Cardinal tetra

Paracheirodon axelrodi

Blue above an extended red flank

Red extends forward towards the gill cover, unlike the rear-half red of a neon tetra.

Adult length: Up to 3.5 cm (standard length, without the tail fin)
Water temperature: 23–29 °C
pH: 3.5–7.5
Hardness: 1–12 dGH

Native range: South America: Upper Orinoco and Negro River basins.

Natural habitat: Occurs in tributaries of the Negro and Orinoco rivers, often schooling in midwater.

Provide a group, cover and stable water. Wild-caught fish are particularly sensitive to deteriorating conditions.

View comparison →

Appearance and identification

The blue stripe ends near the adipose fin; a green neon tetra has less red and a stripe reaching the tail base.

Same-species behaviour

Keep at least 8–10 together. Allow space for the group and other residents.

Space requirements

At least 60 × 30 cm, with more space as the group grows. Keep swimming room beside planted or woody cover.

Diet and feeding

Offer small dry foods and small frozen foods as a varied diet.

Compatibility limits

Check size, predation risk, water conditions and space.

Aquarium environment

Use plants, wood and floating cover while retaining swimming space. Choose plants suited to subdued lighting and keep up maintenance.

Identification guides

Neon tetra vs cardinal tetra: markings and care differences

Start with the extent of the red band, then assess each species’ environment and group needs. These are separate species, not colour grades of one fish.

Sources

www.fishbase.se ↗ 2026-10-25

www.seriouslyfish.com ↗ 2026-10-22

researcharchive.calacademy.org ↗ 2026-10-22