Compatibility Overview
Molly and Oscar can generally share an aquarium with appropriate planning. Both species prefer overlapping temperature and pH ranges, and neither poses a major aggression risk to the other. A minimum 100-gallon tank is recommended to provide adequate territory and water volume for both species.
| Factor | Molly | Oscar | Verdict |
|---|---|---|---|
| Temperature | 72–82°F | 74–81°F | ✅ 74–81°F |
| pH Range | 7.5–8.5 | 6.0–8.0 | ⚠️ 7.5–8.0 (narrow) |
| Temperament | peaceful | aggressive | ❌ Risk |
| Adult Size | 4 in | 14 in | ⚠️ 3.5× difference |
| Min. Group | 3+ | 1+ | See below |
| Min. Tank Size | 100 gallons (for both species) | — | |
✅ Compatibility Positives
⚠️ Caution Points
Species Profiles
Molly — Poecilia sphenops
Hardy livebearers that prefer alkaline, hard water — sometimes slightly brackish. Prolific breeders; peaceful community fish.
Oscar — Astronotus ocellatus
Intelligent but aggressive cichlids that will eat any fish small enough to fit in their mouth. Require large tanks (75+ gallons) and robust tank mates.
Frequently Asked Questions
Can Molly live with Oscar?
Yes, in a well-planned setup. Molly and Oscar can generally share an aquarium with appropriate planning. Both species prefer overlapping temperature and pH ranges, and neither poses a major aggression risk to the other. A minimum 100-gallon tank is recommended to provide adequate territory and water volume for both species.
What tank size do I need for Molly and Oscar together?
A minimum of 100 gallons is recommended for keeping Molly and Oscar together. A larger tank improves water stability and reduces territorial conflict.
What temperature suits both Molly and Oscar?
74–81°F
Is a Molly aggressive toward a Oscar?
Molly is peaceful and Oscar is aggressive. Limited pH overlap (7.5–8.0) — maintain pH carefully within this narrow window.