Cardinal Tetras – The Ultimate Care Guide

Cardinal Tetras are striking fish with intense red accents who originate from tropical rivers in South America. Keeping these fish can be worthwhile but demanding at moments. Despite the challenges, they are becoming progressively more attractive to aquarium enthusiasts of all degrees. Another name they occasionally go by is the Red Neon Tetra, so keep an eye out when looking for them in local aquarium stores.

Cardinal And Neon Tetras
Cardinal Tetra – Chewy

These can be an excellent starter fish, but it will take the correct care to ensure they stay healthy, happy and live long lives.

Their Origins

Cardinal tetras, scientific name being Paracheirodon axelrodi, is a popular freshwater fish that comes from the elegant Orinoco and Negro Rivers that pass through South America. They come from within the eastern parts of the river throughout Venezuela, but researchers have observed them as far west as Colombia.

The rivers in these rainforests stay preserved by the dense landscape around them, sheltering them from most light and wind. This allows the water to be still and crystal clear, which Cardinal Tetras love! These are social fish that can group into schools numbering into the hundreds. The transparent water makes it easy for them to mingle with other fish and develop their school to such large scales.

History of Domestication

This specific characiform fish became officially categorized in 1956 by American ichthyologist, Leonard Peter Schultz. Pinpointing when this specific fish started being kept in home aquariums is difficult though. The fish keeping hobby has been going on for thousands of years, though ancient fish keepers liked to stick mainly to Koi, Goldfish and Beta Fish. Cardinal Tetra are well known within the fish keeping community, but until recently, they were not as popular and common as Neon Tetra due to them being finicky to breed.

Amazon Blackwater Biotope - Cardinal Tetra (Paracheirodon axelrodi ...
Cardinal Tetra Amazon – YouTube

Over the years breeders have worked on more effective ways to breed a steady supply of the Cardinal Tetra, with that comes a rise in popularity. Now they are found in specialty fish stores at $2.00 – $4.00 for each healthy fish. Still, because of the extra cost attached to breeding and raising baby fry, most fish found in stores continue to be wildly caught. This is a sensitive topic of debate for aquarist whether it is ethical to catch wild fish, but many locals to Venezuela and Colombia praise the industry and rely on it.

Cardinal Tetra Appearance

Cardinal Tetras get their name from their vivid cardinal colored ventral parts that run horizontally down the length of the fish’s body, bleeding into parts of the tail. Above the red stripe is an iridescent blue stripe that pairs with the red line parallel down the fish, stopping just before the tail with no bleeding. Similar to other tetra fish, the blue line changes hue depending on the angle the fish is being viewed from. This kaleidoscopic color change comes from their pigment being chromatophore, which means they contain light-reflecting cells that, when illuminated, generate a stunning blue iridescence. On their underbelly, there is a complimentary soft flush of translucent white coloring.

Neon Tetras and Cardinal Tetras - Aquarium Co-Op
Cardinal Tetra – Aquarium COOP

The rest of their body is otherwise transparent, including their fins. When compared to the physical traits of a classic Neon Tetra, the Cardinal Tetra’s red stripe is more prominent and stretches along the entire body. It can be somewhat tricky to spot the difference to an untrained fish keeper, so pay attention to the length of the red stripe.

Tank Set Up and Optimal Requirements

Cardinal Tetras are relatively easy to take care of as long as the tank is pre-established and mature before the fish get introduced. A good percentage of these fish are still wild caught in South America causing them to be less adaptive to tanks do not meet their needs.

When thinking of getting Cardinal Tetras, the first thing to do before purchasing the fish is to set up a tank at least a week in advance. This is a crucial step unless they are being introduced as a cohabiter to an already established tank with other fish. By doing this, the tank will gradually mature and become the proper ecosystem the fish require if they are to thrive.

To get started, the first thing to work on is a getting the water to a soft acidic state with stable chemistry. These fish require a pH 6 and the water hardness should be no higher than 4. Regular weekly water changes of around 25% of the tank are required to keep the ecosystem ideal, anymore than that can cause problems with the water chemistry and lead to illness. It is also vital to take extra care with treating the fresh water before introduced into the tank. Introducing incorrect temperature water or improper chemistry can shock Cardinal Tetras and cause them to get sick or die.

The ideal tank size will be no less than 20 gallons for a healthy school of at least six fish. Getting less than six can make it difficult for the fish to school together, leading to stressed fish. Ideally an excellent school of fish will be over 12 as this is a very social species. These are peaceful fish that need lots of room to swim and swim together otherwise they will become upset and could lose their vibrant color.

The Basic Requirements Are:

  • pH: 5.0 – 6.0; soft acidic
  • Temperature: 72 °F – 81 °F
  • Hardness: 2-4 dGH
  • School Size- Minimum of 6
  • Size: 1.5” – 2”
  • Minimum Aquarium Size: 20 Gallons
  • Water Changes: 25% Weekly

Quality of Life Requirements

Decorating a tank for Cardinal Tetras is just as important to the fish’s health as proper water chemistry is. Their general activity is swimming around the tank together, but providing them shelter in case they become scared is vital. Ideal shelter for them is plants scattered throughout, taking care not to overcrowd the tank. The goal is to give them the option to have shelter while still giving them enough room to swim around.

betta tank set ups | Freshwater+aquarium+tank+setup (With images ...
Aquarium – Pinterest

Most standard tank lighting will be good enough for the fish unless the intentions are to breed them or pair with live plants. Breeding these fish will require a lot of extra attention to the tank set up, temperature, chemistry and mimicking their natural environment to make them feel comfortable. Live plants will also have their own requirements to stay alive and healthy. But if paired with live plants, Cardinal Tetras will normally adapt to the specific lighting requirements of the live plants as long as it’s not too bright.

