Cardinal Tetra Species Profile: Care, Tank Mates & More

Although it is fun to keep large fish, you should not overlook the small ones either!

The Cardinal Tetra is one of the best nano fish and is perfect for adding some life and color to the background of your tank.

Despite their small size their bright red and neon blue colors are unmistakable. These little red wonders travel in groups of 6 to 10 and attract attention everywhere they go.

Cardinals also happen to make excellent beginner fish and can fit into all kinds of setups.

If this beautiful nano fish has captured your attention then keep reading to learn more about them…

Cardinal Tetra

What is a Cardinal Tetra?

Cardinal Tetra In Tank

The Cardinal Tetra (Paracheirodon axelrodi) is a tiny South American freshwater fish. It inhabits small streams in the Rio Negro and Orinoco River and is best known for being the cousin of the Neon Tetra.

You may have heard people call them Red Neon Tetras.

Cardinal Neon Tetras are primarily used to add color to community tanks. They are quite similar to the Neon Tetra and you can use the two as substitutes for one another. Their red and blue colors will bring attention to the background of a planted tank.

These little guys are only 2 inches long and must be kept in shoals of at least 6 to feel safe. On average they live from 3 to 5 years.

You can find them everywhere and a bundle of 6 will cost between $3-$5 on average.

These Tetras need a 20 gallon tank to host a shoal of them.

Key Facts:

  • Experience Required: None.
  • Nicknames: Red Neon Tetra.
  • Color Forms: Red and blue.
  • Size: 2 inches.
  • Tank Size: Minimum 20+ gallon.
  • Tank Temperature: 73-81°F.

Pros and Cons

Pros:

  • Wonderful colors
  • Mixes well with other Tetras
  • Very active and entertaining
  • Fits into community setups

Cons:

  • Skittish in small groups
  • Susceptible to overcrowding
  • Easy prey for larger fish

Appearance

Paracheirodon axelrodi

The Cardinal Tetra is a bright red fish with an icy blue streak down its lateral line.

This vivid blue streak begins at the head and stops just before the tail. The red appears on the ventral side of the fish, from the pectoral fins to the caudal fin. The dorsal side above the lateral line is translucent.

Depending on the fish’s mood their color will change in shade and intensity.

The body is shaped like a bullet which helps them swim at different depths. It has a rounded snout, a thin abdomen, and eyes that take up most of its head.

Cardinals have 6 translucent fins which are arranged so that the fish looks almost like a tiny shark. A pointed, triangular dorsal fin sits right at the center of the body. The tiny pectoral fins can be hard to see, especially when they are always tucked against the body. The rounded pelvic fin and pointed anal fin are much more visible, and they are followed by the V shaped caudal fin.

Interestingly there are a few small anatomical difference between the Rio Negro and Orinoco populations, such as the position of the gill rakers and the number of rays on the fins. These differences may have arisen from differences in water quality between the two rivers.

You should only expect them to reach 2 inches long, but shoaling helps them look much larger to potential predators.

Because this fish is so small telling the genders apart can be difficult.

Male Tetras are brighter and they also have tiny hooks protruding from their anal fins. They are also thinner and more streamlined in body shape.

Females lack these hooks, are bulkier in body shape, and have paler colors than the males. Their abdomens swell up with eggs when they are in breeding condition too.

Cardinal Tetra vs Neon Tetra

Cardinal Tetra vs Neon Tetra
Cardinal Tetra (Right) vs Neon Tetra (Left)

Beginners can have difficulties telling the Cardinal and Neon Tetra apart. It can get very confusing if the two species are in the same tank. Fortunately, there are a few simple ways to tell them apart.

Cardinal Tetras are a brighter red and this red appears from head to tail on the ventral side of the fish. A Neon Tetra’s red color only appears on the tail.

Neon Tetras also have a paler blue lateral line, which looks green in some lights.

Cardinals are about a half inch bigger than the Neons.

Neons are slightly easier to care for but the species are pretty much interchangeable when it comes to care and maintenance. They can shoal together too and will often create a larger shoal for safety.

Habitat and Aquarium Set-Up

A School Of Cardinal Tetra

In its natural habitat you will find them swimming in the wide open areas of small streams.

