type locality in the Taquarizinho stream — a white-water river system with moderate current flowing over a bed of rock and sand. It is demersal, living directly on and in the substrate rather than in open water.
Congeners in Ernstichthys are known to settle on the bottom in fast-running water and bury themselves in fine sand, an ambush and camouflage strategy consistent with the flattened, cryptic body shape of the family; E. taquari likely behaves the same way, though this has not been directly documented for the species itself. Water chemistry reported for the genus spans a moderate range — roughly pH 6.0–7.5 at 75–81 °F — typical of well-oxygenated, flowing South American streams rather than still, acidic blackwater.
Feeding
Ernstichthys taquari has not been the subject of a dedicated dietary study, but the genus is characterised as a nocturnal benthic forager, sifting sand and gravel after dark for small insects and crustaceans. This fits the broader Aspredinidae pattern of bottom-dwelling micro-predators that rely on camouflage and cover by day and become active foragers at night.
Congeneric Ernstichthys are reported to also accept frozen and prepared foods in the aquarium once settled, suggesting E. taquari would do the same, though this is inferred from the genus rather than confirmed for this species specifically. Any captive feeding should be timed for after lights-out, mimicking the fish's natural nocturnal foraging window so it is not out-competed by more active tankmates.
Mating
No courtship or mating behaviour has been documented for Ernstichthys taquari; the species was described from preserved material and reproductive biology was not part of that description. Breeding biology across the Aspredinidae is generally poorly studied, and this species — described only in 2021 — has had essentially no time to accumulate field or aquarium observations of its reproductive behaviour.
Breeding
Breeding in Ernstichthys taquari is not documented, but the family it belongs to gives a useful (though unconfirmed) clue. In several Aspredinidae genera — including Platystacus, Aspredo and Aspredinichthys — the female carries her fertilised eggs attached to the skin of her belly on fleshy stalks called cotylephores, effectively brooding the clutch externally until the eggs hatch; the cotylephores are thought to function almost like an umbilical cord, helping keep the eggs oxygenated in the often muddy or sediment-laden waters these fish inhabit. Whether Ernstichthys shares this exact strategy has not been confirmed in the literature reviewed here.
Given the complete absence of species-specific breeding records and the very recent description of E. taquari, it should be treated honestly as essentially unbred and unstudied in this respect — there is no reliable report of successful captive breeding, and any home aquarium spawning would be a novel observation worth documenting rather than an expected outcome.
In the aquarium
Ernstichthys taquari is a genuinely tiny fish — maximum recorded size is only about 1 in SL (roughly 1 in TL) — so unlike many catfish in this atlas there is no size trap here; it will never outgrow a modestly sized aquarium. What it does need is a fine, soft sand substrate to bury into, moderate water flow to mimic its rocky-stream habitat, and water in the range the genus is known to tolerate, roughly pH 6.0–7.5 and 75–81 °F.
Because it is scaleless, it shares the medication sensitivity of other naked-skinned catfishes — dose copper-based treatments and many other medications conservatively, at reduced strength. Its pectoral spines can lock and are easily tangled in a net, so it should be moved by container rather than netted. As a nocturnal, cryptic bottom-dweller it needs a fine substrate to disappear into by day and is unlikely to be seen much outside low light; it is a specialist fish for keepers prepared to replicate a small, flowing, sandy-bottomed stream rather than a general community tank.
Conservation
The IUCN Red List has not yet formally assessed Ernstichthys taquari; its status is Not Evaluated. This is unsurprising for a species described only in 2021 from a restricted stream system — the Taquarizinho and wider Rio Taquari drainage in Mato Grosso do Sul — that has not yet been the subject of range-wide surveys or a conservation review.
As with many recently described, narrow-range South American stream fishes, its conservation outlook depends on the health of its specific home waters; pressures on the upper Rio Paraguay basin such as land-use change, sedimentation and water-quality degradation are the general concerns for fish restricted to small tributary systems in the region, though no species-specific threat assessment exists to confirm impacts on E. taquari.