Taxonomy & naming
Gymnocorymbus flaviolimai was described by Benine, Melo, Castro & Oliveira in 2015, in a revision of the genus Gymnocorymbus published in Zootaxa. The holotype (INPA 47805, 2 in SL) was collected from the Rio Guaporé at Costa Marques, Rondônia, Brazil (12°26'S). Eschmeyer's Catalog of Fishes treats Gymnocorymbus flaviolimai Benine, Melo, Castro & Oliveira, 2015 as the valid name.
The 2015 paper was the first to include a molecular phylogeny of the genus and established that only four species are valid: the three previously recognised (G. bondi, G. ternetzi, and G. thayeri) plus G. flaviolimai as the fourth. Phylogenetically, G. ternetzi and G. thayeri form a sister pair, with that clade in turn sister to G. bondi; the placement of G. flaviolimai within this topology was explored in the original description. The genus belongs to the subfamily Stethaprioninae within Characidae.
The genus name Gymnocorymbus is derived from the Greek gymnos (naked) and korymb (summit or cluster), a reference to the unscaled or exposed nature of certain body regions shared by genus members. The specific epithet flaviolimai honours Dr. Flávio César Thadeo de Lima, a Brazilian ichthyologist who has contributed substantially to the systematics of Neotropical freshwater fishes.
Morphology
Gymnocorymbus flaviolimai reaches a maximum recorded standard length of 2 in, making it among the smaller members of its genus. Like its congeners it is a laterally compressed, deep-bodied characin with the family's characteristic silvery flanks and a contrasting dark rear-body and caudal peduncle — the general 'black tetra' body plan associated with the genus.
The species is distinguished from its congeners by a combination of dental and fin characters. Its dentary and premaxillary teeth are roughly half the size of those in other Gymnocorymbus species; the premaxillary teeth bear five cusps rather than the three found in G. ternetzi. The anal fin is strongly elongated, with 40–45 soft rays (compared with the shorter anal fins of related species), and its distal margin is markedly convex. Vertebral count is 32–34. The fish is benthopelagic in habit, spending time in the mid and lower water column.
Habitat
Gymnocorymbus flaviolimai is known from the Rio Madeira drainage of the Amazon basin, with records from Bolivia, Brazil, and Peru. The type locality is the Rio Guaporé at Costa Marques, Rondônia, Brazil — the Guaporé being a major right-bank tributary of the Madeira that forms part of the Brazil–Bolivia border.
As a benthopelagic freshwater species, G. flaviolimai inhabits the middle and lower reaches of the water column in these lowland Amazonian river systems. Specific microhabitat preferences — substrate type, vegetation cover, current speed — have not been documented in the available literature. The Madeira basin is one of the most biodiverse river systems in South America, draining portions of Bolivia, Brazil, and Peru across a range of elevations from Andean foothills to Amazonian lowlands.
Feeding
No direct dietary data for Gymnocorymbus flaviolimai have been published. Based on the feeding ecology of Characidae more broadly, and on larval feeding studies of characins in general, the species is expected to be an opportunistic feeder. Small characins in Amazonian lowland rivers typically take a mixture of small invertebrates, zooplankton, insect larvae, and organic detritus according to availability and body size.
In captivity — should the species become available to hobbyists — it could reasonably be managed on the diet suited to small characins generally: good-quality flake and micropellet foods supplemented with small live or frozen foods such as Daphnia, Artemia nauplii, and chironomid larvae. Data specific to this species are lacking, and any husbandry notes here represent inference from congener and family-level data.
Mating
No specific mating or reproductive behaviour data have been published for Gymnocorymbus flaviolimai. Its congener G. ternetzi — the black skirt tetra — is an egg-scattering open spawner in which males pursue females, and pairs release eggs into the water column or among fine-leaved vegetation with no parental guarding. By analogy with G. ternetzi and general characid biology, G. flaviolimai is likely to reproduce in a similar manner: brief courtship pursuits by males, scattered egg release, adhesive or semi-adhesive eggs settling among substrate or vegetation, and no parental involvement after spawning.
No courtship structures, secondary sexual dimorphism, or seasonal spawning cues specific to this species have been described in the literature available at the time of writing.
Breeding
Gymnocorymbus flaviolimai has not been recorded in the ornamental fish trade or bred in captivity as of the 2015 description, and no breeding data appear in the literature. Inference from the genus suggests egg-scattering spawning over fine-leaved plants or open substrate, with small adhesive eggs, no parental care, and fry requiring very small initial foods.
Given the close relationship to G. ternetzi — one of the most commonly kept and bred small characins — the husbandry principles applicable to that species would be a reasonable starting point. However, direct breeding records for G. flaviolimai are absent, and any claims beyond this would be speculation.
In the aquarium
Gymnocorymbus flaviolimai is not currently known in the ornamental hobby; it has only been scientifically described since 2015 and the original description contains no husbandry information. Its small size (to 2 in SL), benthic-to-mid-water habit, and probable compatibility with other peaceful small characins suggest it could in principle be kept similarly to other small Gymnocorymbus species — a well-planted tank with subdued lighting and conspecific or similarly sized tankmates.
Any aquarist fortunate enough to obtain specimens — whether through research collection or eventual commercial availability — should refer to the ecology of the Rio Madeira basin for guidance: warm, soft-to-moderately-hard Amazonian water, temperatures in the tropical range typical for lowland South American rivers (approximately 75–82 °F), and stable water quality. Data are sparse, and field-based water chemistry parameters for the Guaporé at the type locality have not been formally published.
Conservation
Gymnocorymbus flaviolimai has not been assessed by the IUCN Red List and carries no formal conservation status. The species was only described in 2015, and newly described taxa from the Amazon basin often accumulate a lag of years or decades before formal assessment.
The Rio Madeira and its tributaries, including the Rio Guaporé, face pressures from hydroelectric development — notably the Jirau and Santo Antônio dams on the Madeira itself — as well as from agriculture-driven deforestation, sedimentation, and mercury pollution from artisanal gold mining in parts of the drainage. Whether G. flaviolimai is affected by these pressures, and over what range extent, cannot be determined from published data. Its occurrence across parts of Bolivia, Brazil, and Peru suggests a distribution broader than a single locality, which would be a positive factor in any future assessment. Formal taxonomic and distributional surveys remain a prerequisite for a meaningful conservation evaluation.