Dwarf pencilfish
Nannostomus marginatus
FreshwaterFish
Care at a glance
- Temperature
- 72–82°F
- 22–28°C
- pH
- 5.0–7.0
- Adult size
- 1 in
- 2.5 cm
- Minimum tank
- 12 gal
- 45 L
- Temperament
- Peaceful
- Social behavior
- Shoaling
- Swim level
- Middle
- Difficulty
- Medium
- Breeding
- Medium
- Rarity
- Rare
- Family
- Lebiasinidae
- Origin
- Peru, Colombia, Brazil
Overview
Keep dwarf pencilfish in a group of at least six, in a tank of around 45 liters or more. They hold the middle of the water and move in a slow, deliberate way rather than darting. Their mouths are tiny, so feed small foods like crushed flakes, micro-pellets, baby brine shrimp, and daphnia. They are peaceful and best matched with other small, calm fish in soft, acidic water.
In the wild
Dwarf pencilfish live in slow, heavily planted blackwater across Peru, Colombia, and Brazil, in streams and flooded forest with leaf litter underfoot. The water is soft, acidic, and dark with tannins. A tank with dim lighting, fine plants, driftwood, and dried leaves suits them, with a pH on the low side, down toward 5 to 7. Keep flow gentle and the water warm.
Good to know
This is a pencilfish in the family Lebiasinidae, one of the smaller species at around 2.5 cm. The slim body carries a dark horizontal stripe with bordering lines and red on the fins. It is an egg scatterer, and breeding takes some effort. It does best in warm, soft, acidic water in the mid to high 20s C.
Did you know
Like other pencilfish, they switch their coloring at night. The crisp daytime stripe breaks up into a blotchy pattern once the lights go out, then snaps back in the morning.
Weekly picks
Tank mates
Dwarf pencilfish is a peaceful, shoaling species that keeps to the middle. These picks share a community profile with it, are safe together in both directions, and overlap on water type, temperature and pH.

Nano cory
Gastrodermus gracilis
Freshwater1.4 in (3.5 cm) · 12 gal (45 L)72–79°F (22–26°C)
Honey blue-eye
Pseudomugil mellis
Freshwater1.4 in (3.5 cm) · 11 gal (40 L)68–82°F (20–28°C)
Bamboo shrimp
Atyopsis moluccensis
Freshwater3.9 in (10 cm) · 13 gal (50 L)72–84°F (22–29°C)
Wandering snail
Ampullaceana balthica
Freshwater0.8 in (2 cm) · 11 gal (40 L)50–84°F (10–29°C)
Glowlight rasbora
Trigonostigma hengeli
Freshwater1.6 in (4 cm) · 12 gal (45 L)73–82°F (23–28°C)
Violet cory
Hoplisoma simile
Freshwater2.2 in (5.5 cm) · 12 gal (45 L)70–81°F (21–27°C)
Common questions
What size tank does a Dwarf pencilfish need?
A Dwarf pencilfish needs at least 12 gal (45 L). It spends most of its time in the middle.
What temperature and pH does a Dwarf pencilfish need?
A Dwarf pencilfish is comfortable at 72–82°F (22–28°C) with a pH of 5.0–7.0.
How big does a Dwarf pencilfish get?
An adult Dwarf pencilfish reaches about 1 in (2.5 cm).
Does a Dwarf pencilfish need a group?
Yes. A Dwarf pencilfish is a shoaling species and should be kept in a group, not singly.
Related species
1.1 in (2.8 cm)11 gal (40 L)75–82°F (24–28°C)Least pencilfish
Nannostomus minimus
1.1 in (2.8 cm) · 11 gal (40 L)
1.2 in (3 cm)15 gal (55 L)72–82°F (22–28°C)Barred pencilfish
Nannostomus espei
1.2 in (3 cm) · 15 gal (55 L)
1.2 in (3 cm)15 gal (55 L)75–82°F (24–28°C)Coral red pencilfish
Nannostomus mortenthaleri
1.2 in (3 cm) · 15 gal (55 L)
0.7 in (1.9 cm)5 gal (20 L)75–82°F (24–28°C)Anduzei pencilfish
Nannostomus anduzei
0.7 in (1.9 cm) · 5 gal (20 L)
1.3 in (3.3 cm)15 gal (55 L)72–82°F (22–28°C)Three-lined pencilfish
Nannostomus trifasciatus
1.3 in (3.3 cm) · 15 gal (55 L)
1.4 in (3.5 cm)15 gal (55 L)72–82°F (22–28°C)Hockeystick pencilfish
Nannostomus eques
1.4 in (3.5 cm) · 15 gal (55 L)
