Cardinal Tetra

Family: Characidae Cardinal Tetra, Paracheirodon axelrodiParacheirodon axelrodiPhoto © Animal-World: Courtesy David Brough
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I have had 5 Cardinal Tetras in my tank for a year now.Lately,one of them has been acting strangely.It started by keeping itself away from the other fish and seemed... (more)  BJ.

The startling coloration of the Cardinal Tetra is all natural, and arguably unsurpassed in freshwater fish!

The Cardinal Tetra Paracheirodon axelrodi is a spectacular fish and one of the most popular aquarium fish of all time. It very charming in appearance and behavior. This is a serene yet gregarious fish that needs to be kept in a school. A group of these flashing tetras will make a brilliant display in the aquarium,.

The distinctive color pattern of the Cardinal Tetra is the brilliant neon blue center line with a bright red below. It is known as the “big brother” of the Neon Tetra. The two are very similar with that color pattern. However the Cardinal Tetra has the red coloration extending through its whole body length while on the Neon the red is limited to the back half. To add a bit of variety, there is also a “gold” strain of Cardinal Tetra that's been been developed and appears from time to time .

The Cardinal Tetra is also slightly more delicate than the Neon Tetra. But like the Neon, it will only be comfortable in a school. Buy the best stock available to you, preferably from a local breeder as opposed to a mass produced type. Also choose its tank mates well, as it is the natural prey of many fish, even many of the other tetras.

With optimal water conditions and a well thought out tank, the colors will become even more radiant. Keep its water soft and acid. Plant the tank heavily, providing some hiding places and a lot of swimming space. Dark substrate and bogwood will make this fish's coloring even brighter. They also do not like harsh light, nor will it help its coloration.

If it is kept in good conditions, the Cardinal Tetra is easy to keep and will resist disease. However, if the tank is unstable, it will die off very quickly. The worst fear of a tetra keeper is the Neon Tetra disease, an essentially incurable and a highly contagious disease of unknown origin and cause. It was first diagnosed in Neons, so earned its name, but it can actually affect many other species.

For Information on keeping freshwater fish, see:
Freshwater Aquarium Guide: Aquarium Setup and Care

Geographic Distribution
Paracheirodon axelrodi
Data provided by
  • Kingdom: Animalia
  • Phylum: Chordata
  • Class: Actinopterygii
  • Order: Characiformes
  • Family: Characidae
  • Genus: Paracheirodon
  • Species: axelrodi
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Cardinal Tetra - Quick Aquarium Care
  • Aquarist Experience Level: Intermediate
  • Size of fish - inches: 2.0 inches (5.08 cm)
  • Minimum Tank Size: 15 gal (57 L)
  • Temperament: Peaceful
  • Aquarium Hardiness: Moderately Difficult
  • Temperature: 73.0 to 81.0° F (22.8 to 27.2° C)
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Habitat: Distribution / Background

The Cardinal Tetra Paracheirodon axelrodi was described by Schultz in1956. This species is not listed on the IUCN Red List. They are found in forested areas, in slow moving blackwater tributaries in South America, notably the Rio Negro and Orinoco.  They are also native to Venezuela and Brazil.The rainforest that cover their water ways are usually very dense and letting very little light through. They live in shoals, mainly in the middle water layers and feed on worms and small crustaceans.

Most individuals available for sale are wild caught for the aquarium trade, making it necessary to recreate their natural lifestyle in captivity. There are also captive bred specimens available and more recently a “gold” strain of Cardinal Tetra has been been developed that appears from time to time.

  • Scientific Name: Paracheirodon axelrodi
  • Social Grouping: Groups
  • IUCN Red List: NE - Not Evaluated or not listed


The Cardinal Tetra is a very small tetra species. This fish will reach about 2 inches in length (5 cm) with a life span of about 2 - 5 years in the aquarium. They have a bluish body with an electric blue neon stripe running vertically from the nose along the length of the body. It is underscored with a very beautiful broad red stripe from the head on back. It is similar in appearance to the Neon Tetra, but the red stripe on the Neon runs only halfway up the body.

  • Size of fish - inches: 2.0 inches (5.08 cm)
  • Lifespan: 5 years - They can have a lifespan of about 2 - 5 years in the aquarium.

Fish Keeping Difficulty

The Cardinal Tetra is a bit less durable than other tetra species, including the similar looking Neon Tetra. It is intolerant of fluctuations in water conditions. This is especially true of wild caught specimens so this species is suggested for a fish keeper with some experience. Because most are wild caught, they will do best if kept in a biotype aquarium mirroring their natural habitat. These fish should not be added to newly cycled tanks as they are very sensitive to water quality changes that are common to new tanks.

