Try feeding your turtle eathworms, wax worms, crickets, aqutic insect larva, boiled lettuce/spinach. Goldfish are bad and can carry disease, try to avoid feeding them.
Sure, they can trasfer diseases/parasites to a turtle or an oscar. That's one of the reasons why feeder goldfish are not good to feed to turtles or fish, plus they aren't very nutritionus.
Can I feed it wild baby bass & bluegill?(i think that's what he's been eating)
Would the bones in the fish harm the turtle?
What about frogs and tadpoles?