Breed 500 or more Cardinal Tetras

by: Bryan Jones, Auckland Fishkeepers Association

With this article I hope to encourage FNZAS members to have a try at breeding one of the most popular tropical fishes worldwide – the cardinal tetra, Paracheirodon axelrodi. Cardinals have been spawned in NZ but, to my knowledge, this has not been maintained on a regular basis. From time to time since obtaining my first cardinals about 1960, successes have been obtained in my fish room but not continually such as with other tetras including neons, rummy-noses etc.

The cardinal tetra was introduced to aquarists in the late 1950’s and was considered to be the most strikingly coloured freshwater fish since the arrival of the neon tetra in the 1930’s. A large school of cardinals in a suitably aquascaped aquarium is a stunning sight, particularly if attention is given to subdued lighting, dark substrate and quality water.

Cardinals are frequently available in many NZ retail petshops, usually priced from $5 – $10, and are virtually all from wild caught stock. They are not a cheap fish compared to, say, the neon tetra at $1.50 – $2.50 each. This is probably why many NZ aquariums, although displaying a few cardinals, seldom house a large school of 50 – 100 which would give a much more visual impact. The main reason for this is cost, as the hopes of commercial aquaculture breeders overseas to mass produce cardinals following their introduction has not, to date, been achieved – unlike what has been done by the Chinese in rural Hong Kong with the many millions, per annum, of neon tetras bred for the world markets.

Following the discovery of cardinals by Dr Harold Sioli in Sept. 1952, near Sao Filippe in the Rio Negro region, wild caught cardinals supply the world markets. Many millions are exported from Brazil, and to a lesser degree Colombia, each year (40,000,000 in 1996). This is an important income earner for the local populace centred around Barcellos on the Rio Negro, 386kms upstream from Manaus, where most are flown overseas to world markets.

There is concern that a large number of cardinals captured do not survive the first stages of export (up to 50 million PA) and efforts are now being made to reduce such losses. Further more, due to the large demand for this species (which is the highest exported ornamental fish by far from Brazil) they are getting harder to catch. What took one day some years ago, now takes one week for the same number, and the fishermen must travel further afield. There are concerns that more attention must be made to control the fishery, which could mean a limit on volumes taken and closed collection periods, to protect cardinal exports in the future.

For the intending breeder of this fish, a study of the bio type is of interest. Cardinals do not habit the main Rio Negro river or its tributaries but rather their source in dense forests and swamplands. In the rainy season, December to March, when many waterways and lowlands become flooded, cardinals move further upstream over areas that were dry, or at best only swampland, in the drier months. This is the time when cardinals breed, stimulated by fresher water, extra food availability, and temperature changes.

A common myth is that cardinals breed in water that is dark brown and very peaty with low acid readings more relevant to the water found in main rivers in the dry season. The water, however, at all times in this area is very soft due to soils having the lowest mineral content in the world. The water during the heavy rainy season, when the cardinals breed, is therefore further softened and acidity diluted as shown in low hardness and conductivity readings. Another factor to be noted in this bio type is that cardinals are found only in dark and shaded waters away from sunlight and they have a distinct dislike of strong light.

If you are interested in producing, say, 500 cardinals, now is the time to purchase some breeding stock. About 20 will be needed and should be young imported fish, not old fish from established aquariums. Set up a 60 x 30 x 30cm aquarium with a black painted bottom, back and sides, subdued lighting, and soft water. Use no substrate which could harden the water. Plants can be kept held down with waterlogged driftwood. A plastic box type filter is appropriate using glass wool and a little peat to slightly acidify the water but provide water changes as needed to keep the conductivity low ie Below 200 micro-siemens.

A varied diet is needed including daphnia, white and blood worms, and particularly brine shrimps, to bring our growing cardinals into breeding condition. Consider setting up a sea monkey tank to provide larger brine shrimp adults for your breeding stock. I have a 45 x 23 x 23cm tank sitting on a window sill in the fish room containing salt water of .130 specific gravity and provided with strong aeration. The shrimps grow to about 1cm in a month if fed on a yeast and water solution which I keep in a plastic 1litre lemonade bottle. Feed a little regularly only when the salt water tank clears by the shrimp eating the food.

As we will be testing the hardness and pH values of our water conditions, I would suggest the purchase, or acquisition, of a conductivity and pH meter. I have one of each which I use for quick and accurate tests when required.

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