At a glance the quick version
Looks how to spot one
Small scaled characin with structural (iridescent) colour
A slim, torpedo-shaped little fish with a glowing electric-blue stripe running from the eye to the tail. Everything below that stripe, from the snout right back to the tail, is a deep scarlet red, and the belly is pale. Like other tetras it carries a tiny adipose fin between the dorsal fin and the tail. Grown females look fuller and slightly larger than males.243
Personality what they are like
A calm, gentle fish that gets along well with other small, peaceful species. It feels most confident moving as part of a tight group in the middle of the tank, and a larger school brings out its best colour and natural behaviour.34
Daily activity how busy a day looks
Active by day and spends most of its time cruising the middle water layer with its shoal. Give it open swimming space along the front of the tank with planted or wood-filled areas behind for cover.143
Grooming and care the hands-on bits
Keep the water soft, warm and slightly acidic, with regular partial water changes to keep conditions stable. Dim light, floating plants and leaf litter or driftwood echo its blackwater home and show off its colour.31
Home where they are happiest
Aquarium with a footprint of at least 60 x 30 cm (about 54 litres). Water temperature roughly 23-29 C (FishBase gives 23-27 C), pH about 4.0-7.5 with acidic water preferred (FishBase 4.0-6.0, Seriously Fish 3.5-7.5), and hardness around 1-12 dGH. Densely planted areas, roots and leaves suit it well.31
Food basics what goes in the bowl
An omnivorous micropredator that in the wild picks at midge larvae, water fleas, copepods, rotifers and other tiny animals among leaves and plants. In the aquarium it does well on a good small flake or granule, supplemented with live or frozen foods such as daphnia, bloodworm and mosquito larvae.234
Company who they like around
A true schooling fish. Keep at least 8-10 together (ADW suggests 10 or more), alongside similar-sized peaceful tankmates such as other small characins, small catfish and gentle dwarf cichlids.341
The story where it all began
The cardinal tetra lives in shaded rainforest streams and flooded forest of the upper Rio Negro and Orinoco, where the water is soft, acidic and tea-coloured. Western science named it in 1956, when the American ichthyologist Leonard P. Schultz described it as Cheirodon axelrodi in honour of the aquarium book publisher Herbert R. Axelrod; it was later moved into the genus Paracheirodon alongside the neon tetra. The fish quickly became one of the most prized aquarium species in the world. Most cardinals in the trade have traditionally been collected by local fishers around Barcelos on the Rio Negro, a fishery that supports riverside communities and gives them a reason to keep the forest standing. Project Piaba, set up in 1991, studies and promotes this home-aquarium fishery as a sustainable use of the rainforest. Breeding in captivity was long considered hard, but a growing number of breeders now produce the fish.2315
Fun facts for the dinner table
- 1
Its colour is structural: tiny guanine crystals in skin cells bend light, so the stripe can look sapphire blue from one angle and greenish from another.2
- 2
In the wild it may be close to an annual fish, often living about a year, while in a home aquarium it commonly lives several years.4
- 3
From 2006 to 2015 more than 92 million cardinal tetras were exported from Brazil's Amazonas State, about 65 percent of all ornamental fish exported from there in that period.2
- 4
You can tell it from the neon tetra at a glance: the cardinal's red runs the full length of the body, while the neon's red covers only the rear half.2
- 5
Wild schools can number in the thousands, and the fish make small seasonal migrations as river levels rise and fall.4
- 6
A female can lay around 500 eggs, which hatch in roughly 24 to 30 hours.4
- 7
The species name axelrodi honours Herbert R. Axelrod, an influential publisher of fishkeeping books.3
Recognised by the official bits
- IUCN Red List
- Assessed as Least Concern (March 2021)1
- FishBase
- Listed as highly commercial in both fisheries and the aquarium trade1
Popularity Described by FishBase as one of the most popular aquarium fishes; over 92 million exported from Amazonas State, Brazil, between 2006 and 2015 (64.57% of the state's ornamental fish exports)
The care rhythm Furry Diary remembers it for you
A typical home-care rhythm for a Cardinal Tetra. It is our own starting plan, not a vet's advice, and you can change every line in the app.
- FeedingSmall amounts once or twice a dayevery day
- Temperature checkevery day
- Water changeAbout 25% of the waterevery week
- Water testevery week
- Glass cleanevery week
- Filter rinseRinse in old tank water, never tap waterevery month
You might also like
Neon Tetra
Green Neon TetraLike what we are building? Buy us a coffee.
The breed atlas is free for everyone, with a source on every fact, and it will never show ads. If it helped you, a small tip keeps the research going. Any amount is lovely, and no is a perfectly fine answer too.
Where this comes from
Every breed page shows where each fact comes from. If we got something wrong, sorry, we are pet people, not a science magazine. Tell us at support@furrydiary.app and we will fix it.
- FishBase: Paracheirodon axelrodi fishbase.seused for size, distribution, water parameters, diet, IUCN status, tank size, popularity
- Wikipedia: Cardinal tetra en.wikipedia.orgused for description, colour mechanism, diet, history, export figures, neon comparison
- Seriously Fish: Paracheirodon axelrodi seriouslyfish.comused for tank size, water parameters, diet, behaviour, habitat, taxonomy, colour forms
- Animal Diversity Web: Paracheirodon axelrodi animaldiversity.orgused for size, mass, lifespan, behaviour, reproduction, diet
- Project Piaba projectpiaba.orgused for sustainable Rio Negro aquarium fishery history
Checked 2026-09-30. Text is written in our own words from these sources.