Care at a glance
Brighter and slightly more demanding than the neon, prefers soft, warm, acidic water. Stunning in a dark-substrate Amazon biotope.
By Mike ElmiraUpdated 2 min read
Part of our complete guide to aquarium fish for the planted tank.
Fish
Cardinal Tetra
Paracheirodon axelrodi
Upper Orinoco and Rio Negro basinsIntermediate
TL;DR, Cardinal Tetra
Brighter and slightly more demanding than the neon, prefers soft, warm, acidic water. Stunning in a dark-substrate Amazon biotope.
Cardinal Tetra (Paracheirodon axelrodi) reaches 4–5 cm as an adult and needs a minimum tank of 75 L. Native to Upper Orinoco and Rio Negro basins, it lives in the mid water column with a peaceful temperament. Aim for 23–27 °C, pH 4.5–6.5, and 1–6 dGH hardness. Lifespan is 4–6 years with good care. Keep cardinal tetra in groups of 8+, yes schoolers need numbers to display natural behaviour. Diet: omnivore, Micro pellets, frozen daphnia, baby brine shrimp, finely crushed flake. Plant-safe: Yes. Shrimp-safe: Mostly (may eat shrimplets).
Tank fit
The parameters that decide whether cardinal tetra fits in your tank.
Parameters
15 °C20 °C25 °C30 °C
4.05.06.07.08.0
0 dGH5 dGH10 dGH15 dGH20 dGH25 dGH
0481115
Water column
Mid
Schooling
Yes
Group of 8+
Still
Low
Medium
High
V. high
Profile
Family
Characidae
Diet
Omnivore
Micro pellets, frozen daphnia, baby brine shrimp, finely crushed flake.
Lifespan
4–6 yrs
Breeding
Hard
Habitat
Tannin-stained streams of the upper Rio Negro, Brazil
Upper Orinoco and Rio Negro basins
Who it lives with
Tank-mate safety and the species this one is documented to thrive (or fail) alongside.
Good tank mates
Corydoras (sterbai, pygmaeus), apistogrammas, German blue rams, hatchetfish, otocinclus.
Avoid
Hard-water community fish (livebearers), aggressive tetras (serpae), angelfish (will eat them).
Pro tips
Hard-won lessons from the tank.
Stable RO water + remineraliser + tannins is the secret. Once acclimated to a proper blackwater tank, cardinals live 5+ years. If buying from a chain store, ask when they arrived — fish 'fresh in' have the worst survival; wait two weeks.
Etymology
Species 'axelrodi' honours Herbert R. Axelrod, the American ichthyologist and aquarium publisher.
Things to watch for
What can go wrong and how to spot it.
Things to watch for
Failure modes, in order of how dramatic the fix is.
Health
Common diseases
More sensitive to swings than neons. Susceptible to ich during transport (cold-shocked fish). Less prone to NTD than neons but not immune.
Often wrong
Misconceptions
Cardinals are NOT just 'better neons' — they're more demanding water-wise. A neon-tetra-easy tank will see cardinals die slowly over months. Match the water to the fish.
How to care for it
The practical routine, read top to bottom.
Tank setup
Same as neons but warmer (24–27 °C) and softer/more acidic. Catappa leaves and alder cones are practically required. Co-stock with similar blackwater species.
Quarantine
4 weeks. They ship stressed — give them dim, quiet QT with tannins and minimal handling.
Background
Where it comes from, how it behaves, and the variants you'll see at retail.
Show backgroundHide background
In the wild
Where it lived before it came home.
Native rangeRio NegroOrinoco basin
Origin · Upper Orinoco and Rio Negro basins
Upper Rio Negro and Orinoco basins (Venezuela, Colombia, Brazil). Extremely soft, acidic blackwater (pH down to 4.0, conductivity <30 μS/cm). Dense leaf litter and submerged tree roots.
Wild diet
Small crustaceans, fallen ants and other terrestrial insects, biofilm.
Conservation status
Project Piaba (Brazil) is one of aquarium's success stories — wild harvest funds rainforest preservation. Buy 'wild Brazil' cardinals when possible.
Behavior & breeding
How they pair, reproduce, and grow.
- Stage 1
Telling them apart Sexing
Females are visibly fuller-bodied when in spawning condition. Males slimmer with slightly more vivid red. Often difficult to sex with confidence outside breeding condition.
- Stage 2
Pairing & spawning Breeding
Notoriously difficult in home tanks — needs very soft (~1 dGH), pH 4.5–5.5, tannin-stained water, very dim lighting, and meticulous parameter stability. Egg scatterers. Most cardinals in the trade are still wild-caught from Brazil's Project Piaba sustainable fishery.
Variants & identification
The named cultivars and the lookalikes worth flagging.
Color forms
Wild type. No widely accepted cultivars.
Frequently asked questions
Direct answers to the questions search engines and AI assistants surface most often about this species.
What is the minimum tank size for Cardinal Tetra?
Cardinal Tetra (Paracheirodon axelrodi) needs a minimum tank of 75 L. They live in the mid water column and should be kept in groups of 8+, so a longer footprint matters more than depth.
What water parameters do Cardinal Tetra need?
Target 23–27 °C, pH 4.5–6.5, and 1–6 dGH hardness. Acclimate slowly when moving them between water sources.
Are Cardinal Tetra safe with shrimp?
Shrimp safety: Mostly (may eat shrimplets). Plant safety: Yes.
What do Cardinal Tetra eat?
Cardinal Tetra are omnivore. Micro pellets, frozen daphnia, baby brine shrimp, finely crushed flake.
Are Cardinal Tetra beginner-friendly?
On Fin & Stem's 1–5 difficulty scale this species rates 3/5. Intermediate, stable parameters and a mature tank matter. Breeding difficulty: hard.
How long do Cardinal Tetra live?
Typical lifespan in a well-maintained tank is 4–6 years.
Sources & further reading
More fish
See all fishAdjacent specimens in the catalogue.
Cross-references
Build the rest of the tank.
A planted tank is a system. Pair this fish with one entry from each other pillar to plan the whole scape.
