One-lined Pencilfish

Nannostomus sp.

One-lined Pencilfish (Nannostomus sp.) — Varies care, Peaceful, under Other. Minimum tank in the app: 17.2 US gal min; aim for 73–82°F and pH 6.5–7.5. The One-lined Pencilfish is a captivating choice for aquarists seeking a small, mid-water fish with a unique profile.

One-lined Pencilfish (Nannostomus sp.) in a planted freshwater aquarium
Care levelVaries
TemperamentPeaceful
Min tank size17.2 US gal min
pH range6.5–7.5
Temperature73–82°F
Max size1.6 in (4.0 cm)
Captive lifespan5–10 years
SchoolingNo

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

Aim for a 65L tank with a balance of open swimming space and ample hiding spots, such as plants and driftwood. A gentle water flow will encourage natural behaviour, and softer substrates will help reduce stress during movement. Lighting should be moderate to highlight their colors without causing undue stress, creating a comfortable atmosphere for these mid-water swimmers.

What Do One-lined Pencilfishs Eat?

As omnivores, they adapt well to a variety of diets but prefer smaller, high-quality pellets or flakes. Feeding speed is moderate, so watch for competition; faster or larger fish may outcompete them, affecting their health.

One-lined Pencilfish Tank Mates

Ideal tank mates include similarly sized, non-aggressive species that share the mid-zone, such as small tetras or rasboras. Avoid larger or overly active fish that may intimidate them. Intraspecies aggression can be mitigated by providing sufficient cover and space, as they are less territorial when they feel secure in their environment.

Are One-lined Pencilfishs Good for Beginners?

Care demand varies with setup and individual fish; use the numbers above as your baseline. A frequent oversight is underestimating their need for both space and cover; inadequate setups can lead to stress and aggression, especially if housed with more dominant species. neglecting water quality and parameters can exacerbate health issues, resulting in a decline in their vibrant appearance and activity levels.

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