I've got a female goldfish who is at least nine years old. She has just started moving and eating again after the winter and I've noticed that she isn't symmetrical anymore. One side bulges a little bit - enough to make the scales over that area stick out from her sides a little. As far as I can make out from reading around this is like dropsy. Doesn't dropsy affect the whole fish though? Also, I've read that poor water quality is often the cause but I tested a week ago and the ammonia and nitrites were both 0 ppm. I didn't check the nitrates but I will do now. In the meantime is there anything else it could be? What course of action do you recommend? All the other fish including lasts years youngsters seem absolutely fine. I don't want to lose her!

Thanks.