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Maximum size : 3.5 cm

Dwarf Pencilfish - Nannostomus marginatus : Complete Fish Profile & Care Guide

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The Dwarf Pencilfish (Nannostomus marginatus) stands out as the smallest member of its species. These charming and peaceful fish can be somewhat shy, tending to hide and refuse food if their tankmates are overly exuberant. To create a comfortable environment for these tranquil mid-to-top-dwelling fish, set up a well-established aquarium with a dark substrate and background, and ample plant life, including both rooted and floating varieties. Efficient filtration and gentle water movement are crucial. Ideally, maintain these fish in groups of at least 10, with larger groups preferred if possible. Occasional disputes may arise among dominant males, but a well-designed habitat with numerous hiding spots and visual barriers can mitigate potential harm. A higher female-to-male ratio can further alleviate minor aggression concerns. In the wild, these fish share their habitat with an array of small characins, including Axelrodia stigmatias, and various Copella and Hemigrammus species. Dwarf Cichlids from the Apistogramma or Mikrogeophagus genera, as well as Corydoras Catfish and small loricariids, can also be considered suitable tankmates. Sporting a silver body, these fish captivate observers with their two striking black horizontal stripes that extend from head to tail. Additionally, they feature a distinctive red patch at the base of the caudal fin, nestled between the primary and secondary dark lateral lines, adding a touch of vibrancy to their appearance.

Dwarf Pencilfish Photos

Sexual Dimorphism

Distinguishing between male and female Dwarf Pencilfish is a straightforward task. Males exhibit a more slender physique and more intense coloration compared to females. Additionally, some males have a modified anal fin with the third to sixth rays being widened, further aiding in differentiation.

Quick Facts

Scientific NameNannostomus marginatus
Year Described1909
Other Names
OriginsGuyana Suriname
Max Size3.5 cm
Aquarium LevelMiddle - Top
Best kept asN/A
Lifespan2 - 5 years

Water Parameters

Water TypeFreshwater
PH5.5 - 7.5
GH3 -10
75 - 79
23.9 - 26.1

Natural Habitat

Prepare to be transported to the exotic backwaters, tributaries, and swamplands of Guyana and Suriname, where the stunning Dwarf Pencilfish can be found thriving in their natural habitat. These exquisite creatures inhabit the soft, acidic waters of Maduni Creek, creating a serene and tranquil environment that is perfect for observing their beauty. But the wonder of this species doesn't stop there - you can also find them in the middle to lower Amazon Basin East of the Andes Mountains in Brazil, Peru, and Colombia. Here they can be found in the Essequibo River, Demerara River, Nickerie River, Inírida River, Caquetá River, Ucayali River, Javari River, Putumayo River, Napo River, Juruá River, the Rio Negro, Branco River, and the Trombetas River. In these breathtaking waterways, the Dwarf Pencilfish gracefully maneuvers through the almost still, shallow waters, surrounded by a dense and vibrant vegetation, creating a picturesque and lively scene. The waters are stained a warm, tea-like color from the tannins in the decaying wood and leaves, providing a unique and fascinating backdrop for observing these stunning fish in their natural habitat. For those with a passion for aquatic life and nature, the opportunity to encounter the Dwarf Pencilfish in their natural habitat is a once-in-a-lifetime experience. Witnessing their vibrant colours and playful behaviour in such a serene environment is truly a sight to behold.
 Rio Napo - Ecuador
Ecuador Flag
 Nickerie River - Suriname
Suriname Flag
 Essequibo River - Guyana
Guyana Flag
 Demerara River - Guyana
Guyana Flag
 Japurá River - Colombia
Colombia Flag


Breeding Dwarf Pencilfish can be a challenging endeavor, with successful outcomes being quite rare. A dedicated breeding tank is necessary, featuring dim lighting, gentle air-driven filtration, an abundance of fine-leaved plants, and low pH water. The substrate should consist of marbles or small rocks and pebbles, or alternatively, a mesh can be used at the base of the tank, allowing the eggs to fall through while preventing adult access. During spawning, the male and female swim alongside each other. The male will nudge the female's abdomen, initiating fertilization. The female will then lay a small number of eggs, which fall onto the plants or substrate, repeating this process until she has laid up to 100 eggs. After the eggs have been laid, it is crucial to remove the parents from the tank, as they are notorious egg eaters. The eggs typically hatch within 36-72 hours, and the fry become free-swimming 3-4 days later.

Diet & feeding

Dwarf Pencilfish are receptive to a variety of foods, as long as they are small enough to accommodate their tiny mouths. High-quality granular or flake foods will fulfill their nutritional needs, but these fish also greatly appreciate small frozen or live foods. Ideal options include mosquito larvae, bloodworms, daphnia, and baby brine shrimp.

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