oscars and same size koi

Question
will the oscar bite or kill the koi if the fishes are fed properly even if there about the same size?

Answer
No probably not unless you have an overly aggressive oscar or koi as they may bug the oscar. Koi are coldwater and Oscars are tropical so keep that in mind. Keep the fish in tropical water if you want the oscar to live and they koi will but will be stressed.