Cardinal tetra
Encyclopedia
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, however.
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 that 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. It has been suggested that if those fishermen lost their livelihood catching Cardinals and other tropical fish, they might turn their attention to engaging in deforestation
.
The fish might also be effectively an annual species and may have 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. It may be said that the local people do 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 (in the upper 70s F or warmer (20°C)), 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
.
Given the origins of the cardinal tetra, namely blackwater river
s whose chemistry is characterised by an acid
ic pH
, low mineral content
and the presence of humic acid
s, 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 and fecundity
. The preferred temperature range of the fish is 21°C to 28°C (70°F to 82°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 the species is a shoaling
species in the wild, groups of six or more individuals should be maintained in an aquarium. They will shoal with their close cousins neon tetra
s however, so a combination of these two species totalling at least six should suffice. 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 upon 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 an additional biological filtration component that assists with nitrate management in the aquarium, 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 the cardinal tetra. Floating plants providing shade will also be welcomed by the species: this is connected with the breeding of the fish, which will now be covered. A perfect biotope to promote breeding, would be lots of bogwood, a few live native plants, with 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 have 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 posteriorly of the adipose. The Orinoco phenotype may represent a subspecies of P. axelrodi.
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: the breeding aquarium 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 mitigating against success in captive breeding of the species is the nature of the newly laid and fertilised eggs. The eggs of the cardinal tetra are photosensitive, and 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.
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 7 and 14 days of age. Growth continues at a modest rate, and the fishes assume full adult colouration only after a period of approximately 8 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 iridocyte
s in the subcutaneous layer. The exact shade of blue that is seen will depend upon the viewing angle of the aquarist relative to the fish - if the aquarist changes viewpoint so as to look at the fish from the substrate upwards, 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.
Freshwater
Fresh water is naturally occurring water on the Earth's surface in ice sheets, ice caps, glaciers, bogs, ponds, lakes, rivers and streams, and underground as groundwater in aquifers and underground streams. Fresh water is generally characterized by having low concentrations of dissolved salts and...
fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
of the characin family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
(family Characidae
Characidae
The Characidae, characids or characins are a family of freshwater subtropical and tropical fish, belonging to the order Characiformes. The name "characins" is the historical one, but scientists today tend to prefer "characids" to reflect their status as a by and large monophyletic group at family...
) of order
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...
Characiformes
Characiformes
The Characiformes are an order of ray-finned fish, comprising the characins and their allies. Grouped in 18 recognized families, there are a few thousand different species, including the well-known piranha and tetras.-Taxonomy:...
. It is native to the upper Orinoco
Orinoco
The Orinoco is one of the longest rivers in South America at . Its drainage basin, sometimes called the Orinoquia, covers , with 76.3% of it in Venezuela and the remainder in Colombia...
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
Paracheirodon
Paracheirodon is a genus of freshwater fish in the characin family of order Characiformes. The type species isParacheirodon innesi, the well-known neon tetra, and the Paracheirodon species are among the fishes known as tetras...
species laterally bisecting the fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
, with the body below this line being vivid red in color
Color
Color or colour is the visual perceptual property corresponding in humans to the categories called red, green, blue and others. Color derives from the spectrum of light interacting in the eye with the spectral sensitivities of the light receptors...
, hence the name "cardinal
Cardinal (color)
Cardinal is a vivid red, which gets its name from the cassocks worn by Catholic cardinals...
tetra
Tetra
thumb|right|250px|Pristella tetra — [[Pristella maxillaris]].thumb|right|250px|Golden Pristella tetra, a [[morph |morph]] of [[Pristella maxillaris]].thumb|right|250px|[[Silvertip tetra]] — Hasemania nana....
". The cardinal tetra's appearance is similar to that of the closely related neon tetra
Neon tetra
The neon tetra is a freshwater fish of the characin family of order Characiformes. The type species of its genus, it is native to blackwater or clearwater streams in southeastern Colombia, eastern Peru, and western Brazil, including the tributaries of the Solimões where the water is between...
