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One-Lined Pencilfish
Nannostomus unifasciatus
📍 South America
The One-Lined Pencilfish is a slender, peaceful nano fish native to South American blackwater streams, characterized by a single dark horizontal stripe running the length of its body. These tiny fish are excellent for planted nano tanks and community setups, displaying graceful, deliberate swimming patterns. They are best kept in small schools and thrive in soft, acidic water conditions.
Care Guide
Diet
One-Lined Pencilfish are micropredators that feed on small live foods such as infusoria, micro worms, and newly hatched brine shrimp. Supplement with high-quality micro pellets and finely crushed flake food. Feed small amounts 2-3 times daily, offering only what they can consume in a few minutes.
Behavior
These fish are shy, peaceful schoolers that spend most of their time in the middle water column, often hovering near plants. They exhibit a characteristic head-down posture when at rest and are most active during low-light periods. They should never be kept singly, as they become stressed and hide constantly without companions.
Breeding
One-Lined Pencilfish are egg scatterers that breed readily in well-established, heavily planted tanks with soft, acidic water. Breeding pairs will scatter eggs among fine-leaved plants; remove adults after spawning to prevent egg predation. Fry are extremely small and require infusoria or liquid fry food for the first week.
Tank Mates
Similar size, peaceful temperament, and water parameter requirements
Comparable nano fish with matching care needs and peaceful behavior
Peaceful bottom dweller that won't compete for food or space
Provides shelter and natural environment without competing
Peaceful invertebrate that occupies different ecological niche
Provides essential cover and natural habitat structure
Common Diseases
Ich (Ichthyophthirius multifiliis)
White spots on body and fins, flashing against objects, rapid breathing, lethargy
Raise temperature gradually to 28-30 C (82-86 F), perform daily 25% water changes, use aquarium salt at 1 teaspoon per 5 gallons, or treat with copper-free ich medication
Fin Rot
Frayed or deteriorating fins, discoloration at fin edges, lethargy, loss of appetite
Perform 50% water change immediately, improve water quality, reduce stocking density, treat with antibacterial medication or salt baths
Bacterial Infection
Cloudy eyes, open sores, torn fins, loss of appetite, color fading
Isolate affected fish, perform frequent water changes, treat with broad-spectrum antibiotic medication, maintain optimal water parameters
Parasitic Infection
Excessive scratching, visible parasites, weight loss, clamped fins, lethargy
Quarantine affected fish, treat with anti-parasitic medication, perform daily water changes, maintain elevated temperature if tolerated
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Quick Facts
- diet
- omnivore - small live foods and high-quality micro pellets
- lifespan
- 3-5 years
- max size
- 3.5 cm (1.4 in)
- tank size
- 10 gallons minimum
- temperament
- peaceful
Water it likes
- ph
- 5.5-7.0
- ammonia
- 0 ppm
- nitrate
- <20 ppm
- hardness
- 2-8 dGH
- temperature
- 72–79°F (22–26°C)