Not furry, but we like them anyway.

Dwarf Pencilfish

Nannostomus marginatus

Also called Marginal pencilfish

SpeciesShort profile

From South America east of the Andes: Guyana, Suriname, Venezuela, Colombia, Peru, Ecuador and Brazil, including the Essequibo, Rio Negro, Napo and Ucayali systems1 2

At a glance the quick version

Length2.5 to 3.5 cm1 2

Sizetiny

Very peaceful

Tiny size suits small planted tanks

Several attractive regional colour forms

1 3

Looks how to spot one

Short, stocky scaled characin

One of the smallest pencilfish, with a shorter, chunkier body than its relatives, rather like a pencil stub. It wears three dark lengthwise stripes with a red stripe or patch whose length depends on where the fish comes from, plus a red spot at the base of the tail. Males are slimmer than females.1 3

Coloursgoldblack stripesredyellow (some Peruvian forms)1

Personality what they are like

A gentle and somewhat shy fish that fits best with other small, calm species. It also works well as a dither fish that encourages dwarf cichlids to come out.1

Daily activity how busy a day looks

Moves calmly among plants in the middle and lower water levels.1 2

Grooming and care the hands-on bits

Prefers soft, acidic water. Suggested ranges: about 22-28 C (FishBase gives 24-26 C), pH 4.0-7.0 (FishBase gives 5.8-7.5), hardness 1-10 dGH. Keep conditions clean and stable.1 2

Home where they are happiest

Tank of at least 45-60 cm length (about 41 litres) with dense planting, leaf litter, soft lighting and very gentle flow.1 2

Food basics what goes in the bowl

Feeds on tiny invertebrates. Small dried foods are taken, but daily small live or frozen foods such as brine shrimp nauplii, moina and grindal worms are recommended.1

Company who they like around

A sociable fish best kept in a group of 10 or more (FishBase gives 5 as a minimum).1 2

The story where it all began

Described by Carl Eigenmann in 1909, this species has several regional colour forms. A form once named as a separate subspecies has since been merged into it, and the coral red pencilfish from Peru was first described as one of its subspecies.1 2 4

Fun facts for the dinner table

1
The genus name means 'small mouth'.2
2
Unlike many pencilfish, males and females have similar colours.1
3
Each region has its own look: the red stripe can be a short dash in Guyana fish or run along most of the flank in Rio Negro fish.1
4
At night it turns pale with slanting bars behind the dorsal fin.1

Recognised by the official bits

IUCN Red List: Least Concern (assessed September 2020)2
FishBase: Described by Eigenmann in 19092

The care rhythm a typical week and year

A typical home-care rhythm for a Dwarf Pencilfish. A starting point, not a vet's advice.

FeedingSmall amounts once or twice a dayevery day
Temperature checkevery day
Water changeAbout 25% of the waterevery week
Water testevery week
Glass cleanevery week
Filter rinseRinse in old tank water, never tap waterevery month

Owner questions the things everyone asks

How often should I feed my Dwarf Pencilfish?

Feed your Dwarf Pencilfish small amounts once or twice a day. Furry Diary's starting plan is to feed daily, offering only what they can eat in a few minutes.1 Pet Wiki plan

What does a Dwarf Pencilfish eat, and what should it never eat?

They eat tiny invertebrates and will take small dried foods, but daily live or frozen foods like brine shrimp nauplii, moina, and grindal worms are best. Never feed large or hard foods that could harm their small mouths.1

How much space does a Dwarf Pencilfish need?

A tank of at least 45-60 cm length (about 41 litres) is recommended. This gives them room to swim calmly among plants.1 2

What temperature, light or water does a Dwarf Pencilfish need?

They prefer soft, acidic water with a temperature of 22-28°C, pH 4.0-7.0, and hardness 1-10 dGH. Soft lighting and very gentle water flow are also important.1 2

How often should I clean a Dwarf Pencilfish's home?

Furry Diary's plan suggests a weekly 25% water change, weekly glass cleaning, and a monthly filter rinse in old tank water. Keep conditions clean and stable. Pet Wiki plan

Can a Dwarf Pencilfish live with others?

Yes, they are sociable and best kept in a group of 10 or more with other small, calm fish. They also work well as dither fish for dwarf cichlids.1 2

How long does a Dwarf Pencilfish live?

Lifespan varies depending on care and environment. For specific details, ask a good breeder or an exotic-pet vet.

Can I handle a Dwarf Pencilfish?

It's best not to handle them, as they are delicate and shy. They prefer to swim calmly among plants and can be stressed by handling.1 2

Written from the sources on this page, a few checked guides (VCA, ASPCA, RSPCA) and Pet Wiki's own starting care plan. A friendly guide, not a vet's advice.

Coral Red Pencilfish

Golden Pencilfish

Three-lined Pencilfish

Where this comes from

Every fact on this page has a numbered source. Spotted an error? support@petwiki.app.

Nannostomus marginatus - Seriously Fish seriouslyfish.comused for origin, size, care, diet, behaviour, colour forms
Nannostomus marginatus summary - FishBase fishbase.seused for size, water parameters, IUCN, etymology
Nannostomus - Wikipedia en.wikipedia.orgused for body shape, genus lifespan
seriouslyfish.com seriouslyfish.com

Checked 2026-09-30. Text is written in our own words from these sources.