Golden Pencilfish

Quick summary

The Golden Pencilfish (Nannostomus beckfordi) is a peaceful, slender characin that adds a warm golden glow to any well-planted community aquarium. Ideal for beginners and experienced hobbyists alike, it thrives in soft, slightly acidic water alongside other gentle species, making it an excellent choice for a calm, densely planted setup.

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Last researched and fact-checked: June 2025.

• Introduction
• Quick Stats
• Appearance
• Natural habitat
• Tank size and setup
• Water parameters
• Filtration and equipment
• Diet and feeding
• Behaviour and temperament
• Tank mates
• Breeding
• Common diseases and health
• Frequently asked questions
• Related guides

Introduction

The Golden Pencilfish, Nannostomus beckfordi, is one of the best-known and most widely available members of the genus Nannostomus, a group of small, elongated characins belonging to the family Lebiasinidae. First described by Günther in 1872, it has been a staple of the freshwater hobby for well over a century and remains popular today thanks to its manageable size, attractive colouration, and peaceful disposition.

The species takes its common name from the warm golden to reddish-gold sheen that develops along the flanks of well-conditioned specimens, particularly dominant males. Like all pencilfish, N. beckfordi has a characteristic torpedo-shaped body and a habit of hovering in the upper and middle layers of the water column, picking at tiny food items with its small, upturned mouth. It is a shoaling species that looks its best and behaves most naturally when kept in groups of at least six, though larger groups of ten or more are preferable.

One of the most distinctive traits shared across the Nannostomus genus is their nocturnal resting posture. Rather than lying horizontally as most fish do, pencilfish adopt an oblique, head-up angle when resting at night. This behaviour can be startling if you switch the lights on unexpectedly, as the fish look quite different from their normal daytime posture, but it is entirely normal and healthy. The night-time colour pattern also differs noticeably from the daytime pattern, with broad dark bars or blotches replacing the usual horizontal stripe.

In the wild, N. beckfordi inhabits slow-moving, often tannin-stained waters in the northern Amazon basin and surrounding regions. In the aquarium, it adapts well to a range of conditions but does best in soft, slightly acidic water with gentle filtration. Its calm nature and modest adult size of around 3.5 – 4 cm (1.4 – 1.6 inches) make it an outstanding choice for smaller planted aquariums, nano community setups, and blackwater biotope displays.

Several colour forms and regional variants have been imported over the years, and some older literature refers to the species under synonyms including Nannostomus anomalus (in part) and Nannostomus aripirangensis. The taxonomy of the genus has been revised multiple times, but N. beckfordi as currently understood is well-defined and widely accepted.

Appearance

Nannostomus beckfordi has the classic pencilfish body plan: slender, elongated, and slightly laterally compressed with a small, subtly upturned mouth adapted for feeding at and just below the surface. Adults typically reach 3.5 – 4 cm (1.4 – 1.6 in) in total length, making it one of the medium-sized members of the genus.

The base body colour is a warm golden to olive-gold, with a prominent dark lateral stripe running from the tip of the snout through the eye and along the full length of the body to the base of the caudal fin. This dark band is bordered above by a narrower golden or iridescent stripe that can appear almost luminous under good aquarium lighting. Below the dark stripe, the belly is typically pale cream to white. The overall impression is one of understated elegance rather than flashy colour.

Males are generally more intensely coloured than females, developing deeper reddish or orange-red tones along the lower flanks and on the anal fin, particularly when in breeding condition or when displaying to rival males. The anal fin of the male often shows a reddish flush with white tips, whereas the female’s anal fin tends to be more subdued and rounded. Males are also typically slightly more slender than females when viewed from above, while gravid females appear noticeably plumper in the belly region.

As noted in the introduction, all pencilfish display a dramatically different colour pattern at night. In N. beckfordi, the horizontal stripe breaks up and is replaced by a series of broad, dark, roughly vertical bars or blotches. The golden tones fade, and the fish takes on a much paler, more washed-out appearance. This transformation is entirely normal and reverses quickly once the lights come on and the fish become active again.

The fins are generally transparent to slightly tinted. The caudal fin has red markings at the base in many populations, and the adipose fin (characteristic of many characins) is absent in Nannostomus, which is one of the features distinguishing Lebiasinidae from the true Characidae.

Several colour variants and geographical morphs have appeared in the hobby over the years. A particularly popular form is sometimes sold as the “Red Pencilfish” or “Golden Red Pencilfish,” which displays more intense red pigmentation along the body. Whether these represent distinct populations, selectively bred forms, or simply well-conditioned specimens in optimal water chemistry is sometimes debated, though geographical variation is documented across the species’ broad range.

