Don't feed goldfish!

oscars are opportunistic piscivores (fish eaters), as are the majority of larger freshwater fishes.

you really think feeding them only processed food is better than natural diet?

disease risk and vitamin deficiencies aside, feeders (properly gutloaded with algae and invertebrates as suggested above) are a great supplement to the diet of any predatory fish.

Goldfish in particular are too high in fat and thiaminase to be good feeders though. I raise guppies just for that reason.