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Cardinal Tetra – Paracheirodon axelrodi

Cardinal Tetra

Tetras are amongst the most popular aquarium fishes. There are probably more than 150 distinct species of tetra from which the aquarist may choose and this includes a large number of visually stunning fishes that are bound to enhance any home aquarium.

Is the Cardinal Tetra a good community fish? The Cardinal Tetra should be considered to be an excellent community fish because it can live quite happily amongst a wide variety of other species. It is best to avoid keeping Cardinal Tetras with large, aggressive species which may bully or even eat the Cardinal Tetra.

Key Facts

CategoryKey Facts
Common name(s)Cardinal Tetra
Scientific nameParacheirodon axelrodi
Originate fromUpper Orinoco and Negro Rivers in South America
Care requiredEasy to care for and hugely popular
TemperamentPlacid, shoaling fish
Colour & FormIridescent Blue stripe running from nose to adipose fin and cardinal red pigmentation running beneath along the full length of the body
LifespanUp to 5 years
Adult size1.2 to 2.0 inches
DietOmnivorous – eat aquatic insect larvae in nature
Aquarium size20 gallons or greater
Compatible withMost other Tetras, Barbs, Danios, Guppies and other livebearers, dwarf cichlids, smaller Gouramis, catfish and loaches
Avoid keeping withLarge and/or aggressive species
BreedingEasy if you put the fish in the right environment.
Water temp73 – 82 Fahrenheit
Water pH4.0 to 6.0
Water hardness (dGH or dH)5 to 12 dGH

Origins of the Cardinal Tetra

Tetras, as a “family” of fishes belonging to the biological family Characidae are found in nature in Africa, Central America and South America.

The Cardinal Tetra originates from the upper Orinoco and Negro Rivers in South America. The Cardinal Tetra has, at the time of writing, not been subjected to the massively industrial, captive breeding to which its close relative, the Neon Tetra has been subjected therefore catching the Cardinal Tetra provides extremely valuable employment in its place of origin

The Cardinal Tetra is easily mistaken for the Neon Tetra but it is, upon examination, significantly different. Glowlight Tetras will, in general, shoal with Cardinal Tetras but seemingly not with Neon Tetras.

Characteristics of the Cardinal Tetra

As you can see, the Cardinal Tetra is a beautiful, little fish that will grow to around 1.2 inches in nature but up to 2 inches in the aquarium and live for up to five years. The female Cardinal Tetra tends to be slightly larger than the male and with a fuller, rounder body, especially when gravid (carrying eggs).

The Cardinal Tetra is omnivorous in the aquarium though, in the wild, it generally eats live aquatic insect larvae. In the aquarium, as well as consuming small flake food the Cardinal Tetra will enjoy brine shrimp, freeze-dried bloodworms, daphnia and tubifex worms. In addition, the Cardinal Tetra will benefit from pellet food, as most of these commercial foods include nutrients designed to enhance the vibrant colors of the fish.

The Cardinal Tetra is, by nature, a shoaling fish and it is generally recommended to purchase six or more fish, as their nature is to swim together as a shoal and they will tend to thrive much better as a shoal.

Cardinal Tetras are ideal to be kept in a mixed aquarium (or in a single-species aquarium) as a shoal and are both graceful and beautiful to observe. The smaller Tetras are quite timid fish so they should not be kept with large, aggressive species which may bully or even eat them.

Cardinal Tetras mix well with most other Tetras, Barbs, Danios, Guppies and other livebearers, dwarf cichlids, smaller Gouramis, catfish and loaches.

It is generally advised that the minimum tank size for Cardinal Tetras should be one of 24 inches in length, which will enable a small shoal to move around freely. The tank should be well-planted, preferably including dense foliage, in order to enable them to find cover and open space to enable them freely to swim.

Cardinal Tetras prefer slightly acidic water in nature because, in the wild, this is their natural habitat which is under the canopy of the Amazon rainforest. In nature, the water will get relatively little light and will also tend to be tannin-stained due to the decomposition of leaf matter and this causes the water to be quite acidic.

You can see from the image that the Cardinal Tetra is quite a distinctive fish. At first glance it appears to be very similar to the Neon Tetra but, on closer inspection, you will see that the cardinal red (from which it gets its name) runs from its tail to its eye, beneath the iridescent blue flash, which is also longer than that of the Neon Tetra.

