Description
At about 3.5 cm, the dwarf pencilfish is a lebiasinid from Guyana, Suriname and the middle and lower Amazon. It stays very popular, although its size and shyness rule it out as a community fish and make it moderately difficult: it asks for a mature tank with steady water.
It carries three dark stripes on the flank, and the males show neither red nor violet between them, unlike Nannostomus mortenthaleri and N. rubrocaudatus, whose males are reddish. Colour changes a lot between populations.
Behavior
Very peaceful and gregarious, and being small it does not compete with other fish. Best in a group of ten or more; there is hardly any fighting between males.
It lives well with peaceful characids of its size, corydoras and small loricariids; it also works as a dither fish for dwarf cichlids, since it moves in the middle and upper zones and does not prey on fry.
Avoid housing it with larger or active fish, which intimidate it.
Habitat
Nannostomus marginatus lives in slow creeks, minor rivers and marshy ground with dense vegetation, sunken wood and leaf litter, often in flooded forest and floodplain ponds. The water there is shallow and nearly still, with barely measurable hardness and a pH of 4 to 6.
It asks for mature, stable water, dense planting, a dark substrate and little current.
Pez lápiz enano is a schooling species, which means that in the wild it lives and moves in large, coordinated groups.
Keep at least 6 individuals so they feel comfortable and their stress level stays low.
Details
🌊 Water parameters
🐠 Minimum tank size
Breeding
It has been bred in aquariums, but seldom. To raise fry a separate tank is set up with mature water, filled with wool mops or fine moss, without strong filtration or light; one or several pairs go in, the adults come out two or three days later, and the first fry appear soon after.
Males are less stocky than females.
Diet
A micropredator of tiny invertebrates.
- Staple: very small dry food.
- Supplement: brine shrimp nauplii or grindal worm, live or frozen, daily.
Portions are tiny because of its mouth size.
What about your tank?
Enter your tank's values to see only the compatible species that fit them. Litres apply to fish.
Compatible fish
General guidance based on water parameters, behaviour and known exceptions; always review the individual animals' and aquarium's specific needs.
They share water: pH 6–7.5 and 24–28 °C.
They share water: pH 7–7.5 and 26–28 °C.
They share water: pH 6–7.5 and 22–27 °C.
They share water: pH 6–7.5 and 22–27 °C.
They share water: pH 6–7.5 and 22–27 °C.
They share water: pH 6–7.5 and 24–28 °C.
They share water: pH 5.5–7 and 24–27 °C.
They share water: pH 6–7.5 and 22–26 °C.
They share water: pH 5.5–7.5 and 22–28 °C.
They share water: pH 6–7.5 and 24–28 °C.
They share water: pH 6–7.5 and 25–28 °C.
They share water: pH 6–7.5 and 24–28 °C.
They share water: pH 6.5–7.5 and 24–26 °C.
They share water: pH 6–7.5 and 22–26 °C.
They share water: pH 6–7.5 and 22–25 °C.
They share water: pH 6–7.5 and 24–28 °C.
They share water: pH 6.5–7.5 and 22–24 °C.
They share water: pH 5–7 and 27–28 °C.
They share water: pH 7–7.5 and 22–28 °C.
They share water: pH 6.5–7.5 and 22–28 °C.
They share water: pH 6–7.5 and 25–28 °C.
They share water: pH 6–7.5 and 22–28 °C.
They share water: pH 6–7.5 and 22–28 °C.
They share water: pH 6–7.5 and 24–28 °C.
They share water: pH 6–7.5 and 24–27 °C.
They share water: pH 5.5–7 and 24–28 °C.
They share water: pH 7.5 and 24–28 °C. They only meet at the very edge, so the tank has to hold that value.
They share water: pH 7.5 and 24–28 °C. They only meet at the very edge, so the tank has to hold that value.
They share water: pH 5.5–7 and 22–26 °C.
They share water: pH 4–6.5 and 23–27 °C.
They share water: pH 6.5–7.2 and 22–26 °C.
They share water: pH 6–7.5 and 22–26 °C.
They share water: pH 6–7.5 and 22 °C. They only meet at the very edge, so the tank has to hold that value.
They share water: pH 6.5–7.5 and 22–24 °C.
They share water: pH 4.5–7.5 and 22–28 °C.
They share water: pH 4–7 and 23–28 °C.
They share water: pH 5–7.5 and 22–27 °C.
They share water: pH 7–7.5 and 22–27 °C.
They share water: pH 5.5–7 and 26–28 °C.
They share water: pH 5.5–7 and 22–26 °C.
They share water: pH 6.5–7.5 and 22–26 °C.
They share water: pH 4.5–6.5 and 24–28 °C.
They share water: pH 5.5–7 and 23–28 °C.
They share water: pH 5–7.5 and 23–27 °C.
They share water: pH 5.5–7.5 and 23–28 °C.
They share water: pH 5.5–7.5 and 24–28 °C.
They share water: pH 6–7.5 and 22–26 °C.
They share water: pH 5.5–7.5 and 23–27 °C.
They share water: pH 5.5–7.5 and 22–27 °C.
They share water: pH 7–7.5 and 22–28 °C.
Compatible invertebrates
General guidance based on water parameters, behaviour and known exceptions; always review the individual animals' and aquarium's specific needs.
They share water: pH 7–7.5 and 22–28 °C.
They share water: pH 5.5–6.5 and 22–24 °C.
They share water: pH 6.5–7.5 and 22–27 °C.
They share water: pH 7–7.5 and 22–25 °C.
They share water: pH 7.5 and 24–28 °C. They only meet at the very edge, so the tank has to hold that value.
They share water: pH 7–7.5 and 22–28 °C.
They share water: pH 7.5 and 26–28 °C. They only meet at the very edge, so the tank has to hold that value.
They share water: pH 7–7.5 and 22–28 °C.
They share water: pH 6.5–7.5 and 22–26 °C.
They share water: pH 5.8–6.8 and 22–24 °C.
They share water: pH 5.8–6.8 and 22–24 °C.
They share water: pH 6.5–7.5 and 22–27 °C.
They share water: pH 7.5 and 27–28 °C. They only meet at the very edge, so the tank has to hold that value.
They share water: pH 7–7.5 and 22–28 °C.
They share water: pH 6.5–7.5 and 22–26 °C.
They share water: pH 6.5–7.5 and 22–26 °C.
They share water: pH 6.5–7.5 and 22–26 °C.
They share water: pH 6.5–7.5 and 22–26 °C.
They share water: pH 6.5–7.5 and 22–26 °C.
They share water: pH 6.5–7.5 and 22–26 °C.
They share water: pH 7–7.5 and 22–28 °C.
They share water: pH 7–7.5 and 22–28 °C.
They share water: pH 6.5–7.5 and 22–28 °C.
They share water: pH 7–7.5 and 22–28 °C.
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They share water: pH 7–7.5 and 22–28 °C.
Sources
- FishBaseFroese, R. and D. Pauly. Editors. 2026. FishBase. World Wide Web electronic publication.
- Seriously FishSeriously Fish. Nannostomus marginatus. Ficha de especie; consultada 2026-10.
Water: FishBase gives pH 5.8-7.5, up to 15 dH and 24-26 °C; Seriously Fish, pH 4-7, 1-10 dGH and 22-28 °C. The profile uses the widest range. Size: 3.5 cm TL in FishBase and 2.5 cm SL in Seriously Fish; the larger is taken.
Litres per fish and minimum tank height and depth: the profile's own judgement. Seriously Fish gives only the tank base and FishBase gives no tank sizes.
Plan your next aquarium
Is this fish right for you? Plan a suitable aquarium before setting it up.