Cardinal Tetra

These very popular community tropical fish are a great addition for beginners with a well established tank. They are bright, lively fish that are happy in a shoal of 15 or more.   It’s a gregarious species that appreciates being in a large group and makes for a stunning aquarium showpiece. Adult Size 5 cm, minimum tank size 80 litres.  

The Cardinal Tetra (Paracheirodon axelrodi) is a social fish that is sometimes referred to as Red Neon Tetra due to their similarity to the famous Neon Tetra and are often confused with the Neon Tetra.  If you look closely you will notice that the vibrant red horizontal line of the Neon Tetra only runs from the middle of their body to the tail, whereas Cardinals the red runs the full length of the body. Cardinals are from the soft, acidic waters of the Rio Negro and Rio Orinoco drainages in South America.

Behaviour Cardinal Tetras are a colorful shoaling species that love to be kept in groups – the larger the group the better (just make sure the tank is big enough). They will swim together in the middle and upper levels of the tank.

They are much more confident when around others of their own kind. If kept alone they would become stressed and shy, and also lose some color. They are easily bullied by aggressive fish as they are unable to defend themselves.

Interestingly, except for their blue/red coloring they are transparent; in the wild this will help to hide from predators. When they feel really threaten they can even ‘turn off’ their red/blue iridescent hue to stay safe. Their coloring will also fade when they are sleeping or sick.

Tank Conditions  These fish don’t venture to the bottom of the aquarium very often, so you can choose any substrate. If you are starting a community with bottom-dwellers, a sandy substrate is best because they are less likely to scratch themselves.  You can scatter around some decorations, but plants are ideal if you are trying to provide some shelter. Your Cardinal Tetras will hide in them when stressed.  Anubias Nana, Amazon Swords and Java Fern are some easy species to care for.

Make sure that you leave plenty of open water for swimming, as this is where your fish will spend most of their time together.

The filter outlet will create enough water movement and most standard aquarium lights are fine.

Compatibility  In general Cardinal Tetras are very peaceful fish. They can make the perfect community fish, and a school of them really helps to bring vibrant colors to your tank. As they are such a small fish you should only place them in a community tank with other non-aggressive fish that aren’t big enough to eat them. As for ideal tank mates you should be thinking of:

• Gouramis (Avoid the Giant, Pearl and Opaline)
• Barbs
• Zebra Danios
• Small Catfish (e.g. Cory)
• Dwarf Cichlid
• Kuhli Loaches and Otocinclus (for the bottom of your tank)
• Cherry or Ghost Shrimp
• Mystery Snails

Fish to AVOID in the tank with Cardinals:

• Bettas
• Angelfish
• Cichlids
• Anything big enough to eat Neons

Feeding  In their natural environment in the wild, neon tetras are omnivorous. This means they will eat both meat and vegetables/plant matter.  They eat algae, larvae from insects and other miniscule invertebrates.  Fortunately, they aren’t fussy eaters and will enjoy eating all different types of food including pellets, flakes, frozen and live.  As always a high quality pellet/flake should make the core of their diet. You can supplement the flake with live/frozen food offerings such as:

• Blood Worm
• Brine Shrimp
• Daphnia
• Tubifex

Only feed extremely small pieces otherwise Tetras can have problems trying to swallow them.

One of the most important parts of caring for them is choosing the right diet. If your Cardinal Tetras are not receiving the nutrients they need, then they will lose their color and their immune systems will weaken.

Care Tetras are very sensitive to changes in water conditions. This means that newly cycled tanks are not suitable for your Tetras; generally the changes in the water chemistry during this time will kill them. You should only add Tetras to an established, matured tank.  Tetras produce a very small bioload so their filtering needs are very small; a regular sponge filter will do. Finally in terms of water changes, you should aim to perform a 25% water change each week. Make sure not to exceed this recommendation as too much water change can be deadly for Neons.

Add tannins to both soften and darken the water or use Bio Elite Soft-water Conditioner to simulate the black waters of their natural habitat.

As with all tetras, keep an eye out for Neon Tetra Disease.  It was first diagnosed in Neon Tetras, and so earned its name, but it can actually affect many other species. The Neon Tetra Disease has been identified as a microscopic sporozoan (Pleistophora) parasite in the intestinal tract that will eat the muscles starting from the inside out. Attempts to cure this disease with the use of Methylene Blue have not always been successful, so the disease is considered incurable.

Common symptoms include:

• A sudden loss of color.
• Irregular swimming patterns and turning into a bottom dweller.
• Developing cysts or spots on their stomach and beneath the dorsal fin
• Stomach shrinking and losing mass.

There is currently no cure and if one of your fish catches this disease it’s generally recommend that you destroy ALL the fish in the tank.  The best cure is prevention by maintaining the water temperatures properly. You should also make sure that any fish or live organism added to the tank is healthy and disease free before adding it.  You should always quarantine and inspect new fish before adding them to your main tank.