Cardinal Tetra, Paracheirodon axelrodi
Paracheirodon axelrodi

The startling coloration of the Cardinal Tetra is all natural and arguably unsurpassed by any other freshwater fish!

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

The Cardinal Tetra has a distinctive color pattern with a brilliant neon blue center line above a bright red. It is known as the “big brother” of the Neon Tetra, which it closely resembles in color pattern. However, the Cardinal Tetra’s red coloration extends the whole length of its body, while on the Neon, the red is limited to its back half. To add a bit of variety, breeders have also developed a “gold” strain of Cardinal Tetra that is available 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, preferably from a local breeder as opposed to a mass producer. Also, choose its tankmates carefully. The Cardinal Tetra is the natural prey of many fish, including even many other tetras.

With optimal water conditions and a well-thought-out tank, the Cardinal Tetra’s colors will become even more vibrant. Keep its water soft and acidic. Plant the tank heavily, providing some hiding places and a lot of swimming space. Dark substrate and bogwood will make this fish’s coloring appear even brighter. Avoid harsh lighting because it will not help the Cardinal Tetra’s coloration and because this fish doesn’t like it.

If kept in good conditions, the Cardinal Tetra is easy to maintain and resistant to disease. However, in an unstable tank, it will die off very quickly. The worst fear of a tetra keeper is the Neon Tetra disease, an essentially incurable and highly contagious disease of unknown origin and cause. It was first diagnosed in Neons, where it 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

  • Kingdom: Animalia
  • Phylum: Chordata
  • Class: Actinopterygii
  • Order: Characiformes
  • Family: Characidae
  • Genus: Paracheirodon
  • Species: axelrodi
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&deg 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 rainforests that cover their waterways are usually very dense and let 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. More recently, a “gold” strain of Cardinal Tetra has been been developed that appears in fish stores 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). In nature the Cardinal Tetra is an annual species with a lifespan of just 1 year. In the aquarium, however, they can have a lifespan of about 2 to 5 years.

They have a bluish body with an electric blue neon stripe running vertically from the nose along the length of the body. The neon blue is underscored with a very beautiful broad red stripe. The Cardinal Tetra 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) – These fish will rarely exceed 2 inches in length (5 cm).
  • Lifespan: 5 years – In nature the Cardinal Tetra is an annual species with a lifespan of just 1 year, but can live about 2 to 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 fish keepers with some experience. Because most available Cardinal Tetras 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 the water quality changes that are common in new tanks.

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

Foods and Feeding

The Cardinal Tetras are omnivorous. In the wild they primarily feed on worms and small crustaceans, but in the aquarium they will generally eat all kinds of live, fresh, and flake foods. The Cardinal Tetra will eat most appropriately sized foods.

These fish have high vitamin requirements, so at least 75% of their food should be quality flake food. Cardinal tetras especially appreciate live foods, but if fed them exclusively they may reject prepared food later on. If only doing 1 to 2 feedings a day, offer what they can eat in about 5 minutes. However, It is better to feed these fish several times a day, offering only what they can eat 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. Aquariums are closed systems and regardless of size, all need some maintenance. With home aquariums, the nitrates and phosphates build up over time, and water hardness increases due to evaporation. To combat these ever-changing conditions, water should be replaced on a regular basis. At least 25 to 50% of the tank water should be replaced every other week, especially if the tank is densely stocked.

  • Water Changes: Bi-weekly

Aquarium Setup

Cardinal Tetras are very active swimmers and need an aquarium that is at least 15 gallons or larger. Ideally, they should be kept in 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. Additionally, 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 coloration 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 with 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 for a natural effect. Leaves should be removed and replaced every few weeks. To simulate the blackwaters they come from, add a mesh bag of aquarium-safe peat to the filter. 

