Taxonomy & naming
Eigenmannia vicentespelaea was described by Triques in 1996, based on specimens collected from a cave system discovered in 1978, and placed in the genus Eigenmannia within the family Sternopygidae — the glass and rattail knifefishes of the order Gymnotiformes, the New-World electric knifefishes. The species epithet refers to its type locality, Gruta São Vicente II, and the fish is essentially a cave-adapted offshoot of the widespread surface-dwelling glass knifefish lineage that gives the genus its common name.
Gymnotiformes are bony fish but unusual ones: nearly every species, this one included, produces a weak electric organ discharge (EOD) used for electrolocation and communication, and the group is defined as much by that electric organ and its ribbon-like anal fin as by conventional anatomy. Eigenmannia belongs to the wave-type dischargers — a near-continuous, sine-wave-like signal rather than the intermittent pulses used by some other gymnotiforms — and this species' cave population shows a measurably different discharge profile from its epigean (surface-water) relatives. The Catalog of Fishes is the authority for the valid name; the New-World knifefishes are not related to the superficially similar Asian featherback and clown knifefishes (Chitala, Notopterus).
Morphology
Eigenmannia vicentespelaea reaches roughly 6.5–8.5 in in total length depending on the source, a size broadly in line with other glass knifefish. Its defining features are the ones typical of a troglobite: poorly developed or absent eyes, reduced pigmentation giving it a pale, translucent appearance, and — per the electric-organ-discharge research on the species — possibly enlarged electric organs compared with surface-dwelling Eigenmannia, consistent with a heavier reliance on electrolocation where vision is useless.
As in every glass and rattail knifefish, the body is slender, laterally compressed and tapers to a fine point at the tail, with no dorsal fin and no true tail fin; locomotion comes from a very long anal fin run as a travelling wave along the underside of the body, which lets the fish glide forward or backward with equal control. The skin is scaleless. Electroreceptive pores cover the body and read the electric field the fish projects around itself, effectively substituting for the eyesight it has lost.
Habitat
This species is known only from the São Domingos karst area of Goiás, central Brazil — specifically the cave system anchored by Gruta São Vicente II and the associated Rio São Vicente, a stream that runs underground through the limestone system before eventually feeding the upper Tocantins basin via the Paranã tributary. It is troglobitic: a permanent, obligate cave-dweller, not a surface fish that occasionally wanders into caves.
Inside the cave the water is in total darkness year-round, which is presumably the selective pressure behind its reduced eyes and pigmentation. Because the population is confined to this one hydrological system, its entire habitat is only as large and as stable as the cave stream itself — a strikingly narrow range compared with most Sternopygidae, many of which range across whole river basins.
Feeding
Specific dietary data for Eigenmannia vicentespelaea is not well documented, but as with other Eigenmannia it is reasonable to infer a diet of small aquatic invertebrates — insect larvae, small crustaceans and other invertebrate prey typical of cave-stream food webs — located primarily through electrolocation rather than sight, an ability that would matter even more here than in surface-dwelling relatives given its reduced eyes.
Cave ecosystems generally run on very limited food input, often from organic matter washed in from the surface or carried by bats and other visiting fauna, so the population likely forages opportunistically over a food supply that is naturally scarcer than in an open river. Data on this species' specific feeding ecology is sparse and should not be overstated.
Mating
As in other Sternopygidae, courtship in Eigenmannia is thought to run substantially through the wave-type electric organ discharge — Eigenmannia is the classic laboratory subject for the jamming-avoidance response, in which two fish with similar discharge frequencies each shift their own frequency to reduce mutual interference, and discharge frequency itself differs between males and females and functions as a social and reproductive signal. The cave population of E. vicentespelaea shows a distinct discharge-frequency range (documented at roughly 230–478.6 Hz) from surface Eigenmannia, and territorial behavior has been recorded, suggesting electric signalling continues to structure social interactions even in permanent darkness.
Beyond this electrophysiological picture, specific courtship behavior for E. vicentespelaea — how individuals locate and select mates within the cave stream — is not documented in the available literature. Given the constraints of a low-light, low-food cave environment, its reproductive biology likely differs from its surface relatives in ways that have not yet been studied in detail.
Breeding
No specific breeding account exists for Eigenmannia vicentespelaea; it has not been reported in the aquarium trade and there is no record of captive spawning. Data is sparse to the point that any specific claim about its reproductive protocol would be speculation.
What can be said comes from the wider genus: Eigenmannia species are egg-layers that scatter adhesive eggs among plant roots or fine cover, typically triggered by warmer, softer water resembling a wet-season rise, and they receive little to no parental care afterward. Ordinary glass knifefish are among the more readily captive-bred gymnotiforms, but nothing in the record suggests this cave-restricted species has ever been kept, let alone bred, outside its native habitat.
In the aquarium
Eigenmannia vicentespelaea is not a hobby fish. It is a narrow-range, cave-restricted species with no established presence in the aquarium trade, and given its Vulnerable status and tiny estimated population it should not be collected or kept. Its inclusion here is for record and conservation context rather than as a stocking recommendation.
For context, surface-dwelling Eigenmannia (glass knifefish) are kept successfully in warm (roughly 75–82 °F), soft, near-neutral to slightly acidic water (pH 6.0–7.0) with pristine water quality — undetectable ammonia and nitrite, low nitrate — and do well in a small shoal of their own kind. Like all gymnotiforms they are scaleless and sensitive to copper-based medications and to poor water quality, and as nocturnal electroreceptive predators they are not reliably safe with bite-sized tankmates. None of this is a recommendation to seek out E. vicentespelaea itself.
Conservation
Eigenmannia vicentespelaea is assessed by the IUCN as Vulnerable, with an estimated population of only around 300 individuals confined to the São Domingos karst cave system in Goiás, Brazil. This is about as narrow a range as a fish can have — a single cave hydrological system rather than a river or a basin — which makes the population intrinsically fragile regardless of the exact threat level at any given time.
The primary documented pressure is siltation from destruction of the riparian forest upstream of the cave, which degrades the water quality of the stream the population depends on. Because caves offer nowhere for a species to retreat to if its one habitat deteriorates, protecting the surface vegetation and hydrology feeding into the São Domingos cave system is effectively the entire conservation strategy for this species.