The substrate in these areas is usually enriched with fallen leaves, moss, and dead plants. There are also plenty of thriving live plants there too. This creates an acidic environment with the pH as low as 4.0.

Although Cardinal Tetras look their best in bright lights, they prefer murkier waters where they can stay hidden.

During the rainy season they can be found living in floodplains along the riverbank. In the dry season they stay in the open river and travel along small currents.

To keep Cardinal Tetras you will need a 20 gallon tank – this is the minimum size for a group of 6 to 8.

The temperature should range from 73-81°F, with the ideal temperature being 75-77°F. It is best to keep the water somewhat acidic, with a pH range from 5.5-6.5. Use leaf litter and sphagnum moss to maintain alkaline conditions and make sure to keep the water soft (between 2 and 10 dGH).

Use soft sand or mud for the substrate and mix plant material and moss into it.

A light intensity of about 2 watts per gallon is acceptable as these fish prefer dimly lit areas. Use a basic aquarium light bulb and avoid direct sunlight. You can use a hang on back filter to generate some light currents.

These fish need plenty of room in the center of the tank for swimming.

Make sure your plants are placed along the edges or in the background of your tank, to keep the foreground open for swimming.

Tetras favor shady plants with wide leaves, or those that grow in dense thickets. Use low light plants such as Java Ferns, Amazon Swords, and Cryptocorynes. For carpeting you can plant a thick mat of Java Moss or Micro Swords.

Care

A Cardinal Tetra Swimming

Cardinal Tetras are great beginner community fish.

They are quite resilient for such tiny fish and can handle mild changes in temperature, pH, and water hardness.

Unfortunately there is the possibility of a terminal illness called Neon Tetra Disease. This is caused by a microscopic fungus called a microsporidia. This disease also affects Barbs, Danios, and other small fish,

It is easily spread when one member of a shoal gets infected.

In the early stages of infection the affected fish will separate from its shoal. Its colors will begin to dull and it may have difficulty swimming. Later on, cysts will develop all over the fish’s body and its spine will appear curved. This indicates that the parasite has spread to the bones and organ systems.

There is no cure or treatment for the disease and the affected fish will need to be euthanized to prevent further infection.

The best way to deal with Neon Tetra Disease is through prevention.

It can be prevented with regular tank cleaning and water changes. Parasites are often carried in on new fish, invertebrates, or plants, so always quarantine new additions to your tank before you introduce them.

One final thing to note about these fish is that they are very susceptible to metal poisoning. Many medications and fertilizers contain copper and other metals and these are fatally toxic to this fish. Since copper-based medication is so common it can be difficult to treat these fish when they do get sick.

Feeding and Diet

These fish eat the tiniest prey they can find in the water column. This includes: zooplankton, insect larvae, small worms, and algae. In the wild they also like to munch on leaves and fruits that fall into the water.

In the aquarium Cardinal Tetras should be fed tetra flakes. These flakes are full of everything a Tetra needs to be healthy.

However, you do not want to rely on commercial foods alone when it comes to giving your fish a balanced diet.

Bloodworms, water fleas, mosquito larvae, and brine shrimp can be given. A protein rich diet will help to keep your Tetra’s colors bright.

You can also give them fruits and veggies. Boiled and blanched peas, lettuce, melon, and chopped cucumber can be given as a treat from time to time. Keep in mind that these are high calorie snacks for a small fish. Some of the best foods for Cardinal Tetras include: Tetra flakes, Daphnia, Moina, Bloodworms, Brine shrimp, Mosquito larvae, Algae, Plants, Cucumbers, Melon, Lettuce, and Peas.

You should feed your Tetras twice a day.

Make sure that all of their food can be finished in under three minutes and that any leftovers are immediately removed from the tank.

Behavior

These fish are always in motion and will be found darting around the middle levels of the tank.

In a small group they may behave more anxiously. They may swim slower and try to hide under the cover of leaves and logs. They may even try to shoal with other fish just to feel safe.

However, when kept in a large shoal they are extremely bold for such little fish. The larger their shoal is the more confident they will be.

Cardinal Tetras will get along well with other small fish and may follow them or swim alongside them at times.

Do not expect them to engage in roughhousing or bullying. They are ideal for communities and for first time fish keepers.

Close Up Cardinal Tetra

Tank Mates

Just like other Tetras the Cardinal is excellent for community tanks.

