And this is what I found...
"Firstly, sexing young and juvenile goldfish is virtually impossible, you have to wait until the fish reach breeding age (usually one year old).
Secondly, sexing adult goldfish out of the breeding season is difficult, because the sexually distinguishing features only develop during the breeding season (in the spring time). That said, females may be deeper in the body than males.
Physical sexual characters:
During the breeding season, the following physical features develop:
- males develop breeding tubercles (white pimples) on the gill covers and on the leading edge of the pectoral fins
- females develop a deeper body as they fill with roe (eggs), and have a larger vent (just before the anal fin) than the males
Behavioural sexual characters:
Put quite simply - in the breeding season, males chase after females to induce them to spawn. Easy? No. Why? Because males will chase each other in the absence of females. Use the physical features as well as the chasing behaviour to tell the sexes apart!"
Unfortunately, this doesn't get me any closer to sexing our fish since I have no fish to compare him/her with or for him/her to possibly breed with. Although, this does tell us that whatever Kian is, Katie was too, because I don't remember seeing any of these physical or behavioral characteristics. Maybe Kelly might have though. I'll have to ask him.