Dwarf Pencilfish Care Guide - Aquarium Setup, Diet & Breeding

Dwarf Pencilfish, Nannostomus marginatus, are tiny, elegant characins known for their slim, pencil-like shape and refined swimming style. Their pale golden to olive-brown body is marked by dark horizontal stripes, while red, orange or copper tones can appear in the fins and along the body depending on locality, mood and condition.

These peaceful fish spend much of their time in the middle and upper levels of the aquarium. They move calmly among vegetation rather than darting constantly through open water, and a settled group develops subtle social displays in which males posture and flare their fins without causing serious injury.

In the wild, Dwarf Pencilfish live among roots, leaf litter and overhanging vegetation in quiet forest waters. Their narrow body and subdued, striped pattern help them blend into the broken shadows of these habitats, where they feed on tiny aquatic organisms and insects.

Their small size and gentle nature make them especially appealing for planted nano and community aquariums. They are at their most confident and attractive when kept in a proper group, where their natural behaviour and delicate colouration become much more apparent.

Dwarf Pencilfish are native to slow-moving, shaded waters of the upper Amazon and Orinoco regions of South America, including parts of Peru, Colombia, Brazil and the Guianas. They inhabit forest streams, tributaries and flooded areas that are often stained by tannins and naturally low in mineral content.

A group of Dwarf Pencilfish should be kept in an aquarium of at least 40 litres, with a footprint of roughly 60 by 30 cm or larger. Use gentle filtration and subdued lighting, with dense plants, moss, floating vegetation, roots and small areas of open swimming space. A dark, fine-grained substrate helps display their colours and creates a natural-looking setting, while leaf litter and a modest amount of tannin-stained wood can provide useful cover. Keep the aquarium mature, stable and securely covered, as these small fish may jump.

Up to around 3.5 cm (1.4 inches) in total length. Females are usually slightly larger and noticeably deeper-bodied than males.

Dwarf Pencilfish are small omnivores and should receive a varied diet of appropriately sized foods. Offer fine flakes or micro pellets alongside freshly hatched brine shrimp, daphnia, cyclops and other small frozen or live foods. Live and frozen foods are particularly useful for bringing out their colour and conditioning them for breeding. Feed small portions frequently, making sure the food is fine enough for their small mouths.

Dwarf Pencilfish suit peaceful communities with similarly small South American fish, including small tetras, ember tetras, celestial pearl danios, small rasboras, pygmy Corydoras and Otocinclus. They can also live with peaceful freshwater shrimp, although newly hatched shrimp may be eaten. Avoid large tetras, angelfish, cichlids, fin-nipping barbs, boisterous danios and other aggressive or very active fish that may intimidate them or outcompete them for food.

Dwarf Pencilfish are egg-scatterers that breed most readily in a mature, softly lit aquarium with very soft, slightly acidic water. Condition a group with plenty of small live foods, then provide fine-leaved plants, moss or a spawning mop for the eggs. Adults may eat both eggs and fry, so remove the parents or protect the spawning area. The tiny young need infusoria or another suitably microscopic first food before they can take newly hatched brine shrimp.

Males are generally slimmer and more vividly marked, with stronger red or orange colouration in the fins and body markings. Females are usually fuller through the abdomen, particularly when carrying eggs, and may appear slightly larger overall.