Cardinal Tetra 101: Care, Diet, Tank Size, Tank Mates, & More

Fish keepers love the Cardinal Tetra, and the reason is simple — it is beautiful. With its vivid neon blue stripe that covers the entire body and a brilliant red color band that bleeds into the tail, the Cardinal Tetra makes for a gorgeous display.

Like other tetra species, Cardinal Tetras are social and peaceful, meaning they thrive well in community aquariums. But while this is the case, there’s still some work you have to do if you want to keep one.

cardinal tetra
Cardinal Tetra

Species Summary

The Cardinal Tetra (Paracheirodon axelrodi), originally from the Amazon Basin, has enjoyed explosive popularity since its discovery in 1934. Its original territory extends along the rivers of Brazil, Peru, Colombia, and Ecuador.

In nature, it is used to living in dark waters of acidic Ph and low light. It forms schools with thousands of fish that live and feed together to avoid predators.

Most of the Cardinal Tetra found for sale are of wild origin, as it is not the easiest species to breed in home aquariums, but this has changed in recent years. Its current popularity is mainly due to its bright colors, ease of care, and also great adaptability to different types of aquarium companions. 

Cardinal Tetra Care Guide

In this section of the article, we’ll show you how you can provide the best care for your Cardinal Tetra.

Tank Size

These tetras are great to keep in small to medium-sized aquariums. An aquarium with minimum dimensions of 24″ X 11″ X 11″ (12 gallons) is required to maintain a small school of these magnificent fish.

As this is a schooling fish, it will need companions to have a healthy life and shine brighter in your aquarium.

If you choose to keep more fish together with a small school of Cardinal Tetra, consider purchasing a larger aquarium.

Tank Mates

This species of fish is very friendly and can easily interact with other fish species.

When choosing a companion species for your shoal, the most important thing is to avoid any fish that is bigger than these tetras. Also, note the aggressiveness of companion species. Peaceful fish deal best with friendly fish, aggressive ones with the same temperament, and so on.

You can keep it in a community aquarium without problems, as long as you don’t have much larger fish. Keeping them to at least ten individuals is essential so they are uninhibited and at ease.

Some aquarists keep them with larger fish, such as Discus and Acará Bandeiras, as long as they breed them with these juvenile cichlids to get used to them long-term. Corydoras, Plecos, Dwarf Cichlids, and other tetra species like Bleeding Heart Tetra also make great tank mates.

Same Species Tanks

The Cardinal Tetra is a fish very common in aquariums of only one species, mainly in tanks of the biotope type. This is because it is a species with bright and vivid colors and lives in large schools with high ornamental potential.

Water Parameters

Cardinal Tetras live in the warm waters of the Amazon rainforest region. Therefore, it requires a tropical habitat, where you must maintain the aquarium water temperature between 26ºC and 30ºC.

The pH of these waters, being transparent or dark, varies a lot, but it always remains acidic; in the aquarium, it must be between 4 and 7. You can purchase a water pH monitor to control this better, as these factors will significantly influence the beauty of your fish.

In nature, they are found in water with low hardness; in an aquarium, you must maintain the water hardness from 1 to 8. The maintenance of low hardness has an essential role in the reproduction of the species.

These fish are found at different pH in the wet and dry seasons but always tend toward the acidic side. Low pH also plays an essential role in inducing the reproductive phase.

What to Put in Their Tank

As for any other aquatic animal, an aquarium heater and a filtering system are essential to keep the tank with Cardinal Tetra healthy. The filtration system must be well-sized, creating a low flow.

Make sure that the tank is well decorated with hiding places and territories. They also go well in densely planted aquariums. Sandy, dark substrate will further enhance their colors. 

Common Diseases

Cardinal Tetra is a very resistant fish but cannot live in waters with a high nitrogen content for a long time. High pH and hardness also drastically shorten its lifespan in aquariums.

Keep in mind that it is highly susceptible to Ich when poorly maintained, especially at low temperatures.

Another disease to look out for is the famous “Neon Tetra Disease.” This disease affects almost all tetra species. When ingesting parts of the parasite, it settles in the intestine of the fish. It spreads in the intestinal wall, producing cysts within the muscle tissue, which start to necrose, possibly verifying the loss of color in the upper blue band of the fish.

The band turns white or opaque from the back to the tail. The most common symptoms are loss of color, irregular swimming, and irregularity of the spine due to the formation of parasite cysts.

Food and Diet

Cardinal Tetras are omnivorous animals with a strong tendency towards carnivorism and are generally very easy to feed. Hence, any food small enough for their mouths is usually accepted once they are acclimated to the aquarium.

In the wild, most of their diet is based on crustaceans such as Cladocera, some Copepods, rotifers, and secondarily diatom and green algae, ants, detritus, mites, fish larvae, and pieces of fruit.

In captivity, offering live food will help the fish’s well-being. In addition to making the fish more active and lively, live or frozen foods are a good source of protein and help trigger reproduction. Some options you can offer are brine shrimp, tubifex, and daphnia.

