Taxonomy & naming
Trachelyichthys varii was described in 2026 by Bruno B. Calegari, Alany Akama, Carl Ferraris Jr., and Roberto E. Reis, one of four new species that expanded the genus Trachelyichthys from two recognised species to six. The genus was established by Mees in 1974 for T. decaradiatus, its type species, and gained only one further name — T. exilis, described in 1977 — before this revision. Trachelyichthys belongs to the family Auchenipteridae, the driftwood catfishes, within the subfamily Auchenipterinae; recent phylogenetic work places the genus in the tribe Auchenipterichthyini, sister to Trachelyopterichthys.
In the genus's phylogeny, T. varii — called 'Trachelyichthys "Roraima"' in earlier molecular studies — is placed as the sister lineage to T. decaradiatus of Guyana, the genus's type species; together they form a clade sister to the pair T. exilis and T. displicatus. The species is named for the ichthyologist Richard P. Vari, who died before the manuscript describing it was completed (see Etymology).
Morphology
Trachelyichthys varii is among the smallest species in its genus, reaching a maximum of 1.6 in standard length in the type series — the holotype, a mature male, is the largest measured specimen, with other measured paratypes ranging 1.1–1.6 in SL and smaller, unmeasured juveniles down to about 0.7 in SL also present in the type series. The body is nearly cylindrical from behind the head through the abdomen, becoming increasingly compressed toward the caudal fin, with a rounded head and a very short, rounded snout.
The species is immediately recognisable by its colour pattern: a dense concentration of black spots fuses into a wide, continuous stripe running along the midline of the body from the dorsal-fin base almost to the caudal peduncle, bordered by dark brown dorsally and cream ventrally — a pattern unique among the six known Trachelyichthys species, which otherwise show either plain brown colouration or scattered, disconnected spots. In life the stripe is even more strongly contrasted than in preserved specimens. The dorsal fin has 4 soft rays on three free pterygiophores; the pectoral fin has 6 rays; the anal fin carries 36–38 total rays.
Habitat
Trachelyichthys varii is known only from the rio Jufari and its tributaries, a blackwater affluent entering the north bank of the middle rio Negro upstream of its confluence with the rio Branco, in Roraima, Brazil. All type specimens were collected from small streams and river beaches within this single drainage.
The type series was collected directly from a piece of driftwood in the igarapé Tubana, a tributary of the Jufari — documented, rather than presumed, evidence of the wood-dwelling habit that gives driftwood catfishes their name. The same log held an adult Tatia strigata, another auchenipterid, and specimens of Auchenipterichthys were collected at the same site, showing this species shares its wood-cavity habitat with other driftwood-catfish genera.
Feeding
No dietary study has targeted Trachelyichthys varii specifically. The only ecological data published for the genus, Freitas & Zuanon (2022), described a predominantly carnivorous, piscivore-leaning diet, but that material is now attributed to a different species, T. displicatus, from the Santarém region. A broadly similar diet is plausible for T. varii given the shared family biology and its documented association with wood-cavity microhabitats, but this is inference, not direct observation.
Mating
Trachelyichthys varii shows no sexually dimorphic modification of the maxillary barbel or dorsal fin between males and females. As in the rest of the subfamily Auchenipterinae, nuptial males form an intromittent organ from the genital tube attached to the anterior anal-fin rays, used to inseminate the female internally; in this species the first unbranched, elongated anal-fin rays that form the structure are not bound to the remaining rays by membrane during the reproductive season, a fine anatomical detail that distinguishes it from some congeners.
Breeding
No breeding of Trachelyichthys varii has been documented, in the aquarium or in the wild. As in other Auchenipteridae, internal fertilisation is understood to let the female store sperm and lay fertile eggs after mating, with adhesive eggs and little to no parental care — a family-level pattern that has not been directly confirmed for this species.
In the aquarium
Trachelyichthys varii has never appeared in the aquarium trade; the type series was collected for a biodiversity survey of the rio Jufari, and no husbandry account exists for the species.
Extrapolating from the driftwood-catfish family generally, and labelled clearly as inference: its documented habit of sheltering inside submerged logs alongside other auchenipterids suggests it would do well in a soft, blackwater-style aquarium furnished with driftwood offering tight crevices and cavities, under subdued lighting. Like all Trachelyichthys it is scaleless, so careful netting and caution with copper-based medications would be standard precautions if the species were ever kept.
Conservation
Trachelyichthys varii has not been formally assessed by the IUCN Red List, having only been described in 2026. The authors recommend a category of Least Concern under IUCN criteria, noting that although the species is currently known only from the rio Jufari drainage, the surrounding area is not densely sampled and the species likely occurs more widely through the middle rio Negro basin. No specific threat has been identified, though data on abundance and population trend are unavailable.