Mixing with Tiger Oscar

Question
What are the chances of a goldfish approximately 4 inches long, surviving in a 55 gal tank with one Tiger Oscar, 7 inches long and a pleco.  The goldfish is a former feeder that one of my daughters "rescued" about 4 years ago, she stuck in my tetra tank.  Now the goldfish dominates that tank, 10 gal. I had two Oscars in the 55 gal tank but, one recently died.

Answer
Dear Charles,
Wow, that'll be quite difficult to predict. Every oscar has his own personality and temperament! Some oscars may ignore the goldfish and live peacefully with him. While others will just give them a curious look and then ignore them. And then you may have an aggressive oscar who won't allow other fish to intrude on his territory (plecos are usually allowed because they are very quiet and don't swim in the same water region as the oscar)

So this is a risk you have to take. Just know that oscars can be very predatory and/or territorial. And even if they do get along, the Oscar will probably outgrow the goldfish and may decide that he doesn't want to share his tank when he's that much bigger.

Is there any way you could give the goldfish to the petstore? Sometimes petstores will gladly take unwanted fish including goldfish (and not just to resell them as 'feeders' )

I really hope this helps!
Sorry I couldn't give a definite answer, you know how oscars are!
best wishes,
Karen~