One-lined Pencilfish
Nannostomus sp.
The One-lined Pencilfish (Nannostomus sp.) is a peaceful fish that's rewarding to keep. Give it a tank of at least 65 litres (17 US gallons), water held at 73-82°F, and a pH of 6.5-7.5.
Captive lifespan reflects typical experience in a home aquarium, not maximum recorded age; genetics, sourcing, and care vary.
Natural distribution
South America
- South America
Regional colours match the stocking calculator's origin map.
One-lined Pencilfish Tank Setup
A tank of at least 65 litres (17 US gallons) works well. Keep the water at 73-82°F with a pH around 6.5-7.5, and set up both cover and open swimming space where they spend most of their time (Mid).
What Do One-lined Pencilfish Eat?
They're not fussy eaters - feed a varied diet, rotating good-quality dry, frozen, and gel foods rather than the same thing every day, and match the food size to their mouths.
One-lined Pencilfish Tank Mates
The One-lined Pencilfish is peaceful, which is the first thing to weigh up when you choose tank mates. Good matches come down to the whole stocking list working together - temperature, tank size, and temperament - not any single label. Before you buy, run your full stocking list through our stocking calculator. It weighs temperament, adult size, and water needs together, which a single species page can't do on its own.
Are One-lined Pencilfish Good for Beginners?
Care demand varies by line and setup. Match the care level to how often you actually test and change water.
One-lined Pencilfish - frequently asked questions
What size tank do One-lined Pencilfish need?
One-lined Pencilfish need a tank of at least 65 litres (17 US gallons). A bigger tank is always easier to keep stable, and gives them more room to settle in and behave naturally.
What water parameters do One-lined Pencilfish need?
Keep them at 73-82°F with a pH of 6.5-7.5, steady rather than chased to an exact figure. In a cycled tank, ammonia and nitrite should both read 0 ppm, with nitrate kept low through regular water changes.
What do One-lined Pencilfish eat?
One-lined Pencilfish are omnivores and aren't fussy eaters. Feed a varied mix of good-quality dry, frozen, and gel foods, and match the food size to their mouths. Feed small amounts once or twice a day, and remove anything they don't eat.
Are One-lined Pencilfish good for beginners?
It depends on the setup. Match One-lined Pencilfish to how often you actually test water and perform maintenance.
Building a community? Run the full list through the stocking calculator before you add anything else.
Great tank mates
Chosen from temperament, overlapping temperature/pH bands, plausible minimum tank footprints, and size versus yours in App-aquatic data. Hobby nuance always wins - verify stocking and temperament before purchasing.
Fish to avoid mixing with One-lined Pencilfish
These well-known species are commonly sold alongside this fish but are not recommended tank mates - verify before purchasing.
- OscarPredator - Oscar will eat or injure smaller tank mates
- Pea PufferPredator - Pea Puffer will eat or injure smaller tank mates
- Betta (Male)Predator - Betta (Male) will eat or injure smaller tank mates
