Freshwater Fish

Cardinal Tetra – Paracheirodon Axelrodi: Care Guide

The Cardinal Tetra (Paracheirodon axelrodi) is a brightly colored, active schooling fish that is the perfect peaceful candidate for a community tank.

Also sometimes called the Red Neon tetra or the “big brother” of the smaller Neon tetra, the Cardinal tetra sports a bright blue neon stripe and scarlet band. Did you know that there is also a beautiful golden variant?

These charming tetra fish can create a brilliant display in a small or large aquarium. Read this care guide to find out everything you need to know about the dazzling Cardinal tetra.

The Cardinal Tetra is a wonderful freshwater fish that is often overlooked. This species is pretty, easy to care for, and quite peaceful.

However, there are some aspects of their care that are noticeably different from other fish in their family.

This guide will teach you the basics of Cardinal Tetra care, so you’ll be fully prepared once you decide to purchase some. You’ll learn things like ideal water parameters, tank mates, diet, size, and even breeding tips!

Species Summary

The Cardinal Tetra (scientific name: Paracheirodon axelrodi) is an impressive freshwater fish that can liven up any aquarium. Known for their bright coloration and relatively lax breeding needs, these fish do very well in both natural tanks.

Like its similar-looking cousin, the Neon Tetra, the Cardinal Tetra is frequently bred in captivity, resulting in a large number of fish in the trade. In the wild, these fish form groups of hundreds, creating large schools of moving colors!

Author’s Note: Even in small groups, the Cardinal Tetra will huddle together and exhibit beautiful shoaling behavior.

The Cardinal Tetra resides throughout South America. They are found mainly in the Orinoco and Negro rivers. However, its distribution is quite wide.

These fish do very well in captivity. Peaceful by nature, Cardinal Tetras make wonderful additions to community tanks large and small.


Scientific name Paracheirodon axelrodi
Common name (species) Cardinal tetra, red neon tetra,
Family Characidae
Source Río Negro and Orinoco in South America, also parts of Venezuela and Brazil
Diet Omnivore
level of care Moderate
Exercise Active fish in schools
Life expectancy Annual in the wild, but 2-5 years when kept in a tank.
Temper Calm
tank level Swims around the water column, but mainly in the central area.
Minimum tank size 20 gallons
Temperature range Tropical 73° to 81° Fahrenheit
Hardness of water 2-8 dGH
pH range 4.5 to 7.0
Filtration / Flow Rate Prefers moderate to low flow with extremely good filtration
type of water Sweet water
Breeding Egg layer but difficult to breed in captivity
Compatibility peaceful community fish
OK, for planted tanks? insurance with plants


Schultz first described the cardinal tetra in 1956. The species is found in South America, specifically the Orinoco and Rio Negro, and are also native to Brazil and Venezuela.

Most of the Cardinal tetras you find for sale at fishmongers are wild-caught. This is partly because the fish are not easy to breed in captivity, but also because catching fish for trade provides employment for people who would otherwise turn to deforestation for a living.

Interestingly, the appearance of the cardinal varies, depending on where the fish originates from. For example, silvery-gold blond forms are found in the Río Negro drainage, and fish from the Orinoco drainage have a shorter blue stripe than specimens taken from other areas.

Thanks to the abundance of numbers in the wild, cardinal tetras are not currently listed on the IUCN Red List.


Cardinal tetras inhabit slow-moving river tributaries in densely forested areas. The waterways here are surrounded by dense rainforest, where overhanging trees and fallen leaves create a low-light blackwater habitat.

Here, the fish live in large schools, feeding on small crustaceans, worms, and plant matter.


Many people confuse the Cardinal Tetra with the Neon Tetra, and it’s not hard to see why! These two species have very similar appearances.

The Cardinal Tetra is a slender fish with a torpedo-shaped profile. Like neon, these fish have two distinct stripes of red and blue.

From the tip of the nose to the tail, the blue stripe shimmers in the light. It has an iridescent finish that makes it sparkle in the right lighting conditions.