, with which it is often confused; the neon's red coloration extends only about halfway to the nose
Nose
Anatomically, a nose is a protuberance in vertebrates that houses the nostrils, or nares, which admit and expel air for respiration in conjunction with the mouth. Behind the nose are the olfactory mucosa and the sinuses. Behind the nasal cavity, air next passes through the pharynx, shared with the...
, and the neon's blue stripe is a less vibrant blue, however.
The cardinal tetra is a very popular aquarium
Aquarium
An aquarium is a vivarium consisting of at least one transparent side in which water-dwelling plants or animals are kept. Fishkeepers use aquaria to keep fish, invertebrates, amphibians, marine mammals, turtles, and aquatic plants...
fish but is less widespread than the neon tetra
Neon tetra
The neon tetra is a freshwater fish of the characin family of order Characiformes. The type species of its genus, it is native to blackwater or clearwater streams in southeastern Colombia, eastern Peru, and western Brazil, including the tributaries of the Solimões where the water is between...
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 that 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. It has been suggested that if those fishermen lost their livelihood catching Cardinals and other tropical fish, they might turn their attention to engaging in deforestation
Deforestation
Deforestation is the removal of a forest or stand of trees where the land is thereafter converted to a nonforest use. Examples of deforestation include conversion of forestland to farms, ranches, or urban use....
.
The fish might also be effectively an annual species and may have a lifespan of just a single year in nature. It lives for several years in captivity.
An entire industry
Industry
Industry refers to the production of an economic good or service within an economy.-Industrial sectors:There are four key industrial economic sectors: the primary sector, largely raw material extraction industries such as mining and farming; the secondary sector, involving refining, construction,...
is in place in Barcelos
Barcelos, Amazonas
Barcelos is a municipality located in the Brazilian state of Amazonas. Its population was 32,169 and its area is , making it the second largest municipality in Brazil , equivalent in size to New York state in the United States and slightly larger than North Korea.The city is served by Barcelos...
on the banks of Brazil
Brazil
Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...
'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. It may be said that the local people do 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 (in the upper 70s F or warmer (20°C)), 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
Cardinal (Catholicism)
A cardinal is a senior ecclesiastical official, usually an ordained bishop, and ecclesiastical prince of the Catholic Church. They are collectively known as the College of Cardinals, which as a body elects a new pope. The duties of the cardinals include attending the meetings of the College and...
's robes. The specific
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
epithet honors ichthyologist
Ichthyology
Ichthyology is the branch of zoology devoted to the study of fish. This includes skeletal fish , cartilaginous fish , and jawless fish...
Herbert R. Axelrod
Herbert R. Axelrod
Herbert Richard Axelrod is a tropical fish expert, publisher of pet books, and entrepreneur. In 2005 he was sentenced in U.S. court to 18 months in prison for tax fraud.-Early life:...
.
Aquarium maintenance
Given the origins of the cardinal tetra, namely blackwater river
Blackwater river
A blackwater river is a river with a deep, slow-moving channel that flows through forested swamps and wetlands. As vegetation decays in the water, tannins are leached out, resulting in transparent, acidic water that is darkly stained, resembling tea or coffee. Most major blackwater rivers are in...
s whose chemistry is characterised by an acid
Acid
An acid is a substance which reacts with a base. Commonly, acids can be identified as tasting sour, reacting with metals such as calcium, and bases like sodium carbonate. Aqueous acids have a pH of less than 7, where an acid of lower pH is typically stronger, and turn blue litmus paper red...
ic pH
PH
In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...
, low mineral content
Hard water
Hard water is water that has high mineral content . Hard water has high concentrations of Ca2+ and Mg2+ ions. Hard water is generally not harmful to one's health but can pose serious problems in industrial settings, where water hardness is monitored to avoid costly breakdowns in boilers, cooling...
and the presence of humic acid
Humic acid
Humic acid is a principal component of humic substances, which are the major organic constituents of soil , peat, coal, many upland streams, dystrophic lakes, and ocean water. It is produced by biodegradation of dead organic matter...
s, 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 and fecundity
Fecundity
Fecundity, derived from the word fecund, generally refers to the ability to reproduce. In demography, fecundity is the potential reproductive capacity of an individual or population. In biology, the definition is more equivalent to fertility, or the actual reproductive rate of an organism or...
