Paracheirodon axelrodiNeon(Also: Neon tetra; Red neon; Scarlet characin)

Geographic Range

Cardinal tetras live in Brazil, Colombia, and Venezuela, in the upper Orinoco and Negro River drainages. (Froese, et al., 2004; Lundie, 2004)


Paracheirodon axelrodi individuals prefer slow moving, middle layer water in shoals. They prefer a slightly acidic pH (5.8) and a temperature of 24°C. Cardinal tetras do not migrate and are generally found in open water. (Froese, et al., 2004; Lundie, 2004)

  • Aquatic Biomes
  • rivers and streams

Physical Description

Cardinal tetras are small fish, males grow to about 2.5 cm in length in the wild, but can attain lengths of 5 cm in an aquarium. This species is characterized by a horizontal neon blue stripe and deep red markings. The neon stripe of Paracheirodon axelrodi becomes iridescent because of external lighting. As the angle of light that strikes them changes, the color of the neon stripe turns from green to blue or vice versa. During the night, when no light hits the stripe, cardinal tetras are a transparent, brownish color. Cardinal tetras, as well as many other tetras, have a small adipose fin on their dorsal side at the tail end of their bodies. Cardinal tetras have a single row of dentary teeth. (Butler, 2003; "Tempting Terrific - The Tetras", 2004; "Poisson : Paracheirodon axelrodi", 2004; Butler, 2003; Bydzovsky, 2000; Fink and Weitzman, 1983; Froese, et al., 2004; Lundie, 2004)

Sometimes cardinal tetras are confused with neon tetras, Paracheirodon innesi. Cardinal tetras, however, have a longer red band dorsally. ("Poisson : Paracheirodon axelrodi", 2004)

Paracheirodon axelrodi exhibit some sexual dimorphism. Females are slightly larger and wider than males. Females have larger stomachs as well. Mature male cardinal tetras have bony pelvic fin hooks. (Fink and Weitzman, 1983; Lundie, 2004; Fink and Weitzman, 1983; Lundie, 2004)

  • Sexual Dimorphism
  • female larger
  • sexes shaped differently
  • Average mass
    0.13 g
    0.00 oz
  • Range length
    in wild - 2.5 cm, in aquarium - 5 (high) cm


Eggs hatch within 24 to 30 hours of fertilization. Fertilized fish eggs, in general divide by discoidal meroblastic cleavage. Because fish eggs are telolecithal (have a large percentage of yolk) cleavage can only take place in a small part of the egg. (Gilbert, 2003)


Female cardinal tetras release their eggs during the rainy season. The eggs become fertilized by the milt (sperm) of males in close proximity. Mating takes place at twilight during the rainy season. The male embraces the female while swimming. Fertilization is external. As the female scatters about 500 eggs into the water, males fertilize the eggs. ("Tempting Terrific - The Tetras", 2004; Norris and Chao, 2002)

Female cardinal tetras may release about 500 eggs. Once the eggs have been laid, they sink and some adhere to plants. Because cardinal tetra eggs are light sensitive, the only eggs that can develop into adult fish are released in a shaded river habitat. To breed cardinal tetras successfully in captivity, the pH should be between 5.5 and 6, the temperature should be at 24°C and the light should be dim. Fry are independent within 3 to 4 days of hatching. Both males and females reach sexual maturity by approximately 9 months of age. (Froese, et al., 2004; "Cardinal Tetra", 2002; "Tempting Terrific - The Tetras", 2004; "Poisson : Paracheirodon axelrodi", 2004; Butler, 2003; Froese, et al., 2004; Norris and Chao, 2002; "Cardinal Tetra", 2002)

  • Breeding interval
    The breeding interval of these animals is not reported.
  • Breeding season
    The spawning season of cardinal tetras in their natural environment is during the rainy season.
  • Average number of offspring
  • Range time to hatching
    24 to 30 hours
  • Range time to independence
    3 to 4 days
  • Average age at sexual or reproductive maturity (female)
    9 months
  • Average age at sexual or reproductive maturity (male)
    9 months

