Cardinal Tetra (Paracheirodon axelrodi)

Cardinal Tetras bring a clear band of electric blue and deep red to the middle of a peaceful aquarium. This listing is for Paracheirodon axelrodi, a small South American shoaling fish that is best suited to a mature, stable setup with subdued areas and calm companions.

One quantity means one unsexed fish in the approximate size grade selected above. Cardinal Tetras should not be kept alone, so plan the complete group and aquarium capacity before ordering. Our practical starting policy is a group of at least ten in a mature aquarium around 60 litres or larger with at least 60 cm of swimming length. More space is needed when the aquarium already contains other fish or when you want a larger shoal.

The photographs are representative of the species. Colour intensity, body shape and size vary with age, condition, lighting and the individual fish. The images do not confirm the exact fish’s sex, collection locality or captive-bred status.

Appearance and natural behaviour

The Cardinal Tetra is recognised by its reflective blue stripe and the red band that runs along most of the lower body. This helps distinguish it from the Neon Tetra, whose red marking is mainly on the rear half. The colour can appear brighter against dark substrate, wood and planting, but healthy water and low stress matter more than decorative colour contrast.

Cardinals naturally use the middle water layers and become more confident in a coherent shoal. A proper group can spread out while relaxed and draw together when startled. Buying one or two fish for colour does not meet that social need. FishBase gives a published aquarium floor of five or more; our more conservative sales policy starts at ten where the aquarium can support them.

Aquarium size and layout

Use a fully cycled aquarium with reliable biological filtration. A tank at least 60 cm long and around 60 litres provides a practical starting footprint for ten Cardinals before companions are added. The usable capacity depends on swimming room, filter maturity, oxygen exchange, feeding access and every other adult occupant, so the nominal volume is a starting screen rather than a stocking formula.

Planting, wood and other aquarium-safe cover around the sides and rear can provide security, while an open route through the middle gives the group room to move. Keep the current gentle enough that the fish can swim and feed without constantly fighting it. Floating plants or shaded sections can help in a brightly lit aquascape.

Water and filtration

Our routine house target is 24–27°C, pH 5.5–7.0 and 1–8 dGH. This favours warm, soft-to-moderately-soft water while allowing the retailer’s measured holding water and the established aquarium to be compared. FishBase publishes a narrower wild-water pH range, while general OATA guidance for captive-bred tetras is broader. Ask about the current holding conditions, test your aquarium and make any adjustment gradually.

Ammonia and nitrite must remain at zero. Keep nitrate controlled through suitable stocking, measured feeding and regular maintenance. Cardinals are a poor choice for a newly filled aquarium or a system that has not demonstrated stable biological filtration. Most UK homes will need a thermostatically controlled heater to maintain the target throughout the year.

Feeding

Cardinal Tetras have small mouths. Use a suitably fine complete flake, granule or micro-pellet as the staple, supported by small frozen or live foods such as cyclops, daphnia or appropriately sized brine shrimp. Offer measured portions and make sure timid fish receive food when faster tank mates are present. Remove uneaten food before it damages water quality.

New arrivals may be pale or hesitant after transport. Keep the aquarium calm and lighting subdued, then offer a small familiar food after the fish have settled according to the current delivery guidance.

Tank mates

Choose peaceful fish that share the same measured water range and cannot swallow a slender adult Cardinal Tetra. Small rasboras, pencilfish and appropriately sized peaceful bottom dwellers can work when their own group, substrate and temperature needs are also met. Avoid fin nippers, aggressive feeders, territorial fish that dominate the swimming area and any predator large enough to take a tetra.

Adult shrimp may coexist in a carefully planned planted aquarium, but no fish should be sold as shrimp-safe. Cardinal Tetras can eat shrimplets and other very small invertebrates. Angelfish and larger cichlids require particular caution because a calm fish can still be a predator when the tetra fits in its mouth.

Sex and breeding

Retail juveniles are sold unsexed. Mature females can look deeper-bodied when carrying eggs and males may appear slimmer, but age, feeding and condition also affect shape. Colour alone is not a reliable way to promise sex.

Cardinals are egg layers. Breeding requires a separate mature system, carefully measured soft acidic water, suitable spawning material, protection for the eggs and specialist first food for the fry. A community aquarium is designed for the display group, not dependable fry production.

Choosing a size and ordering

Select the available size grade that suits the established occupants and feeding competition in your aquarium. The measurements are approximate growth grades, not guaranteed exact lengths for every individual. Smaller juveniles need particular protection from large mouths and fast feeders. If possible, introduce the planned group together while following any quarantine process used for the aquarium.

Check the live selector for current sizes and prices. Review the Cardinal Tetra Care Guide for the supporting evidence and planning detail, browse the tetra collection for compatible alternatives, and read the current live-fish delivery information before choosing a dispatch date.