Oscars are real carnivores. These fishes can eat anything smaller than their mouth. It's not a good idea to keep other small fishes with these giant Oscars. Me too once kept two Oscars with two rainbow sharks and five Sepae tetras. But each day one or two Serpae Tetras became disappeared. But the rainbow sharks survived as they were a little bigger than Oscars could handle. But two days before one of my albino rainbow shark became food for one of the Oscar as the Oscar became enough big to eat them up.
See attached images and videos.
See video of Oscar eating Albino Rainbow Shark here on this link https://www.youtube.com/watch?v=_1GFOqN-4OA