Taxonomy & naming
Eigenmannia pavulagem was described in 2015 by Peixoto, Dutra & Wosiacki as one of seven new species erected in a single revision of the Eigenmannia trilineata species-group, published in the Zoological Journal of the Linnean Society. It belongs to the family Sternopygidae — the glass and rattail knifefishes — within the order Gymnotiformes, the New-World electric knifefishes. Gymnotiformes are bony fish, but unusual ones: nearly every species in the order produces a weak electric organ discharge (EOD) around its body, used to sense the world and to signal to other fish, and the order is defined by that trait as much as by its shared ribbon-fin body plan.
Despite the shared common name, gymnotiforms are not related to the Asian featherback or clown knifefishes (Chitala, Notopterus), which are bonytongues in a different order entirely; the knife-shaped body is convergent, not inherited. Within Gymnotiformes, Sternopygidae is set apart by a continuous, high-frequency "wave-type" EOD, in contrast to the intermittent pulses of families like Gymnotidae. The species epithet pavulagem honours "Arraial do Pavulagem," a cultural movement from Pará associated with traditional Amazonian music — a nod to the region the fish calls home. The Catalog of Fishes (Eschmeyer, CAS) is the authority for the valid name.
Morphology
Eigenmannia pavulagem has the classic glass-knifefish silhouette: a slender, laterally compressed, almost translucent body tapering to a fine point at the tail, with no dorsal fin and no true caudal fin. Locomotion comes entirely from a very long anal fin running most of the length of the underside, thrown into travelling waves that let the fish glide forward or backward with equal ease. FishBase records 176–201 soft rays in that anal fin and a maximum total length of about 10.5 in, making it a mid-sized member of the genus.
As in all Sternopygidae, an electric organ runs along the body and drives the fish's continuous wave-type discharge, picked up by electroreceptor pores scattered over the scaleless skin. That scalelessness is a defining feature of the group and matters directly to how the fish must be kept in captivity. Eigenmannia pavulagem was distinguished from its close relatives in the trilineata species-group on the basis of fine anatomical and genetic differences rather than obvious external markings, so field identification within the genus is difficult without expert examination.
Habitat
This species is known from the Rio Capim and Rio Guamá basin in northeastern Pará, Brazil — a Neotropical, freshwater, benthopelagic fish restricted, as far as is currently documented, to that drainage. It has not been reported from elsewhere in South America, and like several of its trilineata-group relatives it appears to be a narrow-range basin endemic rather than a widely distributed species.
Waters across the genus Eigenmannia are typically warm, soft to moderately mineralised, and near-neutral to acidic, often dimly lit or tannin-stained — exactly the low-visibility conditions in which an electric sense pays off. Specific water-chemistry data for E. pavulagem itself is sparse in the literature, so aquarists should default to the conditions well documented for the wider genus rather than assume anything more precise for this species.
Feeding
Dedicated dietary studies of Eigenmannia pavulagem were not found; the genus as a whole is made up of nocturnal micro-predators that hunt small invertebrates — aquatic insect larvae, worms and tiny crustaceans — largely by electrolocation in the dark, rather than by sight. As a benthopelagic species it likely forages both over the substrate and in open water within its river channel.
In the aquarium, glass knifefish of this genus are generally kept on small meaty foods such as bloodworm, blackworm, brine shrimp and finely chopped prawn or fish, offered after dark when the fish become active. Data specific to E. pavulagem's feeding behaviour is sparse, so this account follows the well-documented pattern for Eigenmannia generally.
Mating
Courtship in Eigenmannia is built around the wave-type electric organ discharge. The genus shows clear sexual dimorphism in EOD frequency — males typically discharge at a lower frequency than females of the same size — and courtship involves modulating that signal: dominant males raise their discharge amplitude on the night of spawning, and fish exchange brief frequency "chirps" as they interact. The pacemaker nucleus in the medulla that drives the EOD undergoes measurable neuronal changes as fish reach sexual maturity, tying the electric signal directly to reproductive readiness. Eigenmannia is also the classic subject of the jamming avoidance response, the reflex by which two fish with similar discharge frequencies each shift their own frequency apart to avoid interference — a mechanism thought to double as a social and courtship signal when fish meet in the dark.
Whether courtship in E. pavulagem specifically has been observed and documented is not established in the available literature; this account follows what is well studied in the genus, particularly in the widely researched Eigenmannia virescens.
Breeding
Sternopygidae are egg-layers, and Eigenmannia is reported to spawn 100–200 adhesive eggs scattered onto aquatic plant leaves or other fine vegetation, typically in warm, soft water. There is little to no parental care after spawning — eggs are left among the vegetation to develop on their own — and subordinate females may lay peripherally near an established dominant pair rather than being excluded outright.
Eigenmannia as a genus is bred in captivity more readily than most gymnotiforms, but no species-specific breeding reports for E. pavulagem were found in the sources reviewed here; given its narrow, recently described range, it should be treated as effectively unbred in the hobby, with genus-typical husbandry as the best available guide.
In the aquarium
Eigenmannia pavulagem is not established in the aquarium trade — it was described only in 2015 from a limited Brazilian range, and no husbandry record specific to this species was found. Aquarists are far more likely to encounter its widespread congener, the common glass knifefish (Eigenmannia virescens), which is one of the more approachable gymnotiforms and does well kept in a small shoal of its own kind.
Any fish from this genus that does reach the hobby should be treated with the same care as other Sternopygidae: it is scaleless, so ammonia, nitrite, nitrate and copper-based or harsh medications must be watched closely and dosed conservatively; it is a nocturnal micro-predator best given dim lighting, cover such as plants or driftwood, and tankmates too large to be eaten; and given how little is documented about this particular species, keepers should treat any specimen as a conservation-sensitive, poorly known animal rather than a routine community fish.
Conservation
Eigenmannia pavulagem is listed as Data Deficient on the IUCN Red List, assessed 25 January 2021. Data Deficient does not mean the species is safe — it means too little is known about its population size, trend and threats to make a formal risk assessment, which is unsurprising for a fish described only in 2015 and known from a limited stretch of Pará's Rio Capim and Rio Guamá drainage.
As with other narrow-range Amazonian basin endemics, the plausible pressures on this species are habitat change, deforestation, and water-quality degradation within its home rivers, though specific threat data for E. pavulagem itself was not found in the sources reviewed. Its conservation status is best read as an open question rather than a clean bill of health.