Directly below the blue stripe is a thicker stripe of bright red. It runs along the entire body and even bleeds into the transparent tail.

The main difference between Cardinal Tetras and Neon Tetras is the length of this stripe. For neons, the red color only marks the middle of the body.

All the fins of Paracheirodon axelrodi are transparent. The belly is usually white. These fish are very colorful with some unique variations that exist as well (such as gold and silver). However, these colors are very rare.

The physical differences between men and women are very subtle. Females will generally appear more rounded. This is especially true in the breeding season. Meanwhile, the males have a small hook accent on their anal fins.


Both sexes look very alike. However, female cardinal tetras are often plumper than males, and males tend to be brighter in color.


As mentioned above, you can sometimes find a gold variant, which has a pale silver-blue stripe.

Average size

The average size of the Cardinal Tetra is around two inches long when fully grown. That makes them a fairly small freshwater species that can be kept in fairly compact tanks.

Life expectancy of the Cardinal Tetra

The typical life expectancy of the Cardinal Tetra is between four and five years when healthy.

Author’s Note: Interestingly, these fish are known to live longer in captivity than in the wild. In many areas, they are believed to be annual species with a very short lifespan.

When kept in captivity, the Cardinal Tetra needs stable conditions to live a long life. Failure to attend to his needs could result in stress, illness, and even early death.


Cardinal Tetras are very active and peaceful fish that are happiest when kept in a large school.

Unfortunately, like many species of tetra, the cardinal can be a fin prick.

behavior and temperament

Cardinal Tetras are very docile and peaceful creatures, which makes them easy to care for. They are not known to show signs of aggression in general!

Author’s Note: This is something to keep in mind when finding compatible tankmates (more on that in the section below). They are often the target of bullies due to their peaceful nature.

Being with other Cardinal Tetras is very important. When alone, these fish become shy and stressed. Most will even begin to lose their color.

Cardinal Tetras are best kept in groups of at least six. A larger school will help the fish feel safe and help them stay healthy. Throughout the day, the fish will explore the tank and swim together.


Since cardinal tetras are schools, I recommend that you have a school of half a dozen or more of these beautiful fish. Fish will not only be happier in a conspecific group, they will create a more impressive display in the aquarium. So that’s a win-win for you and your tetras!

Paracheirodon axelrodi tankmates

Beyond other Cardinal Tetras, these fish do well in community tanks. There are many possibilities when it comes to tankmates.

Good tankmates for cardinal tetras are other small, peaceful species such as rasboras, danios, corydora catfish, pygmy gouramis, and bighorn sheep.

Invertebrates such as shrimp and snails are suitable companions for cardinal tetras and can also provide a useful cleaning crew in the tank.

Some good Cardinal Tetra tankmates to consider include:

  • Tetra black skirt
  • dwarf gourami
  • guppies
  • Ember Tetra
  • rasbora chili
  • hatchet fish
  • neon green tetra
  • Mollies
  • harlequin rasbora
  • zebra danios
  • emperor tetra
  • Small types of aquarium catfish


As a general rule, avoid any fish that is even slightly aggressive. Territorial species will intimidate the Cardinal Tetra. These fish are finicky and don’t have much in terms of defense, so it’s best to keep things quiet.

I recommend avoiding large, aggressive species as they could harass or even try to eat the Cardinals.

That said, tetras can also be a nuisance, nipping at the fins of fish with flowing tails like bettas.

Care of the Cardinal Tetra

Cardinal Tetra Care is pretty easy for the most part. This species is not very picky and can thrive as long as you keep it in the right conditions.

With that said, many aquarists recommend that you have at least some prior experience keeping fish before attempting to breed the Cardinal Tetra. That’s because they require a very stable environment to stay healthy!

To help you, here are some important care guidelines to follow:

Food and Diet

Cardinal Tetra fish are omnivores that generally feed on worms and small crustaceans in the wild. They are willing to accept a wide variety of foods, which makes it easy for them to eat.

However, these fish have high vitamin needs!

