Cardinal tetra (Paracheirodon axelrodi)

Cardinal tetra (lat. Paracheirodon axelrodi) are amazingly beautiful fishes and they are the most popular ones in aquarium husbandry. The most of the fish beauty can be seen in the fish school – in a thickly planted tank such a school looks especially glamorous.

When keeping cardinal in soft and acidic water (black water) the fish coloring becomes more bright. Also fish looks quite fascinating in a thickly planted tank with soft lights and dark bottom substrate.

If your tetra inhabits in a tank with stable good conditions, it’ll live for a long time and it’ll resist diseases. But if the tank has unstable changeable conditions, the fish dies very quickly.

Besides as well as a common neon fish the cardinal tetra is also susceptible to neon tetra disease (NTD). When fish gets ill, its coloring sharply turns pale. As we already mentioned, sadly, there’s no cure for disease.

Habitat in the wild

Cardinal tetra (lat. Paracheirodon axelrodi, Schlutz, 1956) is one of three representatives of Paracheirodon genus, that includes neon tetra (Paracheirodon innesi, Myers, 1936) and green neon tetra (Paracheirodon simulans, Géry, 1963).

In the wild these schooling fishes inhabit in the middle water layers of flooded forests and tributaries of the river Orinoco and Rio-Negro middle and upper basin.

Huge overflow lands appear there during the annual flood rise and cardinal tetra just like many other fishes use these areas for feeding, breeding and shelter.

Since the floods begin tetras migrate upstream from the river tributaries to overflow lands and they come back only for the dry season.

The river “black water” is called so because the rotting plants evolve tannin into the water and it colors the water into dark brown (brew color).

As a result of high organic load the water has specific composition and properties. Inhabit in water with temperature +23…+27 °C, pH = 4,0—6,0 and hardness dH = 5—12°.


Female body length is up to 5 cm (2 in) and the male size is about 2.5-3.0 cm (1-1.25 in).

The fish back is olive and beige, it has a neon opalescent bright-blue stripe that goes from its eye to the flesh fin, below this stripe there’s a wide bright-red stripe, the abdomen is whitish.

Cardinal tetra vs neon tetra

First of all they are different fishes, though cardinal tetra is sometimes called red neon tetra.

Cardinal tetra is sufficiently larger and its red stripe goes through the whole lower body when neon tetra stripe takes only half of its body.

Difficulties in keeping

Care is rather complicated, since the fish is more demanding than neon.

The thing is that tetra is very sensitive to water parameters and purity, if water parameters are changeable the fish tends to get ill and die. The fish is recommended for experienced aquarists, since it rather often dies in a new tank of aquarists beginners.


The study of gastrointestinal tract contents of 80 species in the wild showed that they are micropredators. Food consists mainly from zooplankton and blood worm.

The fish is easy to feed, it’s not demanding and it eats all types of feed – live, frozen and artificial.

It’s important that the feed is small grained, because the fish has rather small mouth, favorite food is blood worm and tubifex.

Care and keeping in a tank

The lights should be moderate with lots of plants in the tank. It’s better to shade that tank with fluctuants. Although they needs to have covers in the tank, it also needs some open space for swimming.

Thickly planted tank with some free space in the middle will be an ideal one for such a fish. The capacity of such tank may be not large – for a school of 10 fish species 15-20 gallons tank will be enough.

Compatibility and tank mates

Is a peaceful fish which just like all tetra fishes loves company. It’s desirable to keep a school of 10 species, this is the way they’ll show their best coloring in the tank and also feel comfortable.

The fish will do for community tanks at the condition that water parameters are stable and tank mates are not troublesome.

Gender differences: male vs female

Gender dimorphism is very little pronounced as well as of other species of this kind. When total body size of tetra kept in a tank is 3.5-5 cm (in the wild it’s up to 2.5 cm) the female tends to be larger and fatter than male (especially during their spawning period).

The fish becomes reproductive at the age of 9 month. In the wild lifespan isn’t more than a year, however in the tank the fish may live up to 5 years.


Breeding may be performed both in couples and in school. Usually there 2-3 males for 1 female in a tank. In case of the fish couples breeding you may need a tank about 0,5 gallons capacity, if the breeding will be of schooling type the tank capacity should be about 1 gallon.

The water level in a spawning pond should be about 30 cm. Water hardness is 1-2°dH, since if the water is harder the eggs may not get fertilized; pH= 5 – 5,5 and water temperature about 24 -26 °C.

The water should be disinfected by means of ozonizer or ultraviolet lamp. The spawning net and plants with small leaves are put on the tank bottom.

In about a week before the spawning starts it’s desirable to put males apart from females. The fish that are to breed are kept in the water with low temperature (about 22 — 23 °C) and fed high and well. You should stop feeding the fishes the day before putting into the spawning pond.

Sometimes the spawning process is delayed for about 5-7 days.

You shouldn’t feed the fishes in the spawning tank , though there’s no sense in keeping them there more than a week. If the eggs weren’t laid during this period of time, you have to remove the fishes from the spawning tank and a few days later try to make them breed again.

The spawning starts when it gets dark and it lasts for several hours. About 300-500 transparent orange eggs appear in the tank during this time.

The tank with eggs should be shaded, since they are very sensitive to light. In 20-36 hours larva appears from the eggs. They start to swim in 5-6 days after that.

As soon as the juveniles start to swim you should start feeding them. Start feed for juveniles is infusorians and crustaceans nauplii. After you start feeding the juveniles in the tank, you have to start slow aeration of the water.

Also gradually make the water more hard, because it’s necessary for the juveniles. To do this it’s enough to add some water from the community tank into the spawning pond.

As the juveniles grow the start eating feed of larger size. During the first 2 weeks of their lives juveniles hide under the tank plants leaves.

During the 3rd week a blue stripe appears along their body. At about the age of 1 month and a half they have a shape and coloring the same as the adult fish has and they can be transferred to the community tank.

About author: Sergey Schulz

Sergey is a founder and author of He’s been fond of aquarium husbandry since his early childhood. His favorite aquariums are biotopes (Amazon River), with Echinodorus and freshwater angelfish. However, through the years he’s had experience of keeping almost all types of freshwater fish and shrimps.