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Right. They're two different species. There's also another species called a green neon, but I won't go into that...

Basically, cardinals look like neons, with the blue upper stripe with red under it, but cardinals have much more red, and on the cardinal, the red extends all the way up to the head.

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But aren't their habits, temperaments and needs the same?

I imagine (if I was a fish)they can tell that their "cousins" was not exactly the same...but they still would school together, right.

Or would they not, and keep mostly to their own kind in schooling/grouping?

Given no other options, you'd probably find neons and cardinals would choose to school with each other than another type of tetra, BUT colour and shape are important and there is an obvious colour difference between the two. If you have enough neons and enough cardinals in a big enough space, they'd be more likely to school with their own kind.

For animals, the entire universe has been neatly divided into things to (a) mate with, (b) eat, (c) run away from, and (d) rocks. - Terry Pratchett

Our cardinals and neons school together. We have enough for schools of each, small schools, but full schools, but they stil hang out together all the time.

Here's your primer on Paracheirodon species.

The first of these fishes to be introduced to the aquarium trade was the Neon Tetra, which was originally named Hyphessobrycon innesi in 1936 after Dr William T. Innes, author of one of the oldest textbooks on aquarium fishes still in circulation. As a side note, that textbook (which I refer to as "The Venerable Innes Book" is still a valuable source of information even today, because it was the first such book that was so comprehensively right about so many different fishkeeping issues in the one book. But I digress. Back to the fish. The Neon Tetra has a blue iridescent stripe along the upper part of the body, which passes through the head (and the eye) and reaches back to a point a short way before the caudal peduncle. The ventral parts of the body are evenly divided between a silvery anterior portion (the stomach area just behind the gill plate) and a red posterior portion stretching approximately from the beginning of the anal fin to the end of the caudal peduncle.

The second fish was the Cardinal Tetra, which was the recipient of two scientific names - one group of authors proposed calling it Cheirodon axelrodi, and another group of authors proposed calling it Hyphessobrycon cardinalis. The former name won because the relevant paper was published a day earlier than the other, and in the world of taxonomy, the Rule of Priority applies (a Google search on ICZN will tell you all about this). This fish differs in outward appearance from the Neon Tetra by courtesy of the fact that its red ventral body colouration extends across the entire ventral portion of the body, right up to the head.

There is a third fish in this group, the Green Neon or False Neon, Paracheirodon simulans, which resembles the Neon Tetra but for the fact that its iridescent stripe is greenish in colour when seen from a much wider range of viewing angles.

Now, these fishes were originally placed in three entirely different Genera by taxonomists, who based their work entirely upon specimens preserved in alcohol, with all traces of the original colouration having long disappeared. They based their determinations upon lateral line scale counts, fin ray counts and a host of other morphometric characteristics. However, aquarists had for a long time puzzled over why these three fishes, so much alike, should have been placed in three different Genera. So, eventually, they started asking the taxonomists why. Initially, there was some resistance to the idea of revising the classification of these fishes (taxonomists tend to be a fairly conservative lot and tend not to like changing classifications unless there are sound reasons, though I'll leave the lumper-splitter dispute to another post!) but eventually, they were won round to the idea that the whole fish, including the fish in its live state, should be examined where possible before launching into classification decisions, and more recent fish taxonomists such as Dr Paul Loiselle and Sven Kullander are also keen aquarists, which means that they take the live fish into account much more readily than some of their predecessors.

As a consequence of this, it was decided that these three Characins, the Neon Tetra, Cardinal Tetra and Green Neon Tetra, should all be placed in the same Genus. The Rule of Priority I mentioned briefly applied here, and since Paracheirodon was the first Genus erected for any of these fishes, this became the new home for all three.

Now, maintenance and breeding wise, the fishes require virtually identical treatment. Being Amazonian fishes from "blackwater" habitats, they prefer soft, acidic water, preferably with noticeable concentrations of humic acids present staining the water a particular dark brown hue (hence "blackwater" habitat - take a look at aerial photos of the Rio Negro and see why!) and for breeding, the one BIG requirement is very low light levels. Indeed, these fishes not only need soft, acidic water for breeding, but for the eggs to survive, the parent fishes need to spawn in darkened surroundings, because that's where they spawn in the wild - in isolated creeks that are completely shut off from daylight by rainforest canopy closing and interlocking over the water. Ambient light levels in such water bodies are almost down to night-time levels even at the height of midday, and consequently, the eggs have become photosensitive over time - exposure to light will kill them. This accounts for why these fishes are so difficult to breed, because not only does the aquarist need to supply stringently controlled water conditions, but the breeding aquarium needs to be constructed in such a fashion that it can be kept in total darkness for whatever period of time is required for the eggs to hatch and the fry to become free-swimming. Additionally, the fry are so tiny that they need infusoria or the finest of egglayer baby fish foods (usually liquid foods) for a longer period than most other Characin fry, and so persuading these fishes to spawn and raising the fry successfully is a severe test of an aquarist's skill. If you breed Neons or Cardinals successfully, you can call yourself a serious aquarist.

