The
cardinalCardinal is a vivid red, which gets its name from the cassocks worn by Catholic cardinals . The family of birds takes its name from the color.-Cardinal in other color systems :...
tetrathumb|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....
,
Paracheirodon axelrodi, is a
freshwaterFreshwater is naturally occurring water on the surface such as bogs, ponds, lakes, rivers and streams, and underground in aquifers and underground rivers. Freshwater is characterized by having low concentrations of dissolved salts...
fishA fish is any aquatic vertebrate animal that is typically ectothermic , covered with scales, and equipped with two sets of paired fins and several unpaired fins...
of the characin
familyIn 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...
(family
CharacidaeThe 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
orderIn 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...
CharaciformesThe Characiformes are an order of ray-finned fish, comprising the characins and their allies. There are a few thousand different species, including the well-known piranha and tetras.-Taxonomy:...
. It is native
to the upper
OrinocoThe Orinoco is one of the longest rivers in South America at 2,140 km, . Its drainage basin, sometimes called the Orinoquia covers 880,000 km², 76.3% in Venezuela with the rest in Colombia. The Orinoco and its tributaries are the major transportation system for eastern and interior Venezuela...
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
ParacheirodonParacheirodon 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
fishA fish is any aquatic vertebrate animal that is typically ectothermic , covered with scales, and equipped with two sets of paired fins and several unpaired fins...
, with the body below this line being vivid red in
colorColor or colour is the visual perceptual property corresponding in humans to the categories called red, yellow, 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 tetra".
The
cardinalCardinal is a vivid red, which gets its name from the cassocks worn by Catholic cardinals . The family of birds takes its name from the color.-Cardinal in other color systems :...
tetrathumb|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....
,
Paracheirodon axelrodi, is a
freshwaterFreshwater is naturally occurring water on the surface such as bogs, ponds, lakes, rivers and streams, and underground in aquifers and underground rivers. Freshwater is characterized by having low concentrations of dissolved salts...
fishA fish is any aquatic vertebrate animal that is typically ectothermic , covered with scales, and equipped with two sets of paired fins and several unpaired fins...
of the characin
familyIn 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...
(family
CharacidaeThe 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
orderIn 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...
CharaciformesThe Characiformes are an order of ray-finned fish, comprising the characins and their allies. There are a few thousand different species, including the well-known piranha and tetras.-Taxonomy:...
. It is native
to the upper
OrinocoThe Orinoco is one of the longest rivers in South America at 2,140 km, . Its drainage basin, sometimes called the Orinoquia covers 880,000 km², 76.3% in Venezuela with the rest in Colombia. The Orinoco and its tributaries are the major transportation system for eastern and interior Venezuela...
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
ParacheirodonParacheirodon 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
fishA fish is any aquatic vertebrate animal that is typically ectothermic , covered with scales, and equipped with two sets of paired fins and several unpaired fins...
, with the body below this line being vivid red in
colorColor or colour is the visual perceptual property corresponding in humans to the categories called red, yellow, 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 tetra". The cardinal tetra's appearance is similar to that of the closely related
neon tetraThe 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
noseAnatomically, 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....
, and the neon's blue stripe is a less vibrant blue, however.
The cardinal tetra is a very popular
aquariumAn 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 tetraThe 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
deforestationDeforestation is the clearance of naturally occurring forests by the processes of logging and/or burning of trees in a forested area. There are several reasons deforestation occurs: trees or derived charcoal can be sold as a commodity and used by humans, while cleared land is used as pasture,...
.
The fish is also effectively an annual species and has a lifespan of just a single year in nature. It lives for several years in captivity.{7 years|date=March 2009}
An entire
industryAn industry is the manufacturing of a good or service within a category. Although industry is a broad term for any kind of economic production, in economics and urban planning industry is a synonym for the secondary sector, which is a type of economic activity involved in the manufacturing of raw...
is in place in
BarcelosBarcelos is a municipality located in the Brazilian state of Amazonas. Its population was 32,169 and its area is 122,476 km² , making it the largest municipality in Brazil, equivalent in size to New York state in the United States and slightly larger than North Korea....
on the banks of
BrazilBrazil , officially the Federative Republic of Brazil , is a country in South America. It is the fifth largest country by geographical area, occupying nearly half of South America, the fifth most populous country, and the fourth most populous democracy in the world. Bounded by the Atlantic Ocean...
