Definitions for "Gonopodium"
An modified anal fin which is elongated. Only appears on the males, which helps to fertilize the females. You would expect to see these organs in Livebearers. Go Livebearers
Rays of the anal fin modified into a copulatory organ in male live-bearers, e.g., mosquitofish
a term given to the anal fin (or the anterior portion of it) of a male fish when it is modified to function as a copulatory organ, e.g., in guppies