Oscar

A. ocellatus have been reported to grow to about 45 centimetres (18 in) in length and 1.6 kilograms (3.5 lb) in weight. The wild caught forms of the species are typically darkly coloured with orange ringed-spots or ocelli on the caudal peduncle and on the dorsal fin. It has been suggested that these ocelli function to limit fin-nipping by piranha (Serrasalmus spp.) which co-occur with A. ocellatus in its natural environment. The species is also able to rapidly alter its colouration, a trait which facilitates ritualised territorial and combat behaviours amongst conspecifics. Juvenile A. ocellatus have a different colouration from adults and are striped with white and orange wavy bands and have spotted heads.