Taxonomy & naming
Sternopygus sabaji was described by Torgersen and Albert in 2022 in Ichthyology & Herpetology, based on a holotype (ANSP 208090, 14.5 in total length) from the Atlantic-draining rivers of the Guiana Shield in northern South America. It belongs to the family Sternopygidae — the glass and rattail knifefishes — within the order Gymnotiformes, the New-World electric knifefishes, a group of bony fish defined by their electric organs and their ribbon-like anal fin rather than by any resemblance to more familiar aquarium families.
The description separates S. sabaji from its congeners by a combination of characters: it lacks teeth on the anteroventral surface of the endopterygoid bone, has a relatively wider mouth than other Sternopygus, and shows a reduced, low-contrast humeral spot, a pale mid-lateral stripe along the rear part of the lateral line, one to three dark saddle-like markings on the back of smaller individuals, and a comparatively low count of precaudal vertebrae. It is the third Sternopygus species now recognised as endemic to the Guiana Shield, alongside S. astrabes and S. macrurus, underlining how much cryptic diversity this genus still holds. The Catalog of Fishes (Eschmeyer, CAS) is the authority for the valid name.
As with all Gymnotiformes, S. sabaji is unrelated to the Asian featherback and clown knifefishes (Chitala, Notopterus) despite the shared common name — those are bonytongues from a different order entirely, and the knife-shaped body is convergent, not inherited.
Morphology
Sternopygus is the classic "rattail" body form within the family: an elongated, laterally compressed fish that tapers gradually to a fine, whip-like tail, with no dorsal fin and no discrete caudal fin. Locomotion comes almost entirely from a single, very long anal fin running along most of the underside, thrown into travelling waves that let the fish glide forward or backward with equal control — useful in a fish that spends much of its life backing in and out of root tangles and crevices. The holotype measured 14.5 in (14.5 in) total length, making S. sabaji a member of a genus that includes some of the largest gymnotiforms.
Like its relatives, S. sabaji is scaleless, and it carries an electric organ running down the body together with electroreceptor pores across the skin that read the field the organ produces. The species' diagnostic features are subtle and largely internal or meristic — mouth width, dentition on the endopterygoid, precaudal vertebra count — alongside external markings: a reduced humeral spot, a light mid-lateral stripe toward the tail, and faint dark saddles on the back in smaller fish. Sexual dimorphism has not been documented for this species specifically; in the well-studied congener S. macrurus, males and females differ in the frequency of their electric organ discharge rather than in obvious external anatomy.
Habitat
Sternopygus sabaji is known from the Atlantic-draining rivers of the Guiana Shield region of northern South America — a landscape of ancient crystalline rock cut by blackwater and clearwater river systems distinct from the main Amazon and Orinoco basins proper, though it sits within that greater Neotropical drainage complex. As with its Guiana Shield congeners S. astrabes and S. macrurus, it appears to be a narrow-range endemic rather than a widely distributed species.
Data on this species' specific habitat use is sparse, since it was described only in 2022 and has not been the subject of ecological study. Congener data from S. macrurus — a much larger, widely distributed rattail found across the Amazon, Orinoco and Atlantic drainages — points to warm, soft, acidic water in swamps, creeks and the lentic margins of rivers, generally structured, tannin-stained and dimly lit environments where electroreception outperforms vision. It is reasonable to expect S. sabaji occupies similar habitat within its home rivers, but this should be read as informed inference from its genus, not a confirmed account of the species itself.
Feeding
No species-specific feeding data has been published for Sternopygus sabaji; the original description is a taxonomic one focused on distinguishing morphology, not natural history. Across the genus, Sternopygus species are nocturnal carnivores that hunt small invertebrates — aquatic insect larvae and other small benthic prey — locating them in the dark largely through electrolocation, sensing the way prey distorts the weak electric field the fish generates around itself rather than by sight.
In the absence of direct observation of S. sabaji, the safest statement is that it is very likely to follow this same pattern as an electroreceptive nocturnal micro-predator, consistent with the rest of its family, but this is inference from genus-level biology rather than a documented fact about the species.
Mating
Nothing has been published on courtship behaviour in Sternopygus sabaji specifically — again, the 2022 description is a taxonomic paper, not a natural-history study. What can be said with confidence comes from the biology of the family and from well-studied congeners: Sternopygidae are wave-type electric fish, producing a continuous, quasi-sinusoidal electric organ discharge rather than the intermittent pulses used by some other gymnotiform families. In the congener S. macrurus, this discharge is sexually dimorphic in frequency, with females running a higher baseline frequency than males, and the electric signal itself functions in species and sex recognition as well as in the jamming-avoidance response that lets two wave-type fish avoid interfering with each other's signals when they meet.
Males of S. macrurus are known to defend territories and to use electric signalling as part of courtship approach during the breeding season. It is reasonable to expect S. sabaji shares this basic wave-type courtship pattern as a fellow Sternopygus, but no direct behavioural observations of this species have been published, and this should be treated as data sparse rather than confirmed.
Breeding
Sternopygus sabaji has no documented breeding record in the literature or in the aquarium trade — it is too recently described and too little known in captivity. Family-level biology offers the best available guide: Sternopygidae are egg-layers that spawn adhesive eggs among plant roots and floating vegetation, typically timed to warm, soft, higher-water conditions around the onset of the rainy season. In the congener S. macrurus, eggs of around 0.5 in hatch after roughly four days, larvae begin feeding around day eleven, and fish reach maturity at about a year old; parental care beyond initial territory defence by males is minimal, with eggs essentially left among vegetation to develop unguarded.
Given the complete absence of specific data, S. sabaji should be treated as an unbred, poorly documented species for aquarium purposes — a taxonomic curiosity rather than a fish with any established husbandry or breeding protocol.
In the aquarium
Sternopygus sabaji is not an established aquarium fish; it does not appear to be present in the hobby trade, and this entry exists primarily for taxonomic completeness. Any care recommendations must be drawn from the genus and family rather than from direct experience with the species.
Were it to appear in the trade, the same rules that govern its relatives would apply: as a scaleless fish it would need great care with medications (no copper-based treatments, reduced doses generally) and would be sensitive to ammonia and nitrate, requiring mature filtration and warm, soft, gently moving water. As a nocturnal electroreceptive predator it would need a dimly lit tank with secure cover — root tangles, pipes or caves — to retreat into by day, and, given the holotype's size of 14.5 in, a genuinely large aquarium with long, open swimming space. It would not be a safe companion for fish or shrimp small enough to be hunted after dark. None of this is tested for S. sabaji specifically; it is a projection from how its relatives are kept.
Conservation
Sternopygus sabaji has not been formally assessed by the IUCN Red List — as a species described only in 2022, it postdates most recent assessment cycles, and no dedicated evaluation could be found. Its status is best described as Not Evaluated.
As a narrow-range endemic of the Guiana Shield's Atlantic-draining rivers, sharing that distribution pattern with congeners S. astrabes and S. macrurus, it would be reasonable to expect the general pressures that affect Guiana Shield freshwater fish more broadly — habitat change, mining-related pollution and deforestation in parts of the region — could matter to its long-term status, but no species-specific threat assessment exists. This is a fish that needs a proper conservation evaluation, not one that can currently be said to be at risk or secure with any confidence.