  • Minimum Tank Size: 15 gal (57 L)
  • Suitable for Nano Tank: Yes
  • Substrate Type: Any
  • Lighting Needs: Low – subdued lighting – This fish will not show good coloration in brightly light tanks. A dark substrate and some dense plant cover combined with free swimming space will display this fish optimally.
  • Temperature: 73.0 to 81.0° F (22.8 to 27.2&deg C)
  • Breeding Temperature: 75.0° F – Provide a minimum breeding temperature of 75° F (25° C), up to 80-82° F (26.6-27.8° C)
  • Range ph: 4.5-7.0 – Provide a pH range between 5.0 – 6.0 for breeding.
  • Hardness Range: 2 – 8 dGH – Provide a hardness range between 1.0 – 2.0 for breeding.
  • Brackish: No
  • Water Movement: Moderate
  • Water Region: All – This fish will swim anywhere, but it 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
Courtesy David Brough

The Cardinal Tetra is a good, schooling community fish that gets along with everyone. The bigger the school, the better its coloration becomes. They should always be kept in a group of 5 or more individuals, with larger groups of at least 10 or more being best.

Keep in mind that it will be eaten by most any fish that can fit it in its mouth, so choose tankmates carefully. The Cardinal Tetra is the natural prey of many fish, even of many other tetras. it does best with other small tetras, pencil fish, hatchet fish, dwarf cichlids, small Loricariids, small rasboras, and anabantoids.

  • Venomous: No
  • Temperament: Peaceful
  • Compatible with:
    • Same species – conspecifics: Yes – They do best in a school with a minimum of 5 individuals. They prefer larger groups of at least 10 or more.
    • Peaceful fish (): Safe – They do well with other small, peaceful fish.
    • Semi-Aggressive (): Threat
    • Aggressive (): Threat
    • Large Semi-Aggressive (): Threat
    • Large Aggressive, Predatory (): Threat
    • Monitor – Tetras can out compete them for food.
    • Shrimps, Crabs, Snails: Safe – not aggressive
    • Plants: Safe

Sex: Sexual differences

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

Breeding / Reproduction

The Cardinal Tetra has been bred in captivity, but breeding them successfully in home aquariums can be very tricky. An aquarist who wants to attempt breeding them must be sure to have optimal water conditions and compatible pairs. These fish require highly specific water conditions that match those of its natural habitat. Obtaining compatible breeding pairs is not always easy either. However, given the right conditions, these fish will spawn in a community tank. Unfortunately, the eggs and fry will most often be eaten. A separate breeding tank is best.

They can be bred as pairs or in a school, but it is best to condition the fish prior to breeding. A mature female’s belly will become nicely rounded when she is full of eggs. The breeding tank can be as small as a gallon for a pair or up to 20 gallons for a school. The water should be shallow, around 5 to 6 inches deep, as well as very soft, clean, and bacteria free. They will also need subdued lighting, as will the fry. The suggested breeding conditions are a minimum temperature of 75° F (25° C) up to 80-82° F (26.6-27.8° C), very soft water with hardness between 1.0 – 2.0 dGH and pH between 4.5 – 6.0, and low light levels.

They will spawn in the evening, generally laying between 130 and 500 eggs. Eggs will be scattered, and the parents will eat them if not removed. The eggs will hatch in a day. Fry are very tiny and delicate and therefore difficult to care for. Feed them liquid fry food or infusoria until they are large enough to eat baby brine shrimp. For a description of breeding characin fish, see Breeding Freshwater Fish: Characins, and see Fish Food for Fry for more information on feeding the young fish.

  • Ease of Breeding: Difficult – Breeding this fish is difficult. It requires highly specific water conditions that match those of its natural habitat. Compatible pairs are also not always easy to obtain.

Fish Diseases

The Cardinal Tetra is naturally disease resistant. 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, where it 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 incurable. This disease has also been spotted on the Glowlight TetraHemigrammus erythrozonus, and the Rosy TetraHemigrammus erythrozonus.

As with most fish, the Cardinal Tetra 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 its resilience, an outbreak of disease can often be limited to just one or a few fishes if dealt with 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 a well-balanced diet. The more closely their environment resembles their natural habitat, the less stress the fish will have, making them healthier and happier. Stressed fish are more likely to acquire disease. Anything you add to your tank can introduce disease. 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 as not to upset the balance. It is recommended to read up on the common tank diseases. Knowing the signs and catching and treating them early makes a huge difference. For information about freshwater fish diseases and illnesses, see Aquarium Fish Diseases and Treatments.


The Cardinal Tetra is reasonably priced and available almost everywhere, both in fish stores and online. Many shops, however, may choose to stock the more reliable Neon Tetra, so the Cardinal Tetra may need to be special ordered.


Featured Image Credit: InsectWorld, Shutterstock