Taxonomy & naming
Phenacorhamdia bermejo was described in 2026 by Gastón Aguilera, Gastón E. Terán, Miguel Á. Cortés Hernández, Ariel M. Katz, Valter M. Azevedo-Santos, Mariana Benitez and Marcelo Mirande, in Neotropical Ichthyology (volume 24, issue 1, article e250189). Before this description, P. tenebrosa was the only species of the genus recorded from Argentina, though the authors note that record — based on specimens from the Yacyretá dam area — is itself doubtful and needs re-examination. With the addition of P. bermejo, Phenacorhamdia now comprises 16 valid species distributed across the major South American river basins, and this is the fifth described from the Paraná River system, alongside P. hoehnei, P. roxoi, P. tenebrosa and P. unifasciata.
The genus is placed in the tribe Heptapterini within the family Heptapteridae, closely related to Magdalenichthys and Pariolius, and Eschmeyer's Catalog of Fishes treats Phenacorhamdia bermejo Aguilera, Terán, Cortés Hernández, Katz, Azevedo-Santos, Benitez & Mirande, 2026 as a valid, currently accepted name. A phylogenetic analysis based on the mitochondrial COI and Cytb genes recovered P. bermejo as sister to a clade containing P. tenebrosa and P. unifasciata, with P. boliviana sister to that group of three; genetic distance between P. bermejo and its closest external match, P. tenebrosa, exceeded 8%, supporting its status as a distinct species despite notable morphological similarity between the two. The holotype (CI-FML 8284, 1.68 in SL) was collected from the San Francisco River at Yuto, Ledesma Department, Jujuy Province, Argentina (23°40'02.0"S, 64°28'44.6"W, 1132 ft elevation); paratypes are held at CI-FML and MACN.
Morphology
Phenacorhamdia bermejo reaches at least 2.01 in SL among examined specimens (the holotype measures 1.68 in SL); the body is elongate and elliptical in cross-section, deepest at the dorsal-fin origin and compressed toward the caudal peduncle. The head is depressed and widest at the occipital region, with a short snout, a terminal-to-slightly-prognathous mouth, and conical teeth arranged in a rectangular patch of four to eight irregular rows. The maxillary barbel is notably long for the genus, surpassing the tip of the adpressed pectoral fin and, in some specimens, reaching all the way to the dorsal-fin origin — one of several measurements (alongside longer mental barbels, a longer head, and longer caudal-fin lobes) that separate it from most congeners.
Meristically, the species carries 11–12 anal-fin rays, 15 branched caudal-fin rays, 7–8 branched pectoral-fin rays, and 41–42 total vertebrae — a lower vertebral count than most other Phenacorhamdia species. The caudal fin is deeply forked with the ventral lobe (29.0–33.8% of SL) longer than the dorsal (24.2–28.6% of SL). In preservative the body is light beige, almost white ventrally, with the pectoral, pelvic, anal and dorsal fins hyaline; in life it shows a uniform, finely mottled reddish-brown across the body, a slightly darker head, denser pigment concentrated along the dorsal-fin rays and at the base of the adipose and caudal fins, and a silvery band of unpigmented skin running from the pectoral-fin origin to the anal-fin origin. Phenacorhamdia bermejo has a long snout (36.0–45.7% of head length) and a relatively short, slender body, placing it in the "long-snouted" clade of the genus, supported by nine shared skeletal characters described by earlier workers — including a distinctively shaped premaxilla, lateral ethmoid and pterosphenoid, and a reduced optic foramen — all of which the authors confirmed in this species.
Habitat
Phenacorhamdia bermejo is known from four localities in the upper Bermejo River basin (part of the wider Paraná River system): three sites on the San Francisco River and one on the Bermejo River itself, all in Jujuy and Salta Provinces, northwestern Argentina, at elevations of roughly 300–370 metres above sea level. No temperature, pH or other water-chemistry figures accompany the description.
The basin as a whole is described by the authors as facing some environmental pressure from agricultural runoff, deforestation and industrial pollution affecting freshwater habitats in the region, though the species itself is reported from relatively well-preserved stretches of river within that broader landscape.
Feeding
No dietary study has been published for Phenacorhamdia bermejo specifically. As general context for the genus, not a documented finding for this species: Phenacorhamdia catfishes are small, bottom-associated heptapterids generally presumed to feed on aquatic invertebrates, in keeping with the family's typical benthic, nocturnal foraging habits.
Mating
No courtship or spawning behaviour has been documented for Phenacorhamdia bermejo. As with many small, recently described South American stream catfishes, its reproductive biology in the wild has not been studied, and nothing specific can be stated here without guessing.
Breeding
Breeding is not documented for this species, and Phenacorhamdia bermejo is not known to be established in the aquarium hobby — unsurprising for a fish described in 2026 from wild-collected material across a handful of Argentine localities. There is no basis here for describing a spawning mode, egg type, or parental-care pattern.
In the aquarium
Phenacorhamdia bermejo is not a trade species; it was described in 2026 and no aquarium husbandry information exists for it. Any care regime would have to be inferred, cautiously, from the wider genus and family — small heptapterids of this size (up to roughly 2 in SL among specimens examined) are generally kept, where relatives appear in the hobby at all, in soft, warm-temperate to subtropical stream water with cover to hide beneath during the day — but none of that is documentation for this species, and its true adult size, temperament and specific requirements remain unconfirmed.
Conservation
Phenacorhamdia bermejo has not yet received a formal IUCN Red List assessment, as is typical for a species described in 2026. The describing authors, however, assessed it as best matching Least Concern (LC) under IUCN criteria, noting that while the upper Bermejo basin faces some environmental pressure from agricultural runoff, deforestation and industrial pollution, the species occurs in relatively well-preserved habitat and does not currently meet the criteria for a threatened category — a recommendation from the primary literature rather than a completed Red List listing.