The Red Pencil Fish "Cenepa" (Nannostomus mortenthaleri or possibly a Nannostomus variant from the Cenepa River) is a rare and highly sought-after nano fish known for its striking red coloration, slender torpedo-shaped body, and elegant schooling behavior. At around 3cm, these juveniles already showcase vivid red hues, especially under soft, warm lighting. Originating from the Cenepa River region of Peru, this species thrives in soft, acidic waters rich in tannins—making it a perfect addition to blackwater or heavily planted aquariums.

Their peaceful, almost delicate temperament makes them best suited for calm community tanks or species-only setups where their true beauty can shine without competition or stress.

🐠 Key Features:

• Scientific Name: Nannostomus mortenthaleri (or Cenepa locality variant)

• Common Names: Red Pencil Fish “Cenepa,” Scarlet Pencilfish

• Size: ~3cm (adults may reach 3.5–4cm)

• Lifespan: 4–5 years

• Temperament: Peaceful, shy, schooling

• Difficulty Level: Moderate (sensitive to water quality)

• Origin: Cenepa River, Peru (Amazon Basin)

• Best kept in groups of 8 or more

🌊 Water Conditions

Red Pencil Fish are sensitive to water changes and thrive in soft, slightly acidic water that mimics their native blackwater habitat.

• Temperature: 24–28°C (75–82°F)

• pH: 5.0–6.8

• Hardness: 1–8 dGH

• Tank Size: 10 gallons minimum (preferably larger for schooling)

• Water Type: Freshwater

• Filtration: Gentle flow, sponge filters ideal

• Lighting: Low to moderate (highlight red colors best)

• Décor: Leaf litter, driftwood, botanicals, and dense plants provide natural cover and comfort

Adding Indian almond leaves or alder cones enhances water conditions and simulates the tannin-rich Cenepa environment.

🐟 Tank Mates

The Red Pencil "Cenepa" is a peaceful micro-predator that fits best in calm community tanks with small, non-aggressive fish.

Compatible tank mates:

• Ember or Neon Tetras

• Chili and Strawberry Rasboras

• Corydoras (dwarf species)

• Otocinclus

• Peaceful dwarf shrimp (e.g., Amano or Neocaridina)

• Snails

Avoid:

• Fast-moving or fin-nipping species

• Larger fish that may outcompete them or cause stress

• Aggressive tank mates

🍽️ Feeding Habits

Red Pencil Fish are micro-predators and appreciate a varied, protein-rich diet of small-sized foods.

Ideal diet includes:

• High-quality micro pellets

• Live or frozen foods: daphnia, baby brine shrimp, bloodworms

• Crushed freeze-dried options

• Microworms or cyclops for juvenile fish

Feed once or twice daily, offering tiny amounts they can eat within a few minutes.

🧼 Care and Maintenance

• Perform gentle weekly water changes (15–25%)

• Keep water parameters stable and soft

• Avoid strong flow; long, narrow tanks are ideal for their swimming behavior

• Use a soft sponge filter to preserve calm water conditions

• Provide plenty of plant cover and visual barriers to reduce stress

These fish do not tolerate poor water quality and should be added only to mature, well-maintained aquariums.

🌿 Why Choose the Red Pencil Fish "Cenepa"?

The Red Pencil Fish "Cenepa" is a breathtaking nano species perfect for aquarists seeking rare and vivid centerpiece fish for peaceful tanks. Their intense coloration, graceful movement, and compatibility with blackwater or planted aquascapes make them a standout species worth the extra care.

Bring a flash of red elegance to your tank—add the rare and radiant Red Pencil “Cenepa” to your collection today!