One-Lined Pencilfish Care Guide
Nannostomus unifasciatus · Freshwater Fish
What One-Lined Pencilfish look like
The One-Lined Pencilfish (Nannostomus unifasciatus) exhibits a slender, torpedo-shaped body that typically reaches a maximum adult size of approximately 2 inches (5 cm). This species is characterized by its distinctive single, bold dark horizontal stripe that extends from the snout to the caudal fin, contrasting sharply with its golden-brown dorsal coloration and pale ventral surface. The body is laterally compressed, enhancing its streamlined appearance, which is advantageous for quick movements in its natural habitat. Unlike many other members of the family Lebiasinidae, this species displays minimal sexual dimorphism, although males may exhibit slightly more vibrant coloration and a more pronounced stripe. Defensive adaptations include its small size and schooling behavior, which helps reduce individual predation risk. Unique morphological features include a well-developed adipose fin and a small mouth with fine, comb-like dentition, adapted for grazing on small invertebrates and plant matter.
Behavior & temperament
The One-Lined Pencilfish is a social species that typically exhibits a schooling behavior, preferring to inhabit the upper to mid-water column of slow-moving streams and floodplains in its native South America. This species is generally peaceful and non-aggressive, making it suitable for community tanks. During breeding, they are known to be egg scatterers, releasing their eggs among fine-leaved plants or in open water, where the eggs will develop without parental care. Their temperament is generally calm, although they may display shyness when kept in smaller groups or in less densely planted aquaria.
Diet & feeding
In the wild, the One-Lined Pencilfish is an omnivore, feeding primarily on small invertebrates, zooplankton, and plant matter. In captivity, it thrives on a varied diet that includes high-quality flake foods, micro-pellets, and live or frozen foods such as daphnia and brine shrimp to ensure optimal health and coloration.
Behind the name
Nannostomus (small mouth); unifasciatus (single stripe).
Plan your tank
Check the numbers before you buy: tank volume, a stocking plan, cycle progress, water changes, and your ongoing care routine.
Keeping One-Lined Pencilfish?
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