Is this oscar new to you, or have you had him a while, also if you have had him a while, is there anything else that has changed in his environment? I've known a few oscars to get finicky, bt in most cases a three day fast will change their attitude without hurting them one bit. Oscars are notoriuos for training their owners on how to feed them.
If this fish is new to you, do some checking to find out what he's used to. many oscars get way too many feeders and not enough variety which makes them picky. once again they can be re-trained, but it sometimes takes a while with a fish that recieved feeders as a staple. Feeders (guppies not comets) are great and IMO very important but not as a staple food like a lot of people believe.
