Beckford's pencilfish

Water parameters

Tolerated range for this species. Aim for the middle of each band rather than the extremes.

Tank and habitat

Substrate: any.

Behavior

Plant interaction: plant safe.

Feeding

Small flake or micro pellets, plus the usual range of small frozen and live foods (daphnia, baby brine shrimp, cyclops, mosquito larvae, microworms). The mouth is small even for a fish of this length, so crush flake before dropping it in. The fish hovers near the surface and picks at food as it drifts past rather than chasing it down. Live baby brine shrimp produces the most enthusiastic response. In a community tank they are not the fastest feeders, so a feeding ring or a spot near their usual hover zone keeps faster fish from grabbing everything first. Two small meals a day is plenty.

Compatibility

• Peaceful upper- and mid-water fish that mostly minds its own business. Males do flare and posture at each other, but the contests are bluff and do not produce injuries. Useful as a dither species for shy tankmates lower in the column
• Strongly social. Groups of six or more are the minimum if the fish are to behave naturally; smaller groups tend to hide and lose colour
• Pair with other calm small fish: tetras, small rasboras, corydoras, otocinclus, dwarf cichlids. Avoid anything fast, boisterous, or large enough to view a 6 cm fish as food. Tiger barbs and giant danios are particularly poor matches
• Jumpers. The fish launches out of open tanks without warning, and there are multiple keeper reports of losses through filter cutouts and tank rims. A tight-fitting lid is necessary, and floating plants seem to reduce the urge to leap

Origin and habitat

A small pencilfish from northern South America, well distributed through the river systems of the Guiana Shield (Guyana, Suriname, French Guiana), the eastern Amazon drainage in Amapa and Para states in Brazil, the Madeira, the lower and middle Amazon as far upstream as the lower Negro, and the Orinoco system in Venezuela. The type locality is Goedverwagting, a plantation on the Demerara coast of Guyana, where the holotype was collected in the 19th century by F.J.B. Beckford, an English naturalist who passed the specimens on to the British Museum. Gunther described the species in 1872 in the Proceedings of the Zoological Society of London. The genus name Nannostomus is built from Latin nannus and Greek stoma, in a reference to the small mouths the group is known for. The species sits in the family Lebiasinidae (subfamily Pyrrhulininae), the pencilfish and splashing-tetra family, inside the order Characiformes. Several earlier names (anomalus, simplex, aripirangensis, surinami) have since been treated as synonyms of N. beckfordi, partly because populations from different river systems look different enough to have been mistaken for separate species in older literature. Modern trade fish are mostly captive-bred, and selectively bred orange and red colour forms exist. The species is small, reaching a maximum standard length of around 6.5 cm, with pet-trade specimens commonly smaller. Like the rest of the genus, the fish drops most of its day colour at night and switches to a cryptic, vertically barred pattern; the same shift has been observed in blind individuals, which suggests an automatic response the fish does not consciously control. The species has been exported to aquarists since at least the early 1910s. IUCN Least Concern.

Breeding

Continuous egg scatterer rather than batch spawner. A breeding pair drops a few eggs at a time into fine leaved plants or a spawning mop, with a male nudging the female's belly during the act, and a single pair will accumulate to roughly 100 to 200 eggs over the course of a few days. The parents have no brood instinct at all and will eat the eggs and fry as soon as they notice them, so the standard setup is either to use a dense mat of java moss or fine mops that the eggs fall into and out of reach, or to move the parents out after a couple of days of spawning. Hatching is fast at typical aquarium temperatures, around 24 to 40 hours depending on temperature, with fry going free-swimming about five to six days later once the yolk is absorbed. The fry are very small and need fine first foods such as infusoria, paramecium culture, or commercial green water for the first few days before they can take baby brine shrimp nauplii. Survival through the first week is variable and tends to be the bottleneck for getting numbers up. Soft, acidic water (pH around 5.5 to 6.5, GH below 6) produces the best fertilization and hatch rates. Spawning is not difficult to set up, but the trickle-spawning approach means a single event yields far fewer fry than a tetra would.

Common problems

The colour shift at night is normal and not a health problem, but it surprises new keepers regularly. Real issues are mostly two: jumping and food competition. The fish has a torpedo-shaped body built for bursts, and in an open-top tank or any setup with gaps around filter intakes, heater cords, or airline tubing, expect to lose fish over the rim. A close-fitting cover and floating plants are the simplest fixes. In a community tank, the small mouth and gentle feeding style mean they lose out to faster species at the surface and can gradually drop weight even when food is being offered; target feeding near their usual hover spot keeps them eating. Ich shows up sometimes in newly purchased fish and responds to a standard heat-and-medicate treatment around 30 C. Otherwise the species is undemanding once settled, and males will spar visually but not damage each other; that display behaviour is part of why they are sold in the first place.

Bioload

Further reading

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