Taxonomy & naming
Pyrrhulina lugubris was described by Carl H. Eigenmann in 1922. Eschmeyer's Catalog of Fishes (the authority for valid names) lists the valid combination as Pyrrhulina lugubris Eigenmann, 1922. The genus Pyrrhulina Valenciennes, 1846 belongs to the family Lebiasinidae and the subfamily Pyrrhulininae, a group of small, elongate characiform fishes distributed broadly across tropical South America.
The roughly 20 species recognised in Pyrrhulina share a characteristic body plan — slender and slightly depressed, with an oblique mouth adapted for taking prey at or near the water surface. The genus has a complex taxonomic history and several species boundaries remain poorly resolved; Pyrrhulina lugubris is among the less-studied members and detailed revisionary work is sparse. No synonyms are recorded under this name in the current literature.
Morphology
Pyrrhulina lugubris is a small, slender fish with the elongate, somewhat cylindrical body typical of the pyrrhulinines. The mouth is distinctly oblique and directed upward, an adaptation for feeding at the water surface. The dorsal fin is short and set far back, roughly above the anal fin, and the caudal fin is slightly forked. Colouration, as described from preserved specimens, includes a dark lateral stripe running from the snout to the caudal peduncle and variable brownish pigmentation on the body and fins.
Data on maximum size for this species is sparse in accessible sources. As a member of Pyrrhulina, it is unlikely to exceed 3 in total length, consistent with the general size range of the genus, though this figure should be treated as provisional in the absence of confirmed measurements.
Habitat
Pyrrhulina lugubris is recorded from northern South America, in the drainage systems documented by Eigenmann's 1922 survey work. Members of Pyrrhulina are characteristically found in shallow, slow-moving to still waters — forest streams, flooded margins, backwaters, and vegetated ditches — where overhanging and floating vegetation provides cover and concentrates surface-prey.
Water conditions for Pyrrhulina in northern South America are generally soft to moderately soft and acidic to slightly acid, reflecting the typical blackwater and clearwater drainages of the region, though exact water-chemistry data for P. lugubris specifically are not available in published sources accessible here. The species is presumed to favour shallow, heavily vegetated microhabitats close to the surface.
Feeding
Pyrrhulina lugubris, like other members of the genus, is a predator oriented toward the water surface. The natural diet consists primarily of small invertebrates — terrestrial and aquatic insects, insect larvae, and other small arthropods — taken at or just below the surface film. The upturned mouth is specifically adapted for this mode of feeding.
In the aquarium, Pyrrhulina species readily accept small live and frozen foods such as fruit flies, small crickets, bloodworm, and brine shrimp. Floating or slow-sinking dry foods are also taken. Because these fish focus their attention upward, food that sinks rapidly may be ignored; surface or near-surface presentation is most effective.
Mating
Pyrrhulina species are known to deposit adhesive eggs on a substrate — typically a broad leaf, a flat stone, or a cleared patch of substrate — which the male then guards. This guarding behaviour is notable within the broader context of characiform fishes and distinguishes pyrrhulinines from the open-water egg-scatterers that dominate the order.
No specific mating observations for Pyrrhulina lugubris appear in accessible hobby or scientific literature, but by analogy with well-documented congeners such as Pyrrhulina australis and Pyrrhulina spilota, courtship likely involves lateral displaying and the male preparing and defending a spawning site. Females are generally rounder-bodied when gravid, providing a basis for sexing conditioned adults.
Breeding
In Pyrrhulina generally, spawning involves the female depositing a clutch of adhesive eggs onto a cleaned surface, after which the male drives the female away and guards the eggs, fanning them with his fins. Clutch sizes are modest — typically a few dozen to a few hundred eggs. Eggs hatch after a few days at tropical temperatures, and the male typically continues to guard the free-swimming larvae for a short period before care ends.
No captive-breeding reports specific to Pyrrhulina lugubris are documented in sources available here. Aquarists attempting to breed the species should follow the general pyrrhuline protocol: a separate, well-planted breeding tank with broad-leaved plants or flat spawning substrates, soft to moderately soft acidic water in the mid-to-upper 20s Celsius, and live or frozen conditioning foods to bring the pair into breeding condition.
In the aquarium
Pyrrhulina lugubris is rarely seen in the aquarium trade and is regarded as a specialist fish. Like other pyrrhulines it is best kept in a dedicated or carefully chosen community setup: a tank with a tight-fitting lid is essential, as these fish are strong jumpers. Water surface cover — floating plants, overhanging leaves — replicates their natural microhabitat and makes them more confident and behaviourally interesting to observe.
Water chemistry should lean soft and slightly acidic, consistent with the drainages of northern South America. Temperatures in the range of 72–82 °F are broadly appropriate for the genus. Tankmates should be chosen carefully: Pyrrhulina can be predatory toward small, surface-oriented companions, and may be outcompeted by boisterous midwater fish. Calm, similarly sized species occupying different water layers — small corydoras, peaceful dwarf cichlids, or other quiet characins — make the best companions. The species requires a quiet environment and will stress easily in a busy, high-turnover community.
Conservation
Pyrrhulina lugubris has not been assessed by the IUCN Red List and carries a status of Not Evaluated (NE). The species is not frequently encountered in trade surveys or recent field collections, and published data on its current distribution and population status are sparse.
Without a formal assessment it is not possible to characterise the conservation risk, but its apparent rarity in collections and the limited published information warrant attention. As with many small-bodied, habitat-specialist fishes of northern South America, potential threats include habitat loss and degradation of shallow, vegetated riparian habitats through deforestation, agricultural encroachment, and waterway modification. Aquarists who obtain the species from confirmed captive-bred sources contribute to reducing pressure on wild populations.