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Compatibility

Compatibility brief

Can Harlequin Rasbora live with Oscar?

Harlequin Rasbora

Harlequin Rasbora

Trigonostigma heteromorpha

peaceful~5cm
Oscar

Oscar

Astronotus ocellatus

aggressive~35cm
VerdictRISKY

Risky. This mix is commonly discouraged for typical setups.

Harlequin Rasbora + Oscar: Aggression mismatch. Oscar is aggressive, while Harlequin Rasbora 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
Harlequin RasboraOscarShared window
pH
Range6–7.5 shared
Harlequin RasboraOscarShared window
Size / predation

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

Temperament / behaviour

Harlequin Rasbora (peaceful) and Oscar (aggressive) are far apart on aggression — bullying or injury is a common outcome in average community layouts.

Assessment details

  1. Aggression mismatch

    Top issue

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

  2. Oscar may eat Harlequin Rasbora

    Oscar (35cm) is predatory and Harlequin Rasbora (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 Harlequin Rasbora is peaceful”

Aggression mismatch

Next steps

Concrete changes, not "research more" filler.

  • •Harlequin Rasbora 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 Harlequin Rasbora + 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 Harlequin Rasbora

Instead of Oscar, consider

Safer companions listed for Harlequin Rasbora. Check each pair individually.

Harlequin Rasbora + Oscar — common questions

Can Harlequin Rasbora live with Oscar?
For most keepers, no. The verdict is RISKY: at least one check fails hard for a typical home tank. Choose a different pairing, or read the assessment details on this page to see exactly what fails before deciding.
What tank size do you need for Harlequin Rasbora 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?
Harlequin Rasbora 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.