Xeruin tetra

Geographical Origin and Habitat: This species is native to the Amazon River basin in South America, with specimens collected primarily from the Xeruini River basin in Brazil. It inhabits slow-moving streams, small tributaries, flooded forests, and blackwater areas characterized by slow currents, dense leaf litter substrates, and acidic waters rich in dissolved tannins.

Taxonomy and Morphology: Belongs to the family Characidae and the genus Tyttobrycon, which contains some of the smallest tetras in the world. It is an extremely small fish, with adult specimens reaching a maximum length of only 1.5 to 2 cm. The body is slender, semi-transparent, and elongated, with a small, slightly upturned mouth.

Social Behavior: A very peaceful, shy, and schooling species. It must be kept in groups of at least 10 to 15 individuals to help reduce their shyness and encourage natural shoaling behavior. They show no aggression towards other species and are easily intimidated by large, active, or boisterous tankmates.

Coloration and Sexual Dimorphism: The body is mostly semi-transparent with silvery or golden iridescence under aquarium lights. A thin, dark or gold longitudinal stripe runs along the flanks from the mid-body to the base of the tail fin. Adult males are generally more slender and show slightly brighter highlights, whereas adult females are noticeably plumper.

Aquarium Setup: Requires an aquarium of at least 40 to 50 liters (approx. 10-12 gallons) to house a small school. The tank should be densely planted with fine-leafed vegetation (such as Java Moss, Java Fern, and Vallisneria) and decorated with driftwood branches to create shaded retreats. Adding dried leaves (like Catappa or Oak leaves) to the dark sandy substrate helps replicate their native blackwater environment.

Diet and Feeding: Omnivorous. Due to their extremely small mouth size, they require microscopic foods. Feed high-quality powdered fry foods, crushed flakes, newly hatched brine shrimp nauplii, infusoria, rotifers, and tiny frozen foods. Feed small amounts 2 to 3 times daily, keeping food suspended in the water column as they rarely feed from the bottom.

Water Quality: Highly sensitive to water quality. Demands soft, acidic conditions: pH 5.5-6.5, very low hardness (GH 1-5, KH 1-3), and temperatures between 23°C and 27°C (73-81°F). Peat filtration is recommended to enrich the water with tannins and humic acids. Ammonia and nitrites must be zero, and nitrates must be kept low with regular, gentle water changes.

Compatibility and Cohabitation: Suitable only for dedicated nano community aquariums with other tiny, peaceful species. Ideal tankmates include dwarf shrimp (Neocaridina), small Otocinclus, chili rasboras (Boraras brigittae), and other dwarf tetras. Never house with medium or large fish (such as angelfish, barbs, or larger tetras) that will easily eat or stress them.

Aquarium Breeding: Breeding in captivity is exceptionally difficult. They are egg-scatterers that deposit eggs among fine plants without parental care. Requires a dedicated breeding tank with warm, highly acidic, and soft water, egg-crate mesh on the bottom, and dense moss. Parents must be removed after spawning. Fry are microscopic and need infusoria.

Risks and Diseases: Due to their minute size, they have low fat reserves and can starve quickly if not fed regularly. They are highly sensitive to osmotic shock; slow drip acclimation is mandatory. They are prone to skin fungal infections if kept in alkaline water or if water conditions deteriorate.