Visiting Jem Aquatics shop I saw some pretty young Cardinal Tetras from a recent shipment. The fish were in excellent condition, of good shape and young, just ready and promising.

Cardinal Tetras

In the past I have bought, tried to breed and wasted probably well over 300 dollars on Cardinals. The visit to the shop tempted me once more. With Bob’s (the owner) permission I was able to select two pairs by myself because my ‘spending spree’ would stop a shop assistant from doing business for a long time. At home I conditioned the Cardinals with live food only and they quickly grew to the spawning size of the Neon Tetra. Mature Cardinals are larger when well fed.

The rule for breeding Tetras is to try to spawn young fish as soon as possible to avoid egg-bound females.

The Cardinal Tetra was discovered in 1952 in the upper reaches of the Rio Negro in Brazil. After being given the initial name of Hyphressobrycon cardinali, there was a genus revision in 1983 and they are now known as Paracheirodon axelrodi.

Cardinals live in coloured water and shaded areas with slow water movement. These quiet parts of the river are known as remansos. The local collectors know well “no remansos – no Cardinals”. The richest spots can yield 5-8 fish per metre square. The remansos are typically 1.5 – 6.0 metres long and 0.8 to 2.5 metres wide. Depth of water 0.2 to 0.4 metres with a maximum of 0.7 metres, water temperature 26.5 C.

The water is extremely poor in food. The Cardinals live in schools of mature specimens (23 – 28 mm long ~ ready to spawn) and juveniles around 13 mm long. The largest Cardinals in the wild are 30 to 33 mm. Aquarium fish grow to 50 to 65 mm and live 6-7 years while the Cardinals in nature only manage 12 to 16 months.

Young Cardinals should be grown in soft water (Canberra water is perfect) to stop degeneration of their kidney. Spawning conditions require (according to European breeders) pH 4.6 to 6.2 (optimum 5.8), hardness of 40-60 mS.

Cardinals lay their eggs in darkness, thus darkening of the spawning tank is required. Eggs are laid in 8-14 day intervals with up to 150 even 350 eggs. They are ready to spawn at 6-7 months of age.

With all the knowledge available from the hobby literature and my European friends I have set up spawning tanks for this species probably a hundred times, without much hope. It was extremely demoralising when someone in our Society claimed a spawning of Cardinals and raising them in a community tank. It puzzled me as I have bred hundreds of Neon Tetras, and fry up to 3 weeks of age are sensitive and require properly sized food.

The spawning tanks were little 200 x 200 mm by 150 mm high (hold 4 litres of water) similar to those used in Europe. On the bottom I placed a stainless steel gridmesh to protect the eggs from their hungry parents. The water used was from the Snowy Mountains, melted snow creek, pH 6.8 and extremely soft. I didn’t bother to lower the pH or add peat moss. If the fish spawned, then I would adopt a more scientific approach.

I added the fish and spawning medium, a bunch of nylon fishing line. I darkened the tanks, each containing a pair of fish. I prefer spawning Tetras in pairs. This gives perfect control of productive pairs and limits interference from other fish. The tanks can be very small. This is not applicable for spawning Congo or African Flag Tetras where the spawning ‘run’ is fast and long, or some aggressive Tetras where larger tanks are better.

My friends in Europe tell me they keep each pair in the spawning tank for 3 days (remember no food) and then they try a new pair. With my two pairs it was easy, 3 days in, 7 days out. After a few cycles, checking daily revealed eggs under the gridmesh. It was great. A few eggs were fungussed but most were glassy. The pair was removed. Water temperature was 26 0 C.

After 11/2 days around 60 fry developed. I kept them darkened by the fourth day started to observe when they needed food. The problem was they kept standing vertically against the glass when the light penetrated. Determining when to start feeding was a nightmare. A magnifying glass and careful observation of the egg yolk tummy size helped.

I was expecting very small fry as the eggs are smaller than Neon Tetras’. They were 3-4 mm, similar to Neons. Growth is described in the literature as slow. I found it disgustingly slow and to provide tiny live food I had to collect nauplii of Cyclops (freshly born small Cyclops: crustaceans that live in the paddock ponds) on a daily basis, strain them to the required size and not overfeed. Future followers please note: Brine Shrimp are monster food and are taken only after 4 to 6 weeks, so big are they!

In that time I quashed the claim of breeding Cardinals in a community tank. The fry would be wiped out in no time by the other fish.

After 3 weeks I introduced by mistake some larger food, some still very small Cyclops. The fry were attacked by a few adult Cyclops and I quickly lost 30 fry.

In 4 weeks the Neon Tetra fry shine like their parents and their length is 10-12 mm. The little Cardinals were 8-9 mm and at that time the red colouration started to appear dully, but the neon strip wasn’t shining at all. They took another 5-6 weeks to start looking like miniature adults. Still, feeding was a problem. Microworms were not taken terribly enthusiastically. Introduction of larger Cyclops was always a disaster with the loss of a few more fry. Neon Tetras, once they have their full colours although still small, are pretty tough and are willing to eat relatively large food (the same size as their eyes) but Cardinals are finicky.

With all the problems of getting two Cardinals willing to spawn, fulfilling the requirements of water chemistry, extremely slow growth of the fry, and the feeding difficulties I have very little patience left to breed them in larger numbers. This is a pleasure that I leave to others.

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