Filamentous pyrrhulina

Geographical Origin and Habitat: Pyrrhulina filamentosa is native to South America, with a distribution range that covers the Amazon River basin, particularly in Brazil, Venezuela, the Guianas, and Suriname. It inhabits slow-moving forest streams, small tributaries, swamps, and flooded forest floors characterized by dense aquatic vegetation and overhanging tree branches that touch the water surface. It prefers shallow, quiet waters, often tinted dark with tannins released by decaying organic leaf litter.

Taxonomy and Morphology: This species belongs to the family Lebiasinidae and the subfamily Pyrrhulininae. It has a slender, cylindrical body, slightly compressed towards the tail. The mouth is upturned, which is a clear adaptation for feeding on insects and small invertebrates at the water surface. Adult males develop a highly pronounced filamentous extension on the upper lobe of the caudal fin and the dorsal fin, a characteristic from which the species name is derived.

Social Behavior: It is a peaceful, schooling fish that thrives when kept in groups of at least 6-8 individuals, where non-violent hierarchies are established among the males. During the breeding season, males establish small, temporary territories near the water surface to attract females, but they never display harmful aggression toward tankmates. They spend most of their time in the upper and middle levels of the water column.

Coloration and Sexual Dimorphism: The body background color is silver-grey or bronze with golden reflections along the flanks. A dark horizontal stripe runs through the snout, passes through the eye, and fades gradually along the body. The scales have dark margins, creating a reticulated pattern. Sexual dimorphism is highly visible: males are larger, more colorful with orange or reddish tints on their fins, and possess the long caudal filaments, while females are smaller, rounder, and have short fins.

Aquarium Setup: Requires an aquarium of at least 80-100 liters to house a small group. The layout should include dense planting along the back and sides (using plants like Vallisneria and Limnophila) combined with floating plants (like Pistia stratiotes or Salvinia) to diffuse the light and create a secure environment. A tight-fitting lid is mandatory, as this species is an exceptional jumper and can escape through very small gaps.

Diet and Feeding: It is primarily carnivorous and insectivorous. In the wild, it feeds on terrestrial insects that fall onto the water surface and small aquatic invertebrates. In the aquarium, it easily accepts high-quality floating flakes or micro-pellets. However, its diet should be regularly supplemented with live or frozen foods such as daphnia, brine shrimp, mosquito larvae (bloodworms), and small fruit flies (Drosophila).

Water Quality: It prefers soft, slightly acidic water, mirroring its Amazonian habitats. Recommended parameters are: temperature 22-26 °C, pH 6.0-7.0, and water hardness (GH) between 2 and 10 dGH. The filter should produce a very gentle water flow, as these fish avoid strong currents. Using peat filtration or adding Indian almond leaves (Catappa) to release beneficial tannins is highly recommended.

Compatibility and Cohabitation: An excellent candidate for a peaceful South American community aquarium. It can be housed with small tetras (like neon or cardinal tetras), dwarf cichlids (Apistogramma), Corydoras, and small Loricariid catfish. Avoid keeping them with large, boisterous, or predatory fish that could eat them, or with species known to nip fins (such as some active barbs).

Aquarium Breeding: Breeding in captivity is fascinating and relatively easy. The pair deposits adhesive eggs on the upper surface of a broad submerged or floating leaf, or on a flat surface near the water level. The male takes full responsibility for egg care: he guards them aggressively and fans them constantly with his fins. In the wild, if eggs are laid just above the water line, the male splashes them with tail flicks. Hatching occurs in 24-36 hours; fry should be fed infusoria initially, followed by brine shrimp nauplii.

Risks and Diseases: The main risk is jumping out of the tank if the cover is not secure. From a health perspective, it is a hardy fish but can be sensitive to sudden temperature drops or organic waste build-up (nitrates), which can lead to white spot disease (ich) or fungal infections on the long, delicate fins of the males.