Pet Forum / Aquaria / Goldfish / April 2004

Well I don't have much experience with sexing goldfish, but I've seen the
tubercule on 5 of my fish. There's a guy at my local goldfish specialized
store that says he's been running a goldfish breeding farm for the last 20
years in China. He actually showed me the tubercules growing on the fins of
his fish, and since seeing that it has been A LOT easier for me. They sort
of grow on the hard ridge of the "arm" fins, and look like hard bumpy spots.
They're not really white like people say, more like a bit translucent in
color, so you have to look really closely. He didn't mention the gill
covers, so I think maybe looking in that area is unreliable. I do have one
goldfish that has tubercules on his gill covers and not on his fins though.
He also said that when it is breeding season, he sometimes squeezes the fish
around the belly so that stuff (eggs) come out. You might want to try that,
if you can.
I think your best bet is to find a male fish yourself by closely examining
the ones at the fish store.