The cardinal tetra is a small shoaling characin from the soft, acidic blackwaters of the upper Amazon and Rio Negro.
Its red stripe runs the full length of the body, distinguishing it from the similar neon tetra and giving a dense shoal a strong visual effect under subdued light.
Many cardinals are still wild-caught, so they arrive sensitive to shipping stress and need stable, mature water.
In a settled, well-cycled tank they are hardy and long-lived, but they are not as forgiving as a true beginner fish.
Housing
Keep a shoal of at least ten in 75 litres (20 gallons) or more, filtered and heated to 24-28C.
They show best in a dim, heavily planted tank with dark substrate, driftwood and tannin-stained water that mimics their native habitat.
They prefer soft, slightly acidic water and dislike high mineral content.
A fully cycled, stable system matters more than decor.
Provide gentle flow and floating cover so these timid fish feel secure.
Diet
Cardinals are micro-predators that eat small invertebrates and zooplankton in the wild.
Offer a quality micro-pellet or crushed flake as the staple, rotated with frozen or live daphnia, baby brine shrimp, cyclops and finely chopped bloodworm.
Feed small amounts once or twice daily, only what is taken within a minute.
Their small mouths need appropriately sized food, and varied feeding supports colour and overall condition.
Health
The main concern is neon tetra disease, an untreatable Pleistophora infection that causes fading colour, lumps and spinal curving; affected fish should be removed promptly.
Ich and fin rot appear when fish are chilled or stressed during acclimation.
Stable warmth, soft water and slow, careful acclimatisation prevent most losses.
Quarantine new stock, as wild imports can carry parasites, and avoid adding cardinals to an immature tank where swinging parameters weaken them.
Temperament
Peaceful, social and active, cardinals shoal tightly when secure and scatter when kept in too-small groups.
A large shoal settles faster, colours up and swims more openly.
They make good community fish alongside other peaceful soft-water species such as dwarf cichlids, corydoras and small rasboras.
Avoid large, boisterous or predatory tankmates that will eat them or keep them hiding.
Intermediate
Intermediate
Intermediate
Intermediate
Intermediate
Intermediate