Natural habitat

Nannostomus beckfordi has a wide distribution across northern South America. It is found in Guyana, Suriname, and French Guiana, as well as in the lower and middle Amazon basin in Brazil, including tributaries of the Rio Negro, Rio Madeira, and other blackwater and clearwater systems. This broad range contributes to the variation in appearance noted among different imported populations.

In the wild, the species inhabits slow-moving or still waters such as small forest streams, flooded forest margins, swamps, and oxbow lakes. These habitats are typically heavily vegetated, with dense growths of aquatic plants, submerged roots, and overhanging riparian vegetation providing both shelter and a source of food in the form of tiny invertebrates and organic detritus. Fallen leaves, branches, and other woody debris litter the substrate, and tannins leaching from this decaying organic matter often stain the water a deep amber or tea colour.

Water conditions in these habitats are characteristically soft and acidic, often with a pH as low as 4.0 – 5.0 in blackwater tributaries, though populations from clearwater streams may experience somewhat higher pH values. The water is typically warm, ranging from around 24 – 28 °C (75 – 82 °F), with very low mineral content. Dissolved oxygen levels can be modest in still, leaf-litter-choked pools, but the fish’s small size and low metabolic demands mean it copes well in these conditions.

N. beckfordi is typically found in small groups among aquatic vegetation or tangled root systems near the water’s surface. It shares its habitat with a wide variety of other small characins, dwarf cichlids such as Apistogramma species, and various catfish and loricariids. The pencilfish occupies a fairly specific niche in the upper water column, picking tiny invertebrates and organic particles from the surface film and from among plant leaves.

The IUCN Red List classifies N. beckfordi as Least Concern, reflecting its wide distribution and apparent abundance across much of its range. The vast majority of specimens in the aquarium trade are commercially bred in Southeast Asian and Eastern European fish farms, which reduces collection pressure on wild populations considerably.

Tank size and setup

A minimum tank size of 60 litres (approximately 15 US gallons) is recommended for a small group of Golden Pencilfish. Because these fish are active swimmers within the upper and middle layers and are best kept in groups of at least six (ideally ten or more), a tank with a reasonable horizontal footprint is more useful than a tall, narrow design. A standard 60 cm (24 inch) tank is a good starting point for a species-only group or a small community built around pencilfish.

Planting is one of the most important aspects of setting up a tank for N. beckfordi. Dense clusters of fine-leaved plants such as Cabomba, Myriophyllum, or Limnophila provide shelter and help the fish feel secure, reducing stress and encouraging natural behaviour. Floating plants are highly recommended, as they dim the light (pencilfish tend to look washed out and behave nervously under harsh overhead lighting) and also provide surface cover where the fish naturally forage. Salvinia, Limnobium (Amazon frogbit), and Pistia (water lettuce) all work well for this purpose.

The substrate choice is not critical from the fish’s perspective, as pencilfish rarely interact with the bottom of the tank. A dark substrate, however, helps bring out the best colours and reduces the washed-out appearance that can occur over pale sand or gravel. Fine, dark sand or aquasoil suits planted setups perfectly and complements the species’ natural appearance.

For a blackwater biotope approach, consider adding dried Indian almond leaves (Terminalia catappa), oak leaves, or alder cones to the tank. These release tannins that tint the water a natural amber colour, lower the pH gently, and provide additional surfaces for biofilm growth, which in turn supports microfauna that pencilfish will graze on. Pieces of driftwood, twisted roots, and branches can further replicate the tangled underwater environment these fish inhabit in the wild.

A secure lid is advisable. Pencilfish are not habitual jumpers in the way some surface-dwelling killifish are, but they can and do leap when startled, and a gap between the water surface and the tank rim is always a risk with small, surface-oriented fish.

Water parameters

Nannostomus beckfordi is relatively adaptable compared to some of its congeners, tolerating a wider range of water chemistry than, for instance, N. eques or N. mortenthaleri. That said, it will always look its best and behave most naturally in soft, slightly acidic water that mirrors its native habitat.

While the species will survive in moderately hard, neutral water, aiming for the softer, more acidic end of the range (pH 6.0 – 6.8, GH 2 – 6) will promote the best colouration and is essential if you intend to breed them. In areas of the UK with hard tap water, the use of RO (reverse osmosis) water blended with tap water, or remineralised RO water, may be necessary to achieve suitable conditions. Alternatively, peat filtration or the addition of botanical materials (leaves, alder cones, driftwood) can help soften and acidify the water naturally, though this is typically insufficient on its own to bring very hard water into the ideal range.

