Pencilfish Care Guide
Pencilfish (genus Nannostomus) are slender, peaceful South American nano fish that bring subtle color and gentle movement to a planted tank. Their pencil-thin bodies, often striped with red and gold, make them a favorite for aquascapes and nano aquariums. We carry several species, including the Golden Pencilfish, the Beckford's Red Pencilfish, the Purple Pencilfish, and the striking Peruvian Red Pencilfish. One honest note up front: pencilfish are small, gentle, and a little shy, so they do best in calm tanks with a tight group and plenty of cover rather than busy community setups.
Meet the Pencilfish
Pencilfish are members of the family Lebiasinidae, native to slow, soft, tannin-stained waters of the Amazon basin. Most species top out around 1 to 2.5 inches, putting them firmly in the nano fish category alongside small tetras. A fun quirk: many pencilfish change their coloration at night, with the horizontal daytime stripe breaking up into a blotchy "sleeping" pattern. They are true schooling fish that feel secure and color up best when kept in groups, so they reward an aquarist who plans around their gentle nature.
Tank Size and Setup
A group of pencilfish is comfortable in a 10-gallon tank, and a 20-gallon long gives them more room to school and display. Because they are small and a little timid, the setup matters as much as the size. Aim for a heavily planted tank with floating plants to diffuse the light and make them feel safe; pencilfish often hang near the surface and appreciate the cover overhead. A dark substrate makes their colors pop, and a gentle filter is important because they are weak swimmers that dislike strong current. Low-light plants pair nicely with their preference for subdued lighting. Always keep a lid on, as they can be jumpy.
Water Parameters and Heating
Pencilfish are tropical and prefer warm water of 75-82°F, so a reliable aquarium heater is essential. They naturally come from soft, acidic blackwater and look their best at a pH between 6.0 and 7.0, though tank-raised stock adapts to slightly harder water. What matters most is stability and pristine water quality: cycle the tank fully using the nitrogen cycle before adding fish, treat tap water with a water conditioner, and keep up with small regular water changes using your maintenance supplies. Adding driftwood or botanicals to gently tint the water can encourage their richest coloration.
Feeding Your Pencilfish
Pencilfish have small, upturned mouths, which is the single most important thing to keep in mind at feeding time: they can struggle with large foods. Offer finely crushed flakes, micro-pellets, and small prepared foods sized for tiny mouths. They especially relish small live and frozen foods like baby brine shrimp, daphnia, and microworms, which bring out their best color and breeding condition. Because they feed near the top and middle of the water column, choose foods that stay in suspension rather than sinking quickly, and feed small amounts a couple of times a day.
Tankmates and Temperament
Pencilfish are among the most peaceful fish you can keep, which is both their charm and their main limitation. They should be housed with other calm, similarly sized species and never with anything large, boisterous, or fin-nipping that will outcompete them for food or stress them out. Excellent companions include small tetras, corydoras catfish, and peaceful dwarf shrimp (adult shrimp are generally safe with these small-mouthed fish). Keep pencilfish in a group of at least 6, and ideally 8 or more, so they school, feel secure, and spend less time hiding. In too small a group they become withdrawn and pale.
Breeding Pencilfish
Pencilfish can be bred at home, though it takes a bit of planning. They are egg scatterers that show no parental care and will readily eat their own eggs, so a dedicated breeding setup gives the best results. Condition a group on live and frozen foods, then provide fine-leaved plants, spawning mops, or a mesh barrier so the eggs fall out of reach. Soft, slightly acidic, dimly lit water encourages spawning. Remove the adults after eggs are laid, and feed the tiny fry infusoria and then baby brine shrimp once they are free-swimming. It is a rewarding project for a patient nano-fish keeper.
Is the Pencilfish Right for You?
Pencilfish are perfect if you want a calm, elegant schooling fish for a planted nano tank or a peaceful community of small species. They are not the right fit for a busy tank full of fast, larger, or aggressive fish, where they will hide and struggle to eat. If you can offer a gentle, well-planted home and a proper group, they are hardy and long-lived. For more ideas, see our guides on the best nano fish for planted tanks and the best beginner fish. When you are ready, browse our available species in the nano fish collection.
Frequently Asked Questions
How many pencilfish should I keep together? Keep at least 6, and ideally 8 or more. They are schooling fish that color up, feel secure, and behave more naturally in a larger group.
Are pencilfish good for beginners? They are peaceful and fairly hardy, but their small mouths, shy nature, and preference for stable, clean water make them best for beginners willing to set up a calm, planted tank.
Do pencilfish need a heater? Yes. They are tropical fish that prefer 75-82°F, so a reliable heater is needed to keep them healthy and well colored.