Language English The golden pencilfish (Nannostomus beckfordi) lives near the surface. Photo: Alamy/blickwinkel OngletsDescriptionDistinguishing featuresThe golden pencilfish is a very small fish with a broad black band on its side (from the mouth to the base of the tail). The fish has a silver stripe on its flank near the belly, while its back is pale brown. The base of its caudal fin displays two dark-red spots, and its distal portion a clear-blue color. The ventral fins are colored pearl-blue and white. All pencilfish species 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. ReproductionIn the spawning period, the male and female swim head downward. Then the couple place themselves side by side, quivering and rubbing their flanks together. The female lays 175 semi-adhesive eggs, in small clutches of 1 to 5 eggs among fine-leaved plants. Sometimes the eggs disperse, because this fish does not build a nest, and neither does it protect its eggs. Egg laying lasts 8 hours. The eggs hatch after 24 to 40 hours. The fry begin to swim after a period of 6 days. DietThe golden pencilfish feeds on tiny invertebrates (worms, crustaceans, insects and zooplankton). It catches primarily insects that fall to the water surface. PredatorsGiven its small size, this fish is preyed on by a number of species of large tropical fish. HabitatThe golden pencilfish can be observed in the Brazilian Amazon and in Guyana and French Guiana, where it prefers a temperature of between 24 and 26 degrees Celsius and a pH between 5.5 and 7.0. The pencilfish therefore normally lives in acidic water. That acidification stems from the decomposition of plant matter, which explains this water’s tendency to grow very dark (like brewed tea), almost black when there is really a lot of organic matter. This little fish can be found near the banks of waterways as well as in slow-moving streams and rivers, and in the standing water of small river offshoots. It likes shallow water (less than 50 centimeters) where a lot of vegetation can be found: aquatic plants, branches, a floor of dead leaves, and decomposing plant matter. Ecology, behaviourThe golden pencilfish lives in schools in midwater and near the surface. It is often seen either horizontally or at an angle, but at the first sign of danger it rushes to one of its hiding places. It is not especially active during the day. On the calm side, it is also highly independent, interacting very little with other species of fish. On the other hand, it is very lively at night when out looking for food, turning paler so as not to be spotted by predators. The broad horizontal band will shrink and form thin stripes for camouflage purposes. Also to be observed is a very rapid change in color and patterns during courtship behavior, or when males fight. French namePoisson-crayon doré Scientific nameNannostomus beckfordiPhylumChordataClassOsteichthyes (bony fish)OrderCharaciformesFamilyLebiasinidaeSizeLength: 4 to 5 cm, until 6,5 cmLife span2 yearsStatusNot evaluated (IUCN) Common species, commercially exploited for sale to aquarists.