The Cardinal Tetra, Paracheirodon axelrodi is closely related to the very popular Neon Tetra Paracheirodon innesi and the Green Neon Tetra Paracheirodon simulans. It is less closely related to the hundreds of other tetra species. The Cardinal’s specific name, axelrodi was given to honour the great fish expert, Herbert R. Axelrod. The Black Neon Tetra Hyphessobrycon herbertaxelrodi is not a very close relative of the Neon or the Cardinal. Its name is misleading.
In an aquarium, under good conditions, the Cardinal should live for up to 5 years, although I have seen reports of them living longer than this.
An Annual Fish?
The Cardinal Tetra is often described as annual fish, living only one year in the wild. For a discussion of this question, see the end of this article.
The Cardinal Tetra’s maximum length is a little over 4cm.
are a peaceful community fish suitable for keeping with other small, peaceful
fish. Common companions include other small tetras, small Rasboras,
Guppies and other livebearers like platies and swordtails, as well as Corydoras
Cardinal Tetras are often kept successfully with discus and seem better able to tolerate the high temperatures Discus fish need than Neons. They are also a little bigger than Neons and less likely to be eaten by discus.
Fish I would not recommend putting with Cardinals include all large fish, Buenos Aires Tetras and Tiger Barbs. I have known cases where people have successfully kept Cardinals with some larger fish, but there is some danger if you attempt it. If you keep Angel Fish and Cardinal Tetras together, you need to accept the likelihood of the Angel Fish growing big enough to eat the Cardinals.
The Cardinal Tetra comes from the upper reaches of the Amazon River. This is a tropical area and The Cardinal Tetra is a tropical fish. Cardinals should have heated water, unless they can be kept in a room that never gets cold. The obvious way to heat the water is with an aquarium heater. I suggest setting the thermostat to 24̊ C.
The Cardinal comes from acidic and extremely soft water. This is the ideal water for them and is probably essential if you want to breed Cardinals. However, they can be kept successfully in water with Ph ranging from 5.0 to 7.4. They will tolerate moderately hard water for living in, but extremely soft water is needed if you attempt to breed them. When they are kept with mixed other fish in an aquarium, I recommend a Ph of about 7. Some cover like plants are beneficial for the fish.
Cardinals can be kept successfully, even in the strange water that comes through the taps in the Adelaide Hills as long as you get rid of the high level of Chloramine and adjust the Ph. These are both covered in more detail in separate Fact Sheets.
Like many tetras, the Cardinal is a schooling fish and I recommend that at least five be kept together. A school of Cardinals in an aquarium is a surpassingly beautiful sight. When it is dark, the Cardinal losses its bright colours, but quickly regains them when it gets light again.
Although Cardinals will school with their own species for preference, if there are too few Cardinals to form a school they can school with Neons.
Like many fish, Cardinal Tetras are naturally omnivores and will eat a wide variety of food in the aquarium. Flakes are the normal basic diet for them. I find they also benefit from dry fry food. They enjoy small live food like small wrigglers (mosquito larvae) and small crustaceans like daphnia. Frozen foods like blood worms are also good. Remember they are small fish. DO NOT OVERFEED.
Is the Cardinal Tetra an Annual Species in the wild?
On the internet, there are a number of articles about the Cardinal Tetra which contain a statement about this fish very similar to the following one: “One that is effectively an annual species, and has a lifespan of just a single year in nature, but lives for several years in captivity.”
Many of these are not sourced, and most of the ones that are give each other as sources. Few of the articles give an explanation of the statement. A couple of these articles explain that the Cardinal Tetra adults die of starvation after spawning. I was sceptical about this. The Cardinal tetra spawns in the flooded Amazonian forests. This habitat is not only very large, but it has copious food for the young fry. If the baby Cardinal tetras can find enough food to grow, surely the adults can find enough to survive?
I researched the question further, and found that the original reference appears to be a book published in 1977 by TFH Publications called "Characoids of the world", written by Jacques Géry.
The scientific paper "The food spectrum of the cardinal - tetra (Paracheirodon axelrodi, Characidae) in its natural habitat" confirmed my suspicion that the Cardinal Tetra is not likely to die of starvation. This paper also explains the smaller size of the Cardinal tetra in the wild compared with aquariums specimens.
While I have no doubt that some Cardinal Tetras only live for one year in the wild, I seriously doubt that it necessarily does.
One of the reasons I suggest this is the reasonably long life-span of the Cardinal Tetra in captivity. I have found many references to this fish living five years or more, and I have had Cardinals myself that have lived much longer than one year.
Another reason is that I cannot see that in the wild there would be any condition that would allow huge numbers of the baby fish to survive, but would kill nearly all the adults.
There would be selective advantage to any of these fish that can live to spawn for several years rather than just one.
"The food spectrum of the cardinal - tetra (Paracheirodon axelrodi, Characidae) in its natural habitat", Characoids of the world by Jacques Géry.