You can't find red devils? They're pretty common from what I know. I had to separate the fry by size because they will attack the weaker/smaller ones. If there's a lot of fry it's not uncommon for one or two to get killed by the others. They will also gang up on a gold fish their own size or bigger and try to eat it. Let me know what area you live in, are you even in the US?

Oscars are VERY mean when they're about 5" to 7", usually 6"...Oscar pair just laid eggs

Joe
Cichlidfish.com