Taxonomy & naming
Pyrrhulina capim was described by Vieira & Netto-Ferreira in 2019. The specific epithet capim refers to the Capim River (Rio Capim), a tributary of the lower Amazon drainage in the state of Pará, Brazil, which forms the type locality of the species. Eschmeyer's Catalog of Fishes (Fricke, Eschmeyer & Fong) is the governing authority for the valid name Pyrrhulina capim Vieira & Netto-Ferreira, 2019.
The genus Pyrrhulina belongs to the family Lebiasinidae and is placed in the subfamily Pyrrhulininae. Lebiasinids are small, elongate characiform fishes distributed across tropical South and Central America; Pyrrhulina itself is the largest and most diverse genus in the subfamily, with species occurring across the Amazon, Orinoco, and Guiana basins as well as coastal drainages. The family-level placement of Pyrrhulina within Lebiasinidae is stable and well-supported by morphological and molecular studies.
Morphology
Pyrrhulina species are slender, elongate fishes with a slightly dorsoventrally flattened body that reflects an essentially surface-dwelling lifestyle. The mouth is small, terminal to slightly superior, and the eyes are large relative to head size. The dorsal fin is positioned well back on the body, and the caudal fin is moderately forked. Coloration in the genus typically involves a dark lateral stripe, variable amounts of reddish or orange pigment on the fins and flanks, and in many species small dark spots on the body or a peppered pattern.
Detailed morphometric and meristic data for P. capim specifically are not widely available in secondary sources accessible to this survey; data-sparse claims about precise scale counts or fin-ray counts have been omitted to avoid fabrication. The species is described as a member of the Pyrrhulina semicincta species group based on characters evaluated at the time of its description.
Habitat
Pyrrhulina capim originates from the Capim River drainage of Pará state, in the eastern Amazon basin of Brazil. The Capim is a blackwater to clearwater river system with the low mineral content, soft and acidic water conditions typical of Amazonian drainages. Pyrrhulina species generally occupy shallow, slow-moving or standing waters — flooded forest margins, stream edges choked with leaf litter, oxbow lakes, and roadside ditches — where they cruise just beneath the surface film hunting invertebrates.
Like most lebiasinids, P. capim almost certainly favours heavily vegetated or structurally complex habitats offering overhead cover, drifting leaves, and aquatic plant roots. Water conditions in the Capim basin are likely warm year-round (broadly 75–82 °F), soft, and mildly to moderately acidic, in line with the wider eastern Amazon lowland hydrology, though specific published records for this species' exact collection sites are not available in sources accessed for this survey.
Feeding
Pyrrhulina are surface-oriented micropredators. Their superior mouth and strongly surface-hugging posture reflect a diet dominated by small invertebrates seized at or just beneath the water surface — fallen insects, small arthropods, micro-crustaceans, and similar prey that become available at the air-water interface. The genus name itself (Greek: pyrrhos, flame-red; hulinos, of wood, alluding to the reddish coloration) has nothing to do with feeding habits, but the surface niche is a defining ecological trait.
In captivity Pyrrhulina accept live and frozen small invertebrates readily — Daphnia, mosquito larvae, small bloodworm, brine shrimp — and will take good-quality small dried foods once settled, though many individuals prefer moving prey. Feeding at the surface with minimal competition keeps them in best condition.
Mating
Pyrrhulina species are notable within Lebiasinidae for a paternal egg-guarding system unusual among small characiform fishes. Males defend territories and court females with lateral displays; spawning typically occurs on a firm substrate — the underside of a broad leaf, a flat stone, or a smooth root surface just below the water film — rather than among fine-leaved vegetation. The male prepares or selects a spawning site and guards it aggressively.
Courting males display beside or beneath the chosen substrate, and the female deposits small clutches of adhesive eggs directly onto the surface. The male fertilises the clutch and then assumes sole care of the eggs, fanning them and defending against intruders. This pattern of substrate-spawning with paternal care is consistent across most Pyrrhulina species and distinguishes the genus from the more typical egg-scattering pattern seen in many other small characoids.
Breeding
In the aquarium, Pyrrhulina breed in a manner consistent with the genus account above. A flat-leaved plant such as a broad Echinodorus or Amazon sword leaf near the surface, or a smooth flat stone, serves as the spawning substrate. The female deposits a small clutch of adhesive eggs, and the male guards and fans them until hatching.
Egg numbers per spawning in the genus tend to be modest — tens rather than hundreds. Incubation at typical tropical temperatures takes roughly 24–36 hours, and the larvae remain adhered to the substrate or hang near it for a further day or two until the yolk sac is absorbed. The male should be removed once the fry are free-swimming to prevent predation. First foods are infusoria and very small zooplankton; newly hatched brine shrimp are taken once the fry have grown slightly. Data-specific clutch sizes or exact incubation times for P. capim are not confirmed in published secondary sources.
In the aquarium
Pyrrhulina capim is not established in the aquarium trade and is unlikely to be encountered outside of specialist collections or importers dealing in wild-caught Amazonian novelties. The genus as a whole is underrepresented in the hobby relative to its ecological and behavioural interest; the combination of surface orientation, active behaviour, and paternal egg care makes any Pyrrhulina a rewarding species-tank or biotope subject.
A suitable setup would replicate Amazonian lowland conditions: soft, acidic water (pH 5.5–6.8, low hardness), temperatures in the mid-to-upper 20s Celsius, dim or dappled lighting, a layer of dried leaf litter, emergent and floating plants to reduce open surface exposure, and a tight-fitting lid — Pyrrhulina are surface-skimmers capable of jumping. A species-only or conspecific-group tank avoids competition at feeding. Tank size can be modest given their small size; a 23.5–31.5 in aquarium accommodates a small group comfortably.
Conservation
Pyrrhulina capim has not been assessed for the IUCN Red List and carries a status of Not Evaluated (NE). As a species described only in 2019, it has not yet been through the assessment process. The Capim River basin, while part of the broader eastern Amazon system, is subject to deforestation and agricultural expansion pressure in Pará state, and the biodiversity of the region's smaller stream systems is not comprehensively monitored.
No specific threats to P. capim have been documented in accessible literature. As with many recently described Amazonian small fishes, its conservation status is best considered unknown rather than secure; the absence of an IUCN assessment should not be taken as evidence that the species is not at risk. Survey and assessment of the fish fauna of the Capim drainage would be a valuable contribution to Amazonian ichthyological conservation.