Taxonomy & naming
Compsaraia samueli was described by Albert & Crampton in 2009 as part of a revision that split the genus Compsaraia from Sternarchorhynchus, based on a new species of electric knifefish from the Amazon River showing extreme sexual dimorphism in snout and jaw length. It belongs to the family Apteronotidae, the ghost knifefishes, within the order Gymnotiformes — the New-World electric knifefishes. Apteronotidae is distinguished within the order by an electric organ built from modified nerve tissue rather than muscle, which produces the fastest, most refined wave-type discharges of any knifefish group.
Despite the shared common name, gymnotiform "knifefishes" are unrelated to the Asian featherback and clown knifefishes (Chitala, Notopterus), which belong to a different order entirely; the similarity is convergent body shape, not kinship. The Catalog of Fishes (Eschmeyer, CAS) is the authority for the valid name Compsaraia samueli.
Morphology
Like other apteronotids, Compsaraia samueli has the classic ghost-knifefish silhouette: a laterally compressed, blade-shaped body with no dorsal fin and no true tail fin, propelled by an elongated anal fin that runs most of the length of the underside. The species is scaleless. Reported maximum length is around 9 in standard length in males, per FishBase.
The standout feature of this species is its extreme sexual dimorphism in snout and jaw length — the trait the original description was built around. Mature males develop conspicuously elongated snouts and jaws, sometimes described as grotesque, that females do not; males also mature at a slightly larger size (around 7.5 in) than females (around 6 in). The electric organ discharge is wave-type and itself sexually dimorphic in frequency: FishBase reports females discharging around 1.242–1.243 kHz and males around 1.337–1.396 kHz, and a PMC/NIH electrophysiology study places the baseline discharge around 1,100–1,200 Hz with variation between individuals. Males use chirps (large, abrupt frequency jumps) and rises (smaller jumps) during aggressive encounters, and the elongated jaws are thought to function in ritualized jaw-locking combat between males, and possibly in mate attraction as well.
Habitat
Compsaraia samueli is a western Amazon endemic, known from the Rio Amazonas near Iquitos in Peru, the Rio Solimões below its confluence with the Rio Purus in Brazil, and the lower Rio Iça in Brazil. It is a river-channel fish rather than a still-water species, occupying the main Amazon channel and its larger tributaries.
As with other Apteronotidae, it lives in the warm, often turbid or tannin-stained water of the Amazon basin, where the electric sense does the work eyesight cannot in the dark or sediment-clouded channel. FishBase gives a trophic level of 3.3 ± 0.3, consistent with a piscivorous diet taken from within the water column and near cover rather than pure benthic foraging.
Feeding
FishBase places Compsaraia samueli at a trophic level of 3.3 ± 0.3, indicating a piscivorous diet — it preys on other fish, in keeping with the predatory habits typical of larger Apteronotidae. As in related ghost knifefishes, prey is most likely located primarily by electrolocation in low-visibility water, with the fish probing the water column and structure for the electrical signatures of prey rather than hunting by sight.
Detailed field data on diet composition for this species specifically are sparse in the available literature. In captivity, generic aquarium-care sources report the species taking Tubifex worms and small feeder fish such as Tanichthys (white cloud minnows), consistent with an opportunistic piscivore/invertivore diet.
Mating
Courtship in Compsaraia samueli is inseparable from its electricity. The wave-type electric organ discharge is sexually dimorphic in frequency — females around 1.24 kHz, males running higher, roughly 1.34–1.40 kHz per FishBase, with a PMC/NIH study recording a baseline nearer 1,100–1,200 Hz — so the discharge itself likely signals sex and identity to other fish in the dark. Males produce chirps and rises, sudden shifts in discharge frequency, that correlate with aggressive and agonistic behavior in laboratory study, the same signalling repertoire used elsewhere in the family during courtship and rivalry.
The species' most striking sexual trait, its extreme male snout and jaw elongation, is thought to function primarily in ritualized jaw-locking combat between rival males, though the original description also raises the possibility of a role in mate attraction. Beyond this electrophysiological and morphological picture, the fine detail of pairing and spawning behavior is poorly documented — the PMC/NIH study notes its subjects were in only marginal reproductive condition, underscoring how little of this species' reproductive life has been observed directly.
Breeding
Compsaraia samueli is an egg-layer, as is typical of the Apteronotidae, but breeding in this species is rarely observed and poorly documented, whether in the wild or in captivity. There is no record in the cache of a reliable spawning account, egg count, or rearing protocol for this species, and no evidence of parental care beyond spawning.
Given how rarely the species is even kept, let alone bred, the honest position is that its reproductive biology is data sparse outside of the electric-signalling and morphological studies discussed above. Aquarists should not expect to reproduce it; wild collection remains the source of any specimens that do reach the trade.
In the aquarium
Compsaraia samueli is essentially a specialist's fish, rarely if ever seen in the ornamental trade, and the limited husbandry information available comes from generic knifefish care guidance rather than species-specific accounts. Where water parameters are given, they suggest 72–79 °F with an optimum of 77–81 °F, and soft, slightly acidic water in the pH 5.5–6.5 range — warmer and softer than many community setups, and consistent with its Amazon river-channel origin.
As with all Apteronotidae, the species is scaleless and should be presumed sensitive to ammonia, nitrate, and copper-based or otherwise harsh medications, which call for reduced dosing. It is a nocturnal, electrolocating predator that would need dim lighting, ample cover, and tankmates too large to be eaten. Adult males are reported to be extremely aggressive toward one another, engaging in jaw-locking combat, so multiple mature males should not be housed together. Given the scarcity of reliable husbandry data and its predatory, specialist nature, this is not a fish for a general community tank, and captive-bred stock is essentially unheard of.
Conservation
Compsaraia samueli is assessed by the IUCN as Least Concern, an assessment dated 21 July 2020. This reflects its occurrence across a stretch of the western Amazon mainstem and associated tributaries in Peru and Brazil rather than a single, highly restricted locality.
As with other Amazon-basin fishes, the broad regional pressures on its habitat are ongoing deforestation, water-quality change, and development along the river system, though no species-specific threat has been documented in the sources reviewed here. It is not a species under particular conservation concern at present, and it is not meaningfully present in the aquarium trade, so collection pressure is not considered a driver of any decline.