Stability is more important than hitting a precise number. Sudden swings in pH or temperature are far more stressful to small fish than a parameter that sits slightly outside the textbook ideal but remains steady. Regular partial water changes of around 20 – 25% weekly, using water matched for temperature and chemistry, will help maintain consistent conditions and keep nitrate levels low.

Filtration and equipment

Golden Pencilfish come from slow-moving or still waters and are not strong swimmers. Filtration should therefore be gentle, providing adequate biological and mechanical cleaning without generating a powerful current. A small internal filter, a sponge filter, or a hang-on-back filter with an adjustable flow rate are all suitable choices. If using a canister filter or any unit with a stronger output, use a spray bar, lily pipe, or baffle to diffuse the outflow and reduce current in the main body of the tank.

Sponge filters deserve special mention as an excellent option for pencilfish tanks. They provide reliable biological filtration, create minimal water movement, are extremely gentle on fry if you are attempting to breed, and their surfaces grow biofilm that supports the microfauna pencilfish naturally graze upon. An air-driven sponge filter paired with a small, adjustable air pump is a simple and effective setup.

Heating is necessary in the UK, as the species requires tropical temperatures of 24 – 28 °C (75 – 82 °F). A reliable, thermostatically controlled heater rated appropriately for the tank volume should be used. For a 60-litre tank, a 50-watt heater is typically sufficient, though this will depend on room temperature and how well-insulated the tank is. Always use a separate thermometer to verify the heater’s accuracy.

Lighting should be moderate rather than intense. Pencilfish naturally inhabit shaded, dimly lit waters, and they tend to appear washed out and skittish under very bright lights. If you are growing high-light demanding plants, provide shade through floating plant cover, which serves the dual purpose of reducing light intensity and offering the surface shelter pencilfish prefer. A timer set to a photoperiod of around 8 – 10 hours per day helps establish a natural day/night rhythm and keeps algae growth in check.

Diet and feeding

In the wild, Nannostomus beckfordi is a micro-predator, feeding primarily on tiny aquatic invertebrates, zooplankton, and organic particles found at or near the water surface and among vegetation. Its small, upturned mouth is well-adapted for picking individual food items from the surface film, from plant leaves, and from the water column.

In the aquarium, this species accepts a wide range of small foods but has a notably tiny mouth, so particle size is an important consideration. Crushed or micro-pellet dry foods, fine flakes broken into small pieces, and freeze-dried or frozen foods in appropriately small sizes all form a good staple diet. High-quality micro-granules designed for small tropical fish are particularly convenient and are readily accepted.

Live and frozen foods are greatly appreciated and should be offered regularly to supplement the staple diet. Daphnia, baby brine shrimp (Artemia nauplii), cyclops, and micro-worms are all excellent choices. These foods are particularly valuable for conditioning fish for breeding and for bringing out the best colouration. Larger live foods such as adult brine shrimp or bloodworm may be too big for pencilfish to manage comfortably, so choose smaller varieties or chop them finely.

Feed small amounts two to three times per day rather than one large feeding. Pencilfish have small stomachs and high metabolic rates typical of tiny tropical fish, and they benefit from frequent, modest meals. Any food that sinks to the bottom is unlikely to be retrieved by pencilfish, which rarely feed from the substrate. If uneaten food accumulates on the bottom, you are likely overfeeding or offering particles that are too large.

In a mature, well-planted tank with plenty of biofilm-covered surfaces (driftwood, leaves, sponge filter), pencilfish will also graze on naturally occurring microfauna and biofilm between meals. This supplementary natural foraging is beneficial and is another reason why a well-established, biologically rich tank suits this species so well.

Behaviour and temperament

Nannostomus beckfordi is a peaceful, somewhat reserved species that spends most of its time hovering in the upper and middle layers of the water column. It is a shoaling fish rather than a tightly schooling one: in a group, individuals will spread out across the tank but remain in loose visual contact with one another, occasionally coming together more closely when alarmed or when competing for food.

Males establish small, temporary territories among plants and will display to one another with mild lateral displays, fin flaring, and intensified colour. These interactions are generally benign, involving posturing rather than physical contact, and rarely result in injury. In very small groups (fewer than six), a dominant male may persistently harass subordinates, so keeping a larger group helps distribute any aggression and allows subordinate fish to fade into the background when needed.

