Taxonomy & naming
Phenacogaster guayupe was formally described by Romero-Figueroa and Carvalho in 2024, as part of a revision published in Ichthyology & Herpetology (volume 112, issue 4) that recognised four new Phenacogaster species from Colombia. The type locality is the Abrote Stream, a tributary of the Ariari River in the department of Meta, Colombia — part of the upper Guaviare River drainage within the broader Orinoco River basin. Eschmeyer's Catalog of Fishes (Romero-Figueroa & Carvalho 2024) confirms the valid name.
The genus Phenacogaster belongs to the family Characidae and comprises small, slender tetras distributed across northern and central South America. The Colombian members of the genus were poorly known before this revision, and the description of P. guayupe illustrates how systematically productive detailed morphological work in the Orinoco tributaries continues to be. The species is diagnosed by a combination of an incomplete lateral line, 2–3 tricuspid premaxillary teeth, and a pre-ventral length of 36.4–43.3% of standard length, along with the distinctive large round humeral spot prominent in females.
The specific epithet guayupe honours the Guayupe people, an indigenous group that historically inhabited the Ariari River region in what is now the Colombian department of Meta. The name is a toponym tied to human geography rather than to the fish's morphology, a reminder that the river systems of the Orinoco piedmont carry deep cultural as well as biological significance.
Morphology
Phenacogaster guayupe is a very small characid, with a maximum recorded standard length of 1.5 in. Like other members of the genus it has a slender, laterally compressed body typical of many small Orinocan tetras. The incomplete lateral line is a key diagnostic feature — not all scale rows carry perforated pores, a condition shared with several congeners but expressed in a pattern specific to this species.
The humeral spot — a large, round, dark blotch just behind the operculum — is particularly conspicuous in females, and its size and shape are among the characters used to distinguish P. guayupe from the other new Colombian Phenacogaster described in the same revision. The premaxillary dentition is modest, with 2–3 tricuspid (three-cusped) teeth, a detail that places this species among the less heavily armed characids. Pre-ventral length, the distance from the snout tip to the origin of the pelvic fins, falls between 36.4 and 43.3% of standard length, indicating a body plan with the pelvic fins positioned relatively far forward compared with some relatives.
As a newly described species, detailed colour notes in life are limited in the published literature. The overall coloration is likely the translucent silvery-grey common to many small Phenacogaster, with the humeral spot providing the most visible field mark.
Habitat
Phenacogaster guayupe is known from the upper Guaviare River drainage, with the type locality in the Abrote Stream, a tributary of the Ariari River in Meta department, Colombia. The Guaviare is the longest Colombian tributary of the Orinoco, stretching approximately 1,405 mi, and drains a mosaic of Andean rainforest, humid paramo grassland, and flooded savanna as it descends toward the Llanos and the main Orinoco channel.
The upper Guaviare and its Andean-foothill tributaries, including the Ariari, occupy a transitional zone between the cooler, faster streams of the Andean slopes and the warm, low-gradient rivers of the Llanos. Water chemistry in Orinocan piedmont streams varies considerably: clearwater tributaries can have near-neutral pH and moderate conductivity, while blackwater reaches from forested catchments may be distinctly acidic (pH 4–6) with very low conductivity. Published data from comparable Orinocan clearwater systems suggest temperatures in the range of 79–86 °F, with pH around 7 and conductivity near 50 µS/cm, though conditions at the type locality have not been independently characterised in the open literature.
FishBase categorises P. guayupe as a benthopelagic freshwater species, consistent with the small-tetra habit of occupying mid-water to near-bottom zones in slow or moderate current amid vegetation and leaf litter.
Feeding
No specific dietary study exists for Phenacogaster guayupe. As a small characid, it is expected to be an opportunistic omnivore in line with what is known for the genus and family more broadly. Small Phenacogaster species in similar Orinocan habitats feed on minute aquatic and terrestrial invertebrates — microcrustaceans, insect larvae, small insects at the surface — as well as organic detritus and algal matter.
In the aquarium, Phenacogaster species generally accept a wide range of appropriately sized foods: high-quality micro-pellets, crushed flake, and frozen or live offerings such as baby brine shrimp, micro-worms, Daphnia, and Cyclops. Given the species' small adult size of under 1.5 in, food particle size must be kept small throughout its life. A varied diet with a live or frozen component supports both condition and natural foraging behaviour.
Mating
No breeding observations specific to Phenacogaster guayupe have been published. Based on general Characidae biology, the species is presumed to be an open-water egg scatterer with no parental care, the reproductive strategy shared by the vast majority of small tetras. Males likely pursue and display to females, with spawning occurring in short bursts among fine-leaved vegetation or over submerged surfaces.
In related small tetras, spawning is often triggered by environmental cues associated with the onset of the rainy season: a slight drop in temperature, an increase in water flow, and a shift toward softer, slightly more acidic water. Males may show subtle intensification of colour or fin extension during courtship, though no specific courtship descriptions are available for this species.
Breeding
Phenacogaster guayupe has not been bred in captivity under documented conditions, and no published breeding protocol exists for the species. By analogy with other small Characidae, breeding would be expected to follow the standard tetra pattern: egg scattering over fine-leaved plants or spawning mops, with small, adhesive eggs hatching within 24–48 hours at typical tropical temperatures. The larvae are initially fragile and require infusoria-scale first foods before graduating to larger items such as newly hatched brine shrimp.
Because adults — like most tetras — will readily consume their own eggs, breeders working with related species remove parents immediately after spawning or use mesh inserts to protect eggs in the bottom of the breeding vessel. Conditioning adults on live and frozen foods before any breeding attempt improves spawn quality and fecundity.
In the aquarium
Phenacogaster guayupe is not currently established in the aquarium hobby and is unlikely to be available through the retail trade, given that it was described only in 2024 and originates from a region not routinely targeted by ornamental collectors. As with many newly described small tetras from the Colombian Orinoco, hobby interest may grow as the species becomes better known among specialist collectors and importers.
Should the species become available, its care requirements would follow those of other small Orinocan tetras. A well-planted aquarium of modest size, soft to moderately hard water with a near-neutral to slightly acidic pH, and a temperature in the range of 79–84 °F would suit it. Because it reaches only about 1.5 in, it is best kept with similarly small, peaceful tankmates. A group of six or more individuals would encourage natural schooling behaviour. Feeding presents no unusual challenges: standard small-tetra fare of micro-pellets, crushed flake, and small live or frozen invertebrates is appropriate.
Conservation
Phenacogaster guayupe has not been assessed by the IUCN Red List. The species was described in 2024 and is too recently recognised to have undergone formal conservation evaluation. Its known range is restricted to the upper Guaviare River drainage in Colombia, with the type locality in a single stream tributary of the Ariari River in Meta department.
The Colombian Orinoco piedmont faces increasing pressure from agricultural expansion, particularly cattle ranching and oil-palm cultivation in the Llanos, as well as from hydrocarbon extraction in the Ariari valley and adjacent areas. Small, range-restricted endemics in these habitats are inherently vulnerable to catchment-level disturbance. No targeted conservation measures are in place for this species, and its population status and extent of occurrence remain undocumented. Future IUCN assessment and survey work in the Ariari drainage would help clarify whether the species warrants conservation concern.