Oscar

The oscar is recognized by its velvety dark body and orange–red blotches; the orange-ringed eyespot (ocellus) on the caudal peduncle gives the species its name. Red, tiger, albino and "lemon" forms are common. Among aquarium fish it is one of the few interactive enough to be called a "pet": it recognizes its owner, comes to the front glass when the door opens and rearranges the decor.

It is sold in stores as 3–4 cm juveniles and reaches 20–25 cm within the first year. An aquarium of 300 liters or more should be planned before buying one.

It lives in slow-flowing tributaries, flooded forests and lakes of the Amazon, among fallen trees and roots. In the wild it eats small fish, crayfish, insects and fruit.

• Volume: at least 300 liters for a single adult, 450 liters or more for a pair.
• Filter: a canister filter or sump turning over 5–10 times the tank volume per hour. Oscars eat a lot and produce a lot of waste.
• Decor: sturdy, large rocks and roots; oscars dig through sand and knock over light objects. Plants are usually uprooted.
• Heater: should be guarded or placed outside the tank; oscars can break glass heaters.
• Lid: it jumps at feeding time or when frightened.

An omnivore leaning toward meaty foods. Large cichlid granules as the staple; occasionally frozen shrimp, mysis, worms and vegetables such as peas. Live feeder fish (guppies, goldfish) are not recommended: they carry disease and create fat/thiaminase imbalances. Adults are fed once a day.

It is usually manageable toward its own kind and fish of similar size, but it eats anything that fits in its mouth. During breeding it fiercely defends its territory.

Good companions: calm, large fish of the same size — large plecos, silver dollars, silver arowana (in a very large tank), South American cichlids such as the severum.

Avoid: all small community fish, shrimp, snails, slow and long-finned fish.

The oscar is a fish that can be kept alone and is not unhappy about it; most hobbyists keep a single oscar.

A pair can only be obtained by raising juveniles together and letting them pair off naturally, and it needs an aquarium of 450 liters or more. Once paired, they can be harsh toward other individuals. Whether two oscars get along in the same tank depends on their individual personalities; a spare aquarium should be ready to separate them if they prove incompatible.

Mature pairs (about 15 cm and up) lay hundreds, sometimes more than a thousand, eggs on a flat stone they have cleaned. The parents guard the eggs and fry. To form a pair, several juveniles are usually raised together; once a pair forms, the others are removed.

• Hole-in-the-head disease (HLLE): erosion and pits on the head and along the lateral line. It is associated with poor water quality, activated carbon residue and poor nutrition.
• Fin and body wounds: from sharp decor and broken heaters.
• Constipation: with a monotonous diet and overfeeding.

Hard to tell apart externally. Some breeders say the male has a few dark spots at the base of the dorsal fin, but this is not reliable. Sexing is confirmed by the shape of the papilla during spawning.