Cardinal Tetra (Paracheirodon axelrodi)
The cardinal tetra (Paracheirodon axelrodi) is a small, colorful, freshwater fish from the Amazon River. It belongs to the family Characidae.
The Difference Between Cardinal and Neon Tetras
Cardinal tetras look very similar to neon tetras (Paracheirodon innesi). The two fish can be distinguished from one another in that the red stripe or band on the cardinal tetra extends from the head to the base of the tail, whereas in the neon tetra the red band begins about mid-way between the head and the tail and then extends to the tail base. Compare the two photos of the cardinal and neon tetra and you will see the difference between them.
Cardinal tetras are even more colorful than neon tetras.
Cardinal Tetra Temperament and Aquarium Conditions
Cardinal tetras are peaceful, shoaling fish that do well in a community aquarium with peaceful fish that aren't large enough to eat them. Cardinal tetras reach approximately 2 inches (5 cm) in length, so they are a little larger than neon tetras.
Like all fish from the Amazon, they do best in soft, slightly acidic water. The water temperature should be between 70-79°F (21-26°C). They are shoaling fish and so you need to keep several (6-8) cardinal tetras together in your tank. Like the neon tetras, cardinal tetras won't thrive as solitary fish.
They are omnivores (both plant and meaty foods) and will readily eat flakes, frozen, freeze-dried, and live foods.
Although they are small fish, they still need ample swimming room. They usually swim back and forth as a shoal. Your tank should be fairly long, rather than tall, so your tetras can swim back and forth with enough room. You should provide plants at the sides and back of the tank so the middle of the tank is open. Cardinal tetras swim in the middle layer of the tank.
You should also provide them with floating plants.
Spawning and Fry
Cardinal tetras are egglaying fish.
Sexing cardinal tetras is difficult because males and females are identical in color. Females usually have a more rounded body than males if they are full of eggs.
It is best to place the pair (or several cardinal tetras if you don't know what sex they are) in a separate breeding tank with some plants (floating is best) and soft, slightly acidic water (pH around 6.0-6.2). They won't breed in alkaline, hard water. You can filter the water through peat or add a thin layer of peat to the substrate. Make sure there are no other additives in the peat that could be harmful to the fish.
Cardinal tetras are most likely to spawn at night or when the tank lights are dim.
Cardinal tetras are egg scattering fish. After spawning is complete remove the adult fish or they will probably eat the eggs. The tiny cardinal tetra fry will hatch in about 24 hours. Once they are free swimming the fry can be fed commercial liquid fry food, infusoria, or a small amount of mashed up hard-boiled egg yolk.
When the fry grow a little larger supplement their diet with newly hatched brine shrimp and powdered fry food. If you find hatching live brine shrimp too cumbersome or if you want to make sure that you have baby brine shrimp available when your cardinal tetra fry are ready for it you can always buy some instant baby brine shrimp made by Ocean Nutrition.