The Cardinal Tetra is a difficult target for predators because, like the Neon Tetra, the iridescent blue stripe will mirror back off the surface of the water to present a false target to prospective predators. Bearing in mind the “blackwater” environment in nature, the slow-flowing water will offer a smooth surface and an excellent mirror.

It is somewhat difficult to determine with certainty the sex of most Tetras. It is easier to determine the sex of Cardinal Tetras because the female is slightly larger than the male and has a rounder belly, particularly when she is gravid with eggs but, otherwise, it can be difficult to differentiate between the sexes.

The general rule for Tetras is that by keeping six or more of the same species in an aquarium they will be fully aware of which is male and which is female and they will act accordingly.

Most (but not all) Tetras have an additional fin which identifies them as being Tetras and the Cardinal Tetra is no exception. If you look between the dorsal fin and the caudal (tail) fin of the Cardinal Tetra you will observe a tiny, additional fin, known as the adipose fin. The purpose of this fin is not fully understood but, if it is present on a fish then you can be pretty certain that the fish is a Tetra.

Tetra comes from the Greek word “Tetragonopterus” which means square-finned and appears to relate to the four fins on vertical plane of the fish (dorsal, adipose, caudal and anal fins) which span the central line of the fish (when viewed from above or below, front or rear) and are not present as a pair (e.g. the pectoral fins).

The iridescence of your Cardinal Tetras may fade when the tank is dark and this is quite natural but if a Cardinal Tetra shows poor coloring compared with others then this is a sign that it may be ill so is best removed from the aquarium.

Cardinal Tetra – Video

How do Cardinal Tetras breed?

Tetras, in general, will scatter eggs by laying them over fine plants such as Cabomba, Fontanalis or Java Moss.

As the female Cardinal Tetra becomes ripe with eggs, the difference between the sexes is self-evident. If you plan to attempt to breed Cardinal Tetras then it is recommended that you have a breeding tank prepared which will be unlit and well planted.

The female will swim amongst the plants in which she will lay her eggs and the male will follow her or swim alongside her and fertilize the eggs as they are laid. Once spawning is complete, remove the adults, as they are likely to consume the eggs and take no further parental responsibility.

Breeding tank for Cardinal Tetras

You should prepare an unlit tank of around 20 gallons in size with mature water. Ensure that there is plenty of fine vegetation (e.g. Cabomba, Fontanalis or Java Moss) in the tank. Cardinal Tetras tend to breed in the evening or during the night. The water should be at a pH of around 5.0 to 5.5 and, ideally around 80 degrees Fahrenheit.

You may wish to introduce mosquito larvae as an inducement to reproduction.

The female will swim amongst the plants, laying her eggs whilst the male will swim alongside or behind her and fertilize the eggs as they are laid. Typically, the female will lay up to 500 eggs, which will land on the plants or fall to the bottom of the tank.

In nature, Cardinal Tetras swim upstream in large shoals and have a mass-spawning where the females all lay their eggs and the males fertilize them. It is thought that the natural lifecycle of the Cardinal Tetra may only be one year but this is not yet confirmed or otherwise.

Once the female has scattered her eggs and the male has fertilized them then both should be removed carefully from the breeding tank because neither will have anything more to do with the eggs but they may simply eat them.

Keep the lights off because the eggs are particularly sensitive to the light.

The eggs will hatch typically in around 72 hours. Keep the tank unlit for the first week or so then gradually increase the lighting.

The newly hatched fry can be fed infusoria (particularly rotifers) and will also thrive on egg yolk during the first two to four weeks. After around four days or so add baby brine shrimp. Once the fry are sufficient in size not to be treated as a snack then they can be introduced into the community tank where they will join the existing shoal. Before moving the adolescent fish into the community tank ensure that you have balanced the water temperatures to mitigate the risk of White Spot or other diseases being triggered.

Should your Cardinal Tetras have a special diet for breeding?

Adult Cardinal Tetras don’t need any particular inducement to breed. That said, it has been suggested that adding mosquito larva may encourage them, presumably because the addition of a new food may “fool” the fish into thinking that it is breeding time. 

Mike Wheeler

I started keeping freshwater tropical fish in 1972 and it has been something of a passion ever since. In this website, my aim is to build up an everyman's guide to help the everyday aquarist get the best from this inspiring and entertaining hobby.

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