Three-lined pencilfish

Nannostomus trifasciatus

Three dark bands with a fine red line above the main stripe

A slender pencilfish with three longitudinal dark bands and red fin-base patches. The fine red line can be inconspicuous.

Adult length: Up to 3.6 cm (standard length, without the tail fin)
Water temperature: 24–28 °C
pH: 5.5–7

Natural habitat: Native to the Peruvian, Bolivian and Brazilian Amazon, the Negro basin and Guyana.

Male aggression and injury occur in cramped, exposed tanks.

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Appearance and identification

Compare its slender body and fine red line with the more compact dwarf pencilfish. Trade labels may also include N. erythrurus. Night-time markings change.

Same-species behaviour

Keep ten or more, and watch chased individuals.

Space requirements

A 75 × 30 cm base for a mixed-sex group, or at least 60 cm of length. Provide shelter and swimming space.

Diet and feeding

Offer fine dry food and small frozen or live foods; check actual feeding.

Compatibility limits

Confirm identity and watch chasing, feeding competition and companion size.

Aquarium environment

Plants and wood can break sight lines while leaving swimming space and gentle flow.

Sources

researcharchive.calacademy.org ↗ 2026-10-22

www.fishbase.se ↗ 2026-10-22

pdfs.semanticscholar.org ↗ 2026-10-22

www.aquariumglaser.de ↗ 2026-10-22

fishdb.sinica.edu.tw ↗ 2026-10-22