Overview

Comprehensive Description

Biology

Occurs mainly in shoals in the middle water layers. Feeds on worms and small crustaceans (Ref. 7020). Breeding in captivity is possible but difficult and most specimens in the aquarium trade are caught in the tributaries of the Rio Negro and Orinoco. Eggs hatch in 24 to 30 hours and fry are free-swimming after 3 to 4 days in captivity (Ref. 7020). One of the most popular and beautiful aquarium fishes. Aquarium keeping: in groups of 5 or more individuals; minimum aquarium size 60 cm (Ref. 51539).
  • Lima, F.C.T., L.R. Malabarba, P.A. Buckup, J.F. Pezzi da Silva, R.P. Vari, A. Harold, R. Benine, O.T. Oyakawa, C.S. Pavanelli, N.A. Menezes, C.A.S. Lucena, M.C.S.L. Malabarba, Z.M.S. Lucena, R.E. Reis, F. Langeani, C. Moreira et al. … 2003 Genera Incertae Sedis in Characidae. p. 106-168. In R.E. Reis, S.O. Kullander and C.J. Ferraris, Jr. (eds.) Checklist of the Freshwater Fishes of South and Central America. Porto Alegre: EDIPUCRS, Brasil. (Ref. 38376)   http://www.fishbase.org/references/FBRefSummary.php?id=38376&speccode=10622 External link.
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Distribution

Upper Orinoco and Negro River basins: Brazil, Colombia and Venezuela.
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South America: Upper Orinoco and Negro River basins.
  • Lima, F.C.T., L.R. Malabarba, P.A. Buckup, J.F. Pezzi da Silva, R.P. Vari, A. Harold, R. Benine, O.T. Oyakawa, C.S. Pavanelli, N.A. Menezes, C.A.S. Lucena, M.C.S.L. Malabarba, Z.M.S. Lucena, R.E. Reis, F. Langeani, C. Moreira et al. … 2003 Genera Incertae Sedis in Characidae. p. 106-168. In R.E. Reis, S.O. Kullander and C.J. Ferraris, Jr. (eds.) Checklist of the Freshwater Fishes of South and Central America. Porto Alegre: EDIPUCRS, Brasil. (Ref. 38376)   http://www.fishbase.org/references/FBRefSummary.php?id=38376&speccode=10622 External link.
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Geographic Range

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

Biogeographic Regions: neotropical (Native )

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Physical Description

Morphology

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.

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

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Size

Maximum size: 50 mm TL
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Max. size

2.5 cm SL (male/unsexed; (Ref. 38376))
  • Lima, F.C.T., L.R. Malabarba, P.A. Buckup, J.F. Pezzi da Silva, R.P. Vari, A. Harold, R. Benine, O.T. Oyakawa, C.S. Pavanelli, N.A. Menezes, C.A.S. Lucena, M.C.S.L. Malabarba, Z.M.S. Lucena, R.E. Reis, F. Langeani, C. Moreira et al. … 2003 Genera Incertae Sedis in Characidae. p. 106-168. In R.E. Reis, S.O. Kullander and C.J. Ferraris, Jr. (eds.) Checklist of the Freshwater Fishes of South and Central America. Porto Alegre: EDIPUCRS, Brasil. (Ref. 38376)   http://www.fishbase.org/references/FBRefSummary.php?id=38376&speccode=10622 External link.
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Type Information

Paratype for Paracheirodon axelrodi
Catalog Number: USNM 164484
Collection: Smithsonian Institution, National Museum of Natural History, Department of Vertebrate Zoology, Division of Fishes
Collector(s): H. Axelrod
Locality: Brazil: Porto Velho (Probably From Stream Near Tomar, Rio Negro), Amazonas, Brazil, South America
  • Paratype: Schultz, L. P. 1956. Tropical Fish Hobbyist. 4 (4): 42, text-fig.
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Holotype for Paracheirodon axelrodi
Catalog Number: USNM 164483
Collection: Smithsonian Institution, National Museum of Natural History, Department of Vertebrate Zoology, Division of Fishes
Collector(s): H. Axelrod
Locality: Brazil: Porto Velho (Probably From Stream Near Tomar, Rio Negro), Amazonas, Brazil, South America
  • Holotype: Schultz, L. P. 1956. Tropical Fish Hobbyist. 4 (4): 42, text-fig.
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Ecology

Habitat

Environment

pelagic; non-migratory; freshwater; pH range: 4.0 - 6.0; dH range: 5 - 12
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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

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Trophic Strategy

Occurs mainly in shoals in the middle water layers. Feeds on worms and small crustaceans.
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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.

