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 ; tactile
Perception Channels: visual ; tactile ; chemical
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.
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.
Known Predators:
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.
Average mass: 0.13 g.
Range length: in wild - 2.5 cm, in aquarium - 5 (high) cm.
Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry
Sexual Dimorphism: female larger; sexes shaped differently
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.
Range lifespan
Status: captivity: 10 (high) years.
Average lifespan
Status: wild: 1 years.
Average lifespan
Status: captivity: 5 years.
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 ; freshwater
Aquatic Biomes: rivers and streams
Cardinal tetras live in Brazil, Colombia, and Venezuela, in the upper Orinoco and Negro River drainages.
Biogeographic Regions: neotropical (Native )
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.
Commensal/Parasitic Species:
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
Paracheirodon axelrodi has no known negative affect on humans.
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.
Cardinal tetras are common in their native range, they are not considered threatened.
US Federal List: no special status
CITES: no special status
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.
Animal Foods: eggs; carrion ; insects; terrestrial non-insect arthropods; aquatic or marine worms; aquatic crustaceans; zooplankton
Plant Foods: fruit; phytoplankton
Other Foods: fungus; detritus ; microbes
Primary Diet: carnivore (Eats non-insect arthropods); planktivore
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)
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.
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: 500.
Range gestation period: 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.
Key Reproductive Features: semelparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (External ); 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)
The cardinal tetra (Paracheirodon axelrodi) is a freshwater fish of the family Characidae of order Characiformes. It is native to the upper Orinoco and Negro Rivers in South America. Growing to about 3 cm (1.2 in) total length, the cardinal tetra has the striking iridescent blue line characteristic of the genus Paracheirodon laterally bisecting the fish, with the body below this line being vivid red in color, hence the name "cardinal tetra". The cardinal tetra's appearance is similar to that of the closely related neon tetra, with which it is often confused; the neon's red coloration extends only about halfway to the nose, and the neon's blue stripe is a less vibrant blue.
The cardinal tetra is a very popular aquarium fish, but is less widespread than the neon tetra because until recently, it was difficult to breed in captivity. However, many breeders are now producing the fish; in most cases, one can determine if the cardinal tetra is bred or wild-caught due to damaged fins on wild-caught specimens. Some ichthyologists believe fishkeepers should continue to support the sustainable cardinal fishery of the Amazon Basin, since thousands of people are employed in the region to capture fish for the aquarium trade. If those fishermen lost their livelihoods catching cardinals and other tropical fish, they might turn their attention to engaging in deforestation.[2]
American ichthyologist Leonard Peter Schultz described the cardinal tetra in 1956 as Cheirodon axelrodi.[1] The specific epithet honors ichthyologist Herbert R. Axelrod. Hyphessobrycon cardinalis is an obsolete synonym. The fish's common name, cardinal tetra, refers to the brilliant red coloration, reminiscent of a cardinal's robes. P. axelrodi is also often called the red neon tetra.
The species exists in a number of different color forms or phenotypes. A "gold" and "silver-blonde" form exists in the Rio Negro drainage that has less blue in the longitudinal stripe. The normal form from the Rio Negro drainage has a blue stripe, which extends to the adipose fin, while the Orinoco drainage phenotype has a stripe that stops posterior to the adipose. The Orinoco phenotype may represent a subspecies of P. axelrodi.
The cardinal tetra has bright red ventral parts and an iridescent blue line that runs horizontally along its body. The characteristic iridescence of this and related fishes, such as the neon tetra, is a structural color, caused by refraction of light within guanine crystals that develop within special cells called iridocytes in the subcutaneous layer. The exact shade of blue seen depends on the viewing angle of the viewer relative to the fish - if the viewpoint changes so as to look at the fish more from below, the colour will change hue, becoming more deeply sapphire blue and even indigo. Change of viewpoint to one above the fishes, however, and the color becomes more greenish. Cardinal tetras appear to grow larger in captivity than they do in the wild.[3] They have a large stomach and small gut.[3]
Cardinal tetras are found on the upper Orinoco and the Negro, which are located in Colombia and Venezuela and Brazil, respectively.
The cardinal tetra forages in areas of slow-moving, shallow water. It is predominantly predatory, feeding on tiny animals found on underwater plants, roots, and leaf litter. Creatures commonly eaten include the larvae of chironomid midges and microcrustaceans such as water fleas (Cladocera) of the families Moinidae, Macrotrichidae, and Daphniidae, and copepods of the family Harpacticidae. Other organisms eaten include other fly larvae, insect eggs, rotifers, and testate amoebae.[3]
The cardinal tetra, in the wild, swims upstream in large numbers to parts of its native river habitat completely enclosed above by rainforest canopy. Such waters are subject to heavy shading by the rainforest trees, and virtually no sunlight reaches them. Here, the fishes spawn in large aggregations. If the fishes are ready to spawn, the male, which will be the slimmer of the two fishes in outline, pursues the female into fine-leaved plants; her fuller outline, which usually indicates the presence of ripe eggs within her reproductive tract, should be readily apparent at this point. If the female is ready, she allows the male to swim alongside her, and together, the pair release eggs and sperm.
The fish might also be effectively an annual species with a lifespan of just a single year in nature. It lives for several years in captivity. For those seeking to breed them in the aquarium, the best way to do so is by mimicking the same natural setup. A study conducted in Manaus, Brazil, subjected cardinal tetras to adverse water conditions for 96 hours. The fish perished at a low temperature of 19.6 °C and high of 33.7 °C, and pH below 2.9 or above 8.8.[4]
The cardinal tetra (Paracheirodon axelrodi) is a freshwater fish of the family Characidae of order Characiformes. It is native to the upper Orinoco and Negro Rivers in South America. Growing to about 3 cm (1.2 in) total length, the cardinal tetra has the striking iridescent blue line characteristic of the genus Paracheirodon laterally bisecting the fish, with the body below this line being vivid red in color, hence the name "cardinal tetra". The cardinal tetra's appearance is similar to that of the closely related neon tetra, with which it is often confused; the neon's red coloration extends only about halfway to the nose, and the neon's blue stripe is a less vibrant blue.
The cardinal tetra is a very popular aquarium fish, but is less widespread than the neon tetra because until recently, it was difficult to breed in captivity. However, many breeders are now producing the fish; in most cases, one can determine if the cardinal tetra is bred or wild-caught due to damaged fins on wild-caught specimens. Some ichthyologists believe fishkeepers should continue to support the sustainable cardinal fishery of the Amazon Basin, since thousands of people are employed in the region to capture fish for the aquarium trade. If those fishermen lost their livelihoods catching cardinals and other tropical fish, they might turn their attention to engaging in deforestation.
