Sexing a Goldfish

Can you tell whether you have a male or a female goldfish? I couldn't and had no idea how to tell which was which. It is a difficult task at best but there are a few ways to help determine the sex of your fish. It is a most difficult task on fry less than a year old, but as a general rule, females are likely to be bigger than the males of the same age. When they reach spawning age, and the eggs begin to mature in the female fish, she will thicken in the ventral area. At the same time, the male will start to develop small white tubercles on his gill plates and on the leading rays of his fins, particularly on the first ray of the pectoral fin which can usually be detected on fish with head growth.

Then there is the anal opening. With practice, so I'm told you can distinguish the difference between the sexes. Below are pictures of the anal opening of the male and female goldfish. These differences become much more apparent as spawning time approaches.

A & B are the female anal openings. They are larger, protrude slightly and is round in shape. The anal fin is thicker and has a heavier first anal fin spine. The male is C & D. The male's opening is small and oval with no noticeable anal fin thickness. These differences become more apparent as spawning time approaches. The female opening will be larger and more distended when the eggs are ripe. When the male is ready, milt may be pushed out of the ventral opening by running a finger lightly along the sides of the fish, which shouldn't be necessary as the tubercles will be plainly viewed.