Taxonomy & naming
Chaetostoma alternifasciatum was described by Henry Weed Fowler in 1945 in the Proceedings of the Academy of Natural Sciences of Philadelphia (volume 97). The Catalog of Fishes (Eschmeyer, CAS) recognises the valid combination Chaetostoma alternifasciatum Fowler, 1945. No synonyms are recorded. The type locality is Morelia, in the Río Caquetá drainage, Colombia.
The genus Chaetostoma sits within the tribe Ancistrini of subfamily Hypostominae. Members of Chaetostoma — often called rubber-nose plecos or rubber plecos in the aquarium trade — are characterised by a distinctive suite of features: moveable interopercular odontodes (spines behind the gill cover), an unplated abdomen, and the absence of the fleshy snout tentacles that define Ancistrus. The name Chaetostoma derives from the Greek chaite (long flowing hair, used here to indicate bristle-like odontodes) and stoma (mouth), referring to the prominent odontodes fringing the head.
The specific epithet alternifasciatum is Latin for "alternating bands" (alternī, alternating + fasciātum, banded), describing the contrasting light-and-dark pattern seen in the type series.
Morphology
Maximum recorded size is 6 in SL, consistent across both FishBase and PlanetCatfish records. Body form is compact and strongly dorsoventrally flattened, with an exceptionally broad, spatulate head — the rubber-nose profile that gives the genus its common name. The undersurface of the head is fleshy and unplated, forming a large oral disc well suited to pressing tight against smooth boulders in fast current. Flanks are covered with bony scute armour; the abdomen lacks plates, which is diagnostic for Chaetostoma.
Coloration follows the epithet: a pattern of alternating lighter and darker transverse bands or fasciae across the body. Field-fresh specimens are more vivid; preserved material, from which Fowler worked, shows the underlying banding pattern in reduced contrast.
Moveable interopercular odontodes — enlarged, hypertrophied spines behind the gill cover — are present and can be deployed when the fish is handled or threatened. These odontodes, together with the prominent pectoral fin spines, give Chaetostoma defensive capability and present a handling hazard.
Sexual dimorphism in Chaetostoma generally runs to males having broader heads, slimmer ventral profiles, and disproportionately large pelvic fins — structures that may help shield the sperm mass during fertilisation in the turbulent fast-water spawning sites typical of the genus. Species-specific dimorphism data for C. alternifasciatum are not documented.
Habitat
The Río Caquetá (known in Brazil as the Río Japurá) drains the eastern slopes of the Colombian Andes and its foothills before crossing the lowland Amazon. The type locality at Morelia places C. alternifasciatum in the upper-to-middle Caquetá drainage, in streams likely characterised by moderate to fast current, rocky or cobble substrates, and clear to moderately turbid water.
All Chaetostoma are rheophilic — current-loving — loricariids. They are adapted to oxygen-rich, fast-moving water running over hard substrates where biofilm and algal growth colonise smooth boulders and bedrock surfaces. In general terms, Andean-foothill streams in the Caquetá basin can be expected to show moderate temperatures (roughly 68–79 °F at relevant altitudes), slightly acidic to near-neutral pH, and soft-to-moderate hardness reflecting the geological mix of the drainage. Specific physicochemical data from the type locality are not available in the sources reviewed.
Feeding
Chaetostoma species are algae grazers and biofilm scrapers. The broad ventral oral disc and the numerous fine rasping teeth allow them to graze efficiently on the encrusting algae, diatoms, and bacterial biofilm that grow on exposed boulder surfaces in their fast-water habitat. Unlike the wood-eating Panaqolus or the detritivore Hypostomus, Chaetostoma feed primarily on periphyton — the living film of photosynthetic organisms and associated microbes that coats hard substrates in clean, illuminated streams.
In the aquarium, this diet translates to sinking algae wafers, spirulina pellets, blanched vegetables (courgette, cucumber, spinach), and the natural algae growth encouraged by a well-lit tank. Access to smooth flat stones or slate on which algae can establish provides a more natural and behaviorally enriching grazing surface. Because clean fast water is the source of their food in nature, water quality must be high.
Mating
No breeding observations specific to C. alternifasciatum are recorded. General Chaetostoma reproductive biology, drawn from related species, indicates that males become territorial around potential spawning sites — typically shallow crevices beneath flat stones or overhanging cobbles in areas of strong current. Male pelvic fins may serve a functional role in guiding or shielding the sperm mass during fertilisation in turbulent water, as has been suggested for the genus as a whole based on the disproportionate size of this fin relative to the female's.
Conditioning in the aquarium would logically follow the same cues relevant to other Andean stream loricariids: clean, well-oxygenated, slightly cool water with moderate current, and provision of flat stones or slate as potential spawning substrate.
Breeding
No captive breeding reports for Chaetostoma alternifasciatum are documented on PlanetCatfish or in the primary literature reviewed. The species has no registered keepers and no spotter records, consistent with its near-complete absence from the ornamental trade. What can be inferred from genus-wide observations is that Chaetostoma breeds in shallow fast-water shelters: eggs are adhesive and attached to the underside of flat stones or crevice roofs, and the male guards the clutch while fanning it with his fins to maintain oxygen supply — a pattern shared broadly across rheophilic loricariids.
Given the complete absence of captive records, specific clutch sizes, incubation periods, or fry development data cannot be reported here.
In the aquarium
Chaetostoma alternifasciatum is effectively absent from the aquarium hobby. No keepers are registered, no images are available, and the species has likely never been deliberately imported. Its range in the upper Río Caquetá of Colombia makes it logistically difficult to collect and export.
Hypothetically, husbandry would follow the requirements known for the genus as a whole: fast, well-oxygenated water with high dissolved oxygen, a strong filtration and flow setup, rocky substrate with cobbles and flat stones, water temperature in the range of approximately 68–79 °F, and a diet centred on algae and biofilm. Chaetostoma are notably sensitive to low oxygen and stagnant conditions; flow rate and surface agitation are non-negotiable.
If specimens ever became available, a dedicated species tank or a biotope setup with similarly current-adapted fish (small Andean characins, other small rheophilic loricariids) would be the appropriate approach. The moderate adult size of 6 in SL is compatible with a tank of 40–55 US gal with strong flow.
Conservation
The IUCN Red List assessed Chaetostoma alternifasciatum as Data Deficient (DD) in October 2014. The DD designation reflects insufficient distributional and population data to make a determination of threat level — not necessarily that the species is stable. The Caquetá basin in Colombia has experienced significant deforestation, agricultural expansion, and historical pressure from illicit crop cultivation, all of which degrade stream water quality through increased sedimentation and runoff. These pressures are real but their specific impact on C. alternifasciatum populations has not been studied.
The restricted range in the upper Caquetá drainage, combined with ongoing habitat change in the Colombian Amazon foothill zone, means the Data Deficient status may mask genuine conservation risk. Targeted field surveys would be needed to establish the species' current distribution, population size, and habitat condition before a more informed threat assessment could be made.