Why is your Oscar fish not eating guppies?

Oscars will usually eat guppies if they feel hungry enough. There are a few things that may cause an Oscar to not eat a guppy, it may already have eaten enough, or it may be sick or stressed. Additionally, the size of the guppy may be too large for the Oscar to swallow comfortably, or the Oscar may be used to eating a different type of food and may not recognize the guppy as food.