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

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Associations

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.

Commensal/Parasitic Species:

  • Nematodes

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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.

Known Predators:

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Diseases and Parasites

White spot Disease. Parasitic infestations (protozoa, worms, etc.)
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Tetrahymena Disease. Parasitic infestations (protozoa, worms, etc.)
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Skin Fungi (Saprolegnia sp.). Fungal diseases
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Skeletal deformities. Others
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Pop-eye disease. Bacterial diseases
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Old-age Disease. Others
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Metacercaria Infection (Flatworms). Parasitic infestations (protozoa, worms, etc.)
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Livoneca Infestation. Parasitic infestations (protozoa, worms, etc.)
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Ichthyobodo Infection. Parasitic infestations (protozoa, worms, etc.)
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Hole-in-the-Head Disease. Parasitic infestations (protozoa, worms, etc.)
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Fish tuberculosis (FishMB). Bacterial diseases
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Fin-rot Disease (late stage). Bacterial diseases
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Fin Rot (early stage). Bacterial diseases
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False Neon Disease. Bacterial diseases
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DMS. Others
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Congenital Deformities. Others
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Columnaris Disease (l.). Bacterial diseases
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Columnaris Disease (e.). Bacterial diseases
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Bacterial Infections (general). Bacterial diseases
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Life History and Behavior

Behavior

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 ; tactile

Perception Channels: visual

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Life Cycle

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.

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

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.

Range lifespan

Status: captivity:
10 (high) years.

Average lifespan

Status: wild:
1 years.

Average lifespan

Status: captivity:
5 years.

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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)

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 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.

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)

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Molecular Biology and Genetics

Molecular Biology

Barcode data: Paracheirodon axelrodi

The following is a representative barcode sequence, the centroid of all available sequences for this species.


There is 1 barcode sequence available from BOLD and GenBank.   Below is the sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.  See the BOLD taxonomy browser for more complete information about this specimen.  Other sequences that do not yet meet barcode criteria may also be available.

ACCCTCTATCTAGTATTCGGTGCCTGAGCTGGAATGGTTGGAACAGCTTTG---AGCCTTTTAATTCGGGCAGAACTTGGCCAACCCGGAACCTTACTTGGTGAT---GACCAAATCTACAATGTTCTAGTTACCGCACATGCTTTCGTTATAATTTTTTTTATAGTTATACCCATCATAATCGGCGGATTCGGAAACTGGTTAGTTCCGTTAATA---ATTGGCGCCCCCGACATGGCCTTCCCCCGAATAAATAATATAAGCTTTTGACTCCTTCCCCCCTCTTTTCTTCTGCTTCTAGCATCCTCTGGAGTAGAGGCTGGAGCTGGTACCGGGTGAACTGTATACCCACCCCTTGCTGGCAACCTAGCACACGCCGGAGCTTCCGTAGACCTC---ACCATCTTCTCGCTTCACCTGGCTGGTGTTTCTTCAATTTTAGGAGCAATTAATTTTATCACGACCATCATTAATATAAAACCCCCCGCCATTTCACAATATCAAACACCTTTATTTGTCTGAGCTGTTCTTGTTACAGCCGTTCTCCTTCTGCTCTCGCTCCCAGTTCTGGCAGCT---GGTATTACTATACTCCTAACAGATCGTAACCTAAATACTTCATTCTTTGATCCGGCCGGAGGGGGAGACCCAATTCTTTACCAACACCTA
-- end --

Download FASTA File
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Statistics of barcoding coverage: Paracheirodon axelrodi

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 1
Specimens with Barcodes: 4
Species With Barcodes: 1
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Conservation

Conservation Status

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

US Federal List: no special status

CITES: no special status

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Threats

Not Evaluated
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Relevance to Humans and Ecosystems

Benefits

Importance

fisheries: of no interest; aquarium: highly commercial
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Economic Importance for Humans: Negative

Paracheirodon axelrodi has no known negative affect on humans.

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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

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Wikipedia

Cardinal tetra

The cardinal tetra, Paracheirodon axelrodi, is a freshwater fish of the characin family (family Characidae) of order Characiformes. It is native to the upper Orinoco and Negro Rivers in South America.

Growing to about 3 cm (1.25 in) total length, the cardinal tetra has the striking iridescent blue line characteristic of the Paracheirodon species 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. Normally, aquarists prefer to buy tank-bred fish, but some Brazilian 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.

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.

An entire industry is in place in Barcelos on the banks of Brazil's Rio Negro in which the local population catches fish for the aquarium trade. The cardinal fishery here is highly valued by the local people who act as stewards for the environment. The local people may not become involved in potentially environmentally damaging activities, such as deforestation, because they can make a sustainable living from the fishery.

