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  Cardinal Tetras:
A School of Beauty

Cardinal Tetras: A School of Beauty, Part 2
Cardinals, Part I

Alesia Benedict

In the last issue of Conscientious Aquarist, I discussed the process I use in selecting, purchasing, quarantining and acclimating the huge schools of Cardinal Tetras (Paracheirodon axelrodi) which I own. In this last installment of my two-part series on these fish, I'll discuss the care I provide them, encompassing their tank environment, feeding, disease treatment, and overall maintenance.

Without a doubt, this is truly a magnificent fish and while many hobbyists agree, these same hobbyists struggle to keep these fish alive for any length of time. The trick in having a magnificent school of brilliant red and blue stream through your tank is to first carefully purchase healthy stock, acclimate them slowly, and quarantine the fish. Then, once they are in your home tank the trick becomes keeping them alive and healthy. So...How do I get mine to live long enough to grow to about two inches in length?

Yes, the Tetras in this picture are actually neons.... but cardinals appreciate the security that comes with this level of stocking density!  This school was actually displayed in a very large (about 10 feet long!) aquarium at the 2004 Interzoo trade show in Germany.  Photo by Adam Cesnales.


First and foremost, understand what I mean when I say that you need a SCHOOL of these fish. Most people think of a school of aquarium fish as five or six of the same species.  There is a great deal of difference between fish that like to shoal -- fish that like to hang around each other- (think corydora cats, clown loaches) vs. fish that like to truly school -- fish that swim in unison, forming a tight mass of seemingly one body of color all moving together (now think cardinals). In order for a fish to school, it needs to have the company of many like fishes.  Hence, in a 90 gallon tank, 75+ cardinals is fine; 55 gallon tanks can house 30 or so. Please don't think that having six or seven cardinals in your 75 gallon tank is enough of these fish. Denying the instinctive behavior of cardinals to school is a sure way to stress these fish to death.  Having inadequate numbers of these fish in a tank definitely lessens their chances.

Got it? Plenty of cardinals in the tank so they are happy. What's next?


Let's talk about water.  Suffice it to say that all fish do well with partial water changes -- the definition of which is always a bit murky.  For some, this equates to 20% every other week and for others, it is that amount every month.  MY definition however, is based on the type of fish that are my primary focus -- Discus. My Cardinals reside within my big Discus show tanks, so they are subjected to the same water conditions as the Discus fish.  Hence, for me partial water changes in my show tanks equate to 40% - 50% every two to three DAYS (vs. weeks)! Now I am not saying that Cardinals need that in order to thrive, but it does pay to note that mine -- and indeed, other fellow Discus keepers' Cardinals -- do get along exceptionally well living in Discus tanks.  I'm not suggesting you change the water quite as much as that if you are just housing Cardinals or have them in some form of community tank (How cool is the water?  Cardinals like warmer water than many other tropicals), but if you have had some problems keeping these beauties alive, it would be wise to step up the water changes. Remember too, that all of my Discus show tanks are heavily planted tanks, so again, the water quality is very high.  Plants do an AMAZING job at removing those nasties we don't want in our tanks (ammonia, nitrite, nitrate) and keeping the water oxygen rich. Ah, Mother Nature -- you really have to hand it to Her!

My Cardinals are notorious for being "extra active" during and following a water change. They will purposely swim right where the nozzle releases water into the tank when I am re-filling it, much like the way a small child will play under the spray of the garden hose or sprinkler. You can tell by watching them that they are having a great time "playing" in the incoming water column.  Also, immediately after a water change the school will rhythmically file in unison across the tank.  First a couple will the lead the way, and then almost like a liquid rainbow of red and blue the others all follow.  They go back and forth  across that tank for 15 - 20 minutes, non stop. It makes for a FABULOUS view and the first time my boyfriend saw them doing this he exclaimed "What on earth are those fish doing?"  To which I replied: "Playing!" 


I think one of the reasons my Cardinals do so well is indeed because they are housed in my discus show tanks -- and I take very, very good care of my discus!  Hence, all the living things in those tanks receive a great deal of care and attention.  Unlike some hobbyists who simply feed their cardinals a constant pinch of every day flake food, mine are feed a host of variations including live food.  While I do provide some flake food here and there, I tend to use vitamin-soaked pellet food much more and all the fish in the tank have been seen nibbling on the Spirulina tabs and shrimp tablets I feed the Catfish residing in those tanks. Hence, even without the live food my Cardinals receive a plethora of foodstuffs to meet their nutritional needs on a deeper level than just plain flake food could. The two live foods that they are fed include brine shrimp and protein rich black worms (these are NOT Tubifex worms!!!), the latter of which are  dispersed in worm cones for ease of nibbling. Some folks chop up the black worms for fear the little Cardinals won't be able to eat them, but I never have.  The Cardinals make quick breakfasts and dinners out of the black worms that the discus miss and everyone in the tank (Apistogrammas and Rams alike) thrive on the mix. Hence, if your Cardinals are not doing very well, take a look at what (and how often) you are feeding them and perhaps rethink their menu.