. The preferred temperature range of the fish is 21°C to 28°C (70°F to 82°F). The water chemistry of the aquarium water should match that of the wild habitat - filtration of the aquarium water over peat
Peat
Peat is an accumulation of partially decayed vegetation matter or histosol. Peat forms in wetland bogs, moors, muskegs, pocosins, mires, and peat swamp forests. Peat is harvested as an important source of fuel in certain parts of the world...
is one means of achieving this.
As the species is a shoaling
Shoaling and schooling
In biology, any group of fish that stay together for social reasons are said to be shoaling , and if, in addition, the group is swimming in the same direction in a coordinated manner, they are said to be schooling . In common usage, the terms are sometimes used rather loosely...
species in the wild, groups of six or more individuals should be maintained in an aquarium. They will shoal with their close cousins neon tetra
Neon tetra
The neon tetra is a freshwater fish of the characin family of order Characiformes. The type species of its genus, it is native to blackwater or clearwater streams in southeastern Colombia, eastern Peru, and western Brazil, including the tributaries of the Solimões where the water is between...
s however, so a combination of these two species totalling at least six should suffice. 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 upon 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
Daphnia
Daphnia are small, planktonic crustaceans, between 0.2 and 5 mm in length. Daphnia are members of the order Cladocera, and are one of the several small aquatic crustaceans commonly called water fleas because of their saltatory swimming style...
.
Aquarium furnishings should be planned with some care. Live aquatic plants, as well as providing an additional biological filtration component that assists with nitrate management in the aquarium, 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 the cardinal tetra. Floating plants providing shade will also be welcomed by the species: this is connected with the breeding of the fish, which will now be covered. A perfect biotope to promote breeding, would be lots of bogwood, a few live native plants, with 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 have 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 posteriorly of the adipose. The Orinoco phenotype may represent a subspecies of P. axelrodi.
Breeding
The cardinal tetra, in the wild, swims upstream in large numbers to parts of its native river habitat that are completely enclosed above by rainforestRainforest
Rainforests are forests characterized by high rainfall, with definitions based on a minimum normal annual rainfall of 1750-2000 mm...
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: the breeding aquarium 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 mitigating against success in captive breeding of the species is the nature of the newly laid and fertilised eggs. The eggs of the cardinal tetra are photosensitive, and 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
If the eggs are fertile, and kept in darkened surroundings, they will hatch in approximately 3 days at 28°C. Free swimming fry remain photosensitive for at least the first 7 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 infusoriaInfusoria
Infusoria is a collective term for minute aquatic creatures like ciliates, euglenoids, protozoa, and unicellular algae that exist in freshwater ponds...
or liquid fry food. Newly hatched brine shrimp
Brine shrimp
Artemia is a genus of aquatic crustaceans known as brine shrimp. Artemia, the only genus in the family Artemiidae, has changed little externally since the Triassic period...
and other similar live foods such as sifted Daphnia can be fed to the growing fry at between 7 and 14 days of age. Growth continues at a modest rate, and the fishes assume full adult colouration only after a period of approximately 8 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 iridocyte
Chromatophore
Chromatophores are pigment-containing and light-reflecting cells found in amphibians, fish, reptiles, crustaceans, and cephalopods. They are largely responsible for generating skin and eye colour in cold-blooded animals and are generated in the neural crest during embryonic development...
s in the subcutaneous layer. The exact shade of blue that is seen will depend upon the viewing angle of the aquarist relative to the fish - if the aquarist changes viewpoint so as to look at the fish from the substrate upwards, 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.
External links
- Video of Cardinal Tetras feeding
- More info about Cardinal Tetra, petinfospot.com website
- Cardinal tetra, Paracheirodon axelrodi, Practical Fishkeeping magazine
- Life in the shallows - the Rio Negro, Practical Fishkeeping magazine
- River to retailer - the Cardinal tetra fishery in Brazil, Practical Fishkeeping magazine
- Breeder produces gold Cardinal tetras, Practical Fishkeeping magazine news