'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
cardinalA cardinal is a senior ecclesiastical official, usually a bishop, 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 making themselves available...
's robes. The
specificIn biology, a species is:* a taxonomic rank or* a unit at that rank ....
epithet honors
ichthyologistIchthyology is the branch of zoology devoted to the study of fish. This includes skeletal fish , cartilaginous fish , and jawless fish...
Herbert R. AxelrodHerbert 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 riverA 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...
s whose chemistry is characterised by an
acidAn acid is traditionally considered any chemical compound that, when dissolved in water, gives a solution with a hydrogen ion activity greater than in pure water, i.e. a pH less than 7.0...
ic
pHpH is a measure of the acidity or basicity of a solution. It is defined as the cologarithm of the activity of dissolved hydrogen ions . Hydrogen ion activity coefficients cannot be measured experimentally, so they are based on theoretical calculations...
, low
mineral contentHard water is water that has high mineral content . Hard water minerals primarily consist of calcium , and magnesium metal cations, and sometimes other dissolved compounds such as bicarbonates and sulfates...
and the presence of
humic acidHumic acid is one of the major components of humic substances which are dark brown and major constituents of soil organic matter humus that contributes to soil chemical and physical quality and are also precursors of some fossil fuels...
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
fecundityFecundity, derived from the word fecund, generally refers to the ability to reproduce. In biology and demography, fecundity is the potential reproductive capacity of an organism or population, measured by the number of gametes , seed set or asexual propagules. Fecundity is under both genetic and...
. The preferred temperature range of the fish is 21°C to 28°C (70°F to 82°F), and a bowl containing these fishes should be well
filteredFiltration is a mechanical or physical operation which is used for the separation of solids from fluids by interposing a medium through which only the fluid can pass...
, in order to remove assorted pollutants: in particular, a well established
biological filter that controls
ammoniaAmmonia is a compound of nitrogen and hydrogen with the formula NH
3. It is normally encountered as a gas with a characteristic pungent odor. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to foodstuffs and fertilizers...
,
nitriteThe nitrite ion is NO2−. The anion is bent, being isoelectronic with ozone. More generally, a nitrite compound is either a salt or an ester of nitrous acid.-Examples:* nitrous acid, HNO2...
s and
nitrateIn inorganic chemistry, a nitrate is a salt of nitric acid with an ion composed of one nitrogen and three oxygen atoms . In organic chemistry the esters of nitric acid and various alcohols are called nitrates.-Chemical properties:...
s is beneficial. If the intention of the aquarist is to breed the species in captivity, then the water chemistry of the aquarium water should match that of the wild habitat - filtration of the aquarium water over
peatPeat is an accumulation of partially decayed vegetation matter. Peat forms in wetlandbogs, moors, muskegs, pocosins, mires, and peat swamp forests...
is one means of achieving this.
As the species is a
shoalingIn 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 tetraThe 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
DaphniaDaphnia 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. With this add 5+ Hatchets, 15+ Cardinals,
ottocinclus &
corydoras catfish (2 each per 10 gallons).
The species exists in a number of different colour 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
rainforestRainforests are forests characterized by high rainfall, with definitions setting minimum normal annual rainfall between 1750–2000 mm . The monsoon trough, alternately known as the intertropical convergence zone, plays a significant role in creating Earth's tropical rain forests.From 40 to 75%...
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 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 shrimpBrine shrimp is the English name of the genus Artemia of aquatic crustaceans. Artemia, the only genus in the family Artemiidae, have evolved little 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 colour, caused by refraction of light within guanine crystals that develop within special cells called
iridocyteChromatophores 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 colour becomes more greenish.
External links