I thought about that too. I have heard that sunfish can be a bit mean. Upon reading into Rudd, I found that they like to be in groups. I was thinking of a group of 3 fish. If the sunfish end up going after them or not getting along with them I can take the rudd and put them in my larger 700 gallon pond with the goldfish. I thought the Rudd's colors would be a nice contrast to the sunfish's. Do you think a group of 3 Rudd would be good enough for them?