My oscar is only 4 inches right now. Can I keep guppies until the oscar grows?

No. A 4-inch oscar will eat 1-2.5 inch guppies without hesitation. Oscars begin eating other fish as soon as they are large enough to swallow them, and guppies are always large enough.

Will a bigger tank save the guppies?

No. Tank size does not change the oscar's prey drive. In a 200-gallon tank, the oscar will still spot movement, swim over, and eat any guppy it encounters. Size of the tank only matters for swimming room, not predator behavior.

Can I add tank dividers or hiding spots to protect the guppies?

Oscars are powerful enough to push through or destroy most dividers. Hiding spots help prey species survive, but oscars are persistent and will work through every hiding spot in time. This pairing does not work in any configuration.

What about juvenile oscars with adult guppies?

Even juvenile oscars will eat guppies. The guppies may escape a small juvenile oscar briefly, but the oscar grows fast and will catch up. The oscar will eat all of them before reaching half its adult size.

Can Guppy Live With Oscar?

By Alex WalshLast reviewed Apr 18, 2026

No, oscars are large predatory cichlids that grow to 12-14 inches and will eat guppies on sight in any tank size.

Why

Oscars reach 12-14 inches as adults and will eat anything that fits in their mouth. Guppies stay at 1-2.5 inches. In a 75-gallon tank, an adult oscar is capable of eating every single guppy within days of introduction.
Oscars are carnivorous cichlids with a strong prey drive. They hunt by watching for movement and lunging. Guppies are fast-moving, colorful fish that trigger this hunting response immediately.
Guppies reproduce constantly, and oscars will quickly learn to guard the breeding area and eat every fry as it appears. No guppy colony survives intact with an oscar in the tank.
Oscars produce massive bioload and need 75-100 gallon tanks minimum. Guppies need a heated tropical tank of 10-20 gallons. The minimum tank size for oscars is 5 times larger than what guppies need, and the oscar dominates the space entirely.
Even a juvenile oscar will eat guppies. Oscars grow fast, reaching 6-8 inches within the first year. Any guppy present will be consumed long before the oscar reaches adult size.

Minimum shared tank

75 gallons

Shared temperature range

74-81°F

What could go wrong

Oscars will systematically eat every guppy in the tank. Any guppy that survives the first week will be eaten within a month. The oscar will learn the feeding schedule and position itself to intercept guppies during feeding time.

If you keep them in separate tanks

Sized for the 75 gallon minimum this pairing needs. Affiliate links — we earn a small commission if you buy through them.

Fluval 307 Performance Canister Filter

Oversized filtration is what lets you stock two species together without water quality crashing. Rated for a tank slightly larger than the 75 gallon minimum.

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Eheim Jager 300W Thermostat Heater

Holds a steady temperature inside the 74-81°F window both species need.

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API Freshwater Master Test Kit

Keep ammonia, nitrite, and nitrate in check. Two-species tanks have more bioload and less margin for error than single-species setups.

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Better pairings to consider

Oscars do well with other large cichlids (jack dempseys, convicts), large plecos, or tinfoil barbs. Guppies do well with neon tetras, bronze corydoras, or cherry shrimp in a dedicated tropical community tank.