Taxonomy & naming
Ernstichthys intonsus was described by the American ichthyologist Donald J. Stewart in 1985, in a review of the South American catfish tribe Hoplomyzontini (Aspredinidae) that introduced several new species from Ecuador (Fieldiana Zoology, new series, no. 25). It belongs to the family Aspredinidae — the banjo catfishes — within the tribe Hoplomyzontini, a group of small, slender-tailed aspredinids restricted to Andean-draining Amazonian rivers. The genus Ernstichthys currently holds only a handful of species, and the Catalog of Fishes (Eschmeyer, CAS) treats Ernstichthys intonsus as the valid combination; there is no evidence it was ever placed in an older catch-all genus.
The genus name honours the ichthyologist Carl H. Eigenmann's associate or collaborator Ernst (the exact dedicatee is not detailed in accessible sources) combined with -ichthys, Greek for "fish". The species epithet intonsus is Latin for "unshaved" or "bearded", chosen because this species carries an extreme proliferation of barbels around the head compared to its relatives — a genuinely descriptive name for a genuinely hairy-faced little catfish.
Morphology
Ernstichthys intonsus shows the classic banjo-catfish silhouette: a broad, flattened head and anterior body tapering abruptly into a long, slender, whip-like tail, giving the fish its "banjo" outline. The skin is completely scaleless and covered instead with small tubercles and ridges, an armour substitute typical of the family. True to its epithet, the head carries a dense fringe of barbels — more numerous and more elaborated than in related Ernstichthys and Hoplomyzon species — which likely serve a sensory role for a fish that forages by touch over sand and silt.
Maximum recorded size is only about 2 in standard length, making this one of the smallest banjo catfishes in the atlas. Colouration in aspredinids of this tribe is typically a cryptic mottled brown-to-sand pattern that breaks up the outline against a substrate background; as with all Aspredinidae, the pectoral and dorsal fins carry stiffened spines that can be locked erect.
Habitat
The species is known from the Napo River basin in Ecuador, an Andean-fed tributary system of the upper Amazon; the type locality is the Río Napo at Añangu, Napo Province, at roughly 0°30.8′S, 76°24.0′W. Like other Hoplomyzontini it is a demersal, freshwater fish of moderate to swift-flowing lowland river channels, where it lies on or half-buried in sand and fine sediment.
Detailed water-chemistry data for this specific population have not been published in the sources available here, so exact temperature and pH figures are not given with confidence; Napo basin waters are generally warm, soft-to-moderately mineralised lowland Amazonian river water. Data on this species' precise habitat requirements remains sparse.
Feeding
No dedicated dietary study of Ernstichthys intonsus has been published. By analogy with its tribe and family, it is presumed to be a nocturnal benthic micro-predator/omnivore, sifting sand and silt after dark for small invertebrates, worms and organic detritus rather than actively pursuing prey in open water.
In captivity, related small aspredinids are generally maintained on sinking pellets, frozen bloodworm and other small meaty foods offered after lights-out, since these fish are reluctant to compete for food in bright light or against faster midwater tankmates. This should be treated as an inference from the genus rather than a confirmed account for this species.
Mating
Courtship and spawning behaviour have not been documented for Ernstichthys intonsus. In several better-studied Aspredinidae, the female carries the fertilised eggs attached to the skin of her belly via small fleshy stalks (cotylephores) that develop temporarily during the breeding season, brooding the clutch externally until the eggs hatch — a highly unusual reproductive strategy found almost nowhere else among catfishes. Whether this applies to E. intonsus specifically has not been confirmed in the available literature, and it should not be assumed without direct evidence.
Breeding
Breeding biology in Ernstichthys intonsus is essentially unrecorded. No aquarium spawnings or field observations of reproduction in this species appear in the sources consulted here. Given the family's tendency toward egg-carrying by the female (in genera such as Aspredo and Bunocephalus), a similar mode is plausible, but this remains an inference rather than a documented fact for this particular species, and it has no established aquarium breeding history. Data on this species' reproduction is genuinely sparse; keepers should not expect to breed it.
In the aquarium
Ernstichthys intonsus stays genuinely small — about 2 in SL at maximum — so the size trap that plagues so many catfish is not a concern here; a modest tank with a deep, soft sand substrate and gentle-to-moderate flow suits it far better than an undersized setup for a large species. It is scaleless, like all Aspredinidae, and therefore medication-sensitive: dose copper-based and other treatments conservatively, following the same caution used for loaches, puffers and eels.
It carries locking pectoral and dorsal spines typical of the family, which can snag in a net, so it is best scooped in a container rather than netted. Being a small, cryptic, nocturnal sand-dweller, it needs a fine substrate to bury into and is easily outcompeted for food by boisterous tankmates — target feeding after dark with sinking foods is advisable. Because so little is documented about its husbandry, this species should be considered one for the experienced, patient keeper rather than a beginner community fish, and its availability in the trade is essentially nil — this is not a species most aquarists will ever encounter.
Conservation
The IUCN Red List assesses Ernstichthys intonsus as Data Deficient, with the assessment dated 7 November 2020. This reflects how little is known of its distribution, population size and trends rather than any confirmed stability or decline; the species is known only from the Napo River basin of Ecuador and possibly nearby drainages.
As with many small, range-restricted Amazonian catfishes, the relevant long-term pressures are the general ones facing Andean-Amazonian rivers — deforestation, sedimentation, water pollution from oil extraction and agriculture, and damming — though no species-specific threat assessment has been published. It is not part of the aquarium trade in any meaningful way, so collection pressure is not a factor.