Is my goldfish male or female?

    There are a few ways to sex goldfish. This is best done after the fish has reached sexual maturity, which may occur anywhere from 9 months to 2 years after hatching. This is easiest to accomplish during breeding, when males chase and nip at females. The males also develop “breeding tubercles”, which look like small white spots or pimples on their gill covers and this should not be confused with the parasite, Ich, which would also be on other areas of the body. It is possible for females to develop tubercles, but this is rare and they develop fewer than the males do. During breeding, the female goldfish's body may become larger, indicating that she is carrying eggs.

     The most reliable method of determining your goldfish’s gender is by examining the fish's vent (anal opening), which is located under its’ underside between the tail and anal fins. If the vent sticks out a bit, you have a female. A male’s vent does not stick out, but instead goes inward.

     In general, females are usually larger in body and have larger anal fins than males. Males usually have thicker and longer pectoral fins than females. Another sexing technique, which is not very reliable, looks at symmetry of the goldfish’s body. With this technique, when viewing the goldfish from the top down, the sides of the male’s body are more narrow and symmetrical, while the female's sides are more broad and asymmetric.