Name: Paracheirodon axelrodi
Origin: Amazon Basin
The Cardinal Tetra is one of the most desired fish to have in a tank, mainly because of its awesome coloration. However, keeping these little fish requires a certain knowledge that many owners do not have. These fish are extremely hard to breed in captivity, virtually all of the fish available in shops have been taken from the Amazon basin, and unfortunately thousands of them die every year in inappropriate tanks. It is quite common, for example, to see a little kid walk into a shop with a few coins and buy one or two cardinals to add to his goldfish bowl.
My experience is that these fish are actually quite hardy, as long as they are properly adapted into captivity. First of all, they are very sensitive to changes in water parameters after being caught, so the water should be kept as close as possible to their natural habitat (see table above). Second, they should be kept in large numbers (at least 5, many more if possible) in a well planted tank with lots of shades and hiding places. This greatly reduces the stress that leads to many of the deaths. Needless to say, their tankmates should be peaceful and preferably small. After a while in these conditions, the cardinals tend to become more healthy and confident. They don't bother to hide anymore and become much more tolerant of changes in water conditions.
It is possible to successfully keep Cardinals in a higher pH. My tank's pH is over 7, and I have had a Cardinal school for a year. The key was an extremely long and drawn out acclimation process, gradually using less and less RO water until I was only using the tap at school. I should also mention that the pet store's pH was 6.8. While not ideal or practical I just thought I'd mention that it can be done :-)
I had the HARDEST time starting up a school of Cardinals, and I am not an entirely unexperienced aquarist. All the other fish in my community tank did quite well...I have a mix of baby Angels, Platies, Kuhli Loaches, 2 Dwarf Gouramis and a Pleco in my 110 L tank, all with no problems after 2 months of setup. But over this period, I tried to introduce school after school of cardinals (maybe about 40 total in several batches) into the tank, and they all died rather suddenly, ranging from within hours or under a week. All this was mysterious as none showed signs of harrassment or specific sickness. They would just stop eating one day and be found dead the next, one at a time. I tested my water for nitrates, pH, everything you could think of and it was high in quality. I had all but given up, when one day I decided to make one last go of it, and bought 6 more fish from the same store and added them. This time, they did well from the very beginning, showing no signs of weakness and competing the first day for food. Today, they are among the most hardy of my fish. In the end, I attribute this success to two things: 1) the tank took longer to establish than I thought even at 2 months, some of balance had not entirely established in the tank and 2) the batch of Cardinals I bought this time were simply from a better source (although it was the same store, they had been subjected to less stress during their transport). Cardinals are extremely succeptable to small changes in water quality, and anyone who wants them as much as I did should not take this point lightly. Once they get started however, Cardinals are not only beautiful but even robust little fish.
If I had to pick my all-time favorite tropical fish, it would be the Cardinal Tetra, ever since I was a little girl. It's a cliche, but they really are living jewels. No matter what I keep, I will always have one "peaceful" tank with some Cardinals. I keep mine at a neutral pH of 7 (the Rainbows wouldn't appreciate acid water) in a large school with Neons. I've found that it's a pain to establish Cardinals and Neons in a tank, but that once I have, new additions seem to do well. I make it a rule to NEVER buy Cardinals that haven't been in a store and doing well for at least a couple of weeks, and to only buy from a dealer who writes the dates of fishes' arrival in the store on his tanks. It's always a good idea to ask how many they've lost since getting the fish in, and to take a good look at how the whole school seems to be doing. I've often seen seemingly healthy Tetras in tanks whose filters are almost clogged with tiny dead bodies, and any of the survivors that I got from those tanks almost inevitably died. I also wait until my dealer gets some Cardinals that are a pretty good size - those little slivers of babies that some places sell 3 for a dollar are awfully tempting, but also awfully fragile. I also make sure to give them some extra floating time (I know I should quarantine, but I'm a student and don't have the room for another tank!) and to feed them a few extra servings of high-protein food like live brine, live blackworms, and frozen prawn eggs (fish go bananas for them!) for a week or so to build them up a little. So far (knocking on wood) this seems to have worked well for me.
I bought 15 Cardinal Tetras just 6 days ago and they seem to be doing fine. A couple of them looked famished (I couldn't choose the healthy ones as the shop doesn't allow that at 66 Singapore cents per fish instead of the usual S$1.50). Did a recount today and there's 14 with none looking famished. They don't tend to school and swim in groups of 3 to 5 mainly. They are also surviving peacefully with my 2 Albino Corydoras, Albino Red-Tailed Shark, 2 Siamese Algae Eaters, 2 Otos, and about 16 assorted shrimps. I think that they need a lot of fauna as they are rather timid. Singapore's water is rather soft and they seem to be doing fine. I add that a few of them had tails bitten off when I bought them and they seem to be alright as well.
Cardinal Tetras are fish that no Amazon community aquarium should be without. They are very peaceful fish, and for me, they have also been very hardy. I used to keep Neon Tetras, but then I gave Cardinal Tetras a try, and since then, Cardinal Tetras are my favorite fish. Now that I have kept my Cardinals for over a year, they are almost 5 cm in length, and are doing very well. They are living as a school of 16, with two Golden Angelfish, happily in a very well planted 200 liter tank. Here's a very good tip for keeping these fish: at first, have your tank running, and plant it well. Let the plants grow and establish themselves. Then purchase only about SIX of these fish. Let them establish themselves, and then you may add as many fish as you like GRADUALLY! I know that this process takes a lot of patience and waiting, but if a good fish tank means anything to you, then you will take this advice. And as with any fish or animal which you will buy, read up on them BEFORE you make a purchase! (By the way, it wasn't unusual for me to see my Cardinals and Neons schooling together. Strange, isn't it?)