Nannostomus mortenthaleri – Coral Red Pencilfish

Nannostomus mortenthaleri, commonly called the Coral Red Pencilfish, is one of the most vibrant and sought-after nano fish in the aquarium hobby. Native to Peruvian Amazon tributaries, this species is admired for its intense red coloration, slender body shape, and elegant swimming behavior.

Unlike many other small fish, the Coral Red Pencilfish has a distinctive pencil-like body form with horizontal dark markings that contrast beautifully against its red body. Males usually display deeper red coloration and darker patterns, making them especially striking in well-maintained aquariums.

This species thrives in planted aquariums and aquascapes, where the combination of lush greenery and soft lighting enhances their brilliant coloration. When kept in groups, they display interesting social interactions and add a unique visual element to the upper levels of the aquarium.

Because of their peaceful nature and small size, Nannostomus mortenthaleri is an excellent choice for nano community aquariums and is often kept alongside other calm nano fish and shrimp.

Key Features

• Popular Coral Red Pencilfish species

• Intense red body coloration with dark markings

• Slender pencil-shaped body

• Peaceful and suitable for nano aquariums

• Ideal for planted tanks and aquascapes

• Interesting schooling and social behavior

Size

• Adult size: 2.5 – 3 cm

• Juveniles: typically 1 – 1.5 cm when sold

• Slim and lightweight body structure

Temperament

Nannostomus mortenthaleri is generally peaceful but slightly more active than other pencilfish.

• Best kept in groups of 6–10 or more

• Males may display mild territorial behavior toward each other

• Non-aggressive toward other species

• Often swims in the upper to mid-water levels

Keeping a proper group helps reduce territorial displays and encourages natural behavior.

Water Conditions

Stable water conditions help maintain their vibrant coloration and health.

• Temperature: 24 – 28°C (75 – 82°F)

• pH: 5.5 – 7.0

• GH: 1 – 8 dGH

• Ammonia/Nitrite: 0 ppm

• Nitrate: < 20 ppm

Regular 20–30% weekly water changes are recommended.

Tank Setup

Coral Red Pencilfish prefer aquariums with plants and gentle water movement.

Recommended setup includes:

• Dense aquatic plants such as stem plants and moss

• Floating plants to diffuse lighting

• Driftwood and natural décor

• Open swimming areas near the surface

• Soft lighting to enhance coloration

Minimum recommended tank size: 40 liters (~10 gallons) for a small group.

Feeding Habits

Nannostomus mortenthaleri are omnivores that prefer small foods.

Diet can include:

• Micro pellets or crushed flakes

• Baby brine shrimp

• Daphnia and cyclops

• Frozen micro foods

Feed 1–2 times daily in small portions suitable for nano fish.

Tank Mates

This species does well in peaceful community aquariums.

Suitable tank mates:

• Ember tetras

• Chili rasboras

• Small tetras

• Corydoras pygmaeus

• Otocinclus

• Shrimp and snails

Tank mates to avoid:

• Large fish that may prey on them

• Aggressive or fin-nipping species

Care and Maintenance

To keep Coral Red Pencilfish healthy:

• Maintain stable water parameters

• Keep them in groups for social stability

• Provide planted areas and shaded zones

• Perform regular water changes

• Feed small high-quality foods

With proper care, Nannostomus mortenthaleri can live 4–5 years in captivity.

Why Choose Nannostomus mortenthaleri?

• One of the most colorful nano fish species

• Unique pencil-shaped body

• Ideal for planted aquariums and aquascapes

• Peaceful and community friendly

• Adds vibrant red color to nano tanks

Nannostomus mortenthaleri is a stunning nano fish that brings elegance, color, and natural behavior to planted aquariums. Its vivid red coloration and graceful swimming make it a favorite among aquascapers and nano fish enthusiasts. 🐟🌿