  • Aquarium Hardiness: Moderately Difficult - This fish is less hardy than other tetras. It is still very populous in the wild and most aquarium specimens are wild caught, so are less tolerant of varying water conditions.
  • Aquarist Experience Level: Intermediate

Foods and Feeding

Since they are omnivorous the Cardinal Tetra will eat most appropriately sized foods. It has high vitamin requirements, so at least 75% of its food should be quality flake food. Cardinal tetras especially appreciate live foods, but if fed them exclusively it may reject prepared food later on.  With only one to two feedings a day, offer what they can eat in about 5 minutes. It is better to feed these fish several times a day, but in that case make sure to offer only what they can eat with in about 3 minutes.

  • Diet Type: Omnivore
  • Flake Food: Yes
  • Tablet / Pellet: Yes
  • Live foods (fishes, shrimps, worms): Some of Diet
  • Vegetable Food: Some of Diet
  • Meaty Food: Some of Diet
  • Feeding Frequency: Several feedings per day

Aquarium Care

Cardinal Tetras are not exceptionally difficult to care for provided their water is kept very clean. At least 25 - 50% of the tank water should be replaced every other week, especially if the tank is densely stocked.

  • Water Changes: Bi-weekly

Aquarium Setup

The Cardinal Tetras are very active swimmers and need an aquarium that is at least 15 gallons or larger.  Ideally a tank that is at least 20 inches long to give them plenty of swimming space. This is a blackwater fish, so the aquarium should be dimly illuminated and the water needs to be very soft. Hard water can be problematic, building up calcium salts in their kidney tubulli. Keep the tank very clean as they will not tolerate poor water quality.

A dark substrate and some dense plant cover combined with free swimming space will display this fish optimally. Lighting should always be dim as this fish will not show good colouration in brightly lit tanks. Additionally, the tank should be securely covered as these fish can jump and may do so if given the opportunity.

A biotype setup is the best choice for this tetra and is very easy to put together. The substrate should be made up of river sand and some driftwood branches and twisted roots. Their natural habitat does not have many plants so no need to add them. Some dried leaves can be added to stain the water and give them a natural feel.  Leaves should be removed and replaced every few weeks. To simulate the black waters that they come from add a mesh bag of aquarium safe peat to the filter. 

  • Minimum Tank Size: 15 gal (57 L)
  • Substrate Type: Any
  • Lighting Needs: Low - subdued lighting
  • Temperature: 73.0 to 81.0° F (22.8 to 27.2° C)
  • Range ph: 4.5-7.0
  • Hardness Range: 2 - 8 dGH
  • Brackish: No
  • Water Movement: Moderate
  • Water Region: All - These fish will swim anywhere, but favors the middle of the aquarium or wherever the most swimming space is. It will spend a lot of time in the shadows, mimicking its natural behavior.

Social Behaviors

Picture of a Cardinal Tetra
Photo © Animal-World

The Cardinal Tetras are good schooling community fish that will get along with everyone. The bigger the school, the better its coloration becomes. Keep in mind that it will be eaten by most any fish that can fit it in its mouth, so choose its tank mates well. It is the natural prey of many fish, even many of the other tetras.

The Cardinal Tetra does best with other small tetras, pencil fish, hatchet fish, dwarf cichlids, small Loricariids, small rasboras and anabantoids.  They should always be kept in a group of 5 or more individuals, with larger groups of at least 10 or more being best.

  • Venomous: No
  • Temperament: Peaceful
  • Compatible with:
    • Same species - conspecifics: Yes - They do best in a minimal school of 5 or more, with larger groups of at least 10 or more being best.
    • Peaceful fish (): Safe - They do well with other small peaceful fish.
    • Semi-Aggressive (): Threat
    • Semi-Aggressive (): Threat
    • Aggressive (): Threat
    • Large Semi-Aggressive (): Threat
    • Large Aggressive, Predatory (): Threat
    • Slow Swimmers & Eaters (): Monitor
    • Shrimps, Crabs, Snails: Safe - not aggressive
    • Plants: Safe

Sex: Sexual differences

Males are generally more slender and though It is difficult to spot, males have a hook protruding from the anal fin.

Breeding / Reproduction

Breeding the Cardinal Tetra is very tricky in home aquariums. Water conditions must be optimal, and pairs compatible. They will need subdued lighting, as will the fry. They will spawn in the evening, laying up to 500 eggs. Eggs will be scattered, and parents will eat them if not removed. Fry are very tiny and delicate, therefore very difficult to care for. For a description of breeding characin fish, see Breeding Freshwater Fish: Characins, and Fish Food for Fry for more information.

  • Ease of Breeding: Difficult - Breeding is difficult. This fish requires highly specific water conditions which match those of the natural habitat. Compatible pairs are also not always easy to obtain.

