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Compatibility

Compatibility brief

Can Cardinal Tetra live with Oscar?

Cardinal Tetra

Cardinal Tetra

Paracheirodon axelrodi

peaceful~5cm
Oscar

Oscar

Astronotus ocellatus

aggressive~35cm
VerdictRISKY

Risky. This mix is commonly discouraged for typical setups.

Cardinal Tetra + Oscar: Aggression mismatch. Oscar is aggressive, while Cardinal Tetra is peaceful. The aggressive fish will likely bully or harm the peaceful one. Real tanks add variables Fishori cannot model; treat this as a high-risk read, not certainty.

Compatibility score

30/100

Profile confidence: medium

Order of checkstank volume vs adults → predation mouth gap → temperament / fin nipping → shared water windows.

Min tank

300L

Combined minimum footprint reference for these two species: about 300L (larger active fish often want more length).

Temperature
Range in °C23–27°C shared
Cardinal TetraOscarShared window
pH
Range6–7 shared
Cardinal TetraOscarShared window
Size / predation

Oscar (35cm adult) may treat small Cardinal Tetra (~5cm) as food once grown — plan adult sizes, not shop sizes.

Temperament / behaviour

Oscars are large predatory cichlids; cardinal tetras are small midwater schoolers that fit easily into an adult oscar mouth. Fishori’s live verdict is RISKY for that size and aggression mismatch. Keepers who add cardinals as “dither fish” for a juvenile oscar often lose the school as the cichlid grows. Water overlap does not matter when one fish is food. If the oscar is the priority, stock appropriately sized tank mates or keep a species-focused setup.

Assessment details

  1. Aggression mismatch

    Top issue

    Oscar is aggressive, while Cardinal Tetra is peaceful. The aggressive fish will likely bully or harm the peaceful one.

  2. Oscar may eat Cardinal Tetra

    Oscar (35cm) is predatory and Cardinal Tetra (5cm) is small enough to be eaten. This pairing is unsafe.

  3. Compatible temperature range

    Both fish can comfortably share similar water temperatures.

“Oscar is aggressive, while Cardinal Tetra is peaceful”

Aggression mismatch

Next steps

Concrete changes, not "research more" filler.

  • •Do not stock cardinal tetras with oscars. Keep cardinals in a peaceful soft-water community, and keep oscars with robust, large companions or alone.
  • •Cardinal Tetra should be kept in a group of at least 6 for best health and behaviour.
  • •Oscar reaches ~35cm: tank length and turning room matter more than the litre number. A tall, short tank of the same volume is not equivalent.

Try instead

  • →Build a species-only tank for the larger fish, or restock with fish too large to be eaten at adult sizes.
Sources from both profiles
Only URLs that exist on the species records are shown. We do not fabricate citations.

Try this next

Build the full stocking list with Cardinal Tetra + Oscar

Compare another pairOpen tank builder

Plan further

Check each species’ mates list, size the glass, then verify the full stock in the builder. Methodology explains how verdicts are produced.

Individual fish vary in personality. Fishori uses conservative hobby rules. Observe any new introduction closely, feed thoughtfully, and keep a quarantine or backup plan. This is not veterinary advice.

Profile data confidence: high. Checked against several solid care sources that mostly agree.

Full tank-mate guides

Related pair checks

Other tank mates for Cardinal Tetra

Cardinal Tetra + Oscar — common questions

Can Cardinal Tetra live with Oscar?
For most keepers, no. Fishori’s verdict is RISKY because oscars are aggressive predators relative to cardinal size. Juvenile calm weeks do not make the adult pairing safe.
What tank size do you need for Cardinal Tetra and Oscar together?
Plan around 300 litres as the working minimum. That figure comes from each species' published minimum and their group needs, and it assumes adult sizes, not shop sizes.
What's the main risk?
Aggression mismatch. That is the check that fails outright for this pair. The matching entry under assessment details on this page explains the reasoning and the numbers behind it.
What should you check before buying?
Cardinal Tetra should be kept in a group of at least 6 for best health and behaviour. Oscar reaches ~35cm: tank length and turning room matter more than the litre number. A tall, short tank of the same volume is not equivalent.