LOL
I think the whole breeding of many of these "fancy" goldfish is the big experiment. For crying out loud, some of them can hardly swim their features are so mis-shape and distorted. Huge bulging eyes, massive heads, and long flowing fins that create so much drag them seem to hinder their movement more then they help propel them.
I've kept a few of them in my pond, most developed swim bladder problems and eventually went to fishy heaven. I think it was more a genetic problem than one of predators or not getting enough to eat, because they tripled in size in one year, and my one black moor even survived a few of our cold winters when a few of the regular comets didn't make it.
This thread reminds me of some of the debates about keeping turtles in the same pond as fish, so many people saying it can't be done. "the turtles will eat all the fish" they cried, or "the turtles will eat all the plants" was the other disaster they warned about. Many people claimed the turtles won't survive the winters unless you have mud on the bottom of the pond for them to overwinter in. I've been keeping turtles in with my fish for many years now and I'm still waiting for all these horrible calamities to befall me. No mud, but the turtles over winter fine. The turtles have never touched my plants that I have ever noticed, and I have yet to see the turtles ever even try to bite one of my fish adult fish. In truth though, I have seen my turtles chasing some of the tiny fry that hang around close to the shoreline, but I see this as a service since every year I end up with more new fish, and need some sort of population control as they are starting to get out of hand. Perhaps I need more turtles? In any case, it's a highly nutritional, protein rich snack for the turtles and that much less food I have to supply.
I've conducted a few experiments that didn't work out too well as far as harmony in the pond. I've scooped fry from local ponds and wetland areas, and released them in my pond to see what they grew up to be. The few that survived, and didn't get eaten by the turtles, generally turned out to be sunfish or perch. Both are way better and eating all the fry then the veracious turtles, but when they run out of fry they start picking on the smallest goldfish. Nipping at their fins and generally making life pretty uncomfortable for the small fish. But hey, this sort of stuff goes on in natural ponds everywhere, day after day, so I don't know if it can rightfully be called an experiment.