Taxonomy & naming
Sternarchorhynchus marreroi was described by de Santana and Vari in 2010 and placed in the family Apteronotidae — the ghost knifefishes — within the order Gymnotiformes, the New-World electric knifefishes. Gymnotiformes are bony fish, but unusual ones: they are defined by an electric organ and by a single long ribbon-like anal fin used for locomotion, and they are only distantly related to the far more familiar aquarium families. The Apteronotidae are distinguished within the order by an electric organ derived from modified nerve cells rather than muscle tissue, which produces the fastest, highest-frequency discharges of any knifefish group.
The genus Sternarchorhynchus is recognisable by its elongated, tube-like snout, a feature that separates it from the blunter-headed Apteronotus (which includes the familiar black ghost, A. albifrons) and from other genera in the family. Despite sharing the common name "knifefish", Sternarchorhynchus and its Apteronotidae relatives are not related to the Asian featherback and clown knifefishes (Chitala, Notopterus); the resemblance is convergent body shape, not kinship. The Catalog of Fishes (Eschmeyer, California Academy of Sciences) is the authority for the valid name.
Morphology
As in other Apteronotidae, Sternarchorhynchus marreroi has a blade-like, laterally compressed body with no dorsal fin and no functional tail fin; forward and backward movement is driven almost entirely by a long anal fin run as a travelling wave along the underside of the body. The species reaches a maximum recorded total length of about 11 in, making it a modestly sized member of the genus. Its most distinctive feature is the elongated, tubular snout for which Sternarchorhynchus is named — a specialised structure associated with probing tight spaces such as root mats and sediment for hidden prey.
The skin is scaleless, as in all gymnotiforms, and carries the sensory pores that read the fish's own electric field alongside an electric organ running down the body that generates a continuous, weak wave-type discharge. This discharge is the animal's primary means of sensing its surroundings in the dark, turbid water it inhabits, largely substituting for vision. Data on external sexual dimorphism in this species is sparse; no reliable visual method for distinguishing males from females has been documented.
Habitat
Sternarchorhynchus marreroi is known from the central and delta regions of the Río Orinoco in Venezuela, with specimen records confirming its presence in that basin; the available evidence points to a narrow, Orinoco-endemic distribution rather than the broad, multi-basin range seen in some relatives such as the black ghost. Like other Apteronotidae, it is a fish of flowing river channels rather than still water — likely occupying deeper channel habitat, consistent with the genus's typical ecology, though detailed habitat notes specific to this species are not well documented in the available sources.
The wider family occupies warm, often tannin-stained or turbid Neotropical river water where visibility is poor and an electric sense is a major advantage over eyesight. Specific water-chemistry data for this species' native habitat is data sparse; aquarists working with Sternarchorhynchus should default to the well-studied water parameters of the family as a whole rather than to figures reported for this species specifically.
Feeding
No species-specific diet study is available for Sternarchorhynchus marreroi in the cited sources. By analogy with its family and its tube-snouted morphology, it is presumed to be a nocturnal carnivore that locates small invertebrate prey — insect larvae, worms and other benthic animals — largely through electrolocation, probing sediment, root tangles and other tight cover with its elongated snout rather than hunting by sight.
This species is essentially unknown in the aquarium trade, so there is no husbandry record of feeding behaviour in captivity to draw on. Any care based on this species should treat diet as data sparse and default cautiously to the feeding pattern documented for better-studied Apteronotidae, offering small meaty foods after dark.
Mating
Courtship in Apteronotidae is closely tied to the family's electric sense. In well-studied relatives such as Apteronotus leptorhynchus, the wave-type electric organ discharge carries information about a fish's identity, sex and readiness to spawn, and males and females are known to shift their discharge frequency during courtship in an electrical exchange, while rival fish produce distinctive interruptions on encounter. It is reasonable to expect a broadly similar electric-signalling component to courtship in Sternarchorhynchus, given the shared electric-organ physiology across the family, but no courtship observations specific to S. marreroi have been documented.
Beyond the general family pattern, mating behaviour in this species is data sparse. No pair-bonding, territorial, or approach behaviour specific to S. marreroi is recorded in the available literature.
Breeding
Sternarchorhynchus marreroi is not known to be bred in aquaria, and no spawning account for this species exists in the sources reviewed. Apteronotidae in general are egg-layers that spawn among cover such as roots and crevices, without substantial parental care, but reproduction even in the aquarium-trade species of this family is rarely observed and poorly documented outside the laboratory.
Given the complete absence of trade or captive-breeding history for this species, its breeding biology should be treated as unknown rather than inferred in detail. The honest summary is: presumed egg-layer by family pattern, rarely if ever encountered in captivity, no parental care documented.
In the aquarium
Sternarchorhynchus marreroi is not an aquarium fish in any practical sense — it is a deep-channel Orinoco specimen known mainly from museum and survey collections rather than the ornamental trade, and no meaningful husbandry record exists for it. Anyone who did encounter it would need to apply the general precautions that govern all scaleless gymnotiforms: no copper-based medications, reduced dosing of standard treatments, scrupulous water quality, and a dim, cover-rich tank suited to a nocturnal, electrosensory predator.
Given the total lack of documented care requirements specific to this species, and its apparent restriction to a fairly narrow stretch of the Orinoco, it should not be treated as a candidate for hobbyist keeping. Fish enthusiasts wanting a tube-snouted Sternarchorhynchus experience are better served researching whichever species, if any, is being legitimately exported and captive-documented at the time.
Conservation
Sternarchorhynchus marreroi is assessed by the IUCN as Least Concern. It appears to be restricted to the central and delta Orinoco in Venezuela, and while narrow-range endemism can make a species more vulnerable to localised pressures, the current assessment does not flag major population decline.
As with many deep-channel, single-basin Apteronotidae, the species is not a target of the aquarium trade and faces no meaningful collection pressure; its main long-term risks, as for other Orinoco basin fish, would be habitat and water-quality change within its home range rather than overharvest. Detailed population trend data is not available.