Nannostomus trifasciatusThree-lined pencilfish(Also: Threebanded pencilfish; Threestripe pencilfish)

Geographic Range

Nannostomus trifasciatus is a freshwater fish native to Guyana, the Rio Negro, and the middle portion of the Amazon River (Wheeler, 1975; Sterba, 1963).


N. trifasciatus prefers slow-moving, peaty, slightly acidic water. It is also usually found in shaded, weedy areas. This species fares best at temperatures between 78-80° F. Within these conditions, N. trifasciatus is found in several different habitat types. In the Rio Negro, it inhabits the large swamps that form where tributaries meet the main branch of the river. When the river floods, it moves into the inundated rainforest. During the low water season, it often becomes trapped in small lakes that are left behind, or stays close to the wooded edges of the forest. N. trifasciatus rests near the water surface at night and during the day inhabits the middle to upper water layers (Torres et al., 2002; Masagaki et al., 1999; Goulding et al., 1988; Wheeler, 1975; Sterba, 1963; McInerny, 1958).

  • Aquatic Biomes
  • rivers and streams

Physical Description

The three-lined pencilfish is a small fish, with adults not reaching more than 6 cm in length. It has a small terminal mouth, and an adipose fin may or may not be present. Many characiform fishes of the Amazon basin possess distinct daytime and nighttime color patterns, and N. trifasciatus is no exception. During the day, it has three dark longitudinal stripes that run the length of the body. At night, the stripes disappear and three large dark spots materialize on the sides of the fish, extending from its back to its belly. Recent research has shown that this change in coloration is due to the differential action of the pineal hormone melatonin on pigment cells in different regions of the integument. It has been suggested that the daytime color pattern may serve an aposematic or recognition function for individuals of the same species, and that the nighttime pattern may help hide the fish from nocturnal predators. In between the variable, darkly-pigmented regions, N. trifasciatus is greenish-gold in color on its back and sides and silver underneath. The gill cover and dorsal, pelvic, anal, and caudal fins possess large red blotches. Males of the species may have an additional row of red spots in the gold area between the middle and uppermost stripes (Masagaki et al., 1999; Wheeler, 1975; Sterba, 1963; McInerny, 1958; Innes, 1956).

  • Range length
    6.0 (high) cm
    2.36 (high) in
  • Average length
    4.4 cm
    1.73 in


Immediately after hatching, the young hang on to plants or rest on the bottom. They do not swim freely until their 5th day. A juvenile N. trifasciatus does not look like its parents; it is long, thin, and darkly colored. It also possesses an extended adipose fin that it uses to swim. Growth is slow in this species, and juveniles reach adulthood in seven months (Sterba, 1963; McInerny, 1958; Innes, 1956).


N. trifasciatus spawns during the daytime among plant leaves. The eggs are adhesive and are sometimes placed on plants and sometimes scattered throughout the water. Fertilization takes place externally, and anywhere from 30-70 eggs are produced at a time. The eggs hatch in 18-72 hours, depending on the water temperature (Torres et al., 2002; Sterba, 1963; McInerny, 1958; Innes, 1956).

  • Range number of offspring
    30 to 70
  • Range time to hatching
    18 to 72 hours
  • Average time to hatching
    24 hours
  • Average age at sexual or reproductive maturity (female)
    7 months
  • Average age at sexual or reproductive maturity (male)
    7 months

Parents do not guard their eggs or care for fry (Torres et al., 2002).

  • Parental Investment
  • no parental involvement


This species is active during the day, resting at night in the upper layers of the water. It swims with its body in a horizontal position. The fact that its daytime coloration may be an aposematic signal to members of its own species suggests that it may exhibit some degree of territoriality or dominance hierarchy in the wild. N. trifasciatus may also be migratory, as it moves from the main river channels to flooded forest during the rainy season (Masagaki et al., 1999; Goulding et al., 1988; Sterba, 1963).

Communication and Perception

Little is known about communication in N. trifasciatus. As mentioned above, its bright daytime coloration may serve either to warn or help it to recognize conspecifics (Masagaki et al., 1999).

  • Communication Channels
  • visual

Food Habits

N. trifasciatus spends much of its time near the water surface, where it feeds primarily on insects. It has also been reported to eat detritus and algae. In captivity, it will eat just about any type of standard fish food (Goulding et al., 1988; Wheeler, 1975; Sterba, 1963; Innes, 1956).


N. trifasciatus often falls prey to other fish species, such as the striped pike-characin, Boulengerella lateristriga. Its blotchy nocturnal pattern may be a means of avoiding predation at night, as the blotches serve to break up the outline of its body. (Goulding, et al., 1988; Masagaki and Fujii, 1999)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

N. trifasciatus is a primary, secondary, and tertiary consumer, because it feeds on a variety of invertebrate prey and plant material. It also provides food for animals at higher trophic levels (Torres et al., 2002; Goulding et al., 1988).

Economic Importance for Humans: Positive

Due to its attractive coloration and ease of keeping, N. trifasciatus is a popular aquarium fish (Sterba, 1963; McInerny, 1958; Innes, 1956).

Economic Importance for Humans: Negative

Nannostomus trifasciatus have no known adverse effects on humans.

Conservation Status

N. trifasciatus is fairly common throughout its home range, and because it is bred easily in captivity for the aquarium trade, it is unlikely that this species will face extinction in the near future (Torres et al., 2002; Goulding et al., 1988; Sterba, 1963; McInerny, 1958; Innes, 1956).


William Fink (editor), University of Michigan-Ann Arbor.

Allison Poor (author), University of Michigan-Ann Arbor.



living in the southern part of the New World. In other words, Central and South America.

World Map

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.


an animal that mainly eats meat


uses smells or other chemicals to communicate


having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.


an animal that mainly eats decomposed plants and/or animals

external fertilization

fertilization takes place outside the female's body


union of egg and spermatozoan


mainly lives in water that is not salty.


An animal that eats mainly insects or spiders.


offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).


makes seasonal movements between breeding and wintering grounds


having the capacity to move from one place to another.


specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.


an animal that mainly eats all kinds of things, including plants and animals


reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

pet trade

the business of buying and selling animals for people to keep in their homes as pets.


reproduction that includes combining the genetic contribution of two individuals, a male and a female


a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.


uses touch to communicate


the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.


uses sight to communicate


Goulding, M., M. Carvalho, E. Ferreira. 1988. Rio Negro, Rich Life in Poor Water. The Hague: SPB Academic Publishing.

Innes, W. 1956. Exotic Aquarium Fishes. Philedelphia: Innes Publishing Co..

Masagaki, A., R. Fujii. 1999. Differential actions of melatonin on melanophores of the threeline pencilfish, *Nannostomus trifasciatus*. Zoological Science, 16: 35-42.

McInerny, D. 1958. All About Tropical Fish. New York: MacMillan.

Sterba, G. 1963. Freshwater Fishes of the World. New York: Viking Press.

Torres, A., C. Casal, S. Weitzman. 2002. "*Nannostomus trifasciatus*" (On-line). Accessed November 13, 2002 at

Wheeler, A. 1975. Fishes of the World. An Illustrated Dictionary. New York: MacMillan.