Coral Red Pencilfish
Coral Red Pencilfish(Nannostomus mortenthaleri) is arguably the most spectacular pencilfish available — males develop an extraordinary coral-red to deep red coloration covering the entire lower body and fins, with the upper body silvery-white. Listed asIUCN Near Threatenedand endemic to the Río Nanay drainage near Iquitos in Peru.
Feeding & Care Tip:Hikari Micro Pellets(crushed or soaked briefly) andSera Vipan Babymake excellent daily staples. Supplement 2–3× per week withHikari Frozen or Freeze-Dried Baby Brine ShrimpandHikari Frozen Daphnia. Pencilfish are slow, deliberate feeders — avoid fast tankmates that will outcompete them. Feed small amounts 2–3 times daily.
AllNannostomusspecies inhabit the blackwater and clearwater streams, lakes, and flooded forests of the Amazon and Orinoco basins — soft, acidic, tannin-stained water with dense vegetation and leaf litter. A mature blackwater setup with Indian almond leaves, dark substrate, and very soft slightly acidic water produces the most vivid coloration. Males are territorial with each other — keep more females than males and provide visual breaks with dense planting.
The oblique resting posture — head elevated, body angled downward at roughly 45 degrees — is a characteristic behavior of theNannostomusgenus. Schools adopt synchronized oblique positions at rest, which is both fascinating to observe and unmistakable once seen. The angle varies by species — some hold a gentle tilt while others are nearly vertical. The coral-red coloration is most vivid in soft, acidic water with tannins. A mature blackwater setup is important. Keep in groups of 8+ with more females than males.
One of the most beautiful nano fish available — the coral-red male coloration is extraordinary. The restricted range and Near Threatened status make captive breeding a meaningful contribution.
Care & Ideal Parameters
| Difficulty | Easy — Moderate |
| Temperament | Peaceful — slow feeder; avoid fast tankmates |
| Typical Adult Size | 1.5 inches (3.8 cm) |
| Min. Group Size | 8 minimum — more females than males |
| Ideal Temp | 73–82°F (23–28°C) |
| Ideal pH | 5.0–7.0 |
| Ideal GH | 0–10 dGH |
| Ideal KH | 0–5 dKH |
| Staple Food | Hikari Micro Pellets (crushed/soaked); Sera Vipan Baby |
| Treat / Supplement | Hikari Frozen or Freeze-Dried Baby Brine Shrimp; Hikari Frozen Daphnia |
| Origin | Río Nanay drainage, Loreto region, Peru (IUCN Near Threatened) |
| Notes | IUCN Near Threatened. Endemic to Río Nanay, Iquitos, Peru — very restricted range. Most spectacular pencilfish — extraordinary coral-red male coloration. Captive breeding supports conservation. |
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