Care
The One-lined Pencilfish is a small shoaling species known from tributaries, backwaters, and swamplands, where the water is sluggish or almost still, and crowded with dense vegetation and an abundance of leaf litter. The water in the native habitat is very soft and acidic, and stained a tea colour from the tannins in the decaying leaves and wood.
The home aquarium should be mature, with a dark substrate and background and with plenty of plant cover - both rooted and floating - in order for these peaceful mid-to-top-dwelling fish to feel secure. Filtration should be efficient but water movement gentle. These fish are best maintained in groups of at least 10, and more than this wherever possible. Dominant males may occasionally bicker with one other, but providing there is a good network of hiding places/visual barriers for them to retreat into if necessary, no harm should ensue. Keeping more females than males will also help to reduce any minor aggression-related problems. In the wild, these fish are found alongside many other small characins, including representatives from the Copella, Hemigrammus, Hyphessobrycon, and Paracheirodon genera. Dwarf cichlids from the Apistogramma or Mikrogeophagus genera could also be considered as good tankmates, as well as Corydoras catfish and small loricariids. Choose companions wisely as Pencilfish can be fairly timid and will hide away and refuse to feed if tankmates are too boisterous. If unfussy about creating an exact biotope, some of the smaller Rasbora and Boraras species from Asia would get along well with the pencilfish, as would Kuhli loaches (Pangio spp.). As with other Nannostomus, N. unifasciatus assume a cryptic colour overnight so may look a little pale when the lights first switch on. This species also swims in an oblique position with tail slightly down and head angled towards the water's surface, a trait that, amongst congeners, is shared only by N. eques (the Hockeystick Pencilfish). Acclimatisation should be carried out very carefully, and be sure to keep up with small regular water changes to keep nitrogenous wastes at a minimum. Tight fitting coverslides are a must, as these fish are capable of jumping from an open topped aquarium.
This species is often imported in mixed batches alongside the Hockeystick pencil (N. eques). With such a broad distribution, it is likely that this fish is actually more than one species and DNA work seems to suggest that there's a few cryptic species waiting to be discovered.
Feeding
Flake, micropellets, plus small frozen foods such as bloodworm, white mosquito larvae, daphnia, and baby brineshrimp (Artemia nauplii).
Breeding
This species has been bred in the home aquarium, although it is challenging and reports are few and far between; this would make an excellent breeding project for the dedicated hobbyist. A separate softwater breeding aquarium should be set up (peat filtration recommended as the water should ideally have a pH below 6) with plenty of fine-leaved plants, a substrate of marbles, subdued lighting, and gentle air-driven filtration. One or more pairs of well-conditioned adults should then be carefully acclimatised across. When ready to spawn, and whilst swimming alongside one another, the male will nudge the female's abdomen. The eggs will be laid/fertilised a few at a time, and these should fall into the mass of plants or down into the safety of the marbles. This will continue until up the female is spent of eggs, and the parents, being voracious egg-eaters, should be removed immediately. It should be noted that some aquarists find breeding is more successful with a single pair, rather than a group, as the smaller number of adult fish present will mean less chance of predation. The eggs should hatch after 24-36 hours (temperature dependent) with the miniscule fry using up their yolk sacs and becoming free-swimming around 5-6 days later. Feed on infusoria, rotifers, and powdered first foods to begin with, moving on to larger foods such as microworm and Artemia nauplii as they grow.