The most distinctive behavioural trait of this species, shared with all members of the Nannostomus genus, is its nocturnal resting posture. At night, or when the lights are off, pencilfish adopt an oblique, head-up angle rather than resting horizontally as most fish do. This posture is accompanied by a dramatic change in colour pattern, with the daytime horizontal stripe breaking up into a series of broad, dark vertical bars or blotches. The fish may rest motionless among plant stems in this position for extended periods. This is entirely normal and not a sign of illness. If you observe your pencilfish “standing on their tails” among the plants when you turn on the light first thing in the morning, there is no cause for concern.

Golden Pencilfish are slow, deliberate feeders and can be easily outcompeted at mealtimes by faster, more boisterous species. This is one of the most important considerations when choosing tank mates. In a mixed community, pencilfish may fail to get enough food if housed with greedy, fast-moving feeders, leading to gradual weight loss and declining health. Ensuring food reaches them, whether by spreading it across the surface, target-feeding with a pipette, or feeding at multiple points in the tank, is essential in any community setup.

The species is not particularly shy by pencilfish standards, but it does appreciate cover in the form of floating plants and dense vegetation. In a bare or sparsely decorated tank, pencilfish tend to be nervous, pale, and reluctant to venture into open water. In a well-planted tank with subdued lighting, they are much more confident, more colourful, and more likely to display their full repertoire of natural behaviours.

Tank mates

Golden Pencilfish are ideal community fish provided their tank mates share a similar temperament. The key requirements are gentle, non-aggressive species that will not outcompete the pencilfish for food or harass them with boisterous behaviour. Avoid anything large enough to view pencilfish as food, anything with a nippy or aggressive disposition, and any fast, greedy feeders that will monopolise meals.

Good tank mates

• Ember tetra, a tiny, peaceful tetra that occupies a similar gentle niche
• Cardinal tetra, a classic soft-water companion with compatible requirements
• Green neon tetra, a small, quiet shoaler ideal for blackwater setups
• Harlequin rasbora, a calm mid-water swimmer that coexists peacefully
• Pygmy corydoras, a diminutive bottom-dweller that stays out of the pencilfish’s way
• Otocinclus, a small, peaceful algae grazer that occupies a different niche entirely
• Apistogramma cacatuoides, a small dwarf cichlid that shares soft-water preferences
• Chocolate gourami, a quiet surface-dweller for experienced keepers with suitable water
• Kuhli loach, a shy, nocturnal bottom-dweller that poses no competition
• Amano shrimp, a useful algae-eating invertebrate too large for pencilfish to bother

Fish to avoid

• Tiger barb, an active fin-nipper that will stress and harass pencilfish
• Serpae tetra, known for fin-nipping and overly boisterous behaviour
• Buenos Aires tetra, too large, too fast, and likely to outcompete for food
• Convict cichlid, far too aggressive and territorial for pencilfish
• Angelfish, large enough to eat pencilfish and may do so as adults
• Chinese algae eater, becomes aggressive and territorial as it matures
• Red-tail black shark, aggressively territorial and far too boisterous
• Betta, may view pencilfish as threats or targets, and flow requirements differ
• Jack Dempsey, a large, predatory cichlid entirely unsuitable as a companion
• Common pleco, grows far too large and produces excessive waste for a pencilfish tank

Breeding

Nannostomus beckfordi is one of the more frequently bred pencilfish in the hobby, and documented breeding reports are reasonably plentiful compared to some of its congeners. That said, it is not a species that typically breeds prolifically in a community tank, as the eggs are tiny and vulnerable to predation, including by the parents themselves.

The species is an egg-scatterer with no parental care. Ripe females will scatter small, semi-adhesive eggs among fine-leaved plants or spawning mops, usually in the early morning hours. The eggs are tiny, translucent, and easy to overlook. Both parents and other tank inhabitants will readily eat the eggs and any resulting fry, so deliberate breeding efforts require either a dedicated breeding tank or a method for protecting the eggs.

To condition a pair or small group for breeding, separate the sexes for a week or two and feed a varied diet rich in live and frozen foods such as baby brine shrimp, daphnia, and micro-worms. Males in breeding condition will display intensified red and gold colouration, while females will appear noticeably rounder in the belly when full of eggs.

A small breeding tank of around 20 – 30 litres is sufficient. Fill it with mature water matching the display tank’s parameters, ideally on the softer and more acidic end (pH 5.5 – 6.5, GH below 6). The temperature can be raised slightly to around 26 – 28 °C (79 – 82 °F). Provide clumps of fine-leaved plants such as Java moss, Cabomba, or spawning mops to catch the eggs. Some breeders use a mesh or grid on the bottom of the tank to allow eggs to fall through and out of reach of the adults. Lighting should be very dim, or the tank can be kept in near-darkness, as pencilfish eggs and fry are sensitive to bright light.

