Taxonomy & naming
Phenacogaster maculoblonga was described by Lucena and Malabarba in 2010 as a new species within the genus Phenacogaster, a group of small South American characids that had been subject to limited revision at the time of the original description. The valid name as listed in Eschmeyer's Catalog of Fishes is Phenacogaster maculoblonga Lucena & Malabarba, 2010; the authors are not parenthesised because the species was placed directly in Phenacogaster at the time of description and has not been moved.
Molecular species-delimitation work using COI mitochondrial DNA confirms P. maculoblonga as a genetically distinct species, with a mean intraspecific divergence of approximately 0.007 ± 0.006, well below typical interspecific thresholds. The genus Phenacogaster belongs to the family Characidae and occupies riverine systems across lowland South America; most members are small, laterally compressed fishes rarely exceeding about 2.5 in standard length.
Morphology
Phenacogaster maculoblonga is a small characid with a standard length range of approximately 1–2 in in known specimens. Like other members of the genus it is laterally compressed and slender, with the typical Characidae body plan: a single dorsal fin, adipose fin, forked caudal fin, and a relatively small, terminal mouth suited to invertebrate feeding.
The species is distinguished by its humeral spot, which is described as straight and elongated — oblong — and positioned vertically on the humeral region behind the operculum. This feature is the diagnostic character referenced in the specific name. Males bear small hooks on the rays of the pectoral, pelvic, and anal fins, a form of sexual dimorphism widespread in characids and used in specific and generic diagnoses within the family.
Habitat
The type locality and known range of Phenacogaster maculoblonga lies in the upper Cuyuni River basin and lower Orinoco tributaries of Venezuela. The species was collected in transparent, acidic water characterised by strong to very strong currents and substrates of large rocks — a fast, well-oxygenated riverine environment rather than the still blackwater habitats favoured by many other small Venezuelan characids.
Water parameters for the Cuyuni system in this region are consistent with nutrient-poor, soft, acidic Guiana Shield drainage: low conductivity, pH well below 7, and relatively cool water compared with lowland Amazonian rivers. The combination of clear water and powerful current over rocky substrates suggests a benthic or near-benthic micro-habitat for at least part of the time, though the species likely uses the water column in calmer sections as well.
Feeding
No specific dietary data have been published for Phenacogaster maculoblonga in the wild. By analogy with the broader genus and with congeners studied in similar habitats, the species is assumed to be an opportunistic microcarnivore, feeding on small aquatic invertebrates — insect larvae, microcrustaceans, and similar prey — taken from the current or gleaned from rock surfaces.
In aquaria, congeners such as Phenacogaster tegatus accept a range of small live and frozen invertebrates including Artemia nauplii, Moina, and small worms, and likely take good-quality micro-pellets as well. Given the fast-water origins of P. maculoblonga, a diet emphasising live and frozen items is likely to be closest to its natural intake.
Mating
No observations of spawning behaviour have been published specifically for Phenacogaster maculoblonga. Characids of this size and body form are typically egg-scatterers that broadcast adhesive or semi-adhesive eggs among fine-leaved vegetation or over the substrate, with no parental care by either sex. Males of the genus bear fin hooks, structures commonly associated with clasping during spawning in characids, which indicates that physical contact between the sexes occurs during gamete release.
The fast-current habitat of P. maculoblonga in the wild may mean that spawning occurs in calmer refugia — among aquatic plants or submerged debris in marginal areas — where eggs are retained long enough to be fertilised. This is speculative, however, and direct observation of wild or captive spawning has not been reported.
Breeding
Phenacogaster maculoblonga has not been reported bred in captivity. Based on the general biology of small, egg-scattering Characidae and the husbandry notes available for congeners, breeding would be expected to follow the pattern of open-water egg scattering over fine-leaved plants or spawning mops, with the adults removed after spawning to prevent egg predation. Eggs would be expected to be small and adhesive, hatching within a few days at tropical temperatures.
No data on clutch size, incubation duration, or fry requirements are available for this species specifically. Aquarists working with related Phenacogaster species typically condition adults on varied live and frozen foods before breeding attempts, and rear fry on infusoria and newly hatched Artemia nauplii — an approach that should apply here given the similarity in body size.
In the aquarium
Phenacogaster maculoblonga is essentially unknown in the aquarium hobby and is not commercially available through normal trade channels. Any specimens kept would almost certainly come from scientific collections or specialist importers dealing in Orinocan and Guiana Shield fishes. The fast, transparent, acidic waters it inhabits in the Cuyuni basin suggest it would appreciate good flow, well-oxygenated water, soft and acidic conditions, and a tank with open swimming space over a dark, smooth substrate.
Congeners such as Phenacogaster tegatus are described as peaceful, delicate fishes best kept in groups of eight or more, unsuitable for general community tanks, and thriving at 68–82 °F with a pH of 6.0–7.5. These parameters likely represent a reasonable starting point for P. maculoblonga, though its fast-current origins may mean it benefits from higher flow rates than typical community characids require. Data sparse — specific husbandry recommendations await firsthand captive experience with the species.
Conservation
Phenacogaster maculoblonga has not been assessed by the IUCN Red List and carries no formal conservation status. Its known range in the upper Cuyuni River and lower Orinoco tributaries of Venezuela falls within a region of the Guiana Shield that, while relatively intact compared with lowland Amazonian systems, is subject to increasing pressure from gold mining activity — both artisanal and industrial — which introduces sediment and mercury into otherwise pristine clear-water rivers and may significantly alter the transparent, fast-flowing habitat the species requires.
The restricted and apparently localised distribution suggested by the original description means that habitat degradation in even a portion of its range could affect the species substantially. Systematic surveys to establish the full extent of P. maculoblonga's range, combined with an IUCN assessment, would be valuable steps in understanding its conservation needs.