Oscar

Astronotus ocellatus

Freshwater South America Usually captive bred

A big, intelligent cichlid that grows to 30 cm and needs a tank of 400 litres or more. It digs, rearranges decor and eats smaller fish. Often kept alone or as a pair.

Also called: Marble cichlid.

30 cm adult length, drawn to scale. deep body.

Outgrows a typical home tank. Check this fish against the adult size above before buying a juvenile. The minimum shown is the least it is kept in for good, not a comfortable size.

Try it in the planner Opens a tank sized to its minimum with 1 fish added.

What it needs

Item	Value	Because
Adult length	30 cm	Used for the Space check: the tank must be long enough for the fish to turn round.
Smallest tank	300 L, at least 150 cm long estimated	The least water and floor length this species is kept in for good, as a single fish or smallest group.
Extra water per added fish	150 L estimated	What each further fish adds once the minimum is met.
Waste load	Class 5 of 5 estimated	How much waste an adult makes against its size. Feeds the Load check.
Temperature	23 to 28 C	Stock sharing a tank need overlapping ranges.
pH	6.5 to 7.5	Compared with tankmates in the Water check.
Hardness	GH 5 to 18, KH 3 to 10	Degrees of general and carbonate hardness.
Flow	Medium	Low-flow fish are stressed in a strong current.
Light	Moderate	Matched to the lighting class on the needs sheet.
Group size	Single fish is fine	Not a schooling species.
Temperament	Aggressive	Territorial: strong.
Swims in	All levels	Fish that use different levels share a tank more easily.
Lifespan	About 12 years	A fish is a long commitment.
Experience	Some experience helps	A guide to how forgiving the species is of mistakes.
Jumps	Yes	Keep the tank covered.

Tags marked estimated are judged from the size and habits of the species rather than measured, so treat them as a sensible default.

Diet and tank layout

Oscar is an carnivore that swims in all levels of the tank. It eats or uproots plants, so choose hard-leaved species or none. Give it some cover. It digs, so anchor plants and keep hard rock off loose sand. It will eat fish small enough to swallow.

Tankmates

Works with

No close matches in the data. Check the pair tool.

Depends

Avoid

Compare any two fish on the compatibility page, or print the equipment for a stock on the needs sheet. How this is worked out: the method.