Beckford's pencilfish

Quick facts

Adult size

6.5 cm

Lifespan

can live up to 5 years

Tank zone

top

Temperament

peaceful

Difficulty

beginner

Schooling

recommended 8+ (critical minimum 6, thrives at 12+)

Typically wild-caught

yes - acclimate slowly

Water parameters

Temperature

22–28°C

pH

5.5 to 7.5

Hardness

2 to 15 dGH

Tank requirements

Minimum volume

60 L

Minimum length

60 cm

Flow

low

Lighting

moderate

Substrate

any

Open swimming room

needed

Lid

required - jumper

Feeding

Diet: omnivore, feeds primarily at the top.

Small flake, micro pellets, frozen daphnia, frozen baby brine shrimp, and frozen cyclops are the standard diet. The mouth is small even for a fish this size, so crush standard flake before adding it. They hover near the surface and intercept food as it drifts down, rarely chasing anything to the bottom. Live baby brine shrimp triggers the most active feeding response. In community tanks they're not competitive feeders and can miss out if faster species grab everything at the surface. A feeding ring or spot-feeding near their preferred corner helps. Feed twice daily in small amounts.

Compatibility

• Peaceful upper-column fish that minds its own business. Males flash their fins at each other but the sparring is ritualized and never causes damage. Good dither fish for shy species lower in the tank.
• Keep in groups of 6+. Smaller groups produce skittish fish that hide behind plants and lose color. In a proper school they hover in the open and display frequently.
• Pair with other calm species: small tetras, rasboras, corydoras, otocinclus, dwarf cichlids. Avoid anything boisterous or large enough to view them as food. Tiger barbs and giant danios are poor choices.
• Jumpers. The torpedo-shaped body is built for bursts of speed and they launch out of open tanks without warning. A tight-fitting lid with no gaps is mandatory. Floating plants help because they break the surface tension and seem to reduce jumping frequency.

Habitat

Found across the Guianas and the central Amazon basin in slow-moving blackwater streams with dense bankside vegetation and heavy leaf litter. Water is soft, acidic, and tannin-stained. Beckford's pencilfish (Nannostomus beckfordi) is the most commonly available pencilfish species in the trade, owing to its hardiness and ease of commercial breeding. The body is a warm golden-brown to olive with a bold dark horizontal stripe from snout to caudal peduncle and a thinner gold line above it. Males develop more red in the lower fins and a deeper body color than females. One quirk worth knowing about: the species displays a dramatic color shift at night. The horizontal stripe breaks into blotchy, irregular patches that look alarming if you've never seen it before. New owners regularly post panic threads about their pencilfish looking diseased. It's completely normal. The pattern reverts within minutes of lights-on. This nocturnal camouflage response is shared by several Nannostomus species and is thought to be an adaptation to reduce visibility to nocturnal predators. Adult size is about 6 cm. Commercially bred in Southeast Asia and Eastern Europe; inexpensive and almost always available.

Breeding

Egg scatterer. Pairs deposit a few eggs each day among fine-leaved plants or java moss rather than producing a single large clutch. No parental care at all; adults eat eggs and fry on sight. A dedicated breeding tank with a thick layer of java moss or spawning mops on the bottom works best. Introduce a conditioned pair (fed frozen food heavily for a week), let them spawn over 2-3 days, then remove the adults. Eggs hatch in 24-36 hours. Fry are tiny and need infusoria or paramecium culture for the first 3-5 days before they're large enough to take baby brine shrimp nauplii. Fry mortality in the first week is high even under good conditions; expect 30-50% losses from starvation and sensitivity to water quality. The survivors grow steadily but slowly, reaching sellable size in about 3 months. Water for breeding should be soft and acidic (pH 5.5-6.5, GH below 6). Not a difficult species to breed, but the continuous egg-scattering strategy means yields per spawning event are lower than a typical tetra.

Common problems

The nighttime color change causes unnecessary worry (covered above). Jumping is the real hazard. Pencilfish are strong leapers and will find any gap in the lid, including the cutout for filter tubing or the space around a hang-on-back filter. Block every opening. Lost pencilfish on the floor behind the tank are a regular occurrence for keepers who underestimate this. Ich can appear in newly purchased fish but responds to standard heat treatment (30°C for 3 days). The species is otherwise hardy in stable conditions. Color fading happens in tanks with bright overhead lighting and no surface cover; floating plants and subdued lighting bring out the best markings. Old fish (5+ years) gradually lose stripe contrast.

Bioload

Bioload coefficient: 1.2 (slim 6.5 cm fish, very low waste).

Bioload coefficients are calibrated against the neon tetra as the anchor (1.0). See the methodology page for the formula and how each value was derived.

Further reading

• How to cycle a fish tank
• Stocking ideas by tank size