cichlid · freshwater

Oscar: adult size, tank size & tankmates

The Oscar (Astronotus ocellatus) grows to about 17 in (35 cm SL). It needs a tank at least 60 inches long and about 143 gallons. It doesn't need a group of its own kind, at 72–82°F.

Try it in the tank builder See tankmates

How big it really gets

Drawn to scale against common tank lengths. Green bars meet the minimum tank length from our sources.

Outgrows most home tanks. Sold as an endearing 2-inch pet; reaches 12-14 inches in a year, destroys decor, produces immense waste, and eats fish.

Will it fit your tank?

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Quick facts

Adult size: 17 in (35 cm SL)
Minimum tank: 60 inches long and about 143 gallons
Temperature: 72–82°F
pH: 6–7.5
Hardness: 5–19 dGH
Group size: 1 (solitary or pair)
With other fish: semi-aggressive
With its own kind: semi-aggressive
Swims: middle of the tank
Diet: carnivore
Care level: intermediate
Lifespan: 15 years

Watch for: eats small fish · eats shrimp · eats snails · eats live plants · jumps, so keep a lid

Oscar tankmates

Checked with the same rules as our tank builder: temperature overlap, pH and hardness, predation and mouth size, fin-nipping and temperament. Tank size is left out here; check it in the builder.

