Taxonomy & naming
Phenacogaster tukano was formally described by Romero-Figueroa & Carvalho in 2024 in a revision published in Ichthyology & Herpetology that erected four new Phenacogaster species simultaneously. The type locality is the Vaupés River in the Guaviare department of Colombia, within the upper Amazon basin. Catalog of Fishes records the valid name as Phenacogaster tukano Romero-Figueroa & Carvalho, 2024.
The genus Phenacogaster was erected in the nineteenth century and now comprises roughly twenty species distributed across South American drainages from Colombia to the Río de la Plata basin. Molecular and morphological work has repeatedly revised its boundaries, and the 2024 paper reflects ongoing efforts to resolve species limits within the group. P. tukano is distinguished from its congeners principally by the posteriorly displaced humeral spot and its complete lateral line — characters that separate it from P. tegatus of the Paraguay basin and other related forms.
Morphology
Phenacogaster tukano is a small, slender characid of typical Phenacogaster build: a compressed, elongate body with a relatively small head and the subterminal mouth common to many small stream characids. The most diagnostic external features are the position of the humeral spot — displaced rearward compared with sister species — and the complete lateral line extending the full length of the flank.
Data on maximum size are sparse given the species' recent description; like other Phenacogaster it is a small fish, and detailed meristic and metric data are available in the original description. No common name has been established in the hobby.
Habitat
The species is known from the lower Vaupés River of Colombia, a major blackwater tributary of the Rio Negro in the upper Amazon basin. The Vaupés in this reach carries dark brown to black water with relatively high transparency, a defining feature of blackwater Amazonian rivers. Water temperatures in the documented stretch range from approximately 82–86 °F.
Phenacogaster tukano occupies rheophilic habitat — fast-flowing rapids — rather than the slow backwaters typical of many small characids. This preference for current-exposed rocky runs over blackwater is notable within the genus and helps define its microhabitat niche within the Vaupés system. The species appears endemic to Colombia.
Feeding
No dedicated feeding study has been published for Phenacogaster tukano. Genus-level and broader Phenacogaster data suggest an insectivorous to omnivorous diet typical of small stream characids: small invertebrates, aquatic insect larvae, and microcrustaceans taken near the substrate and in the water column.
In an aquarium setting, small Phenacogaster species readily accept live and frozen invertebrate foods such as Daphnia, Cyclops, and baby brine shrimp, as well as fine-particle prepared foods. A varied diet is advisable given the limited published data on this species' specific nutritional requirements.
Mating
No direct observations of mating behaviour in Phenacogaster tukano have been published. Based on the biology of the genus and Characidae broadly, the species is presumed to be an egg-scattering open spawner. Males likely court females with short chasing displays common to small characids, without establishment of permanent territories.
Spawning is expected to occur among fine-leaved aquatic vegetation or over coarse substrate in current, consistent with the species' rheophilic habitat. Eggs are presumed adhesive or semi-adhesive. No parental care is expected.
Breeding
Captive breeding of Phenacogaster tukano has not been documented in the published literature. Given its recent formal description in 2024, the species is not yet established in the aquarium hobby and breeding reports are absent.
If kept in captivity, the approach used for other small Characidae from blackwater Amazonian systems would serve as a reasonable starting point: soft, acidic water mimicking the dark, warm conditions of the lower Vaupés, with fine-leaved plants or spawning mops, separation of adults after spawning to prevent egg predation, and very small first foods for fry. These are extrapolations from congeners and family-level knowledge, not observations specific to this species.
In the aquarium
Phenacogaster tukano is not established in the aquarium hobby as of 2024 and is unlikely to be encountered in the trade in the near term. The species' rheophilic lifestyle in fast, warm blackwater suggests that, if maintained in captivity, it would require good water movement, soft to very soft acidic water, warm temperatures around 82–86 °F, and the low-light conditions associated with blackwater environments.
Small schooling characids from similar Amazonian habitats typically do best in groups of six or more, with calm tankmates and a well-established, mature aquarium. Any future hobby keeping of this species should prioritise captive-bred stock and avoid collection pressure on what appears to be a geographically restricted wild population.
Conservation
Phenacogaster tukano has not been assessed by the IUCN Red List; as a species described in 2024, it is too recently named to have undergone formal evaluation. Its conservation status is therefore Not Evaluated (NE).
The species' apparent endemism to the Vaupés River drainage of Colombia, combined with its restricted rheophilic microhabitat in the lower Vaupés, makes it a candidate for conservation attention once its full range is better established. The Vaupés region is home to the Tukano indigenous people, whose stewardship of the watershed — the reason the species was named in their honour — provides some degree of de facto habitat protection. Formal range surveys and population assessments would be necessary before a Red List category could be assigned.