As a result, about three quarters of their diet should consist of dry flakes or pellets. Stick with a balanced food product that is marketed specifically for Tetras.

To complement that meal, you can provide live or frozen snacks. Brine shrimp, bloodworms, and other popular high-protein foods are always appreciated. Just make sure the food is small enough to fit in the Cardinal Tetra’s mouth.

It is best to feed these fish several times a day if your schedule allows. Give them only enough food that they can eat in about three minutes (anything more will result in overfeeding).


Cardinal tetras are classified as omnivores.

In the wild, cardinal tetras eat insects, worms, and some plant matter. Captive cardinals are not picky eaters and will accept a diet of tropical fish scales, pellets, frozen brine shrimp, bloodworms and the like.

Cardinal tetras have very high vitamin requirements, so their diet should contain at least 75% high-quality tropical flakes.


Cardinal tetras love live food and will be very appreciative of what you offer them. However, unless you have your own brine shrimp hatchery, it is safer not to feed your fish live food.

How is that?

Well, unfortunately, live food tends to come with some unwanted extras in the form of bacteria and parasites, which you certainly don’t want in your aquarium. If you buy live food from a pet store, always remove the food from the water it is supplied in before feeding it to your fish.

Similarly, you should never harvest worms and insect larvae from the natural environment. Although that may seem like a good idea, you could accidentally bring parasites into your tank.

The best source of meaty protein for your Cardinals is frozen foods. You can buy a wide variety of different frozen creatures, all of which your fish will love.


You should feed your cardinal tetras two to three times a day.

Offer the fish what it will eat in two or three minutes.

Don’t overfeed your tetras. Any food left uneaten will end up in the substrate, where it will gradually rot and contaminate the water, placing a greater load on your biological filter.



It is not uncommon to see a pair of Paracheirodon axelrodi living in a small 10 gallon tank. These fish do well in tanks of that size.

However, we always recommend using an aquarium that can hold at least 20 gallons. If you can go with a larger sized tank, that’s even better!

A larger aquarium is better if you have room for one, as these are live, active fish that need plenty of room to swim, especially if you plan to keep a community tank.

Author’s Note: The Cardinal Tetra loves to swim in groups. Having more open space to encourage this behavior is great for their overall health and quality of life. Fish that live longer usually have more space!

Although a long tank offers more room to swim and more surface area to allow for good gas exchange, Cardinals will be just as happy in a tall tank as they swim in all areas of the water column.

Tetras are very capable jumpers, so you will need a tank with a lid or a sliding lid to prevent accidental escapes.



Cardinal tetras live in a blackwater river environment. So, add a bag of aquarium-grade peat moss to the filter and sprinkle some dry leaves over the substrate to help create blackwater.

The best substrate to use is dark river sand, which looks natural and helps show off the bright colors of the fish.


Your tank decor can continue the natural-looking theme with rocks, twisted roots, water-smoothed stones, and driftwood. Make sure your aquascape provides plenty of open water for swimming and studying.

There aren’t many plants in the Cardinal River house, largely because the lighting is so poor. However, you may want to include some specialized low-light plants for aesthetic reasons and to give the fish some hiding places to seek out if they choose. Floating plants are ideal for this type of setup as they help diffuse light and provide shelter for fish.


Cardinal tetras are fairly easy to care for, but you must provide them with very clean, well-filtered water. Ideally, Cardinal tetras should be added to an established tank rather than an entirely new setup.


As mentioned above, Cardinals need very clean water, so you’ll need a high-quality filtration system. The water these fish live in tends to move slowly, so an external cooktop or canister filter system would probably be the best option.


To give the Cardinal Tetra the best life possible, it is best to replicate its natural habitat as far as water parameters are concerned. These fish come from slow-moving waters in South America, where the environment is warm, clear, and heavily shaded.

Author’s Note: This is not a species that can just be dropped into a newly established tank. The water chemistry must be stable before they can be introduced. Give your aquarium some time to cycle and monitor parameters closely.