Good tankmates

Use caution

Avoid

All 105 species we checked against the Oscar

Species	Verdict	Why
Angelfish	Compatible	No conflicts found
Bala Shark	Compatible	No conflicts found
Blood Parrot Cichlid	Compatible	No conflicts found
Chinese Algae Eater	Compatible	No conflicts found
Clown Loach	Compatible	No conflicts found
Common / Comet Goldfish	Compatible	No conflicts found
Common Pleco	Compatible	No conflicts found
Convict Cichlid	Compatible	No conflicts found
Dwarf Gourami	Compatible	No conflicts found
Electric Blue Acara	Compatible	No conflicts found
Firemouth Cichlid	Compatible	No conflicts found
Iridescent Shark	Compatible	No conflicts found
Kissing Gourami	Compatible	No conflicts found
Pictus Catfish	Compatible	No conflicts found
Rainbow Shark	Compatible	No conflicts found
Red-Tail Shark	Compatible	No conflicts found
Three-spot Gourami	Compatible	No conflicts found
Tinfoil Barb	Compatible	No conflicts found
Weather Loach	Compatible	No conflicts found
Yoyo Loach	Compatible	No conflicts found
Boesemani Rainbowfish	Caution	Oscar and Boesemani Rainbowfish only share 81–82°F. That's a tight window.; Oscar can bully smaller, peaceful Boesemani Rainbowfish.
Bristlenose Pleco	Caution	Oscar can bully smaller, peaceful Bristlenose Pleco.
Clown Pleco	Caution	Oscar can bully smaller, peaceful Clown Pleco.
Denison Barb	Caution	Oscar can bully smaller, peaceful Denison Barb.
Discus	Caution	Oscar can bully smaller, peaceful Discus.
Electric Yellow Lab	Caution	Oscar (pH 6–7.5) and Electric Yellow Lab (pH 7.7–8.6) prefer different pH.
Kribensis	Caution	Oscar can bully smaller, peaceful Kribensis.
Kuhli Loach	Caution	Oscar can bully smaller, peaceful Kuhli Loach.
Moonlight Gourami	Caution	Oscar can bully smaller, peaceful Moonlight Gourami.
Pearl Gourami	Caution	Oscar can bully smaller, peaceful Pearl Gourami.
Rosy Barb	Caution	Oscar can bully smaller, peaceful Rosy Barb.
Scissortail Rasbora	Caution	Oscar can bully smaller, peaceful Scissortail Rasbora.
Siamese Algae Eater	Caution	Oscar can bully smaller, peaceful Siamese Algae Eater.
Swordtail	Caution	Oscar can bully smaller, peaceful Swordtail.
Upside-down Catfish	Caution	Oscar can bully smaller, peaceful Upside-down Catfish.
African Dwarf Frog	Avoid	Oscar eats small fish, and African Dwarf Frog only grows to about 1.4 in.
Amano Shrimp	Avoid	Oscar will eat Amano Shrimp.
Assassin Snail	Avoid	Oscar eats snails, including Assassin Snail.
Bamboo Shrimp	Avoid	Oscar will eat Bamboo Shrimp.
Betta	Avoid	Oscar eats small fish, and Betta only grows to about 3.3 in.
Black Neon Tetra	Avoid	Oscar eats small fish, and Black Neon Tetra only grows to about 1.7 in.
Black Skirt Tetra	Avoid	Oscar eats small fish, and Black Skirt Tetra only grows to about 3.5 in.
Bleeding Heart Tetra	Avoid	Oscar eats small fish, and Bleeding Heart Tetra only grows to about 2.9 in.
Bolivian Ram	Avoid	Oscar eats small fish, and Bolivian Ram only grows to about 3.8 in.
Bronze Cory	Avoid	Oscar eats small fish, and Bronze Cory only grows to about 3.5 in.
Buenos Aires Tetra	Avoid	Oscar eats small fish, and Buenos Aires Tetra only grows to about 2.8 in.
Bumblebee Goby	Avoid	Oscar eats small fish, and Bumblebee Goby only grows to about 1.7 in.
Cardinal Tetra	Avoid	Oscar eats small fish, and Cardinal Tetra only grows to about 1.7 in.
Celestial Pearl Danio	Avoid	Oscar eats small fish, and Celestial Pearl Danio only grows to about 1 in.
Cherry Barb	Avoid	Oscar eats small fish, and Cherry Barb only grows to about 2.4 in.
Cherry Shrimp	Avoid	Oscar will eat Cherry Shrimp.
Chili Rasbora	Avoid	Oscar eats small fish, and Chili Rasbora only grows to about 0.9 in.
Clown Killifish	Avoid	Oscar eats small fish, and Clown Killifish only grows to about 1.6 in.
Cockatoo Dwarf Cichlid	Avoid	Oscar eats small fish, and Cockatoo Dwarf Cichlid only grows to about 3.5 in.
Congo Tetra	Avoid	Oscar eats small fish, and Congo Tetra only grows to about 3.8 in.
Crystal Red Shrimp	Avoid	Oscar will eat Crystal Red Shrimp.
Diamond Tetra	Avoid	Oscar eats small fish, and Diamond Tetra only grows to about 2.8 in.
Dwarf Neon Rainbowfish	Avoid	Oscar eats small fish, and Dwarf Neon Rainbowfish only grows to about 3.8 in.
Ember Tetra	Avoid	Oscar eats small fish, and Ember Tetra only grows to about 0.9 in.
Endler's Livebearer	Avoid	Oscar eats small fish, and Endler's Livebearer only grows to about 1.2 in.
Fancy Goldfish	Avoid	Oscar (72–82°F) and Fancy Goldfish (50–70°F) need different temperatures.; Oscar can bully smaller, peaceful Fancy Goldfish.
Forktail Blue-eye	Avoid	Oscar eats small fish, and Forktail Blue-eye only grows to about 2.8 in.
German Blue Ram	Avoid	Oscar and German Blue Ram only share 81–82°F. That's a tight window.; Oscar eats small fish, and German Blue Ram only grows to about 1.9 in.
Ghost Shrimp	Avoid	Oscar will eat Ghost Shrimp.
Giant Danio	Avoid	Oscar eats small fish, and Giant Danio only grows to about 3.5 in.
Glass Catfish	Avoid	Oscar eats small fish, and Glass Catfish only grows to about 3.1 in.
Glowlight Tetra	Avoid	Oscar eats small fish, and Glowlight Tetra only grows to about 1.9 in.
Gold Barb	Avoid	Oscar eats small fish, and Gold Barb only grows to about 3.5 in.
Guppy	Avoid	Oscar eats small fish, and Guppy only grows to about 2.8 in.
Harlequin Rasbora	Avoid	Oscar eats small fish, and Harlequin Rasbora only grows to about 2.1 in.
Head-and-tail-light Tetra	Avoid	Oscar eats small fish, and Head-and-tail-light Tetra only grows to about 2.1 in.
Hillstream Loach	Avoid	Oscar eats small fish, and Hillstream Loach only grows to about 3.1 in.
Honey Gourami	Avoid	Oscar eats small fish, and Honey Gourami only grows to about 2.6 in.
Japanese Trapdoor Snail	Avoid	Oscar eats snails, including Japanese Trapdoor Snail.
Julii Cory	Avoid	Oscar eats small fish, and Julii Cory only grows to about 2.6 in.
Lambchop Rasbora	Avoid	Oscar eats small fish, and Lambchop Rasbora only grows to about 1.4 in.
Lemon Tetra	Avoid	Oscar eats small fish, and Lemon Tetra only grows to about 1.9 in.
Malaysian Trumpet Snail	Avoid	Oscar eats snails, including Malaysian Trumpet Snail.
Marbled Hatchetfish	Avoid	Oscar eats small fish, and Marbled Hatchetfish only grows to about 1.7 in.
Molly	Avoid	Oscar eats small fish, and Molly only grows to about 3.8 in.
Mystery Snail	Avoid	Oscar eats snails, including Mystery Snail.; Oscar (pH 6–7.5) and Mystery Snail (pH unknown) prefer different pH.
Neon Tetra	Avoid	Oscar eats small fish, and Neon Tetra only grows to about 1.4 in.
Nerite Snail	Avoid	Oscar eats snails, including Nerite Snail.; Oscar (pH 6–7.5) and Nerite Snail (pH 8–8.4) prefer different pH.
Odessa Barb	Avoid	Oscar eats small fish, and Odessa Barb only grows to about 2.2 in.
Otocinclus	Avoid	Oscar eats small fish, and Otocinclus only grows to about 1.7 in.
Panda Cory	Avoid	Oscar eats small fish, and Panda Cory only grows to about 2.4 in.
Paradise Fish	Avoid	Oscar and Paradise Fish only share 72–72°F. That's a tight window.; Oscar eats small fish, and Paradise Fish only grows to about 3.8 in.
Pea Puffer	Avoid	Oscar eats small fish, and Pea Puffer only grows to about 1.4 in.
Pearl Danio	Avoid	Oscar eats small fish, and Pearl Danio only grows to about 2.6 in.
Penguin Tetra	Avoid	Oscar eats small fish, and Penguin Tetra only grows to about 1.7 in.
Peppered Cory	Avoid	Oscar eats small fish, and Peppered Cory only grows to about 3.3 in.
Platy	Avoid	Oscar eats small fish, and Platy only grows to about 2.4 in.
Pristella Tetra	Avoid	Oscar eats small fish, and Pristella Tetra only grows to about 2.1 in.
Pygmy Cory	Avoid	Oscar eats small fish, and Pygmy Cory only grows to about 1.4 in.
Ramshorn Snail	Avoid	Oscar eats snails, including Ramshorn Snail.
Rummy-nose Tetra	Avoid	Oscar eats small fish, and Rummy-nose Tetra only grows to about 2.4 in.
Serpae Tetra	Avoid	Oscar eats small fish, and Serpae Tetra only grows to about 1.9 in.
Silver Hatchetfish	Avoid	Oscar eats small fish, and Silver Hatchetfish only grows to about 1.9 in.
Silver Tip Tetra	Avoid	Oscar eats small fish, and Silver Tip Tetra only grows to about 2.4 in.
Sparkling Gourami	Avoid	Oscar eats small fish, and Sparkling Gourami only grows to about 1.9 in.
Sterbai Cory	Avoid	Oscar eats small fish, and Sterbai Cory only grows to about 3.2 in.
Tiger Barb	Avoid	Oscar eats small fish, and Tiger Barb only grows to about 2.8 in.
Variatus Platy	Avoid	Oscar eats small fish, and Variatus Platy only grows to about 2.4 in.
White Cloud Mountain Minnow	Avoid	Oscar and White Cloud Mountain Minnow only share 72–72°F. That's a tight window.; Oscar eats small fish, and White Cloud Mountain Minnow only grows to about 1.9 in.
Zebra Danio	Avoid	Oscar eats small fish, and Zebra Danio only grows to about 2.4 in.

