* Clown loaches: Clown loaches are peaceful fish that can grow up to 12 inches long. However, they are also territorial and can be aggressive towards other fish, especially Oscars.
* Green terror cichlids: Green terror cichlids are aggressive fish that can grow up to 12 inches long. They are known to attack other fish, including Oscars.
* Jaguar cichlids: Jaguar cichlids are aggressive fish that can grow up to 24 inches long. They are known to attack other fish, including Oscars.
* Plecos: Plecos are peaceful fish that can grow up to 24 inches long. However, they are also known to eat the slime coat of other fish, which can lead to infection and death.