Taxonomy & naming
The species was described by Carl H. Eigenmann and Clarence H. Kennedy in 1903 as Bunocephalus rugosus, part of the wider banjo catfish genus Bunocephalus as it was understood at the time. In 2008, the ichthyologist John P. Friel revised the family Aspredinidae and split off a distinct genus, Pseudobunocephalus, for a group of species — including rugosus — that differ from the type species Bunocephalus verrucosus and other true Bunocephalus. The Catalog of Fishes now treats Pseudobunocephalus rugosus as the valid combination, and the original authority is cited in parentheses to show the genus has changed since the original description.
The genus name Pseudobunocephalus combines "pseudo-" (false) with the older genus name Bunocephalus, signalling its close but distinct relationship to that genus. The species epithet rugosus is Latin for "wrinkled" or "shrivelled", a direct reference to the rough, tubercle-covered skin that gives the fish its rasp-like texture and camouflaged look.
Morphology
Pseudobunocephalus rugosus shows the classic banjo catfish silhouette: a broad, dorsoventrally flattened head and forebody that narrows abruptly into a long, slender, whip-like tail, giving the fish its "banjo" outline. The skin is completely scaleless and fully keratinized, and in this species it is conspicuously rugose — covered in small warts and tubercles rather than being smooth, which is where the name comes from.
Colouration is cryptic, typically mottled brown, grey and tan tones that break up the outline against sand, mud and leaf litter. This is a genuinely small species: maximum recorded size is only about 1 in standard length, making it one of the smallest catfish an aquarist is likely to encounter. Being scaleless, it shares the medication sensitivity common to naked-skinned catfish — copper-based treatments and many standard medications should be dosed conservatively.
Habitat
The species is native to the Paraguay-Paraná River basin in South America, a vast lowland river system draining parts of Brazil, Bolivia, Paraguay and Argentina. Like other small aspredinids it is a bottom-dweller, associated with soft substrates — sand, silt and accumulations of leaf litter — where its flattened shape and cryptic skin let it lie motionless and effectively disappear.
Detailed water chemistry data for wild populations is sparse in the available literature, and the type locality itself is not precisely documented in accessible sources. As a lowland South American river fish it is reasonable to expect warm, soft-to-moderate water, but specific temperature and pH figures for this species have not been confirmed and should not be assumed.
Feeding
Pseudobunocephalus rugosus is best understood as a nocturnal benthic micro-predator and detritivore, in keeping with the general pattern for small banjo catfish. It forages over the substrate after dark, picking up small invertebrates, detritus and other bottom material rather than hunting in open water.
Specific dietary studies for this species are not available, but the family's foraging strategy translates well to aquarium care: sinking pellets, small frozen foods (such as bloodworm or brine shrimp) and other bottom-delivered foods offered after lights-out are the most appropriate approach, mirroring its natural nighttime feeding rhythm.
Mating
Courtship and spawning behaviour in Pseudobunocephalus rugosus has not been documented in the sources available for this account. Breeding biology across Aspredinidae varies, and without direct observation of this species it would be misleading to describe a specific courtship sequence.
Breeding
Breeding in banjo catfish is not well studied as a whole, and P. rugosus is no exception — its reproductive biology has not been documented in detail. In several other Aspredinidae, females carry the fertilised eggs attached to the skin of the belly via small fleshy stalks called cotylephores, brooding the clutch externally until the young hatch; this is a distinctive strategy found nowhere else among catfish. Whether P. rugosus follows this pattern has not been confirmed, so it should be treated as plausible for the family rather than established fact for this species. There are no reports of this species being bred in the home aquarium.
In the aquarium
This is one of the rare catfish where the size trap runs the other way: at roughly 1 in maximum, Pseudobunocephalus rugosus stays genuinely tiny and is suitable for modestly sized tanks, unlike most catfish that are sold small and grow into a problem. A soft sand substrate and leaf litter let it exhibit its natural camouflaging behaviour and should be considered essential rather than decorative.
Being scaleless, it needs the same conservative approach to medication as other naked-skinned catfish — copper treatments in particular should be used cautiously or avoided. It is a nocturnal fish and appreciates dim lighting and cover during the day, becoming active to forage after dark. Tankmates should be small and peaceful; this is not a fish built to compete with fast, boisterous species for food, and its low profile means it is easily missed and can go unfed in a busy community tank unless food reaches the bottom after lights-out.
Conservation
The IUCN Red List assesses Pseudobunocephalus rugosus as Least Concern. It occupies a wide river system across the Paraguay-Paraná basin and is not currently considered at risk at the species level.
As with many small, cryptic riverine fish, there is little species-specific monitoring, and its conservation status reflects a broad distribution rather than detailed population data. Habitat pressures common to the Paraguay-Paraná basin — agricultural runoff, water management and sedimentation — are the relevant long-term considerations, though no specific threats to this species have been documented.