well that depends on the size of the goldfish, i have personally seen goldfish over 6", my friend had 2 in a 45 or 55 i dont remember i was young. but i know they were huge. and a good fish that size would not be eaten by a oscar.jaws19;1101554; said:petsmart. i screwed with them and asked if in 12in oscar could go in a tank with gold fish, and some koi. he said yeah there coldwater but he will be fine. rubbish! the oscar would have a feast! they also said that a sting ray they had wont eat anything but alge waffers. then right in front of me a guy buy 2 feeder guppy in and they were gone in mins.!! tisk tisk tisk but i did get this guy a year ago check my avatar. he was my flordia gar i think