I have a 4-5" comet that I'm SURE is a female. Miko laid eggs in January, as the only fish in the tank, and hadn't been exposed to males since she was at the pet store back in September. So that was odd, but whatever. They obviously didn't hatch. So now I have another comet, but I really can't tell the sex of it. I'm leaning towards male (and his name is Fernando, so I'll be disappointed if he's not a "he"), as his body is quite streamlined, and in comparison to Miko's ginormous anal opening - sorry, but it's true - his is a bit more slit like. Anyway, around the first week or 2 that they were introduced, Fernando kept chasing Miko, pushing her by her anal opening. So I felt like my gender conjectures were confirmed. He let up, and now, almost 2 months later, Miko is the one doing the chasing. In the exact same fashion - nose all up in his anal opening.

Would a female do this to a male? Or does this mean that Fernando is more likely a female, and they're just playing? I also have a pair of 2-3" shubunkins, (not sure of their sexes either), and Miko has started to chase them in the same way, though not nearly as often.

Any thoughts? I'll post pics of Fernando, once my camera cable stops being a jerk and let's me connect it to my comp. Thanks!

Funny things happen, I guess... Of course, since Miko laid eggs, and she being the only one in the tank back then, she definetely is a female. About Fernando being a male or female, that seems to be still in the stars at this point.
Are there any signs of breeding stars (whitish raised pumps) on Fernando's gill plates, or a fine white line on the first rays of his pectoral fins? It of course could be that Miko is just a bullying girl.
How does Fernando's anal area look? There is a pretty good (yet not fool proof) comparision between male' and female's anal area...
http://www.kokosgoldfish.invisionzone.com/...showtopic=18264

There are other tips on how to somewhat successfully sex your goldfish by the shape of the pectoral fin....

Apparently I missed that reply... Haha sorry about that, I do appreciate the response I swear. There are definitely no tubericles/stars or whatnot. I had seen that image floating around here, yet Miko almost more resembles the male pic, so I have nothing to reference by... I guess it's not that important, I just want little Mikos. She has more personality than my OSCAR. Which is the other little factor that makes me think Fernando's a lady: Miko chases/sucks on/swims though my hands NONSTOP whenever I stick them in the tank. Seems like she's just a cocky attention-whore (but I love her for it), and doesn't care if Fernando's a dude or a chick... She just likes to play. Meh.