Cardinal Tetra: Fish Species Profile

Arguably the most popular of the small tetras, the cardinal tetra is similar in appearance to a longtime aquarium favorite, the neon tetra—you can tell them apart by one particular detail: a slight difference in their red stripe. Cardinal tetras are active schooling fish, and they live peacefully in a community aquarium.

Although they are difficult to breed in captivity, tetras remain a very popular aquarium fish. Here’s everything you need to know to keep cardinal tetras happy and healthy in your tank.  

Characteristics

Origin and Distribution

Originating in South America, this species is found from the Orinoco River to the Rio Negro tributary of the Amazon River. It is found as far west as western Colombia. Other locations have also reported schools of cardinals, likely comprised of fish that have escaped from collectors. Manaus, in northern Brazil, is one such location where clusters of cardinals have made themselves at home. Since overfishing this quick-replenishing species would be nearly impossible, Project Piaba's "Buy a Fish, Save a Tree" project has become a UN global model for sustainable wild fisheries designed to preserve rainforest habitats.

The rainforests that cover their waterways are usually very dense and let very little light through. Cardinal tetras favor these shaded areas with slow-moving or standing waters that are very clear. They live in large schools, and it is not unusual to find them in groups numbering into the hundreds. Their native habitat generally has extremely soft, acidic water, often with a pH of 5. They live in shoals, mainly in the middle water layers, where they feed on worms and small crustaceans.

Colors and Markings

The cardinal tetra has a brilliant neon blue stripe running from the nose to the tail. Below this blue stripe is a brilliant red stripe. The vivid red coloration bleeds into the tail, which is otherwise transparent, as are the other fins. The underbelly is a soft white, setting off this beautifully colored fish.

A cardinal tetra can be distinguished from a neon tetra by the red color band that extends the entire length of the body. In the neon tetra, the red band runs from only mid-body to tail. Adults will display the best colors when provided with very soft, acidic water. 

There are also cardinal tetra varieties that have distinguishing features:

• Gold cardinal tetra: These fish have a more golden or opal body color that isn’t as vibrant but is just as beautiful.
• Albino cardinal tetra: These tetras are transparent, with eyes that are pink or purple, and their distinctive red and blue stripes are not as vibrant.

Tankmates

Cardinal tetras, like other tetra species, are peaceful, social fish that should be kept in schools. Schools should be large, with a minimum size of a half-dozen fish. They are suitable for community tanks as long as water conditions are favorable and other species are peaceful.

Potential tank mates that may be suitable include:

• Other tetra species, such as the flame tetra and glowlight tetra
• Danios
• Rasboras, such as the harlequin rasbora and scissortail rasbora
• Dwarf gouramis
• Small members of the catfish family, especially Corydoras catfish

Do not keep them with any fish that are known to eat smaller, slim-bodied fish. If the companion fish has a big enough mouth to swallow the cardinal tetra, it is not a suitable tank mate.

Cardinal Tetra Habitat and Care

Much like the neon tetra, this species requires a mature tank that has soft, acidic water. More importantly, water chemistry should be stable. This is not a species that does well in a newly started aquarium.

The ideal pH is below 6, and the hardness should not be above 4 dGH. Subjecting this species to water that has a high mineral content is a recipe for poor health and shortened lifespans. The water temperature can encompass a broader range, from 73 to 81 F (23 to 27 C).

Lighting should be subdued, as should the décor. Floating plants are a good means for moderating the lighting. Although they require some hiding spaces, it is important to provide cardinal tetras with open-water swimming area as well. A well-planted tank with an open center space is an ideal habitat for this species.  

Cardinal Tetra Diet and Feeding

The cardinal tetra is an omnivorous species and will accept most commercial fish foods. These fish have high vitamin requirements, so at least 75% of their food should be quality flake food. Cardinal tetras especially appreciate live and frozen foods, but if fed them exclusively they may reject prepared food later on.

If only doing one to two feedings a day, offer what they can eat in about five minutes. However, it is better to feed these fish several times a day, offering only what they can eat in about three minutes. All foods should be in small pieces, as cardinals have a small mouth. When conditioning breeders, live foods are important.

Gender Differences

Males and females show few clear differences between the genders. Females will have a somewhat deeper body with a rounder belly, while males are more slender. Males also have a hook protruding from the anal fin.

Breeding the Cardinal Tetra

Breeding cardinal tetras is challenging at best. A separate breeding tank is important, and it must have stable water chemistry: a pH of 5.0 to 6.0 and very soft water of 3 to 5 dGH or below are essential. They will spawn in the evening, generally laying between 130 and 500 eggs. Spawning will continue even late into the night hours.

In approximately 24 hours, the eggs hatch, and the fry live off of their yolk sac for another four to five days. Once the fry are free swimming, feed them infusoria, rotifers, hardboiled egg yolk, or commercially prepared fry food. Follow this with freshly hatched brine shrimp as the fry grow. Lighting must be kept very low; use floating plants to ensure the tank remains dark. The young tetra fry are highly photosensitive.  

This species reaches a mature size of up to 2 inches in home aquaria.

More Pet Fish Species and Further Research

The cardinal tetra is a tiny beauty, but it is also the strongest ambassador for preservation of the rainforest ecosystem. Breeding them can be tricky, but the wild-caught fish are robust and plentiful. If you are interested in similar species, check out:

• Buenos Aires tetra
• Serpae tetra
• Rosy barb​​

Check out additional fish species profiles for more information on other freshwater fish.