The water should be slightly acidic and very soft. Too many dissolved minerals in the water could be detrimental to the health of the fish.

Below are the water parameters to aim for.

  • Water temperature: 73°F to 81°F (over 75°F preferred)
  • pH levels: 5.0 to 7.5 (below 6.0 is ideal)
  • Water hardness: 2 to 6 KH

To make sure the parameters are stable and consistent, it is important to test your water regularly. Get a reliable and accurate test kit and make sure everything is adequate before introducing this species to its new home.


In the Cardinal’s natural habitat, the water is shaded by the forest canopy. Therefore, you should use dim lighting in the tank to replicate the tetra’s wild environment.

An LED lighting unit that offers adjustable lighting effects is a good option, allowing you to set light levels to suit your fish and plants.


pro tip

You will need to do 25% to 50% water changes every two weeks or 30% weekly if the tank is thickly stocked.

As you change the water, you should vacuum the substrate, paying special attention to areas where debris accumulates, such as the corners of the tank, under decorations, and between plant bases.

Keep display panels clear by using an algae magnet to remove algae.

Once a month, you should clean the filter media by rinsing it with dirty aquarium water, and replace worn cartridges and media when necessary. Consult the filter manufacturer’s recommendations for guidance.

Set up the rest of your tank

Natural decoration that mimics its natural habitat is the best. These fish can live in all kinds of environments. However, they are usually found in shallow rivers and streams surrounded by a ton of vegetation.

Cardinal Tetras stick to the center of the tank, but that doesn’t mean you can ignore the substrate. Your best option would be fine sand. Sand looks a lot like riverbeds and acts as the perfect anchor for living plants.

Speaking of which, you will need a lot of plants! Anubias, Java Fern, and Amazon Swords are good cultivars to try. Strike a good balance between floating plants and submerged plants.

When arranging the plants, leave an open space in the middle. Vegetation is important to block light and provide shelter, but that open swimming area is also crucial.

At the bottom of the tank, you can also incorporate rocks and driftwood. Larger pieces of driftwood work well because they extend to the middle of the water column where the Cardinal Tetra can use them.

For lighting, keep things relatively toned down. These fish do not like harsh lights and are more comfortable when things are slightly dark.


Gather what you’ll need to set up your new tank, including:

  • dark river sand
  • LED lighting unit
  • HOB Filtration System
  • water conditioner
  • Heater
  • aquarium thermometer
  • Driftwood, twisted roots, smooth stones, rock work
  • Dry leaves
  • Peat suitable for aquariums
  • Low light plants, floating plants


  1. Rinse the dust from the river sand under running water.
  2. Put two to three inches of sand in your aquarium. Place a plate or bowl upside down on the sand in the center of the tank. (You’ll see why in a moment!)
  3. Plug in the heater and filter, but do not turn them on yet.
  4. Add non-chlorinated tap water to the tank, pouring the water over the dish or container upside down so the sand doesn’t dislodge.
  5. The water must contain a small amount of ammonia for the nitrogen cycle to start. That’s crucial, as you can’t safely add any fish to the tank until the cycle has completed successfully. So, add a few drops of pure ammonia to the water, sprinkle some fish scale on the surface of the water, or place a handful of existing recycled tank substrate in the aquarium.
  6. Wash the dust off your decoration and place the items in the aquarium as you like.
  7. If you have decided to include live plants in your aquascape, you will need to prepare them by cutting off dead leaves and damaged stems. Add the plants to the configuration.
  8. Turn on the aquarium heater and filtration system. Live plants need eight to ten hours of light a day to photosynthesize, so set the timer on your lighting unit to accommodate that.

Now you need to sit back, relax and wait for the tank to turn on! This can take ten days or more, depending on how long it takes for the nitrifying bacteria to grow in the biological filter media and on surfaces within the aquarium.

Test the water every day or so until ammonia and nitrite levels are zero and nitrates are ideally below 20 ppm. You may need to allow more time for the cycle to complete, so patience is key here.


The main cause of health problems with Cardinal tetras is poor water quality. So as long as you maintain your tank properly and keep it clean, you shouldn’t have any problems with disease.