Care notes

Needs: Extreme bioload necessitates heavy canister filtration and large water changes; prone to Hole-in-the-Head disease; uproots plants

Group: Keep singly or as a bonded pair; arbitrary groups fight violently over territory unless tank volume exceeds 200 gallons

Temperament: semi-aggressive toward other fish, semi-aggressive toward its own kind. Lives in the middle of the tank.

Common questions

How big does a Oscar get?

About 17 inches (35 cm SL) as an adult, according to seriouslyfish.com.

What size tank does a Oscar need?

At least 60 inches long and about 143 gallons. The smallest standard tank that meets that is a 180 gallon.

How many Oscars should be kept together?

It can be kept on its own. Keep singly or as a bonded pair; arbitrary groups fight violently over territory unless tank volume exceeds 200 gallons

What fish can live with a Oscar?

Species that passed every check include Dwarf Gourami, Angelfish, Electric Blue Acara, Firemouth Cichlid, Convict Cichlid, Three-spot Gourami.

Gear for a Oscar setup

TankSmallest standard tank that meets its minimum: 180 gallon (72 in long).Find on Amazon →HeaterAbout 2 × 300 W for 180 gallons, holding 72–82°F.Find on Amazon →LidIt jumps. A full lid keeps it in the tank.Find on Amazon →FoodMeaty frozen foods suit its diet.Find on Amazon →Test kitCheck ammonia, nitrite and pH. Cycle the tank before adding fish.Find on Amazon →

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Sources

Values come from these pages, in our own words. Status: verified. Last reviewed 2026-10-12.

seriouslyfish.com /species/astronotus-ocellatus
fishbase.se /summary/Astronotus-ocellatus.html