These fishes belong to the family Lebiasinidae and several species are available in the trade at one time or another. They may be kept in a community aquarium, but if the water conditions are less than ideal, or they are prevented from feeding by more boisterous fishes, it is better to house them in species tanks.
Pencilfishes are small and timid surface dwellers, and much of the day is spent motionless just below the surface so that they look like pieces of twig. Only at dusk do they come to life, when they start to feed on insects that have fallen on the surface or on small aquatic invertebrates. Some species will also search the substrate for food, sifting the mud and silt in search of small worms and so on. In the aquarium, they accept flake, brine shrimp, and small frozen foods but prefer live Daphnia and other pond foods. As they are most active in the evening, this is the time to feed them.
Ideally the water in the aquarium should be soft, slightly acid, and free from nitrates. Maintenance of good quality water is essential if you wish to succeed with these fishes. The pH may vary between 5.5 and 7.0 provided any changes are gradual. Use a dark substrate, and plant with clumps of Cryptocoryne with some floating plants such as Indian fern (Ceratopteris thalictroides} to keep down the light and also provide hiding places among its trailing roots. The temperature should be in the range 23-28°C (73-82°F).
The colour patterns on their bodies change from day to night; what appear as faint vertical black patches during the day become predominantly black markings at night, while those which were prominent during the day fade away.
Breeding, these fishes is difficult but not impossible. The main requirements are a breeding tank with mesh that the eggs can fall through, a clump or two of Java moss or synthetic substitute on top of the mesh, very soft (2 dH or less) slightly acid water (about pH 6.0), dim light, a dark bottom (black paper beneath the tank works well), and a pair of willing fishes. If everything goes to plan, the eggs will be released and fall through the mesh before the parents can devour them, but sometimes the fishes will not spawn. This is usually because they have not been fed the right foods so that the diet has been lacking in amino acids. Feeding mosquito larvae and Drosophila (fruit flies) will usually rectify this. Of the two genera, Nannobrycon and Nannostomus, the latter is the easier to breed.
We suggest you try Nannobrycon eques (Hockey stick pencilfish or Three-striped pencilfish), Nannobrycon unifasciatus (One-striped pencilfish), Nannostomus beckfordi (Golden pencilfish), Nannostomus harrisoni (Harrison’s pencilfish), Nannostomus marginatus (Dwarf Pencilfish), and/or Nannostomus trifasciatus (Threelined pencilfish).