Disease Treatment:

I'm including how to medicate sick Cardinal fish because it does differ from how one treats many other fish. Most hobbyists will say it is best to remove a sick fish and isolate it in a separate hospital tank void of plants, gravel, decorations, etc. for ease of treatment and observation. 

I'm not saying that's a bad idea -- I'm just saying it is not an easy thing to do with a 200 gallon tank housing gobs of plants, big Discus and 150 Cardinals all swimming around.  Never mind being able to identify the actual cardinals that are sick -- try netting them! It's just not feasible, which is why, I SO STRONGLY talk about quarantining new arrivals before adding them to an established show tank. If you purchase a bad batch of Cardinals and mix them in with your existing ones, within a couple of days the entire school can perish.  It just isn't worth the risk!!! Do yourself (and your fish) a BIG favor and push back on the joy of instant gratification -- quarantine the fish for a least a week.

But what do you do if your prize tank's fish does come down with something? Ich, say- or a bacterial disease? Then what?

Well, you have to treat the tank.  The whole tank.  This can be both tricky and expensive, as the dose for many treatments is per 10 gallons of water -- and treatment lasts for several days. It also gets nerve racking, because the medication will build up in the tank, so you have to watch the fish carefully to see if they start to react poorly to the treatment. Many ich medications need to be cut in half for Tetras and Cardinals are quite sensitive Tetras at that! So watch the fish carefully, be prepared to do an emergency water change and feed the tank VERY lightly during treatment.  Many medications can't even be used with plants and even if you don't have live plants some medications can destroy the biological filter bacteria, allowing ammonia to build up -- which can also be toxic to fish. So you see, it really does pay to take a preventative approach.

Overall Maintenance:

Try to make your Cardinal fish happy. I know that sounds basic, but really, sometimes people just want to keep a fish because they like it, and hope it will somehow adapt to the conditions the owner sets up.  Some fish amazingly do adapt, but don't count on cardinals to be one of them.  They are more likely to die than to adapt. Keep their water temperatures warm and stable. Fluctuating temperatures are a trigger of stress, and stress brings out ich. Stable conditions are very much preferred, so if you have neutral or somewhat hard water, don't go nuts trying to lower it only to have it bounce back up with a water change. I keep my show tanks around 7.0, and the cardinals do fine. They don't need a very low pH or too soft water -- sure, they like it, but they don't need it.  What they DO NEED though is stability and consistency. Keep their water in excellent condition. Up your water changes and/or add some easy live plants. For heaven's sake, don't keep them with 'rough' fish, or fish that are likely to make them a snack. Keep a relatively large group of them, and don't think that all tetras are alike. Yes, Rummy Noses will often school with Cardinals, but many Tetras won't. Just because a fish is a tetra doesn't mean it will be part of the cardinal's school, so resist the temptation to have "a few of this Tetra fish and some of that tetra fish and, oh yes, a little bit of this other tetra fish..." and instead, stick with a large school of ONE type of Tetra -- the stunningly beautiful Cardinal Tetra!

Characoids/Tetras & Relatives on WWM

Related FAQs: & FAQs on: Cardinal Tetras, & Characoids/Tetras & Relatives

Articles on Characiform families, subfamilies...: Cardinals, Part I, The Larger Pencilfishes, Family Anostomidae, Characid/Tetra Fishes, Alestiine Characid Fishes, Characinine/Tetra Fishes Piranhas and Relatives, subfamily Serrasalminae, Tetragonopterine/Tetra Fishes, Distichodus and More, Family Citharinidae, Pike-Characoids, Family Ctenoluciidae, Curimatidae, Trahiras, Family Erythrinidae, Hatchetfishes, Family Gasteropelecidae Hemiodus "Sharks" and More, Family Hemiodontidae The Pike-Like Hepsetid, Family Hepsetidae Smaller Pencilfishes, Splashing Tetras & More, Family Lebiasinidae, Prochilodus/ontids

Survey Articles on: Freshwater Fishes



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