Taxonomy & naming
Phenacogaster pectinata was described by Edward Drinker Cope in 1870, with the original description placing it among the many small characids collected from South American river systems. The valid name, as recognised in Eschmeyer's Catalog of Fishes, is Phenacogaster pectinata (Cope, 1870), with the parenthetical authority indicating it was described in a different genus from the one it now occupies.
The genus Phenacogaster Eigenmann, 1907 belongs to the family Characidae and encompasses a cluster of small, laterally compressed characins distributed across the major lowland drainages of South America. The group has been subject to periodic revision as molecular and morphological studies have refined the limits of the many informal species-groups within the large and heterogeneous Characidae. Phenacogaster is characterised by a combination of dentition, squamation, and fin-ray counts that distinguish it from superficially similar small characin genera, but species-level identification within the genus can require close examination of preserved material.
No subspecies or widely used geographic variants are recognised for P. pectinata. The specific epithet pectinata (Latin: comb-like, or pectinate) likely refers to a dentition or squamation feature observed in the type material, though the exact morphological referent is not noted in widely available secondary literature.
Morphology
Phenacogaster pectinata is a small, slender, moderately compressed characid. Like other members of the genus it has the typical tetra body plan: a streamlined fusiform profile, a forked tail, an adipose fin, and a relatively large eye that occupies a substantial proportion of the head length. Total length in adults is in the range of approximately 1–2 in, consistent with others in the genus, though precise maximum-length data for this species specifically are sparse in the published literature.
Colouration in life is likely the translucent-to-silvery pattern common to small stream characins of the region: a pale to yellowish body with some iridescence along the flank, a variably developed dark lateral stripe or caudal spot, and unpigmented to lightly yellowish fins. Preserved specimens show the dark lateral pigment band more clearly. Sexual dimorphism is not strongly developed, though females in breeding condition typically show a rounder abdomen than males of similar size.
The dentition follows the general Phenacogaster pattern: multicuspidate teeth on both jaws, the exact cusp formula being a diagnostic character used to distinguish species within the genus. The adipose fin is present and well developed, as in all members of the family Characidae.
Habitat
Phenacogaster pectinata is recorded from lowland river systems in central and eastern South America. Records place it in tributaries associated with the Amazon and Río de la Plata drainages, in habitats typical for small stream characids: clear to slightly tea-coloured or turbid lowland streams and river margins, often in areas with aquatic vegetation, submerged roots, and leaf litter, where small schooling fish find both cover and invertebrate prey.
Lowland stream habitats in these drainages typically offer warm water throughout the year, with temperatures in the range of roughly 72–82 °F, soft to moderately hard water, and pH conditions that vary from slightly acidic in blackwater streams to near-neutral in clearwater and whitewater systems. Specific water-chemistry data for collection sites for P. pectinata are not widely documented in the secondary literature, and the range of conditions tolerated by the species in nature is difficult to specify precisely from available sources.
Like most small characins, P. pectinata is likely found in loose aggregations in the mid-water and near-surface zones of its habitat, exploiting the invertebrate and microcrustacean prey that drift in the water column and accumulate at stream margins.
Feeding
Phenacogaster pectinata is an opportunistic micropredator, consistent with the dietary habits documented for the genus and for small characids of similar body form throughout South America. The diet in the wild centres on small invertebrates taken from the water column and the surface film — aquatic insect larvae, microcrustaceans such as copepods and cladocerans, small terrestrial insects that fall to the water surface, and occasionally filamentous algae or organic detritus.
In an aquarium context, the species should accept a wide range of small prepared and live foods. Good-quality micro-pellets and fine flake are a practical staple, supplemented with small live or frozen foods — newly hatched brine shrimp, micro-worms, Daphnia, and Cyclops — to maintain condition and encourage breeding readiness. Like other small characins, it feeds throughout the day and does best with frequent small meals rather than infrequent large ones. Competition with significantly larger tankmates at feeding time should be avoided.
Mating
Phenacogaster pectinata is, like all characids for which reproductive biology is known, an egg-scattering open spawner with no parental care. Courtship in small characins typically involves males pursuing females through vegetation or open water, with brief side-by-side positioning at the moment of egg release. There is no territory defence, nest building, or pair bonding; spawning may occur in loose groups rather than as a strict pair event.
Eggs are small and adhesive or semi-adhesive, scattered among fine-leaved plants, root masses, or leaf litter, where they settle out of reach of the adults. Males in breeding condition often show slightly more intense colouration and slimmer body profiles than gravid females. Specific behavioural accounts for P. pectinata in the literature are absent from widely available secondary sources, and the above reflects the general pattern for the genus and the broader characid group.
Breeding
No detailed captive-breeding account for Phenacogaster pectinata specifically is available in the hobby or scientific literature accessible for this article. Based on the well-documented breeding biology of related small Characidae, breeding in captivity would follow the egg-scattering pattern standard for the family: conditioned adults placed over fine-leaved plants or synthetic spawning mops in a separate breeding tank, with a slight temperature increase and frequent live or frozen food feeding used to trigger spawning.
Adhesive eggs would be deposited among the spawning medium and should be separated from the adults promptly, as no parental care is offered and eggs and fry will be consumed. At warm temperatures (around 79–82 °F) incubation for similarly sized characids typically takes 24–48 hours, with fry becoming free-swimming after a further 3–5 days once the yolk sac is absorbed. First foods for the tiny fry would be infusoria, rotifers, or commercial micro-fry preparations, graduating to newly hatched brine shrimp as the fry grow. Data sparse — hobbyists are encouraged to document breeding observations for this species.
In the aquarium
Phenacogaster pectinata is rarely encountered in the mainstream aquarium trade and does not appear to have been commercially bred or imported in appreciable numbers. It is known primarily from ichthyological collections and occasionally from specialist importers dealing in wild-caught South American characids. For aquarists who obtain it, husbandry would follow standard practice for small, peaceful schooling characins from the central South American lowlands.
A group of at least six individuals is recommended to provide the social structure the species requires and to allow natural schooling behaviour. A planted aquarium with subdued lighting, some surface cover, and gentle filtration suits the species well. Water conditions in the soft-to-neutral range (pH approximately 6.5–7.5, low to moderate hardness, temperature 73–81 °F) are a reasonable starting point based on the drainage systems from which it is collected, though the species may prove adaptable to a wider range in practice. It is peaceful with other small, non-aggressive fish of similar size. Its rarity in the hobby means that detailed long-term husbandry data are limited.
Conservation
Phenacogaster pectinata has not been formally assessed by the IUCN Red List, and no targeted conservation evaluation of the species appears in the widely available literature. As a small, inconspicuous characid with a distribution spanning portions of major South American drainage systems, it does not appear to face imminent extinction risk at the range-wide level, though localised populations may be affected by the habitat degradation, agricultural runoff, and hydrological modification that threaten freshwater biodiversity across much of lowland South America.
The species' status in the aquarium trade is negligible — it is not a commercially significant import and is not subject to the collection pressure that affects some popular ornamental species. Its scientific interest lies primarily in the systematics and biogeography of Characidae, where it contributes to understanding of the diversification of small characins across the continent's major river systems. Aquarists keeping the species are encouraged to note collection data and to document husbandry and breeding observations, as the baseline natural-history data for most Phenacogaster species remain sparse.