Taxonomy & naming
Knodus figueiredoi was described by Esguícero and Castro in 2014 on the basis of material collected from the Rio Piranhas basin in Paraíba state, north-eastern Brazil. The valid name, as recorded in Eschmeyer's Catalog of Fishes (CAS), is Knodus figueiredoi Esguícero & Castro, 2014; no senior synonyms are recorded.
The genus Knodus Eigenmann, 1911 belongs to the diverse subfamily Stevardiinae within Characidae and encompasses a number of small characins distributed widely across Amazonian and other South American river systems. Most Knodus species are modest in size and plain in colour, and several are known primarily from their original descriptions. K. figueiredoi, from the Atlantic-slope Rio Piranhas drainage, sits outside the core Amazonian range of the genus and represents one of the more geographically peripheral members of Knodus.
Morphology
Knodus figueiredoi is a very small characid, reaching approximately 1 in standard length. Like other members of the genus it is slender and fusiform, with the typical Knodus profile of a small, laterally compressed body, a relatively large eye, and the complete lateral line characteristic of many characins.
Detailed morphological data — meristic counts, colour pattern description, and diagnostic characters separating it from congeners — were established in the original 2014 description by Esguícero and Castro. Published information accessible outside the primary literature is limited; the species is rarely encountered in collections and has not been profiled in English-language aquarium sources.
Habitat
The species is known from small forest streams within the Rio Piranhas basin of Paraíba state, north-eastern Brazil. This drainage flows from the interior of the north-east toward the Atlantic coast; its headwaters and minor tributaries pass through areas of Atlantic Forest and Caatinga transition zones, where small, narrow streams run over sandy or gravelly substrates beneath gallery forest canopy.
FishBase notes that the species inhabits small forest streams with acidic water and heavy vegetation. Conditions in such streams typically include low conductivity, low pH (often below 7), and considerable organic loading from leaf litter and overhanging vegetation. Water temperature in north-eastern Brazilian lowland streams generally falls in the range of 72–79 °F seasonally.
Feeding
FishBase records Knodus figueiredoi as an omnivore, with a diet based on small invertebrates and plant material — a feeding strategy common to many small, forest-stream characids that exploit the diverse invertebrate community associated with leaf litter, aquatic insects, and allochthonous debris falling from the canopy.
No detailed dietary study specific to this species has been published in accessible literature. In the aquarium, comparably sized omnivorous characids of this type accept fine-grade prepared foods, micro-pellets, and small live or frozen invertebrates such as Artemia nauplii and micro-worms.
Mating
No specific mating observations for Knodus figueiredoi have been documented in the aquarium literature. Based on the biology of congeners and small characids generally, the species is expected to be an egg-scattering open spawner without parental care, releasing adhesive eggs among fine-leaved vegetation or over the substrate.
Males in small Knodus species typically show minor nuptial or permanent sexual dimorphism, but specific data on courtship behaviour or mate-choice cues in K. figueiredoi are not available in published sources accessible as of the time of writing.
Breeding
No captive breeding accounts for Knodus figueiredoi have been published in accessible English-language sources. Given the species' very limited hobbyist distribution outside Brazil, it is unlikely to have been bred in captivity beyond its country of origin, if at all.
By analogy with related small characids, spawning would likely involve egg-scattering over fine-leaved plants or a soft substrate, with eggs being adhesive and hatching within a few days at typical tropical temperatures. No parental care would be expected, and adults would require separation from eggs to prevent predation. These details remain speculative pending documented breeding observations.
In the aquarium
Knodus figueiredoi is essentially absent from the mainstream aquarium trade as of 2026 and has not been profiled by major English-language hobbyist resources such as Seriously Fish. Any specimens encountered would most likely derive from specialist collectors working in north-eastern Brazil.
For an aquarist fortunate enough to obtain the species, the habitat data suggest a small, well-planted aquarium with soft, slightly acidic water, subdued lighting, and a gentle current, replicating the shaded forest-stream environment of the Rio Piranhas headwaters. As a very small fish (~1 in SL), it would require appropriately sized tankmates and fine-grade foods. Water temperature in the 72–79 °F range is indicated by the species' range in Paraíba state.
Conservation
Knodus figueiredoi has not been evaluated by the IUCN Red List; its status is Not Evaluated (NE). The species is known from the Rio Piranhas drainage of Paraíba state in north-eastern Brazil, a region where Atlantic Forest cover has been severely reduced by centuries of agriculture, livestock farming, and urban expansion. Small-stream characids with restricted distributions in degraded catchments are often among the most vulnerable freshwater fishes in the Atlantic Forest region, even when formal assessments have not been completed.
No conservation measures specific to K. figueiredoi are documented. Given the scarcity of information and the lack of a formal assessment, the conservation needs of the species remain poorly understood. Future surveys and a formal IUCN evaluation would be warranted.