Hmmm still it's very Fatty for the fish(what i've read).And isn't good.
Anyway in my Opinion and im sure im right, goldfish aren't ment to
eat other fish.There more peaceful fish.... no need in killing another fish
and feeding it to your goldies... in the end your goldfish will get sick and most probly die

... So i would recomend treats like blood worms, shrimp, earth worms, peas stuff like that It's alot healthier in the first place. (Just MO)