When mixed in with other colorful fish they can really make a tank stand out.

In the wild you will find this fish with Cory Catfish, Red Phantom Tetras, Plecos, and Cichlids.

The following make great tank mates for Cardinal Tetras:

You should avoid keeping these Tetras with Cichlids which are known for their boisterous personalities which a little Tetra cannot keep up with.

Large Pleco Catfish should also be avoided as there is always a possibility that the Tetra may end up being eaten.

You should avoid any fish that is large enough to make a meal of your Tetras. Rainbow Sharks, Red Tail Sharks, and other freshwater sharks often come with pushy personalities that are too much for a Tetra to handle so they should be avoided as well.

Keeping Cardinal Tetras Together

You should keep Cardinal Tetras in groups of at least 6.

An ideal group size is about 8 to 10.

The larger the group is, the more confident your Tetras will be. If the shoal is too small, they will spend most of their time hiding.

Breeding

Group Cardinal Tetra

Cardinal Tetras will often breed on their own and without any external help.

However, you will need to set up a breeding tank if you want to make sure that the offspring survive.

The breeding tank should be a miniature version of the main tank with the same temperature and pH range. It should be equipped with a sponge filter and furnished with a leafy plant and a crop of moss.

To increase the likelihood that your fish will breed you should keep a mixed gender group of 8 to 12 individuals. Half of the group should be male and half should be female.

Feed them on bloodworms, brine shrimp, and other live foods up to 3 times per day.

Once they reach breeding condition the males will show their brightest colors and the females’ abdomens will round out.

When a pair of Cardinal Tetras is ready to spawn they will begin to clear out a spot for the female to lay her eggs. Spawning will occur overnight and the female will lay up to 500 eggs. You should remove the parents immediately once the eggs are fertilized as these fish are brood cannibals.

The eggs will hatch in 2 to 3 days and the fry will be free swimming after another 3 days.

Free swimming fry must be given infusoria until they are large enough to eat larval brine shrimp. As they grow bigger you can add bloodworms and microworms to their diet.

The fry will develop their famous red and blue colors after about 3 months.

History and First Sighting

The Cardinal Tetra was first discovered in 1956 by Myers and Weitzman.

It was originally classified as Hyphessobrycon cardinalis.

Later that same year the species was reclassified as Paracheirodon axelrodi in honor of the founder of Tropical Fish Hobbyist magazine.

This magazine introduced the species to the general public and it was made available for aquariums in the 1960s. By the 1980s it had become the number one ornamental fish export in its region.

Unfortunately such popularity caused issues for wild populations.

As a result in 1991 Project Piaba was established to protect its populations. Project Piaba introduced a captive breeding program and provided educational materials for running a sustainable fishery. Its logo even features a Cardinal Tetra!

Now the Cardinal Tetra is one of the most popular freshwater Nano fish and continues to be the most important ornamental fish export in the Rio Negro region. Many specimens in the aquarium trade are still harvested from the wild.

Facts about Cardinal Tetras

Cardinal Tetra
Other Common Names: Red Neon Tetra
Scientific Name: Paracheirodon axelrodi
Family Name: Characidae
Distribution: Rio Negro and Orinoco Rivers (South America)
Size: 2 inches
Color: Red and blue
Care Level: Easy
Temperament: Peaceful
Lifespan: 3-5 years
Minimum Tank Size: 20 gallons
Tank Mate Compatibility: Peaceful Nano community fish

Final Thoughts

The Cardinal Tetra brings color and activity to your aquarium.

This adorable little fish will get along with just about everyone in a freshwater community.

Cardinals make a great introduction to Tetras and can thrive in either a community tank or a single species setup.

Just remember they need a decent sized shoal and a lot of room to swim to feel safe.

With a clean tank, a proper diet, and plenty of room to explore, your Tetras will surely show their best colors.

How many Cardinal Tetras do you keep in your tank? Let us know in the comments section below…

David Thomas Author Bio Picture
David Thomas leads the team at Everything Fishkeeping as the Editor-in-Chief. David has been keeping fish since he was a child. In his first tank he kept goldfish and since then he has kept over 30 different species. Now he has 4 separate tanks and his favorite is a 100 gallon freshwater tank with a school of Rasboras, Tetras and Loaches.