The Care and Keeping of Nannostomus eques in the Home Aquarium
A Comprehensive Guide to the Diptail Pencilfish
Nannostomus eques, commonly known as the Diptail Pencilfish or Brown Pencilfish, is a captivating and delicate addition to the freshwater aquarium, adored for its slender form, unique oblique swimming posture, and subtle iridescence. Native to the slow-moving, tannin-rich waters of South America, particularly the Amazon Basin, these fascinating fish are both a delight and a gentle challenge for aquarists. In this guide, we’ll explore every facet necessary to ensure the thriving of Nannostomus eques in your aquarium, from tank setup and water chemistry to feeding, social structure, and breeding.
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| Nannostomus eques (shutterstock.com) |
1. Natural Habitat and Behavior
To keep Nannostomus eques healthy, it is essential to emulate their natural environment. In the wild, these fish inhabit calm blackwater streams and floodplain lakes, often shaded by overhanging vegetation and littered with leaf debris. The water is soft, acidic, and stained a tea-like hue by dissolved tannins from fallen leaves and roots.
Nannostomus eques are famous for their distinctive oblique swimming position, holding their bodies at a 45-degree angle with their snouts pointed upwards. This posture, paired with their peaceful temperament, makes them an intriguing species for both novice and experienced aquarists.
2. Aquarium Setup
Tank Size
Although Pencilfish are small (typically 3 to 4 cm in length), they are active swimmers and should be kept in groups. A minimum tank size of 60 liters (about 15 gallons) is recommended for a small shoal of 8-10 individuals. Larger tanks provide more stable water parameters and allow for more natural behavior.
Aquascaping and Decor
Recreate their native blackwater environment by using a dark, sandy or fine-grained substrate. Scatter dried Indian almond leaves (Catappa leaves), beech, or oak leaves across the bottom to release tannins and offer hiding spots. Incorporate driftwood, twisted roots, and branching branches to provide cover and mimic submerged roots.
Dense planting, especially with floating plants like Amazon frogbit or water lettuce, helps diffuse the aquarium’s lighting and offers the shade these fish appreciate. Open swimming areas should still be available, as Nannostomus eques enjoy exploring the mid and upper water columns.
Lighting
Moderate to subdued lighting is ideal. Bright lights can stress these fish, making them reclusive and less likely to display their natural behaviors and colors.
Filtration and Water Movement
Use a gentle filter, such as a sponge filter or a hang-on-back filter with a pre-filter sponge. These fish are not found in turbulent waters, so avoid strong currents. The filter should efficiently maintain water cleanliness without producing excessive flow.
3. Water Parameters
• Temperature: 24–28°C (75–82°F)
• pH: 5.0–7.0, with slightly acidic water being ideal
• Hardness: 1–8 dGH (very soft to moderately soft)
• Ammonia and Nitrite: 0 ppm (these compounds are highly toxic to Pencilfish)
• Nitrate: <20 ppm
Weekly partial water changes (20–30%) are crucial to maintain high water quality. Use dechlorinated, temperature-matched water to avoid shocking the fish. If your tap water is hard or alkaline, consider using reverse osmosis water and remineralizing as needed.
4. Social Structure and Tankmates
Nannostomus eques are shoaling fish and must be kept in groups of at least 8, though 10-15 is preferable for natural schooling and reduced stress. When kept solitary or in too-small groups, they become timid and may lose their color.
• Other small pencilfish species (e.g., Nannostomus beckfordi, Nannostomus marginatus)
• Small tetras (e.g., Ember, Neon, or Cardinal Tetras)
• Small rasboras (e.g., Boraras brigittae)
• Dwarf catfish (Corydoras pygmaeus, Corydoras hastatus)
• Otocinclus catfish
• Dwarf shrimp (Neocaridina or Caridina species)
Avoid aggressive or much larger fish, as well as fin-nippers like some barbs and danios. Nannostomus eques can be bullied or stressed by boisterous tankmates.
5. Feeding and Nutrition
• Staple foods: High-quality micro pellets or flakes designed for small tropical fish.
• Frozen/live foods: Daphnia, baby brine shrimp, microworms, and cyclops are excellent choices for regular feeding.
• Occasional treats: Finely chopped bloodworms or tubifex worms (use sparingly).
Feed small amounts 2–3 times daily, offering only what they can consume in a few minutes. Uneaten food should be promptly removed to prevent water quality degradation.
6. Health and Disease Prevention
Nannostomus eques are sensitive to poor water quality. Maintain a consistent cleaning schedule, avoid overfeeding, and ensure the tank is fully cycled before introducing new fish. Quarantine new arrivals for at least two weeks to prevent introducing parasites or diseases.
• Ich (white spot disease): Treated with temperature elevation and aquarium-safe medications.
• Fin rot and fungal infections: Result from poor water quality; improve conditions and use appropriate treatments.
• Stress: Main causes are poor water quality, incompatible tankmates, or improper group sizes.
Observing your fish daily and responding quickly to behavioral changes is key to early treatment and long-term health.
7. Breeding Nannostomus eques
While breeding in captivity can be challenging, it is possible with proper conditioning and setup.
Conditioning
Feed the group a protein-rich diet, including live and frozen foods, to bring them into breeding condition. Males will display more vibrant colors.
Breeding Tank Setup
Set up a separate 10–20 liter tank with soft, acidic water, fine-leaved plants or spawning mops, and very gentle filtration. Add a mesh or marbles at the bottom to prevent adults from eating the eggs.
Spawning
Pairs or small groups should be introduced in the evening. Spawning typically occurs in the early morning, with females scattering adhesive eggs among the plants. Adults should be removed after spawning to prevent predation of the eggs.
Eggs hatch in about 24–36 hours, and fry become free-swimming after another 4–5 days. Feed fry with infusoria or liquid fry food initially, graduating to baby brine shrimp as they grow.
8. Special Considerations
• Acclimatization: Take extra care when introducing Nannostomus eques to a new tank. Use a slow drip acclimation process to prevent shock from water chemistry differences.
• Observation: These fish are subtle in their behaviors. Watch for signs of stress, such as hiding, faded color, or clamped fins, and address issues promptly.
9. Conclusion
Nannostomus eques is a beautiful and rewarding species for the aquarist willing to provide a naturalistic, peaceful, and well-maintained aquarium. With careful attention to water quality, social needs, and nutrition, Diptail Pencilfish can thrive and display their fascinating behaviors, adding an understated elegance to any freshwater community tank. Their unique swimming style and gentle presence make them an enchanting choice for aquarists aiming to recreate a slice of Amazonian tranquility in their own home.