Cardinal Tetra

About the Cardinal Tetra

Species Type: Freshwater Fish
Category: Characins

Care Level: Moderate. May tolerate only a narrow range of water parameters, have specific dietary requirements including frozen or even live foods, may have behaviors that severely limit potential tankmates or may require a specialized aquarium setup.

Origin: Amazon Basin, northern tributaries of the Rio Negro in Brazil and Peru [Brazilian form], Orinoco basin in Columbia and Venezuela [Columbian form]. Occurs in forest streams and creeks in slow or standing water, well shaded by vegetation and frequently having aquatic plants.

Compatibility/Temperament: Very peaceful; suitable in a species tank or combined with similar peaceful characins, rasbora, small catfish and loaches. Good tankmate for rarer gouramis, discus and dwarf cichlids that require higher temperatures.

Description

Two forms of the cardinal tetra are known, one from the Rio Negro basin [the "Brazilian" form] and one from the upper Rio Orinoco basin in Columbia. The forms were determined to be morphologically different by Dr. Jacques Gery in the late 1990's, and they may be distinct species, sub-species or variants. They are outwardly recognizable in three ways. On the Columbian form, the neon line ends at the adipose fin, the red colouration does not extend as far under the belly so there is slightly more white, and the fish is chunkier in general build. By contrast, the neon line on the Brazilian form extends below the adipose fin and is straighter in appearance, the red extends slightly further down on the belly, and the fish is more slender and thus appears longer than the Columbian form. In the accompanying photos, the Columbian form is shown on the left [green background]and the Brazilian form on the right [brown background].

In their natural habitat cardinals are found in small slow-moving streams and still waters having a pH from 3.4 to 4.5, some locations a bit higher but never above 6, and less than 1 degree of hardness. The water is always shaded by dense trees and either land vegetation or aquatic plants are always present. They congregate in groups amid aquatic plants, branches, or under overhanging land vegetation. They may be an annual fish in nature, only living one season due to shortages of food.

In the aquarium, they thrive best and can live more than 10 years when kept in soft, acidic water, and while they will somewhat adapt to other water conditions provided they are acclimated properly, their life span will be shorter. When maintained in harder water they can develop calcium blockage of the kidney tubes. It is also believed they have a light phobia, and the aquarium should not be brightly lit. The majority of the cardinal tetras available in the trade are wild-caught and attention must be given to their habitat preferences. Wild-caught fish generally are more demanding of their preferred conditions, and this can be even more important when the fish itself is very sensitive with respect to water parameters and environmental conditions.

To replicate their habitat, the aquarium should have a sand or fine gravel substrate, and plenty of aquatic plants like Echinodorus (swords), Cabomba, Pennywort, and floating plants. Water flow from the filter should be minimal, with subdued lighting.

Sexual dimorphism, like most other tetras, can be difficult to determine but male cardinals are often smaller and always slimmer in comparison with the females when viewed from above. Spawning is not easy to achieve. They are egg scatterers and require very soft and acidic water and darkness.

The cardinal tetra shares a very similar appearance with three other distinct species, all commonly referred to as "neons" because of the blue/green lateral line. Three of these, the neon tetra [Paracheirodon innesi], cardinal tetra [Paracheirodon axelrodi] and false or green neon tetra [Paracheirodon simulans], are available in the hobby; the fourth species was discovered by Heiko Bleher in 2006 and has yet to be described and named. According to DNA studies, this new species is very close to the true Neon Tetra, whereas the Cardinal Tetra is genetically closer to the Green/False Neon Tetra.

Cardinal Tetra Diet

Cardinal tetras are carnivorous in nature and are not fussy eaters so they will readily accept most prepared foods such as flake and frozen bloodworms and daphnia.

Size

Grows to 2 inches, usually smaller.

Ideal water parameters for Cardinal Tetra

Soft (hardness below 4 dGH) acidic (pH below 6.0) water, temperature 23-27C/73-81F. May tolerate harder and slightly basic water short-term, but will be more susceptible to disease and a shorter life span.