Fish Diet

Feeding these fish is easy and inexpensive, they are omnivores and can accept most foods provided for them. The only requirement they have will be a high vitamin content, so feeding them a diverse diet is advised. It is most cost efficient to feed them generic flake food, but consider adding in frozen or live food as a supplement to their diet to aid in reaching their vitamin requirements. To make sure they stay well fed, feed adults twice daily. Only feed them what they can eat within two minutes; if they do not finish the food, clean it up before it breaks down in the water. Leftover food can cause unnecessary bad bacteria to form and could make fish sick.

Life Span                   

Typical lifespan is different for captive fish and wild fish. In the wild, Cardinal Tetras are considered annual fish and have brief lives of about a year. Put them in a tank and their average lifespan increases to about 3-6 years. Once born, this species of tetra takes around 8-10 weeks to show color and at least 7 months to become sexually mature.

Fish that can Cohabit with Cardinal Tetras

Finding cohabiters is easy as long as we keep one rule in mind; do not keep any fish that eats smaller fish, with Tetra. Large fish need to be avoided as Tetra are small slender fish that are easily be eaten by those with large mouths. Another fish to avoid is any fish that is highly territorial as they will bully and intimidate Tetra. So even smaller fish such as Beta can be highly aggressive and stress them out. It is sometimes possible to have Tetra and Beta fish live together if the tank is big enough and set up correct. But it still can be a lot of work to balance the amount of open water and hiding space in a tank.

Suitable tank mates for the Cardinal Tetra will be other small, peaceful minded fish such as other kinds of Tetra, Ghost Shrimp, Zebra Danio and Guppies. Making sure there is enough quality space for each fish and all fish have their basic requirements met will be important when trying to create a community of fish.

Common Diseases and Prevention

Cardinal Tetras are relatively disease resistant and normally die to improper water conditions or old age. They are so sensitive to drastic water changes that adding water that is only a few degrees off to their tank can lead to death. Therefore, it is important when doing water changes every week to treat the fresh water properly and bring it to the correct temperature.

The deadliest illness they can contract is ‘Neon Tetra Disease’. This is a highly contagious disease that was first identified in Neon Tetra but can affect many other species of fish. This devastating illness is incurable and will spread rapidly. The only treatment is to isolate infected fish and hope they have not already spread it to healthy ones.

Staying alert and attentive to the fish will make it easier to spot the signs of Neon Tetra Disease before it infects the whole tank. The first sign to watch out for is any Tetra that has become upset and stopped schooling with the others. These fish are social schooling fish, so when one breaks off this can be a worrisome first sign. In advanced stages, the fish will lose their beautiful colors and may pass away.

My 10 Gallon Quarantine Tank - YouTube
Quarantine Tank – YouTube

If a tank is having an outbreak of Neon Tetra Disease, separate infected fish into a separate tank and monitor healthy fish closely. Cardinal Tetras will be more resilient to the infection than others but can still catch and die from the disease.

Other health problems Cardinal Tetras can be prone to are common fish ailments such as parasitic infestations, ich and skin flukes. The pleasant news is they are tough and even when an infection gets introduced to the tank, it’s easy to isolate sick fish and assume the others have not caught it yet.

The best way to treat any illness is by staying proactive before they are even brought in to the tank. This means any new vegetation or decorations that are to be introduced will need to be quarantined and properly cleaned before being placed. Same goes for new tank mates that will be added to the community. Additional fish need to get quarantined in a separate tank for at least a week to ensure they are not harboring any hidden ailments before allowing them to enter the main tank.

Making sure the fish have a quality diet full of vitamins as well as keeping their water clean and at a perfect chemistry will produce healthy fish that can fight off any illness they may contract with greater success.

Breeding Fry

Breeding the Cardinal Tetra can be extremely tricky at times. However, it’s similar to Breeding Neon Tetras, which you can read about in our article here.

The first step is making sure the tank is at excellent health and in superb condition. They will need conditions that illustrate the natural rivers of Venezuela and will not breed without them. Lighting will also need to be more subdued to mimic the dense vegetation that shades their natural habitat.

A breeder will need a compatible pair of male and female fish to breed together. Male fish are slimmer in body shape, females have a rounded belly and are normally slightly bigger. They need to be bred in a separate breeding tank so once the eggs are laid, the parent fish can be removed before they eat the eggs. Once mated to, the female will lie between 100-500 eggs scattered throughout the tank in the evening time.

Paracheirodon axelrodi – Cardinal Tetra (Cheirodon axelrodi ...
Cardinal Tetra Fry – Seriously Fish

Baby fry will hatch from their eggs and be ready for feeding in 5-6 six days. Fry are sensitive to an inconsistent schedule, so regular feedings are important. Breeders will use a sparing amount of liquid fry diet and Baby Brine Shrimp. Fry won’t accept the Brine ship until a few days of age. They will need to be fed twice daily so they do not starve, a few drops of liquid diet will be enough.

After 2-4 days of feeding, it will be time to start minor water changes. Remove tiny amounts of water from each change and replace it with water of the same chemistry and temperature. Cardinal tetras take a while before they show their stunning colors at 7-11 weeks. They will become full grown and sexually mature when they reach 7-8 months.


When prepared with excellent tank conditions, I cannot overstate the beauty of Cardinals. Their luminous red and blue hues gleam under a subdued light in such eye-catching ways. As long as you put in the effort to provide their tank with optimal conditions, keeping these fish can be immensely satisfying. They are beginner friendly with appropriate education, making it an interesting project to set up for. When these fish school together and show off their dynamic colors, it can certainly be relaxing and hypnotic to witness.

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