Red Pencil Tetra

Species Profile

• Scientific Name: Nannostomus mortenthaleri
• Common Name: Red Pencil Tetra, Coral Red Pencilfish
• Adult Size: Up to 1.2 inches (3 cm)
• Life Expectancy: 3 to 5 years
• Habitat: Native to slow-moving, blackwater tributaries in Peru (Amazon River Basin); prefers densely vegetated areas with leaf litter and soft, acidic water

Tank Requirements

• Minimum Tank Size: 10 gallons (38 liters) for a small group
• Ideal Temperature: 75°F to 82°F (24°C to 28°C)
• pH Range: 5.5 to 7.0
• Water Hardness: 1 to 8 dGH

• Temperament: Peaceful but can be slightly territorial among males; best kept in groups of 6 or more with more females than males to reduce aggression

Diet & Nutrition

• Omnivorous: Yes
  Eats small food items such as:

  • High-quality micro pellets and flakes
  • Live or frozen foods like daphnia, baby brine shrimp, and micro worms
  • Occasional finely chopped vegetables or algae-based foods

Appearance

• Coloration: Vibrant red body with subtle horizontal striping; more intense coloration in males
• Fins: Clear to reddish fins with minimal markings
• Size/Form: Slender, elongated body resembling a pencil (hence the name)

Distinctive Features

• Males display brilliant coral red coloration, especially when courting or in ideal conditions
• Peaceful nature makes them suitable for nano and community aquariums
• Sensitive to water quality—requires stable, clean, and soft water
• Prefers dim lighting and planted tanks with dark substrates to show best coloration