The similarities are such that members of these three species will shoal with each other if no other option is available. However, if you set up a 75 gallon tank, put in 24 Cardinals and 24 Neons, it's possible that the two species will form separate shoals. An interesting experiment for you to try someday if you're feeling like doing something different with a 75 gallon tank other than popping in large Cichlids.

Oh, by the way, as to diet, one interesting fact about Cardinals I learned from Herbert Axelrod is that the stomach contents of wild Cardinals consisted of pieces of leaf litter. Not aquatic plant leaves, but the leaves of terrestrial forest trees that had fallen into the water (and helped to provide the humic acid content of the water into the bargain). So in the wild, Cardinals are actually herbivorous, but not on aquatic flora. They will, however, readily take to eating various small aquatic organisms that they encounter, so that if you feed them baby Brine Shrimp or, when adult, Daphnia, they'll munch on these quite happily. However, you will find it instructive to try and watch them eat, because in the 14 years I've had Cardinals, I've noticed that they are "stealth feeders", and catching them in the act of taking something into their mouths actually requires a fair amount of diligent attention. In fact, they appear to engage in a lot of their behaviours "by stealth", presumably as a means of ensuring that they don't come to the attention of predators in their natural habitat, and are much more likely to continue exhibiting this behaviour in the aquarium than other Tetra species, which will rise to the water surface in a feeding frenzy when the food hits the water (I had Lemon Tetras that were like miniature Piranhas in this regard for the best part of 8 years, the moment the food hit the water, they were at the surface gnashing away!).

So there you go. Everything you ever wanted to know about Paracheirodon species, and a few things you probably didn't too.


Panda Catfish fan and keeper/breeder since Christmas 2002

See folks.
Everyone should have a big book of their own.

I'll be first in line the minute Cali writes one.

Heck, I could probably compile all of his posts into a giant anthology and make millions. MILLIONS!

Me Too....

WOW....Thank you very much!

Let me add one very important note that Cali forgot to mention -- store-bought Neons, being raised in giant fish farms, are unfortunately widely endemic carriers now of Neon Tetra Disease, which is the Fish Disease From Hell. It's incurable once the fish shows any visible symptom (pale whitish areas on the body); it spreads like crazy; it is caught by a lot of other fish (including many non-Tetras); and it's EXTREMELY hard to get out of your tank.

If you ever see a fish with visible signs of it, euthanize that fish immediately -- NTD is spread largely by fish eating infected corpses, although the organism can also be free-swimming. You might use quinine, nitrofurazolidine, or neomycin to try to kill off the free-swimming organism -- but for the love of God avoid Nalidixic Acid, which is sometimes recommended as an anti-NTD drug, but which is the only fish medicine I've ever encountered which is seriously toxic to fish. I once followed the advice of a reliable guy to use it at 1/2 the bottle-recommended dosage, cut 50-50 with neomycin, and lost half the fish in my tank.

Now Cardinals, being wild-caught, are virtually free of NTD, which in itself is enough for me to very strongly recommend them. Some books say they're a bit more delicate than Neons, but -- even apart from NTD -- I haven't noticed it.

cardinal has constant stripe along body - neon's ends half way

Cardinal at the top, Neon the bottom.

well, all that being said my neons and cards have schooled together and lived in harmony for years. Never have I seen the cards on one side of the tracks and the neons on the other.Of course, they don't have a lot of choice in the ten gal. Soon I'll be putting up another 29 and possibly either neons and cards or cards and harleys

Wow, that was quite a thread necro.

A small aquarium and single digit sizes of schools is insignificant to the habitats and schooling sizes these fish have in the wild. It's not surprising that they'll school together in captivity, but given enough numbers and space of each, as Cali pointed out two years ago, and it's possible they will group out.

Whether they will or not is an interesting question, though.

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The aquarist is one who must learn the ways of the biologist, the chemist, and the veterinarian.

wow, two years. been awhile since I've been in I guess. maybe i'll try