Oscar

Quick facts

Adult size

35 cm

Lifespan

can live up to 15 years

Tank zone

all

Temperament

semi-aggressive

Difficulty

intermediate

Water parameters

Temperature

24–28°C

pH

6.0 to 8.0

Hardness

2 to 18 dGH

Tank requirements

Minimum volume

280 L

Minimum length

120 cm

Flow

low

Lighting

dim preferred

Substrate

any

Hiding spots

needed

Open swimming room

needed

Feeding

Diet: carnivore, feeds primarily at the all.

Will accept almost anything. Cichlid pellets are the staple. Avoid feeding feeder goldfish or rosy reds - they spread disease and lack proper nutrition; this advice is decades old and pet stores still push it

Compatibility

• Will eat any fish that fits in their mouth, which becomes a lot of fish as they grow
• Notorious tank-rearrangers; will move substrate, dig holes, push decor around
• Develop visible personalities and recognize their keeper; one of the few fish that arguably enjoys interaction
• Most-mis-sold large cichlid in the hobby. Sold as 5 cm juveniles to people with 75 L tanks; reaches 30 cm+ and needs 280 L+
• Compatible tankmates limited to similar-sized non-aggressive species: larger plecos, similarly-sized peaceful cichlids in 400 L+ tanks
• Tap water from a hose has been known to kill them via temperature shock; acclimate water changes carefully

Habitat

Native to slow-moving rivers and floodplains in the Amazon and Orinoco basins. Tannin-stained water, soft acidic conditions in the wild, but adapts to almost any community-tank parameters. Tiger oscar (orange/black) and red oscar are color morphs of the same species; black, lemon, and albino versions also exist.

Breeding

Substrate spawner. Pairs (which can take months to form from a group; forced pairing often fails) clean a flat surface and lay 1,000-3,000 eggs. Both parents guard aggressively. Fry become free-swimming in about a week and are easy to raise on baby brine shrimp, then crushed pellets. The difficulty isn't getting them to breed; it's providing enough tank space for a breeding pair (500 L) and dealing with the aggression. A pair of oscars guarding eggs will kill anything else in the tank.

Common problems

Tank size is the number one issue. Stores sell juvenile oscars at 5–8 cm. They grow to 30 cm in 12-18 months and produce an extraordinary amount of waste. A single oscar needs 250 L; a pair needs 400+. Many end up in undersized tanks, leading to stunted growth, chronic health issues, and aggression. HITH (hole-in-the-head) is very common in oscars fed a monotonous diet of feeder fish or pellets. Varied diet with quality pellets, frozen food, and vegetables prevents it.

Bioload

Bioload coefficient: 12.0 (very large carnivorous cichlid with intense feeding; comparable to two adult goldfish in waste output).

Bioload coefficients are calibrated against the neon tetra as the anchor (1.0). See the methodology page for the formula and how each value was derived.

Further reading

• Stocking ideas by tank size