Cardinal Tetra (Paracheirodon axelrodi)

Common Name:

Cardinal Tetra.

Scientific Name:

Paracheirodon axelrodi.

Other Names:

None that used with any frequency. Axelrod's Neon Tetra has been used as a common name at some LFS, but most call it the Cardinal.

Family:

Tetragonopteridae (though some taxonomists place it in the subfamily Tetragonopterinae within the family Characidae).

Distribution:

The Rio Negro and its Brazilian tributaries.

Size:

They can achieve 2", but just over an inch seems to be a more reasonable and more common length.

Diet:

Obligate carnivores in the wild, may need to be weaned to acceptance of standard aquarium fare.

Water Temperature:

73-84 F (23-29 C): Shooting for 73-78 F will be best for Cardinals.

Water Chemistry:

(dH < 5, by Mark Phillip Smith).

pH:

6.0 to 7.0 (by Mark Phillip Smith), though they can take water of 4.0-6.0 (and may indeed come from that acidic of water). Rigorous acclimatization processes may allow for Cardinals to live in alkaline water, but I strongly discourage the practice.

Life Span:

5-7 years is cited by the Oregon Zoo.

Description:

These small fish can achieve lengths of 2" (but they generally get to be just over an inch) and their bodies, like those of their congeners (Neon and Green Neon Tetras) are streamlined to the point that they can be classified as having the shape of a torpedo. Their translucent skin is accented by an electric blue stripe along with a red stripe that starts at the midpoint of the tailfin and continues, below the lateral line, until fading into the a purplish patch that appears just behind the jaw.

Species Behaviour:

This is THE ultimate schooling fish in the hobby and has been since its 1950s-era discovery revolutionized the aquaria of the general public. The shoaling behaviour only occurs when Cardinals are in a group of conspecifics and when there is some sort of fear stimulus (something that won't eat them but may corral them every so often). One has to be careful as those fear stimuli may stress them to the point of lowering the threshold of immunity. The Cardinals are still mostly wild-caught, so their immune systems may be compromised merely by their status as captives. A heavily planted tank will make them feel safest and will cause them to show their best coloration. As schooling fish, it should be noted that they will not do well without at least six in a tank.

The Cardinal spends much of its time in the middle and upper levels of the tank.

Unlike its congener, the Neon Tetra, the Cardinal is not often cited as a fin-nipper.

Sexing:

Upon maturity, females will be slightly plumper than males. The blue line may seem to be slightly diffracted on the female as well. Other than that, the dimorphism of this fish is not obvious at all.

Breeding:

Not very many hobbyists have been able to breed Cardinals in their tanks but those who have report that their spawning and rearing processes are similar to those used by hobbyists who have spawned Neons. You can check the Neon profile in order to view these steps. One caveat: Cardinals, since they are largely wild-caught, have less of a tolerance for breeding in waters of less-than-optimal parameters.

Water Quality:

Cardinals are reputedly weak fish (mainly because they are primarily wild-caught), but much of that also has to do with forced acclimation to a large variety of water qualities. If properly acclimated, the Cardinal may be able to thrive in high pH water that is relatively hard. Still, though, I do not recommend keeping these in alkaline pH (shoot for 4.0-6.0) nor do I condone keeping them in hard water (opt for soft water).

Natural Conditions:

The Cardinal Tetra spends its days in slow-moving creeks, rivers choked with vegetation, and shaded waterways.

Minimum recommended tank size:

10 gallons is the absolute minimum for a small group.

Tank levels:

Top-Middle.

Miscellaneous:

This species has been classified in two genera: Cheirodon, and Paracheirodon. The accepted scientific name, though, has always included the honorific specific name axelrodi, the name of the editor of the fledgling magazine whose first issue was released early in order to scoop other established magazines racing to describe the Cardinal.

This fish is THE schooling fish as stated before, but it was, at one point, an upstart introduced in an upstart magazine's first issue that knocked the Neon Tetra from its throne. Even today, the Cardinal Tetra and the magazine in which it was first described, Tropical Fish Hobbyist, remain among the crown jewels of the aquarium hobby.