I am gonna give this a little bump as the same thing happened to me today. I've got a trio of green sunfish who are looking a little more lively after disease wrought havoc on my tank. I figured a few little fish swimming around would be a good judge of how they are recovering, so I went to Petsmart to pick up a few zebra danios as food. After she asked me what size tank I was putting them in (125g) she seemed ready to net them for me. She said that they would appreciate the large tank, and I said probably not for long. She then climbed down and refused the sale, with the exception of "feeder" goldfish and rosys. I didn't bother arguing, mainly because of my own lack of solid knowledge on health issues associated with goldfish, but thought it would make an interesting discussion on here. I'd also appreciate any links to info about the health issues associated with feeding goldfish vs other fish. Is it only Cyprinids who are bad for fish health? What is the best "feeder" fish?