Taxonomy & naming
Hoplomyzon cardosoi was described in 2017 by Carvalho, Reis and Friel in Neotropical Ichthyology, based on a holotype (MCNG 375, 0.5 in SL) collected from Caño La Raya in the Maracaibo Basin of Zulia state, Venezuela, with additional type material from the río Ariquaisa (also spelled río Aricuaisa) and río Santa Ana in the same drainage. It belongs to the family Aspredinidae, the banjo catfishes, and to the small genus Hoplomyzon, which also contains H. atrizona, H. papillatus and H. sexpapilostoma.
The species was diagnosed on osteological grounds using high-resolution computed microtomography rather than external characters alone — a reminder that many of the smallest catfishes are separated from their relatives by skeletal detail rather than obvious colour or shape differences. Diagnostic features include a straight anterior margin of the mesethmoid, a smooth ventral surface of the premaxilla, absence of teeth on the dentary, a single ventral vertebral process anterior to the anal fin, filamentous barbel-like structures on the ventral surface of the head, and eight anal-fin rays. The species epithet cardosoi honours Alexandre Rodrigues Cardoso, recognising his contributions to the taxonomy of Aspredinidae.
Morphology
Hoplomyzon cardosoi is tiny even by banjo-catfish standards: the holotype measured just 0.5 in SL, and the species is presumed to mature at a similarly minute size, well under 1 in. Like other Aspredinidae it has the classic banjo-catfish silhouette — a broad, flattened, disc-like head and forebody tapering to a slender, almost eel-like tail, giving the whole animal the outline of the instrument the family is named for.
The skin is naked, without scales, and covered in small tubercles and filamentous barbel-like papillae on the underside of the head, a texture typical of the genus. As in all catfishes this scaleless skin has no protective scale layer, which matters for keepers because it makes the fish considerably more sensitive to copper-based medications and many standard treatments than a scaled fish. Detailed body proportions and fin-ray counts are documented in the original description, but no separate account of adult coloration in life has been published; preserved specimens show the pale, mottled ground colour typical of small, cryptic Aspredinidae.
Habitat
The species is known only from small streams of the Maracaibo Basin in Zulia, Venezuela — Caño La Raya, río Ariquaisa and río Santa Ana — placing it firmly in South America's Maracaibo drainage rather than the Amazon or Orinoco systems more commonly associated with banjo catfishes. No detailed limnological data (temperature, pH, hardness) were published alongside the description, and the species has not been the subject of any ecological study since.
Banjo catfishes in general are bottom-dwellers of slow to moderate river reaches, resting motionless on sand, gravel or leaf litter where their flattened shape and mottled skin make them nearly invisible. Given its minute size, H. cardosoi almost certainly occupies the finest interstitial spaces of the streambed — fine gravel, sand and leaf-litter pockets — rather than open riverbed, but this is inferred from its build and relatives rather than documented directly.
Feeding
No feeding study exists for Hoplomyzon cardosoi. By analogy with other small Aspredinidae, it is presumed to be a nocturnal benthic micro-predator and detritivore, picking small invertebrates, aquatic insect larvae and organic detritus from the substrate after dark rather than actively hunting in open water. At under 1 in, prey items would necessarily be tiny — micro-crustaceans, worms and similar interstitial fauna.
Nothing is documented about the species in captivity, since it does not appear to be traded, so there is no aquarium feeding record to draw on. Any statement beyond the general nocturnal-detritivore pattern shared by its relatives would be speculation.
Mating
No courtship or spawning behaviour has been recorded for Hoplomyzon cardosoi; the species is known only from a small series of preserved museum specimens collected for the original description, not from field or aquarium observation of live behaviour.
Breeding
Reproduction in Hoplomyzon cardosoi is undocumented. In several other Aspredinidae, notably the genus Bunocephalus and some banjo catfishes more broadly, the female is known to carry fertilised eggs attached to the skin of her belly via fleshy stalks (cotylephores) until they hatch — an unusual form of external egg-carrying rather than nest-building or mouthbrooding. Whether Hoplomyzon shares this strategy has not been confirmed for this species, and no spawning has ever been reported in captivity or the wild. Given the total absence of published data, the honest statement is that breeding biology is unknown.
In the aquarium
Hoplomyzon cardosoi is not a fish anyone should expect to find for sale: it is a recently described micro-endemic known from a few Venezuelan streams, with no aquarium trade history and no husbandry record. This account is included for completeness, not as a stocking recommendation.
What can be said follows from its family and its size. As a scaleless catfish it would be sensitive to copper and many standard medications, warranting conservative half-dosing as with other naked-skinned Siluriformes. At under 1 in adult size it would need to be housed only with the smallest, gentlest tankmates if it were ever kept, and — like other banjo cats — would need soft sand or fine gravel to settle into and dim lighting, since it is presumed nocturnal. Any specimen would also need careful, container-based handling rather than netting, since even at this scale the stiff fin spines typical of catfishes can snag in mesh. None of this is verified husbandry; it is inference from family-level biology, offered with that caveat.
Conservation
Hoplomyzon cardosoi has not been formally assessed by the IUCN Red List; its status is Not Evaluated. It is known only from a small number of localities in the Maracaibo Basin of Zulia, Venezuela, and no population or range data beyond the type series have been published.
As a microendemic restricted to a handful of streams in a single drainage, it is inherently vulnerable to habitat degradation, pollution and water extraction in the Maracaibo Basin, even though no formal threat assessment exists to quantify that risk. Its conservation profile is best summarised as data-deficient in practice, if not in formal IUCN category: a species science barely knows beyond its original description.