I have a 3 year old fantail and just recently lost a 3 year old oranda. Would like to get another goldfish, but am not sure the larger sized one will be okay with a smaller sized new(er) fish. Does size matter when buying within the goldfish family...ie, will a larger one eat a smaller one? What is the most compatible kind to go with a fantail?

I had two very large ranchus and bought a tiny baby one, and they seemed fine. I thought the bigger fish would try and eat the little one, but they all live happily together. The baby one is slowy catching up to his two larger tank mates in size. Any type of fancy would go with a fantail.

As long as the smaller one is bigger than your older fish's mouth you shouldn't have any problems.

well not so small, yes I agree with RYuu, but I would buy a reasonable size. my fantail like to pick on my small comet goldfish. but then after 2 - 3 days together, they got use to each other now.

I added a tiny oranda in january with my bigger orandas and shubunkin. No problems with the big ones, but the little one is male and like to chase the big females ones!! Other than that they get on great and he has grown a lot. Just so long as they cant fit in the big ones mouths you should be fine. Just check with the pet store that you can bring him/her back if there is a problem.