Taxonomy & naming
Apteronotus acidops was described by Triques in 2011 in Vertebrate Zoology, along with a key to the apteronotid species of the upper rio Paraná basin. The holotype, MZUSP 45685, measured 12.5 in and came from the primary type locality at roughly 20°30'S, 51°0'W, with a paratype collected further south near 23°50'S, 48°W. It belongs to the family Apteronotidae — the ghost knifefishes — within the order Gymnotiformes, the New-World electric knifefishes, a bony-fish lineage defined by its electric organs and its long, undulating anal fin rather than by any resemblance to the unrelated Asian featherback and clown knifefishes (Chitala, Notopterus).
Within Apteronotidae, the electric organ is built from modified nerve cells rather than muscle, giving these fish an unusually fast, high-frequency wave-type discharge — the most refined electrosensory system in the order. A. acidops is distinguished from its Paraná-basin relatives by details of its fin-ray counts (118–122 anal-fin rays) and by having four branchiostegal rays; the species epithet acidops joins Greek roots for "point" and "face", describing the fish's elongated, pointed snout. The Catalog of Fishes is the authority for the valid name.
Morphology
Like other ghost knifefishes, A. acidops has the family's characteristic blade-shaped, laterally compressed body, tapering toward the tail, with no dorsal fin and no distinct caudal fin. Movement comes from a long anal fin running most of the length of the underside, which the fish throws into travelling waves to glide forward or backward with equal ease. A slender dorsal filament runs along the midline, and the skin is scaleless, as in all apteronotids.
The feature that sets this species apart within its genus is its snout: an elongated, pointed head — the source of the name acidops — that differs from the blunter profile of better-known relatives such as the black ghost (A. albifrons). Specimens on record reach a total length of about 12.5 in, based on the type series and floodplain survey material; detailed data on coloration, sexual differences and other external features have not been recovered from the sources checked, so those points are left undescribed rather than guessed at.
Habitat
Apteronotus acidops is known from the upper rio Paraná basin in Brazil, including floodplain habitat around the Itaipu region, where a voucher specimen (NUP 1750, 9.5 in) was recorded in a survey of the upper Paraná floodplain fishes. FishBase lists it as a freshwater, benthopelagic species — living and feeding near the bottom but ranging up into open water — consistent with the deeper channels and floodplain habitats used by other apteronotids in the basin.
As with its relatives, the species almost certainly depends on its electric sense to navigate and hunt in the basin's often turbid, low-visibility water, where vision offers little advantage. Beyond the confirmed localities and general habitat type, further detail on water chemistry or seasonal habitat use at this species' sites was not found in the sources checked.
Feeding
No species-specific feeding data for A. acidops turned up in the sources checked. Ghost knifefishes as a group are nocturnal carnivores that hunt small bottom-dwelling invertebrates — insect larvae, worms, small crustaceans — locating them chiefly by electrolocation rather than sight, and A. acidops, as a benthopelagic apteronotid from the same basin, is expected to feed in a broadly similar way. This is inference from family-level biology rather than a documented account of this species, and should be treated as such.
Mating
Nothing specific to A. acidops on courtship or spawning behaviour was found in the sources checked. Across Apteronotidae, however, the electric organ discharge doubles as a social signal carrying information about identity, sex and readiness to spawn, and in the best-studied relative, the brown ghost (A. leptorhynchus), males and females shift their discharge frequencies toward one another during courtship in an electrical duet. It is reasonable to expect a similar role for electric signalling in A. acidops, but this has not been documented for the species itself — data sparse.
Breeding
No breeding records for A. acidops were found in the sources checked, and the species does not appear to be established, or even present, in the aquarium trade. Ghost knifefishes in general are egg-layers that scatter eggs among cover such as roots and crevices, with no substantial parental care documented, and are only rarely bred even in captivity by hobbyists who do keep the family's aquarium species. For A. acidops specifically, breeding biology is best described as poorly documented rather than assumed.
In the aquarium
Apteronotus acidops is not a hobby species. It was described in 2011 from museum and survey material from the upper rio Paraná basin, and nothing in the sources checked indicates it is collected or traded for aquariums. Were it ever to appear, the general cautions that apply to its scaleless, electrosensitive relatives would hold: sensitivity to ammonia, nitrate and copper-based medications, a need for dim, cover-rich, warm water reflecting its natural floodplain and channel habitat, and a nocturnal, predatory temperament unsuited to small tankmates. For now this species belongs to ichthyological collections and river surveys, not to the trade.
Conservation
FishBase lists Apteronotus acidops as IUCN Data Deficient, assessed in November 2018, with no CITES listing and a low estimated fishing vulnerability. As a species described only in 2011 and known mainly from a handful of museum specimens and one floodplain survey, there simply is not enough distributional or population data yet to assign a threat category — a common situation among the many narrow-range Neotropical knifefishes.
Its confirmed range sits in the upper rio Paraná, a basin that has been heavily modified by damming, agriculture and urbanization, so the pressures typical of that system — habitat alteration and water-quality change from impoundments and land use — are the plausible long-term concerns for a species this narrowly known, even though no specific population trend has been documented.