Cardinal Tetra
Paracheirodon axelrodi
Brighter and slightly larger than the neon, with red running the full length of the body.
| Difficulty | Intermediate |
| Min. Tank Size | 55 L |
| Temperature | 24.0–28.0 °C |
| pH Range | 4.5–6.5 |
| Max Size | 3.5 cm |
| Lifespan | 4-5 years |
| Diet | Omnivore |
| Temperament | Peaceful |
Overview
The Cardinal Tetra (Paracheirodon axelrodi) is brighter and slightly larger than the neon, with red running the full length of the body. It is one of the most recognisable members of the tetras group kept by Australian aquarists, valued for its appearance, manageable adult size of around 3.5 cm and its peaceful nature.
This guide covers everything you need to keep the Cardinal Tetra successfully - ideal tank size and setup, water parameters, diet, suitable tank mates, breeding, how to tell males from females, and the health problems to watch for. Rated Intermediate to care for, it can live for roughly 4-5 years when its needs are met.
Natural Habitat & Origin
Tetras of this kind originate from the slow, soft, tea-stained blackwater rivers, streams and flooded forest pools of South America. The water there is warm, acidic and stained brown by decaying leaves (tannins), with dim light filtering through overhanging jungle. Recreating a hint of that environment - subdued lighting, dark substrate, driftwood and live plants - brings out their best colour and most natural behaviour.
Understanding where a fish comes from is the shortcut to keeping it well: matching the temperature, water chemistry and amount of cover it evolved with is far more effective than fighting against its nature.
Tank Size & Aquarium Setup
Provide a minimum of 55 litres for the Cardinal Tetra. Because it is a shoaling fish kept in groups, floor space and swimming length matter more than height.
Fit a lid to prevent jumping and to keep the tank warm and stable.
Dark substrate, driftwood, leaf litter and dense planting with some open swimming space recreate its shaded blackwater home and intensify its colours.
Mature, well-cycled biological filtration is essential before adding any fish. Match the filter's flow to the fish - moderate for most, stronger and more oxygenated for hillstream and riverine species.
Water Parameters
Keep the Cardinal Tetra in stable water at 24-28 °C with a pH of 4.5-6.5. Soft, acidic water brings out its best colour and is important for long-term health and any hope of breeding.
Test your water regularly: ammonia and nitrite must always read zero, and nitrate should be kept low (ideally under 20-40 ppm) with routine partial water changes. Sudden swings in temperature or chemistry cause far more illness than water that is slightly 'wrong' but stable, so always dechlorinate and temperature-match new water.
Diet & Feeding
The Cardinal Tetra is an omnivore and an easy feeder. A quality flake or micro-pellet forms a good staple, enriched several times a week with frozen and live foods such as bloodworm, daphnia and brine shrimp for colour and condition.
Feed small amounts once or twice a day - only as much as the fish clears in a minute or two - and consider one fasting day a week. Overfeeding is the single most common cause of pollution and disease in home aquariums.
Temperament & Tank Mates
The Cardinal Tetra is an excellent peaceful community fish. It mixes happily with other calm species that share its temperature (24-28 °C) and pH (4.5-6.5) needs, are too large to be eaten, and are not large enough to eat it.
Crucially, the Cardinal Tetra must be kept in a group of at least 6 of its own kind (8-12 is better). A proper shoal is calmer, bolder, more colourful and far less likely to pester other fish - skimping on numbers is the most common cause of stress and nipping.
Breeding
The Cardinal Tetra is an egg-scattering species. To breed it, condition a group on live and frozen foods, then move them to a dim tank with fine-leaved plants or a spawning mop; the parents scatter eggs and will eat them, so remove the adults after spawning.
Even if you do not plan to breed it, understanding this behaviour helps you recognise it in the tank and respond appropriately - for example by adding cover for fry or by giving a guarding pair some space.
How to Tell Males from Females
Sexing tetras takes a careful eye: females are usually rounder and fuller-bodied (especially when carrying eggs), while males tend to be slimmer and often slightly more intensely coloured.
Common Health Problems
Like most aquarium fish it is susceptible to white spot (ich), fin rot and fungal infections, almost always triggered by stress or poor water quality. It can also fall victim to the incurable neon tetra disease, so quarantine new stock and remove affected fish promptly. Quarantine new arrivals for 2-4 weeks to keep your main tank disease-free.
Prevention is far easier than cure: keep water pristine, avoid overstocking and overfeeding, quarantine new arrivals for two to four weeks, and watch daily for early warning signs such as clamped fins, loss of appetite, flashing (rubbing on objects) or laboured breathing. Caught early, most problems are very treatable.
Is the Cardinal Tetra Right for You?
The Cardinal Tetra is a rewarding choice for fishkeepers with a little experience and a stable, mature tank, as long as you can provide at least 55 litres, water at 24-28 °C and pH 4.5-6.5, the right diet and a proper group of its own kind.
Get those basics right and you will enjoy a healthy, colourful Cardinal Tetra for around 4-5 years. For tank planning, try our free aquarium tools, and browse our fish, plant and disease guides to build the perfect community.