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Dwarf Pencilfish
Nannostomus marginatus
Animalia›Chordata›Actinopterygii›Lebiasinidae
📍 Guyana & Surinam, South America
One of the smallest pencilfish species, featuring three bold black horizontal stripes with a red accent between them. Perfect for nano and planted tanks. Males develop more intense red colouration and spar gently for territory.
Care Guide
Diet
Dwarf Pencilfish are omnivores requiring small, high-quality micro foods. Feed a varied diet of micro pellets, crushed flakes, and small frozen foods like brine shrimp and daphnia once daily in small portions. Supplement occasionally with live foods such as copepods or infusoria, which they naturally consume in planted tanks.
Behavior
These tiny, peaceful fish are schooling species that exhibit their best colors and behavior when kept in groups of at least 6. They are active mid-water swimmers with a gentle temperament, spending much of their time grazing and exploring dense vegetation. They display characteristic horizontal striping and may show subtle color changes based on mood and lighting conditions.
Breeding
Breeding in captivity is possible but challenging and rarely achieved by hobbyists. They require very soft, acidic water (pH 5.5-6.5), dense vegetation for egg scattering, and pristine water conditions. Fry are extremely small and require infusoria or liquid fry food; parents do not guard eggs, making successful breeding difficult without dedicated breeding tanks.
Tank Mates
Similar size, peaceful temperament, and preference for planted tanks with soft water
Comparable size and water parameters; both thrive in densely planted nano aquariums
Peaceful invertebrates that share similar water preferences; pencilfish may occasionally nip at shrimp
Peaceful community fish with overlapping temperature range, though larger and may intimidate pencilfish
Common Diseases
Ich (Ichthyophthirius multifiliis)
White spots on body and fins, rapid breathing, lethargy, rubbing against plants
Raise temperature gradually to 28-30°C, perform daily 25% water changes, use aquarium salt (1 teaspoon per 5 gallons) or ich medication; treat for 10-14 days
Fin Rot
Frayed or deteriorating fins, discoloration at fin edges, lethargy
Improve water quality with frequent partial water changes, maintain stable parameters, use antibacterial medication if severe; ensure good filtration and avoid overcrowding
Neon Tetra Disease (Pleistophora)
Loss of coloration, curved spine, lethargy, erratic swimming behavior
No cure exists; isolate affected fish to prevent spread, maintain excellent water quality, and consider humane euthanasia if severely affected
Bacterial Infection
Cloudy eyes, open sores, torn fins, loss of appetite
Perform 50% water change immediately, treat with broad-spectrum antibiotic medication, maintain pristine water conditions, and isolate if possible
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Quick Facts
- diet
- Micro omnivore – micro pellets, baby brine shrimp, crushed flake
- lifespan
- 3–5 years
- max size
- 3.5 cm (1.4 in)
- tank size
- 5 gallons minimum
- school size
- 8+
- temperament
- Peaceful, schooling
Water it likes
- ph
- 5.0–7.0
- ammonia
- 0 ppm
- nitrate
- <20 ppm
- hardness
- 1–8 dGH
- temperature
- 73–82°F (23–28°C)