Instructions
Check the fish̵7;s vent. This is the sole opening on the bottom side of the fish. A female̵7;s vent will protrude outward, whereas a male̵7;s vent will curve inward.
Examine the fish̵7;s gills. Males will develop breeding tubercles, which look like white bumps on the sides of their gills. These may also be present on their pectoral fins (the fins protruding from the sides of their body closest to their gills).
Study the sides of the fish̵7;s body from above. This method is much less reliable than the previous ones, but if the picture you are examining is an overhead shot of the fish then you will not be able to use the first two methods. The two sides of a male goldfish will appear symmetrical, whereas one side of the female̵7;s body will appear larger. Male goldfish also tend to be narrower than female fish.
Look at the size of the goldfish. Females are usually larger than males. This can help to determine sex when you are looking at a picture of many mature (full grown) goldfish, or if you are familiar with goldfish and thus have a basis for judging size.
Determine what is occurring in the picture. If the picture is of multiple fish and one appears to be bumping another fish̵7;s vent with its mouth, then the fish being bumped is almost certainly a female, and the fish doing the bumping is almost certainly a male. This is a type of breeding behavior exhibited by goldfish.
How to Tell If a Gold Fish Is Male or Female in a Picture
With a good picture and a discerning eye, you will likely be able to determine the sex of a mature goldfish. Fortunately, there are several methods for determining the sex of a goldfish. Which method you use will depend largely on the angle of the shot and the quality of the picture. Read each of the methods and look at your picture to determine whether or not the method is applicable to your image. Sexing goldfish is very difficult to do reliably until they have reached maturity, which usually takes about a year.