Would those Goodeids do okay with fantail Goldfish?
I have not tried it before, but I would think the Trout Goodieds that Paul has would probably do fine. They are a pretty large, fast fish so it’s going to be unlikely a goldfish would have a chance at them.
As for the characodon lateralis that I have, I think they might not be a great fit. They are pretty small and I could see a goldfish stumbling across a fry/juvi and sucking it not even knowing it.