Furry Diary

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 systems12

At a glance the quick version

Length2.5 to 3.5 cm12
Sizetiny
Very peaceful
Tiny size suits small planted tanks
Several attractive regional colour forms
13

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.13

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.12

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.12

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.12

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).12

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.124

Fun facts for the dinner table

  1. 1

    The genus name means 'small mouth'.2

  2. 2

    Unlike many pencilfish, males and females have similar colours.1

  3. 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. 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 Furry Diary remembers it for you

A typical home-care rhythm for a Dwarf Pencilfish. It is our own starting plan, not a vet's advice, and you can change every line in the app.

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Where this comes from

Every breed page shows where each fact comes from. If we got something wrong, sorry, we are pet people, not a science magazine. Tell us at [email protected] and we will fix it.

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

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