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Nannostomus marginatus Eigenmann 1909

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Dwarf pencilfish

Nannostomus marginatus is a freshwater characin that belongs to the family Lebiasinidae. The most notable characteristic is its size: it is one of the smallest members of the genus Nannostomus.

The Dwarf Pencilfish is a pretty little shoaling species known from tributaries, backwaters, and swamplands, where the water is sluggish or almost still, and crowded with dense vegetation and an abundance of leaf litter. The water in the native habitat is very soft and acidic, and stained a tea colour from the tannins in the decaying leaves and wood.

Distribution: Amazon and Orinoco river basins: Brazil, Ecuador, Colombia, Guyana, Peru, Suriname and Venezuela.

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Water Chemistry

Water information

Water type
Fresh water
Water color
Black water
Water transparency
Concentration of sediments
Water temperature
26-29 °C
Water flow/curent

Chemical parameters

up to 8 mg/l
Dissolved Oxygen


Standard length
3.5 cm
Water volume (min. aquarium)
20 l
Social behaviour
Group fish
Behaviour description

Nannostomus marginatus is a very peaceful community fish ideal to be maintained with other small non-aggressive characids, callichthyid and loricariid catfishes.

Aggression grade
Day active
Sexual dimorphism

Mature females fuller bodied. Males in breeding condition will be more brightly coloured. In the majority of geographical variants, the males possess thickened rays on the anal fin.

Nutrition in Nature

Micropredator, feeding on tiny invertebrates and other zooplankton.


Breeding tank set-up

Should ideally be kept in a heavily-planted set-up. Floating plants are a useful addition as are driftwood branches and dried leaf litter.

Nutrition parents

Nannostomus marginatus will accept dried foods of a suitable size but should also be offered daily meals of small live and frozen fare such as Artemia nauplii, Moina, grindal worm, etc.

Mating type
Spawning behaviour

One or more pairs of well-conditioned adults should then be carefully acclimatised in a separate softwater breeding aquarium with plenty of fine-leaved plants. One or more pairs of well-conditioned adults should then be carefully acclimatised across. When ready to spawn, and whilst swimming alongside one another, the male will nudge the female’s abdomen. The eggs will be laid/fertilised a few at a time, and these should fall into the mass of plants.

Breeding habits
Hatching period
48-72 hours
Number of eggs in average
up to 100 eggs
Parental care
Fry number
Nutrition fry

Initial food should be Paramecium or a proprietary dry food of sufficiently small (5-50 micron) grade, introducing Artemia nauplii, microworm, etc.,once the fry are large enough to accept them.

Notes on reproduction

The fish is an egg eater, so it is necessary to remove the parents after spawning.