Fish Diseases

The Cardinal Tetra will resist disease. However, if the tank is unstable, it will die off very quickly. The worst fear of a tetra keeper is the Neon Tetra disease, an essentially incurable and a highly contagious disease of unknown origin and cause. It was first diagnosed in Neons, so earned its name, but it can actually affect many other species.

The 'Neon Tetra Disease' has been identified as a microscopic sporozoan in the genus Plistophora. It shows up on the fish as a spreading spot or blemish beneath the dorsal fin. There have been attempts to cure this disease with the use of Methylene Blue, but it is not always successful, so the disease is considered uncurable. This disease has also been spotted on the Glowlight Tetra Hemigrammus erythrozonus, and the Rosy Tetra Hemigrammus erythrozonus.

As with most fish, this species can be prone to skin flukes, parasitic infestations (protozoa, worms, etc.), ichthyobodo infection, parasitic infestations (protozoa, worms, etc.), bacterial infections (general), and bacterial disease. A good thing about this characin is that due to their resilience, an outbreak of disease can often be limited to just one or a few fishes if you deal with it at an early stage. When keeping more sensitive types of fish, it is common for all fishes to be infected even before the first warning signs can be noticed.

The best way to proactively prevent disease is to give your Cardinal Tetra the proper environment and give them a well balanced diet. The closer to their natural habitat the less stress the fish will have, making them healthier and happy. Stressed fish are more likely to acquire disease. Anything you add to your tank can bring disease to your tank. Not only other fish but plants, substrate, and decorations can harbor bacteria. Take great care and make sure to properly clean or quarantine anything that you add to an established tank so not to upset the balance.

For information about freshwater fish diseases and illnesses, see Aquarium Fish Diseases and Treatments. This is a great source for information on disease and treatments. It is recommended to read up on the common tank diseases. Knowing the signs and catching and treating them early makes a huge difference


The Cardinal Tetra is available almost everywhere, in stores and in online catalogs, however many shops choose to stock the more reliable Neon Tetra.


Author: Barbara Roth, Clarice Brough CFS
Lastest Animal Stories on Cardinal Tetra

BJ. - 2015-02-23
I have had 5 Cardinal Tetras in my tank for a year now.Lately,one of them has been acting strangely.It started by keeping itself away from the other fish and seemed to prefer a quiet corner.Now it seems to have a problem when it stops swimming because its tail goes up and it ends up being vertical.It still feeds with the others,but not so eagerly.I have just spotted a brown patch on top of its tail fin.Has anyone any ideas about this?

  • Clarice Brough - 2015-02-24
    It's really hard to say what's going on with that one Cardinal. These fish are known to swim vertically if there is a water problem, usually its from chlorine, which can be introduced with a water change if the replacement water isn't' treated.
Connor - 2014-10-15
I have 3 of these cardinal tetras and they are lovely fish and get on with everyone in my tank such as neon tetras, glow light tetras, lemon tetras, cherry barbs and zebra danios. I am planning on getting some more in my community tank because they show lovely colours and they bond with other fish and swim with them especially neon tetras. I would advise you to get these lovely fish in your tank.

Angie Higgs - 2014-06-27
I have twelve of these guys with my Neon Tetra's and my green Neon Tetra's which is sometimes called the False Neon Tetra. They are all Cousins and all school together and they also group off and they mix up, so I'm unsure if they see each other as all the same. The Cardinal Tetra is Beautiful, but so are their cousins, and if anything the Green Neons are colouring up just like my Cardinals. They love to School in the Flow and its a Beautiful Sight. The Green Neon Tetra's usually start this and then the Cardinals join in and the Neon Tetra's. They all seem so happy together and make my tank look Beautiful. I just can't stop watching them!

Kate - 2006-06-08
I bought 6 of these fish for my 30 gallon tank over a year ago now. By no means an 'expert' fish keeper at the time i didn't expect to have much luck with them (Especially as they were very very small at the time of purchase). The store owner recommended many 'Cardinal water products' that i declined and i took these fish home and hoped for the best. A year later i have 5 healthy and quite large Cardinal tetra's (i lost 1 within a few days of purchse).
These fish really are beautiful and peaceful. They live happily with my Lemon and Flame tetra and a recently purchased pair of dwarf gourami. The flame tetra often show courting and mating behaviour which seemed to 'excite' the cardinals into courtship and mating behavour themselves. Although i don't intend to breed them - for those who do they seemed most willing to mate whilst they were younger.
All in all i havn't found them anymore difficult to keep than any other fish and have avoided the use of expensive 'Cardinal specific products'.

  • john j hanley - 2011-11-09
    take 2 cups of real peat moss put into a cotton sock boil with one gallon of water and to four gallons of water adjust temp and chlorine use this for your water change all your tetras will love it