Language English The brown pencilfish (Nannostomus eques) lives in shaded areas. Photo: Alamy/blickwinkel OngletsDescriptionDistinguishing featuresThe brown pencilfish is very small, slender and elongated. It has a pointy head, and a broad black stripe runs down its side, contrasting with the light color of its back. The black-edged produce a mesh-like effect. This fish gives the impression of having a half-tail, because the lower lobe of its caudal fin is bigger and darker than the upper lobe, which is small and transparent. A red mark is clearly visible on the anal fin. ReproductionBreeding begins with courtship behavior. Spawning later takes place under the leaves of aquatic plants. The brown pencilfish lays four eggs at a time. These sink to the bottom, and after 24 to 30 hours, the young are born. Five days after hatching, the young reach the fry stage and begin to swim in open water. They feed on little microorganisms. DietThis fish can catch the little insects that fall to the water’s surface. It also eats other small invertebrates and zooplankton. In an aquarium, they can be fed on microorganisms like daphnia and Artemia so that they retain their bright colors. PredatorsThe brown pencilfish’s predators are larger piscivorous fish, especially the Monocirrhus polyacanthus (leaffish). Overnight, the fish’s appearance changes to a camouflage of vertical lines. That adaptation in synch with diurnal rhythm takes place beyond the control of the fish. HabitatThe brown pencilfish is found in waters where plant life is very dense. It lives in small streams or on the banks of larger waterways, but always in shaded areas. This fish hails from the central regions of the Amazon rainforest, notably from the Rio Negro. It can be seen in flooded forests or in shallow, rather opaque water. It prefers acidic water with a temperature of between 23 °C and 28 °C. Ecology, behaviourPencilfish adopt a characteristic 60º oblique posture looking upwards. A number of pencilfish may gather together, immobile, in that position, just under the surface of the water. That habit, which they share with other fish like the hatchetfish, allows them to catch insects as soon as they touch the water’s surface. Additionally, this mild-mannered and calm fish can easily share an aquarium with small bottom feeders, like certain tetras or corydoras. French namePoisson-crayon brun Scientific nameNannostomus equesPhylumChordataClassOsteichthyes (bony fish)OrderCharaciformesFamilyLebiasinidaeSizeLength: 2,5 to 5 cmLife span2 yearsStatusNot evaluated (IUCN) Common species, commercially exploited for sale to aquarists.