Paracheirodon axelrodi

Geographic Range

Cardinal tetras live in Brazil, Colombia, and Venezuela, in the upper Orinoco and Negro River drainages.

• Biogeographic Regions
• neotropical neotropical
  • native native

Habitat

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.

• Habitat Regions
• tropical tropical
• freshwater freshwater

• 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.

Sometimes cardinal tetras are confused with neon tetras, Paracheirodon innesi . Cardinal tetras, however, have a longer red band dorsally.

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.

• Other Physical Features
• ectothermic ectothermic
• heterothermic heterothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• female larger
• sexes shaped differently

Development

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.

Reproduction

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.

• Mating System
• polygynandrous (promiscuous) polygynandrous (promiscuous)

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.

• Key Reproductive Features
• semelparous semelparous
• seasonal breeding seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• fertilization fertilization
  • external external
• oviparous oviparous

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.

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

Lifespan/Longevity

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.

Behavior

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.

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

• Key Behaviors
• natatorial natatorial
• diurnal diurnal
• motile motile
• migratory migratory
• sedentary sedentary
• social social
• colonial colonial

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.

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.

• Communication Channels
• visual visual
• tactile tactile

• Perception Channels
• visual visual
• tactile tactile
• chemical chemical

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.

• Primary Diet
• carnivore carnivore
  • eats non-insect arthropods
• planktivore planktivore

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

• Plant Foods
• fruit
• phytoplankton phytoplankton

• Other Foods
• fungus
• detritus detritus
• microbes

Predation

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.

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

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.

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.

• Positive Impacts
• pet trade pet trade

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 .

Additional Links

Encyclopedia of Life

Contributors

Tanya Dewey (editor), Animal Diversity Web.

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

References

Butler, R. 2003. "Cardinal Tetra, Cardinal Neon Paracheirodon axelrodi " (On-line). mongabay.com. Accessed October 23, 2004 at http://fish.mongabay.com/species/Paracheirodon_axelrodi.html .

Bydzovsky, V. 2000. "Roter Neon Superstar" (On-line). http://www.aquaristik.de/neu_su.htm . Accessed October 23, 2004 at http://www.aquaristik.de/artikel/suss9.htm .

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). fishbase.org. Accessed October 01, 2004 at http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=8195&genusname=Paracheirodon&speciesname=axelrodi .

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

Lundie, A. 2004. "Paracheirodon axelrodi" (On-line). FishProfiles.com. Accessed October 22, 2004 at http://www.fishprofiles.com/files/profiles/cardinal.xml .

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

Sharpie, S. 2004. "Freshwater Aquariums Fish Trivia #1" (On-line). freshaquarium.about.com. Accessed October 24, 2004 at http://freshaquarium.about.com/library/weekly/aa011899a.htm .

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 http://www.scielo.br/scielo.php?pid=S0044-59672004000100009&script=sci_arttext&tlng=en .

Oregon Zoo. 2002. "Cardinal Tetra" (On-line). Oregon Zoo Animal Fact Sheets. Accessed September 02, 2006 at http://www.oregonzoo.org/Cards/Amazon/cardinal.tetra.htm .

AquaBase.org. 2004. "Poisson : Paracheirodon axelrodi" (On-line). AquaBase.org. Accessed October 22, 2004 at http://www.aquabase.org/fish/view.php3?id=3 .

2004. "Tempting Terrific - The Tetras" (On-line). The Goldfish Bowl. Accessed November 11, 2004 at http://www.thegoldfishbowl.co.uk/temptingtetras.html .

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 http://www.scielo.br/scielo.php?pid=S0044-59672004000100009&script=sci_arttext&tlng=en .