Cardinal tetra

Identity and search names

Single-species profile for Paracheirodon axelrodi. Distinguish it from neon and green neon tetras by full-body pattern and accepted identity. Search names: cardinal neon

Environment and housing

Dark substrate, leaf litter or wood, shaded margins, an unobstructed central swimming lane and stable warm low-nitrogen water

Feeding and nutrition

Feeding ecology: Micropredatory omnivore taking tiny invertebrates, zooplankton and appropriately sized prepared foods

Feeding routine: Offer small varied meals once or twice daily and spread food across the shoal

Breeding and reproduction

Egg scatterer that requires very soft acidic water for dependable egg development; adults may eat eggs

Parental care: No parental care; adults may consume eggs and fry

System demands

Filtration: Use mature biological filtration sized for the adult stock and feeding load, with guarded intakes and a flow pattern the species can use without continual effort.

Aeration: Maintain strong gas exchange and stable dissolved oxygen, especially overnight, during warm weather, medication, crowding or any interruption to filtration.

Maintenance: Test ammonia and nitrite after changes or abnormal behaviour; remove waste from the occupied zone and perform regular water changes matched to temperature and mineral chemistry.

Detailed husbandry

Identity scope

Single-species profile for Paracheirodon axelrodi. Distinguish it from neon and green neon tetras by full-body pattern and accepted identity.

Adult size and space

Up to about 5 cm total length. At least 90 L with horizontal swimming room for ten or more. Adult dimensions, activity, social structure and waste production matter more than sale size.

Social structure

Keep at least ten; larger groups improve schooling, confidence and feeding access

Swimming zone

Primary zone: Middle water. Keep that zone usable and provide unobstructed feeding access, movement and refuge appropriate to the species.

Feeding ecology

Micropredatory omnivore taking tiny invertebrates, zooplankton and appropriately sized prepared foods

Feeding plan

Offer small varied meals once or twice daily and spread food across the shoal

Water stability

Maintain 24–29 °C; pH: 4.5–7.0; hardness/minerals: Very soft to moderately soft. Stable temperature, oxygen, mineral chemistry and nitrogen-cycle control matter more than chasing a single exact number.

Habitat structure

Dark substrate, leaf litter or wood, shaded margins, an unobstructed central swimming lane and stable warm low-nitrogen water

Compatibility plan

Keep with peaceful warm-water fish too small to prey on the shoal and calm enough not to dominate feeding

Breeding plan

Egg scatterer that requires very soft acidic water for dependable egg development; adults may eat eggs. Parental care: No parental care; adults may consume eggs and fry. Do not trigger reproduction without capacity for aggression, eggs or fry and lawful long-term placement.

Quarantine

Quarantine new fish in a separate cycled aquarium with dedicated nets, containers and siphons. Match temperature and mineral chemistry gradually, confirm normal feeding, respiration, skin, fins and waste, and never pour transport water into the established aquarium.

Welfare checks

Check shoal cohesion, colour, body condition, gill rate, feeding response and whether individuals remain isolated or pale.

Biosecurity and release

Never release fish, eggs, fry, aquarium water, sediment, plants or foods into drains, dams or natural waterways. Check the exact accepted identity in current BICON, Australian live-fish import requirements and applicable South Australian rules before import, sale or movement; import eligibility does not authorise release or wild collection.

Main risk

Cardinal tetras prefer warmer water than many common community fish. Do not choose companions on appearance alone or keep a token group.

Adult Projected Load

Moderate for a correctly sized shoal. Individual fish are small, but a large group, warm water and regular feeding create meaningful oxygen and nitrogen demand.

Filtration

Use mature mechanical and biological filtration with protected intakes and enough turnover for the adult group while preserving species-appropriate current and refuge.

Aeration

Provide strong gas exchange and backup aeration; increase oxygen support before warm weather, heavy feeding, crowding, medication or filter interruption reduces the safety margin.

Maintenance

Remove uneaten food and bottom waste, clean prefilters before flow falls, test ammonia and nitrite after changes, and perform regular temperature- and chemistry-matched water changes.

Overridable Warnings

A token group or unstable newly cycled aquarium is not acceptable. Do not override shoal size, quarantine or temperature and oxygen stability.

Welfare and risk

Check shoal cohesion, colour, body condition, gill rate, feeding response and whether individuals remain isolated or pale.

Sources

• Eschmeyer’s Catalog of Fishes — Paracheirodon axelrodi — Accepted name, synonym and taxonomic placement
• Acta Amazonica — diet of cardinal tetra in the Rio Negro — Natural feeding ecology and blackwater habitat context
• IUCN Red List search — Paracheirodon axelrodi — Conservation and provenance cross-check
• Australian Government — importing live ornamental fish — Australian import pathway and biosecurity requirements
• PIRSA — South Australian noxious fish list — South Australian possession, trade and release context
• Eschmeyer’s Catalog of Fishes current search — Paracheirodon axelrodi — Current accepted-name, synonym, distribution and habitat cross-check