Taxonomy & naming
Chaetostoma platyrhynchus was described by Henry Weed Fowler in 1943 in the Proceedings of the Academy of Natural Sciences of Philadelphia (volume 95, pp. 252, figs. 36–39), from specimens collected at Florencia in the Río Orteguaza basin, Colombia. The Catalog of Fishes (Eschmeyer, CAS) treats Chaetostoma platyrhynchus as the valid combination.
The species has an unusually complex synonymy for a Chaetostoma: it has been placed at various times in the genera Cordylancistrus, Hemiancistrus, and Peckoltia, accumulating the combinations Chaetostoma platyrhyncha, Cordylancistrus platyrhyncha, Hemiancistrus platyrhynchus, Peckoltia platyrhyncha, and Peckoltia platyrhynchus. FishBase notes that the current valid assignment follows 'a new combination based on the examination of paratypes'. This turbulent nomenclatural history reflects the broader difficulty of resolving generic boundaries within the armoured catfishes (Loricariidae) prior to modern phylogenetic analysis.
The genus Chaetostoma belongs to the tribe Chaetostomini within subfamily Hypostominae. The generic name combines Greek chaite (bristle) and stoma (mouth). The species epithet platyrhynchus is from Greek platys (broad, flat) and rhynchos (snout), describing the distinctively wide, depressed rostrum. No common name is established for this species.
Morphology
Chaetostoma platyrhynchus is a small loricariid, reaching a maximum recorded size of 3.5 in standard length (SL) — approximately 3.5 in total length (TL) per FishBase. It shares the heavily armoured, dorsoventrally depressed body plan typical of the genus, adapted for life in fast-flowing rivers.
The species is distinguished from most other Chaetostoma by a notable morphological character: it bears bony plates along the snout edge, a feature absent in the majority of its congeners. The interopercular odontodes (cheek bristles) are also present. The abdomen lacks plates — it is naked or only partially plated ventrally, as in many Chaetostoma. Fleshy branched tentacles are absent on the snout, distinguishing it clearly from Ancistrus.
Coloration data are not well documented in the available sources. The genus as a whole tends toward dark brown to greyish ground colours with variable pale spotting or mottling.
Sexual dimorphism follows the general Chaetostoma pattern: males develop a larger, broader head, slimmer ventral profile, and disproportionately large pelvic fins compared with females. The enlarged pelvic fins in males are thought to assist in covering and guarding the egg clutch in fast current — preventing sperm washout during spawning and maintaining water circulation over the eggs.
Habitat
Chaetostoma platyrhynchus is known from the upper Caquetá River basin in southern Colombia — specifically the Río Orteguaza, which drains into the upper Caquetá (the Colombian name for the river known as Japurá in Brazil, a major western tributary of the Amazon). The type locality is Florencia, Caquetá department, Colombia.
The upper Caquetá system in this region descends from the Andes into Amazonian lowland forest, creating a gradient of highland torrent streams and fast-flowing foothill rivers. As a Chaetostoma, this species almost certainly inhabits the rocky, current-swept sections characteristic of the genus — clean, well-oxygenated water over boulders and cobbles, where periphyton mats develop on sun-exposed rock surfaces.
Water temperature in the upper Caquetá is typically 73–81 °F per PlanetCatfish records for this species. Beyond temperature, specific water chemistry data (pH, hardness) for this population are not documented in the available sources.
Feeding
Chaetostoma platyrhynchus is, like all Chaetostoma, a periphyton and algae grazer. Its broad, flat snout and ventrally placed sucker-mouth are adaptations for pressing against exposed rock surfaces in current and rasping the attached algal and biofilm community. In fast-flowing Andean-foothill rivers, periphyton is often the dominant food resource available on rock surfaces in well-lit reaches.
In the aquarium, the diet should be plant-based: high-quality algae wafers, spirulina pellets, blanched courgette (zucchini), cucumber, and other vegetables. The fish will also graze naturally on biofilm that develops on rocks and tank glass. Protein-rich foods should be offered only in small amounts, as the gut of a grazing catfish is adapted for high-fibre plant material rather than protein-rich invertebrate prey.
Mating
No aquarium breeding records for Chaetostoma platyrhynchus are on file at PlanetCatfish, and the species is rarely kept in captivity. By inference from closely related species in the genus, males likely establish and defend territories around suitable flat-stone spawning sites in fast-flowing water, displaying to rivals with their enlarged pelvic fins and broader heads. The disproportionately large pelvic fins seen in male Chaetostoma are hypothesised to function both in mate competition and in covering the egg clutch to assist oxygenation and prevent fertilisation loss in strong current.
Breeding
No breeding reports for Chaetostoma platyrhynchus in the aquarium are currently documented. Based on the spawning biology described for other Chaetostoma — including closely related Colombian species — the species likely deposits an adhesive clutch on the underside of a flat rock or object in fast-flowing, shallow water. The male is expected to guard the clutch by positioning himself over or beneath it, using his body and fins to maintain water movement across the eggs.
Successful captive breeding of Chaetostoma generally requires strong water movement, clean water, flat stone furnishings, and temperatures appropriate to the natural range. For C. platyrhynchus, a temperature of 73–81 °F would be the starting point. Until aquarium breeding is documented for this species, specific recommendations remain extrapolated from congeners.
In the aquarium
Chaetostoma platyrhynchus is a rarely imported species with no established aquarium trade presence, and fewer than five specimen records appear on PlanetCatfish. Its care requirements, extrapolated from its Chaetostoma membership and upper Caquetá origin, are those of a rheophilic algae grazer: strong water movement, clean and well-oxygenated water, a rocky substrate with grazing surfaces, and a primarily vegetarian diet.
Temperature should be maintained at 73–81 °F. A tank of 25 US gal or more with a powerful external filter and ideally a supplemental powerhead for current would be appropriate for an adult. Smooth river cobbles, flat stones, and slate provide the grazing and sheltering surfaces the fish uses in the wild. The species should not be mixed with other Chaetostoma or similar-sized plecos in tanks too small to support individual territories.
Given the paucity of aquarium records and the IUCN's Data Deficient assessment reflecting limited wild survey data, C. platyrhynchus should be considered a specialist fish for hobbyists experienced with rheophilic loricariids. Observations on its behaviour and breeding would be a valuable contribution to the wider knowledge of the species.
Conservation
Chaetostoma platyrhynchus was assessed by the IUCN Red List as Data Deficient (DD) on 8 October 2014. The Data Deficient designation reflects insufficient information on the species' population size, extent of distribution, and ecology to make a meaningful assessment of extinction risk — it is not an indication that the species is secure, only that knowledge is lacking.
The IUCN assessment notes that the species is known only from the upper Caquetá and Orteguaza basin in Colombia, and that further surveys are needed across this region to characterise its distribution and abundance. The upper Caquetá region faces pressures from deforestation, agricultural expansion, and colonisation that reduce water quality and increase sedimentation in Andean foothill rivers — conditions incompatible with the clean, rocky substrates on which Chaetostoma depend.
Until survey work clarifies the species' range and population status, its conservation standing cannot be formally determined.