Introduce the conditioned pair or a small group (one or two males to two or three females) to the breeding tank in the evening. Spawning typically occurs the following morning. After spawning, remove the adults promptly to prevent egg predation. The eggs hatch in approximately 24 – 36 hours at tropical temperatures, and the fry become free-swimming roughly three to four days after hatching, once the yolk sac has been absorbed.

The fry are extremely small and require correspondingly tiny first foods. Infusoria, commercially available liquid fry food, or vinegar eels are suitable initial feeds. After a week or so, the fry should be large enough to accept freshly hatched baby brine shrimp (Artemia nauplii), which is an excellent growth food. Keep the rearing tank dimly lit, maintain pristine water quality with very gentle filtration (a small air-driven sponge filter is ideal), and perform small, frequent water changes using water of identical chemistry.

Growth is steady but not rapid, and it may take several months before the fry develop recognisable adult colouration and reach a size suitable for introduction to a community tank.

Common diseases and health

Nannostomus beckfordi is a reasonably hardy species when kept in appropriate conditions, and it is not notably susceptible to any species-specific diseases. Like all small tropical fish, however, it is vulnerable to the common ailments associated with poor water quality, stress, and inappropriate husbandry. Ich (white spot disease), caused by the protozoan Ichthyophthirius multifiliis, is perhaps the most commonly encountered problem. It typically arises following a temperature drop, the introduction of new fish without quarantine, or a decline in water quality. Affected fish display the characteristic white cysts on the body and fins and may clamp their fins or flash against hard surfaces. Treatment with a proprietary ich medication at the recommended dose, combined with a gradual increase in temperature to around 28 – 30 °C (82 – 86 °F), is usually effective, though care should be taken with medication dosages in soft, acidic water, as some treatments can be more potent under these conditions.

Fungal infections, bacterial fin rot, and velvet disease (caused by Piscinoodinium) can also occur, particularly in tanks with fluctuating parameters, poor filtration, or overcrowding. Pencilfish are small and have limited energy reserves, so any disease that takes hold can progress rapidly. Early detection and prompt treatment are therefore important. Quarantining new fish for two to three weeks before introducing them to an established tank is one of the most effective preventative measures available.

Beyond infectious diseases, the most common health issues in pencilfish are related to chronic stress and malnutrition. Fish kept in groups that are too small, in tanks with insufficient plant cover, or alongside boisterous or aggressive tank mates will often display pale, washed-out colours, reduced appetite, and clamped fins. Similarly, fish that are consistently outcompeted for food will gradually lose condition, becoming thin and lethargic. Ensuring a well-planted tank, an appropriate group size, compatible tank mates, and a varied diet of suitably small foods will prevent the vast majority of health problems in this species. Regular water changes, stable parameters, and careful observation during feeding times are the cornerstones of good pencilfish health management.

Frequently asked questions

How many Golden Pencilfish should I keep together?

A minimum of six is recommended, but a group of ten or more is ideal. Larger groups allow males to spread their mild territorial behaviour across multiple rivals, reducing stress on any one individual. In bigger groups, the fish are also more confident, more colourful, and more likely to display their full range of natural behaviours.

Why are my pencilfish standing at an angle at night?

This is completely normal. All members of the Nannostomus genus adopt an oblique, head-up resting posture at night. They also change their colour pattern in the dark, with the horizontal stripe breaking up into vertical bars. This behaviour reverses quickly once the lights come on and the fish become active again. It is not a sign of illness.

Can I keep Golden Pencilfish in hard water?

The species is more adaptable than some pencilfish and can tolerate moderately hard water (up to around 12 dGH) and a neutral pH. However, it will always look its best and behave most naturally in soft, slightly acidic conditions. If you want to breed them, soft, acidic water is essentially required. In areas with very hard tap water, using RO water blended with tap water is the most reliable way to achieve suitable conditions.

Will Golden Pencilfish eat shrimp?

Adult pencilfish may eat very small shrimp fry (shrimplets), as they are micro-predators by nature. However, they are generally safe with adult cherry shrimp, Amano shrimp, and other commonly kept ornamental shrimp. If you are trying to breed shrimp in the same tank, some predation of the smallest juveniles is likely.

Do Golden Pencilfish need a heater?

Yes. In the UK, room temperatures are too low and

Related guides

• Hockeystick Pencilfish
• Three-lined Pencilfish
• One-lined Pencilfish
• Ember Tetra
• Green Neon Tetra
• Cardinal Tetra