Coral Red Pencilfish: A Comprehensive Care Guide (Nannostomus mortenthaleri)
The Coral Red Pencilfish (Nannostomus mortenthaleri) is one of the most colorful and striking species in the pencilfish family. Native to South America, this small fish is prized by aquarists for its intense red coloration and bold black striping.
Often called the Coral Red Pencilfish, this species displays vibrant red tones along the body that contrast beautifully with dark horizontal bands. When kept in groups, their coloration becomes even more impressive, creating a vivid display in planted aquariums.
Because of their small size and peaceful nature, Coral Red Pencilfish are excellent fish for nano aquariums and community tanks with other small species.
Natural Habitat and Distribution
Coral Red Pencilfish originate from South America, particularly within parts of the upper Amazon basin in Peru.
In the wild they inhabit:
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Small forest streams
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Blackwater tributaries
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Flooded forest areas
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Slow-moving waterways with leaf litter and dense vegetation
These environments typically feature soft, acidic water and subdued lighting created by forest canopy.
Size
Adult size: approximately 1–1.2 inches (2.5–3 cm)
Coral Red Pencilfish remain small throughout their lives, making them ideal for nano aquariums and planted tanks.
Tank Size
Minimum tank size: 10 gallons
Recommended tank size: 15–20 gallons
Coral Red Pencilfish should be kept in groups of at least 6–8 individuals, though larger groups often produce more natural behavior and brighter coloration.
Providing a longer aquarium allows them to swim comfortably and interact with other members of the group.
Water Parameters
Coral Red Pencilfish prefer stable water conditions similar to their natural habitat.
Temperature: 74–82°F
pH: 4.5–6.8
Hardness: very soft to soft
Clean water and stable parameters are important for maintaining their health and coloration.
Aquarium Setup
A planted aquarium with natural elements works very well for Coral Red Pencilfish.
Recommended tank features include:
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Dense aquatic plants
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Floating plants to diffuse lighting
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Driftwood and botanicals
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Dark substrate
These features help replicate their natural blackwater environment and make their red coloration stand out.
Diet
Coral Red Pencilfish are omnivorous micro-predators that feed on very small foods.
In the aquarium they will accept:
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High-quality nano pellets
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Crushed flakes
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Frozen foods such as baby brine shrimp or daphnia
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Small live foods
Because of their tiny mouths, food should be finely sized.
Behavior and Temperament
Coral Red Pencilfish are peaceful and relatively calm fish.
Typical behaviors include:
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Swimming near the surface and middle levels of the aquarium
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Loose group formation rather than tight schooling
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Gentle interaction with tank mates
Males may occasionally display toward each other but rarely cause harm.
Tank Mates
Due to their small size, Coral Red Pencilfish should be kept with other peaceful nano fish.
Good tank mates include:
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Ember tetras
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Small rasboras
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Corydoras
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Dwarf shrimp
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Other pencilfish species
Avoid larger or aggressive fish that may prey on them.
Breeding
Coral Red Pencilfish are egg-scattering fish that may spawn in well-planted aquariums.
During spawning:
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Eggs are scattered among plants or moss
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Adults do not guard the eggs
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Eggs typically hatch within 24–48 hours
The fry are extremely small and should initially be fed infusoria or powdered fry foods before transitioning to baby brine shrimp.
Fun Facts
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Coral Red Pencilfish are sometimes considered one of the most colorful pencilfish species available in the hobby.
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Their bright red coloration becomes especially vivid in aquariums with dark substrates and plants.
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Males often show more intense coloration than females.
Conclusion
The Coral Red Pencilfish (Nannostomus mortenthaleri) is a beautiful and peaceful nano fish that thrives in planted aquariums and small community tanks. Their brilliant red coloration and gentle swimming behavior make them a favorite among aquascaping enthusiasts. With proper care and stable water conditions, Coral Red Pencilfish can become a stunning addition to freshwater aquariums.
Looking to Add Fish to Your Aquarium?
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