All About the Cardinal Tetra (Red Neon Tetra)

Characteristics, origin, and helpful information for hobbyists

Paracheirodo ncardinalis
Axel Rouvin

Arguably the most popular of the small tetras, the cardinal tetra is similar in appearance to a longtime aquarium favorite, the neon tetra. Cardinal tetras are an active schooling fish and they live well in a peaceful community aquarium. Although they are difficult to breed in captivity, tetras remain a very popular aquarium fish. 

Breed Overview

Common Names: Cardinal tetra, large neon tetra, red neon, roter neon

Scientific Name: Paracheirodon axelrodi

Adult Size: 2 inches (5 cm)

Life Expectancy: Four years


Family Characidae
Origin Brazil, Colombia, and Venezuela
Social Peaceful, suitable for a community tank
Tank Level Top to mid-dweller
Minimum Tank Size 20 gallon
Diet Omnivore
Breeding Egglayer
Care Intermediate
pH 4.6 to 6.2
Hardness Up to 4 dGH
Temperature 73 to 81 degrees F (23 to 27 degrees C)

Origin and Distribution

Originating from South America, this species is found in the Orinoco and Rio Negro tributaries all the way to 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.

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 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 its body. In the neon variety, the red band runs from only the mid-body to tail.

Adults reach a mature size of up to two inches and will display the best colors when provided with very soft acidic water. 


Cardinal tetras, like other tetra species, are a peaceful fish and they 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 tankmates that may be suitable include other tetra species, danios, rasboras, dwarf gouramis, and small to medium members of the catfish family. 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.

Habitat and Care

Much like the neon tetra, this species requires a mature tank that has soft acidic water. 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 degrees F (23 to 27 degrees C). More importantly, the water chemistry should be stable. This is not a species that does well in a newly started aquarium.

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 them with some open swimming area as well. A well-planted tank with an open center space is an ideal habitat for this species.  


The cardinal tetra is an omnivorous species and will accept most foods. These fish have high vitamin requirements, so at least 75 percent 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 they have a small mouth. When conditioning breeders, live foods are important.

Sexual Differences

Males and females show few clear differences between the sexes. 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 of the Cardinal Tetra

In home aquaria, breeding cardinal tetras is challenging at best. A separate breeding tank is important and must have stable water chemistry: a pH of 5 to 5.5, and very soft water of 3 to 4 dGH or below is essential. Stock the tank well with fine-leaved plants, as this species will scatter their eggs on the vegetation. They will spawn in the evening, generally laying between 130 and 500 eggs. Spawning will occur late in the day or even into the night hours. The mating pair will consume the eggs, so remove them from the tank once spawning is complete.

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

More Pet Fish Breeds and Further Research

If cardinal tetras appeal to you, and you are interested in similar fish for your aquarium, read up on:

Check out additional fish breed profiles for more information on other freshwater or saltwater fish.