Taxonomy & naming
Xyliphius sofiae was described in 2017 by Mark Sabaj, together with Carvalho and Reis, in a paper devoted to describing a new blind and rare species of Xyliphius (published in Copeia). It belongs to the family Aspredinidae, the banjo catfishes, a distinctive South American group whose flattened, guitar-shaped bodies give the family its common name. The Catalog of Fishes treats Xyliphius sofiae as the valid name, and no older combination under a different genus is known — this is a fish that entered the literature already placed correctly.
The genus Xyliphius currently holds a handful of small, poorly known, often blind or eyeless banjo catfishes restricted to deep river channels in South America, a very different lifestyle from the shallow-water, egg-carrying Bunocephalus and Aspredo species most aquarists picture when they hear "banjo cat". Xyliphius sofiae is one of the smallest and most obscure members of that genus.
Morphology
This is an extremely small catfish: the holotype measured only 1.5 in standard length, and FishBase lists a maximum size of 1.5 in SL — smaller than a thumbnail. Like the rest of its banjo-catfish family it has a flattened, elongated body tapering to a slender tail, and like several of its Xyliphius relatives it shows complete loss of the eyes, an adaptation to a life spent in deep, sediment-heavy river channels where vision is of little use.
The body is pale, essentially lacking the pigment patterning seen in shallow-water relatives — again consistent with a deep-channel existence away from light. The barbels are notably elongated and the fin spines carry flexible filaments, both read as tactile adaptations that let the fish sense its surroundings by touch rather than sight. As in other banjo catfishes the skin is naked and scaleless, and the dorsal and pectoral fins carry stiff spines.
Habitat
Xyliphius sofiae is known from a single locality: the main channel of the Río Amazonas near Iquitos, Peru, at roughly 276 ft elevation. The holotype was collected in August 2005 from the main channel of this large whitewater river using a floating net, indicating a fish that lives well off the bank, out in open river-channel habitat rather than along quiet margins or on floodplains.
The original description does not document the water chemistry of the capture site, so specific pH, hardness or temperature figures for this species are not available. What can be said with confidence is that it inhabits deep, fast, sediment-rich whitewater river channel — a genuinely difficult habitat to sample, which explains both its late description and the near-total absence of ecological data beyond the type collection.
Feeding
No diet has been documented specifically for Xyliphius sofiae. Banjo catfishes as a family are nocturnal bottom foragers, and the family profile for Aspredinidae describes them taking high-quality sinking foods and live or frozen fare offered in the evening, consistent with a benthic micro-predator/omnivore habit — sifting sediment and picking off small invertebrates and detritus after dark.
Given the near-total absence of wild diet data for this specific species, any aquarium feeding regime would have to extrapolate from the family: sinking pellets and frozen foods offered after lights-out, rather than food competed for at the surface in daylight. This is inference from the wider Aspredinidae, not a documented fact for X. sofiae itself.
Mating
Nothing has been published on the mating behaviour of Xyliphius sofiae; the species is known from a single preserved holotype and the original taxonomic description, not from field observation of live behaviour or aquarium spawning. Data are simply not available.
Breeding
Breeding in Xyliphius sofiae is undocumented. In the wider banjo-catfish family (Aspredinidae), several species are notable for female egg-carrying, in which the female carries the fertilised eggs attached to her belly skin via fleshy stalks (cotylephores) until they hatch — an unusual mode among catfishes. Whether X. sofiae follows this pattern is not established in the available literature; it has not been recorded breeding in captivity, and given its extreme rarity in the trade and its deep-channel habitat, a home aquarium spawning has essentially no precedent to report. It is honest to say that breeding biology here is simply unknown rather than to assume a mode by analogy.
In the aquarium
Xyliphius sofiae is essentially not an aquarium fish. It is extremely rare in the trade — known from a single wild locality and a handful of scientific specimens — and its biology (a blind, tiny, deep-river-channel specialist) makes it a poor candidate for captive care even where it can be sourced. Anyone who does encounter it should still respect the general rules that apply to banjo catfishes: the skin is scaleless, so it is medication-sensitive and copper-based or harsh treatments should be dosed conservatively, as with loaches, puffers and eels; the dorsal and pectoral fins carry stiff spines that can lock and snag in a net, so the fish is best moved in a container rather than netted.
At 1.5 in maximum size this is not a species that presents the usual catfish "size trap" of outgrowing its tank — if anything the opposite risk applies, that its habitat needs (soft, fine, sediment-like substrate; darkness; and likely strong or at least consistent water movement echoing a river channel) are poorly matched to typical aquarium conditions. Given the absence of husbandry data, water chemistry and temperature should not be guessed; this is a fish for which "data sparse" is the honest and only responsible answer.
Conservation
Xyliphius sofiae has not been evaluated by the IUCN Red List; no species-specific assessment could be located. Known from only a single locality in the main channel of the Amazon near Iquitos, Peru, it has not been assessed for conservation status, and its rarity in both scientific collections and the aquarium trade means population trends and threats are essentially undocumented.
As with many recently described, single-locality catfishes, the honest conservation picture is one of a data gap rather than either safety or danger: its true range may extend well beyond the one known collection point, but until further surveys of the deep whitewater channels it favours are carried out, nothing more can be said.