Cardinals are active fish that should go to school with their tank mates and busily explore their surroundings.


Here are some signs to watch out for that could indicate potential health issues for your Cardinals:

  • not eat
  • Inactivity
  • without schooling
  • Ulcers, open sores, or red spots on the body.
  • Hitting the body against the substrate or decorations.

potential diseases

There are a few different diseases that you need to watch out for. These fish are susceptible to common freshwater problems such as Ich, dropsy, and fin rot.

The good news is that these diseases are easy to treat with some over-the-counter medications. They are even easier to prevent with good tank maintenance!

Do regular water changes and use test kits to analyze the chemistry of the water. Make sure your filtration system is also in good working order to prevent ammonia and nitrate levels from getting out of whack.

A unique health problem to watch out for is Neon Tetra disease. Despite its name, this disease affects a wide range of different types of tetras.

It is a parasitic disease that is often carried into tanks through other infected fish or infected live food. The disease causes spinal problems, cysts, and many other health problems. Unfortunately, there is no known cure for it.

Author’s Note: If you want to play it safe before adding new fish to the mix, quarantine them to make sure you’re not bringing any disease into the wider community environment.


Health problem Symptoms or causes suggested action
Ich (white spot disease) Ich is also called white spot disease and is caused by a parasite.

Infected fish have a rash of small white spots on their bodies, fins, and gills, and are usually bumped or rubbed against objects in the tank.

Raise the tank temperature to 82o
F for three days.
Use an OTC White Spot treatment to dose the tank.
Flukes Flukes is a general term that describes various species of external fish parasites.
You may see flukes or worms attached to the body or gills of the fish.
Treat the aquarium with an antiparasitic drug.
fungal infections White, fluffy growths on the fish’s mouth, head, and body. Quarantine infected fish.
Treat with an over-the-counter fungal medication.
Bacterial infections Torn and bloody fins.
Red spots, sores, ulcers on the body.
Treat the aquarium with an antibacterial treatment.

Breeding of the Cardinal Tetra

For a time, the breeding of the Cardinal Tetra was a great challenge for breeders. While there are established breeding methods, it remains a major challenge. You have to get the right conditions to trigger spawning.

Create a separate breeding tank with stable water conditions. Keep the lights low, as the fry are very sensitive to light. Add your conjoined pair and condition with live foods.

If successful, the pair will breed overnight. The female will lay over 500 eggs at a time! The male will usually swim alongside the female while he distributes the eggs on the plants.

Remove the pair immediately after all the eggs are laid. These fish do not show any parental instinct and eat the eggs.

It only takes about 24 hours for the eggs to hatch. The fry will survive outside the egg sac for about five days until they are free swimming.

At that time, provide infusoria, powdered fry food, and brine shrimp. In about two to three months, babies will begin to take on the same coloration as adults.


You can buy Cardinals at most fishmongers for a few dollars each. You can usually get a discount price if you buy a group of fish, which makes sense since they are a schooling species.

  • water conditioner / dechlorinator
  • algae magnet
  • aquarium thermometer
  • aquarium vacuum cleaner
  • Books on tropical fish farming
  • HOB filter
  • Aquarium (minimum size 20 gallons)
  • Heater
  • High quality tropical fish flakes, mini pellets, frozen food
  • LED lighting unit
  • Floating and low light plants
  • Smooth stones, driftwood, twisted roots
  • Dark river sand substrate


Provided you have the correct information, Cardinal Tetra care should not be too difficult to manage. While we generally recommend that beginning aquarists try another species first, these are far from a fish for experts only.

We know many owners who absolutely love these fish and plan to keep tanks with them for years to come. Maybe you should do the same!

I hope you liked our guide to the bright and beautiful Cardinal tetra.

These dazzling nano fish are a brilliant addition to a peaceful community aquarium and are quite easy to care for, given the right water conditions.

Tell us about your Cardinals in the comments box below!

And please share this guide if you have enjoyed it.

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