Taxonomy & naming
Platyurosternarchus macrostoma was described by Albert Günther in 1870, in the Catalogue of Fishes in the British Museum, from a holotype collected at Xeberos (Jeberos) in the Río Marañón drainage of the Amazon system in Peru. It belongs to the family Apteronotidae, the ghost knifefishes, within the order Gymnotiformes — the New-World electric knifefishes, a group of bony fish defined by their electric organs and by a single long anal fin used for propulsion in place of a normal tail and dorsal fin. The Catalog of Fishes (Eschmeyer, CAS) is the standing authority for the valid name; some sources render the specific epithet as "macrostomus," reflecting Latin gender agreement with the genus.
Apteronotidae are set apart from other gymnotiform families by an electric organ built partly or wholly from modified nerve tissue rather than muscle, which allows the fastest, most stable discharge frequencies in the order — the trait that gives the family its "ghost" reputation for near-invisibility to casual observation and a highly refined electric sense. Despite the shared English name "knifefish," Platyurosternarchus and its New-World relatives are not related to the Asian featherback and clown knifefishes (Chitala, Notopterus); the resemblance is convergent body shape, not common ancestry.
Morphology
As in other Apteronotidae, Platyurosternarchus macrostoma has a laterally compressed, blade-like body that tapers toward the tail, no dorsal fin, and no distinct caudal fin; movement is generated almost entirely by undulations of a long anal fin running along the underside of the body, letting the fish move forward or backward with equal control. The species is scaleless, a trait shared across the family that carries directly into how sensitive the fish is to water chemistry and medication. FishBase records a maximum length of about 15.5 in total length for males and unsexed individuals.
The defining internal feature is the electric organ, which in this species — as described from electric organ discharge (EOD) recordings — produces a biphasic, wave-type signal in the roughly 750–1,031 Hz range, among the higher frequencies documented in the family. Sensory pores distributed over the head and body read the distortions of the fish's own electric field, giving it a functional substitute for vision in dark or turbid water. Data on external sexual differences are sparse; no reliable dimorphic markers are documented for this species.
Habitat
Platyurosternarchus macrostoma is a Neotropical freshwater fish, recorded across the Amazon, Orinoco and Essequibo river basins, with country records spanning Brazil, Bolivia, Colombia, Ecuador, Guyana, Peru and Venezuela. FishBase describes it as benthopelagic in tropical waters of roughly 72–82 °F, and behavioral/EOD research places it specifically near shore among submerged tree trunks and branches, over sand or clay substrate covered in leaf litter — structurally complex cover close to the riverbank rather than open channel or still swamp.
That combination of warm water, cover, and low visibility is consistent with the rest of the ghost knifefishes: an electrically-sensed environment where eyesight plays a secondary role. Nothing in the available sources documents seasonal movement or breeding migration for this species; its ecology beyond basic habitat association with submerged wood is essentially undescribed.
Feeding
No species-specific dietary study is available for Platyurosternarchus macrostoma in the cited sources. By family pattern, Apteronotidae are nocturnal carnivores that hunt small invertebrates — aquatic insect larvae, worms and small crustaceans — located largely by electrolocation rather than sight, working over submerged wood, leaf litter and sediment after dark.
Given its habitat association with tree trunks, branches and leaf litter over sand and clay, it is reasonable to infer a similar benthic-invertebrate diet foraged among that cover, but this is an inference from family biology and habitat, not a documented feeding record for the species — data sparse.
Mating
As in other Apteronotidae, the wave-type electric organ discharge in Platyurosternarchus macrostoma is understood to serve a dual role beyond electrolocation: it also functions as a communication signal, with discharge characteristics carrying information about the identity and possibly sex of the signaling fish. In the best-studied relative, the brown ghost knifefish (Apteronotus leptorhynchus), courting males and females are known to shift their discharge frequencies toward one another in an electrical exchange, and rival fish signal aggression through characteristic interruptions of their discharges.
Whether Platyurosternarchus macrostoma performs comparable frequency signaling during courtship has not been documented in the available sources; the EOD literature located for this species describes the discharge itself (750–1,031 Hz, biphasic) rather than its use in social or reproductive behavior. This is inferred by family pattern, not confirmed for the species — data sparse.
Breeding
No breeding record — captive or wild — is available for Platyurosternarchus macrostoma in the cited sources. Apteronotidae as a family are egg-layers that are only rarely bred in aquaria, with most trade specimens either wild-caught or, for the handful of commercially significant species, farmed under hormone induction rather than spontaneous captive spawning; eggs are scattered among cover such as roots or submerged wood, and no substantial parental care is documented across the family.
Given that this species has essentially no aquarium history, there is no basis to describe a breeding protocol for it specifically. The honest statement is that its reproductive biology in both the wild and captivity is undocumented — poorly known rather than reported.
In the aquarium
Platyurosternarchus macrostoma is not an established aquarium fish; it does not appear to have a foothold in the ornamental trade, and no hobbyist care literature was located for it. Anyone keeping it would need to work from the family pattern shared with the black ghost and other Apteronotidae: because it is scaleless, it should be treated with great caution around copper-based and other harsh medications (reduced doses, if any), and it is expected to be sensitive to ammonia and nitrate, requiring mature filtration and clean, warm, soft to moderately mineralised water in the 72–82 °F range documented by FishBase.
Its habitat association with submerged wood and leaf litter over sand or clay suggests it would need generous cover and subdued lighting to feel secure, consistent with the nocturnal, electrolocating habits of its relatives. At a maximum recorded length of roughly 15.5 in TL, it would need a large, long aquarium if ever kept. Given the total absence of husbandry data, any current keeping of this species should be considered experimental, and it is not a fish to recommend without further documented experience.
Conservation
Platyurosternarchus macrostoma is assessed as Least Concern on the IUCN Red List, per the Catalog of Fishes (2022 listing under the name P. macrostomus), reflecting its broad distribution across the Amazon, Orinoco and Essequibo basins spanning seven countries. FishBase's own summary listing shows the species as Not Evaluated, which likely reflects the lag between a formal IUCN assessment and third-party database updates rather than a conflicting assessment.
As a wide-ranging, multi-basin Neotropical species rather than a narrow single-river endemic, it is not currently flagged as facing significant conservation pressure. It nonetheless shares the broader vulnerabilities of Amazonian and Orinoco fish generally — habitat alteration from deforestation, damming and pollution — even though no species-specific threat data is documented in the cited sources.