Parent cardinal tetras take no care of their eggs or young. After eggs are released, some parent cardinal tetras may even eat some of their spawn. ("Tempting Terrific - The Tetras", 2004)

  • Parental Investment
  • no parental involvement
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female


Cardinal tetras are able to live longer in captivity than in the wild. In the wild, they are expected to live about 1 year. In captivity, the life expectancy is about 5 years, although individuals may live as long as 10 years. ("Poisson : Paracheirodon axelrodi", 2004; "Cardinal Tetra", 2002)

  • Range lifespan
    Status: captivity
    10 (high) years
  • Average lifespan
    Status: wild
    1 years
  • Average lifespan
    Status: captivity
    5 years


Paracheirodon axelrodi individuals are active during the day, and live in schools of several thousands in natural habitats. At least 10 of this species should be kept together in an aquarium in order for them to feel safe. In cases of fewer than 10 individuals living together in a tank, cardinal tetras tend to develop sickness due to stress. ("Poisson : Paracheirodon axelrodi", 2004; Lundie, 2004)

Cardinal tetras are known to make small scale seasonal migrations upstream or downstream depending on the height of water during a particular season. (Bydzovsky, 2000)

Home Range

The home range of these fish has not been reported.

Communication and Perception

Communication has not been described in this species. However, tactile communication occurs during mating. It is likely that these fish use tactile and visual cues as part of their communication, since they seem aware of the number of other cardinal tetras in a tank in captivity. ("Poisson : Paracheirodon axelrodi", 2004; Froese, et al., 2004; "Cardinal Tetra", 2002)

Little is known about how cardinal tetras perceive their environment. They use their eyesight and tactile cues and are able to perceive sound through the water.

Food Habits

The diet of P. axelrodi consists of very small crustaceans, mesofauna, eggs, algae, detritus, and some other types of prey. Most types of small crustaceans eaten are cladocera (small, spherical moinids, daphnids, and macrothricids), as well as some copepods (benthonic Harpacticidae). Rotifera and Thecamoebae are included in the mesofauna that cardinal tetras eat. The types of algae that they eat include unicellular diatoms (Navicularia and Pinnularia), and some green algae (Chlamydomonas, Conjugatophyta, and Volvocaceae). Cardinal tetras sometimes feed on dead fish, eating the detritus of their muscular, proteinous, and membraneous tissues. Paracheirodon axelrodi individuals may also eat ants, Diptera larvae or pupae, mites, newly hatched shrimp, fungus, pieces of fruit, and fish larvae. ("The food spectrum of the cardinal - tetra (Paracheirodon axelrodi, Characidae) in its natural habitat", 2004)

  • Animal Foods
  • eggs
  • carrion
  • insects
  • terrestrial non-insect arthropods
  • aquatic or marine worms
  • aquatic crustaceans
  • zooplankton


The bright, neon, lateral stripe of cardinal tetras makes it difficult for predators to single out and attack an individual. Their schooling behavior also helps to protect individuals from predators. Although little is known on the specific predators of cardinal tetras, they likely fall prey to larger fish and other small to medium aquatic predators as adults, fry, and eggs. (Sharpie, 2004)

When kept in an aquarium with larger fish, such as angelfish, cardinal tetras may become their prey. (Butler, 2003)

Ecosystem Roles

In relatively few cardinal tetras (6.3% of 80 dissected), existence of parasitic nematodes was found in the coelom, or stomach. Cardinal tetras serve as important predators of their small, invertebrate and zooplanktonic prey. They are important food sources, in all life stages, for larger predators. ("The food spectrum of the cardinal - tetra (Paracheirodon axelrodi, Characidae) in its natural habitat", 2004)

Commensal/Parasitic Species
  • Nematodes

Economic Importance for Humans: Positive

Cardinal tetras are often kept and enjoyed as a beautiful aquarium fish. Because of their peaceful nature, cardinal tetras are highly recommended for tanks with more than one species of fish. Most of the cardinal tetras sold come straight from South America because of the difficulty of breeding them in nature; between the years 1977 and 1981, an average of 12 to 17 million cardinal tetras were exported annually. (Bydzovsky, 2000; Froese, et al., 2004; Lundie, 2004)

Economic Importance for Humans: Negative

Paracheirodon axelrodi has no known negative affect on humans.

