Taxonomy & naming
Sternopygus astrabes was described by Francisco Mago-Leccia in 1994 and placed in the genus Sternopygus, within the family Sternopygidae — the glass and rattail knifefishes — in the order Gymnotiformes, the New-World electric knifefishes. Gymnotiformes are bony fish, but unusual ones: nearly every species produces a weak electric organ discharge (EOD) around its body, used both to electrolocate prey and obstacles in the dark and to communicate with other knifefish, and the order is defined as much by that electric sense as by its skeleton. The Catalog of Fishes (Eschmeyer, CAS) confirms Sternopygus astrabes as a currently valid species name.
Sternopygus is the rattail genus, so called for the long, thread-like taper of the body behind the anal fin, and it includes some of the largest species in the order. Within the family, Sternopygus is set apart from its relative Eigenmannia (the true glass knifefishes) by size, more robust build, and a lower-frequency wave discharge. The New-World gymnotiforms are not related to the superficially similar Asian featherback and clown knifefishes (Chitala, Notopterus) of the order Osteoglossiformes — the resemblance is convergent body shape, not shared ancestry.
Morphology
Like other Sternopygus, S. astrabes has the classic rattail knifefish outline: a compressed, elongate body that narrows steadily behind the vent into a slender, whip-like tail, with no dorsal fin and no distinct caudal fin. FishBase records specimens up to about 9 in total length in males and unsexed fish, with females reaching a notably larger maximum of around 14 in — an unusually strong size difference between the sexes for a gymnotiform. The species carries two to four dark vertical saddle-like bands across the body and a long anal fin — reported at 170 to 302 soft rays — that runs almost the entire underside of the animal and is the sole means of propulsion, rippled in travelling waves to drive the fish forwards or backwards.
The body is scaleless, as in all gymnotiforms, and runs the length of an internal electric organ whose discharge is picked up by electroreceptor pores scattered over the skin. Sternopygus produces a wave-type electric organ discharge in the 40–150 Hz range, generated by a myogenic (muscle-derived) electric organ; discharge frequency is sexually dimorphic and modulated by androgens, so males and females of the genus can typically be told apart by the pitch of their electric signal even when their bodies look similar.
Habitat
Sternopygus astrabes is known from the upper Orinoco basin of Venezuela, including the Casiquiare canal and Río Negro drainages that link the Orinoco to the Amazon. Its type locality is a terra firme stream, Caño Pozo Azul at Agua Linda, roughly 14 mi northeast of Puerto Ayacucho in Amazonas state — the kind of clear-to-stained forest stream typical of this part of the upper Orinoco.
As a benthopelagic freshwater species, it occupies the water column just above the bottom of these streams and channels, in the warm, generally soft, often tannin-tinted water typical of Neotropical blackwater and clearwater habitats. That dim, low-visibility environment is exactly where a continuous electric field earns its keep: with eyesight of limited use in stained or turbid water, S. astrabes reads its surroundings — cover, obstacles, prey, and other fish — through the field generated by its own electric organ.
Feeding
Specific dietary data for Sternopygus astrabes has not been documented in the sources available. Based on the well-studied feeding ecology of its genus and family, it is almost certainly a nocturnal micro-predator, foraging after dark over the streambed and among submerged roots and leaf litter for small invertebrates — aquatic insect larvae, worms and small crustaceans — located largely by electrolocation rather than sight.
Like other Sternopygus, it is likely an active, probing forager rather than an ambush predator, working the electric field generated by its own body to detect the faint signatures of prey hidden in sediment or cover. Data on this species specifically remains sparse, and any feeding account should be read as inferred from its relatives rather than confirmed for S. astrabes itself.
Mating
No species-specific courtship data for Sternopygus astrabes has been documented. In the wider genus, the wave-type electric organ discharge is central to social and reproductive behaviour: because discharge frequency is sexually dimorphic and androgen-modulated, a fish's electric signal effectively advertises its sex and readiness to breed to any other knifefish sharing its stretch of water, and courtship in wave-type Sternopygidae is understood to unfold substantially as an exchange of electric signals in the dark, alongside physical approach.
Beyond that general pattern, which is best documented in the related glass knifefish Eigenmannia, little has been published specifically on courtship behaviour in S. astrabes, and this account should be treated as inference from the family rather than direct observation of the species.
Breeding
Breeding biology for Sternopygus astrabes has not been documented in the available sources, and the species is essentially absent from the aquarium trade. Sternopygidae as a family are egg-layers that scatter adhesive eggs among plant roots and floating or submerged vegetation, typically triggered by warm, soft, rising-water conditions in the wet season, with little to no parental care afterward — the eggs are left among cover rather than guarded.
Captive spawning is best documented in the family's more commonly kept member, the glass knifefish Eigenmannia, which breeds far more readily than most gymnotiforms; there is no comparable body of aquarium data for Sternopygus astrabes. For this species the honest position is that its reproduction is essentially undocumented and it should not be assumed to follow any specific protocol.
In the aquarium
Sternopygus astrabes is not a fish of the aquarium trade — it is known only from scientific collections and is not something a hobbyist is likely to encounter for sale. Were it to be kept, the general husbandry rules for Sternopygidae would apply: because it is scaleless, it would need scrupulous water quality and great caution with medications, avoiding copper-based treatments entirely and reducing standard doses of anything else, since scaleless fish are markedly more sensitive to chemical stress than scaled species.
As a nocturnal electroreceptive predator reaching upwards of 14 in in females, it would require a large tank with dim lighting, plenty of cover such as driftwood and root tangles to retreat into by day, and tankmates too large to be hunted after dark — the same logic that applies to its better-known relatives. In practice, though, this is a species to know about rather than to plan a tank around.
Conservation
Sternopygus astrabes has not been formally assessed by the IUCN Red List; its conservation status is Not Evaluated. It is known only from the upper Orinoco basin in Venezuela, including the type locality near Puerto Ayacucho and records from the Casiquiare and Negro River drainages — a real but not exhaustively surveyed range within one of South America's least-disturbed major basins.
Without a formal assessment there is no basis for calling out any specific threat to the species. Its narrower, upper-Orinoco distribution places it among the many gymnotiforms whose fortunes are tied to the health of a single basin, where habitat change, deforestation and pollution are the pressures generally facing small-range Neotropical freshwater fish — but for S. astrabes itself, data remains sparse and no conservation concern is documented.