Perhaps due to their wild-caught origins, cardinal tetras tend to be somewhat delicate in captivity. In the wild, these fish inhabit extremely soft, acidic waters, but seem to be tolerant of harder, more alkaline water conditions; a greater concern is probably polluted tank water (including high nitrate levels). They prefer warmer water temperatures [above 75°F (24°C) or warmer], and will readily accept most forms of dry food. Captive-bred cardinals tend to adapt to hard water better than wild-caught cardinals.

P. axelrodi is also often called the red neon tetra. Cheirodon axelrodi (the original name) and Hyphessobrycon cardinalis are obsolete synonyms. The fish's common name, cardinal tetra, refers to the brilliant red coloration, reminiscent of a cardinal's robes. The specific epithet honors ichthyologist Herbert R. Axelrod.

Aquarium maintenance[edit]

A shoal of cardinal tetras in an aquarium

Given the origins of the cardinal tetra, namely blackwater rivers whose chemistry is characterised by an acidic pH, low mineral content and the presence of humic acids, the species is adaptable to a wide range of conditions in captivity, though deviation from the soft, acidic water chemistry of their native range will impact severely upon breeding, fecundity, and life expectancy. The preferred temperature range of the fish is 26°C to 28°C (78.8°F to 82.4°F).however if necessary they will live at 24°C (75.2°F). The water chemistry of the aquarium water should match that of the wild habitat - filtration of the aquarium water over peat is one means of achieving this, as is the use of reverse osmosis water.

As the species is a shoaling species in the wild, groups of six or more individuals should be maintained in an aquarium although bigger groups are preferred. They will shoal with their close cousins neon tetras, though, so a combination of these two species totalling at least six should suffice (again, larger groups are preferred). Tank currents can help encourage shoaling behavior. The larger the numbers present in an aquarium (subject to the usual constraints imposed by space and filtration efficiency), the better, and large shoals in any case form an impressive and visually stunning display.

The species will feed on a wide range of aquarium foods, though again, conditioning fishes of this species for breeding will usually require the use of live foods such as Daphnia.

Aquarium furnishings should be planned with some care. Live aquatic plants, as well as providing additional biological filtration components to assist with nitrate management, provide an environment that resembles at least part of the wild habitat, and fine-leaved plants such as Cabomba are usually the plants of choice, though other plants such as Amazon swordplants and Vallisneria are equally suitable for an aquarium housing them. Floating plants providing shade will also be welcomed by the species; this is connected with the breeding of the fish. A perfect biotope to promote breeding would be bogwood, a few live native plants, dark substrate and subdued lighting with floating plants.

The species exists in a number of different color forms or phenotypes. A "gold" and "silver-blonde" form exist in the Rio Negro drainage which 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 which stops posterior to the adipose. The Orinoco phenotype may represent a subspecies of P. axelrodi.

Breeding[edit]

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. In the aquarium, a single pair can be conditioned for breeding, but the breeding aquarium not only needs to contain water with the correct chemical parameters cited above, but the breeding aquarium also needs to be heavily shaded to mimic the low light conditions of the fish's native spawning grounds. If the fishes are ready to spawn, the male, which will be the slimmer of the two fishes in outline, will pursue 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 will allow the male to swim alongside her, and together, the pair will release eggs and sperm.

Apart from the stringent requirements with respect to water chemistry, one of the major difficulties in captive breeding of the species is the photosensitivity of the eggs; they will die if exposed to bright light. Consequently, after spawning, the fishes should be removed and the aquarium covered to darken it, thus providing the developing eggs with the conditions necessary for development.

Development[edit]

If the eggs are fertile, and kept in darkened surroundings, they will hatch in about three days at 28°C. Free-swimming fry remain photosensitive for at least the first seven days of life, and need to be introduced to increasing light levels on a gradual basis. During this time, they are approximately 4 mm in length, and require infusoria or liquid fry food. Newly hatched brine shrimp and other similar live foods, such as sifted Daphnia, can be fed to the growing fry at between seven and 14 days of age. Growth continues at a modest rate, and the fishes assume full adult colouration only after a period of around eight to 12 weeks, depending upon quality of food and aquarium water.

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 will depend on the viewing angle of the aquarist relative to the fish - if the aquarist changes viewpoint so as to look at the fish more from below, the colour will change hue, becoming more deeply sapphire blue and even indigo. Change the viewpoint to one above the fishes, however, and the color becomes more greenish.

See also[edit]

References[edit]

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