Conservation Status

Cardinal tetras are common in their native range, they are not considered threatened.

Other Comments

Paracheirodon axelrodi was first described by Schultz in 1956. Paracheirodon axelrodi is sometimes also called cardinal tetra, red neon, or roter neon. Cheirondon axelrodi or Hyphessobroycon cardinalis are synonyms of P. axelrodi. ("Poisson : Paracheirodon axelrodi", 2004; Butler, 2003)


Tanya Dewey (editor), Animal Diversity Web.

Sarah Fintushel (author), University of Michigan-Ann Arbor, William Fink (editor, instructor), 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


flesh of dead animals.


uses smells or other chemicals to communicate


used loosely to describe any group of organisms living together or in close proximity to each other - for example nesting shorebirds that live in large colonies. More specifically refers to a group of organisms in which members act as specialized subunits (a continuous, modular society) - as in clonal organisms.


particles of organic material from dead and decomposing organisms. Detritus is the result of the activity of decomposers (organisms that decompose organic material).

  1. active during the day, 2. lasting for one day.

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

external fertilization

fertilization takes place outside the female's body


union of egg and spermatozoan


mainly lives in water that is not salty.


having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.


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.


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.


photosynthetic or plant constituent of plankton; mainly unicellular algae. (Compare to zooplankton.)


an animal that mainly eats plankton


the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

seasonal breeding

breeding is confined to a particular season


remains in the same area


offspring are all produced in a single group (litter, clutch, etc.), after which the parent usually dies. Semelparous organisms often only live through a single season/year (or other periodic change in conditions) but may live for many seasons. In both cases reproduction occurs as a single investment of energy in offspring, with no future chance for investment in reproduction.


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


associates with others of its species; forms social groups.


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


animal constituent of plankton; mainly small crustaceans and fish larvae. (Compare to phytoplankton.)


Oregon Zoo. 2002. "Cardinal Tetra" (On-line). Oregon Zoo Animal Fact Sheets. Accessed September 02, 2006 at 2004. "Poisson : Paracheirodon axelrodi" (On-line). Accessed October 22, 2004 at

2004. "Tempting Terrific - The Tetras" (On-line). The Goldfish Bowl. Accessed November 11, 2004 at

Instituto Nacional de Pesquisas da Amazônia. 2004. "The food spectrum of the cardinal - tetra (Paracheirodon axelrodi, Characidae) in its natural habitat" (On-line). Accessed October 24, 2004 at

Butler, R. 2003. "Cardinal Tetra, Cardinal Neon Paracheirodon axelrodi " (On-line). Accessed October 23, 2004 at

Bydzovsky, V. 2000. "Roter Neon Superstar" (On-line). Accessed October 23, 2004 at

Fink, W., S. Weitzman. 1983. Relationships of the Neon Tetras, A Group of South American Freshwater Fishes (Teleostei, Characidae), with Comments on the Phylogeny of New World Characiforms. Bulletin of the Museum of Comparative Zoology, 150: 339-395.

Froese, R., L. Malabarba, C. Binohlan. 2004. "Paracheirodon axelrodi" (On-line). Accessed October 01, 2004 at

Gilbert, S. 2003. Developmental Biology. 7th ed. Sunderland, Ma: Sinauer Associates, Inc.

Lundie, A. 2004. "Paracheirodon axelrodi" (On-line). Accessed October 22, 2004 at

Norris, S., N. Chao. 2002. Buy a Fish Save a Tree?. Conservation In Practice, 3: 30-35. Accessed November 11, 2004 at arquivos/ProjectPiabaSummer02.pdf.

Sharpie, S. 2004. "Freshwater Aquariums Fish Trivia #1" (On-line). Accessed October 24, 2004 at

Walker, I. 2004. The food spectrum of the cardinal - tetra (Paracheirodon axelrodi, Characidae) in its natural habitat. Acta Amazonia, 34/1: 69-73. Accessed November 07, 2004 at