Taxonomy & naming
Pyrrhulina elongata was formally described in 2001 by D. Zarski and J. Géry, making it one of the more recently named members of its genus. The original description was published in Zoologische Abhandlungen and drew on material from the Rio Tapajós basin of Brazil. The valid name and authorship are confirmed by FishBase and GBIF as Pyrrhulina elongata Zarski & Géry, 2001; the species has not been subject to subsequent synonymy or transfer.
Pyrrhulina belongs to the family Lebiasinidae, a Neotropical lineage that encompasses the pencilfishes (Nannostomus, Lebiasininae) and the splash tetras (Copella, Pyrrhulina, and their allies). Lebiasinidae itself sits within the large freshwater-fish order Characiformes alongside the true characid tetras, though the family's members diverge from that group in several anatomical and reproductive details. Within Pyrrhulina, the species is characterised by a combination of its elongated body, the posterior placement of the dorsal fin (body depth at the start of the dorsal fin measuring 4.8–5.1 times standard length), and meristic counts including 2 dorsal spines with 7–8 dorsal soft rays and 3–4 anal spines with 7–8 anal soft rays.
Morphology
Adults of Pyrrhulina elongata reach approximately 1.5 in standard length, making it one of the smaller Pyrrhulina. The body is notably elongated and slender compared with the more robust members of the genus, which is the feature most immediately useful for identification. The dorsal fin insertion is set far back — the relationship between body depth and dorsal-fin origin placement (depth at dorsal-fin start 4.8–5.1× SL) distinguishes it from shorter-bodied congeners.
FishBase records 32–33 vertebrae and classifies the species as benthopelagic, associating it with the water column above the substrate in small creeks and pond habitats. Detailed colour-pattern data for preserved and live specimens are sparse in available sources, and a thorough comparative account of the species' in-life coloration appears to require primary examination of fresh material. As in other Pyrrhulina, some degree of sexual dimorphism in colour and fin shape is likely, but specific data for P. elongata are not available in the current record.
Habitat
The species is known from the Rio Tapajós basin in the state of Pará, Brazil — a major right-bank tributary of the Amazon draining the Cerrado-Amazon transition zone and the southern Amazonian lowlands. Within this drainage, FishBase records its habitat as creeks and small ponds, the slow, heavily vegetated microhabitats typical of smaller lebiasinids across the Neotropics.
Water conditions in Tapajós tributaries vary considerably by season and sub-catchment, but small forest creeks and isolated ponds in the region are commonly soft, slightly acidic blackwater or clearwater environments with low conductivity, dense leaf litter, and overhanging riparian vegetation. The IUCN assessment, which assigns the species Least Concern status, characterises it as an Amazon basin endemic restricted to the Tapajós drainage. This relatively narrow geographic footprint — a single major river drainage rather than a basin-wide distribution — nonetheless places it within one of the better-studied and legally protected areas of Brazilian Amazonia.
Feeding
FishBase assigns Pyrrhulina elongata a trophic level of 3.2 ± 0.4, placing it in the mid-level omnivore range typical of small characiform fishes. This trophic position is consistent with a diet combining small invertebrates — aquatic insect larvae, microcrustaceans, and zooplankton — with plant material, algal films, and surface-fallen terrestrial insects.
Pyrrhulina species generally feed at or near the water surface and in the upper water column, and P. elongata's slender body form and the family's characteristic upturned mouth suggest a similar surface-skimming and mid-water foraging strategy. In aquarium care, related Pyrrhulina accept small live and frozen foods such as Daphnia, artemia nauplii, micro-worms, and finely crushed flake, and surface-presented foods are typically taken with preference. Detailed wild dietary studies for P. elongata specifically are not documented in available sources.
Mating
Pyrrhulina species are egg-depositing fishes with courtship behaviours driven by male display; males typically defend small territories or spawning sites and court females with lateral displays that show off fin and body colouration. Spawning is carried out among fine-leaved aquatic plants or at the water surface on a firm substrate — several Pyrrhulina deposit adhesive eggs on a leaf surface, which the male then guards.
Specific courtship data for P. elongata are not recorded in available sources, but the genus's mating system is reasonably well characterised through related species such as P. australis and P. spilota, and the basic egg-guarding pattern is likely shared across the group. The male's role in defending the egg clutch distinguishes Pyrrhulina from the completely non-guarding egg-scatterers of many other characiform families, and is one of the behavioural features that makes the group of interest to aquarists willing to provide adequate space and cover.
Breeding
Pyrrhulina elongata has not been documented in captive breeding in the available literature, and detailed accounts of its reproductive biology are absent from current sources. Based on the genus, spawning is expected to involve the deposition of adhesive eggs on a cleaned leaf or other firm surface, with the male subsequently guarding the clutch and fanning it with his fins until hatching.
For related Pyrrhulina species bred in aquaria, water conditions of pH 6.0–7.0 and temperatures in the 75–82 °F range are commonly recommended, with a well-planted, low-flow environment providing spawning sites and refuge. Incubation periods of 24–36 hours are typical within the genus at these temperatures. The fry are initially very small and require fine first foods — infusoria, vinegar eels, or commercial liquid fry diets — before graduating to newly hatched Artemia. Because P. elongata is rarely encountered in the hobby, captive-bred stock essentially does not exist in commerce, and breeding data remain sparse.
In the aquarium
Pyrrhulina elongata is essentially absent from the mainstream aquarium trade as of the current record. Its small size (under 1.5 in SL), preference for vegetated slow-water habitats, and the general aquarium compatibility of the Pyrrhulina genus suggest that a species-appropriate setup would resemble that used for other small Lebiasinidae: a well-planted, low-flow aquarium with a dark substrate and floating cover, soft to moderately soft water (pH 6.0–7.0), and temperatures in the 75–82 °F range.
Related Pyrrhulina species are regarded as peaceful, surface-oriented community fish best kept in groups, and unsuitable for housing with much larger or highly active tankmates that would outcompete them for food. Regular partial water changes — on the order of 20–30% monthly or more frequently in smaller tanks — and control of nitrate below 50 mg/L are standard recommendations for the genus. Given its rarity, any specimens encountered are very likely wild-caught, and acclimation to aquarium conditions should be approached with care.
Conservation
Pyrrhulina elongata is assessed as Least Concern (LC) on the IUCN Red List, with the most recent assessment recorded in November 2018. The assessment characterises the species as an Amazon basin endemic restricted to the Tapajós drainage of Brazil. The Tapajós basin, while subject to ongoing pressures from deforestation, agriculture, and infrastructure development in the broader Amazon region, supports a large and mostly intact forest cover in its upper and middle reaches, and a substantial portion of the drainage falls within legally protected areas.
No targeted commercial collection of this species for the ornamental trade has been documented, and its small size and obscurity in the hobby mean collection pressure is not a recognised threat. As with many narrow-range Amazonian stream fishes, the primary long-term risks would be habitat degradation from land-use change and hydrological alteration within the Tapajós catchment, rather than direct exploitation. The Least Concern listing reflects current population stability but should be understood in the context of the broader pressures facing Amazonian biodiversity.