Photographs by Paul Winters

Firstly, sexing young and juvenile goldfish is virtually impossible, you have to wait until the fish reach breeding age (usually one year old).

Secondly, sexing adult goldfish out of the breeding season is difficult, because the sexually distinguishing features only develop during the breeding season (in the spring time). That said, females may be deeper in the body than males.

Physical sexual characters

During the breeding season, the following physical features develop:

Male breeding tubercles

male breeding season tubercles on gill cover male breeding season tubercles on gill cover and leading edge of pectoral fin
male breeding season tubercles on leading edge of pectoral fin (gill cover tubercles are out of focus)

Illustrated above are the small white breeding tubercles that develop on the gill covers and the leading edges of the pectoral fins of males. It has been suggested that these may play a role in stimulating the female to spawn during chasing.


female goldfish vent female goldfish vent

The female vent enlarges slightly and appears slightly out-turned (convex), as shown above.

male goldfish vent

The male vent remains normal (slightly concave) in appearance, as shown above. (The vent is the common/single orifice for reproduction and excretion).

Behavioural sexual characters

Put quite simply - in the breeding season, males chase after females to induce them to spawn. Easy? No. Why? Because males will chase each other in the absence of females. Use the physical features as well as the chasing behaviour to tell the sexes apart!

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