The rule of thumb is to feed them several times a day in small amounts. Any food that remains in the water for more than 2 or 3 minutes should be removed to avoid problems such as over-consumption by fish and degradation of water quality.


These tetras, when in captivity, live for 3 to 5 years. In nature, they hardly exceed 2 years.

Several factors influence how long a fish lives, including feeding, environmental conditions, and the presence or absence of predators.


The Cardinal Tetra have striking traits responsible for their popularity and great demand.

It is characterized by two long colored stripes that cover his entire body. At the top, a shimmer shines according to the angle of the reflected light; this one varies between green and blue.

At the inferior part of the fish, right under the blue stripe, is a long reddish line that is not far behind in beauty. The blue and red lines make the Cardinal Tetra fish unmistakable!


When properly cared for, these fish can grow to close to 2 inches in length. The size we usually see in stores and home aquariums is around 1.18 inches.

Behavior and Temperament

Cardinal Tetra is not only a peaceful fish; it is also a peacemaker. In an aquarium with mixed fish species, these little fish encourage others to socialize more in the environment. 

It can also live with Bettas, who are naturally quarrelsome and lonely. However, it is not recommended to include Cardinal Tetra in aquariums with huge fish, as they can quickly become food.


In the past, people believed that the species had a complicated reproduction process and were very difficult to do in aquariums. Today we know this is mainly linked to the low hardness and pH that these fish require to reproduce. It is not difficult to understand why most of the specimens sold are captured in the wild.

When breeding, it is best to isolate the male and female in separate aquariums. The water should have a hardness close to 1 and a pH of around 5. In addition, there must be little or no light in the room.

The eggs are photosensitive, being released in shady places. Larvae are also photosensitive, and at least in the first seven days of life, they are gradually accustomed to the presence of light.

The female will then be full of eggs, attracting the attention of the males, who will follow her in zig zag movements. The female will disperse the eggs freely in the environment, which will soon be fertilized by the males and fall into the substrate; about 500 eggs will sink or adhere to plants (free dissemination).

When this process is complete, the parents should be removed from the aquarium, as they will eat the eggs and fry. In little more than 24 hours, the eggs will hatch, but only after a few days should you feed the fingerlings with infusoria and later with nauplii. During this period, continue doing partial water changes to keep the aquarium clean and with optimal parameters. Then, when they are about 40 days old, start feeding them more significant foods.

And at three months, you can finally transfer them to the main aquarium, as their size will be similar to those of adults; they reach sexual maturity at about nine months.

Gender Differences: Male vs Female

The Cardinal Tetra is not one of the easiest fish to differentiate between male and female, as their sexual dimorphism is not as evident as those of the Betta.

Female Cardinal Tetras have a wider body, especially in the belly region; this is even more accentuated during the breeding season. In addition, females are usually larger than males.

As well as being slender, the male also has a small hook on the pelvic fin, which is not always easy to see.

Cardinal Tetra Fun facts

  • The characteristic iridescence of this fish is a structural color caused by the refraction of light onto the guanine crystals that develop inside special cells, called iridocytes, in the subcutaneous layer.
  • The exact shade of blue will depend on the aquarist’s angle of view of the fish. If the aquarist changes the point of view so that he is looking at the fish further down, the color will change and become bluer. Looking further up, this color becomes more greenish.
  • The function of the intense blue color on its flanks may have evolved as a predator evasion strategy, according to the hypothesis of Ikeda and Kohshima (2009). They published a field study of this species in blackwater streams near Requena in the Peruvian Amazon. 
  • While most characids display a lateral color pattern, having a dark-colored lateral stripe with a lighter dorsal stripe, this pattern is inverted inParacheirodon. It may be an adaptation to form mirror images.
  • As they are found in shoals in nature, the image transmitted to potential predators is that it is a much larger fish than it looks, inhibiting possible attacks, thus uniting their coloration with the fact that they are always in numerous shoals; they become defensive elements, crucial to their survival.
  • They can change the intensity of their overall color pattern, becoming lighter in light conditions with transparent substrate and clear water and duller with a violet side band at night. This could also be a response designed to make them less visible.
  • During the night, they have a slightly transparent brown color. Like other tetras, they have a small adipose fin and a single row of teeth.
  • An economically crucial species in several regions of Brazil, there are several sustainable projects to capture this fish, accounting for about 60% of the annual income of riverside dwellers in the municipality of Barcelos.


Lima, et al., 2003. Genera Incertae Sedis in Characidae. p. 106-168. In R.E. Reis, S.O. 

Kullander and C.J. Ferraris, Jr. (eds.) Checklist of the Freshwater Fishes of South and Central America. Edipucrs.

Mikolji, I., 2009 – Tropical Fish Hobbyist 635: 70-75.

Milinski, M. (1993). Predation risk and feeding behaviour. Behaviour of teleost fishes, 285-305.

Nomura, H., 1984. Nomes científicos dos peixes e seus correspondentes nomes vulgares. In H. Nomura (ed.). Dicionário dos peixes do Brasil. Editerra, Brasília, Brasil: 27-63.