sexing goldfish?

If you allow some cool-down this winter, when the world warms up next spring, mature males will show tubercles on their gill covers (and sometimes beyond) - no it is not Ich. Females will produce eggs in the same time frame and look fatter. Plenty of water changes during that time will help things along. Good covers and plenty of room are needed, along with multiple bunches of Anacharis or comparable plants.

Without that, you may not be able to read the sexes of the fish.