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Maximum size : 4 cm

Three Lined Pencilfish - Nannostomus trifasciatus : Complete Fish Profile & Care Guide

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The Three Lined Pencilfish (Nannostomus trifasciatus) epitomizes a relatively peaceful nature yet displays intriguing social dynamics within its shoaling behaviour. Although naturally sociable, these fish exhibit a distinct shoaling rather than schooling inclination, with territorial males engaging in occasional sparring during daylight hours as they establish and defend their small territories. Consequently, these Pencilfish possess a heightened level of aggression compared to their congeners, and confinement within limited spaces can result in severe injury or even fatality. To mitigate such risks, providing a spacious aquarium environment and strategically arranging decor to create ample broken lines of sight is imperative.

By introducing a group of at least ten individuals, preferably more, the inherent aggression within Three Lined Pencilfish can be distributed among the group, fostering a more harmonious social dynamic. Moreover, a larger shoal instils confidence within the fish, enabling them to exhibit more natural behaviours. Well-suited tankmates for the Three Lined Pencilfish include similarly-sized peaceful Characids, smaller Catfish species, Rasboras, Barbs, and Dwarf Gouramis. Furthermore, these Pencilfish serve as excellent dither fish for Apistogrammas and other Dwarf Cichlids, as they predominantly inhabit the middle-to-upper levels of the aquarium and pose no threat to fry. However, caution should be exercised when selecting tankmates, avoiding calm surface-dwelling species like hatchet fish, as well as larger and more boisterous species, particularly in smaller aquariums.

Creating an optimal habitat for Three Lined Pencilfish involves establishing a heavily-planted aquarium adorned with a dark substrate. Floating plants serve as valuable additions, while dried leaf litter and driftwood branches contribute to an authentic natural aesthetic. Moderate water movement suffices for these fish, making a small air-powered sponge filter more than adequate for providing suitable filtration.

The Three Lined Pencilfish, with its diminutive size and small mouth, presents distinctive visual characteristics that vary throughout the day and night. In daylight, these fish feature three striking black longitudinal stripes spanning their entire body length. As nightfall descends, three prominent dark spots emerge on their sides, extending from the dorsal to the ventral region. Additionally, the fish exhibit a beautiful greenish-gold colouration on their back and sides, accentuated by a silver-toned stomach. Vibrant red blotches grace their dorsal, anal, pelvic, and caudal fins, as well as the gill cover, with the size of these markings varying depending on the geographic origin of the fish.

Three Lined Pencilfish Photos

Sexual Dimorphism

Distinguishing between male and female Three Lined Pencilfish can present a moderate challenge due to the variability in patterning observed across individuals originating from different locations. Nevertheless, males often exhibit an observable characteristic in the form of an extra row of red spots nestled within the gold region positioned between the middle and upper stripes. Moreover, males tend to showcase a slightly slimmer physique and display more vibrant colours compared to females, although these distinctions may not consistently manifest. As such, careful observation and attention to these subtle visual cues are necessary for accurate gender identification within this species.

Quick Facts

Scientific NameNannostomus trifasciatus
Year Described1876
Other NamesThree-stripe Pencilfish
OriginsBrazil Peru Colombia Guyana Bolivia
Max Size4 cm
Aquarium LevelMiddle - Top
DifficultyBeginner - Intermediate
Best kept asGroups 10+
LifespanUp to 5 Years

Water Parameters

Water TypeFreshwater
PH5.5 - 7.0
GH2 - 8
TDS18 - 215
75 - 82
23 - 27

Natural Habitat

Nestled within the captivating realm of the Amazon Basin, the natural distribution of Three Lined Pencilfish encompasses specific regions within Brazil, including the Rio Negro and Rio Tabatinga. However, their presence extends throughout the lush landscapes of Peru, Colombia, Guyana, and northern Bolivia in South America. These Pencilfish thrive in tranquil, sluggish waters characterized by slight acidity, particularly in areas where dense vegetation flourishes or submerged woody structures and leaf litter are prevalent. Notably, these adaptable fish occupy various habitat types within their range. For example, during periods of river flooding, they can be found in Overrun forests. Similarly, they inhabit expansive swamps formed by the confluence of tributaries with the main river channel. Furthermore, as the water levels recede during the low-water season, they may be confined to small lakes that persist or remain in close proximity to the wooded fringes of the forest.


Breeding Three Lined Pencilfish can be a relatively straightforward endeavour, albeit requiring the establishment of a separate breeding tank to maximize fry yield. Creating an ideal breeding environment entails dim lighting and the incorporation of bunches of fine-leaved plants, such as Java Moss, within the tank. Alternatively, spawning mops, plastic grass-like matting, a layer of glass marbles, or a mesh can serve as suitable mediums for the Pencilfish to scatter their eggs upon. These provisions offer ample surfaces for the eggs to adhere to during the spawning process.

To optimize breeding success, it is advisable to maintain slightly acidic to neutral pH levels in the water, coupled with a slightly higher temperature than the community aquarium. Introducing an air-powered sponge filter or an air stone aids in ensuring proper water movement and oxygenation within the breeding tank.

When aiming for group spawning, it is recommended to have approximately half a dozen individuals of each sex within the breeding tank. Conditioning these Pencilfish with a nutritious diet consisting of ample live and frozen foods is crucial before initiating the spawning process. This preparation helps facilitate successful breeding endeavours with minimal complications. Alternatively, pair spawning is another viable approach. To achieve this, it is prudent to condition separate groups of males and females in dedicated tanks, ensuring they receive a high-quality diet consisting of live and frozen foods. Once the females exhibit full egg development and the males display their most vibrant colours, it is advisable to select the healthiest female and the best-coloured male to introduce them to the breeding tank. The spawning process is expected to occur the following morning.

Approximately 2 to 3 days after spawning, removing the adult fish from the breeding tank is recommended, allowing the eggs and subsequent fry to develop undisturbed. Around three days after the removal of the adults, the first signs of fry should become visible within the tank. During the initial stages, nourishing the fry with Paramecium or appropriately sized dry food is recommended. As the fry grows, transitioning them to suitable food sources, such as microworms or baby brine shrimp, becomes essential once they have attained a size suitable for their consumption.

By adhering to these breeding protocols and providing the necessary care, aquarists can enjoy the rewarding experience of successfully breeding Three Lined Pencilfish and witnessing the growth and development of their vibrant fry.

Diet & feeding

Three Lined Pencilfish display a micro predator feeding strategy in their natural habitat, primarily preying upon minuscule invertebrates and zooplankton. However, when acclimated to the aquarium environment, these fish exhibit a versatile diet and readily accept high-quality dried foods of an appropriate size. However, Augmenting their diet with a regular provision of small live and frozen foods is important to meet their nutritional requirements fully. Offerings such as bloodworm, white mosquito larvae, daphnia, and baby brine shrimp serve as excellent supplementary options to ensure the well-being and balanced nutrition of these captivating Pencilfish within the aquarium setting.

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