Cardinal tetras in the wild and in the aquarium

The natural habitat of the cardinal tetra

If you want to recreate a natural "cardinal tetra" biotope in the aquarium, you have to take a tough line on aesthetics. Lots of foliage on the bottom, brown coloured water and no water plants. But there are supposedly aquarists who find beauty in this. At least that's what the original habitats look like.

Cardinal tetras are generally found in shallow water. We found they clearly prefer water depths between 10 (!) and 60 cm. They avoided the river sections with depths of about a metre. The cardinal tetras were found in the same river, but always in the shallow places. When streams and rivers wind through nature, the bends always have a shallow spot (outer side) and a deep spot (inner side). Even without looking under the water surface, you can guess which fish you’ll find in which area. 

Since large cichlids also live in the deeper areas, the shallow area is quite a smart choice for the cardinal tetras. Altum angelfish cannot follow them into the shallow water zones and therefore always stay in the deeper water areas. But Crenicichla species and predatory catfish species also "fit" in shallow water. Therefore cardinal tetras in shallow water prefer regions where there is a lot of foliage on the bottom. In case of danger, they form the famous swarm, which makes it difficult for enemies to concentrate on one individual, and plan B is the foliage, where fish are unable to find each other.

As an alternative to the leafy bottom, we see cardinal tetras in shallow water near the banks, where a dense root network also offers protection. In these biotopes, which can also be 50-60 cm deep, the tetras never swim in a shoal. One might think that they are solitary creatures. Getting more than six fish on a photo is only possible with wide-angle lenses!

If you look closely, you will see in the photos that their bellies are more sunken than full. This is not surprising, because as plankton eaters their table is unfortunately not very richly laid. Blackwater is so hostile to life that you can sit comfortably by the river in the evening without mosquitoes eating you alive. But that also means that there are hardly any insect larvae and small crustaceans in the water. If you drag a plankton net through the blackwater for half an hour, you will catch nothing to 5 small copepods. It is easier to catch a river dolphin!

The cardinal tetra in the Aquarium

In the aquarium, the situation is different. As a rule, we do not put predatory fish in with our tetras, so the base of rotting leaves is not needed. For better aesthetics aquatic plants are perfectly okay. By the way, tetras are quite familiar with the green colour: leafy branches fall into the water again and again and even at high tide you can see a lot of green under water. But only until the next dry season! Tetras need a lot of swimming space. You will rarely find them among the plants. Loose or dense border planting is therefore possible. The substrate does not matter to the small tetras. As a rule, they do not look for food on the bottom, but always in the open water or (with training) on the water surface.

Wood and stones can always be used for aquarium decoration even if the tetras do not attach much value to them. An aquarium for cardinal tetras that is based on their natural habitats has a lot of free swimming space and wooden roots with plants at the edge. Breeding in a community aquarium is difficult and requires a special breeding aquarium. But that’s another story. 

A water temperature of 30 °C, as we find in some cardinal tetra biotopes, does not need to be reproduced in the aquarium! The fish's metabolism would constantly be running at full speed, reducing their life expectancy, and our beautiful aquatic plants do not like such temperatures at all. Water temperatures between 25 and 27 °C are perfectly adequate. 

The water values of these habitats were similar: pH always in the strongly acidic range between 4 and 5.5. General hardness and carbonate hardness were not measurable. The conductivity was 9-10 µS/cm and the water temperatures were between 26 and 29 °C. These values were measured on JBL expeditions to the Puerto Inirida area in Colombia. On a JBL expedition to Barcelos near the Rio Negro, which is definitely the largest transhipment point for cardinal tetras in South America, almost identical water values were determined. Only the conductivity was slightly higher there at 16 µS/cm. The intensity of colouration in the blackwater varied a lot. 

Cardinal tetras live both in extremely tinted blackwater, caused by humic substances, and in moderate blackwater, which only has a tea-coloured tinge. In the aquarium, aquarists can easily add humic substances using appropriate products such as JBL Tropol . At normal dosage, however, the brown colouring is hardly visible, even though there are already many humic substances in the water. Only at 3-4 times the dosage is the brown tinge clearly visible in the water. Of course, there is always the question of how far we should imitate nature for our fish. Unless you live in regions of Germany where the water comes out of the tap as a mineral lump (water hardness over 20 °dGH) and the pH value settles around neutral (6.5-7.5), it is much more important to achieve an ideal climate for the fish by regular partial water changes and good filtering than to lower the pH value by 0.002 by fiddling around and to lower the hardness by 0.5 by adding osmosis water. If you take a closer look at the water flow rate of a stream or river in nature, you will quickly realise why a partial water change in the aquarium is so important.

The diet of cardinal tetras

As already written, the tetras tend to have a lack of food in their natural habitats. The imported animals often have sunken bellies and really don't look well fed. Tetras from offspring are often better fed - the rounder bellies are evidence of this. Therefore, it is important that newly purchased tetras (whether cardinal tetras or neon tetras) are fed well. As with many small animals, more frequent feeding is important, then of course always with adapted, smaller portions. For starved animals, feeding five times a day can be absolutely sensible!

However, the most important thing is the size of the food. Most foods are simply too big and do not fit in the small mouth. With JBL NovoGranoMix XXS , for example, JBL has a really small granulate in its range. The next size up, XS, is too again! In the new JBL PRONOVO range a special food for red and neon tetras (also suitable for other small characins) JBL PRONOVO NEON GRANO S has also been developed. 

The importance of food size has never been properly appreciated in the past and is only now becoming an issue. Since tetras and other small characin species are plankton eaters, a plankton food (e.g. JBL PlanktonPur SMALL ) is an ideal food type. But other foods, as long as they are small enough, are also suitable, as tetras are not particularly choosy. They have small, sharp teeth and look like small piranhas in a good macro shot. 

© 02.04.2023
Heiko Blessin
Heiko Blessin

Tauchen, Fotografie, Aquaristik, Haie, Motorrad


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