Two-stripe Pencilfish

Geographic Origin and Biotope: Guyana basins (Rio Rupununi) and Rio Negro (Brazil). Frequents forested areas with dark waters (blackwater), lingering among the submerged riparian grass (Igapó).

Taxonomy and Morphology: Two-Lined Pencilfish (Nannostomus digrammus). Slender Nannostomus. Characterized by a tiny pointed mouth and a morphology of a static precision swimmer.

Social Behavior: Extremely timid. Remains suspended in mid-water or near the surface, absolutely motionless like a waiting twig. Suffers terribly from food competition.

Coloration and Sexual Dimorphism: The two lines (Digrammus): possesses two thin raven black horizontal lines (one central and one lower) on a pale silvery/transparent body. The male shows fins with ice white or yellow tips. The nocturnal coloration breaks into vertical or oblique bands to camouflage with the reeds.

Aquarium Setup: Peaceful and dense biotope tank (min. 60 cm / 24 inches). The filter must not create visible currents; the amber water from peat extraction will make them feel safe from hypothetical predators.

Diet and Feeding: Meticulous microhunter. The mouth is so fine that it allows it to hunt aquatic mites and nauplii; if forced to dry food, it demands fry powders. Eats extremely slowly.

Water Quality: Sensitive to nitrogenous compounds. Less robust than beckfordi. Needs small water changes (10-15%) but very frequent with osmosis cut water.

Compatibility and Tankmates: In a tank with lively Tetras (e.g. Danios, Harlequin Rasboras) or Barbs it would starve in a few weeks. Pair it only with Corydoras habrosus/pygmaeus or keep it alone (Species Tank).

Aquarium Reproduction: Hardly ever documented. Similar to other Nannostomus, it scatters the eggs in the foliage in dim light, then needing infusoria.

Risks and Diseases: Environmental fragility. Suffer clamorously from pruning or rearranging the furnishings in the tank; a sudden acute stress will make them bleach and hide without eating, triggering ich.