Taxonomy & naming
Pyrrhulina obermulleri was described by George S. Myers in 1926, with the type locality cited as the upper Amazon River basin. The species sits within the family Lebiasinidae, a lineage of small neotropical characoids that includes the splashing tetras (Copella), pencilfish (Nannostomus), and the bloodfin-like Lebiasina. Within Lebiasinidae, Pyrrhulina is the most speciose genus, comprising small, somewhat elongate fishes whose males often develop extended unpaired fins. Eschmeyer's Catalog of Fishes treats Pyrrhulina obermulleri Myers, 1926 as the valid name.
The species is one of several Pyrrhulina described from Amazonian Peru and Brazil, a region where the genus diversified broadly across blackwater and clearwater tributaries. Like other members of the genus it was historically placed alongside Copella in broad treatments of the family, but modern accounts keep the genera separate based on spawning biology and morphological characters. The original description appeared in Copeia in 1926.
Morphology
Pyrrhulina obermulleri is a slender, fusiform fish reaching approximately 2.5 in standard length. The body is elongate, slightly compressed, and typical of the genus in profile: a somewhat flattened dorsal surface, a large eye set high on the head, and an upward-angled mouth suited to surface feeding. The caudal fin is forked.
The common name Red Spotted Splashing Characin reflects the species' colour pattern: a pale to straw-coloured ground on the flanks with reddish or orange-red spots and a dark lateral stripe running from behind the eye toward the caudal peduncle. Males develop more vivid colouration and elongated dorsal fins compared with females, which are rounder in the body and less intensely marked. Overall the species shares the bold, gem-like patterning characteristic of Pyrrhulina and commands attention in a well-lit planted aquarium despite its modest size.
Habitat
Pyrrhulina obermulleri is recorded from the upper Amazon River basin, in Maynas Province, Loreto Region, northeastern Peru. This is a mosaic of lowland tropical forest, flooded forest margins, and slow-moving streams and oxbow lakes draining into the main Amazon system. Like most Pyrrhulina, the species likely inhabits shallow, shaded water near overhanging vegetation and emergent plants where it can exploit the surface film and undersides of leaves for both feeding and spawning.
Water conditions in this part of the upper Amazon tend toward soft and acidic, reflecting the peat-stained blackwater or clearwater nature of many smaller tributaries, with temperatures in the region of 75–82 °F. Specific limnological data for the exact collection site of P. obermulleri are not available in the published literature, and the broad distributional data remain sparse.
Feeding
Pyrrhulina obermulleri is a micropredator feeding primarily at or near the water surface. The natural diet consists of small aquatic invertebrates, surface-borne insects, Daphnia and other microcrustaceans, and any small terrestrial invertebrates that fall onto the water. The upturned mouth and surface orientation of the genus make it well adapted to intercepting prey at the interface between water and air.
In captivity the species accepts a wide range of small live and frozen foods including Daphnia, bloodworms, and brine shrimp, as well as suitably sized dried foods. Offering a variety of small, protein-rich items keeps the fish in good condition and maintains colour intensity in males. Like other surface-feeding characins, it is most active and competitive at feeding time and should not be combined with fish that dominate the surface layer.
Mating
Pyrrhulina obermulleri is a substrate-spawning, egg-depositing species rather than a free scatterer. Males of Pyrrhulina court females through displays that involve spreading the elongated fins and positioning below or alongside the female near a chosen surface — typically the underside of a broad leaf, a flat stone, or an equivalent horizontal substrate just at or above the waterline. The splash-spawning behaviour observed in closely related Copella arnoldi, in which eggs are deposited out of water and kept moist by parental splashing, has been documented in some Pyrrhulina but is not confirmed for P. obermulleri specifically; the genus generally tends toward leaf-spawning with the eggs laid in or just above shallow water among emergent or floating vegetation.
Males are territorial during breeding and will display intensely to rivals. In a spawning aquarium, a small group — a pair or trio in a tank with minimal competitors — reproduces most reliably. Soft, slightly acidic water and a low water level with emergent vegetation or floating leaves reproduce the natural spawning environment.
Breeding
To breed Pyrrhulina obermulleri, a shallow conditioning tank with soft, slightly acidic water and a reduced water level of around 4 in is recommended. Java Moss or fine-leaved floating plants provide both spawning sites and cover. A pair or small trio should be conditioned with live and frozen foods before being moved to the breeding setup.
The female deposits adhesive eggs on a chosen leaf or flat surface, and the male typically guards the clutch, fanning the eggs to maintain oxygenation. Eggs hatch within a few days at tropical temperatures, and the male's guarding behaviour generally diminishes once the fry are free-swimming. The adults should be removed at that point to prevent predation on the fry. First foods for the tiny fry are infusoria or a commercial liquid fry food, followed by newly hatched brine shrimp and finely powdered dry food as they grow.
In the aquarium
Pyrrhulina obermulleri is an uncommon but rewarding aquarium fish suited to a species tank or a carefully chosen community. A group of six or more reduces individual stress and allows natural shoaling and courtship displays; males kept together without adequate space or sight-breaks may become combative. A planted aquarium with floating or broad-leaved surface plants, low to moderate flow, and soft, slightly acidic water replicates the species' Amazonian biotope.
The tank should have a tight-fitting lid: like most Pyrrhulina, this species is an accomplished jumper. Water temperature in the range of 75–82 °F suits it well. Compatible tankmates include small, peaceful characins, pencilfish, and other surface-oriented species of similar size that will not outcompete it. Avoid large, boisterous fish or vigorous surface-feeders. Because P. obermulleri is infrequently available in the trade, sourcing healthy, well-conditioned specimens may require specialist retailers or hobbyist networks.
Conservation
The IUCN Red List assesses Pyrrhulina obermulleri as Data Deficient (DD), with the assessment dated October 2014 under the 2022.2 database version. The Data Deficient classification reflects a lack of sufficient distributional and population data to determine extinction risk — it does not imply that the species is secure, only that an informed assessment cannot yet be made.
The upper Amazon basin of Maynas Province, where the species is recorded, remains largely forested but faces ongoing pressures from deforestation, agricultural expansion, and river modification. As a small, narrowly recorded species from a relatively limited region, P. obermulleri would benefit from focused field surveys to establish its actual range, population status, and habitat requirements. Captive populations in specialist hobbyist collections may represent a useful conservation buffer, though the species is too infrequently kept for this to substitute for wild-population monitoring.