Care guide · Freshwater · fish
Three-lined pencilfish
Nannostomus trifasciatus
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Nannostomus trifasciatus is a slender South American pencilfish marked by three dark lateral stripes. It has a broad distribution in the western Amazon region and should be distinguished from similar pencilfish, including the smaller N. marginatus. Although only a few centimetres long, males spar territorially, so the aquarium needs adequate length and cover. The group is usually more secure when kept in numbers and the layout provides escape routes. Check identification at purchase because pencilfish trade names are sometimes used inconsistently.
Plan your aquarium →At a glance
- Temperature
- 22–28 °C
- pH
- 4.0–7.5
- GH
- 1–12 °dGH
- Aquarium length
- At least 75 cm
- Minimum aquarium volume
- At least 68 L
- Adult size
- At least 3.3 cm
- Group size
- At least 10 individuals
- Temperament
- Peaceful
About this species
The three dark stripes are a useful identification feature, but compare body shape and adult size as well: related species can look very similar in photographs. Seriously Fish gives about 3.3 cm standard length for aquarium planning; FishBase lists a maximum of 3.6 cm standard length. Standard length excludes the tail fin.Natural habitat
The species occurs across parts of Brazil, Peru, Colombia, Bolivia and Guyana in the western Amazon and adjacent drainages. Habitat descriptions are not equally species-specific throughout the range. Treat generalized accounts of calm, vegetated waters as context rather than a confirmed description for every population.Aquarium and layout
For a mixed-sex group, Seriously Fish recommends a base of at least 75 × 30 cm, roughly 68 litres. The space recommendation reflects sparring between males. Use dense plants, floating cover and wood to break sight lines, while leaving open midwater. Gentle flow and a biologically mature aquarium support stable conditions.Water conditions
The aquarium guidance is 22–28°C, pH 4–7.5 and GH 1–12 dGH. FishBase also lists narrower field information for pH and temperature; those data are not the same as a tested aquarium tolerance. Choose stable values appropriate to the fish’s provenance and make changes gradually rather than using rapid pH corrections.Behaviour and group size
The species is relatively peaceful, but shy and easily outcompeted by boisterous or much larger fish. Males may spar territorially; cramped conditions can cause injury. Keep ten or more where possible and select calm companions of similar size. Also consider swimming zone and feeding competition: fast surface fish can make food access difficult, especially in a smaller aquarium.Feeding
This micropredator feeds on small invertebrates and zooplankton. Offer small daily portions of live or frozen foods such as Artemia nauplii, Moina or grindal worms. Fine dry food may supplement the diet if the fish can eat its particle size. Check that subordinate fish also feed, and remove leftovers to protect water quality.Breeding
Breeding in a suitable aquarium is possible but requires preparation and should not be treated as automatic. Fine-leaved plants or a spawning mop provide cover around scattered eggs. Adults may eat eggs and larvae; remove them during a deliberate spawning attempt. Newly hatched fry need very small first foods.Sources & review
This care guide draws on several specialist sources and was last checked on .
View the sources
- California Academy of Sciences — Eschmeyer’s Catalog of Fishes — accepted name and authorship
- Seriously Fish — Nannostomus trifasciatus — aquarium care, group behaviour, space and diet
- FishBase — Nannostomus trifasciatus — taxonomy, distribution, size and ecology
- Aquarium Glaser — Nannostomus trifasciatus — specialist fish-trade overview